Patent Application
20130010017
The present invention relates to display devices, more specifically to a display device, such as a liquid crystal display device, which provides color display using a field-sequential system.
Most of the liquid crystal display devices that provide color display include sets of color filters for transmitting red (R), green (G), and blue (B) light therethrough, such that one set is provided for every three subpixels into which one pixel is divided. However, about ⅔ of backlight irradiated on a liquid crystal panel is absorbed by the color filters, and therefore liquid crystal display devices using color filters have a problem of low light-use efficiency. Accordingly, attention is focused on field-sequential liquid crystal display devices which provide color display without using color filters.
In the field-sequential system, a display period for one screen (one frame period) is divided into three subframe periods. In the first subframe period, a red component of an input signal is inputted to display a red screen, in the second subframe period, a green component is inputted to display a green screen, and in the third subframe period, a blue component is inputted to display a blue screen, so that a color image is displayed on the liquid crystal panel. In this manner, field-sequential liquid crystal display devices can dispense with color filters and therefore have about three times the light-use efficiency of liquid crystal display devices using color filters.
Japanese Laid-Open Patent Publication No. 2006-235443 describes a liquid crystal display device in which color signals included in input signals are distributed to subframes of base colors and complementary colors, such that differences in tone between the subframes are rendered small while maintaining colors expected from input signals of the base colors alone. To take advantage of the response speed of the liquid crystal being proportional to differences in tone, this liquid crystal display device renders differences in tone small between subframes to minimize color shifts between images. Specifically, when there are three base colors, red, green, and blue, colors in an image are distributed to subframes for red, green, blue, and complementary colors thereof, i.e., six colors in total, in accordance with predetermined equations. At this time, a color distribution ratio is obtained such that the sum of the absolute values of differences in tone between adjacent subframes is minimized while maintaining colors expected from input signals of the base colors alone. Color signals are distributed to the subframes on the basis of the color distribution ratio thus obtained, thereby rendering the differences in tone small between the subframes. As a result, the response speed of the liquid crystal becomes faster than in the case where the differences in tone are large, so that the color shifts between images can be minimized.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2006-235443
A description will be given regarding problems with image display on a conventional liquid crystal display device using the field-sequential system. Note that in the following, each of the red, green, and blue components of an input signal externally provided to the liquid crystal display device is 8-bit data. Accordingly, the liquid crystal display device displays each of red, green, and blue at up to 256 tone levels. Moreover, the liquid crystal used is of a normally black type.
A description will be given regarding the case where the liquid crystal display device displays an image with the transmittance of the liquid crystal panel significantly changing between adjacent subframes.
In the case where an image is displayed with tone values for red, green and blue at 255, 0, and 0, respectively, a red backlight emits light in the first subframe period, and a red component with the red tone value at 255 is inputted, as shown in
In the second subframe period, a green backlight emits light, and a green component with a green tone value of 0 is inputted. At this time, the transmittance of the liquid crystal panel is normally at 0%, and the liquid crystal panel blocks green backlight, so that no green image is displayed. However, even when the green component with a green tone value of 0 is inputted, the transmittance of the liquid crystal panel does not instantly fall from 100%, the percentage in the first subframe period, to 0%. In this manner, the transmittance of the liquid crystal panel in the second subframe period is affected by the transmittance in the first subframe period, so that time is taken before the transmittance of the liquid crystal panel falls to 0%, the percentage to be taken naturally. During this time, the green light from the green backlight that is to be blocked by the liquid crystal panel is partially transmitted, so that a green image is displayed.
In the second subframe period, the transmittance of the liquid crystal panel ultimately reaches 0%, so that the transmittance of the liquid crystal panel is 0% from the beginning of the third subframe period. Accordingly, in the third frame period, if a blue component with a blue tone value of 0 is inputted, the transmittance of the liquid crystal panel remains 0%. Therefore, the blue light from the blue backlight is blocked by the liquid crystal panel and cannot be transmitted therethrough, so that no blue image is displayed. As a result, the viewer sees an image of red mixed with green. Such red mixed with green differs in hue from the original color of red that should be displayed.
Furthermore, the method described in Japanese Laid-Open Patent Publication No. 2006-235443 is based on the premise that a delay in response of the liquid crystal is proportional to differences in tone between adjacent subframes. However, the delay in response of the liquid crystal is not determined only by the differences in tone. Accordingly, the delay in response of the liquid crystal often varies even for the same degree of difference in tone. In such a case, even by using the method described in Japanese Laid-Open Patent Publication No. 2006-235443, it is not possible to accurately correct a color shift between images due to a delay in response of the liquid crystal.
Therefore, an objective of the present invention is to provide a display device capable of displaying an image in a color maintaining a hue and a tone expected from an input signal.
A first aspect of the present invention is directed to a display device for displaying a screen in a different color for each of a plurality of subframe periods into which a frame period is divided, the device comprising:
a display panel including a plurality of pixel formation portions arranged in a matrix;
a color correction circuit for outputting correction signals for controlling light transmittances of the pixel formation portions, in each of the subframe periods on the basis of input signals; and
a driver circuit for driving the pixel formation portions on the basis of the correction signals, wherein,
the color correction circuit includes a look-up table having correction signals stored therein in correlation with the input signals specifying colors included in predetermined hues, the correction signals specifying colors maintaining hues and tones of the colors specified by the input signals, and
when the input signals are provided, the color correction circuit reads the correction signals correlated to the input signals from the look-up table, and output the correction signals to the driver circuit.
In a second aspect of the present invention, based on the first aspect of the invention, the correction signals stored in the look-up table in correlation with the input signals specify first pixel display points in a chromaticity diagram, the first pixel display points being on first straight lines extending between a white point with all color components of the input signals at maximum levels and first primary-color chromaticity points with at least one of the color components at a maximum level and the remaining at a minimum level, and the first pixel display points being obtained on the basis of the first primary-color chromaticity points.
In a third aspect of the present invention, based on the second aspect of the invention, when one of the first pixel display points is not on the first straight line, the correction signal stored in the look-up table in correlation with the input signal specifies anew first pixel display point being the closest displayable points to the first display point that is not on the first straight line within a predetermined distance therefrom.
In a fourth aspect of the present invention, based on the second aspect of the invention, the correction signals stored in the look-up table in correlation with the input signals respectively specify a plurality of second pixel display points sequentially obtained between the white point and the first pixel display points on the first straight lines.
