Patent Application
20050184976
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2004-045131, filed on Feb. 20, 2004, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an image display apparatus and a driving method for the same, and more particularly to an image display apparatus and a driving method for the same, particularly suited to drive a plasma display panel (PDP).
2. Description of the Related Art
With the recent trend toward larger-screen displays, the need for thin display apparatuses has been increasing, and various types of thin display apparatus have been commercially implemented. For example, matrix panels that display images by directly using digital signals are being offered, such as PDPs and other gas discharge display panels, digital micromirror devices (DMDs), EL display devices, fluorescent display tubes, and liquid crystal display devices. Among such thin display apparatuses, gas discharge display panels have been commercially implemented as large-area, direct-view HDTV (high-definition television) display devices, because of their simple process facilitating the fabrication of large-area displays, their self-luminescent properties ensuring good display quality, and their high response speeds.
In a plasma display apparatus, each field (frame) is divided into a plurality of weighted subfields (SFs: light-emission blocks) each comprising a plurality of sustain discharge pulses (sustain pulses), and an image is displayed by controlling the light-emission ON/OFF state of each individual subfield so as to achieve multiple grayscale levels. In such an image apparatus that displays an image in multiple grayscale levels by controlling the ON/OFF states of the respective subfields, it is desired to improve the display capability at low grayscale levels, and it is needed to lengthen the period during which the driving mode remains switched to a driving sequence designed to enhance the display capability at low grayscale levels, while reducing the shock associated with the driving sequence switching. It is also needed to reduce the power consumption by shortening the sustain light-emission period.
In the prior art, there is proposed a display driving method in which, when the maximum luminance is low, and there is a subfield that does not emit light, a subfield whose sustain period is one half of that in the least significant subfield is provided to increase the number of grayscale levels on the black side (refer, for example, to Japanese Unexamined Publication (Kokai) No. 11-065521).
There is also proposed in the prior art an image display apparatus equipped with an adjuster for adjusting the number, Z, of subfields based on image brightness information in order to adjust the brightness of the plasma display panel, and thus capable of adjusting the number of subfields according to the brightness (refer, for example, to Japanese Unexamined Publication (Kokai) No. 11-231825).
The prior art further proposes a PDP display driving pulse control device in which an adjuster is provided that adjusts weight multiplier N (N is a positive integer or a decimal fraction) based on image brightness information so that, even when the weight multiplier changes, the brightness does not change abruptly, and so that the brightness of the plasma display panel can be adjusted without giving the viewer an unnatural feeling (refer, for example, to Japanese Unexamined Publication (Kokai) No. 11-231833).
The prior art and its associated problems will be described in detail later with reference to accompanying drawings.
According to the present invention, there is provided an image display apparatus displaying an image in multiple grayscales on a display panel by combining a plurality of weighted subfields into which one field has been divided, comprising an SF usage rate detection circuit detecting the number of pixels used within one field period for each weight of encoded subfield data; a display SF selection circuit outputting a light emission pattern table selection signal, based on an output of the SF usage rate detection circuit; an SF conversion circuit receiving an input image signal as well as the selection signal output from the display SF selection circuit, selecting one of a plurality of prestored light emission pattern tables in accordance with the selection signal, and outputting the encoded subfield data by encoding the input image signal in accordance with the selected light emission pattern table; and a driving control circuit receiving the output of the SF conversion circuit, and driving the display panel in accordance with a prescribed driving sequence.
The SF usage rate detection circuit may include an adder circuit counting up the number of pixels for each of the subfields. The SF usage rate detection circuit may include a usage rate calculating circuit calculating an usage rate of the subfield from an output of the adder circuit.
The SF usage rate detection circuit may take an image input as an input signal. The SF usage rate detection circuit may include an comparator circuit comparing the input image with a predetermined value, and an adder circuit counting up the number of pixels each of which has been determined by the comparator circuit as being equal to or greater than the predetermined value. As many combinations of the comparator circuit and the adder circuit may be provided as the number of light emission tables minus one. The predetermined value used for comparison in the comparator circuit may be a value in the vicinity of a maximum grayscale that is represented by the subfields used for display in the light emission pattern table.
A plurality of the driving sequences may be preset, and wherein the driving control circuit may select one driving sequence that matches the selected light emission pattern table, and may drive the display panel in accordance with the selected driving sequence. The SF usage rate detection circuit may count up the number of pixels over one field period for each weighted subfield data encoded into the subfield data, and may output resulting data on a field-by-field basis. The SF conversion circuit may preselect data to select one of the plurality of light emission pattern tables in accordance with data provided in an arbitrary one of the light emission pattern tables.
