JP2003308057A - Color display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color display device having a superior color reproducing capability. <P>SOLUTION: The color display device is provided with a display panel which has a plurality of first and second color picture elements arranged in a matrix manner having a plurality of rows and columns, a signal side driving circuit which receives color image data and outputs display signal voltages corresponding to the gradation levels of color image data to the display panel and a scanning signal side driving circuit that outputs scanning signal voltages being used to successively select color picture elements, to which the display signal voltages are applied from the plurality of color picture elements, to the display panel. The signal side driving circuit outputs first display signal voltages represented by a first function of the gradation levels in accordance with the gradation levels of first color image data of the color image data and outputs second display signal voltages represented by a second function of the gradation levels in accordance with the gradation levels of second color image data of the color image data. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device capable of color display, and more particularly to a liquid crystal display device.

[0002]

2. Description of the Related Art Color reproducibility is one of the display characteristics required for a color display device. That is, there is a demand for a color display device having a wide displayable color range (color reproduction range). As a conventional color display device, for example, a CRT or a liquid crystal display device is widely used.

[0003]

Although a conventional color liquid crystal display device has a wider display color range than a CRT, it has a problem that the display color range changes depending on the gradation (for example, Nikkei Microdevice magazine). , July 1996, pp. 101-108).

A phenomenon in which the range of display colors changes according to gradation will be described below by taking a normally white (NW) mode transmissive color liquid crystal device as an example. The transmissive color liquid crystal display device is a voltage (display signal voltage) applied to the liquid crystal layer of each picture element by the amount of light transmitted through each of the R (red), G (green) and B (blue) picture elements. Is controlled, and color display is performed by additive color mixing. The NW mode liquid crystal display device exhibits the maximum brightness (bright or white) when the absolute value of the voltage applied to the liquid crystal layer is 0, and the minimum brightness (dark or black) when the saturation voltage is applied.

FIG. 1A is an xy chromaticity diagram showing a result of experimentally obtaining a display color range due to a change in input gradation in a typical NW mode transmissive color liquid crystal device. The range surrounded by each triangle shown in FIG. 1A is when the image signal has 8 bits (256 gradations).
Digital gradation level values of R (red), G (green), and B (blue) are set to 255, 216, 168, 120, and 8, respectively.
The display color range is shown as 8, 56, 40, and 24. As shown in FIG. 1A, in the triangle indicating the display color range, the display color range becomes narrower and the display color range moves in the blue direction as the gradation level value becomes smaller (the brightness becomes lower). I understand.

In order to quantitatively evaluate the degree of movement of the display color range, attention is paid to the "white" display color. In additive color mixing, "white" is obtained by mixing R, G, and B. The color displayed when one gradation level value is given to each of the R, G, and B picture elements is "white". That is, "white" is defined for each gradation level, and is a color that represents the display color range at each gradation level. Less than,
In the present specification, "white" is defined as above, is used in association with gradation (luminance), and white used in correspondence with the highest gradation (so-called NW mode white) is referred to as "white level". To call. Further, black corresponding to the lowest gradation is referred to as a "black level", and gray corresponding to an intermediate gradation is referred to as a "gray level" to distinguish it from a display color.

Point x in FIG. 1A is a point representing the white display color of the highest gradation level. A curve W extending from the point x connects the points indicating the white display color at each gradation level,
It can be seen that the white display color shifts in the blue direction as the gradation level value decreases. The change in white display color due to this gradation will be examined in more detail with reference to FIG. 1B.

FIG. 1B shows the highest gradation level (R = 255,
G = 255, B = 255) to the lowest gradation level (R =
It is the figure which showed the point which shows the white display color when changing a gradation level to 0, G = 0, B = 0) on an xy chromaticity diagram.
For reference, theoretical values showing color temperatures from 5000 K to 11000 K are also shown. As can be seen from FIG. 1B, the highest gradation level (white level) (R = 255, G =
255, B = 255), the color temperature of the white display color is about 710.
0K, intermediate gradation level (gray level) (R = 128, G
= 128, B = 128), the color temperature of the white display color is about 11
It is 000K. Also, the lowest gradation level (black level)
At (R = 0, G = 0, B = 0), blue light transmission is recognized. It is considered that this is because blue light is transmitted from the polarizing plates arranged in the crossed Nicols state that sandwich the liquid crystal panel of the transmissive liquid crystal display device.

The present invention has been made to solve the above problems, and an object thereof is to provide a color display device having excellent color reproducibility.

[0010]

A color display device of the present invention stores a display panel having a plurality of first and second color picture elements arranged in a matrix having a plurality of rows and columns and color image data. A signal side driving circuit which receives and outputs a display signal voltage corresponding to the gradation level of the color image data to the display panel, and a color picture element to which the display signal voltage is applied among the plurality of color picture elements. A scanning signal side drive circuit for outputting a scanning signal voltage to be sequentially selected to the display panel, the signal side drive circuit according to the gradation level of the first color image data of the color image data,
The first display signal voltage represented by the first function of the gradation level is output and represented by the second function of the gradation level according to the gradation level of the second color image data of the color image data. Outputting a second display signal voltage according to which the above-mentioned object is achieved.

