Source: https://patents.google.com/patent/US8305316B2/en
Timestamp: 2019-10-14 03:44:59
Document Index: 756033728

Matched Legal Cases: ['art 500', 'art 500', 'art 500', 'art 20', 'art 23', 'art 20', 'art 20']

US8305316B2 - Color liquid crystal display device and gamma correction method for the same - Google Patents
US8305316B2
US8305316B2 US12/083,011 US8301106A US8305316B2 US 8305316 B2 US8305316 B2 US 8305316B2 US 8301106 A US8301106 A US 8301106A US 8305316 B2 US8305316 B2 US 8305316B2
US12/083,011
US20090153454A1 (en
2006-05-31 Application filed by Sharp Corp filed Critical Sharp Corp
2008-04-03 Assigned to SHARP KABUSHIKI KAISHA reassignment SHARP KABUSHIKI KAISHA ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: IRIE, KENTARO, SHIMOSHIKIRYOH, FUMIKAZU
2009-06-18 Publication of US20090153454A1 publication Critical patent/US20090153454A1/en
2012-11-06 Publication of US8305316B2 publication Critical patent/US8305316B2/en
239000004973 liquid crystal related substances Substances 0 abstract claims description title 111
A color liquid crystal display device, configured to employ a pixel division method with two or more sub-pixels obtained by spatial or temporal division of one pixel in a division ratio, may include pixel formation portions configured to form a pixel with the sub-pixels; a drive circuit configured to provide each pixel formation portion with applied voltages based on a gradation value; a gamma correction part configured to correct a relationship between the gradation and luminance values of the pixel to be formed by that pixel formation portion; and a common electrode. The gamma correction part may suppress gradation dependence of chromaticity when the screen is viewed from a front and from an oblique direction. The gradation value may be determined by an area ratio of a first sub-pixel electrode to a second sub-pixel electrode and a difference in applied voltages between first and second auxiliary electrodes.
Meanwhile, the liquid crystal display device controls the transmittance by applying a voltage across a liquid crystal layer sandwiched between a pair of polarizer plates and thereby changing a phase difference (retardation) of the liquid crystal layer. Recently, a vertical alignmnent (VA) mode of the liquid crystal is used for an application to a television (TV) and a monitor, which is a normally black mode showing a black image without the applied voltage and provides a high quality black image and a high contrast. In this VA mode, the retardation of the liquid crystal has a wavelength dependence. Therefore, in a color liquid crystal display device which displays a color image using three kinds of pixels, R (red), G (green), and B (blue), the VT characteristics are slightly different among the three kinds of pixels.
Accordingly, there has been conventionally proposed a liquid crystal display device which carries out the gamma correction independently for each R, G, and B for obtaining a good color reproducibility in a displayed image (hereinafter, such a gamma correction carried out independently for each R, G, and B is referred to as “RGB independent gamma correction”, or simply “independent gamma correction”). For example, Japanese Unexamined Patent Application Publication No. 2002-258813 (patent reference 1) discloses a color liquid crystal display device which determines γ-curves of R, G, and B individually by generating gradation voltages independently for each R, G, and B (carries out the independent gamma correction). Also, Japanese Unexamined Patent Application Publication No. 2001-222264 (patent reference 2) discloses a liquid crystal display device including a storage means for storing gamma correction data for R, G, and B generated on the basis of each luminance characteristics of an R pixel, G pixel, and B pixel arranged in a matrix on a liquid crystal panel, and a gamma correction means for individually correcting an R signal, G signal, and B signal composing a video signal to be supplied to the R pixel, G pixel, and B pixel, respectively, on the basis of the gamma correction data for R, G, and B (carrying out the independent gamma correction).
a first and a second sub-pixel electrodes disposed facing the common electrode so as to sandwich a liquid crystal layer inbetween;
According to the sixth aspect of the present invention, applying voltages which are different from each other and change in a predetermined period and in a predetermined amplitude to the first and second sub-pixel electrodes provides luminance values different from each other to the sub-pixels in each of the pixel formation portions, and also the independent gamma correction is carried out such that the gradation dependence of the chromaticity is suppressed in the oblique view in the vicinity of the predetermined gradation value determined by the area ratio of the first sub-pixel electrode to the second sub-pixel electrode and the difference in the applied voltage between the first auxiliary electrode and the second auxiliary electrode. Thereby, it is possible to display an image having a high color reproducibility in the oblique view as well as in the front view, while realizing the pixel division method in a comparatively simple configuration to improve the viewing angle dependence of the γ characteristics.