Pattern data indicating a light-emission ON/OFF state for each subfield in an arbitrary one of the light emission pattern tables may be data for driving the display panel, and may be also data based on which to switch between the light emission pattern tables. The driving control circuit may drive the display panel by using pattern data in an arbitrary one of the light emission pattern tables; and the SF conversion circuit may select the light emission pattern table by using pattern data that is not used for driving the display panel in the arbitrary one of the light emission pattern tables. Pattern data used by the driving control circuit for driving the display panel may comprise one or more kinds of pattern data including the least heavily weighted pattern data in the light emission table.
The display SF selection circuit may switch the output of the display SF selection circuit when the output of the SF usage rate detection circuit for each weighted subfield is detected as being equal to or lower than a predetermined value. The display SF selection circuit may switch the output of the display SF selection circuit when the output of the SF usage rate detection circuit for one or a plurality of weighted subfields is detected as being zero. The display SF selection circuit may switch an output bit count of the SF usage rate detection circuit in accordance with the output of the display SF selection.
The display SF selection circuit may switch the output on a field-by-field basis, and may determine the present output value based on an output result of a previous field. The output of the display SF selection circuit may have a hysteresis characteristic. The image display apparatus may further comprise an error diffusion control circuit, provided between an image input and the SF conversion circuit, for switching an output bit count of an error diffusion circuit in accordance with the output of the display SF selection circuit.
The driving control circuit may switch from one driving sequence to another progressively in one or a plurality of steps. The one or the plurality of steps where the driving control circuit switches from one driving sequence to another may involve making a sustain period in a relatively heavily weighted and unused subfield equal to or shorter than a sustain period in the least heavily weighted subfield used for display driving, or equal to zero. The one or the plurality of steps where the driving control circuit may switches from one driving sequence to another may involve stopping a relatively heavily weighted subfield having a usage rate of zero. The one or the plurality of steps where the driving control circuit switches from one driving sequence to another may involve inserting a quiescent period before the first subfield or between arbitrarily selected subfields.
The one or the plurality of steps where the driving control circuit switches from one driving sequence to another may involve lengthening a quiescent period gradually in steps, until the quiescent period becomes substantially equal in duration to the period of the least heavily weighted subfield currently driven. The one or the plurality of steps where the driving control circuit switches from one driving sequence to another may involve lengthening a quiescent period gradually in steps, until the quiescent period becomes substantially equal in duration to the period of a subfield whose weight is smaller by one than the least heavily weighted subfield currently driven. The one or the plurality of steps where the driving control circuit switches from one driving sequence to another may involve, in a final step thereof, inserting in a quiescent period a subfield whose weight is smaller by one than the least heavily weighted subfield currently displayed.
The one or the plurality of steps where the driving control circuit switches from one driving sequence to another may involve, in a final step thereof, inserting in a quiescent period a subfield whose weight is smaller by one than the least heavily weighted subfield currently displayed, and stopping a subfield to which the most heavily weighted subfield data is assigned. The one or the plurality of steps where the driving control circuit switches from one driving sequence to another may involve, in a final step thereof, inserting in a quiescent period a subfield whose weight is smaller by one than the least heavily weighted subfield currently displayed, and rearranging the time order in which to drive the plurality of subfields. The one or the plurality of steps where the driving control circuit switches from one driving sequence to another may involve, in a final step thereof, inserting in a quiescent period a subfield whose weight is smaller by one than the least heavily weighted subfield currently displayed, and rearranging the time order in which to drive the plurality of subfields, in order of increasing weight.
According to the present invention, there is also provided an image display apparatus displaying an image in multiple grayscales in accordance with a signal level of an input signal, wherein the image is displayed by switching, according to video content thereof, between a first grayscale characteristic where an output level monotonically increases with increasing grayscale and a second grayscale characteristic including a region where the output level remains constant despite the increase in grayscale.
Further, according to the present invention, there is provided a driving method for an image display apparatus displaying an image in multiple grayscales on a display panel by combining a plurality of weighted subfields into which one field has been divided, comprising: detecting the number of pixels used within one field period for each encoded subfield; outputting a light emission pattern table selection signal in accordance with the number of pixels detected for each subfield; receiving an input image signal, selecting one of a plurality of prestored light emission pattern tables in accordance with the selection signal, and outputting the encoded subfield data by encoding the input image signal in accordance with the selected light emission pattern table; and displaying an image in accordance with the encoded subfield data by using a prescribed driving sequence.
