Patent Grant
7119766
The present invention generally relates to display driving methods and apparatuses, and more particularly to a display driving method and apparatus suited to drive a plasma display panel (hereinafter simply referred to as a PDP).
The PDP is expected to become one of the display devices of the next generation and to replace the conventional cathode ray tube (CRT), because the PDP can easily realize reduction in the thickness of the panel, reduction in the weight of the panel, flat screen shape and large screen.
A PDP which makes a surface discharge has been proposed, and according to such a PDP, all pixels on the screen simultaneously emit light depending on display data. In the PDP which makes the surface discharge, a pair of electrodes are formed on an inner surface of a front glass substrate and a rare gas is filled within the panel. When a voltage is applied across the electrodes, a surface discharge occurs at the surface of a protection layer and a dielectric layer formed on the electrode surface, thereby generating ultraviolet rays. Fluorescent materials of the three primary colors red (R), green (G) and blue (B) are coated on an inner surface of a back glass substrate, and a color display is made by exciting the light emission from the fluorescent materials responsive to the ultraviolet rays. In other words, fluorescent materials of R, G and B are provided with respect to each pixel forming the screen.
Accordingly, in order to increase the number of displayable gradation levels of the PDP using the limited number of sub fields, the PDP is generally driven with the sustain time proportional to the bit weighting as shown in
When displaying a moving image on the PDP using the above described gradation driving sequence, a contour of an unnatural color which originally does not exist is generated at the surface of the moving object in the image due to the residual image effect and the like of the human eyes. In this specification, such a contour of the unnatural color caused by the residual image effect and the like will be referred to a “pseudo contour”. The pseudo contour becomes particularly conspicuous when a person on the screen moves. The pseudo contour appears to the human eyes as a band of green or red color at the skin-colored portion such as the face of the person, and the pseudo contour greatly deteriorates the image quality.
A description will be given of the mechanism by which the pseudo contour is generated in conjunction with
In a first case, it is assumed for the sake of convenience that a Gray scale image which becomes brighter from the left towards the right of the image, that is, an image in which the luminance increases from the left to right of the image, is displayed on the PDP. If this image continuously moves towards the left of the screen by an amount corresponding to 1 pixel for every 1 field, a portion where the light becomes sparse appears to the human eyes. On the other hand, if this image continuously moves towards the right of the screen by an amount corresponding to 1 pixel for every 1 field, a portion where the light becomes dense appears to the human eyes. These sparse and dense portions where the light appears sparse and dense, respectively, occur when the human eyes focus on the moving object displayed on the screen, because the human eyes follow the moving direction and moving speed of the moving object and the visual point moves along loci indicated by bold arrows in
In a second case, it is assumed for the sake of convenience that a Gray scale image which gradually becomes brighter from the left towards the right of the image, that is, an image in which the luminance gradually increases from the left to right of the image, is displayed on the PDP. If this image moves towards the left of the screen at a constant speed by an amount corresponding to 1 pixel for every 1 field, a portion where the light becomes sparse appears to the human eyes. On the other hand, if this image moves towards the right of the screen at a constant speed by an amount corresponding to 1 pixel for every 1 field, a portion where the light becomes dense appears to the human eyes. These sparse and dense portions where the light appears sparse and dense, respectively, occur when the human eyes focus on the moving object displayed on the screen, because the human eyes follow the moving direction and moving speed of the moving object and the visual point moves along loci indicated by bold arrows in
In a third case, it is assumed for the sake of convenience that a Gray scale image which becomes brighter from the left towards the right of the image, that is, an image in which the luminance increases from the left to right of the image, is displayed on the PDP. In this case, even when the sub field structure is changed and the length ratios of the sustain times in the 4 sub fields are set to 1:4:8:2 in the sequence in which the light emission state is determined, as shown in
The above described phenomenons (1) through (3) become particularly notable at the luminance levels where the sub fields of the light emission state greatly deviate along the time base (or axis). Hence, in the case where the display can be made using 16 gradation levels as shown in
Next, a description will be given of the mechanism by which the pseudo contour becomes visible to the human eyes when the moving object displayed on the screen is a person's face having the skin tone, for example, based on the phenomenons (1) through (3).
For the sake of convenience, it is assumed that the ratios of the luminance levels of R, G and B for the skin tone is R:G:B:=4:3:2. In this case, the gradation characteristic becomes as shown in
In the case of the sub field structure described above, the portion where the luminance level is R1 in
As a result, even if the moving object has a skin tone with a smooth or gradual change in gradation level, a band of a color which originally does not exist appears to the human eyes at the contour portion of the moving object. As described above, this pseudo contour is notably generated at the skin tone portion such as the person's face and makes the image extremely unnatural, thereby deteriorating the image quality.
On the other hand, in the PDP using the sub field structure described above, a change in a least significant bit (LSB) of the image data may result in a large change of the position (time) on the time base of the sub field having the light emission state depending on the luminance level. This large change in the position of the sub field having the light emission state generates a flicker having a frequency lower than the frame frequency which is 60 Hz, for example, thereby deteriorating the image quality.
When it is assumed that the length ratios the sustain times in the 4 sub fields which make up 1 field are set to 1:2:4:8 in the sequence in which the ON state is determined, it is possible to display 16 gradation levels from the level 0 to the level 15, as described above. However, if the luminance level of a pixel changes between the levels 7 and 8 for every field, that is, changes to levels 7, 8, 7, 8, . . . for every field as shown in
Hence, the generation of the flicker is conspicuous at the portions where the sub fields having the light emission state greatly changes on the time base. When a pixel of an original image represented by 256 gradation levels has a luminance level in a vicinity of 128 and is displayed on a PDP which can display 16 gradation levels, the flicker is easily generated due to quantization error, video noise and the like even though the original image is a still image, and the image quality is deteriorated as a result.
Therefore, when the conventional gradation driving sequence is used for the PDP, a band of a color which originally does not exist appears to the human eyes at the contour portion of the moving object, even when the skin tone of the moving object undergoes a gradual change in gradation, thereby resulting in a problem in that the pseudo contour is visible to the human eyes. In addition, the pseudo contour is notably generated at the skin tone portion such as the person's face, and the image becomes extremely unnatural and the image quality is deteriorated thereby.
On the other hand, there is another problem in that the generation of the flicker is notable at portions where the sub fields having the light emission state greatly change on the time base. For example, when a pixel of an original image represented by 256 gradation levels has a luminance level in a vicinity of 128 and is displayed on a PDP which can display 16 gradation levels, the flicker is easily generated due to quantization error, video noise and the like even though the original image is a still image, and the image quality is deteriorated as a result.
Accordingly, it is a general object of the present invention to provide a novel and useful display driving method and apparatus in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide a display driving method which drives a display to make a gradation display on a screen of the display depending on a length of a light emission time in each of sub fields forming 1 field, where 1 field is a time in which an image is displayed, N sub fields SF1 through SFN form 1 field, and each sub field includes an address display-time in which a wall charge is formed with respect to all pixels which are to emit light within the sub field and a sustain time which is equal to the light emission time and determines a luminance level, comprising the steps of setting the sustain times of each of the sub fields approximately constant within 1 field, and displaying image data on the display using N+1 gradation levels from a luminance level 0 to a luminance level N. According to the display driving method of the present invention, it is possible to effectively prevent the generation of the pseudo contour and the generation of the flicker, and the present invention is thus suited for realizing a high image quality on a plasma display panel or the like.
Still another object of the present invention is to provide a display driving method which drives a display to make a gradation display on a screen of the display depending on a length of a light emission time in each of sub fields forming 1 field, where 1 field is a time in which an image is displayed, N sub fields SF1 through SFN form 1 field, and each sub field includes an address display-time in which a wall charge is formed with respect to all pixels which are to emit light within the sub field and a sustain time which is equal to the light emission time and determines a luminance level, comprising the steps of dividing 1 field into a first sub field group and a second sub field group and alternately arranging a sub field belonging to the first sub field group and a sub field belonging to the second sub field group within 1 field, setting the sustain times of each of the sub fields belonging to the first sub field group approximately constant within 1 field, and setting the sustain times of each of the sub fields belonging to the second sub field group approximately constant within 1 field, and displaying image data on the display using [(N−1)/2+1]2+[(N−1)/2]+1 gradation levels from a level 0 to a level [(N−1)/2+1]2+[(N−1)/2] by setting the ratios of luminance levels of the N sub fields SF1 through SFN to satisfy a relation SF1:SF2:SF3: . . . :SF(N−2):SF(N−1):SFN=(N−1)/2+1:1:(N−1)/2+1: . . . :(N−1)/2+1:1:(N−1)/2+1. According to the display driving method of the present invention, it is possible to effectively prevent the generation of the pseudo contour and the generation of the flicker. Furthermore, it is possible to make the apparent number of gradation levels relatively large even when the number of sub fields within 1 field is small. Hence, the present invention is suited for realizing a high image quality on a plasma display panel or the like.
A further object of the present invention is to provide a display driving method which drives a display to make a gradation display on a screen of the display depending on a length of a light emission time in each of sub fields forming 1 field, where 1 field is a time in which an image is displayed, N sub fields SF1 through SFN form 1 field, and each sub field includes an address display-time in which a wall charge is formed with respect to all pixels which are to emit light within the sub field and a sustain time which is equal to the light emission time and determines a luminance level, comprising the steps of displaying input image data on the display using N+1 gradation levels from a luminance level 0 to a luminance level N, and increasing a luminance quantity when displaying a luminance level m by adding 1 sub field which is to assume a light emission state in addition to all sub fields which assume the light emission state when displaying a luminance level m−1, where m is an integer satisfying 0<m<N. According to the display driving method of the present invention, it is possible to effectively prevent the generation of the pseudo contour.