In a fifth aspect of the present invention, based on the fourth aspect of the invention, the correction signals stored in the look-up table in correlation with the input signals respectively specify a plurality of second pixel display points obtained at intervals of equal length into which the first straight lines are divided.
In a sixth aspect of the present invention, based on the fourth aspect of the invention, when one of the second pixel display points is not on the first straight line, the correction signal stored in the look-up table in correlation with the input signal specifies a new second pixel display point being the closest displayable point to the second display point that is not on the first straight line.
In a seventh aspect of the present invention, based on the second aspect of the invention, the correction signals stored in the look-up table in correlation with the input signals respectively specify a plurality of second pixel display points obtained at intervals of equal length into which first curves extending between the white point and the first pixel display points are divided.
In an eighth aspect of the present invention, based on the second aspect of the invention, the correction signals stored in the look-up table in correlation with the input signals respectively specify a plurality of fourth pixel display points sequentially obtained on lines connecting the first pixel display points and third pixel display points obtained on the basis of the second primary-color chromaticity points adjacent to the first primary-color chromaticity points, the fourth pixel display points being positioned between the first pixel display points and the third pixel display points.
In a ninth aspect of the present invention, based on the eighth aspect of the invention, the fourth pixel display points respectively specified by the correction signals stored in the look-up table in correlation with the input signals are obtained at intervals of equal length into which second straight lines connecting the first pixel display points and the third pixel display points are divided.
In a tenth aspect of the present invention, based on the ninth aspect of the invention, when one of the fourth pixel display points is not on the second straight line, the correction signal stored in the look-up table in correlation with the input signal specifies a new fourth pixel display point being the closest displayable point to the fourth pixel display point that is not on the second straight line.
In an eleventh aspect of the present invention, based on the eighth aspect of the invention, the fourth pixel display points respectively specified by the correction signals stored in the look-up table in correlation with the input signals are obtained at intervals of equal length into which second curves connecting the first pixel display points and the third pixel display points are divided.
In a twelfth aspect of the present invention, based on the first aspect of the invention, a thermometer provided on the display panel is further comprised, the correction signals stored in the look-up table are correlated to the input signals for each piece of temperature information provided by the thermometer, and when the input signals are provided, the color correction circuit reads the correction signals from the look-up table on the basis of the temperature information.
In a thirteenth aspect of the present invention, based on the first aspect of the invention, the predetermined hues include red, green, and blue.
In a fourteenth aspect of the present invention, based on the first aspect of the invention, images, including still images, are displayed on the display panel on the basis of the input signals.
According to the first aspect, the correction signals stored in the look-up table in correlation with the input signals specifying colors included in predetermined hues specify colors maintaining the hues and the tones of colors expected to be displayed in accordance with the input signals. Accordingly, when an input signal is provided to the display device, the color correction circuit reads a correction signal correlated to the input signal from the look-up table, and outputs the correction signal to the driver circuit. Thus, the display device can display an image in a color maintaining the hue and the tone of a color expected to be displayed in accordance with an input signal.
According to the second aspect, the first pixel display points specified by the correction signals stored in the look-up table in correlation with the input signals are positioned on the first straight lines extending between the white point and the first primary-color chromaticity points and obtained on the basis of the first primary-color chromaticity points. Thus, the display device can display images in colors maintaining the hues of the colors specified by the first primary-color chromaticity points.
According to the third aspect, when one of the first pixel display points is not on the first straight line, the correction signal stored in the look-up table in correlation with the input signal specifies a new first pixel display point which is a displayable point specifying substantially the same color as the first pixel display point that is not on the first straight line. Thus, the display device can display images in colors of substantially the same hues as the colors specified by the first primary-color chromaticity points.
According to the fourth aspect, the correction signals stored in the look-up table in correlation with the input signals specify the second pixel display points sequentially obtained between the white point and the first pixel display points. Thus, the display device can display images in colors maintaining the hues and the tones of colors specified by chromaticity points between the white point and the first primary-color chromaticity points.
According to the fifth aspect, the correction signals stored in the look-up table in correlation with the input signals specify the second pixel display points sequentially obtained at intervals of equal length into which the first straight lines are divided. Thus, the positions of the second pixel display points can be readily obtained, so that the look-up table can be created with ease.
According to the sixth aspect, when one of the second pixel display points is not on the first straight line, the correction signal stored in the look-up table in correlation with the input signal specifies a new second pixel display point which is a displayable point specifying substantially the same color as the second pixel display point that is not on the first straight line. Thus, the display device can display an image in a color maintaining substantially the same hue and tone as a color specified by a color chromaticity point between the white point and the first pixel display point.
According to the seventh aspect, the correction signals stored in the look-up table in correlation with the input signals specify the second pixel display points sequentially obtained at intervals of equal length into which first curves extending between the white point and the first pixel display points are divided. Thus, the range of color reproduction by the display device can be widened. Moreover, in the case where the range of color reproduction by the display device is represented by a concave shape, the look-up table can be created without including any correction signals specifying displayable points not available for the display device.
According to the eighth aspect, the correction signals stored in the look-up table in correlation with the input signals specify the fourth pixel display points sequentially obtained on lines connecting the first pixel display points obtained on the basis of the first primary-color chromaticity points and the third pixel display points obtained on the basis of the second primary-color chromaticity points adjacent to the first primary-color chromaticity points. Thus, the display device can display images in colors maintaining the hues and the tones of colors specified by chromaticity points between the first and second primary-color chromaticity points.
According to the ninth aspect, the fourth pixel display points specified by the correction signals stored in the look-up table in correlation with the input signals are sequentially obtained at intervals of equal length into which the second straight lines connecting the first pixel display points and the third pixel display points are divided. Thus, the positions of the fourth pixel display points can be readily obtained, so that the look-up table can be created with ease.
According to the tenth aspect, when one of the fourth pixel display points is not on the second straight line, the correction signal stored in the look-up table in correlation with the input signal specifies a new fourth pixel display point which is a displayable point specifying substantially the same color as the fourth pixel display point that is not on the second straight line. Thus, the display device can display images in colors maintaining substantially the same hues and tones of colors as specified by chromaticity points between the first and second primary-color chromaticity points.