The outputting of the light emission pattern table selection signal may detect an usage rate of each subfield based on the number of pixels detected for the each subfield, and may output the light emission pattern table selection signal in accordance with the detected subfield usage rate. The detecting of the number of pixels may take an image input as an input signal. The detecting of the number of pixels may compare the input image with a predetermined value, and may count up the number of pixels each of which has been determined as a result of the comparison as being equal to or greater than the predetermined value. The predetermined value may be a value in the vicinity of a maximum grayscale that is represented by the subfields used for display in the light emission pattern table.
A plurality of the driving sequences may be preset, and wherein the displaying of the image may select one driving sequence that matches the selected light emission pattern table, and may display an image in accordance with the selected driving sequence. The detecting of the number of pixels may count up the number of pixels over one field period for each weighted subfield data encoded into the subfield data, and may output resulting data on a field-by-field basis. The outputting encoded subfield data may prestore data selecting one of the plurality of light emission pattern tables in accordance with data provided in an arbitrary one of the light emission pattern tables.
In the outputting encoded subfield data, pattern data indicating a light-emission ON/OFF state for each subfield in an arbitrary one of the light emission pattern tables may be data for driving the display panel, and may be also data based on which to switch between the light emission pattern tables. The displaying of the image may drive the display panel by using pattern data in an arbitrary one of the light emission pattern tables; and the outputting encoded subfield data may prestore data selecting the light emission pattern table by using pattern data that is not used for driving the display panel in the arbitrary one of the light emission pattern tables. The displaying of the image may drive the display panel by using one or more kinds of pattern data including the least heavily weighted pattern data in the light emission table.
Pattern data used for driving the display panel, from the highest grayscale X, or a grayscale close thereto, that is represented by the subfields used for display driving in the light emission pattern table to the highest grayscale Z that is represented by all the subfields in the light emission pattern table, may be data where all pattern data or most of relatively heavily weighted pattern data indicate a light-emission ON state. The plurality of light emission pattern tables may comprise first and second light emission pattern tables where each corresponding one of the subfields is assigned the same weight; and the first light emission pattern table may provide an output which is linear with respect to an input and may have a one-to-one correspondence therewith, while the second light emission pattern table may be the light emission pattern table corresponding to one driving sequence selected by the driving control circuit in a plurality of the driving sequences.
The grayscale from the grayscale X to the grayscale Z of the data that is the second light emission pattern table to switch between the emission pattern tables and that indicates the light-emission ON state of one or a plurality of pieces of weighted pattern data, may be the same as the grayscale from the grayscale X to the grayscale Z of the data that is the first light emission pattern table, and that indicates the light-emission ON state of one or a plurality of pieces of pattern data of the same weight of the second light emission pattern table to switch between the light emission pattern tables. The data that is used to switch between the light emission pattern tables, and that indicates the light-emission ON state of one or a plurality of pieces of weighted pattern data, may be located at a grayscale lower than the grayscale X in the second light emission pattern table. The number of pieces of data each of which is used in the second light emission pattern table to switch between the light emission pattern tables from the grayscale X to the grayscale Z, and which indicates the light emission ON state for each of one or a plurality of pieces of weighted pattern data, is smaller than the number of pieces of data which indicate the light emission ON state from the grayscale X to the grayscale Z in the first light emission pattern table.
The plurality of driving sequences may include subfields of the same weight and subfields of different weights, and time positions at which the subfields of the same weight may be caused to emit light are substantially the same between the plurality of driving sequences. The plurality of driving sequences may include subfields of the same weight and subfields of different weights, and the order where each of the subfields of the same weight is caused to emit light may be the same between the plurality of driving sequences.
The outputting of the light emission pattern table selection signal may switch the selection signal when the output for each weighted subfield in the detecting of the number of pixels is detected as being equal to or lower than a predetermined value. The outputting of the light emission pattern table selection signal may switch the selection signal when the output for one or a plurality of weighted subfields in the detecting of the number of pixels is detected as being zero. The outputting of the light emission pattern table selection signal may switch an output bit count for the detected number of pixels in accordance with the selection signal.
The outputting of the light emission pattern table selection signal may switch the output on a field-by-field basis, and may determine the present output value based on an output result of a previous field. The outputting of the light emission pattern table selection signal may output the selection signal by providing a hysteresis characteristic thereto. The driving method for an image display apparatus may further comprise changing the number of bits used for error diffusion in accordance with the selection signal.