Another object of the present invention is to provide a display driving apparatus which drives a display to make a gradation display on a screen of the display depending on a length of a light emission time in each of sub fields forming 1 field, where 1 field is a time in which an image is displayed, N sub fields SF1 through SFN form 1 field, and each sub field includes an address display-time in which a wall charge is formed with respect to all pixels which are to emit light within the sub field and a sustain time which is equal to the light emission time and determines a luminance level, comprising means for setting the sustain times of each of the sub fields approximately constant within 1 field, and means for displaying image data on the display using N+1 gradation levels from a luminance level 0 to a luminance level N. According to the display driving apparatus of the present invention, it is possible to effectively prevent the generation of the pseudo contour and the generation of the flicker, and the present invention is thus suited for realizing a high image quality on a plasma display panel or the like.
Still another object of the present invention is to provide a display driving apparatus which drives a display to make a gradation display on a screen of the display depending on a length of a light emission time in each of sub fields forming 1 field, where 1 field is a time in which an image is displayed, N sub fields SF1 through SFN form 1 field, and each sub field includes an address display-time in which a wall charge is formed with respect to all pixels which are to emit light within the sub field and a sustain time which is equal to the light emission time and determines a luminance level, comprising means for dividing 1 field into a first sub field group and a second sub field group and alternately arranging a sub field belonging to the first sub field group and a sub field belonging to the second sub field group within 1 field, and setting the sustain times of each of the sub fields belonging to the first sub field group approximately constant within 1 field, and setting the sustain times of each of the sub fields belonging to the second sub field group approximately constant within 1 field, and means for displaying image data on the display using [(N−1)/2+1]2+[(N−1)/2]+1 gradation levels from a level 0 to a level [(N−1)/2+1]2+[(N−1)/2] by setting the ratios of luminance levels of the N sub fields SF1 through SFN to satisfy a relation SF1:SF2:SF3: . . . :SF(N−2):SF(N−1):SFN=(N−1)/2+1:1:(N−1)/2+1: . . . :(N−1)/2+1:1:(N−1)/2+1. According to the display driving apparatus of the present invention, it is possible to effectively prevent the generation of the pseudo contour and the generation of the flicker. Furthermore, it is possible to make the apparent number of gradation levels relatively large even when the number of sub fields within 1 field is small. Hence, the present invention is suited for realizing a high image quality on a plasma display panel or the like.
A further object of the present invention is to provide a display driving apparatus which drives a display to make a gradation display on a screen of the display depending on a length of a light emission time in each of sub fields forming 1 field, where 1 field is a time in which an image is displayed, N sub fields SF1 through SFN form 1 field, and each sub field includes an address display-time in which a wall charge is formed with respect to all pixels which are to emit light within the sub field and a sustain time which is equal to the light emission time and determines a luminance level, comprising means for displaying input image data on the display using N+1 gradation levels from a luminance level 0 to a luminance level N, and means for increasing a luminance quantity when displaying a luminance level m by adding 1 sub field which is to assume a light emission state in addition to all sub fields which assume the light emission state when displaying a luminance level M−1, where m is an integer satisfying 0<m<N. According to the display driving apparatus of the present invention, it is possible to effectively prevent the generation of the pseudo contour.
Another object of the present invention is to provide a display driving method which makes a luminance representation depending on a length of a light emission time, including the steps of (a) generating a first image signal having a gradation levels from an input image signal having n gradation levels while satisfying a≦n, where n, a and b are integers, (b) generating a second image signal having b gradation levels from the input image signal while satisfying b<a≦n, and (c) switching and outputting the first image signal and the second image signal in units of pixels. According to the display driving method of the present invention, it is possible to make a display on a display which can only have a single fixed driving sequence as if two different gradation driving systems are displayed with the same display characteristic. In addition, it is possible to select an optimum display control in units of pixels depending on the state of the image. Hence, it is possible to carry out a fine driving control, by selecting the driving control which uneasily generates the pseudo contour with respect to an image in which the pseudo contour is conspicuous and selecting the driving control which improves the gradation display capability with respect to an image in which the pseudo contour is originally inconspicuous. For this reason, it is possible to greatly improve the moving image display capability of the display, such as the PDP, which makes the luminance representation depending on the length of the light emission time.
Still another object of the present invention is to provide a display driving method which makes a luminance representation depending on a length of a light emission time, including the steps of (a) generating a first image signal having a gradation levels by carrying out an error diffusion process with respect to an input image signal having n gradation levels while satisfying a<n, where n, a and b are integers, (b) generating a second image signal having b gradation levels by carrying out an error diffusion process with respect to the input image signal while satisfying b<a<n, and (c) switching and outputting the first image signal and the second image signal in units of pixels. According to the display driving method of the present invention, it is possible to make a display on a display which can only have a single fixed driving sequence as if two different gradation driving systems are displayed with the same display characteristic. In addition, it is possible to select an optimum display control in units of pixels depending on the state of the image. Hence, it is possible to carry out a fine driving control, by selecting the driving control which uneasily generates the pseudo contour with respect to an image in which the pseudo contour is conspicuous and selecting the driving control which improves the gradation display capability' with respect to an image in which the pseudo contour is originally inconspicuous. For this reason, it is possible to greatly improve the moving image display capability of the display, such as the PDP, which makes the luminance representation depending on the length of the light emission time.
A further object of the present invention is to provide a display driving apparatus which makes a luminance representation depending on a length of a light emission time, comprising a first processing path generating a first image signal having a gradation levels from an input image signal having n gradation levels while satisfying a≦n, where n, a and b are integers, a second processing path generating a second image signal having b gradation levels from the input image signal while satisfying b<a≦n, and switching means for switching and outputting the first image signal and the second image signal in units of pixels. According to the display driving apparatus of the present invention, it is possible to make a display on a display which can only have a single fixed driving sequence as if two different gradation driving systems are displayed with the same display characteristic. In addition, it is possible to select an optimum display control in units of pixels depending on the state of the image. Hence, it is possible to carry out a fine driving control, by selecting the driving control which uneasily generates the pseudo contour with respect to an image in which the pseudo contour is conspicuous and selecting the driving control which improves the gradation display capability with respect to an image in which the pseudo contour is originally inconspicuous. For this reason, it is possible to greatly improve the moving image display capability of the display, such as the PDP, which makes the luminance representation depending on the length of the light emission time.
Another object of the present invention is to provide a display driving apparatus which makes a luminance representation depending on a length of a light emission time, comprising a first processing path generating a first image signal having a gradation levels by carrying out an error diffusion process with respect to an input image signal having n gradation levels while satisfying a<n, where n, a and b are integers, a second processing path generating a second image signal having b gradation levels by carrying out an error diffusion process with respect to the input image signal while satisfying b<a<n, and switching means for switching and outputting the first image signal and the second image signal in units of pixels. According to the display driving apparatus of the present invention, it is possible to make a display on a display which can only have a single fixed driving sequence as if two different gradation driving systems are displayed with the same display characteristic. In addition, it is possible to select an optimum display control in units of pixels depending on the state of the image. Hence, it is possible to carry out a fine driving control, by selecting the driving control which uneasily generates the pseudo contour with respect to an image in which the pseudo contour is conspicuous and selecting the driving control which improves the gradation display capability with respect to an image in which the pseudo contour is originally inconspicuous. For this reason, it is possible to greatly improve the moving image display capability of the display, such as the PDP, which makes the luminance representation depending on the length of the light emission time.
Still another object of the present invention is to provide a display unit comprising a display which makes a luminance representation depending on a length of a light emission time, a first processing path generating a first image signal having a gradation levels from an input image signal having n gradation levels while satisfying a≦n, where n, a and b are integers, a second processing path generating a second image signal having b gradation levels from the input image signal while satisfying b<a≦n, and switching means for switching and outputting to said display the first image signal and the second image signal in units of pixels. According to the display unit of the present invention, it is possible to make a display on a display which can only have a single fixed driving sequence as if two different gradation driving systems are displayed with the same display characteristic. In addition, it is possible to select an optimum display control in units of pixels depending on the state of the image. Hence, it is possible to carry out a fine driving control, by selecting the driving control which uneasily generates the pseudo contour with respect to an image in which the pseudo contour is conspicuous and selecting the driving control which improves the gradation display capability with respect to an image in which the pseudo contour is originally inconspicuous. For this reason, it is possible to greatly improve the moving image display capability of the display, such as the PDP, which makes the luminance representation depending on the length of the light emission time.
A further object of the present invention is to provide a display unit comprising a display which makes a luminance representation depending on a length of a light emission time, a first processing path generating a first image signal having a gradation levels by carrying out an error diffusion process with respect to an input image signal having n gradation levels while satisfying a<n, where n, a and b are integers, a second processing path generating a second image signal having b gradation levels by carrying out an error diffusion process with respect to the input image signal while satisfying b<a<n, and switching means for switching and outputting to said display the first image signal and the second image signal in units of pixels. According to the display unit of the present invention, it is possible to make a display on a display which can only have a single fixed driving sequence as if two different gradation driving systems are displayed with the same display characteristic. In addition, it is possible to select an optimum display control in units of pixels depending on the state of the image. Hence, it is possible to carry out a fine driving control, by selecting the driving control which uneasily generates the pseudo contour with respect to an image in which the pseudo contour is conspicuous and selecting the driving control which improves the gradation display capability with respect to an image in which the pseudo contour is originally inconspicuous. For this reason, it is possible to greatly improve the moving image display capability of the display, such as the PDP, which makes the luminance representation depending on the length of the light emission time.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.