The display panel further includes a plurality of third color picture elements arranged in a matrix having a plurality of rows and columns, and the signal side drive circuit is configured to output the third color image data of the color image data. A third display signal voltage represented by a third function of the gradation level is further output according to the gradation level, the second color picture element is a blue picture element, and the first and third color picture elements are The pixels are red pixels and green pixels, respectively, and the first, second and third functions are arranged such that the plurality of pixels of the display panel are arranged so that the color temperature of white display in at least two gradations is substantially constant. It may be determined in advance based on the voltage-luminance characteristics of the first, second and third color picture elements.

The color display device is a normally white mode liquid crystal display device, and the absolute value of the second display signal voltage at the intermediate grayscale level corresponds to the first and third display at the corresponding intermediate grayscale level. It may be larger than the absolute value of the signal voltage.

A first gradation voltage generating circuit for generating a first gradation voltage represented by the first function of the gradation level, and a second gradation represented by the second function of the gradation level. A second grayscale voltage generation circuit for generating a voltage and a third grayscale voltage generation circuit for generating a third grayscale voltage represented by the third function of the grayscale level. The circuit selects the first grayscale voltage generated by the first grayscale voltage generation circuit according to the grayscale level of the first color image data of the color image data, thereby selecting the first display signal. A second voltage by outputting a voltage and selecting the second grayscale voltage generated by the second grayscale voltage generation circuit according to the grayscale level of the second color image data of the color image data.
By outputting a display signal voltage and selecting the third grayscale voltage generated by the third grayscale voltage generation circuit according to the grayscale level of the third color image data of the color image data. The third display signal may be output.

The minimum value of the second gradation voltage may be smaller than the minimum value of the first and third gradation voltages.

The minimum value of the second gradation voltage may be larger than the minimum value of the first and third gradation voltages.

The first, second and third gradation voltage generating circuits may be selected from a plurality of gradation voltage generating circuits according to the setting of the white color temperature.

A first gradation voltage generating circuit for generating a first gradation voltage represented by the first function of the gradation level and a first gradation voltage conversion circuit for converting the gradation level of the input first color image data. A first lookup table for outputting the corrected gradation level;
A second look-up table for converting the gradation level of the input second color image data and outputting the second corrected gradation level, and a gradation level of the input third color image data for converting the third correction level. A third look-up table for outputting a gradation level, and the signal side driving circuit is responsive to a first corrected gradation level obtained by converting the gradation level of the first color image data of the color image data. , Outputting the first display signal voltage by selecting the first grayscale voltage generated by the first grayscale voltage generation circuit, and the grayscale level of the second color image data of the color image data is The second display signal voltage is output by selecting the first gradation voltage generated by the first gradation voltage generation circuit according to the converted second correction gradation level, and the second display signal voltage is output. The third power -By selecting the first grayscale voltage generated by the first grayscale voltage generation circuit according to the third corrected grayscale level obtained by converting the grayscale level of the image data, the third display signal voltage is You may output.

The maximum value of the second corrected gradation level may be smaller than the maximum value of the first and third corrected gradation levels.

The minimum value of the second corrected gradation level may be larger than the maximum value of the first and third corrected gradation levels.

The first, second and third look-up tables may be selected from among a plurality of look-up tables according to the setting of the white color temperature.

The operation will be described below.

In the color display device of the present invention, the signal side driving circuit is configured to display the first display signal represented by the first function of the gradation level according to the gradation level of the first color image data of the color image data. The voltage is output, and the second display signal voltage represented by the second function of the gradation level is output according to the gradation level of the second color image data of the color image data. Optimal gamma characteristics can be obtained independently for each of the second color picture elements.
Therefore, it is possible to prevent the phenomenon that the color temperature of the display color changes depending on the gradation and obtain a color display device with improved color reproduction characteristics.

The display panel further has a third color picture element, and the signal side drive circuit is expressed by a third function of the gradation level according to the gradation level of the third color image data of the color image data. Further outputs the third display signal voltage
The color picture element is a blue picture element, the first and third color picture elements are a red picture element and a green picture element, respectively, and the first, second and third functions are for displaying white in at least two gradations. Full-color display with excellent color reproduction characteristics is possible if it is predetermined based on the voltage-luminance characteristics of the plurality of first, second, and third color picture elements of the display panel so that the color temperature becomes substantially constant. It is possible to obtain an excellent color display device.

The color display device is a normally white mode liquid crystal display device, and the absolute value of the second display signal voltage at the intermediate gradation level is the same as that of the first and third display signal voltages at the corresponding intermediate gradation levels. If it is larger than the absolute value,
It is possible to obtain a liquid crystal display panel in which the blue shift of the color temperature of white display is reduced and the fidelity of color display is improved.

A first grayscale voltage generating circuit for generating a first grayscale voltage represented by the first function of the grayscale level, and a second grayscale represented by the second function of the grayscale level. A signal side driving circuit, which has a second grayscale voltage generation circuit for generating a voltage and a third grayscale voltage generation circuit for generating a third grayscale voltage represented by the third function of the grayscale level. Output the first display signal voltage by selecting the first gradation voltage according to the gradation level of the first color image data, and outputs the second display signal voltage according to the gradation level of the second color image data. It is more reliable if the second display signal voltage is output by selecting the adjustment voltage and the third display signal is output by selecting the third gradation voltage according to the gradation level of the third color image data. To
Prevents the phenomenon that the color temperature of the display color changes depending on the gradation,
A color display device having improved color reproduction characteristics can be obtained.