Switching from one driving sequence to another may be done progressively in one or a plurality of steps. The one or the plurality of steps where switching is made from one driving sequence to another may involve making a sustain period in a relatively heavily weighted and unused subfield equal to or shorter than a sustain period in the least heavily weighted subfield used for display driving, or equal to zero. The one or the plurality of steps where switching is made from one driving sequence to another may involve stopping a relatively heavily weighted subfield having a usage rate of zero. The one or the plurality of steps where switching is made from one driving sequence to another may involve inserting a quiescent period before the first subfield or between arbitrarily selected subfields.
The one or the plurality of steps where switching is made from one driving sequence to another may involve lengthening a quiescent period gradually in steps, until the quiescent period becomes substantially equal in duration to the period of the least heavily weighted subfield currently driven. The one or the plurality of steps where switching is made from one driving sequence to another may involve lengthening a quiescent period gradually in steps, until the quiescent period becomes substantially equal in duration to the period of a subfield whose weight is smaller by one than the least heavily weighted subfield currently driven. The one or the plurality of steps where switching is made from one driving sequence to another may involve, in a final step thereof, inserting in a quiescent period a subfield whose weight is smaller by one than the least heavily weighted subfield currently displayed.
The one or the plurality of steps where switching is made from one driving sequence to another may involve, in a final step thereof, inserting in a quiescent period a subfield whose weight is smaller by one than the least heavily weighted subfield currently displayed, and stopping a subfield to which the most heavily weighted subfield data is assigned. The one or the plurality of steps where switching is made from one driving sequence to another may involve, in a final step thereof, inserting in a quiescent period a subfield whose weight is smaller by one than the least heavily weighted subfield currently displayed, and rearranging the time order in which to drive the plurality of subfields. The one or the plurality of steps where switching is made from one driving sequence to another may involve, in a final step thereof, inserting in a quiescent period a subfield whose weight is smaller by one than the least heavily weighted subfield currently displayed, and rearranging the time order in which to drive the plurality of subfields, in order of increasing weight.
The display panel may be driven by selecting one driving sequence from among the plurality of driving sequences for the selected one light emission pattern table. In the plurality of light emission pattern tables, the weight of a relatively lightly weighted subfield may be a value expressed as a power of 2, while the weight of a relatively heavily weighted subfield is not a value expressed as a power of 2.
In addition, according to the present invention, there is also provided a driving method for an image display apparatus displaying an image in multiple grayscales in accordance with a signal level of an input signal, wherein the image is displayed by switching, according to video content thereof, between a first grayscale characteristic where an output level monotonically increases with increasing grayscale and a second grayscale characteristic which includes a region where the output level remains constant despite the increase in grayscale.
The second grayscale characteristic may have a finer grayscale step in a low grayscale region than the first grayscale characteristic. The image display apparatus may be a plasma display apparatus.
The present invention will be more clearly understood from the description of the preferred embodiments as set forth below with reference to the accompanying drawings, wherein:
Before proceeding to the detailed description of the preferred embodiments of the present invention, the prior art image display apparatuses and display driving methods and their associated problems will be described with reference to
In the prior art, there is proposed, for example, in Japanese Unexamined Publication (Kokai) No. 11-065521, a display driving method in which, when the maximum luminance is low, and there is a subfield that does not emit light, a subfield whose sustain period is one half of that in the least significant subfield is provided to increase the number of grayscale levels on the black side.
As shown in
As described with reference to
However, in actual video data such as television broadcasts, the most significant bit (the most heavily weighted subfield SFb10) is used in almost all cases, and the least significant bit driving is seldom selected; therefore, even though the display capability at low grayscale levels can be enhanced by selecting the least significant bit driving, the period during which the driving mode remains switched to the least significant bit driving is extremely short, and no practical effect can be obtained.
Further, between the low-order bit driving sequence and the high-order bit driving sequence in
An object of the invention is to provide an image display apparatus and a driving method for the same that can lengthen the period during which the driving mode remains switched to a driving sequence designed to enhance the display capability at low grayscale levels, and can reduce the shock associated with the driving sequence switching. Another object of the invention is to provide an image display apparatus and a driving method for the same that can reduce the power consumption by shortening the sustain light-emission period.
Below, embodiments of an image display apparatus and a driving method for the image display apparatus according to the present invention will be described in detail with reference to the accompanying drawings.
The field memory 4 stores data for one field and, in the next field period, sequentially outputs the stored data for the one field for each SF. The timing generating circuit 8 is a circuit that generates various timing signals such as synchronization signals. The display panel is, for example, a plasma display panel or the like, and contains various drivers (for example, an X driver, Y driver, and address driver as used in a three-electrode AC-driven type PDP).