1. First Embodiment 1.1 Whole Configuration of a Liquid Crystal Display Device
FIG. 1 is a block diagram illustrating a whole configuration of an active-matrix liquid crystal display device according to a first embodiment of the present invention. This liquid crystal display device is provided with: a display control circuit 200; a pixel electrode drive circuit including a data-signal-line drive circuit (also called “source driver”)-300, a scanning-signal-line drive circuit (also called “gate driver”) 400, and a common electrode drive circuit (not shown in the drawing); an auxiliary electrode drive circuit 600; and a display part 500. The display part 500 includes a plurality of (m) data signal lines S(1) to S(m), a plurality of (n) scanning signal lines G(1) to G(n), and a plurality of (m×n) pixel formation portions provided correspondingly to respective intersections of the plurality of data signal lines S(1) to S(m) and the plurality of scanning signal lines G(1) to G(n). These pixel formation portions include three kinds of pixel formation portions corresponding to the three primary colors for displaying a color image, that is, an R pixel formation portion forming an R (red) pixel, a G pixel formation portion forming a G (green) pixel, and a B pixel formation portion forming a B (blue) pixel. Three pixel formations 10 of R pixel formation portion, G pixel formation portion and G pixel formation portion, neighboring in a horizontal direction as shown in FIG. 2, constitute one of units of display, which are arranged in a matrix on the display part 500.
1.2 Operation of the Liquid Crystal Display Device
Vlca — rms=Vsp−ΔV+(1/2)Vcs(Ccsa/Cpa)−Vcom (1)
Vlcb — rms=Vsp−ΔV−(1/2)Vcs(Ccsb/Cpb)−Vcom (2)
ΔVlc=Vcs(Ccs/Cp) (3)
In the pixel division method described above, the effective value of the first sub-pixel liquid crystal voltage Vlca_rms becomes higher and the effective value of the second sub-pixel liquid crystal voltage Vlcb_rms becomes lower than an apparent applied voltage onto the liquid crystal in the pixel formation portion 10, Vlc_ap=Vsp−ΔV−Vcom. Therefore, a relationship between the apparent applied voltage V=Vlc_ap and transmittance T (VT characteristics) becomes as shown in FIG. 5. That is, the VT characteristics of the first sub-pixel formation portion 10 a becomes as shown by a characteristic curve VTa and the VT characteristics of the second sub-pixel formation portion 10 b becomes as shown by a characteristic curve VTb. Further, the VT characteristics of the pixel formation portion 10 become average characteristics provided by these VT characteristics curves VTa and VTb, that is, characteristics as shown by a dotted line in FIG. 5.
1.3 Color Tracking and Independent Gamma Correction
Accordingly the independent gamma correction is carried out such that the color balance in the front view does not change against the gradation, and thereby flat chromaticity characteristics are obtained against the gradation as shown in (A) of FIG. 10. In an example shown in (A) of FIG. 10, gradation values of 0 to 255 are allotted to each R, G, and B (gradation display with eight bits each).
Note that in the present embodiment, the chromaticity characteristics are adjusted to become flat in a gradation range of 32 to 255. This is because there is a limit to a range where the chromaticity can be corrected by the R, G, and B independent gamma correction of the liquid crystal while suppressing a black luminance, since the chromaticity in a gradation near black is determined by a light leak in polarizer plates in the cross-nicol state and a color filter (CF). Accordingly, in the present embodiment, the R, G, and B independent gamma correction is carried out such that the chromaticity comes gradually close to the chromaticity of black (zero gradation value) in a range below a gradation value of 32 as shown in (A) of FIG. 10. Thereby, the color balance can be maintained in the gradation value range of 32 to 255, when the screen of the liquid crystal display device is viewed from the front (in the front view).
