KR20080058236A - Transmissive-type liquid crystal display device - Google Patents

Abstract

A transmissive-type LCD(Liquid Crystal Display) device is provided to divide a backlight and to set a backlight value optimally to the divided backlight areas, thereby reducing the entire consumption power of the backlight. In an LCD panel, a pixel is divided into four sub pixels such as red, green, blue and white. An active backlight controls the light emission brightness. A chroma reducing member(11) performs the chroma reduction process of the pixel data with high brightness and chroma and converts the first input RGB signal into the second RGB signal. An output signal generating member(12) produces the transmission ratio signals of each sub pixel from the second input RGB signal and also calculates the backlight value at the active backlight. An LCD panel control member(13) controls the driving of the LCD panel on the basis of the transmission ratio signal. A backlight control member(15) controls the light emission brightness of the backlight on the basis of the backlight value calculated by the output signal generating member.

Description

Transmissive liquid crystal display device {TRANSMISSIVE-TYPE LIQUID CRYSTAL DISPLAY DEVICE}

The present invention relates to a transmissive liquid crystal display device using an active backlight for a light source.

There are various types of color displays, and each has been put to practical use. A thin display is roughly classified into a self-luminous display such as a plasma display panel (PDP) and a non-luminous display represented by an LCD (liquid crystal display). In LCDs which are non-light emitting displays, transmissive LCDs are known in which a backlight is disposed on the back side of a liquid crystal panel.

Fig. 13 is a sectional view showing the general structure of a transmissive LCD. This transmissive LCD arranges the backlight 110 on the back of the liquid crystal panel 100. The liquid crystal panel 100 includes a liquid crystal layer 103 disposed between a pair of transparent substrates 101 and 102, and includes polarizing plates 104 and 105 outside the pair of transparent substrates 101 and 102. It becomes the structure. In addition, the color display is enabled by providing the color filter 106 in the liquid crystal panel 100.

Although not shown, an electrode layer and an alignment film are formed inside the transparent substrates 101 and 102, and the amount of light transmitted through the liquid crystal panel 100 is controlled for each pixel by controlling the voltage applied to the liquid crystal layer 103. do. That is, the transmissive LCD performs display control by controlling the amount of light emitted from the backlight 110 in the liquid crystal panel 110.

The backlight 110 irradiates light including wavelengths of three colors of RGB necessary for color display. The backlight 110 adjusts the transmittance of light of each color of RGB by a combination with the color filter 106, thereby reducing the luminance as a pixel. It is possible to set the color arbitrarily. As the backlight 110, a white light source such as an electroluminescence (EL), a cold cathode tube (CCFL), and a light emitting diode (LED) is generally used.

In the liquid crystal panel 100, as shown in FIG. 14, a some pixel is arrange | positioned in matrix form and each pixel is comprised by three subpixels normally. Each subpixel is disposed such that the filter layers of red (R), green (G), and blue (B) in the color filter 106 correspond. Hereinafter, each subpixel is referred to as an R subpixel, a G subpixel, and a B subpixel.

Each subpixel of R, G, and B selectively transmits light of a corresponding wavelength band (ie, red, green, and blue) among white light generated from the backlight 110, and absorbs light of another wavelength band.

In the transmissive LCD having the above-described configuration, since the amount of light emitted from the backlight 110 is controlled in each pixel of the liquid crystal panel 100, light absorbed by the liquid crystal panel 100 is naturally generated. Also, in the color filter 106, each subpixel of R, G, and B absorbs light other than the wavelength band among the white light generated from the backlight 110. FIG. As described above, in the general transmissive LCD, the amount of light absorbed by the liquid crystal panel and the color filter is large, and the utilization efficiency of the irradiation light from the backlight is low, thereby causing a problem that power consumption in the backlight is increased.

As a technique for reducing the power consumption of such a transmissive LCD, a method of using an active backlight whose light emission luminance can be adjusted according to a display image is known (for example, Japanese Patent Laid-Open No. Hei 11-65531 (3 March 1999). Released 9/9).

That is, Japanese Laid-Open Patent Publication No. 11-65531 discloses an LCD display control (luminance control) by using an active backlight whose brightness is adjustable by controlling transmittance of the liquid crystal panel and luminance control of the active backlight. The technique which aims at reduction is disclosed.

In Japanese Patent Laid-Open No. 11-65531, the luminance of the backlight is controlled to match the maximum luminance value in the input image (input signal). And the transmittance | permeability of the transmittance | permeability of a liquid crystal panel is adjusted according to the brightness | luminance of the backlight in that case.

At this time, the transmittance of the subpixel which is the maximum value of the input signal is 100%, and the transmittance of the other subpixels is also 100% or less calculated by the backlight value. Therefore, when the entire image is dark, the backlight can be darkened to reduce the power consumption of the backlight.

