JP2001154636A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To display an image in proper brightness in an RGBW type liquid crystal display device. SOLUTION: This liquid crystal display device calculates output brightness data for W by a decoder from RGB input data. A prescribed operational expression is built in this decoder, and the output brightness data for W is calculated by using a minimum value of the RGB input data as a functional variable of the operational expression. An image can be displayed in proper brightness by using the output brightness data for W together with the RGB input data, to drive each sub-pixel of RGBW.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a liquid crystal display device capable of color display.

[0002]

2. Description of the Related Art In recent years, as display devices for personal computers, video cameras, car navigation systems and the like,
Liquid crystal display devices capable of color display have become widespread. As a method for improving the brightness of the pixels of the liquid crystal panel of the liquid crystal display device, an RGBW type liquid crystal display device (hereinafter, referred to as an “RGBW type liquid crystal”) having a transparent filter (W) installed in addition to a conventional RGB type RGB filter. Display device ”) has been proposed in Japanese Patent Application Laid-Open No. 10-10998.

[0003]

However, even if the luminance of the liquid crystal panel is simply increased by adding a transparent filter, all display colors are required unless the luminance of the pixels of the transparent filter is independently and appropriately controlled. In this case, an image of an unintended display color different from the original image is displayed, such as a decrease in color purity (chroma) due to mixing of white.

Accordingly, the present invention provides a method of determining the luminance of an image output from a liquid crystal panel by independently and appropriately controlling the luminance of pixels of a transparent filter under a predetermined calculation when determining the luminance of the liquid crystal panel. It is an object of the present invention to provide an RGBW type liquid crystal display device which can improve the liquid crystal display device.

[0005]

According to the liquid crystal display device of the present invention, the predetermined arithmetic processing by the data arithmetic means is such that the digital value of the luminance sub-pixel is W and the red input is The minimum value among the digital values of the sub-pixel for green input, the sub-pixel for green input, and the sub-pixel for blue input is Ymin,
When the maximum value is Ymax, the arithmetic expression W = f (Ym
(in, Ymax), a digital value for driving the luminance sub-pixel can be obtained, so that the object can be achieved.

According to the liquid crystal display device of the present invention, the function represented by the arithmetic expression W = f (Ymin, Ymax) is monotonic as the value of Ymin or the value of Ymax increases. Since the function is increasing, the above object can be achieved.

According to the liquid crystal display device of the third aspect, the function represented by the arithmetic expression W = f (Ymin, Ymax) uses the Ymin as a variable and the Ymax
Is a function in which is a constant, and the value of W monotonically increases as the value of Ymin increases, so that the object can be achieved.

According to the liquid crystal display device of the present invention, α, β, and n are arbitrary real values, and each of the red input subpixel, the green input subpixel, and the blue input subpixel is Where MAX is the maximum value that the digital value of can take, W = f (Ymin, Ymax) is expressed as: W = MAX
* {(Ymin + α) / (MAX + β)} Since the digital value for driving the luminance sub-pixel can be obtained by the function represented by ⁿ , the object can be achieved.

According to a liquid crystal display device described in claim 5, in the liquid crystal display device according to any one of claims 1 to 4, each of the red input sub-pixel, the green input sub-pixel, and the blue input sub-pixel. If any one of the digital values of is zero,
Takes the value 0, the above object can be achieved.

According to the liquid crystal display device described in claim 6, the liquid crystal display device according to any one of claims 1 to 5 includes a plurality of types of liquid crystal display devices represented by the arithmetic expression W = f (Ymin, Ymax). Storage means for storing a function, and the plurality of types of arithmetic expressions W = f stored by the storage means
The above-mentioned object can be achieved by providing a selecting means for selecting any one type of arithmetic expression of the function represented by (Ymin, Ymax).

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the liquid crystal display device according to the present invention will be described below.