The gain circuit 30 is a circuit by which the video signal supplied via the video signal input terminal 1 is normalized to the number of grayscale levels used in the light emission pattern employed in the SF conversion circuit 32; for example, when the input video signal is an 8-bit, 256-step signal, and the number of grayscale levels to be converted by the SF conversion circuit 32 is 147, then the gain value of the gain circuit 30 is set to 147/256.
The memory write control signal 33 includes a one-line memory which temporarily stores video data that has been converted into subfield data for one line, and writes the subfield data for the one line to the field memory 4 on a subfield SFb by subfield SFb basis, that is, after parallel-to-serial conversion; at this time, a memory write control signal is also generated.
FIGS. 4 to 6 are diagrams each showing an example of the light emission pattern (light emission pattern table) in the SF conversion circuit in the image display apparatus of the present invention:
As shown in
In the light emission pattern table C of
Here, in the light emission pattern table A, the subfields SFb used for driving are eight subfields SFb3 to SFb10, while in the light emission pattern table B, the subfields SFb used for driving are eight subfields SFb2 to SFb9 and, as a result, the grayscale levels 116 and higher are fixed to 116. Further, in the light emission pattern table C, the subfields SFb used for driving are eight subfields SFb1 to SFb8 and, as a result, the grayscale levels 88 and higher are fixed to 88.
In the error diffusion control circuit 31, when driving eight subfields SFb3 to SFb10 (with reference to SF light emission pattern table A shown in
The adder circuits 601 to 610 add up the number of pixels for one field for the respective subfields SFb1 to SFb10 into which the input data has been converted by the grayscaling circuit 3, and the usage rate calculating circuits 611 to 620 calculate the ratios (usage rates) SFL1 to SFL10 of the respective subfields SFb1 to SFb10 to the total number of pixels of the screen for each field, and output the results.
Here, the adder circuits 601 to 610 each require the number of bits corresponding to the total number of pixels of the screen; for output bits of each of the usage rates SFL1 to SFL10, when the number of pixels is 480 vertically and 640 horizontally, for example, the total number of pixels is 307200 dots and an adder with 20 bits becomes necessary, but in the present invention, 20 bits are not needed for output, but less than 20 bits suffice for the purpose. This is because, in the case of the 8 high-order bits, for example, since the SFL output is a 1 for 1200 dots, the 1200 dots (1/256 in terms of ratio) can be disregarded. In the adder circuit, as the number of output bits increases, the number of pixels disregarded decreases, and the accuracy of the decision increases correspondingly, but the decision becomes more sensitive to video signal noise; therefore, by reducing the number of bits to less than 20 bits, an erroneous detection attributable to noise can be avoided. In the present invention, the usage rate with respect to the full screen is calculated and output, but alternatively, the result of the addition may be output directly.
The SF usage rate detection circuit 6 can be constructed using the adder circuits 601 to 610 only and not using the usage rate calculating circuits 611 to 620.
The zero detection circuits 701 to 710 detect on a field-by-field basis whether the values of the respective outputs SFL1 to SFL10 of the SF usage rate detection circuit 6 are zero “0” or not, and output signals L1 to L10 to the selection number generating circuit 72. Each of the zero detection circuits 701 to 710 outputs “0” when the value of the corresponding one of the usage rates SFL1 to SFL10 is “0”, that is, when the corresponding one of the subfields SFb1 to SFb10 is used, and “1” when the value of the corresponding one of the usage rates SFL1 to SFL10 is not “0”. The selection number generating circuit 72 outputs a signal S, such as shown in
More specifically, when the signal L10 from the zero detection circuit 710 is “0”, that is, when the subfield SFb10 is used, S=0 is output regardless of the values of the signals L9 to L7 (L9 to L1) from the zero detection circuits 709 to 707. On the other hand, when the signal L10 from the zero detection circuit 710 is “1”, and the signal L9 from the zero detection circuit 709 is “0”, that is, when the subfield SFb10 is not used, but the subfield SFb9 is used, S=1 is output regardless of the values of the signals L8 and L7 (L8 to L1) from the zero detection circuits 708 and 707.
Further, when the signals L10 and L9 from the zero detection circuits 710 and 709 are both “1”, and the signal L8 from the zero detection circuit 708 is “0”, that is, when neither the subfield SFb10 nor the subfield SFb9 is used, but the subfield SFb8 is used, S=2 is output regardless of the value of the signal and L7 (L7 to L1) from the zero detection circuit 707. The output S of the selection number generating circuit 72, as the output of the display SF selection circuit 7, is supplied to the driving control circuit 5 as well as to the grayscaling circuit 3.