As described above, Japanese Patent Laid-Open No. 11-65531 discloses a liquid crystal panel because the brightness of the backlight is minimized as necessary based on the input signal RGB of the input image, and the transmittance of the liquid crystal is increased by darkening the backlight. By reducing the amount of light absorbed by the power consumption of the backlight can be reduced.

However, in the above conventional configuration, although the power consumption of the backlight can be reduced by reducing the amount of light absorbed by the liquid crystal panel, the amount of light absorbed by the color filter cannot be reduced. For this reason, if the quantity of light absorbed by a color filter can be reduced, the effect of further reducing power consumption can be obtained.

An object of the present invention is to provide a transmissive liquid crystal display device capable of reducing not only the liquid crystal panel but also the amount of light absorbed by the color filter, and further achieving a reduction in power consumption.

In the transmissive liquid crystal display device of the present invention, in order to achieve the above object, one pixel is divided into four subpixels of red (R), green (G), blue (B), and white (W). The first input RGB signal is subjected to a saturation reduction process on the panel, the white active backlight which can control the light emission luminance, and the pixel data having high luminance and saturation among the pixel data included in the first input RGB signal as the input image. Generating a transmittance signal of each sub-pixel of R, G, B, and W in each pixel of the liquid crystal panel; An output signal generator for calculating a backlight value in the active backlight, a liquid crystal panel controller for driving control of a liquid crystal panel based on the transmittance signal generated by the output signal generator, and based on the backlight value calculated above And a backlight controller for controlling light emission luminance of the backlight.

According to the above-described configuration, by using a liquid crystal panel in which one pixel is divided into four subpixels of R, G, B, and W, a loss of light amount due to filter absorption of a part of each color component of R, C, and B is reduced. Can be assigned to missing (or few) W subpixels. This reduces the amount of light absorbed by the color filter, thereby lowering the backlight value, thereby realizing a reduction in power consumption in the transmissive liquid crystal display device.

Further, by performing a chroma reduction process on the first input RGB signal which is the original input, and calculating the backlight value and the RGBW transmittance based on the second input RGB signal subjected to the chroma reduction process, the backlight value can be reduced more reliably. Can be.

Still other objects, features, and advantages of the present invention will be fully understood from the description hereinafter. Further advantages of the present invention will become apparent from the following description with reference to the accompanying drawings.

EMBODIMENT OF THE INVENTION When one Embodiment of this invention is described based on drawing, it is as follows. First, the schematic structure of the liquid crystal display device (henceforth a liquid crystal display device) which concerns on this embodiment is demonstrated with reference to FIG.

The present liquid crystal display includes a chroma reduction unit 11, an output signal generation unit 12, a liquid crystal panel control unit 13, an RGBW liquid crystal panel (hereinafter simply referred to as a liquid crystal panel) 14, a backlight control unit 15, And a white backlight (hereinafter, simply referred to as a backlight) 16.

The liquid crystal panel 14 is formed by arranging Np pixels on a matrix, and as shown in Figs. 2A and 2B, each pixel includes R (red), G (green), B (blue), and W ( It consists of four subpixels. In addition, the shape and arrangement of the R, G, B, and W subpixels in each pixel are not particularly limited. In addition, the backlight 16 uses white light sources, such as a cold cathode fluorescent lamp (CCFL) and a white light emitting diode (white LED), and is an active backlight which can control the brightness of irradiation light.

Each sub-pixel of R, G, and B in the liquid crystal panel 14 is disposed so that the filter layers of R, G, and B in a color filter (not shown) correspond to each other. Therefore, each of the subpixels R, G, and B selectively transmits light in the wavelength band among the white light generated from the backlight 16, and absorbs light in the other wavelength band. Also, the W subpixel basically does not have a corresponding absorption filter layer in the color filter. That is, the light passing through the W subpixel is emitted from the liquid crystal panel 14 in the state of white light without receiving any absorption by the color filter. However, the W subpixel may have a configuration having a filter layer having less absorption of backlight light than the R, G, and B color filters.

At this time, the light output from the W subpixel is white, and when the transmittances of the respective RGB subpixels are the same, the sum of the light output from each of the RGB subpixels is also white. However, even if the transmittance of the RGB subpixel is the same as the transmittance of the W subpixel, the brightness of the white light output as the sum of the light from the RGB subpixel and the brightness of the white light output from the W subpixel are not the same. This is because the brightness changes depending on the amount of light absorbed by the color filter of each subpixel or the size of the subpixel.