The minimum value of the second gradation voltage is the first and third values.
If it is smaller than the minimum value of the gradation voltage, the color temperature of white display can be increased.

The minimum value of the second gradation voltage is the first and third values.
If it is larger than the minimum value of the gradation voltage, the color temperature of white display can be lowered.

If the first, second and third gray scale voltage generation circuits are selected from a plurality of gray scale voltage generation circuits according to the white color temperature setting, the color temperature setting of the liquid crystal panel and the The gamma characteristics can be changed, and the color display characteristics of the liquid crystal device can be freely switched according to the scene and the preference of the user.

A first gradation voltage generating circuit for generating a first gradation voltage represented by a first function of the gradation level and a gradation level of the input first color image data are converted to perform a first correction. A first look-up table that outputs a gradation level and a second look-up table that converts the gradation level of the input second color image data
A second lookup table for outputting the corrected gradation level; and a third lookup table for converting the gradation level of the input third color image data and outputting the third corrected gradation level. The drive circuit outputs the first display signal voltage by selecting the first grayscale voltage according to the first corrected grayscale level obtained by converting the grayscale level of the first color image data to output the second color image. The second display signal voltage is output by selecting the first gray scale voltage according to the second corrected gray scale level obtained by converting the gray scale level of the data, and the third gray scale voltage is output.
If the third display signal voltage is output by selecting the first grayscale voltage according to the third corrected grayscale level obtained by converting the grayscale level of the color image data, the grayscale of the display color can be more reliably achieved. It is possible to obtain a color display device in which the phenomenon that the color temperature changes is prevented and the color reproduction characteristics are improved.

If the maximum value of the second correction gradation level is smaller than the maximum values of the first and third correction gradation levels, the color temperature of white display can be lowered.

If the minimum value of the second correction gradation level is larger than the maximum values of the first and third correction gradation levels, the color temperature of white display can be increased.

If the first, second and third look-up tables are respectively selected from a plurality of look-up tables according to the white color temperature setting, the color temperature setting and the gamma characteristic of the liquid crystal panel are changed. Therefore, the color display characteristics of the liquid crystal device can be freely switched according to the scene and user's preference.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION In order to solve the problem that the display color range and / or the color temperature of white display changes depending on the gradation, the present inventor has studied the voltage-luminance curve (VT curve) of a color liquid crystal display device. And the gamma characteristic was examined in detail, and as a result, the present invention was achieved. The reason why the conventional color liquid crystal display device found by the inventor of the present application is inferior in color reproducibility will be described below. The VT curve is a curve showing the gradation display characteristic of the display panel (picture element), and shows the relationship between the voltage V (display signal voltage) applied to the picture element and the luminance Y (transmittance T). Show. The VT curve is, for example, Y =
It can be represented as H (V). The gamma curve is a curve showing the gradation display characteristics of the liquid crystal display device, and shows the relationship between the gradation X and the brightness Y of the display data input to the liquid crystal display device. The gamma curve can be expressed as Y = F (X) using the function F, for example.

In the following, an NW mode transmissive color liquid crystal display device will be described as an example, but the same applies to liquid crystal display devices of other modes and color display devices using materials having electro-optical characteristics other than liquid crystal materials. Depending on the cause, there arises a problem that the color reproducibility is lowered depending on the gradation.

FIG. 2 shows a typical VT characteristic of a conventional NW mode transmissive liquid crystal display device. As shown in FIG. 2, the VT characteristic (Y = H (V)) of the conventional NW mode transmissive liquid crystal display device does not have a linear relationship. Also,
The VT characteristics are different for each color of R, G and B. That is, when each color is indicated by the subscripts r, g, and b, the VT curve of each color is Y _r = H _r (V), Y
_{It is represented by g} = H _g (V) and Y _b = H _b (V).

In order to obtain a liquid crystal display device having a linear gamma curve by using the liquid crystal panel having the non-linear VT characteristic, the liquid crystal panel has a non-linear relationship with the gradation level of the input display data ( So-called gamma-corrected)
It was necessary to use the gradation voltage (for example, Hitachi IC manual (HD66326T)). The relationship between the gradation level (digital value) and the gradation voltage is VT of the liquid crystal panel used.
It is decided at the design stage according to the characteristics. Gradation level {G
L} and the gradation voltage are {VG} using the function G as V
G = G (GL) means that the function G is conventionally determined at the design stage. Specifically, for example, the gradation voltage as shown in FIG. 3 is used for 64 gradations (6 bits).

The structure of a conventional color liquid crystal display device will be described with reference to FIG. 4C. Liquid crystal display device,
A display panel in which red (r), green (g), and blue (b) color pixels are arranged in a matrix, and a display signal voltage corresponding to a gradation level of input color image data is displayed in the display panel color. A signal side driving circuit (liquid crystal driver) for outputting to a picture element and a scanning signal side driving circuit for outputting a scanning signal voltage for sequentially selecting a color picture element to which a display signal voltage is applied among a plurality of color picture elements to a display panel And have.
The signal side drive circuit selects the gradation voltage VG corresponding to the gradation level (input digital signal value) of the received color image data from the gradation voltage {VG} generated by the gradation voltage generation circuit. , Output as a display signal voltage to the display panel. The scanning side drive circuit and the signal side drive circuit are timing-controlled by a control signal (clock signal or the like) supplied from the outside. The gradation voltage generation circuit is, for example,
The reference voltage is set to 63 resistors (R0, R1, ... R61, R6
2) by resistance division using the grayscale voltages {VG; V0, V1, V2 ... V61, V62, V63} corresponding to 64 grayscale levels {GL; 0, 1, ... 64}.
To generate. By determining the size of each resistor, the gray scale voltage {V having a predetermined relationship (VG = G (GL))
G} is generated.