According to the eleventh aspect, the fourth pixel display points specified by the correction signals stored in the look-up table in correlation with the input signals are sequentially obtained at intervals of equal length into which second curves connecting the first pixel display points and the third pixel display points are divided. Thus, the range of color reproduction by the display device can be widened. Moreover, in the case where the range of color reproduction by the display device is represented by a concave shape, the look-up table can be created without including any correction signals specifying displayable points not available for the display device.
According to the twelfth aspect, the display device has the thermometer provided on the display panel, and the correction signals stored in the look-up table are correlated to the input signals for each piece of temperature information. Thus, the color correction circuit can read the correction signals from the look-up table in accordance with the temperature information provided by the thermometer. In this case, the display device displays an image in accordance with a correction signal corresponding to the temperature of the display panel, and therefore the influence of the temperature can be minimized even if the display speed of the display device varies in accordance with the temperature.
According to the thirteenth aspect, when an input signal specifying a color with the hue of red, green, or blue is provided, the display device can display an image in a color maintaining the hue and the tone of the color expected to be displayed from the input signal.
According to the fourteenth aspect, the display device is suitable for displaying images including still images.
<1.1 Configuration of the Liquid Crystal Display Device>
In the following, for example, one frame period is 1/60 of a second, and each subframe period is 1/180 of a second. Moreover, each of the red, green, and blue components of an input signal externally provided to the liquid crystal display device 10 is 8-bit data. In this case, the liquid crystal display device 10 can represent each of the colors, red, green, and blue, at 256 tone levels, so that the liquid crystal panel 11 can display about 16.78 million colors (to be exact, 256×256×256 colors).
The liquid crystal panel 11 includes a plurality (m) of image signal lines S1 to Sm, a plurality (n) of scanning signal lines G1 to Gn, and a plurality (m×n) of pixel formation portions 30 provided at their respective corresponding intersections of the image signal lines S1 to Sm and the scanning signal lines G1 to Gn. Each pixel formation portion 30 includes a TFT 31 functioning as a switching element, a pixel electrode 32 connected to a drain terminal of the TFT 31, and a common electrode 33 forming liquid crystal capacitance together with the pixel electrode 32. The TFT 31 has a gate terminal connected to the scanning signal line Gi (1≦i≦n) and a source terminal connected to the image signal line Sj (1≦j≦m).
An input signal DV is externally provided to the timing control circuit 12 and the color signal processing circuit 14. The timing control circuit 12 generates control signals C1 and C2 on the basis of the input signal DV, such that the timing of lighting up red, green, and blue LEDs (light-emitting diodes) 20r, 20g, and 20b included in the backlight unit 20 is synchronized with the timing of the image signal line driver circuit 18 outputting red, green, and blue drive image signals to the image signal lines S1 to Sm. The timing control circuit 12 provides the control signal C1 to the color signal processing circuit 14 and the control signal C2 to the backlight control circuit 13.
The color signal processing circuit 14 includes a color correction circuit 15 and a display control circuit 16, and the color correction circuit 15 includes a look-up table (LUT) 15a. The LUT 15a has stored therein a plurality of input signals DV, and a plurality of correction signals CV respectively correlated to the input signals DV. When an input signal DV is provided to the color correction circuit 15 in the color signal processing circuit 14, the color correction circuit 15 reads in real-time a correction signal CV correlated to that input signal DV from the LUT 15a, and provides that correction signal CV to the image signal line driver circuit 18. Note that each of the input signal DV and the correction signal CV is represented by a set of red, green, and blue components R, G, and B. The red, green, and blue components R, G, and B represent tone values for red, green, and blue, respectively.
On the basis of the control signal C1 provided by the timing control circuit 12 and the externally provided input signal DV, the display control circuit 16 generates a control signal (e.g., a gate clock signal or suchlike) C3 for the scanning signal line driver circuit 17 and a control signal (e.g., a source clock signal or suchlike) C4 for the image signal line driver circuit 18. The display control circuit 16 provides the control signal C4 to the image signal line driver circuit 18 and the control signal C3 to the scanning signal line driver circuit 17.
The scanning signal line driver circuit 17 sequentially outputs active scanning signals to the scanning signal lines G1 to Gn on the basis of the control signal C3. The image signal line driver circuit 18 generates drive image signals on the basis of the correction signal CV, and outputs the drive image signals to the image signal lines S1 to Sm at times determined by the control signal C4. The drive image signals outputted to the image signal lines S1 to Sm are charged in pixel capacitance via the TFTs 31 connected to the active scanning signal lines G1 to Gn. As a result, voltages corresponding to the drive image signals are applied to the liquid crystal, and the transmittance of the liquid crystal changes in accordance with the applied voltages, so that an image is displayed on the liquid crystal panel 11. Note that the scanning signal line driver circuit 17 and the image signal line driver circuit 18 are also collectively called a driver circuit.
The backlight unit 20 includes two-dimensionally arranged red, green, and blue LEDs (light-emitting diodes) 20r, 20g, and 20b. The red, green, and blue LEDs 20r, 20g, and 20b are connected to the power supply circuit 22 via the switch 21. On the basis of the control signal C2 provided by the timing control circuit 12, the backlight control circuit 13 generates a backlight control signal BC for shifting the switch 21 for each subframe period in a sequential manner, and provides the backlight control signal BC to the switch 21. Since the switch 21 is shifted in a sequential manner on the basis of the backlight control signal BC, the red, green, and blue LEDs 20r, 20g, and 20b are sequentially supplied with a source voltage by the power supply circuit 22. As a result, the red, green, and blue LEDs 20r, 20g, and 20b sequentially emit light in accordance with the timing of the drive image signals being applied to the image signal lines S1 to Sm, so that the liquid crystal panel 11 is illuminated from the back by red, green, and blue light sequentially but one in each subframe period. Note that in place of the red, green, and blue LEDs 20r, 20g, and 20b, red, green, and blue CCFLs (cold cathode fluorescent lamps) may be used as light sources included in the backlight unit 20.
In general, the response of the liquid crystal to the drive image signal being provided to the pixel formation portion 30 is late compared to the response of the backlight, and therefore it is necessary to control the timing of lighting up the backlight considering such late response of the liquid crystal. Accordingly, an exemplary backlight control method considering the late response of the liquid crystal will be described specifically.