The ratio of the intensity of the white light output from the W sub pixel to the intensity of the white light output from the RGB sub pixel at this time is referred to as the white luminance ratio WR. Specifically, the display luminance P1 when each transmittance of the RGB subpixels is x% and each transmittance of the W subpixels is 0%, and each transmittance of the W subpixels is set to 0% with each transmittance of the RGB subpixels. The ratio P2 / P1 of the display luminance P2 when x is set to x% is set to the white luminance ratio WR. In addition, in any one liquid crystal panel, the same white luminance ratio WR is generally used for the entire panel (i.e., all pixels).

The liquid crystal display device receives image information to be displayed as an RGB signal (first input RGB signal) from the outside of a personal computer, a television tuner, or the like, and inputs the RGB signal as an input signal Ri, Gi, Bi (i = 1, 2, ..., Np).

The saturation reduction unit 11 performs saturation reduction processing on the first input RGB signal as necessary, and outputs it to the output signal generation unit 12 as the second input RGB signal.

The output signal generator 12 is a means for obtaining the transmittance of each sub-pixel in the liquid crystal panel 14 and the backlight value in the backlight 16 from the second input RGB signal. That is, the output signal generator 12 obtains the backlight value Wbs from the input signals Rsi, Gsi, and Bsi, which are the second input RGB signals, and transmits the input signals Rsi, Gsi, and Bsi to the backlight value Wbs. Convert to gsi, bsi, wsi.

The obtained backlight value Wbs is output to the backlight control unit 15, and the backlight control unit 15 adjusts the brightness of the backlight 16 in accordance with the backlight value Wbs. The backlight 16 uses a white light source such as a CCFL or a white LED, and can be controlled by the backlight controller 15 with brightness proportional to the backlight value. The method of controlling the brightness of the backlight 16 is different depending on the type of light source used. For example, the brightness can be controlled by applying a voltage proportional to the backlight value or by flowing a current proportional to the backlight value. have. In addition, when the backlight is an LED or the like, it is also possible to control the brightness by changing the duty ratio by pulse width modulation (PWM). In addition, when the brightness of the backlight light source has a nonlinear characteristic, there is also a method of controlling the brightness to the desired brightness by determining the voltage applied to the light source, the applied current, and the like from the lookup table from the backlight value.

Transmittance signals rsi, gsi, bsi, and wsi are output to the liquid crystal panel control unit 13, and the liquid crystal panel control unit 13 sets the transmittance of each sub-pixel of the liquid crystal panel 14 to a desired transmittance based on this transmittance signal. Control as possible. The liquid crystal panel control unit 13 includes a scan line driver circuit, a signal line driver circuit, and the like. The liquid crystal panel controller 13 generates a scan signal and a data signal, and controls the liquid crystal panel 14 by panel control signals such as the scan signal and the data signal. Drive. Transmittance signals rsi, gsi, bsi and wsi are used for generation of data signals in the signal line driver circuit. The transmittance control of the liquid crystal panel 14 includes a method of controlling the transmittance of the liquid crystal panel by applying a voltage proportional to the transmittance of the subpixel, or a voltage applied to the liquid crystal panel from the transmittance of the subpixel to linearize nonlinear characteristics. And a method of controlling the liquid crystal panel to a desired transmittance.

In the liquid crystal display of the present invention, the input signal is not limited to the above-described RGB signal, but may be a color signal such as a YUV signal. When a color signal other than an RGB signal is inputted, the configuration may be converted into an RGB signal and then input to the output signal generator 12, or the output signal generator 12 may output a color input signal other than the RGB signal. The configuration may be converted into an RGBW signal.

In the present liquid crystal display device, the display luminance at each sub pixel of the liquid crystal panel 14 is represented by the brightness (irradiation luminance) of the backlight, the transmittance at the sub pixel, and the white luminance ratio WR. When the brightness of each subpixel of RGB is the product of the brightness of the backlight and the transmittance at the subpixel, the brightness of the W subpixel is determined by the product of the brightness of the backlight, the transmittance at the W subpixel, and the white luminance ratio WR. Is expressed. Here, the display luminance in each subpixel is proportional to the transmission amount of the subpixel.

In addition, although the term "backlight value" is used in the present embodiment, the backlight value has a relationship proportional to the brightness of the backlight, and is not exactly the same value as the brightness of the backlight. Similarly, the transmission amount of the subpixel has a relationship proportional to the brightness of the subpixel and is not the same value. In other words, the backlight value in this embodiment is a signal sent to the backlight, and the actual brightness is only in proportion.

Specifically, in the present embodiment, the transmittance can be obtained by multiplying the backlight value by the transmittance (or WR in the case of the W subpixel). In contrast, the brightness of the subpixel is obtained by multiplying the luminance value (brightness) of the backlight by the transmittance of the color filter of each subpixel and the LCD transmittance of the subpixel.

The white luminance ratio WR is regarded as a ratio of (white luminance by RGB subpixels): (white luminance by W subpixels) based on RGB. White luminance ratio can also be calculated | required as (transmittance by W color filter) / (transmittance by RGB color filter).