The present inventors found that when an object having a gradation change Δx on a screen moves and the human eyes follow this moving object, the pseudo contour will not be generated if measures are taken so that to the human eyes the moving object appears to maintain the original gradation change Δx. In addition, the present inventors found that the possibility of the pseudo contour being detected becomes low if the gradation change Δx appears to the human eyes as a gradation change which closely approximates the gradation change Δx as much as possible.
As shown in
Next, a description will be given of how a moving object appears to the human eyes when the sub field structure shown in
The human line of vision follows the moving object, and traces loci indicated by bold arrows in
Accordingly, by using the sub field structure described above, the phenomenon in which the light appears sparse or dense when the conventional gradation driving method is employed will not occur, and no pseudo contour will be generated. In addition, in the sub field structure described above, there exists on the time base no portion where the sub fields having the light emission state greatly change, and thus, no flicker will be generated.
Next, a description will be given of an image in which the light emission time does not increase uniformly from a vicinity of a center point on the time base towards the front and rear of the time base depending on the luminance level, that is, an image in which a change in the gradation is not constant.
In these cases, ratios of the light emission times (amounts of light) of the 3 pixels which are adjacent on the screen and have changing brightness are indicated by PSM:PCM:PTM. In addition, when the ratios of the light emission times (amounts of light) of the 3 pixels when the image moves are indicated by BSM:BCM:BTM, a relationship PSM: PCM:PTM≈BSM:BCM:BTM stands. The light emission times of the 3 pixels for these cases where the image moves are indicated by the black (filled) square mark, the black circular mark and the black triangular mark in
The human line of vision moves and follows the moving object along loci indicated by bold arrows in
Therefore, by using the sub field structure described above, the phenomenon in which the light appears sparse or dense when the conventional gradation driving method is employed is unlikely to occur, and the pseudo contour is unlikely to be generated. In addition, in the sub field structure described above, portions on the time base where the sub fields having the light emission state are likely to change greatly are reduced, thereby reducing the possibility of the flicker being generated.
Next, a description will be given of a first embodiment of a display driving apparatus according to the present invention. This embodiment of the display driving apparatus employs a first embodiment of a display driving method according to the present invention. In addition, it is assumed for the sake of convenience that a sufficient number of sub fields, that is, n sub fields, can be provided within 1 field, and the input image is displayed on the PDP using n+1 gradation levels.
The light emission time control circuit 1 receives RGB signals as the input image signal, and converts the RGB signals into converted data indicating the times and the sub fields that assume the light emission state for the gradation levels of the RGB signals. The converted data are supplied to the PDP driving circuit 2. This embodiment is particularly characterized by the data conversion carried out in the light emission time control circuit 1. A known circuit may be used for the PDP driving circuit 2, and for this reason, a detailed description of the PDP driving circuit 2 will be omitted. In this embodiment, the converted data are written in and read from the field memory 3 under the control of the memory controllers 4. The address driver 7 drives the PDP 8 based on the data read from the field memory 3. The scan controller 5 controls the driving of the PDP 8 by controlling the scan driver 6. When the PDP 8 is driven by the scan driver 6 and the address driver 7, the wall charge is formed with respect to the pixel which is to emit light within each sub field and sustain (light emission) pulses are generated.
In this embodiment, the sustain times of each of the sub fields are approximately uniform (constant) as shown in
In
In this embodiment, the relationship between the gradation levels and the light emission times are set as shown in
The first embodiment described above is effective when a considerable number of sub fields can be provided within 1 field. For example, if 255 sub fields can be provided within 1 field to display an image using 256 gradation levels, it is possible to prevent both the generation of the pseudo contour and the generation of the flicker while securing a sufficiently large number of gradation levels.
However, when the number of sub fields within 1 field is increased, the address display-times (non-light emission times) increase by a corresponding amount. When the number of address display-times increases, the sustain times which can be used for the light emission within 1 field are relatively shortened, thereby deteriorating the screen luminance. Accordingly, there is a limit to the number of sub fields that can be provided within 1 field, and by taking into consideration the increase of the address display-times, it is desirable that the number of sub fields within 1 field is set within a range of approximately 5 to 20.
In the case of the first embodiment, when only 6 fields can be provided within 1 field, for example, the number of displayable gradation levels is 7, and the number of displayable gradation levels is insufficient for the purposes of displaying a natural image.
In addition, as the brightness of the image increases, the light emission times (amounts of light) of the sub fields become relatively large because the light emission times are obtained by equally dividing 1 field into 6 equal parts with respect to all of the gradation levels, that is, 7 gradation levels in this case. For this reason, the light emission times in this case are not exactly increased uniformly from the center point on the time base for the purpose of balancing the sustain times relative to the center point on the time base.
Next, a description will be given of a second embodiment of the display driving apparatus according to the present invention capable of also eliminating the above described inconveniences. In this second embodiment of the display driving apparatus, even when a large number of sub fields cannot be provided within 1 field, it is possible to obtain substantially the same effects as in the case where the optimum sub field structure is employed to prevent the generation of the pseudo contour and to prevent the generation of the flicker. This second embodiment of the display driving apparatus employs a second embodiment of the display driving method according to the present invention.
First, a description will be given of the multi-level gradation processing circuit 12 shown in
In this embodiment, the distribution ratios of the error component to the peripheral pixels are set so as to obtain a satisfactory image quality. In other words, as shown in
According to the error diffusion technique, error calculation results E(n−1, m), E(n−1, m−1), E(n, m−1) and E(n+1, m−1) are used to determine the display level of P(n, m) as shown in
In addition, the separation of the display data and the error data also becomes a problem according to the error diffusion technique. However, this embodiment employs a bit boundary data separation method which is considered effective from the point of view of the moving speed. For example, when the input image data has 8 bits and the number of bits of the actually displayable gradation levels on the PDP 8 is 6 bits, the upper 6 bits are used as they are as the display data in accordance with the number of bits of the displayable gradation levels, and the remaining lower 2 bits are used as the error data. Hence, the separation of the display data and the error data can be realized by the use of a simple bit shift register, and the bit boundary data separation method is effective from the point of view of improving the operation speed of the error accumulation part and the like.
In
An output of the delay circuit 22 is supplied to the delay circuit 23. The delay circuit 23 delays the output of the delay circuit 22 by a delay time 3D and supplies the delayed output to the multiplier 26 which multiplies a coefficient 1/16. The delay circuit 23 also delays the output of the delay circuit 22 by a delay time 2D and supplies the delayed output to the multiplier 27 which multiplies a coefficient 5/16. In addition, the delay circuit 23 delays the output of the delay circuit 22 by a delay time 1D and supplies the delayed output to the multiplier 28 which multiplies a coefficient 3/16. Outputs of the multipliers 26 through 28 are all supplied to the adder 31, and an output of the adder 31 is supplied to the delay circuit 24. As a result, an m-bit display data is output from the adder 33.
The multi-level gradation processing circuit 12 is satisfactory from the point of view of the processing speed and the circuit scale. However, a gradation distortion may be generated depending on the number of gradation levels to be displayed.
In this case, however, the upper 3 bits of the 256 gradation levels “00000000” through “11111111” of the input data are used unchanged as the display data and the lower 5 bits which are ignored are used unchanged as the error data. For this reason, the display characteristic saturates at the bright portion of the image and the contrast undergoes an abrupt change at the dark portion. Such a tendency becomes notable particularly when the number of gradation levels (number of bits) actually displayable on the PDP 8 becomes small.
But in this embodiment, only N+1 gradation levels from the level 0 to the level N can be displayed even through 1 field is made up of N sub fields. For example, when N=6, only 7 gradation levels from the level 0 to the level 6 are displayable. In this case, the flat portion of the display characteristic occupies ¼ of the entire gradation region, and the image quality deterioration of the display data with respect to the all of the gradation levels of the input image data can no longer be neglected.
Accordingly, in this embodiment, the multiplier 11 shown in
As a result, it is possible to solve the problem of saturating display characteristic and the problem of the flat portion of the display characteristic when the display gradation level does not match the bit boundary. For example, when the original image data is represented in 256 gradation levels and the display gradation level has 5 bits (levels 0 through 31), the gain coefficient of the multiplier 11 is set to 31×8/255=248/255. On the other hand, when the original image data is represented in 256 gradation levels and the display gradation level has levels 0 through 6, the gain coefficient of the multiplier 11 is set to 6×32/255=192/255. In each of these cases, the upper bits of the data output from the multiplier 11 are the display data and the remaining lower bits are the error data. For this reason, it is possible to carry out the error diffusion process and obtain a desired display characteristic by supplying the output data of the multiplier 11 to the multi-level gradation processing circuit 12.
As indicated by the thin solid line in
In other words, the gain coefficient is multiplied to the original image data (RGB signals) input to the multiplier 11 and the multiplication result is output from the multiplier 11. In this state, the relationship of the input and the output of the multiplier 11 becomes as indicated by the bold line in
Next, a description will be given of the construction and operation of the light emission time control circuit 1 shown in
First, all of the pixels on the screen are divided into 2 groups A and B so as to have a checker-board arrangement as shown on the left hand side of
In this embodiment, the light emission sequence of the pixels of the groups A and B is set as follows. For example, when 1 field is made up of 6 sub fields SF1 through SF6, the number of sub fields making up 1 field is an even number, and a sub field matching the center point on the time base does not exist. Hence, the light emission with respect to a minimum luminance level 1 is started from the sub field SF3 for the group A and is started from the sub field SF4 for the group B. The light emission with respect to a luminance level 2 is made in the sub fields SF1 and SF2 for the group A and is made in the sub fields SF1 and SF2 for the group B. In other words, the sub fields (times) in which the light emission is to take place are set as shown in
When a person watches the image displayed on the screen, an averaged amount of light from the pixels of the groups A and B which are arranged in the checker-board pattern on the screen is sensed by the human eyes because the human eyes collectively look at a certain area on the screen. Accordingly, although the amount of light from the pixel does not increase uniformly about the center point on the time base for each of the groups A and B alone, the combined amount of light from the pixels of the groups A and B are sensed by the human eyes as increasing uniformly about the center point on the time base.