However, this gradation voltage {VG} is
Since it was used uniformly for all R, G, B,
The VT characteristics shown in FIG. 2 (Y _r = H _r (V), Y _g = H
_{In the} display panel having _g (V) and Y _b = H _b (V), the gray scale voltage (VG = G (G
L)) is applied, the obtained gamma characteristic is Y _r = H _{r
· G (GL), Y g} = H g · G (GL), Y b = H b · G
(GL), which is different for each color, for example, as shown in FIGS. 4A and 4B. The vertical axis in FIGS. 4A and 4B represents the maximum value of the transmittance as the light output by standardizing the maximum value for each color. 4A shows the case where the input digital signal value is 64 gradations (6 bits), and FIG. 4B shows the case where the gradation is 256 gradations (8 bits).

As can be seen from FIGS. 4A and 4B, the light output of B is stronger than that of R and G for the same gradation digital value. Therefore, in such a conventional color liquid crystal device, the display color is biased to blue. Moreover, since the relative values of R, G, and B differ depending on the input digital signal value, the display color range and the color temperature of the white display color change depending on the gradation.

As described above, the main reason why the color reproducibility of the conventional color liquid crystal display device is low is V-of the liquid crystal panel.
The T curve is different depending on the color (color pixel), that is, the VT curve of each of the R, G, and B color pixels is different from each other, using H _r , H _g, and H _b , Y _r = H
_{r (V), Y g =} H g (V), Y b = H b (V)) and despite represented, a common gray scale voltages for any color pixel {VG} It depends on what I used. Further, the gradation dependency of the display color is also due to the fact that the VT curve is different for each color picture element.

Therefore, in order to improve color reproducibility, the color liquid crystal display device according to the present invention, for example, has a voltage value of a blue display signal voltage to be output to the display panel according to a certain gradation level of blue image data, It has a configuration in which the voltage value of the red display signal voltage output to the display panel is made different according to the red image data of the same gradation level. For example, when the image data has the same gradation data Xo for each of R, G and B, conventionally, a certain signal voltage Vo corresponding to the gradation Xo is applied to each of the R, G and B picture elements. Was being applied. In the above-mentioned conventional configuration, the input gradation Xo = GL
, One gray scale voltage Vo is selected from the gray scale voltages {VG} represented by the function G of GL (V _r = V _g = V _b
= G (X)). On the other hand, according to the present invention, even when the image data has the same gradation data Xo for each of R, G, B, the signal voltage applied to each of the R, G, B picture elements Can have different voltage values. That is, the relationship between the gradation data X of the input color image data and the signal voltages Vr, Vg, Vb applied to the respective color picture elements can be different from each other (V _r = G _r (X), V _g = G _g (X), V _b = G _b
(X)). Indeed, the above relationship for at least one, and typically the B picture element, differs from the above relationship for the R and G picture elements.

In order to make the relationship between the signal voltages V _r , V _g and V _b applied to the R, G and B color picture elements and the gradation data X independent, for example, two methods are considered. To be

First, as shown in FIG. 5, the gradation level G
A first gradation voltage generation circuit that generates {VG _r } represented by a function G _r of L, and a second gradation voltage generation circuit that generates {VG _b } represented by a function G _b of the gradation level GL. Third circuit for generating {VG _g } represented by a function G _g of the gradation level GL
A gradation voltage generating circuit is provided to output the R display signal voltage selected from {VG _r } according to the gradation level Xr of the R image data, and {V according to the gradation level _Xb of the B image data.
The B display signal voltage selected from G _b } may be output, and the G display signal selected from {VG _g } may be output according to the gradation level of the G image data.

Alternatively, as shown in FIG. 13, a gradation voltage generating circuit for generating the gradation voltage {VG} represented by the function G of the gradation level GL and the gradation level of the R image data are converted. A first look-up table for outputting the R correction gradation level, a second look-up table for converting the gradation level of the B image data and outputting the B correction gradation level, and a gradation level of the G image data are converted. A third look-up table for outputting the G correction gradation level, and outputting the R display signal voltage by selecting the gradation voltage from {VG} according to the R correction gradation level, and the B correction gradation The B display signal voltage is output by selecting the gradation voltage from {VG} according to the level, and the G display signal voltage is output by selecting the gradation voltage from {VG} according to the G corrected gradation level. As a configuration Good. That is, the input gradation data X is corrected by the first, second, and third look-up tables, and the corrected gradation levels h _r (X), h _b (X), and h _g (X) are corrected.
After each conversion to corrected gray level h _r (X),
According to h _b (X) and h _g (X), the gray scale voltage may be selected from the gray scale voltage {VG} generated by the single gray scale voltage generation circuit as in the conventional case. The first, second and third look-up tables respectively define the functions h _r , h _b and h _g . When expressed using the _{function, V r = G · h r} (X), V
_g = G · h _g (X) and V _b = G · h _b (X).