Here, the display principle in this liquid crystal display device and the power consumption reduction effect are demonstrated in detail below. In the present liquid crystal display device, the backlight value and the sub pixel transmittance are determined by the output signal generator 12. Therefore, the method of calculating the backlight value and the sub pixel transmittance described below is a process performed on the second input RGB signal input from the saturation reducing unit 11 to the output signal generator 12.

In the method for determining the backlight value and the sub-pixel transmittance in the present liquid crystal display, first, a minimum required backlight value is obtained for every pixel in the display area corresponding to the backlight. Next, the maximum value in one image is calculated | required from the required minimum backlight value calculated | required for every pixel, and let that value be a backlight value. Here, when obtaining the required minimum backlight value in each pixel, the method for obtaining the backlight value is divided into two methods according to the display data content of the pixel. Specifically, the backlight value for the pixel of interest according to the relationship between the maximum luminance (ie, max (Rsi, Gsi, Bsi)) and the minimum luminance (ie, min (Rsi, Gsi, Bsi)) in the subpixel in the pixel of interest. There are different ways to obtain.

First, a method for obtaining the required minimum backlight value at the pixel of interest such that min (Rsi, Gsi, Bsi) ≥max (Rsi, Gsi, Bsi) / (1 + 1 / WR) is described.

The maximum value of the second RGB input signals Rsi, Gsi, and Bsi to the output signal generator is maxRGBsi and the minimum value is minRGBsi. Here, although the case where the color component of the subpixel corresponding to the maximum value maxRGBsi is R (red) is demonstrated, the case where maxRGBsi is G (green) and B (blue) can also be considered similarly. In addition, maxRGBsi and minRGBsi are both values represented by the transmission amount of a subpixel.

Here, considering only the display light of the R component having the transmittance maxRGBsi, the backlight value can be most reduced for the display light so that the transmittance of the R subpixel and the W subpixel is 100% so that the R subpixel and This is when the transmission amount is assigned to the W subpixel.

The minimum required backlight value at this time is Blmin, and considering the white luminance ratio WR, since the transmittances of both the R subpixel and the W subpixel are 100%, the luminance of the emitted light from the R subpixel is Blmin, W. The luminance of the outgoing light from the subpixels is WR × Bmin. Then, the sum of the emitted light from the R subpixel and the W subpixel, that is, (1 + WR) × Bmin, becomes the transmission amount of the R component. And since (1 + WR) × Blmin is equal to maxRGBsi, Blmin becomes maxRGBsi / (1 + WR).

However, the above thought is a case where only the display light of the R component is considered, and the G and B components are not considered. In fact, when the backlight value is set to maxRGBsi / (1 + WR) when minRGBsi <maxRGBsi / (l + 1 / WR), the transmission amount of the color component corresponding to the minimum value minRGBsi is expressed by the following equation. The required amount will be exceeded.

maxRGBsi / (1 + WR) × WR

= maxRGBsi / (1 + 1 / WR)> minRGBsi

For this reason, only when minRGBsi≥maxRGBsi / (1 + 1 / WR) holds in any pixel of interest, the required minimum backlight value in that pixel of interest is maxRGBsi / (1 + WR) based on the above idea. Is set to).

In the pixel of interest with minRGBsi < maxRGBsi / (1 + 1 / WR), the maximum transmission amount that can be assigned to the W subpixel is minRGBsi so that the transmission amount of the color component corresponding to the minimum value minRGBsi does not exceed the required amount. In this case, in the subpixel of the color component corresponding to the maximum value maxRGBsi, the same amount of transmission is assigned to the W subpixel, whereby the subsequent transmission amount is maxRGBsi-minRGBsi. As a result, the required minimum backlight value in the pixel of interest becomes maxRGBsi-minRGBsi.

Thus, the minimum required backlight value in each pixel is calculated | required, and the maximum value of the backlight value required in all the pixels of an image is made into backlight value Wbs.

From this backlight value Wbs, the transmittance of each subpixel is obtained as follows. That is, the transmittance of each sub-pixel of RGB can be expressed as (transmission amount) / (backlight value). In addition, the transmittance of the W subpixel can be expressed by (transmission amount) / (backlit value) / (white luminance ratio). This is because the W subpixel has a white luminance ratio of WR times the brightness of each of the RGB subpixels, so the backlight value required for the output luminance value of the W subpixel is calculated at 1 / WR times the backlight value required for the RGB subpixel. Because it can.

3, 4, and 15 to 18, specific examples will be described below.

First, in the case where a white luminance ratio WR is used with a liquid crystal panel of 1, a backlight value is obtained in a pixel in which min (Rsi, Gsi, Bsi) ≥max (Rsi, Gsi, Bsi) / (1 + 1 / WR). The method of obtaining is described with reference to FIGS. 3A and 3B. Here, FIG. 3A is a diagram showing a method for obtaining a backlight value in the present liquid crystal display. 3B is a figure which shows the method of obtaining the backlight value in patent document 1 for a comparison.