The light emission time control circuit 1 generally includes a dot counter 41, a line counter 42, an exclusive-OR circuit 43, and a table 44 made up of a random access memory (RAM) or a read only memory (ROM). The dot counter 41 counts the number of dots (pixels) in the horizontal direction based on a pixel clock or the like, and a LSB of the counted value is supplied to the exclusive-OR circuit 43. On the other hand, the line counter 42 counts the number of dots (pixels) in the vertical direction based on the pixel clock or the like, and supplies a LSB of the counted value to the exclusive-OR circuit 43. The exclusive-OR circuit 43 obtains an exclusive-OR of the LSBs from the counters 41 and 42, and supplies an output value to the table 44 as a most significant bit (MSB) of the address. The table 44 also receives the 3-bit data from the multi-level gradation processing circuit 12 as the remaining bits of the address. Hence, a 6-bit data related to the sub field to assume the light emission state is read from the specified address of the table 44 which has a data map shown in
A memory capacity required of the RAM or ROM which forms the table 44 may be obtained as follows. When making the display in 7 gradation levels, that is, using the luminance levels 0 to 6, 3 bits are required for the address and 1 bit is required to select the pixels of the groups A and B. Hence, a total of 4 bits are required for the address. On the other hand, when 1 field is made up of 6 sub fields, a data width of 6 bits is required. Accordingly, the RAM or ROM which forms the table 44 must have a memory capacity of 15×6=96 bits in this case.
As described above, when 1 field is made up of 6 sub fields, for example, only 7 gradation levels using the luminance levels 0 to 6 can be displayed, and the number of displayable gradation levels is insufficient for the purpose of displaying a natural image. Hence, the multiplier 11 and the multi-level gradation processing circuit 12 are respectively provided at a stage preceding the light emission time control circuit 1 as shown in
When an even number of sub fields form 1 field, such as the case where the even number is 6, a gradation interpolation is made by the error diffusion process of the multi-level gradation processing circuit 12, and the display gradation characteristics of the pixels of the groups A and B respectively become as shown in
To the human eyes, the pixels of the groups A and B having the display gradation characteristics shown in
In other words, even though 1 field is made up of a small number of sub fields, it is possible to set the structure of each field to approximate the optimum sub field structure (that is, the relationship of the gradation levels and the light emission times) that prevents the generation of the pseudo contour and prevents the generation of the flicker. As a result, it is possible to obtain basically the same effects as the first embodiment described above.
On the other hand, when an odd number of sub fields form 1 field, such as the case where the odd number is 7, the relationship between the light emission times of the pixels of the groups A and B and the sub fields becomes as shown in
A gradation interpolation is made by the error diffusion process of the multi-level gradation processing circuit 12, and the display gradation characteristics of the pixels of the groups A and B respectively become as shown in
To the human eyes, the pixels of the groups A and B having the display gradation characteristics shown in
In other words, even though 1 field is made up of a small number of sub fields, it is possible to set the structure of each field to approximate the optimum sub field structure (that is, the relationship of the gradation levels and the light emission times) that prevents the generation of the pseudo contour and prevents the generation of the flicker. As a result, it is possible to obtain basically the same effects as the first embodiment described above.
Therefore, regardless of whether 1 field is made up of a relatively small odd number or even number of sub fields, it is possible to obtain substantially the same effects as those obtainable in the first embodiment described above.
In this embodiment, the sustain times of each of the sub fields are made approximately uniform (constant) as shown in
In
In other words, as shown in
On the other hand, as shown in
Next, a description will be given of modifications of the first and second embodiments described above.
In a first modification of the first embodiment of the display driving method and the first embodiment of the display driving apparatus, the sustain times of each of the sub fields are set approximately uniform (constant) as shown in
In a second modification of the first embodiment of the display driving method and the first embodiment of the display driving apparatus, the sustain times of each of the sub fields are set approximately uniform (constant) as shown in
In a modification of the second embodiment of the display driving method and the second embodiment of the display driving apparatus, the sustain times of each of the sub fields are set approximately uniform (constant) with respect to the pixel of the group A as shown in
Next, a description will be given of a third embodiment of the display driving apparatus according to the present invention. This embodiment of the display driving apparatus employs a third embodiment of the display driving method according to the present invention. In this embodiment the display driving apparatus has the same construction as that of the second embodiment shown in
In this embodiment, it is assumed for the sake of convenience that 1 field is made up of 7 sub fields SF1 through SF7. In addition, it is assumed that the ratios of the luminance levels of the sub fields SF1 through SF7 are set to satisfy SF1:SF2:SF3:SF4:SF5:SF6:SF7=4:1:4:1:4:1:4.
In this case, the sub fields SF2, SF4 and SF6 belong to a sub field group L, while the sub fields SF1, SF3, SF5 and SF7 belong to a sub field group M. A minute change in the luminance, that is, the lower bits of the data, is described by the sub fields belonging to the sub field group L. On the other hand, a large change in the luminance, that is, the upper bits of the data, is described by the sub fields belonging to the sub field group M.
In other words, the luminance ratios of the 3 sub fields SF2, SF4 and SF6 belonging to the sub field group L are the same. Similarly, the luminance ratios of the 4 sub fields SF1, SF3, SF5 and SF7 belonging to the sub field group M are the same. The luminance quantity of each sub field belonging to the sub field group M corresponds to the luminance quantity amounting to one plus all of the sub fields belonging to the sub field group L. Furthermore, with respect to each of the sub field groups L and M, the light emission times are set similarly to the first or second embodiment described above so that the sustain times (light emission times) increase uniformly from the center point on the time base as the luminance within sub field group increases. In addition, the sub fields which form 1 field are arranged so that the sub field belonging to the sub field group L and the sub field belonging to the sub field group M alternately exist.
When the luminance ratios of the sub fields are all set the same as in the first and second embodiments described above, it is only possible to display 8 gradation levels from the level 0 to the level 7 when 1 field is made up of 7 sub fields. However, according to this embodiment, it is possible to display 20 gradation levels from the level 0 to the level 19 by setting the luminance ratios of the sub fields in the above described manner.
Similarly, when 1 field is made up of 9 sub fields SF1 through SF9, for example, the ratios of the luminance levels of the 9 sub fields SF1 through SF9 are set to satisfy SF1:SF2:SF3:SF4:SF5:SF6:SF7:SF8:SF9=5:1:5:1:5:1:5:1:5. In this case, it is possible to display 30 gradation levels from the level 0 to the level 29. Accordingly, when 1 field is made up of N sub fields SF1 through SFN, it is possible to display [(N−1)/2+1]2+[(N−1)/2]+1 gradation levels from the level 0 to the level [(N−1)/2+1]2+[(N−1)/2] by setting the ratios of the luminance levels of the N sub fields SF1 through SFN to satisfy SF1:SF2:SF3: . . . :SF(N−2):SF(N−1):SFN=(N−1)/2+1:1:(N−1)/2+1: . . . :(N−1)/2+1:1:(N−1)/2+1.
With respect to the sub fields belonging to the sub field groups described above, all of the pixels on the screen are divided into 2 groups A and B so as to have the checker-board arrangement shown on the left hand side in
The gradation characteristic which is subjected to the gradation interpolation by the error diffusion process is indicated by a dotted line in
In each of the embodiments described above, the PDP driving circuit 2 itself may have a known circuit construction. However, an embodiment of the PDP driving circuit 2 will now be described with reference to
The PDP driving circuit 2 shown in
The time chart shown in
With respect to the address display-time and the sustain time of the sub field SF3 shown in
By using the error diffusion technique described above, it is possible to increase the apparent number of gradation levels even when the displayable number of gradation levels is relatively small depending on the number of sub fields which form 1 field. On the other hand, the present inventors have found that the use of the error diffusion technique generates a noise (hereinafter referred to as error diffusion noise) which is similar to quantization noise and is peculiar to the case where the error diffusion technique is used. According to the image quality evaluation experiments conducted by the present inventors, it was confirmed that the error diffusion noise becomes conspicuous to the human eyes when the number of actual display gradation levels of the display becomes 40 to 50 or less. It was also found that the error diffusion noise becomes conspicuous to the human eyes particularly at a low luminance portion of the image. In other words, in he case of an image related to a scenery at night, he error diffusion noise becomes notable at the low luminance portion, that is, the entire dark image, thereby deteriorating the image quality.
Next, a description will be given of embodiments in which the apparent error diffusion noise which is peculiar to the case where the error diffusion technique is used can be reduced even when the number of actual display gradation levels is relatively small.
A description will be given of a fourth embodiment of the display driving method according to the present invention. This embodiment focuses on the fact that the error diffusion noise becomes conspicuous at the low luminance portion of the image. That is, this embodiment effectively utilizes the fact that the error diffusion noise becomes less conspicuous to the human eyes as the luminance becomes higher.
The present inventors made evaluations of the number of display gradation levels which are sensed by the human eyes as image quality deterioration due to the error diffusion noise for each luminance level. The evaluations led to the results shown in
As may be seen from
In this embodiment, as indicated by the hatching in
When the above described sub field allocation is employed, the number of sub fields allocated for displaying the high luminance portion relatively decreases because of the limited number of sub fields forming 1 field, and the resolution decreases by a corresponding amount. However, as may be seen from the evaluation results shown in
The display characteristic for the case where the image data subjected to the error diffusion process is input to the display becomes as indicated by a solid line in
Accordingly, by giving the inverse function correction characteristic shown in
For comparison purposes,
As may be seen by comparing
Next, a description will be given of a fourth embodiment of the display driving apparatus according to the present invention. This embodiment of the display driving apparatus employs the fourth embodiment of the display driving method described above.