The driving control circuit 5 switches the driving sequence in accordance with the output S of the display SF selection circuit 7. That is, as shown in
Further, at the instant that switching is made, for example, from the driving sequence A to the driving sequence B, since the number of pixels in the subfield SFb10 of weight 32 is close to zero (when the usage rate SFL is 8 bits, and 1/256 is set as zero, if the usage rate shows zero, the usage rate may not actually be zero), the subfield SFb10 is emitting virtually no light, so that the position of the center of gravity remains substantially unchanged. Furthermore, even when the driving sequence is switched, for example, between the driving sequence B for S=1 and the driving sequence C for S=2, the time positions where the relatively heavily weighted subfields SFb3 to SFb8 emit light remain unchanged at SF1 to SF6 within the one field; as a result, the amount of shift in the position of the center of gravity can be reduced, and thus the switching shock associated with the driving sequence switching can be alleviated. Here, the usage rate of zero is preferable, but if not zero, a usage rate close to zero suffices for the purpose.
The memory read control circuit 50, in accordance with the timing generated by the driving timing generating circuit 51, reads out the data for one field on a subfield SFb by subfield SFb basis from the field memory 4 in which the data for each line has been written on a subfield SFb by subfield SFb basis, and outputs the thus readout data for each subfield SFb to the display panel 9. Further, as the selection signal S output from the display SF selection circuit 7 changes from S=0 to S=1 to S=2, the memory read control circuit 50 reads out the data for each subfield SFb from the field memory 4 in the following order. That is, when S=0 (in the case of the driving sequence A), the data is read out in the order of SFb3, SFb4, SFb5, SFb6, SFb7, SFb8, SFb9, and SFb10; when S=1 (in the case of the driving sequence B), the data is read out in the order of SFb3, SFb4, SFb5, SFb6, SFb7, SFb8, SFb9, and SFb2; and when S=2 (in the case of the driving sequence C), the data is read out in the order of SFb3, SFb4, SFb5, SFb6, SFb7, SFb8, SFb1, and SFb2.
In the plasma display apparatus, for example, the power consumption depends on the length of the sustain period within one field period, that is, the sum of the weights of the subfields; here, the sum of the weights in the driving sequence A for S=0 is 144, the sum of the weights in the driving sequence B for S=1 is 114, and the sum of the weights in the driving sequence C for S=2 is 87, which means that the driving sequence that does not use higher-order subfields SFb consumes less power.
As previously explained with reference to FIGS. 4 to 6, the SF conversion circuit 32 in the grayscaling circuit 3 holds three kinds of SF light emission data tables (SF light emission data tables A to C), and the data table to be used is selected based on the output S of the display SF selection circuit 7. That is, the table to be used is switched to the table A when S=0, to the table B when S=1, and to the table C when S=2.
In the table B, as previously explained with reference to
As earlier described, the larger the number of bits in each output SFL of the usage rate detection circuit 6, the smaller the number of pixels disregarded, and the more accurately the decision can be made in selecting the correct driving sequence, but the decision becomes more sensitive to video signal noise, leading to an erroneous detection or resulting in frequent switching from one driving sequence to another; as a result, the frequency of selecting the driving sequence containing high-order subfields SFb increases, that is, the period during which the driving sequence that does not contain high-order subfields SFb is selected becomes shorter, and a situation can occur where the driving sequence that does not contain high-order subfields SFb is not selected even in the case of a scene containing a relatively dark image, thus defeating the purpose of increasing the number of output bits.
In the present embodiment, in switching from the driving sequence A for S=0 to the driving sequence B for S=1, since, of the outputs (subfields) SFb10 to SFb1 of the SF conversion circuit 32, those actually used in the driving sequence for display (driving) are the eight bits of the subfields SFb10 to SFb3 when S=0 and the eight bits of the subfields SFb9 to SFb2 when S=1, and since, at any gray scale level, the light emission pattern for the subfield SFb10 is the same between the light emission pattern table B and the light emission pattern table A, provisions are made to be able to detect the usage rate SFL10 of the SFb10 that is not actually used for driving in the driving sequence B for S=1.
In this way, according to the image display apparatus of the present embodiment, an image using the low-order bits can be effectively displayed by increasing the time during which the low-order bits are selected and driven for display. Furthermore, provisions are made to reduce the switching shock associated with the driving sequence switching so as not to give an unnatural feeling to the person (viewer) who is viewing the image display apparatus.