3A and 3B, the case where the target panel output luminance of any pixel of interest is (R, G, B) = (50, 60, 40) is considered. At this time, the luminance value 60 of G is max (Rsi, Gsi, Bsi), the luminance value 40 of B is min (Rsi, Gsi, Bsi), and min (Rsi, Gsi, Bsi) ≥max (Rsi, Gsi, The relationship of Bsi) / (1 + 1 / WR) is satisfied.

In the display method of patent document 1, as shown in FIG. 3B, a backlight value is set to max (Rsi, Gsi, Bsi) = 60, and the transmittance | permeability of each sub pixel is determined according to this backlight value. In other words, the respective transmittances in the subpixels of R, G, and B are set to 83% (= 50/60), 100% (= 60/60), and 67% (= 40/60).

On the other hand, in the present liquid crystal display, in each of the R, G, and B components of the input signals Rsi, Gsi, and Bsi, the value corresponding to max (Rsi, Gsi, Bsi) / (1 + 1 / WR) is set to W component. Assign to the amount of transmission. As a result, the input signals R, G, and B represented by the RGB signal = (50, 60, 40) are the transmittances R, G, B, and W represented by the RGBW signal = (20, 30, 10). , 30). Further, in this pixel of interest, the backlight value is set to max (Rsi, Gsi, Bsi) / (1 + WR) = 30. In addition, the transmittance | permeability in each subpixel of R, G, B, and W is determined according to this backlight value. That is, each transmittance in each subpixel of R, G, B, and W is 67% (= 20/30), 100% (= 30/30), 33% (= 10/30), 100% ( = 30/30 / WR). However, the transmittance described in FIG. 3A illustrates the transmittance when the backlight value obtained in this pixel of interest is the largest among the plurality of backlight values determined for all the pixels, and is employed as the luminance value in the backlight.

Moreover, in order to compare the backlight value mentioned above in this liquid crystal display with the backlight value calculated | required by the method of patent document 1, it is also necessary to consider the area ratio of a subpixel. That is, in Patent Document 1, one pixel is divided into three subpixels, whereas in the present liquid crystal display, one pixel is divided into four subpixels. For this reason, if each subpixel is divided equally, in this liquid crystal display device, the area of one subpixel is only 3/4 of the area compared with patent document 1, and the area fall in such a subpixel is reduced. In order to compensate for this, in the present liquid crystal display device, the backlight value can be compared with the same reference as the backlight value obtained by the method of Patent Document 1 by 4/3 times the backlight value.

As a result, if the backlight value in the example of FIG. 3A is corrected on the same basis as the backlight value of FIG. 3B, (4/3) x 60 / (1 + WR) = 40. In the example of FIG. 3B which performs the same display, since the backlight value is 60, it can be seen that the power consumption according to the present invention is reduced in the pixel of interest.

Next, in the case of using a liquid crystal panel having a white luminance ratio WR of 1, the backlight value of the pixel at min (Rsi, Gsi, Bsi) < max (Rsi, Gsi, Bsi) / (1 + 1 / WR) is obtained. The method of obtaining is described with reference to FIGS. 4A and 4B. 4A is a diagram showing a method for obtaining a backlight value in the present liquid crystal display. 4B is a figure which shows the method of obtaining the backlight value in patent document 1 for a comparison.

4A and 4B, the case where the target panel output luminance of any pixel of interest is (R, G, B) = (50, 60, 20) is considered. At this time, the luminance value 60 of G is max (Rsi, Gsi, Bsi), the luminance value 20 of B is min (Rsi, Gsi, Bsi), and min (Rsi, Gsi, Bsi) <max (Rsi, Gsi, Bsi) / (1 + 1 / WR) is satisfied.

In the display method of patent document 1, as shown in FIG. 4B, a backlight value is set to max (Rsi, Gsi, Bsi) = 60, and the transmittance | permeability of each sub pixel is determined according to this backlight value. In other words, the respective transmittances in each of the R, G, and B subpixels are set to 83% (= 50/60), 100% (= 60/60), and 33% (= 20/60).

In the present liquid crystal display, on the other hand, R, G, and B components of the input signals Rsi, Gsi, and Bsi are assigned only the values corresponding to min (Rsi, Gsi, Bsi) to the transmittance of the W component. As a result, the input signals R, G, and B represented by the RGB signal = (50, 60, 20) have a transmission amount R, G, B, and W represented by the RGBW signal = (30, 40, 0). , 20). In this pixel of interest, the backlight value is set to (max (Rsi, Gsi, Bsi) -min (Rsi, Gsi, Bsi)) = 40. In addition, the transmittance | permeability in each subpixel of R, G, B, and W is determined according to this backlight value. Transmittance of each subpixel of R, G, B, and W is 75% (= 30/40), 100% (= 40/40), 0% (= 0/40), 50% (= 20 / 40 / WR).