To carry out the independent gamma correction for obtaining the color tracking curve as described above ((A) of FIG. 11) in the present embodiment, it is necessary to specify the color imbalance range IL of the halftone as a range where the oblique color imbalance correction is carried out (hereinbelow, this range is referred to as an “oblique hue correction range). This oblique hue correction range IL appears due to employment of the pixel division method, and a position thereof (gradation value breaking the color balance) depends on the pixel division ratio and the difference in the effective value of the liquid crystal voltage ΔVlc=Vcs (Ccs/Cp) between the effective value of the first sub-pixel liquid crystal voltage Vlca_rms and the effective value of the second sub-pixel liquid crystal voltage Vlcb_rms. That is, in the present embodiment, the position depends on the area ratio of the first sub-pixel electrode 14 a to the second sub-pixel electrode 14 b in each pixel formation portion 10 and the amplitude Vcs of the first and second auxiliary electrode voltages Vcs1 and Vcs2. Hereinbelow, this point will be described with reference to FIGS. 12 and 13.
255×(front viewing angle normalized transmittance ratio/100)^(1/2.2) (4)
255×(right 45 degree front viewing angle normalized transmittance ratio/100)^(1/2.2) (5)
The gamma correction part 20 includes a gamma correction processing part 23, an R correction table 21 r, a G correction table 21 g, and a B correction table 21 b and, with reference to these correction tables 21 r, 21 g, and 21 b, corrects a relationship between a gradation value indicated by the data signal DAT from outside and a luminance value of a pixel formed by the pixel formation portion 10 according to the gradation value independently for each of the primary colors (red, green, and blue). That is, the data signal DAT, which is received by the gamma correction part 20, is composed of an R gradation signal Lr exhibiting an R (red) gradation value, a G gradation signal Lg exhibiting a G (green) gradation value, and a B gradation signal Lb exhibiting a B (blue) gradation value in an image to be displayed. The gamma correction part 20 carries out an independent gamma correction, which is a combination of the conventional correction (FIG. 10) for maintaining the color balance in the almost whole gradation range (gradation value range of 32 to 255) and the oblique color imbalance correction according to the pixel division ratio and the CS amplitude Vcs, for the R, G, and B gradation signals Lr, Lg, and Lb so as to obtain the color tracking as shown in (A) of FIG. 11.
1.4 Generation Method of Data for the Correction Table
In the present embodiment as described above, the independent gamma correction is carried out such that the values of the chromaticity coordinates, x and y, in the front view is reduced slightly from the values in the state maintaining the color balance in the oblique hue correction range in the halftone (color imbalance range) IL (the chromaticity in the front view is shifted toward blue), as shown in (A) of FIG. 11. Thereby, the values of the chromaticity coordinates, x and y, in the oblique view is suppressed from increasing above the values in the state maintaining the color balance in the oblique hue correction range IL (the shift of the chromaticity in the oblique view toward yellow is reduced). By such oblique color imbalance correction, the color imbalance of the halftone observed in the conventional color liquid crystal display device employing the pixel division method is suppressed to such an extent that matters little for a human visual sense even in the oblique view, and the color balance comes to be maintained substantially (to such an extent that matters little for a human visual sense) for the almost whole gradation range (gradation values of 32 to 255) in the oblique view as well as in the front view. As a result, it is possible to realize a display having high color reproducibility when the screen is viewed from the oblique direction as well as from the front direction, while improving the viewing angle dependence of the γ-characteristics by the pixel division method.
For carrying out such independent gamma correction, correction data (data to be set in the R, G, and B correction tables 21 r, 21 g, and 21 b) can be generated as follows, for example. That is, the correction data obtained by the foregoing generation method in the first embodiment (correction data corresponding to the color tracking in the first embodiment shown by the curves of a fine solid line and dotted line in (A) of FIG. 16) may be adjusted such that a color tracking curve in the front view changes monotonically as shown by the curves of a bold solid line and dotted line. Note that this correction data generation method is an example and the correction data may be generated by another method if the correction data is generated such that the color tracking as shown in (A) of FIG. 16 is obtained.