First, when the image display processing is started, initialization of the image display apparatus is performed in step 141. At this time, the light emission pattern table A shown in
Next, the process proceeds to step 142 where the input image data is converted into subfield SFb data (SF conversion circuit 32), and in step 143, the usage rate of each subfield SFb is detected (SF usage rate detection circuit 6). Then, in step 144, it is determined whether the most heavily weighted subfield SFb10 is used or not, and in step 145, it is determined whether the second most heavily weighted subfield SFb9 is used or not. That is, in the processing of steps 144 and 145, if the subfield SFb10 is used, the process proceeds to step 146 to select the light emission pattern table A; if the subfield SFb10 is not used, but the subfield SFb9 is used, the process proceeds to step 147 to select the light emission pattern table B; and if neither the subfield SFb10 nor the subfield SFb9 is used, the process proceeds to step 148 to select the light emission pattern table C.
Then, the process proceeds to step 149 to drive the display panel 9 based on the selected light emission pattern table A, B, or C. The grayscale display capability can thus be enhanced.
As is apparent from a comparison between
That is, in the processing of steps 154 and 155, if the subfield SFb10 is used, the process proceeds to step 156 to select the light emission pattern table A and the driving sequence A; if the subfield SFb10 is not used, but the subfield SFb9 is used, the process proceeds to step 157 to select the light emission pattern table B and the driving sequence B; and if neither the subfield SFb10 nor the subfield SFb9 is used, the process proceeds to step 158 to select the light emission pattern table C and the driving sequence C.
Then, the process proceeds to step 159 to drive the display panel 9 based on the selected light emission pattern table A, B, or C and driving sequence A, B, or C. In this way, by switching both the light emission pattern table and the driving sequence, not only can the grayscale display capability be enhanced, but also the switching shock can be reduced.
FIGS. 15 to 19 are diagrams each showing an example of the light emission pattern (light emission pattern table) in the SF conversion circuit in the image display apparatus of the present invention:
First, as shown in
Further, as shown in
Further, as shown in
On the other hand, as shown in
Further, as shown in
Here, the SF light emission data tables used in the SF conversion circuit 32 are not limited to the three kinds described above, the only requirement being that two or more kinds of data tables be provided. When the number of SF light emission data tables used in the SF conversion circuit 32 is increased, the number of grayscale levels can be increased for darker images by increasing the number of bits processed in the image display apparatus.
Further, by switching the output bits of the SF usage rate detection circuit 6, the signal S can be provided with a hysteresis characteristic. That is, in the case of the driving sequence A for S=0, for example, the 8 high-order bits including the MSB are set as the output bits of the SF usage rate detection circuit 6, and in the case of the driving sequence B for S=1, the 9 high-order bits including the MSB are set as the output bits of the SF usage rate detection circuit 6; then, the output 0 in the case of the 8 bits for S=0 becomes easier to detect, while the output 0 in the case of the 8 bits for S=1 becomes difficult to detect, thus introducing a hysteresis in switching between the signals S.
First, when the display SF selection processing is started, initialization of the display SF selection circuit 7 is performed in step 161. That is, the display SF selection signal S is set as S=0, and a parameter N is set as N=0. Here, N is the parameter for achieving hysteresis.
Next, the process proceeds to step 162 to detect the usage rate of each subfield SFb. This processing corresponds to the processing performed in the SF usage rate detection circuit 6 described with reference to
In step 166, it is determined whether N equals 10 (N=10), and if SNOW has failed to match S ten times in succession, the process proceeds to step 167; otherwise, the process returns to step 162 to repeat the same processing until N reaches 10. If, in step 166, it is determined that SNOW has failed to match S ten times in succession (that is, N has reached 10), then in step 167 SNOW is changed to S (SNOWS), and the process proceeds to step 168. In step 168, the parameter N is reset to 0 (0
N), and the process returns to step 162 to repeat the same processing.
In the flowchart of
As shown in
As is apparent from a comparison between
That is, when the display SF selection processing is started, initialization of the display SF selection circuit 7 is performed in step 171; here, the display SF selection signal S is set as S=0, and parameters N and M are set as N=0 and M=0, respectively. Here, N and M are the parameters for achieving hysteresis.
Then, after carrying out the steps 172 to 175 which correspond to the previously described steps 162 to 165 in
In step 179, it is determined whether N=M holds, and if it is determined that N=M holds, the process proceeds to step 180, but if it is determined that N=M does not hold, the process returns to step 172 to repeat the same processing until N=M holds.