This embodiment of the display driving apparatus is characterized by the operations of a light emission time control circuit 101, a scan controller 105 and a distortion correction circuit 111, as described hereunder.
The scan controller 105 determines the length of the light emission time of each sub field, that is, the number of sustain pulses applied to the sustain electrode of the PDP 8, with respect to each pixel when driving the PDP 8. In this embodiment, the number of sustain pulses of each sub field is set as shown in the following Table 1.
Accordingly, the luminance ratios of the sub fields SF1 through SF8 are set to SF1:SF2:SF3:SF4:SF5:SF6:SF7:SF8=1:1:1:1:2:2:3:5.
The light emission time control circuit 101 determines which sub field is to assume the light emission state depending on each luminance level, with respect to each pixel when driving the PDP 8. In this embodiment, when the lengths of the light emission times of each of the sub fields are set as shown above, the sub fields having the light emission state are set as shown in
The distortion correction circuit 111 is provided to correct the non-linear characteristic which is introduced by the scan controller 105 and the light emission time control circuit 101. Because it is desirable that the display characteristic of the PDP 8 is linear, a distortion correction process is carried out with respect to the image data at a stage preceding the error diffusion circuit 12. When the display characteristic indicated by the bold line in
In this embodiment, the distortion correction circuit 111 is made of a ROM. In addition, since the display characteristic indicated by the function f(x) is made up of a plurality of straight lines, the distortion correction circuit 111 may be made up of a logic circuit which realizes a straight line described by y=Ax+B.
Therefore, according to this embodiment, the combined display characteristic of the PDP 8 becomes linear as indicated by a solid line in
The setting of the sub fields which are to assume the light emission state for each luminance level in the light emission time control circuit 101 is of course not limited to the setting shown in
In
In other words, as may be seen from
In addition, when 1 field is made up of N sub fields SF1 through SFN and the display is made in N+1 gradation levels from the luminance level 0 to the luminance level N, the scan controller 105 is constructed so as to satisfy the following relationship. That is, when the sub field which does not assume the light emission state for the luminance level m−1 but first assumes the light emission state for the luminance level m is denoted by SFm, the sub field which does not assume the light emission state for the luminance level m but first assumes the light emission state for the luminance level m=1 is denoted by SFm=1, the length of the light emission time of the sub field SFm is denoted by T(SFm), and the length of the light emission time of the sub field SFm+1 is denoted by T(SFm+1), the scan controller 105 is constructed so as to satisfy the relationship T(SF1)≦T(SF2)≦ . . . ≦T(SFm)≦(SFm+1)≦ . . . ≦T(SFN−1)≦T(SFN).
Furthermore, the display characteristic of the PDP 8 for the case where the image data is subjected to the error diffusion process in the error diffusion circuit 12 is of course not limited to the function f(x) indicated by the bold line in
On the other hand, when it is assumed for the sake of convenience that 1 field is made up of 16 sub fields, the display characteristic of the PDP 8 for the case where the image data is subjected to the error diffusion process in the error diffusion circuit 12 becomes as indicated by the hatching in
Moreover, when it is assumed for the sake of convenience that 1 field is made up of 25 sub fields, the display characteristic of the PDP 8 for the case where the image data is subjected to the error diffusion process in the error diffusion circuit 12 becomes as indicated by the hatching in
In
According to the first through third embodiments described above, it is possible to obtain a relatively large number of actual display gradation levels, the signal-to-noise ratio can be improved by carrying out the error diffusion process, and a satisfactory image can be displayed on the display. However, with respect to a specific image, the first through third embodiments cannot completely eliminate the pseudo contour. On the other hand, according to the fourth embodiment described above, the pseudo contour can be eliminated completely regardless of the image. However, the number of actual display gradation levels becomes relatively small according to the fourth embodiment, and the deterioration of the signal-to-noise ratio to a certain extent is inevitable even if the error diffusion process is carried out.
Next, a description will be given of embodiments which can bring out the most out of the advantageous features of the first through third embodiments and the fourth embodiment.
First, a description will be given of the operating principle of a fifth embodiment of the display driving method according to the present invention.
In this embodiment, a main path and a sub path are provided with respect to an input image signal, and the path which processes the input image signal is switched depending on the image which is indicated by the input image signal. The main path carries out a process in conformance with any of the first through third embodiments described above, while the sub path carries out a process in conformance with the fourth embodiment described above.
For example, when it is assumed for the sake of convenience that 1 field is made up of 8 sub fields, the main path processes the input image signal so that the image is displayable in 52 actual display gradation levels, and the pseudo contour is eliminated in a satisfactory manner. On the other hand, the sub path processes the input image signal so that the image is displayable in 9 actual display gradation levels, and the pseudo contour is eliminated completely.
Accordingly, if the input image signal indicates a specific image from which the pseudo contour cannot be eliminated completely by the processing carried out by the main path, this specific image is detected and the processing path is switched so that only the input image signal corresponding to the specific image is processed by the sub path. The switching of the processing path between the main path and the sub path is carried out in units of pixels based on the detection result, that is, whether or not the input image signal indicates the specific image. Hence, it is possible to make the most out of the advantageous features of both the main and sub paths depending on the input image signal. In other words, the generation of the pseudo contour can be positively prevented, and it is possible to carry out a display control in units of pixels depending on the image indicated by the input image signal.
Next, a description will be given of the PDP driving sequence in this embodiment. For the sake of convenience, it is assumed that 1 field is made up of 8 sub fields SF1 through SF8. In addition, it is assumed that the ratios of the luminance levels of the sub fields SF1 through SF8 are set to satisfy SF1:SF2:SF3:SF4:SF5:SF6:SF7:SF8=12:8:4:2:1:4:8:12. Hence, the PDP driving sequence in this case becomes as shown in
In this case, the main path can process the input image signal to be displayable in 52 actual display gradation levels, and the arrangement of the sub fields having the light emission state for each luminance level becomes as indicated by the hatching in
The display characteristic becomes non-linear when the input image signal is simply processed by the sub path. Thus, an inverse function correction process for correcting the non-linear characteristic and an error diffusion process are carried out, so as to correct the non-linear display characteristic into a linear display characteristic. The display characteristics of the main path and the sub path for this case are shown in
Although the input image signal processed by the main path is displayable in 52 actual display gradation levels, the input image signal processed by the sub path is only displayable in 9 actual display gradation levels. Accordingly, the luminance level of the input image signal which is processed by the sub path must be converted to match the luminance level of the input image signal which is processed by the main path. The following Table 2 is used for such a conversion of the luminance level. This Table 2 will be referred to as a luminance conversion table.
When the input image signal has 8 bits, the input luminance value can be represented in 256 gradation levels from level 0 to level 255. Hence, for the sake of convenience, the processing carried out by the main path and the sub path will now be described for a case where the luminance quantity is 50%, that is, the input luminance value is 128.
The main path includes a first gain control circuit which controls the gain of the input image signal, and a first error diffusion circuit (or multi-level gradation processing circuit). The first gain control circuit multiplies a gain coefficient 51·4÷255=208/255 to the input image signal, that is, the input luminance value 128. The first error diffusion circuit carries out an error diffusion process for obtaining a 6-bit output with respect to the multiplication result from the first gain control circuit. As a result, the input luminance value is represented by the levels 25 and 26 in the luminance level of the main path.
On the other hand, the sub path includes a second gain control circuit which controls the gain of the input image signal, a second error diffusion circuit, and a data matching circuit. The second gain control circuit multiplies a gain coefficient 8·16÷255=128/255 to the input image signal, that is, the input luminance value 128. The second error diffusion circuit carries out an error diffusion process for obtaining a 4-bit output with respect to the multiplication result from the second gain control circuit. As a result, the input luminance value is represented by the levels 5 and 6 in the luminance level of the sub path. These luminance levels 5 and 6 are converted into the luminance levels 19 and 27 of the main path by the data matching circuit using the luminance conversion table. Accordingly, the luminance value output from the data matching circuit is represented by the luminance levels 19 and 27 of the main path.
Therefore, according to this embodiment, the input image signal is displayed on the PDP with the same luminance quantity regardless of whether the input image signal is processed by the main path or the sub path.
By processing the input image signal by the main path or the sub path, it is possible to obtain effects as if two different PDP driving sequences are used, even though the PDP is driven by a single PDP driving sequence. However, the input image signal displayed on the PDP is represented by the original luminance quantity of the input image signal, regardless of whether the input image signal is processed by the main path or the sub path.
An extremely good signal-to-noise ratio is obtained when the input image signal is processed by the main path. On the other hand, although an extremely good signal-to-noise ratio is obtained, the generation of the pseudo contour is completely eliminated when the input image signal is processed by the sub path. Hence, in this embodiment, the main and sub paths are switched so that the image signal related to the pixel which makes the pseudo contour conspicuous is processed by the sub path. As a result, it is possible to always completely eliminate the pseudo contour regardless of the image indicated by the input image signal. The pixel which makes the pseudo contour conspicuous or the pixel which easily generates the pseudo contour (such pixels will hereinafter be simply referred to as pixels which make the pseudo contour conspicuous) can be detected by a combination of the detection methods described below.
The pseudo contour is easily generated at a moving object within the image. According to a first detection method, a moving region within the image indicated by the input image signal is detected so as to detect the pixels which make the pseudo contour conspicuous. More particularly, a difference is obtained between the input image signal of the present field and the input image signal of 1 field before or, a difference is obtained between the input image signal of the present field and the input image signal of 2 fields before, and the pixel in the moving region is detected based on the difference, that is, a level difference.