FIG. 1 is a block diagram showing a configuration of a liquid crystal display device 100 according to one embodiment of the present invention. The liquid crystal display device 100 includes a liquid crystal panel 1. FIG. 2 is a plan view schematically showing a horizontal cross section of the liquid crystal panel 100. As shown in FIG. 2, the liquid crystal panel 1 includes column-shaped gate buses G1 to Gm (m: natural number) and row-shaped source buses S1 to Sn (n: natural number).
The gate driver 2 includes gate buses G1 to Gm.
Are sequentially connected, and the source driver 3 is connected to source buses S1 to Sn in order.

The gate buses Gi and Gi + 1 (i =
1 to m) and source buses Sj and Sj + 1 (j = 1 to
n), R (red), G (green), B (blue),
Or, W (white (for luminance enhancement)) sub-pixels Lij are arranged.

The gate bus Gi and the source bus Sj
(Thin film transistor) Qij is arranged near the intersection of. Further, the gate bus Gi is connected to the TFT Qij
, The source bus Sj is connected to the source of the TFT Qij, and the display electrode of each sub-pixel Lij is connected to the drain of the TFT Qij. Also, each sub-pixel Lij
The common electrode 12 is connected to a common voltage supply circuit (not shown).

When the sub-pixels are arranged in a vertical stripe as shown in FIG. 2, the RGBW color filters are arranged for each sub-pixel Lij as follows, and one pixel is composed of RGBW. And four sub-pixels. R: Lij (i = 1, 2, 3,..., M−1, j = 1,
5,9, ..., n-3) G: Lij (i = 1,2,3, ..., m, j = 2)
6,10, ..., n-2) B: Lij (i = 1,2,3, ..., m, j = 3)
7, 11,..., N-1) W: Lij (i = 1, 2, 3,..., M-1, j = 4)
8, 12,..., N) In the liquid crystal panel 1, these sub-pixels form a vertical stripe array.

In a direction perpendicular to the panel surface of the liquid crystal panel 1, although not shown, the TF on which the subpixel electrode is formed is formed.
A T substrate, a color filter substrate on which a common electrode is formed, a glass substrate, and the like are provided, and a liquid crystal is sandwiched and filled between these substrates. On the color filter substrate, translucent color filters of red, green, and blue are provided in portions corresponding to the above-described sub-pixels RGB, however, color filters are provided in portions corresponding to the sub-pixels W. No, or install a transparent filter.

Returning to FIG. 1, description of the liquid crystal display device 100 will be continued. A gate driver 2 is provided around the liquid crystal panel 1.
And eight source drivers 3 are arranged. Each source driver 3 includes an amplifier, a DAC (DA converter), and a latch, not shown. Further, the liquid crystal display device 100 includes a signal control unit 4. The signal control unit 4 includes a gate driver 2, a source driver 3,
A power supply voltage is supplied to the image data holding unit 5 and the decoder 6, and a control signal is supplied. A decoder 6 is connected to each source driver 3. The decoder 6 is connected to an image data holding unit 5 for holding 8-bit red, green, and blue sub-pixel input data Ri, Gi, and Bi of a digitally acquired image. .

The liquid crystal display device 100 includes a reference potential generating circuit (not shown) for supplying a reference potential to each of the source drivers 3.

Hereinafter, the operation of the liquid crystal display device 100 shown in FIG. 1 will be described. A control signal is supplied from the signal control unit 4 to each of the gate driver 2 and each of the source drivers 3. The gate driver 2 applies a TFT Qi to each gate bus (see FIG. 2) based on the control signal.
A signal for turning j on is transmitted.

When a control signal is supplied to each source driver 3, an 8-bit sub-pixel output luminance data Ro, Go is output by a latch unit (not shown) of each source driver 3 based on the control signal. , Bo, and Wo are latched.

The 8-bit sub-pixel output luminance data Ro, Go, Bo, and Wo are sub-pixel input data Ri, Gi, and Bi is obtained as a result of a predetermined operation (described later) performed by the decoder 6 on Bi.

The sub-pixel output luminance data Ro, Go, Bo, and Wo latched by the latch unit are sequentially output and input to a DAC unit (not shown). Further, the control power supply 4 is configured so that the DAC section is generated from a reference potential generation circuit.
A polarity control signal for controlling whether to select a potential from the positive reference potential or a potential from the negative reference potential is output, and the polarity control signal is input to the DAC unit. Based on the input polarity control signal and the sub-pixel output luminance data Ro, Go, Bo, and Wo, the DAC unit obtains the W sub-pixel output luminance data Ro, from the potential generated by the reference potential generation circuit. The potentials corresponding to Go, Bo, and Wo are selected.