That is, the flowchart of
Accordingly, if S is 0, and SNOW is 1 thirty times in succession, S switches to 1, and if S is 1, and SNOW is 0 ten times in succession, S switches to 0; in this way, the number of successive detections can be changed according to the current value of S, and the hysteresis characteristic can thus be adjusted. It will be appreciated here that the value “30” in step 177 and the value “10” in step 178 can be changed as needed.
As shown in
As shown in
In this way, the hysteresis characteristic that occurs in the switching of the output signal S of the display SF selection circuit 7 can be controlled by changing the values to be substituted for M in steps 177 and 178 in the flowchart of
As is apparent from a comparison between
In the foregoing first embodiment of
In the first step ST11, the subfield SFb10 in SF8, which is little used for display in the driving sequence A for S=0, is set as a subfield having a sustain period of weight 4 to display the grayscale level 116 (driving sequence A1). That is, the length (number of pulses) of the sustain period in the subfield SFb10 is shortened from the length of weight 32 to the length of weight 4. Here, the sustain period in the subfield SFb10 may be set to 0, but in that case, the grayscale level 116 is not displayed.
Next, in the second step ST12, a quiescent period SP11 with a length not long enough to cause a shock is inserted before SF1 (driving sequence A2). In the third step ST13, the length of the period SP11 is gradually increased for each field in such a manner that the switching shock will not be perceived, until a quiescent period SP12 just long enough to drive the subfield SFb2 is obtained (driving sequence A3). Then, in the fourth step ST14, the subfield SFb10 is stopped, and the subfield SFb2 is inserted in SF1 (driving sequence B2). When switching from S=1 to S=0, the switching shock can be reduced in like manner by carrying out the above steps in the reverse order.
In the second embodiment of the driving sequences described with reference to
In the driving sequences of the fourth embodiment shown in
When switching the driving sequence, it is desirable that the center of gravity remain unchanged if at all possible, but subfields SFb whose weights are relatively not very large can be reordered because the center of gravity does not shift substantially if such subfields SFb are reordered. That is, since a moving image is moving at all times, the center of gravity of the image when switching from S=1 to S=0 is not always the same as the center of gravity of the image when switching from S=0 to S=1, and as a result, the center of gravity does not change substantially if subfields SFb whose weights are relatively small are reordered. There are, therefore, cases where it is preferable, from the standpoint of stable driving, to reorder the subfields rather than inserting a new subfield with a small weight into the quiescent period. In particular, it is preferable to drive the SFs in the order of increasing weight.
Here, it is desirable that the quiescent period to be inserted be inserted in an early time position in the one field, and that the subfields SFb be reordered in the order of increasing weight wherever possible.
When switching the driving sequence, the switching may be made as shown in the first embodiment of
That is, if the driving sequence switching is performed as shown in the first embodiment when the usage rates of the relatively heavily weighted subfields (for example, SFb7 and SFb8) are high, and as shown in the fifth embodiment when the usage rates of the relatively lightly weighted subfields (for example, SFb3, SFb2, and SFb1) are high, the amount of shift in the center of gravity can be reduced; in this way, the mode of driving sequence switching can be changed according to the usage rate of each subfield SFb. Here, the usage rates of the subfields SFb1 to SFb10 are detected using the adder circuits 601 to 610 and the usage rate calculating circuits 611 to 620 shown in
In
As is apparent from a comparison between
The adder circuits 609 and 610 and the usage rate calculating circuits 619 and 620 in the SF usage rate detection circuit 6 previously shown in
In the above description, it will be appreciated that the present invention can also be implemented for three RGB primary colors if the circuit is provided for each primary color signal. It will also be recognized that the application of the present invention is not limited to plasma display apparatuses.
In the present invention, the subfields may be weighted by data, as described above, or may be weighted by luminance.
As described in detail above, according to the present invention, the period during which the driving mode remains switched to the driving sequence designed to enhance the display capability at low grayscale levels can be lengthened. Further, according to the present invention, the shock associated with the driving sequence switching can be reduced. Furthermore, according to the present invention, the sustain light-emission period can be shortened, achieving a reduction in power consumption.
The present invention can be applied widely to image display apparatuses, including plasma display apparatuses; for example, the invention can be applied widely to image display apparatuses such as those used for personal computers, workstations, etc. or those used as hang-on-the-wall televisions or as apparatuses for displaying advertisements, information, etc.
Many different embodiments of the present invention may be constructed without departing from the scope of the present invention, and it should be understood that the present invention is not limited to the specific embodiments described in this specification, except as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-045131 | Feb 2004 | JP | national |