The pseudo contour becomes notable at a portion of the image where the gradation level smoothly or gradually changes. In other words, it is difficult to detect the pseudo contour at a portion of the image including a large number of high-frequency components. Hence, according to a second detection method, the edge component within the image indicated by the input image signal, that is, the spatial frequency characteristic, is detected, so as to detect the pixel which makes the pseudo contour conspicuous. The processing path is switched to the sub path at the portion of the image where the gradation level smoothly or gradually changes, that is, the portion including a large number of low-frequency components, so that the input image signal is processed by the sub path at such a portion, thereby increasing the sensitivity.
The edge component can also be used when detecting the moving region within the image. At the edge portion of the image, the difference between the input image signals of 2 successive fields, for example, becomes relatively large even for a region which makes an extremely small movement. Hence, in this case, the possibility of the moving quantity becoming unnecessarily large is high. For this reason, the edge component can be used by dividing the difference by the edge component when normalizing the moving quantity.
Furthermore, the pseudo contour is easily generated at specific luminance portions within the image. For example, when the arrangement of the sub fields having the light emission state shown in
Hence, according to the third detection method, the specific luminance portion within the image indicated by the input image signal, that is, the luminance level in the range where the pseudo contour is conspicuous, is detected, so as to detect the pixel which makes the pseudo contour conspicuous.
Of course, the method of detecting the pixel which makes the pseudo contour conspicuous is not limited to the combination of the first through third detection methods described above.
Accordingly, a path selection/switching signal which determines which one of the main and sub paths is to be used to process the input image signal, can be generated based on the pixels which make the pseudo contour conspicuous and are detected by the method such as the first through third methods described above, depending on the image indicated by the input image signal. By use of such a path selection/switching signal, it is possible to switch the processing path to the sub path which has the higher capability of eliminating the pseudo contour, only when processing the data of the pixels which make the pseudo contour conspicuous. As described above, the pixels which make the pseudo contour conspicuous correspond to the moving object within the image, including a smooth change in the gradation level, and having the specific luminance level, that is, the luminance level where the sub fields having the light emission state greatly change with the change in the gradation level of the main path. The data related to the pixels which make the pseudo contour conspicuous and are detected from such features, are processed by the sub path before being supplied to the PDP, while the data related to other pixels are processed by the main path and supplied to the PDP.
Accordingly, the input image signal is normally processed by the main path which realizes an extremely good signal-to-noise ratio and a large number of actual display gradation levels on the PDP. On the other hand, although the signal-to-noise ratio slightly deteriorates, the input image signal at the image portion having a high possibility of generating the pseudo contour is processed by the sub path which has an extremely high pseudo contour elimination capability before being displayed on the PDP. In this case, the sub fields having the light emission state in the main path and the sub fields having the light emission state in the sub path have a close relationship to each other, and for this reason, a boundary portion where the processing path is switched is virtually inconspicuous. In addition, since the image indicated by the input image signal which is processed by the sub path is basically a moving body, the signal-to-noise ratio of the image processed by the sub path slightly deteriorates compared to that processed by the main path, but no problems are introduced from the practical point of view because the image deterioration is virtually undetectable by the human eyes. As a result, this embodiment can greatly improve the display characteristic of the moving image on the PDP.
Next, a description will be given of a fifth embodiment of the display driving apparatus according to the present invention. This fifth embodiment of the display driving apparatus employs the fifth embodiment of the display driving method described above.
In
In addition, the light emission time control circuit 101 determines which sub fields are to assume the light emission state depending on each luminance level and combined. When the table shown in
When the image is divided into two groups A and B having the pixels arranged in the checker-board pattern and the sub fields having the light emission state are to be switched between the two groups A and B, the light emission time control circuit 101 carries out the process of overlapping the arrangement of the sub fields having the light emission state shown in
The main path 61 includes a gain control circuit 611 and an error diffusion circuit 612 which are connected as shown in
The maximum luminance level displayable on the PDP 8 via the main path 61 is 51 using the 6-bit output. In addition, the maximum luminance level of the input image signal is 255 using an 8-bit input. For this reason, the gain control circuit 611 multiplies a gain coefficient 51·28−6/255=204/255 to the input image signal. By multiplying this gain coefficient to the input image signal, it becomes possible to carry out an error diffusion process for the entire region of the input image signal in the error diffusion circuit 612 which is provided at a subsequent stage. The gain control circuit 611 can be formed by a general multiplier, a ROM, a RAM or the like.
The error diffusion circuit 612 carries out an error diffusion process with respect to the image signal which is received via the gain control circuit 611, so as to generate a pseudo-half tone, so as to give an impression as if the number of gradation levels have increased. In this embodiment, the number of display gradation levels of the main path 61 is 52, and the number of output bits of the error diffusion circuit 612 is 6.
The construction of the main path 61 and the constructions of the gain control circuit 611 and the error diffusion circuit 612 which form the main path 61 can easily be understood from the first and third embodiments described above. For this reason, a detailed description thereof will be omitted.
In this embodiment, it is assumed that the sub path 62 represents 9 actual display gradation levels by a 4-bit output. In this case, it is also assumed that the arrangement of the sub fields having the light emission state for each luminance level of the RGB signals is the same as the arrangement shown in
The sub path 62 can represent the gradation in 9 steps from the level 0 to the level 8, however, the luminance quantity increases as 0, 1, 3, 7, 11, . . . , and the change in luminance quantity is not uniform. Hence, a correction using an inverse function is carried out with respect to the display characteristic after the error diffusion process, so as to obtain a linear display characteristic as a whole. The distortion correction circuit 621 stores such an inverse function characteristic in a ROM or RAM table.
The maximum luminance level displayable on the PDP 8 via the sub path 62 is 8 using the 4-bit output. In addition, the maximum luminance level of the input image signal is 255 using the 8-bit input. For this reason, the gain control circuit 622 multiplies a gain coefficient 8·28−4/255=128/255 to the input image signal. By multiplying this gain coefficient to the input image signal, it becomes possible to carry out an error diffusion process for the entire region of the input image signal in the error diffusion circuit 623 which is provided at a subsequent stage. The gain control circuit 622 can be formed by a general multiplier, a ROM, a RAM or the like.
The error diffusion circuit 623 carries out an error diffusion process with respect to the image signal which is received via the gain control circuit 622, so as to generate a pseudo-half tone, so as to give an impression as if the number of gradation levels have increased. In this embodiment, the number of display gradation levels of the sub path 62 is 9, and the number of output bits of the error diffusion circuit 623 is 4.
The construction of the sub path 62 and the constructions of the gain control circuit 622 and the error diffusion circuit 623 which form the sub path 62 can easily be understood from the fourth embodiment described above. For this reason, a detailed description thereof will be omitted.
The data matching circuit 624 is provided to match the luminance level of the sub path 62 to the luminance level of the main path 61. In this embodiment, the data matching circuit 624 is formed by a ROM or RAM table containing the information shown in the Table 2 described above.
The switching circuit 63 switches the path which is used to process the input image signal depending on the input image signal, that is, based on the path selection/switching signal received from the image feature judging unit 64. Hence, with respect to the RGB signals forming the input image signal, the path switching is carried out independently for each of the primary colors R, G and B. Thus, even in the case of the RGB signals related to the same pixel, the R signal may be processed by the main path 61 while the G signal and the B signal are processed by the sub path 62, for example.
Next, a description will be given of the operation of the image feature judging unit 64. The image feature judging unit 64 detects the image in which the pseudo contour is easily generated, and generates the path selection/switching signal which instructs the switching circuit 63 to switch the processing path so that the sub path 62 processes the pixel data of the image in which the pseudo contour is easily generated.
As described above, the pseudo contour is generated at the specific luminance. In other words, even if the gradation level only changes by an extremely small amount, the pseudo contour is easily generated at the luminance level where the sub fields having the light emission state greatly change on the time base. Hence, based on the output of the error diffusion circuit 612 of the main path 61, the level detection circuit 641 supplies to the judging circuit 644 a signal which controls the sensitivity with which the processing path is switched to the sub path 62 in response to the path selection/switching signal which is output from the judging circuit 644. More particularly, the level detection circuit 641 outputs a signal which increases the sensitivity with which the processing path is switched to the sub path 62 at the luminance level where the pseudo contour is conspicuous, and outputs a signal which decreases the sensitivity with which the processing path is switched to the sub path 62 at the luminance level where the pseudo contour is originally difficult to detect even if the image includes a portion which moves considerably.
The level detection circuit 641 detects the luminance level using the output image data of the main path 61, because the luminance level where the pseudo contour is conspicuous is approximately determined depending on the arrangement of the sub fields having the light emission state in the main path 61.
At the portion within the image including a large number of high-frequency components, that is, at the edge portion, a difference is detected between the fields even in a region which moves by an extremely small amount, and the moving quantity is detected with an unnecessarily large value. Hence, the edge detection circuit 642 detects the edge portion within the image based on the input image signal and supplies the detected edge component to the judging circuit 644. Accordingly, the judging circuit 644 can normalize the moving quantity, that is, the degree of motion, by dividing the difference by the edge component, as will be described later. As a result, the moving quantity of the edge portion is suppressed, and the judging circuit 644 generates the path selection/switching signal so that the edge portion will not be processed by the main path 61.
In addition, the pseudo contour becomes conspicuous at the portion of the image where the gradation level smoothly or gradually changes. In other words, the pseudo contour is difficult to detect at a portion of the image including a large number of high-frequency components. Such a characteristic of the pseudo contour is also an important factor to be considered when judging the path switching. The edge detection circuit 642 supplies to the judging circuit 644 a signal which controls the sensitivity with which the processing path is switched to the sub path 62 in response to the path selection/switching signal, based on the input image signal. More particularly, the sensitivity with which the processing path is switched to the sub path 62 is controlled so that the low-frequency region having a smooth change in the gradation level is more easily processed by the sub path, that is, the edge portion is more easily processed by the main path 61.