However, the transmittance described in FIG. 4A illustrates the transmittance when the backlight value obtained in this pixel of interest is the largest among the plurality of backlight values obtained for all the pixels, and is employed as the luminance value in the backlight. In addition, even in the example of FIG. 4A, by backing the backlight value by 4/3, comparison with the same reference value as the backlight value obtained by the method of Patent Document 1 is possible.

As a result, in the example of FIG. 4A, the backlight value is (4/3) × (60-20) = 53.3. In the example of Fig. 4B which performs the same display, since the backlight value is 60, it can be seen that the power consumption according to the present invention is reduced in the pixel of interest.

Next, in the case of using a liquid crystal panel having a white luminance ratio WR of 1.5, the backlight value in the pixel at which min (Rsi, Gsi, Bsi) ≥max (Rsi, Gsi, Bsi) / (1 + 1 / WR) is obtained. The method of obtaining is explained with reference to FIGS. 15A and 15B. Here, FIG. 15A is a diagram showing a method for obtaining a backlight value in the present liquid crystal display. 15B is a diagram showing a method of obtaining a backlight value in Patent Document 1 for comparison.

15A and 15B, the case where the target panel output luminance of any pixel of interest is (R, G, B) = (100, 120, 80) is considered. At this time, the luminance value 120 of G is max (Rsi, Gsi, Bsi), the luminance value 80 of B is min (Rsi, Gsi, Bsi), and min (Rsi, Gsi, Bsi) ≥max (Rsi, Gsi, The relationship of Bsi) / (1 + 1 / WR) = 72 is satisfied.

In the display method in Patent Document 1, as shown in Fig. 15B, the luminance value of the backlight is set to max (Rsi, Gsi, Bsi) = 120, and the transmittance of each sub-pixel is determined in accordance with this backlight value. . That is, each transmittance in each of the subpixels of R, G, and B is set to 83% (= 100/120), 100% (= 120/120), and 67% (= 80/120).

On the other hand, in the present liquid crystal display device, the W component of the input signals Rsi, Gsi, and Bsi is equivalent to max (Rsi, Gsi, Bsi) / (1 + 1 / WR) for each component. It is assigned to the permeation amount of. As a result, the input signals (R, G, B) = (100, 120, 80) represented by the RGB signal have the transmission amounts (R, G, B, W) represented by the RGBW signal = (28, 48, 8). , 72). Further, in this pixel of interest, the backlight value is set to max (Rsi, Gsi, Bsi) / (1 + WR) = 48.

In addition, each transmittance in each subpixel of R, G, B, and W is determined in accordance with the brightness of the backlight produced from this backlight value. Since the W subpixel has a white luminance ratio WR times the brightness of the RGB subpixel, the backlight value required for the transmittance of the W subpixel can be calculated to be 1 / WR times the backlight value required for the RGB subpixel. That is, each transmittance in each of the subpixels of R, G, B, and W is 58% (= 28/48), 100% (= 48/48), 16.7% (= 8/48), 100% ( = 72/48 / WR).

However, the transmittance described in FIG. 15A illustrates the transmittance when the backlight value obtained in this pixel of interest is the largest among the plurality of backlight values determined for all the pixels, and is employed as the luminance value in the backlight. In addition, even in the example of FIG. 15A, by comparing the luminance value of the backlight by 4/3, comparison with the same reference value as the backlight value obtained by the method of Patent Document 1 is possible.

As a result, if the backlight value in the example of FIG. 15A is corrected on the same basis as the backlight value of FIG. 15B, (4/3) x 48 = 64. In the example of FIG. 15B which performs similar display, since the backlight value is 120, it can be seen that the power consumption according to the present invention is reduced in the pixel of interest.

Next, in the case of using a liquid crystal panel having a white luminance ratio WR of 1.5, the backlight value of the pixel at min (Rsi, Gsi, Bsi) < max (Rsi, Gsi, Bsi) / (1 + 1 / WR) is obtained. The method of obtaining is described with reference to Figs. 16A and 16B. Here, FIG. 16A is a diagram showing a method for obtaining a backlight value in the present liquid crystal display. 16B is a diagram showing a method of obtaining a backlight value in Patent Document 1 for comparison.

16A and 16B, the case where the target panel output luminance of any pixel of interest is (R, G, B) = (100, 120, 70) is considered. At this time, the luminance value 120 of G is max (Rsi, Gsi, Bsi), the luminance value 70 of B is min (Rsi, Gsi, Bsi), and min (Rsi, Gsi, Bsi) <max (Rsi, Gsi, Bsi) / (1 + 1 / WR) is satisfied.