The changing speed of the liquid crystal orientation direction varies significantly depending on the ambient temperature, and the change in speed is fast at high temperature and becomes slower as the temperature falls. Accordingly, even if the voltage applied to pixel capacitance is not changed, the transmittance of the liquid crystal panel 11 changes fast when the temperature around the liquid crystal is high, and it changes slowly at lower temperatures. Therefore, to measure the temperature of the liquid crystal panel 11, the thermometer 19 is provided at the liquid crystal panel 11. The temperature of the liquid crystal panel 11 measured by the thermometer 19 is provided to the color correction circuit 15 as temperature information.
The LUT 15a includes the correspondence between the input signals DV and the correction signals CV, created for each piece of temperature information provided by the thermometer 19. When an input signal DV is externally provided, the color correction circuit 15 reads a correction signal CV stored in correlation with the provided input signal DV from the LUT 15a. The correction signal CV being read is provided to the image signal line driver circuit 18 and converted into a drive image signal before it is provided to the liquid crystal panel 11. As a result, the liquid crystal panel 11 displays an image in a color corresponding to the correction signal CV. The color of the image displayed maintains a hue and a tone of a color expected from the input signal DV, as will be described later. The liquid crystal display device 10 displays the image in accordance with the correction signal CV corresponding to the temperature of the liquid crystal panel 11. Accordingly, even when the response speed of the liquid crystal changes in accordance with the temperature, the liquid crystal display device 10 can display an image while minimizing the effect of the temperature. Note that in the case where the liquid crystal display device 10 is intended to be used in an environment where the temperature barely changes, the LUT 15a includes the correspondence between input signals DV and correction signals CV only for specific temperatures.
In the first subframe period, the pixel formation portions 30 are driven on the basis of the red component of the correction signal CV obtained through conversion by the color correction circuit 15, and the red LEDs 20r emit light. Similarly, in the second subframe period, the pixel formation portions 30 are driven on the basis of the green component of the correction signal CV, and the green LEDs 20g emit light. In the third subframe period, the pixel formation portions 30 are driven on the basis of the blue component of the correction signal CV, and the blue LEDs 20b emit light. As a result, the screen of the liquid crystal panel 11 appears red to a degree corresponding to the red component in the first subframe period, green to a degree corresponding to the green component in the second subframe period, and blue to a degree corresponding to the blue component in the third subframe period. In this case, since the subframe periods are short, the liquid crystal display device 10 can display a color image taking advantage of an afterimage on the human retina.
<1.2 Principle of Color Correction>
Color characteristics of an image displayed on a liquid crystal display device are represented by a chromaticity diagram as defined by the International Commission on Illumination (Commission Internationale de l'Eclairage).
Conventional field-sequential liquid crystal display devices can display colors specified by chromaticity points enclosed within triangle r′g′b′ in the horseshoe-shaped area. Triangle r′g′b′ includes about 16.78 million chromaticity points respectively corresponding to about 16.78 million colors that can be displayed. In the following, about 16.78 million chromaticity points that can be displayed by conventional field-sequential liquid crystal display devices will be referred to as displayable points.
The size of triangle r′g′b′ varies in accordance with the response speed of liquid crystal used. Specifically, the size of triangle r′g′b′ increases as the response speed of liquid crystal rises, and it decreases as the response speed of liquid crystal falls. In the case where a normally black-type liquid crystal is used, when all of the red, green, and blue components are at 255, the transmittance of the liquid crystal panel 11 is 100%, so that the liquid crystal panel 11 displays white. In addition, when all of the color components are at 0, the transmittance of the liquid crystal panel 11 is 0%, so that the liquid crystal panel 11 displays black. In
In conventional field-sequential liquid crystal display devices, when the liquid crystal panel 11 is irradiated with red (the color at primary-color chromaticity point r) light emitted by the red LEDs 20r to display a red image, the liquid crystal panel 11 displays a color resulting from red being mixed with green (the color at primary-color chromaticity point g) emitted by the green LEDs 20g, due to a delayed response of the liquid crystal. The color resulting from red being mixed with green is the color specified by chromaticity point r′ in
Likewise, when the liquid crystal panel 11 is irradiated with green light emitted by the green LEDs 20g to display a green image corresponding to primary-color chromaticity point g, the liquid crystal panel 11 displays a color (the color at uncorrected chromaticity point g′) resulting from green being mixed with blue (the color at primary-color chromaticity point b) emitted by the blue LEDs 20b, and when the liquid crystal panel 11 is irradiated with blue light emitted by the blue LEDs 20b to display a blue image, the liquid crystal panel 11 displays a color (the color at uncorrected chromaticity point b′) resulting from blue being mixed with red emitted by the red LEDs 20r. This is similarly true for yellow, cyan, and magenta. In this manner, conventional field-sequential liquid crystal display devices cannot display a color maintaining the hue of a color expected from an input signal DV.
Next, the principle of the color correction to be made in the present embodiment will be described. Initially, signals respectively corresponding to about 16.78 million displayable points enclosed within triangle r′g′b′ shown in
Alternatively, some of the signals respectively corresponding to about 16.78 million displayable points may be selected and sequentially inputted to the liquid crystal display device so that chromatic coordinates of displayable points displayed on the liquid crystal panel are measured with the colorimeter. In this case, chromatic coordinates of displayable points near the displayable points obtained by the colorimeter are sequentially obtained by interpolation. In this manner, the correspondence between chromatic coordinates of about 16.78 million displayable points and signals may be obtained using measurements with the colorimeter in combination with interpolation. In this case, the chromatic coordinates of the displayable points obtained by interpolation are not as accurate as the chromatic coordinates obtained with the colorimeter, but the time to be taken in chromatic coordinate measurements can be reduced.
Described next is a method for generating a correction signal CV representing a color which maintains the hue and the tone of a color expected from an input signal DV provided to the liquid crystal display device 10.
The input signal DV representing primary-color chromaticity point r is a signal with the red component at 255 and both of the green and blue components at 0. The red component is provided in the first subframe period, the green component in the second subframe period, and the blue component in the third subframe period. Note that in the following, an input signal DV with the red, green, and blue components at R, G, and B, respectively, may be represented as an input signal DV (R, G, B) for convenience.