The embodiments of the present invention will be described in more detail below.

(Embodiment 1) FIG. 5 shows Embodiment 1 of the present invention.
Normally white mode color liquid crystal display device 100
Shows the configuration of. The color liquid crystal display device 100 of FIG. 5 is a display having a plurality of R (first color) picture elements 2, B (second color) picture elements 4 and G (third color) picture elements 6 arranged in a matrix. It has a panel 20, an image display memory 50 for outputting color image data of a personal computer, a signal side drive circuit 18, a scanning signal side drive circuit 40, and a gradation voltage generation circuit 10. The gradation voltage generation circuit 10 includes an R (first) gradation voltage generation circuit 12, a B (second) gradation voltage generation circuit 14, and a G (third) gradation voltage generation circuit 16.
Have. The R gradation voltage generation circuit 12 generates the first gradation voltage represented by the first function of the gradation level. Similarly, the B grayscale voltage generation circuit 14 generates a second grayscale voltage represented by a second function of the grayscale level, and the G grayscale voltage generation circuit 16 generates a third grayscale level third function. Third represented by the function of
Generate a gradation voltage.

The image display memory 50 stores the R image data 5
2. Color image data including B image data 54 and G image data 56 is output. These R image data 52, B image 54 data, and G green image data 56 output from the image display memory 50 are stored in the signal side drive circuit 18
Entered in. In the signal side drive circuit 18, the R display signal voltage is output by selecting the R gray scale voltage generated by the R gray scale voltage generation circuit 12 according to the gray scale level Xr of the R image data 52. . Further, according to the gradation level Xb of the B image data 54, the B gradation voltage generation circuit 1
B by selecting the grayscale voltage for B generated in 4
The display signal voltage for output is output. Furthermore, G image data 5
G gradation voltage generation circuit 16 according to the gradation level Xg of 6
The G display signal voltage is output by selecting the G grayscale voltage generated in step S6.

The scanning signal side drive circuit 40 outputs to the display panel 20 a scanning signal for sequentially selecting the color picture elements to which the display signal voltage is applied among the plurality of color picture elements 2, 4 and 6. The R, B and G display signal voltages output from the signal side drive circuit 18 are applied to the R, B and G picture elements 2, 4 and 6 of the liquid crystal panel 20 to perform color display.

As described above, in the conventional color liquid crystal device, only one kind of display signal voltage is supplied to the color picture elements of different colors, but in the present invention, a plurality of kinds of display signal voltages (for R) are supplied. , B and G display signal voltages) to suppress display color change.

A specific example of the display signal voltage applied to each color picture element will be described below.

FIG. 6 shows (added) R, B and G3 when the color temperature is set to 7700K, for example.
In the intermediate luminance region (for example, a region having an input digital value of about 20 to 50 in a 6-bit image), the B display signal voltage for the B image is R.
It is set to a value higher than the R and G display signal voltages for the G and G images. As a result, in the applied voltage-transmittance characteristic of the liquid crystal shown in FIG.
It can be corrected that the B curve exceeds the R and G curves (B transmittance is higher than R and G). In FIG.
R and G when the display signal voltage is determined as shown in
2 shows the gamma characteristics for the three primary colors B and B. From Figure 7,
It can be seen that the gamma curves for the three colors R, G, and B could be made to substantially match.

Further, in order to keep the achromatic color temperature of the color liquid crystal panel constant, it is possible to make the gamma curve for the B image lower than that for R and G. Note that how to design the gamma curve is determined by considering the physical characteristics of the liquid crystal panel. FIG. 8 shows the display signal voltage when the gamma value for the B image is increased and the achromatic color temperature is kept constant, and FIG. 9 shows the gamma characteristic at that time.

The white color temperature of the transmissive color liquid crystal device is determined by the spectral characteristics of the RGB color filters of the backlight and the liquid crystal element, but the color temperature of the liquid crystal device can be changed by changing the gradation voltage characteristics. Is.

FIG. 10 is a diagram showing the gradation voltage output with respect to the input digital signal (6 bits) when the color temperature of white display is increased (for example, the color temperature is 10000K). The minimum gradation voltage value corresponding to the maximum value of the B, R, and G input digital signals (64 in the case of FIG. 10) is V
Bmin, VRmin, and VGmin. In the normally white mode liquid crystal display device as in the present embodiment, white level display can be performed when VBmin, VRmin and VGmin are applied to each color picture element.

As shown in FIG. 10, VBmin <V
The minimum value of the gradation voltage is determined so that Rmin and VBmin <VGmin. That is, the color temperature of white display is increased by making the maximum transmittance of B higher than the maximum transmittances of R and G.

FIG. 11 is a diagram showing gradation voltages output with respect to an input digital signal (6 bits) when the color temperature of white display is lowered (for example, the color temperature is 5500K). As shown in FIG. 11, VBmin> VRmin
Further, the minimum value of the gradation voltage is determined so that VBmin> VGmin. That is, by making the maximum transmittance of B lower than the maximum transmittances of R and G, the color temperature of white display is lowered.