In the display method of Patent Document 1, as shown in Fig. 16B, the luminance value of the backlight is set to max (Rsi, Gsi, Bsi) = 120, and the transmittance of each sub-pixel is determined in accordance with this backlight value. . In other words, the respective transmittances in the R, G, and B subpixels are set to 83% (= 100/120), 100% (= 120/120), and 58% (= 70/120).

In the present liquid crystal display, on the other hand, R, G, and B components of the input signals Rsi, Gsi, and Bsi are assigned only the values corresponding to min (Rsi, Gsi, Bsi) to the transmittance of the W component. As a result, the input signals R, G, B represented by the RGB signal = (100, 120, 70) have a transmission amount R, G, B, W represented by the RGBW signal = (30, 50, 0). , 70). In this pixel of interest, the backlight value is set to (max (Rsi, Gsi, Bsi) -min (Rsi, Gsi, Bsi)) = 50. In addition, each transmittance in each subpixel of R, G, B, and W is 60% (= 30/50), 100% (= 50/50), 0% (= 0/50), 93% ( = 70/50 / WR).

However, the transmittance described in FIG. 16A illustrates the transmittance when the backlight value obtained in this pixel of interest is the largest among the plurality of backlight values determined for all the pixels, and is employed as the luminance value in the backlight. In addition, even in the example of FIG. 16A, by comparing the luminance value of the backlight by 4/3, comparison with the same reference value as the backlight value obtained by the method of Patent Document 1 is possible.

As a result, in the example of Fig. 16A, the backlight value is (4/3) x (120-70) = 66.7. In the example of FIG. 16B which performs similar display, since the backlight value is 120, it can be seen that the power consumption according to the present invention is reduced in the pixel of interest.

Next, in the case of using a liquid crystal panel having a white luminance ratio WR of 0.6, the backlight value of the pixel at which min (Rsi, Gsi, Bsi) ≥max (Rsi, Gsi, Bsi) / (1 + 1 / WR) is obtained. The method of obtaining is described with reference to FIGS. 17A and 17B. 17A is a diagram showing a method for obtaining a backlight value in the present liquid crystal display. In addition, FIG. 17B is a diagram showing a method of obtaining a backlight value in Patent Document 1 for comparison.

17A and 17B, the case where the target panel output luminance of any pixel of interest is (R, G, B) = (100, 120, 50) is considered. At this time, the luminance value 120 of G is max (Rsi, Gsi, Bsi), the luminance value 50 of B is min (Rsi, Gsi, Bsi), and min (Rsi, Gsi, Bsi) ≥max (Rsi, Gsi, Bsi) / (1 + 1 / WR) = 45 is satisfied.

In the display method in Patent Document 1, as shown in Fig. 17B, the luminance value of the backlight is set to max (Rsi, Gsi, Bsi) = 120, and the transmittance of each sub-pixel is determined in accordance with this backlight value. . That is, each transmittance in each of the subpixels of R, G, and B is set to 83% (= 100/120), 100% (= 120/120), and 42% (= 50/120).

On the other hand, in the present liquid crystal display, in each of the R, G, and B components of the input signals Rsi, Gsi, and Bsi, the value corresponding to max (Rsi, Gsi, Bsi) / (1 + 1 / WR) is set to W component. Assign to the amount of transmission. As a result, the input signals (R, G, B) = (100, 120, 50) represented by the RGB signal have the transmission amounts (R, G, B, W) represented by the RGBW signal = (55, 75, 5). , 45). In this pixel of interest, the backlight value is set to max (Rsi, Gsi, Bsi) / (1 + WR) = 75. In addition, each transmittance in each subpixel of R, G, B, and W is 73% (= 55/75), 100% (= 75/75), 6.7% (= 5/75), 100% ( = 45/75 / WR).

However, the transmittance described in FIG. 17A illustrates the transmittance when the backlight value obtained in this pixel of interest is the largest among the plurality of backlight values obtained for all the pixels, and is employed as the luminance value in the backlight. In addition, also in the example of FIG. 17A, by 4/3 times the luminance value of a backlight, it becomes comparable on the same reference | standard as the backlight value calculated | required by the method of patent document 1. As shown in FIG.

As a result, if the backlight value in the example of FIG. 17A is corrected on the same basis as the backlight value of FIG. 17B, (4/3) x 75 = 100. In the example of FIG. 17B which performs similar display, since the backlight value is 120, it can be seen that the power consumption according to the present invention is reduced in the pixel of interest.