Intersection R′ is obtained, which is a point where straight line Wr, which extends between white point W and primary-color chromaticity point r, intersects side r′b′ of triangle r′g′b′, as shown in
On the other hand, when intersection R′ does not coincide with any displayable point, the liquid crystal display device 10 cannot display the color specified by intersection R′. Therefore, when intersection R′ does not coincide with any displayable point, all displayable points within predetermined distance α from intersection R′ are obtained. For example, three displayable points R1′ to R3′ are within distance α from intersection R′ and included within triangle r′g′b′, as shown in
Next, from the signals correlated to the chromatic coordinates of the displayable points obtained in advance, a signal corresponding to the chromatic coordinates of pixel display point R is selected and set as a correction signal CV. As a result, the correction signal CV specifying pixel display point R is correlated to the input signal DV (255,0,0).
Accordingly, when the input signal DV (255,0,0) specifying primary-color chromaticity point r is provided to the color correction circuit 15 in the liquid crystal display device 10, the color correction circuit 15 reads the correction signal CV correlated to the input signal DV (255,0,0) from the LUT 15a, and outputs it to the image signal line driver circuit 18. As a result, the liquid crystal panel 11 displays the color specified by pixel display point R.
Pixel display point R thus obtained is on or near straight line Wr extending between primary-color chromaticity point r and white point W, so that the color specified by pixel display point R has a hue of red or near red, which means that the hue is maintained.
However, the position of pixel display point R is on or near side r′b′ of triangle r′g′b′ and is closer to uncorrected chromaticity point b′ than is uncorrected chromaticity point r′. Therefore, the color specified by pixel display point R is red mixed not only with green but also with blue. That is, to represent the color specified by pixel display point R, blue is required along with red and green. As a result, the color specified by pixel display point R has lower saturation than the color specified by uncorrected chromaticity point r′.
Likewise, for the input signal (255,255,0), which is expected to represent the primary color yellow corresponding to primary-color chromaticity point y, the input signal (0,255,0), which is expected to represent the primary color green corresponding to primary-color chromaticity point g, etc., chromatic coordinates of pixel display points G, B, and the like, displayed on the liquid crystal panel 11 are obtained. Hexagon F having vertices at pixel display points R, Y, G, C, B, and M thus obtained represents the range of color reproduction by the liquid crystal display device 10 according to the present embodiment. Therefore, the liquid crystal display device 10 can display colors specified by displayable points enclosed within hexagon F.
Described next is a case where there is provided an input signal DV for a color desired to be displayed with the same hue as the color displayed at primary-color chromaticity point r, y, g, c, b, or m, the desired color component at its maximum level, and other color components greater than 0.
Line Wr is set between white point W and primary-color chromaticity point r, as shown in
L
WRs′
=L
WR×(255−a)/255 (1)
As shown in equation (1), the position of temporary display point Rs′ is obtained by dividing the distance between white point W and pixel display point R into 255 equal parts and sequentially moving the distance in increments of one in the direction from white point W to pixel display point R. In the case where temporary display point Rs′ thus obtained coincides with a displayable point on straight line Wr, it is set as pixel display point Rs corresponding to chromaticity point rs. In this case, the position of temporary display point Rs′ can be readily obtained, so that the LUT 15a can be created with ease.
Furthermore, in the case where temporary display point Rs′ does not coincide with any displayable point on straight line Wr, pixel display point Rs is obtained as follows. In the case where there are, for example, three displayable points Rs1′, Rs2′, and Rs3′ close to temporary display point Rs′, as shown in
Next, from the signals correlated to the chromatic coordinates of the displayable points measured in advance, a signal corresponding to the chromatic coordinates of pixel display point Rs is selected and set as a correction signal CV. As a result, the correction signal CV specifying pixel display point Rs is correlated to the input signal DV.
Since pixel display point Rs is on or near straight line Wr, the hue of the color specified by pixel display point Rs is also red. Moreover, according to equation (1), the lower the values of color components of the input signal DV other than the red component, the further the distance LWRs′ from white point W, and therefore the correction signal CV specifying pixel display point Rs maintains the tone. Note that since pixel display point Rs is positioned within hexagon F inside chromaticity point rs, the saturation of the color specified by pixel display point Rs is lower than that of the color specified by chromaticity point rs.
Likewise, correction signals CV correlated to input signals DV for the hue of red with the green and blue components in the range from 1 to 255, correction signals CV correlated to input signals DV for the hue of yellow with the blue component in the range from 1 to 255, and correction signals CV correlated to input signals DV for the hue of green with the red and blue components in the range from 1 to 255 are sequentially obtained, and other correction signals CV are also obtained in a sequence up to correction signals CV correlated to input signals DV for the hue of magenta with the green component in the range from 1 to 255.
Correction signals CV corresponding to all pixel display points for the hues of red, yellow, green, cyan, blue, and magenta may be obtained by the aforementioned method, or correction signals CV corresponding to only an appropriately selected group of the pixel display points for the hues may be obtained. In either case, the obtained correction signals CV are stored to the LUT 15a in correlation with input signals DV. Note that in the case where correction signals CV are obtained only for the selected pixel display points using the aforementioned method, the color correction circuit 15 reads necessary correction signals CV from among the correction signals CV stored in the LUT 15a, and obtains correction signals CV corresponding to unselected pixel display points by interpolation. Then, the obtained correction signals CV are outputted to the image signal line driver circuit 18. In this manner, only the correction signals CV corresponding to appropriately selected pixel display points are stored in the LUT 15a, thereby reducing the memory capacity of the LUT 15a compared to the case where all correction signals CV are stored. Moreover, the color correction circuit 15 also obtains correction signals CV corresponding to pixel display points specifying colors other than the hues of red, yellow, green, cyan, blue, and magenta, by interpolation on the basis of the correction signals CV stored in the LUT 15a, and outputs the obtained correction signals CV to the image signal line driver circuit 18.
In the foregoing, the correspondence between the input signals DV and the correction signals CV is obtained using white point W specified by the input signal DV (255,255,255). However, a correction signal CV corresponding to an input signal DV may be obtained and additionally stored to the LUT 15a, using a point specified by an input signal (w,w,w) (where w is an integer such that 0≦w≦254) in place of white point W.