The color temperature of the display panel 20 can be freely set by changing the gradation voltage. The gradation voltage generation circuit for each color may be selected from a plurality of gradation voltage generation circuits according to the setting of the white temperature. As shown in FIG. 12, a plurality of gradation voltage generation circuits 12A and 12
For example, the R gradation voltage generation circuit 12A is selected from B. Similarly, for example, the B gray scale voltage generation circuit 14A is selected from the plurality of gray scale voltage generation circuits 14A and 14B, and the plurality of gray scale voltage generation circuits 16A and 16B are selected.
Among them, for example, the G gradation voltage generation circuit 16A is selected. As a result, the color temperature setting and the gamma characteristic of the liquid crystal panel 20 can be changed, so that the color display characteristic of the liquid crystal display device can be freely switched according to the scene and the preference of the user.

In this embodiment, an example in which different display signal voltages are applied to R, G and B has been described. However, since the display signal voltage output with respect to the input digital signal is shown by the substantially same curve in R and G, for example, a common display signal voltage different from the voltage given to B is R and It may be given to G. In this way, the object of the present invention can be achieved even when two different types of display signal voltages are applied to the corresponding color picture elements.

Although the liquid crystal display device of Embodiment 1 is a normally white mode color liquid crystal display device, the present invention can be similarly applied to a normally black color liquid crystal display device. is there.

Practically, in the TFT color liquid crystal device, dot inversion drive is performed based on the gradation voltage determined as in the present invention in order to prevent deterioration of the liquid crystal.

(Second Embodiment) FIG. 13 shows the structure of a color liquid crystal display device 300 according to a second embodiment of the present invention. The color liquid crystal display device 300 of FIG. 13 has a display panel 20 having a plurality of R picture elements 2, B picture elements 4 and G picture elements 6 arranged in a matrix, and an image display for outputting color image data of a personal computer or the like. Memory 50, the signal side drive circuit 18,
Scan signal side drive circuit 40 and gradation voltage generation circuit 250
And a lookup table 210.

The lookup table 210 has an R (first) lookup table 222, a B (second) lookup table 224, and a G (third) lookup table 226. Lookup table 2 for R
Reference numeral 22 converts the gradation level of the input R image data and outputs the first corrected gradation level. Similarly, the B lookup table converts the tone level of the input B image data, outputs the B (second) corrected tone level, and
The lookup table converts the gradation level of the input G image data and outputs the G (third) corrected gradation level.

The signal side drive circuit 18 converts the R level of the R image data included in the color image data into the R level.
(First) Grayscale voltage generation circuit 2 according to the corrected grayscale level
The display signal voltage for R is output by selecting the gradation voltage generated at 50. Further, similarly, the gradation voltage generation circuit 2 according to the B (second) corrected gradation level obtained by converting the gradation level of the B image data included in the color image data.
The display voltage for B is output by selecting the grayscale voltage generated in 50, and the grayscale voltage generation circuit 250 is output according to the G (third) corrected grayscale level obtained by converting the grayscale level of the G image data. The display signal voltage for G is output by selecting the gradation voltage generated in step S3.

The R, B and G display signal voltages output from the signal side drive circuit 18 in this way are applied to the R, B and G picture elements 2, 4 and 6 of the liquid crystal panel 20, respectively, and color display is performed. Done. As described above, also in the second embodiment, the display color change is suppressed by supplying a plurality of types of display signal voltages (R, B, and G display signal voltages).

Below, look-up tables 222, 2
24 and 226 will be specifically described.

FIG. 14 shows an example of the conversion table by the lookup tables 222, 224 and 226 for R, B and G when the color temperature is set to 7700K, for example. The input digital signal values for the R, B, and G lookup tables 222, 224, and 226 are shown on the horizontal axis, and the output digital signal values are shown on the vertical axis. In FIG. 14, the input digital signal value is 8 bits.

As shown in FIG. 14, the color temperature is set to 7700K.
When set to, in a medium brightness area (for example, an area where the input digital value is about 48 to 208 in an 8-bit image),
In the B lookup table 224, the B correction gradation level output by converting the gradation level of the B color image data is set to be lower than R and G. As a result, B as shown in FIG.
It is possible to suppress a phenomenon in which the display color is biased to blue due to the digital signal output value of R being larger than the digital signal output values of R and G.

FIG. 15 shows the change in white display color temperature when the input digital signal is changed from the white level to the black level when the lookup tables 222, 224 and 226 for performing the conversion shown in FIG. 14 are used. Show. From FIG. 15, it can be seen that the change in color temperature of white display due to gradation is concentrated near 7700K. Therefore, R as described above
Lookup tables 222, 22 for B, G and B
It is clear that faithful color display is possible by using 4 and 226.

When the gradation level is low (for example, R
= 16, G = 16, B = 16), and the color temperature cannot be converted to around 7700K. This is because when the gradation level is low, in the chromaticity diagram shown in FIG. 1A, there is no point indicating white display in the color triangle, and the color temperature cannot be converted to around 7700K due to the balance of R, G, and B. . When the gradation level is low, the image intensity is practically low even if the color temperature cannot be converted, so that there is no visual problem.

FIG. 16A shows another example of the look-up table. With the compensation of the change in the white display color temperature,
In this example, the gamma value is 2.2. As shown in FIG. 16A, lookup tables 22 for R, G, and B are provided.
By using 2, 224 and 226, the B display signal voltage is determined to be lower than the R and G display signal voltages.