When the potential is selected by the DAC unit, DA
The part C appropriately divides the voltage at the potential selected by the resistance division into several stages so that a desired gradation is obtained.
Thereafter, the divided voltage is current-amplified by an amplifier and transmitted to any of the corresponding source buses S1 to Sn (see FIG. 2). The signal representing the potential transmitted to the source bus is transmitted to each sub-pixel electrode via the TFT when the TFT is turned on by a signal transmitted to any one of the gate buses G1 to Gm.

Thus, a potential corresponding to the luminance data for sub-pixel output is applied to each sub-pixel electrode. Therefore, a voltage is applied to the liquid crystal layer sandwiched between the common electrode and each sub-pixel electrode, and the liquid crystal layer is driven in accordance with the potential applied to each sub-pixel electrode, and is applied to the liquid crystal panel 1 by the principle of additive color mixing. The image is displayed.

More specifically, a preferred embodiment relating to the above-described arithmetic processing of the decoder 6 will be described below with reference to FIG. As illustrated in FIG. 3, the decoder 6 acquires the 8-bit red, green, and blue input sub-pixel digital data Ri, Gi, and Bi from the image data holding unit 5 and obtains these Ri, Gi, and Bi. From the Gi and Bi, the source driver 3 sends the RGBW sub-pixel output luminance data Ro, Go,
Outputs Bo and Wo.

On the other hand, the following processing is performed to obtain the luminance data Wo for W sub-pixel output.

The decoder 6 has a comparator 7 and a look-up table 8. Comparator 7
The acquired input sub-pixel data Ri, Gi, and Bi
Are compared, and the minimum value Ymin is selected from the values of Ri, Gi, and Bi, and then this value is converted into the dimension of the luminance data.

Next, the look-up table 8 converts the Ymin value selected and converted by the comparator 7 into W subpixel output luminance data Wo.

The conversion of the Ymin value into the W sub-pixel output luminance data Wo is from 0 to 255 (in the case of 256 gradations).
Can be easily realized by using a PROM in which the operation result of Expression 1 described later is stored in the Ymin address for each value of Ymin that changes to. Furthermore, with such a circuit configuration, the signal control unit 4
Neither a control signal to the decoder 6 nor a memory for storing data is required.

However, the input sub-pixel data Ri, Gi,
And Bi are input to the decoder 6, the comparator and the look-up table are used to output the W sub-pixel output luminance data W.
There may be a delay of several clocks before outputting o to the source driver 3, which may take time. In that case, according to the output of the W sub-pixel output luminance data Wo,
The output of the RGB sub-pixel output luminance data Ro, Go, and Bo needs to be delayed in the decoder 6.

As described above, the decoder 6 outputs the input sub-pixel data R obtained from the input original image.
i, Gi, and Bi to output W subpixel luminance data Wo
Ask for.

Further, the above-mentioned formula 1 will be described.

Equation 1 indicates that the luminance data for W sub-pixel output is W
o, and the minimum value of the digital data for each of the red input sub-pixel, the green input sub-pixel, and the blue input sub-pixel is Ymi.
n, and when the maximum value is Ymax, Wo = f (Ymi
n, Ymax).

As the function represented by the formula 1, a function that monotonically increases as the value of Ymin or the value of Ymax increases can be adopted. For example, it is Wo = (Ymax * Ymin) / MAX 2 becomes function. Here, MAX is the maximum possible value of the input luminance data values of Ri, Gi, and Bi.

Further, as another preferable example of the equation (1),
Wo = MAX * ｛(MINRGB + α) / (MAX +
β)｝ ⁿ (hereinafter, this formula is simply referred to as Formula 2). Hereinafter, Equation 2 will be described in detail. Equation 2 is a function for obtaining the luminance data Wo for the W sub-pixel using the minimum value as a variable among the input luminance data for the RGB sub-pixels output to the decoder 6.