Basically, the moving region detection circuit 643 detects the region including motion within the image based on the difference between the image of the present field and the image of 1 field before, the difference between the image of the present field and the image of 2 fields before and the like. More particularly, the moving region detection circuit 643 calculates the moving quantity of each pixel based on an absolute value of the difference which is obtained from the input image signal.
The judging circuit 644 judges whether or not the pseudo contour is easily generated in the image data to be processed, based on the luminance level detected by the level detection circuit 641, the edge portion within the image detected by the edge detection circuit 642, and the region including motion within the image detected by the moving region detection circuit 643. In addition, the judging circuit 644 generates and supplies the path selection/switching signal to the switching circuit 63 so that only the image data in which the pseudo contour is easily generated is processed by the sub path 62.
The image feature judging unit 64 shown in
The circuit scale becomes extremely large when the motion detection and the edge detection with respect to the image is carried out independently in the three processing systems corresponding to the three primary colors R, G and B. For this reason, this embodiment generates a luminance signal in the RGB matrix circuit 645 from each of the RGB signals. Using this luminance signal as a representative signal, the moving region detection circuit 643 detects the moving region of the image, and the edge detection circuit 642 detects the edge portion of the image. In addition, a luminance signal Y is generated using a generating formula approximated by Y=0.30R+0.59G+0.11B, for example.
The moving region detection circuit 643 detects the region including motion within the image, based on a minimum value of the difference between the luminance signals of 1 field interval and the difference between the luminance signals of 2 field intervals. The detection result of the moving region detection circuit 643 is supplied to the judging circuit 644-1. On the other hand, the edge detection circuit 642 calculates an edge in the horizontal direction (horizontal line) and an edge in the vertical direction (vertical line) from the luminance signal, and obtains an edge quantity by mixing these calculated edges. The obtained edge quantity is supplied to the judging circuit 644-1. Accordingly, the judging circuit 644-1 judges the pixels which easily generate the pseudo contour based on output information of the moving region detection circuit 643 and the edge detection circuit 642. A judgement result of the judging circuit 644-1 is supplied to the judging circuit 644-2.
On the other hand, the level detection circuit 641 detects the luminance level based on each of the RGB signals from the main path 61. The luminance level detected by the level detection circuit 641 is supplied to the judging circuit 644-2. Hence, based on the judgement result from the judging circuit 644-1 and the luminance level detected by the level detection circuit 641, the judging circuit 644-2 generates the path selection/switching signal so that the pixel data greater than a predetermined level are processed by the sub path 62 and supplies this path selection/switching signal to the switching circuit 63. The level detection circuit 641 and the judging circuit 644-2 form a level detection unit 646.
According to this embodiment, the input image signal is normally processed by the main path 61 which secures a certain number of gradation levels, and the processing path is automatically switched to the sub path 62 only with respect to the pixel data of the pixels which easily generate the pseudo contour. For this reason, the input image signal is normally processed by the main path 61 which realizes an extremely good signal-to-noise ratio and a large number of actual display gradation levels on the PDP 8. On the other hand, although the signal-to-noise ratio slightly deteriorates, the input image signal at the image portion having a high possibility of generating the pseudo contour is processed by the sub path 62 which has an extremely high pseudo contour elimination capability before being displayed on the PDP 8. In this case, the sub fields having the light emission state in the main path 61 and the sub fields having the light emission state in the sub path 62 have a close relationship to each other, and thus, a boundary portion where the processing path is switched is virtually inconspicuous. In addition, since the image indicated by the input image signal which is processed by the sub path 62 is basically a moving body, the signal-to-noise ratio of the image processed by the sub path 62 slightly deteriorates compared to that processed by the main path 61, but no problems are introduced from the practical point of view because the image deterioration is virtually undetectable by the human eyes. As a result, this embodiment can greatly improve the display characteristic of the moving image on the PDP 8.
The edge detection circuit 642 includes 1H delay circuits 81 and 82, a delay circuit 83, subtracting circuits 84 and 85, absolute value circuits 86 and 87, maximum value detecting circuits 88 and 89, multiplying circuits 90, 91 and 93, and an adding circuit 92 which are connected as shown in
In addition, the judging circuit 644-1 includes a dividing circuit 131, and in this embodiment, an isolated point elimination circuit 12, a temporal filter 133 and a two-dimensional lowpass filter 134 are coupled to the output side of the dividing circuit 131, as will be described later. Furthermore, the level detection unit 646 includes a sensitivity RAM 141, a multiplying circuit 142 and a comparator 143 which are connected as shown in
In the edge detection circuit 642, the subtracting circuit 84 obtains a difference between the present input luminance signal Y and the input luminance signal Y of 2H before, and the absolute value circuit 86 obtains an absolute value of the difference obtained in the subtracting circuit 84. The maximum value detection circuit 88 detects a maximum value of the absolute value obtained in the absolute value circuit 86. For example, the maximum value detection circuit 88 obtains the three largest absolute values obtained in the absolute value circuit 86, and supplies the three values to the multiplying circuit 90. A coefficient which determines the sensitivity with which the horizontal edge extending in the horizontal direction is detected is input to the multiplying circuit 90, and an output of this multiplying circuit 90 is supplied to the adding circuit 92.
On the other hand, the delay circuit 83 delays the input luminance signal Y by a pixel unit D, and thus, the subtracting circuit 85 obtains a difference between the pixels of the input image signal. The absolute value circuit 87 obtains an absolute value of the difference that is obtained in the subtracting circuit 85. The maximum value detection circuit 89 detects a maximum value of the absolute value obtained in the absolute value circuit 87. For example, the maximum value detection circuit 89 obtains the three largest absolute values obtained in the absolute value circuit 87, and supplies the three values to the multiplying circuit 91. A coefficient which determines the sensitivity with which the vertical edge extending in the vertical direction is detected is input to the multiplying circuit 91, and an output of this multiplying circuit 91 is supplied to the adding circuit 92.
An output of the adding circuit 92 is supplied to the multiplying circuit 93 which multiplies a coefficient that determines the edge detection sensitivity as a whole. As a result, the multiplying circuit 93 outputs a signal which indicates the edge quantity, and this output signal of the multiplying circuit 93 is supplied to the dividing circuit 131 which will be described later.
In the moving region detection circuit 643, the subtracting circuit 123 obtains a difference between the input luminance signals Y of 2 mutually adjacent fields, and supplies this difference to the absolute value circuit 125. The subtracting circuit 124 obtains a difference between the input luminance signals of 1 field intervals, and supplies this difference to the absolute value circuit 126. Hence, the absolute value circuit 125 obtains an absolute value of the difference between the input luminance signal Y of the present field and the input luminance signal Y of 1 field before, and supplies this absolute value to the minimum value detection circuit 127. On the other hand, the absolute value circuit 126 obtains an absolute value of the difference between the input luminance signal Y of the present field and the input luminance signal Y of 2 fields before, and supplies this absolute value to the minimum value detection circuit 127.
The minimum value detection circuit 127 obtains a minimum value out of the absolute values obtained in the absolute value circuits 125 and 126, and supplies this minimum value to the dividing circuit 131 as a signal indicating the moving quantity. When a non-interlace system is employed, there is a possibility of a difference being detected between an odd numbered field and a following even numbered field, even if no movement actually exists within the image. For this reason, the differences are obtained between the input luminance signal Y of the present field and the input luminance signal Y of 1 field before, and between the input luminance signal Y of the present field and the input luminance signal Y of 2 fields before, and the moving quantity is obtained from the minimum value of the absolute values of these differences.
For example, the unit of absolute values of the differences obtained in the absolute value circuits 125 and 126 is level/field, and the unit of the moving quantity obtained in the minimum value circuit 127 is dots/field. The moving quantity can be described by “Moved Quantity (dots/field)”=[(|“Difference (Minimum Value) (level/field)”|)]÷[|Slope (level/dots)|].
The dividing circuit 131 divides the moving quantity obtained from the minimum value detection circuit 127 by the edge quantity obtained from the multiplying circuit 93, and normalizes the degree of motion within the image, that is, normalizes the moving quantity. The normalized moving quantity obtained in the dividing circuit 131 is supplied to the multiplying circuit 142 of the level detection unit 646 via the isolated point elimination circuit 132, the temporal filter 133 and the two-dimensional lowpass filter 134.
The isolated point elimination circuit 132 is provided to eliminate the isolated image data such as noise. For example, if 1 pixel at a central portion within a predetermined range of the image is moving although the pixels in the peripheral portion of this predetermined range do not indicate motion, this 1 pixel at the central portion may be regarded as noise. Accordingly, in such a case, the isolated point elimination circuit 132 eliminates the isolated point. More particularly, the isolated point can be eliminated by comparing the moving quantity of the pixel of each line with a threshold value and regarding that the pixel indicates no motion when the moving quantity of the pixel is less than the threshold value.
The temporal filter 133 is provided to correct the falling edge of the level of the pixel data indicating motion, so that the falling edge becomes gradual on the time base. For example, when a specific pixel within the image is moving but stops suddenly, the pixel data related to this specific pixel is stationary, but the specific pixel does not immediately appear stationary to the human eye due to the after image effect and the like. Hence, the temporal filter 133 corrects the falling edge of the level of the pixel data indicating motion to become gradual on the time base, so as to reduce the unnaturalness of the image displayed on the PDP 8 depending on the characteristic of the human eyes. More particularly, the temporal filter 133 obtains a maximum value from the moving quantity received from the isolated point elimination circuit 132 and a value read from a memory which will be described later, multiplies a coefficient which is less than 1 to this maximum value and stores the multiplication result in the memory. The obtained maximum value is supplied to the two-dimensional lowpass filter 134 as the output of the temporal filter 133. In other words, the moving quantity stored in the memory gradually decreases, and the moving quantity output from the temporal filter gradually decreases even when the actual moving quantity becomes zero.