FIG. 16B shows the change in white display temperature when the look-up table is set as shown in FIG. 16A. From FIG. 16B, it can be seen that the change in color temperature of white display due to gradation is concentrated in the range of 7000K to 8600K except for the low luminance part. Therefore, R shown in FIG.
Lookup tables 222, 22 for B, G and B
It is clear that faithful color display is possible by using 4 and 226.

FIG. 17 shows the lookup tables 222, 224 and 2 for R, B and G when the color temperature setting for white display is set low (for example, the color temperature is about 5500K).
26 shows an example of a conversion table according to 26.

The maximum output values of the R, B, and G gradation voltages output with respect to the maximum input value 255 of the R, G, and B input digital signal values (8 bits) are Rmax, Bmax, and Gmax. Rmax, Bmax and Gma
White level can be displayed when x is applied to each color picture element. As shown in FIG. 17, Bmax <Rmax and Bmax <Gmax.

As shown in FIG. 17, when the input digital signal is changed from the white level to the black level in the case where conversion is performed using the conversion function defined by each look-up table 222, 224 and 226. FIG. 18 shows the change in white display color temperature. From FIG. 18, it can be seen that the change in color temperature due to gradation is concentrated around 5500K. Therefore, it is clear that faithful color display is possible by using the R, B, and G lookup tables 222, 224, and 226 shown in FIG.

FIG. 19 shows R and B when the white display color temperature is set high (for example, the color temperature is about 10000K).
An example of a conversion table by the G lookup tables 222, 224, and 226 is shown. As shown in FIG. 19, Bmax> Rmax and Bmax> Gma
x.

As shown in FIG. 19, from the white level to the black level when conversion is performed using the first, second and third conversion functions defined by the look-up tables 222, 224 and 226. FIG. 20 shows the change in white display color temperature when the input digital signal is changed.
From FIG. 20, it can be seen that the change in color temperature due to gradation is concentrated around 10,000K. Therefore, the lookup tables 222 for R, B and G shown in FIG.
It is clear that the use of 224 and 226 allows faithful color display.

The color temperature of the display panel 20 can be freely set by changing the gradation voltage. A look-up table for each color may be selected from a plurality of look-up tables according to the setting of the white color temperature. As shown in FIG. 21, from among the plurality of R look-up tables 222A and 222B, for example, R
Lookup table 222A may be selected. Similarly, a plurality of B lookup tables 224A and 22B are provided.
Of the 4B, for example, the lookup table for B 22
4A is selected and a plurality of G look-up tables 22 are selected.
For example, the G lookup table 226A can be selected from 6A and 226B. By this,
Since the color temperature setting and the gamma characteristic of the liquid crystal panel 20 can be changed, the color display characteristic of the liquid crystal device can be freely switched according to the scene and the preference of the user.

Although the liquid crystal display device of the second embodiment is also a normally white mode color liquid crystal display device,
The present invention is similarly applicable to a normally black color liquid crystal display device.

According to the second embodiment, by using the look-up table, the image input data can be converted according to the characteristics of the color display device and the fidelity of color display can be increased.

In the present embodiment, the three colors of RGB have been described, but the present invention is not limited to this, and other color display may be used, and further two-color display may be used.

[0081]

As described above, according to the present invention, it is possible to provide a color display device having excellent color display characteristics.
Further, the color display fidelity of the color display device is improved, and the color temperature can be easily set or changed.

The color display device according to the present invention is suitably used not only for display devices for personal computers and video devices, but also for CG display devices, printing display devices and the like which require color reproduction with higher fidelity.

[Brief description of drawings]

FIG. 1A is a diagram showing, on an xy chromaticity diagram, a result of experimentally obtaining a display color range due to a change in input gradation in a NW mode transmissive color liquid crystal device.

FIG. 1B is a diagram showing a change in color temperature of a white display color when a gradation level is changed.

FIG. 2 is a diagram showing typical VT characteristics of a conventional NW mode transmissive liquid crystal display device.

FIG. 3 is a diagram showing a conventional grayscale voltage generated for 64 grayscales.

4A is a diagram showing a gamma characteristic obtained by applying a gradation voltage defined by a curve shown in FIG. 3 to a liquid crystal panel having the VT characteristic shown in FIG.

FIG. 4B is a diagram showing a gamma characteristic obtained by applying the gradation voltage defined by the curve shown in FIG. 3 to the liquid crystal panel having the VT characteristic shown in FIG. 2.

FIG. 4C is a diagram illustrating a configuration of a conventional color liquid crystal display device.

FIG. 5 is a diagram showing the configuration of the color display device of the first embodiment.

FIG. 6 is a diagram showing RGB three types of display signal voltages according to the first embodiment.

7 is an RG when the gray scale voltage shown in FIG. 6 is applied.
It is a figure which shows the gamma characteristic with respect to three B colors.

FIG. 8 is a diagram showing RGB three types of display signal voltages according to the first embodiment.

9 is a graph showing R when the gradation voltage shown in FIG. 8 is applied,
It is a figure which shows the gamma characteristic with respect to G and B three colors.

FIG. 10 is a diagram showing three types of RGB gradation voltages according to the first embodiment.

FIG. 11 is a diagram showing RGB three types of gradation voltages according to the first embodiment.