In this equation 2, output luminance data for the WoW sub-pixel, and MAX is Ri, Gi,
, And Bi are the maximum possible values of the input luminance data values, and MINRGB is the minimum possible value of the input luminance data values of Ri, Gi, and Bi. Also,
α, β, and n are arbitrary real values.

The values of α, β and n are determined by the target optical characteristics of the liquid crystal display device 100 such as luminance. For example, the conditions for β = 0 are Ri, Gi, and B
The minimum value MINRGB (Ymin) of the input luminance data of i
Is MAX, it is derived from the condition that Wo is MAX, that is, the condition that gives the liquid crystal panel 1 of the liquid crystal display 100 the maximum luminance.

Under the condition that α = 0 and β = 0, Wo becomes 0 when the minimum value MINRGB (Ymin) of the input luminance data of Ri, Gi, and Bi is 0, Since Wo = MAX when the minimum value MINRGB of the input luminance data of Ri, Gi, and Bi is MAX, it is derived from the condition that the contrast inherent in the liquid crystal display 100 is not reduced.

It is to be noted that if the color to be displayed on the liquid crystal display device 100 is 256 gradations, MAX = 25
5

The calculation according to Equation 2 can also be realized using the look-up table (LUT) provided in the decoder 6 as described above. Such a lookup table is
Can be easily integrated into the ASIC of the decoder 6,
If each input and luminance data of RGBW is 8 bits,
PROM or EEPROM with a storage capacity of 256 bytes
M can easily be realized. The values of α, β and n are
The look-up table is set in advance according to the desired optical characteristics (luminance) of the liquid crystal display device.

Here, the theory that was the basis for obtaining Equation 2 will be supplementarily described below with reference to the chromaticity diagram of FIG.

Now, when Ri, Gi, and Bi and the respective points R, G, B, and W on the chromaticity diagram of FIG. 4 have the following relationship, that is, Ri = MAX and G = B = 0, point R, G = MAX, and R = B = 0, point G; B = MAX, and R = G = 0, point B; When satisfying the relation of the point W when R = G = B, the following conclusion is obtained. "R, G, and B
Is greater than 0, the chromaticity is inside the triangle RGB of FIG. That is, the color approaches the point W and has a white (gray) color component. "

From the above conclusions, the following conclusions regarding W can be obtained. (1) “If R = G = B, only the luminance can be increased without changing the chromaticity even if W is added.” (2) “The triangle RGW is a color that can be expressed by the liquid crystal display device. , So in order not to narrow this range,
If any one of R, G, and B is 0, W =
Set to 0. "

(3) “The chromaticity when all of R, G, and B are greater than 0 approaches the point W as the minimum value of R, G, and B increases. The minimum value of G and B indicates how white the color is, so if W is given as a function of the minimum value of R, G and B, one pixel will have three RGB values. The luminance can be increased without significantly changing the chromaticity when the sub-pixels are configured. "

In view of the conclusions of (1), (2) and (3), W is set to the minimum value (MI) of R, G and B.
Equation 2 has been derived which can be given as a function of (NRGB).

Next, the decoder 6 calculates W
Some embodiments (Examples 1 to 3) for determining o are described below with reference to the graph of Equation 2 in FIG.

FIG. 5 shows the above MIN obtained by the decoder 6 when the maximum number of gradations of each pixel of the display image is 256 gradations.
Equation 2 where RGB values are used as variables on the X axis, and Wo values obtained by substituting MINRGB values into Equation 2 are used as variables on the Y axis.
It is a graph of.

As an example 1, a case where any one of the values of the luminance data of Ri, Gi, and Bi is 0 will be described. In this case, since MINRGB = 0, Wo = 0 is obtained from the operation of Expression 2 (on the x-axis in the graph of FIG. 5). That is, in this case, Wo = 0 can always be set, and there is no decrease in color purity (chroma).