In the third subframe period, the transmittance of the liquid crystal panel is conventionally at 0%, as shown in
Therefore, to display a blue image in the third subframe period, the blue component included in the correction signal CV is also required to be set to a value corresponding to the chromatic coordinates of pixel display point R, thereby setting the transmittance of the liquid crystal panel 11 to a predetermined value in the third subframe period. As a result, blue light emitted by the blue LEDs 20b is transmitted in part through the liquid crystal panel 11, so that a blue image is displayed as well. In this case, the saturation of red displayed on the liquid crystal panel 11 (red specified by pixel display point R) is lower than the saturation of red expected from the input signal DV (red specified by primary-color chromaticity point r). However, the image displayed on the liquid crystal panel 11 maintains the same or almost the same hue as the hue of red expected from the input signal DV. Moreover, as is apparent from the method for obtaining the correction signal CV, the tone of the color represented by the correction signal CV is also maintained.
<1.3 LUT Creation Method>
The LUT 15a is created in advance using a PC (personal computer), and incorporated in the color correction circuit 15 of the liquid crystal display device 10. The configuration of the PC to be used for creating the LUT 15a will therefore be described.
The CPU 52 determines whether or not intersection R′ coincides with any displayable point on side r′b′ (step S13). When intersection R′ is determined to coincide with any displayable point on side r′b′, the process advances to step S14. Then, the CPU 52 sets intersection R′ as pixel display point R corresponding to primary-color chromaticity point r (step S14). Alternatively, when intersection R′ is not determined to coincide with any displayable point on side r′b′, the process advances to step S15. Then, the CPU 52 sets one of the displayable points within predetermined distance a from intersection R′ as pixel display point R, the displayable point being enclosed within triangle r′g′b′ and also being the closest to primary-color chromaticity point r (step S15). Note that pixel display point R may be a displayable point which is closer to white point W than intersection R′ and is near straight line Wr in the chromaticity diagram shown in
The CPU 52 obtains the length (LR/255) of one of the 255 equal segments of straight line WR extending between white point W and pixel display point R (step S16). Next, variable a is set to 1 (step S17), and a position at a distance of ((255−a)×LR/255) from white point W toward pixel display point R is set as temporary display point Rs′ corresponding to chromaticity point rs (step S18). Note that the length of the segment to be used for obtaining temporary display point Rs′ may be the length of a segment obtained by dividing straight line WR, which extends between white point W and pixel display point R, into 255 parts at an arbitrary ratio, rather than the length of one of the 255 equal segments of straight line WR.
The CPU 52 determines whether or not temporary display point Rs′ obtained in step S18 coincides with any displayable point on straight line Wr (step S19). When temporary display point Rs′ is determined to coincide with any displayable point on straight line Wr, the process advances to step S20. Then, the CPU 52 sets the coincident displayable point as pixel display point Rs corresponding to chromaticity point rs (step S20). Alternatively, when temporary display point Rs′ is not determined to coincide with any displayable point on straight line Wr, the process advances to step S21. Then, the CPU 52 obtains the closest displayable point to temporary point Rs′ within triangle r′g′b′, and sets the obtained displayable point as pixel display point Rs (step S21).
The CPU 52 increments the value of variable a by 1 (step S22), and determines whether or not variable a is 255 or higher (step S23). When variable a is determined to be 254 or lower, the process returns to step S18, and when variable a is determined to be 255 or higher, the process advances to step S24. The CPU 52 obtains a correction signal CV specifying pixel display point Rs, and stores it to the LUT 15a in correlation with an input signal DV (step S24).
In this manner, a correction signal CV that specifies pixel display point R corresponding to primary-color chromaticity point r, and correction signals CV specifying pixel display points Rs obtained on the basis of input signals DV for the hue of red with color components other than the red component in the range from 1 to 254, are obtained and stored to the LUT 15a in correlation with input signals DV. Similarly, for each of the hues of yellow, green, cyan, blue, and magenta, correction signals CV maintaining the hues and the tones are obtained and stored to the LUT 15a in correlation with input signals DV. In addition, correction signals CV specifying colors other than the hues of red, yellow, green, cyan, blue, and magenta are sequentially obtained by interpolation on the basis of the correction signals CV, and stored to the LUT 15a in correlation with input signals DV. This completes the creation of the LUT 15a. Note that in the present embodiment, the pixel display points Rs on straight line WR are sequentially obtained in the direction from white point W to pixel display point R. However, pixel display points Rs on straight line WR may be sequentially obtained in the direction from pixel display point R to white point W.
<1.4 Effect>
As described above, the LUT 15a of the liquid crystal display device 10 according to the present embodiment has correction signals CV stored therein in correlation with input signals DV, the correction signals CV specifying colors that maintain hues and tones of colors expected to be displayed in accordance with the input signals DV. Accordingly, when an input signal DV is provided to the liquid crystal display device 10, the color signal processing circuit 14 can read a correction signal CV correlated to the input signal DV from the LUT 15a in real-time. Thus, the liquid crystal display device 10 can display an image on the liquid crystal panel in a color maintaining the hue and the tone of a color expected to be displayed in accordance with the input signal DV.
<1.5 Variant>
A liquid crystal display device according to a variant of the first embodiment will be described. In this variation, correction signals CV correlated to input signals DV representing hues of red, green, and blue are obtained by computation, and correction signals CV correlated to input signals DV representing other colors, including hues of yellow, cyan, and magenta, are obtained by interpolation. Thus, the number of correction signals CV to be obtained by computation is reduced, so that the LUT 15a can be created with ease.
A liquid crystal display device according to a second embodiment will be described. The configuration of the liquid crystal display device according to the present embodiment is the same as the configuration of the liquid crystal display device 10 shown in
The input signal DV (255,0,0) expected to represent the primary color red corresponding to primary-color chromaticity point r and the input signal DV (255,255,0) expected to represent the primary color yellow corresponding to primary-color chromaticity point y are the same except for the green component. From this, it can be appreciated that there are 254 pixel display points which are different in their green components between primary-color chromaticity points r and y. Accordingly, 254 pixel display points between pixel display points R and Y are obtained. A chromaticity diagram showing the range of color reproduction by the liquid crystal display device of the present embodiment in a u′v′ coordinate system is the same as the chromaticity diagram shown in
Described next is a method for obtaining the 254 pixel display points on side RY which are different in their green components.