The two-dimensional lowpass filter 134 corrects the pixel data of 1 pixel based on the pixel data of the surrounding pixels, so as to average the pixel data within a certain range. Hence, it is possible to prevent 1 pixel from having a level extremely different from the levels of the surrounding pixels. In other words, the two-dimensional lowpass filter 134 corrects the moving quantity in the two-dimensional space. The two-dimensional lowpass filter 134 itself is known, and a detailed description thereof will be omitted in this specification.
The level detection unit 646 includes a detection circuit part which is made up of a sensitivity RAM 141, a multiplying circuit 142 and a comparator 143, with respect to each of the RGB processing systems. Hence, three such detection circuit parts are provided in this embodiment. For example, the output of the main path 61 of the R-processing system is supplied to the sensitivity RAM 141 within the detection circuit part of the R-processing system, and the multiplying circuit 142 multiplies a coefficient which is read from the sensitivity RAM 141 to the moving quantity received from the two-dimensional lowpass filter 134. The multiplied result from the multiplying circuit 142 is supplied to the comparator 143 and compared with a threshold value. The comparator 143 outputs the path selection/switching signal for switching the processing path of the R-processing system to the sub path 62 when the moving quantity from the multiplying circuit 142 is greater than the threshold value. The detection circuit parts of the G-processing system and the B-processing system similarly output the path selection/switching signals for instructing the switching of the processing paths of the G-processing system and the B-processing system based on the independent outputs from the main paths 61 of the G-processing system and the B-processing system.
Accordingly, in each of the RGB processing system,s the input image signal (RGB signals) is normally processed by the main path 61 having a relatively large number of gradation levels. On the other hand, in each of the RGB processing systems, the pixel data of the pixels which easily generate the pseudo contour are processed by the sub path 62 by automatically switching the processing path to the sub path 62. In principle, the signal-to-noise ratio of the image indicated by the pixel data which are processed by the sub path 62 is slightly deteriorated when compared to that of the image indicated by the pixel data which are processed by the main path 61. However, the image indicated by the pixel data which are processed by the sub path 62 correspond to a moving image portion, and no problems are introduced from the practical point of view because such a slight deterioration in the signal-to-noise ratio of the moving image is virtually undetectable by the human eyes. In this case, the operation parameters of the various parts of the main path 61 and the sub path 62 are set so that the deterioration of the signal-to-noise ratio caused by the processing of the pixel data in the sub path 62 is inconspicuous to the human eyes. In addition, the operation parameters of the various parts of the main path 61 and the sub path 62 must of course be appropriately reset to optimum parameters every time the driving sequence of the PDP 8 is changed, the sub field structure of the PDP 8 is changed or the like.
In
Next, a description will be given of a sixth embodiment of the display driving apparatus according to the present invention. The construction of this sixth embodiment of the display driving apparatus is the same as that shown in
In this embodiment, 1 field is made up of 8 sub fields SF1 through SF8, and the ratios of the number of sustain pulses in each of the sub fields are set to SF1:SF2:SF3:SF4:SF5:SF6:SF7:SF8=1:2:4:4:8:8:12:12. Accordingly, the driving sequence of the PDP 8 becomes as shown in
In this embodiment, the number of actual display gradation levels of the main path 61 is 52, and the number of actual display gradation levels of the sub path 62 is 9. Hence, the display characteristic of this embodiment is the same as that of the fifth embodiment described above and shown in
Next, a description will be given of a seventh embodiment of the display driving apparatus according to the present invention. The construction of this seventh embodiment of the display driving apparatus is the same as that shown in
In this embodiment, 1 field is made up of 8 sub fields SF1 through SF8, and the ratios of the number of sustain pulses in each of the sub fields are set to SF1:SF2:SF3:.SF4:SF5:SF6:SF7:SF8=1:2:4:8:8:8:8:8. Accordingly, the driving sequence of the PDP 8 becomes as shown in
In this embodiment, the number of actual display gradation levels of the main path 61 is 48 from the level 0 to the level 47, and the number of actual display gradation levels of the sub path 62 is 9 from the level 0 to the level 8.
Next, a description will be given of an eighth embodiment of the display driving apparatus according to the present invention. The construction of this eighth embodiment of the display driving apparatus is the same as that shown in
In this embodiment, 1 field is made up of 8 sub fields SF1 through SF8, and the ratios of the number of sustain pulses in each of the sub fields are set to SF1:SF2:SF3:SF4:SF5:SF6:SF7:SF8=1:2:4:8:16:32:64:128. In other words, the luminance ratios of the 8 sub fields SF1 through SF8 are set to satisfy 2j, where j is 1 less than the sub field number, that is, j=0, 1, . . . , 7. In this embodiment, the number of actual display gradation levels of the main path 61 is 256, and the number of actual display gradation levels of the sub path 62 is 9.
In addition,
Therefore, according to the fifth through eighth embodiments, it is possible to realize a display driving method and apparatus which make a luminance representation depending on a length of a light emission time, wherein a first image signal having a gradation levels is generated in a main path from an input image signal having n gradation levels while satisfying a≦n, a second image signal having b gradation levels is generated in a sub path from the input image signal independently of the first image signal while satisfying b<a≦n, and the first image signal and the second image signal are switched and output in units of pixels, where n, a and b are integers.
Similarly, according to the fifth through eighth embodiments, it is possible to realize a display driving method and apparatus which make a luminance representation depending on a length of a light emission time, wherein a first image signal having a gradation levels is generated in a main path by carrying out an error diffusion process with respect to an input image signal having n gradation levels while satisfying a<n, a second image signal having b gradation levels is generated in a sub path by carrying out an error diffusion process with respect to the input image signal while satisfying b<a<n, and the first image signal and the second image signal are switched and output in units of pixels, where n, a and b are integers.
The correction process that is carried out with respect to the image signal using an inverse function of a non-linear display characteristic of the PDP in order to correct the non-linear display characteristic into a linear display characteristic, may also be carried out in the main path in addition to being carried out in the sub path.
In each of the embodiments and modifications described above, the present invention is applied to the A.C. type PDP. However, the present invention is of course applicable to any display or display panel which makes the luminance representation depending on the length of the light emission time, that is, depending on a combination of sub fields having the light emission state by dividing a unit field into a plurality of sub fields. Hence, the present invention is similarly applicable to displays such as the D.C. type PDP and the digital micromirror device (DMD). The effect of preventing generation of the pseudo contour can also be obtained by applying the present invention to such displays.
Of course, the present invention also includes a display unit having any of the embodiments and modifications described above.
Further, the present invention is not limited to these embodiments, but various variations and modifications may be made without departing from the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 7-275911 | Oct 1995 | JP | national |
| 8-122075 | May 1996 | JP | national |
| 8-263398 | Oct 1996 | JP | national |
This application is a continuation of application Ser. No. 09/548,362, filed Apr. 12, 2000, now allowed, which is divisional application of application Ser. No. 08/735,750, filed Oct. 23, 1996, now U.S. Pat. No. 6,144,364 issued Nov. 7, 2000.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4414544 | Suste | Nov 1983 | A |
| 4980678 | Zenda | Dec 1990 | A |
| 5014124 | Fujisawa | May 1991 | A |
| 5034990 | Kless | Jul 1991 | A |
| 5075683 | Ghis | Dec 1991 | A |
| 5196839 | Johary et al. | Mar 1993 | A |
| 5198803 | Shie et al. | Mar 1993 | A |
| 5229762 | Itoh et al. | Jul 1993 | A |
| 5311169 | Inada et al. | May 1994 | A |
| 5317334 | Sano | May 1994 | A |
| 5400044 | Thomas | Mar 1995 | A |
| 5475448 | Saegusa | Dec 1995 | A |
| 5483634 | Hasegawa | Jan 1996 | A |
| 5491496 | Tomiyasu | Feb 1996 | A |
| 5541618 | Shinoda | Jul 1996 | A |
| 5572236 | Feig et al. | Nov 1996 | A |
| 5585818 | Sibamiya | Dec 1996 | A |
| 5604514 | Hancock | Feb 1997 | A |
| 5684499 | Shimizu et al. | Nov 1997 | A |
| 5724054 | Shinoda | Mar 1998 | A |
| 5757343 | Nagakubo | May 1998 | A |
| 5874932 | Nagaoka et al. | Feb 1999 | A |
| 6097358 | Hirakawa et al. | Aug 2000 | A |
| 6414658 | Tokunaga | Jul 2002 | B1 |
| 20030231147 | Jeong et al. | Dec 2003 | A1 |
| 20040130509 | Yoon et al. | Jul 2004 | A1 |
| 20040135747 | Yoon | Jul 2004 | A1 |
| Number | Date | Country |
|---|---|---|
| 0 264 302 | Mar 1988 | EP |
| 0 488 891 | Jun 1992 | EP |
| 0 525 527 | Feb 1993 | EP |
| 92-22814 | Dec 1992 | JP |
| 5-108026 | Apr 1993 | JP |
| 7-175439 | Jul 1995 | JP |
| 7-261696 | Oct 1995 | JP |
| 7-261699 | Oct 1995 | JP |
| 7-271325 | Oct 1995 | JP |
| 7-302061 | Nov 1995 | JP |
| 9409473 | Apr 1994 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20040263434 A1 | Dec 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 08735750 | Oct 1996 | US |
| Child | 09548362 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09548362 | Apr 2000 | US |
| Child | 10846754 | US |