In the first and second embodiments, the independent gamma correction based on the correction tables 21 r, 21 g, and 21 b provides an appropriate color tracking and realizes a display having a high color reproducibility in the oblique view as well as in the front view. However, a method of such independent gamma correction for improving the color reproducibility is not limited to a method to correct the gradation signal Lr, Lg, or Lb according to the correction table, but may be any method to correct a relationship between a gradation value indicated by the signal inputted in the liquid crystal display device as a signal representing an image to be displayed and a luminance value of R, G, or B pixel according to the gradation value. For example, the gamma correction may be carried out by a configuration providing R, G, and B γ-correction correction voltage generating circuits for generating R, G, and B gradation voltages from R, G, and B reference input voltages, respectively, (individual setting of R, G, and B γ-correction curve) as described in Japanese Unexamined Patent Application Publication No. 2002-258813 (patent reference 1).
1. A color liquid crystal display device configured to employ a pixel division method in which each pixel of an image displayed in a screen is configured with two or more sub-pixels obtained by spatial or temporal division of one pixel in a division ratio, the device comprising:
a plurality of pixel formation portions corresponding to respective pixels of the image, each of the pixel formation portions configured to form a pixel of any of primary colors for color display with the two or more sub-pixels;
a drive circuit configured to provide each of the pixel formation portions with applied voltages corresponding to the two or more sub-pixels composing the pixel to be formed by that pixel formation portion, based on a gradation value indicated by an input signal provided from outside as a video signal representing the image;
a gamma correction part configured to correct a relationship between the gradation value indicated by the input signal and a luminance value of the pixel to be formed by that pixel formation portion according to the gradation value independently for each of the primary colors for color display; and
a common electrode provided commonly at the plurality of pixel formation portions;
each of the pixel formation portions including,
first and second sub-pixel electrodes facing the common electrode,
a liquid crystal layer between the first sub-pixel electrode and the common electrode, as well as between the second sub-pixel electrode and the common electrode,
a first auxiliary electrode disposed so as to form a first auxiliary capacitance between the first sub-pixel electrode and the first auxiliary electrode, and
a second auxiliary electrode disposed so as to form a second auxiliary capacitance between the second sub-pixel electrode and the second auxiliary electrode,
the drive circuit including,
a pixel electrode drive circuit configured to provide a voltage according to the input signal to the first and second sub-pixel electrodes with the common electrode as a reference, and
an auxiliary electrode drive circuit configured to apply voltages, which are different from each other and change in period and amplitude, to the first and second auxiliary electrodes,
wherein each of the pixel formation portions forms the respective pixel by displaying the two or more sub-pixels with luminance values different from one another based on the applied voltages,
wherein the gamma correction part is further configured to correct the relationship such that gradation dependence of chromaticity is suppressed when the screen is viewed from a front thereof, and also corrects the relationship in a vicinity of the gradation value, which is determined by the division ratio in the one pixel and differences in the applied voltages among the two or more sub-pixels, such that the gradation dependence of chromaticity is suppressed when the screen is viewed from an oblique direction, and
wherein the gradation value is determined by an area ratio of the first sub-pixel electrode to the second sub-pixel electrode and a difference in the applied voltages between the first auxiliary electrode and the second auxiliary electrode.
2. The color liquid crystal display device according to claim 1, wherein the gamma correction part is further configured to correct the chromaticity when viewed from the front to be shifted from a state maintaining a color balance toward blue in the vicinity of the gradation value such that the gradation dependence of chromaticity is suppressed when viewed from the oblique direction.
3. The color liquid crystal display device according claim 1, wherein the gamma correction part is further configured to correct the relationship such that a curve representing the gradation dependence of chromaticity when viewed from the front becomes approximately flat in a range except for the vicinity of the gradation value.
4. The color liquid crystal display device according claim 1, wherein the gamma correction part is further configured to correct the relationship such that a curve representing the gradation dependence of chromaticity when viewed from the front changes approximately monotonically with respect to the gradation value.
5. The color liquid crystal display device according claim 1, wherein the gamma correction part includes a correction table associating a gradation value before correction with a gradation value after correction for each of the primary colors for color display in order to correct the relationship, and outputs the gradation value after correction associated with the gradation value indicated by the input signal referring to the correction table, and
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Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:IRIE, KENTARO;SHIMOSHIKIRYOH, FUMIKAZU;REEL/FRAME:020788/0652