As an example 2, in Expression 2, α = β = 0
And the case where n = 1 is set. In this case, Equation 2 is transformed into Wo = MINRGB, so that a result represented by a straight line in the graph of (Example 2) in FIG. 5 is obtained. Therefore, in this case, the gamma characteristic of the original image before being input to the image data holding unit 5 is held. The configuration of the circuit to be added is simple, and the scale of configuring the circuit can be small.

As an example 3, in Equation 2, the value of n is set to 1
The case where the distance is increased will be described. In this example 3, n = 2
And α = β = 0 is set. MAX = 255. From this setting, Equation 2 gives Wo = 255 * (MI
NRGB / 255) ⁿ (hereinafter, this equation is simply referred to as “Equation 3”).
And ), And Equation 3 is represented by the graph of (Example 3) in FIG.

As can be seen from the graph of (Example 3),
As the value of MINRGB increases, the value of Wo increases sharply. In other words, according to the calculation processing by the equation 2, as the MINRGB value approaches the maximum number of gradations, W
Since the luminance (Wo) for the sub-pixel sharply increases, white display close to 100% can be emphasized with respect to other display colors. As a result, it is possible to display an image such as the glow of a white cloud illuminated on a day and the glittering luster of a metallic surface, which can only be realized by a conventional CRT.

Also, as can be seen from the graph of (Example 3), in the range of the intermediate value that the MINRGB value can take,
In the graph of Wo, a downwardly convex curve shape (monotonic increase) is prominent. As a result, for example, MINRGB = 64 to 1
In a halftone such as 92, the luminance (W
o) can be suppressed, and the original chromaticity (chroma) in the halftone can be maintained in the display image.

As described above, various images can be displayed by appropriately setting the constants of the equation (2). A plurality of functions for obtaining Wo as in the above-described Examples 1 to 3 and other functions based on Expression 1 are stored in advance in a lookup table 8 provided in the decoder 6, and the user intends from the outside. The selection may be made so that an image is obtained.

As described above, according to the above-described embodiment, the arithmetic processing is performed by the decoder 6 on the basis of the mathematical expression 1, so that appropriate luminance data for the W sub-pixel can be obtained according to the image to be displayed. it can. In addition, by setting various functions in the lookup table 8 provided in the decoder 6 in advance, it is possible to provide desired optical characteristics of the liquid crystal display device 100 with various luminances.

The invention described in each claim is not limited to the above-described embodiments, and various modifications are employed within the scope described in each claim as described below. It is possible.

Hereinafter, some modified examples will be described.
(1) Modification Example 1 In the preferred embodiment, the arrangement of the sub-pixels RGBW is a vertical stripe arrangement as shown in FIG. 2, but is formed as a cross-shaped arrangement as shown in FIG. 6. Is also good. In this case, the individual shape of the sub-pixel is substantially square.

(2) Modified Example 2: In Modified Example 1, FIG.
As shown in FIG. 6, the source bus and the gate bus form a mesh, and individual sub-pixels are arranged one by one in the mesh. As shown in FIG. A bus may be wired for each two-stage sub-pixel, and two source buses may be wired for each sub-pixel. According to such a configuration, the number of gate buses is the same as that of the conventional RGB system.
The writing characteristics of the TFT may be the same as before.
In addition, according to this configuration, since the color of the sub-pixel connected to one source bus is one, there is no need to rearrange the source signals in the source driver 3 for each row.

(3) Modification 3 In the preferred embodiment described above, the decoder 6 and the source driver 3 are configured separately as shown in FIG. 3, but as shown in FIG. By arranging it at the entrance inside the source driver, it may be installed as an integrated structure of the decoder and the source driver. With this configuration, it is possible to avoid an increase in the number of data wiring lines in the printed circuit board for the luminance data for the W sub-pixel.

[0059]

As described above, according to the liquid crystal display device of the present invention, the brightness of the image displayed on the liquid crystal display panel can be appropriately improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a liquid crystal display device 100 according to a preferred embodiment of the present invention.

FIG. 2 is a plan view illustrating an arrangement of sub-pixels, a gate bus, and a source bus of the liquid crystal panel 1 shown in FIG.

FIG. 3 is a block diagram conceptually showing a source driver 3 and a decoder 6 shown in FIG.