FIG. 12 is a diagram showing a configuration in which a grayscale voltage generation circuit is selected from a plurality of grayscale voltage generation circuits.

FIG. 13 is a diagram showing a configuration of a color display device according to a second embodiment.

FIG. 14 is a diagram showing a conversion table based on a lookup table according to the second embodiment.

FIG. 15 is a diagram showing a change in white display color temperature when an input digital signal is changed using the lookup table of FIG.

FIG. 16A is a diagram showing a conversion table based on a lookup table according to the second embodiment.

16B is a diagram showing a change in white display color temperature when an input digital signal is changed using the lookup table of FIG. 16A.

FIG. 17 is a diagram showing a conversion table based on a lookup table according to the second embodiment.

FIG. 18 is a diagram showing a change in white display color temperature when the input digital signal is changed using the look-up table of FIG. 17;

FIG. 19 is a diagram showing a conversion table based on a lookup table according to the second embodiment.

20 is a diagram showing a change in white display color temperature when an input digital signal is changed using the lookup table of FIG.

FIG. 21 is a diagram showing a configuration in which a lookup table is selected from a plurality of lookup tables.

[Explanation of symbols]

2 R picture element 4 B picture element 6 G picture element 10 gradation voltage generation circuit 12 R gradation voltage generation circuit 14 B gradation voltage generation circuit 16 G gradation voltage generation circuit 20 display panel 40 Scanning signal side drive circuit 50 image display memory 52 R image data 54 B image data 56G image data 100 color liquid crystal display 300 color liquid crystal display 210 lookup table, Lookup table for 222R Lookup table for 224 B Lookup table for 226 G

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09G 3/20 641 G09G 3/20 641C 641P 642 642L 650 650M H04N 9/30 H04N 9/30 F term (reference) ) 2H093 NA53 NA58 NA64 NB30 NC04 NC13 NC14 NC28 NC49 NC58 ND06 ND17 ND24 5C006 AA16 AA22 AF46 AF51 AF52 AF83 AF85 BB11 BC12 BF24 BF43 FA22 FA25 FA56 5C060 BC01 DA10 DB01 DB01 DB05 HB26 JA18 5C080 ADD05 BB05 A0305 KK04 KK43

Claims (8)

[Claims] 1. A display panel having a plurality of color picture elements arranged in a matrix having a plurality of rows and columns, receiving color image data, and displaying a display signal voltage corresponding to a gradation level of the color image data. A signal side drive circuit for outputting to the display panel, and a scanning signal side drive for outputting to the display panel a scanning signal voltage for sequentially selecting a color picture element to which the display signal voltage is applied among the plurality of color picture elements. A circuit, a gradation voltage generation circuit that generates a gradation voltage represented by a function of the gradation level, and a lookup table that converts the gradation level of the input color image data and outputs a corrected gradation level. The signal-side drive circuit selects the grayscale voltage generated by the grayscale voltage generation circuit according to the corrected grayscale level obtained by converting the grayscale level of the color image data. A color display device that outputs a display signal voltage when selected. 2. A display panel having a plurality of first, second and third color picture elements arranged in a matrix having a plurality of rows and columns, and receiving color image data, and gradation of the color image data. A signal side drive circuit that outputs a display signal voltage corresponding to a level to the display panel, and a scanning signal voltage that sequentially selects a color pixel to which the display signal voltage is applied from among the plurality of color pixels A scanning signal side driving circuit for outputting to the panel, a gradation voltage generating circuit for generating a gradation voltage represented by a function of the gradation level, a gradation level of the input first color image data and converting A first look-up table for outputting the corrected gradation level; and a second look-up table for converting the gradation level of the input second color image data and outputting the second corrected gradation level, A third look-up table for converting a gradation level of the applied third color image data and outputting a third corrected gradation level; and the signal-side drive circuit, The first display signal voltage is output by selecting the grayscale voltage generated by the grayscale voltage generation circuit according to the first corrected grayscale level in which the grayscale level is converted. Outputting a second display signal voltage by selecting the gray scale voltage generated by the gray scale voltage generation circuit according to the second corrected gray scale level obtained by converting the gray scale level of the second color image data. And selecting the grayscale voltage generated by the grayscale voltage generation circuit according to the third corrected grayscale level obtained by converting the grayscale level of the third color image data of the color image data. Therefore, the color display device which outputs the third display signal voltage. 3. The color display device according to claim 2, wherein the second color picture element is a blue picture element. 4. The color display device according to claim 2, wherein the second look-up table outputs the second corrected gradation level at a level different from the first or third corrected gradation level. . 5. The color display device is a normally white mode liquid crystal display device, wherein the absolute value of the second display signal voltage at the intermediate gray scale level corresponds to the first and the first half of the corresponding gray scale level. 3. The color display device according to claim 2, which is larger than the absolute value of the display signal voltage. 6. The color display device according to claim 2, wherein the maximum value of the second corrected gradation level is smaller than the maximum value of the first and third corrected gradation levels. 7. The color display device according to claim 2, wherein the minimum value of the second correction gradation level is larger than the maximum values of the first and third correction gradation levels. 8. The first, second and third look-up tables are each selected from a plurality of look-up tables according to a white color temperature setting.
7. The color display device according to any one of 1 to 7.