Line RY is set between pixel display points R and Y, as shown in
L
RYt′
=L
RY
×t/255 (2)
As shown in equation (2), the chromatic coordinates of temporary display point RYt′ are obtained by dividing the distance between pixel display points R and Y into 255 equal parts and sequentially moving the distance in increments of one (LRY/255) in the direction from pixel display point R to pixel display point Y. In the case where temporary display point RYt′ thus obtained coincides with a displayable point on straight line RY, it is set as pixel display point RYt. In this case, the position of temporary display point RYt′ can be readily obtained, so that the LUT 15a can be created with ease.
Furthermore, in the case where temporary display point RYt′ does not coincide with any displayable point on straight line RY, pixel display point RYt is obtained as follows. In the case where there are, for example, two displayable points RYt1′ and RYt2′, close to temporary display point RYt′, as shown in
Next, from the signals correlated to the chromatic coordinates of the displayable points obtained in advance for each pixel display point RYt, a signal corresponding to the chromatic coordinates of the pixel display point RYt is selected and set as a correction signal CV. As a result, the correction signal CV representing the pixel display point RYt is added to the LUT 15a in correlation with the input signal DV.
Correction signals CV corresponding to all pixel display points on or near straight lines extending between adjacent pixel display points R, Y, G, C, B, and M, such as straight line RY, may be obtained by the aforementioned method, or correction signals CV corresponding to only an appropriately selected group of the pixel display points may be obtained. In either case, the obtained correction signals CV are stored to the LUT 15a in correlation with input signals DV. Note that in the case where correction signals CV are obtained only for the selected pixel display points using the aforementioned method, the color correction circuit 15 reads necessary correction signals CV from among the correction signals CV stored in the LUT 15a, and obtains correction signals CV corresponding to unselected pixel display points by interpolation. Then, the obtained correction signals CV are outputted to the image signal line driver circuit 18. In this manner, only the correction signals CV corresponding to appropriately selected pixel display points are stored in the LUT 15a, thereby reducing the memory capacity of the LUT 15a compared to the case where all correction signals CV are stored.
According to equation (2), the greater the value of the green component of the input signal DV, the further the distance LRYt from pixel display point R to pixel display point RYt, and therefore the correction signal CV specifying pixel display point RYt maintains the tone. Note that since pixel display points R and Y are positioned within hexagon F inside primary-color chromaticity points r and y, the saturation of the color specified by pixel display point RYt on or near straight line RY is reduced.
Similarly, thereafter, correction signals CV specifying 254 pixel display points YGt between pixel display points Y and G, and correction signals CV specifying 254 pixel display points GCt between pixel display points G and C are sequentially obtained, and other correction signals CV are also obtained in a sequence up to correction signals CV specifying 254 pixel display points MRt between pixel display points M and R. Thereafter, the obtained correction signals CV are added to the LUT 15a in correlation with input signals DV.
The LUT 15a of the present embodiment is created using the PC 50 shown in
The CPU 52 obtains the length (LRY/255) of one of the 255 equal segments of straight line RY extending between pixel display points R and Y (step S31). In step S32, variable t is set to 1. A position at a distance of (t×LRY/255) from pixel display point R toward pixel display point Y is set as temporary display point RYt′ (step S33). Note that the length of the segment to be used for obtaining temporary display point RYt′ may be the length of a segment obtained by dividing straight line RY, which extends between pixel display points R and Y, into 255 parts at an arbitrary ratio, rather than the length of one of the 255 equal segments of straight line RY.
The CPU 52 determines whether or not temporary display point RYt′ obtained in step S33 coincides with any displayable point on side RY of hexagon F (step S34). When the CPU 52 determines temporary display point RYt′ to coincide with any displayable point on side RY, the process advances to step S35. Then, the CPU 52 sets the coincident displayable point as pixel display point RYt (step S35). Alternatively, when temporary display point RYt′ is not determined to coincide with any displayable point on side RY in step S34, the process advances to step S36. Then, the CPU 52 obtains the closest displayable point to temporary display point RYt′, and sets the obtained displayable point as pixel display point RYt (step S36).
The CPU 52 increments the value of variable t by 1 (step S37), and determines whether or not variable t is 255 or higher (step S38). When variable t is determined to be 254 or lower, the process returns to step S33, and when variable t is determined to be 255 or higher, the process advances to step S39. The CPU 52 obtains a correction signal CV specifying pixel display point RYt, and adds it to the LUT 15a in correlation with an input signal DV (step S39).
Similarly, correction signals CV specifying pixel display points on sides YG, GC, CB, BM, and MR of hexagon F are obtained and added to the LUT 15a in correlation with input signals DV. This completes the creation of the LUT 15a. Note that in the present embodiment, chromatic coordinates of pixel display points RYt on side RY are sequentially obtained in the direction from pixel display point R to pixel display point Y. However, the chromatic coordinates of pixel display points RYt on side RY may be sequentially obtained in the direction from pixel display point Y to pixel display point R.
As described above, the liquid crystal display device 10 can display an image in a color maintaining the hue and the tone of a color specified by a chromaticity point between primary-color chromaticity points r and y. Moreover, in addition to the correction signals CV obtained in the first embodiment, correction signals CV specifying pixel display points on the sides of hexagon F are further obtained by computation. Such correction signals CV obtained by computation render it possible to display images in colors maintaining the hues and the tones of colors expected from input signals DV with higher accuracy compared to correction signals CV obtained by interpolation.
A liquid crystal display device according to a third embodiment will be described. The configuration of the liquid crystal display device according to the present embodiment is the same as the configuration of the liquid crystal display device 10 shown in
A method for obtaining pixel display point Gz will be described where there is provided an input signal DV for the hue of green with the green component at its maximum level and other color components greater than 0.
K
WGz′
=K
WG×(255−d)/255 (3)
As shown in equation (3), the chromatic coordinates of temporary display point Gz′ are obtained by dividing the distance between white point W and pixel display point G into 255 equal parts along curve Wg and sequentially moving the distance in increments of one in the direction from white point W to pixel display point G. In the case where temporary display point Gz′ thus obtained coincides with a displayable point on curve Wg, it is set as pixel display point Gz corresponding to chromaticity point gz. In this case, the position of temporary display point Gz′ can be readily obtained, so that the LUT 15a can be created with ease.