FIG. 4 is a chromaticity diagram used to explain Equation 2.

FIG. 5 is a graph of a calculation result obtained using Expression 3.

FIG. 6 is a plan view showing a modification of the embodiment shown in FIG.

FIG. 7 is a plan view showing a modification of the embodiment shown in FIG. 2;

FIG. 8 is a block diagram showing a modification of the embodiment shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal panel 2 Gate driver 3 Source driver 4 Signal control part 5 Image data holding part 6 Decoder 7 Comparator 8 Lookup table 100 Liquid crystal display

Continuation of the front page (71) Applicant 590000248 Groenewoodseweg 1, 5621 BA Eindhoven, The Netherlands (72) Inventor Masaru Yasui 4-3-1 Takatsukadai, Nishi-ku, Kobe City, Hyogo Prefecture Hosiden Phillips Display Co., Ltd. (72 ) Inventor Nagao Kamiya 4-3-1 Takatsukadai, Nishi-ku, Kobe City, Hyogo Prefecture Hoshiden Phillips Display Co., Ltd. F-term (reference) 2H093 NA16 NA61 NC14 NC25 NC34 ND08 NE06 5C006 AA16 AA22 AF13 AF46 AF51 AF85 BB16 BC12 BF02 BF14 BF21 BF25 BF26 BF28 FA54 FA56 5C080 AA10 BB05 DD03 EE29 EE30 FF11 JJ02 JJ05

Claims (6)

[Claims] 1. A liquid crystal display device capable of color display, comprising a liquid crystal panel having a red output sub-pixel, a green output sub-pixel, a blue output sub-pixel, and a luminance sub-pixel as one main pixel unit. The luminance sub-pixel is driven by performing predetermined arithmetic processing using digital values of the red input sub-pixel, the green input sub-pixel, and the blue input sub-pixel obtained from the input image. A digital value for driving a luminance sub-pixel obtained by the data operation means, the digital value for driving the luminance sub-pixel, the red input sub-pixel, the green input sub-pixel, and the blue input sub-pixel. Using a digital value for each pixel, a luminance sub-pixel, a red output sub-pixel, a green output sub-pixel,
And the liquid crystal display device for driving the blue output sub-pixel, wherein the predetermined arithmetic processing by the data arithmetic means is such that the digital value of the luminance sub-pixel is W, the red input sub-pixel and the green input sub-pixel are , And the digital value of each blue input sub-pixel, where the minimum value is Ymin and the maximum value is Ymax, the above-mentioned luminance sub-pixel is calculated by a function represented by the following equation: W = f (Ymin, Ymax) A liquid crystal display device for obtaining a digital value for driving a liquid crystal display. 2. The liquid crystal display device according to claim 1, wherein the function represented by the arithmetic expression W = f (Ymin, Ymax) monotonically increases as the value of Ymin or the value of Ymax increases. A liquid crystal display device characterized by a function of: 3. The liquid crystal display device according to claim 1, wherein the function represented by the arithmetic expression W = f (Ymin, Ymax) is a function using the Ymin as a variable and the Ymax as a constant. A liquid crystal display device characterized in that the value of W monotonically increases as the value of Ymin increases. 4. The liquid crystal display device according to claim 1, wherein α, β, and n are arbitrary real values, and said red input subpixel, green input subpixel, and blue input subpixel. When the maximum value that can be taken by each digital value is MAX, the arithmetic expression W = f (Ymin, Ymax) is represented by a function represented by W = MAX * {(Ymin + α) / (MAX + β)} ^n. A liquid crystal display device for obtaining a digital value for driving the luminance sub-pixel. 5. The liquid crystal display device according to claim 1, wherein one of the digital values of each of the red input sub-pixel, the green input sub-pixel, and the blue input sub-pixel is a zero value. Wherein the value of W takes a value of 0. 6. The liquid crystal display device according to claim 1, wherein a plurality of types of functions represented by the arithmetic expression W = f (Ymin, Ymax) are stored. Selecting means for selecting any one of the functions represented by the plurality of types of arithmetic expressions W = f (Ymin, Ymax) stored by the means. Liquid crystal display.