Furthermore, in the case where temporary display point Gz′ does not coincide with any displayable point on curve Wg, the closest displayable point to temporary display point Gz′ is set as pixel display point Gz. The method for obtaining such a pixel display point Gz is the same as the method for obtaining pixel display point Rs on the basis of temporary display point Rs′ in the first embodiment, and therefore any detailed description thereof will be omitted. Thereafter, from the signals correlated to the chromatic coordinates of the displayable points obtained in advance, a signal corresponding to the chromatic coordinates of pixel display point Gz is selected and set as a correction signal CV. As a result, the correction signal CV specifying pixel display point Gz is correlated to the input signal DV (d,255,d).
The LUT 15a of the present embodiment is created using the PC 50 shown in
The CPU 52 obtains the length KWG of one of the 255 equal parts of curve WG extending between white point W and pixel display point G (step S51). In step S52, variable d is set to 1. A position at a distance of ((255−d)×KWG/255) from white point W toward pixel display point G along curve Wg is set as temporary display point Gz′ (step S53).
The CPU 52 determines whether or not temporary display point Gz′ obtained in step S53 coincides with any displayable point on curve Wg (step S54). When the CPU 52 determines temporary display point Gz′ to coincide with any displayable point, the process advances to step S55. Then, the CPU 52 sets the coincident displayable point as pixel display point Gz obtained on the basis of chromaticity point gz (step S55). Alternatively, when temporary display point Gz′ is not determined to coincide with any displayable point in step S54, the process advances to step S56. Then, the CPU 52 obtains the closest displayable point to temporary display point Gz′, and sets the obtained displayable point as pixel display point Gz (step S56).
In step S57, the CPU 52 increments the value of variable d by 1 (step S57), and determines whether or not variable d is 255 or higher (step S58). When variable d is determined to be 254 or lower, the process returns to step S53, and when variable d is determined to be 255 or higher, the process advances to step S59. The CPU 52 obtains a correction signal CV specifying image display point Gz, and stores it to the LUT 15a in correlation with an input signal DV (step S59).
Since pixel display point Gz is on or near curve Wg, the hue of the color specified by pixel display point Gz is also green. Moreover, according to equation (3), the lower the values of color components of the input signal DV other than the green component, the further the distance KGz′ from white point W, and therefore the correction signal CV specifying pixel display point Gz maintains the tone. Note that since pixel display point Gz is positioned within graphic H inside chromaticity point rs, the saturation of the color specified by pixel display point Gz is lower than the saturation of the color specified by chromaticity point gz.
Likewise, correction signals CV correlated to input signals DV for the hue of cyan with the red component in the range from 1 to 255, correction signals CV correlated to input signals DV for the hue of blue with the green and red components in the range from 1 to 255, and correction signals CV correlated to input signals DV for the hue of magenta with the green component in the range from 1 to 255 are sequentially obtained, and other correction signals CV are also obtained in a sequence up to correction signals CV correlated to input signals DV for the hue of yellow with the blue component in the range from 1 to 255.
Correction signals CV corresponding to all pixel display points for the hues of red, yellow, green, cyan, blue, and magenta may be obtained by the aforementioned method, or correction signals CV corresponding to only an appropriately selected group of the pixel display points for the hues may be obtained. In either case, the obtained correction signals CV are stored to the LUT 15a in correlation with input signals DV. Note that in the case where correction signals CV are obtained only for the selected pixel display points using the aforementioned method, the color correction circuit 15 reads necessary correction signals CV from among the correction signals CV stored in the LUT 15a, and obtains correction signals CV corresponding to unselected pixel display points by interpolation. Then, the obtained correction signals CV are outputted to the image signal line driver circuit 18. In this manner, only the correction signals CV corresponding to appropriately selected pixel display points are stored in the LUT 15a, thereby reducing the memory capacity of the LUT 15a compared to the case where all correction signals are stored. Moreover, the color correction circuit 15 also obtains correction signals CV corresponding to pixel display points specifying colors other than the hues of red, yellow, green, cyan, blue, and magenta, by interpolation on the basis of the correction signals CV being read from the LUT 15a, and outputs the obtained correction signals CV to the image signal line driver circuit 18.
Note that in the present embodiment, the chromatic coordinates of pixel display points Gz on curve WG are sequentially obtained in the direction from white point W to pixel display point G. However, the chromatic coordinates of pixel display points Gz on curve WG may be sequentially obtained in the direction from pixel display point G to white point W.
In the foregoing, the correspondence between the input signals DV and the correction signals CV is obtained using white point W specified by the input signal DV (255,255,255). However, a correction signal CV corresponding to an input signal DV may be obtained and additionally stored to the LUT 15a, using a point specified by an input signal (w,w,w) (where w is an integer such that 0≦w≦254) in place of white point W.
The method for obtaining correction signals CV corresponding to pixel display points on or near curves connecting white point W to pixel display points R, Y, G, C, B, and M has been described above. As in the second embodiment, pixel display points on or near curves extending between adjacent pairs from pixel display points R, Y, G, C, B, and M, e.g., pixel display points R and Y, may further be obtained. In this case, from the signals correlated to the chromatic coordinates of displayable points obtained in advance, a signal corresponding to the chromatic coordinates of a pixel display point may be selected and additionally stored to the LUT 15a as a correction signal CV.
As described above, the liquid crystal display device 10 according to the present embodiment achieves effects unique to the present embodiment while achieving the effects as described in the first and second embodiments.
Furthermore, when the response speed of the liquid crystal used in the liquid crystal display device 10 is slow, the distance between a primary-color chromaticity point (e.g., point r) and an uncorrected chromaticity point (e.g., point r′) is longer than in the case shown in
In the embodiments of the present invention, the liquid crystal display device 10 can achieve significant effects particularly when displaying completely still images. However, the same effects can be achieved even in the case where images to be displayed are not completely but mostly still. While the foregoing has been given taking the liquid crystal display device as an example, the present invention can also be applied to other display devices such as organic EL display devices.
The present invention is suitable for display devices, such as liquid crystal display devices, which provide color display using a field-sequential system, particularly for a display device capable of displaying images in colors maintaining hues and tones expected from input signals.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-095965 | Apr 2010 | JP | national |
This application is a national stage application under 35 USC 371 of International Application No. PCT/JP2011/053791, filed Feb. 22, 2011, which claims the priority of Japanese Patent Application No. 2010-095965, filed Apr. 19, 2010, the entire contents of which are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/053791 | 2/22/2011 | WO | 00 | 9/21/2012 |