Next, in the case of using a liquid crystal panel having a white luminance ratio WR of 0.6, the backlight value of the pixel at min (Rsi, Gsi, Bsi) < max (Rsi, Gsi, Bsi) / (1 + 1 / WR) is obtained. The method of obtaining is described with reference to FIGS. 18A and 18B. 18A is a diagram showing a method of obtaining a backlight value in the present liquid crystal display. 18B is a diagram showing a method of obtaining a backlight value in Patent Document 1 for comparison.

18A and 18B, the case where the target panel output luminance of any pixel of interest is (R, G, B) = (100, 120, 40) is considered. At this time, the luminance value 120 of G is max (Rsi, Gsi, Bsi), the luminance value 40 of B is min (Rsi, Gsi, Bsi), and min (Rsi, Gsi, Bsi) <max (Rsi, Gsi, Bsi) / (1 + 1 / WR) is satisfied.

In the display method of patent document 1, as shown in FIG. 18B, a backlight value is set to max (Rsi, Gsi, Bsi) = 120, and the transmittance | permeability of each sub pixel is determined according to this backlight value. That is, the respective transmittances in each of the subpixels of R, G, and B are set to 83% (= 100/120), 100% (= 120/120), and 33% (= 40/120).

In the present liquid crystal display, on the other hand, R, G, and B components of the input signals Rsi, Gsi, and Bsi are assigned only the values corresponding to min (Rsi, Gsi, Bsi) to the transmittance of the W component. As a result, the input signals R, G, B represented by the RGB signal = (100, 120, 40) are the output signals R, G, B, W represented by the RGBW signal = (60, 80, 0, 40). In this pixel of interest, the backlight value is set to (max (Rsi, Gsi, Bsi) -min (Rsi, Gsi, Bsi)) = 80. In addition, each transmittance in each subpixel of R, G, B, and W is 75% (= 60/80), 100% (= 80/80), 0% (= 0/80), 83% ( = 40/80 / WR).

However, the transmittance described in FIG. 18A illustrates the transmittance when the backlight value obtained in this pixel of interest is the largest among a plurality of backlight values obtained for all the pixels, and is employed as the backlight value in the backlight. In addition, in the example of FIG. 18A, by comparing the luminance value of the backlight by 4/3, comparison with the same reference value as the backlight value obtained by the method of Patent Document 1 is possible.

As a result, in the example of Fig. 18A, the backlight value is (4/3) x (120-40) = 107. In the example of Fig. 18B which performs similar display, since the backlight value is 120, it can be seen that the power consumption according to the present invention is reduced in the pixel of interest.

3, 4, and 15 to 18 illustrate a method of obtaining the minimum backlight value required for each pixel. Based on the above method, the minimum required for every pixel in the display area corresponding to the backlight is explained. Find the backlight value. The maximum value among the plurality of backlight values obtained in this manner is set as the luminance value in the backlight.

The procedure for determining the backlight value and the subpixel transmittance in the present liquid crystal display device, which is performed by the above-described method, will be described with reference to FIGS. 5A to 5E.

FIG. 5A shows the input signals Rsi, Gsi, and Bsi of the display area corresponding to any one backlight. Here, for the sake of simplicity, the white luminance ratio WR is set to 1, and the display area is composed of four pixels A to D. The actual white luminance ratio WR is a value determined by the liquid crystal panel, has a value common to all pixels, and is greater than zero.

The results of converting the input signals Rsi, Gsi, and Bsi into output signals Rtsi, Gtsi, Btsi, and Wtsi represented by RGBW signals for these pixels A to D are shown in FIG. 5B. In addition, the backlight value calculated | required for every pixel is shown to FIG. 5C. As a result, the backlight value is set to the maximum value among the plurality of backlight values obtained for each pixel, that is, 100.

The transmittances rsi, gsi, bsi and wsi of each pixel with respect to the backlight value 100 thus obtained are obtained based on the values of the output signals Rtsi, Gtsi, Btsi and Wtsi shown in FIG. 5B. Is shown in Fig. 5D. The final display luminance in each pixel is the result shown in FIG. 5E, and it can be confirmed that the display luminance coincides with the luminance values of the input signals Rsi, Gsi, and Bsi shown in FIG. 5A.

As described above, in the above-described calculation processing of the backlight value and the subpixel transmittance in the output signal generation unit 12, by absorbing the light amount of the white component in the W subpixel, the absorption of the light by the color filter is suppressed, and the backlight 16 It is possible to reduce the power consumption at. For this reason, in the display image data, the allocation of the amount of white component light to the W subpixel becomes an essential condition for obtaining the effect of reducing the backlight power consumption.

That is, the calculation process of the backlight value and the subpixel transmittance in the output signal generator 12 has a large amount of white component light (i.e., low chroma) assigned to the W subpixel in all the pixels in the display area corresponding to the backlight. In this case, the effect of reducing the backlight power consumption is increased. On the other hand, if there is a pixel having a small amount of white component light (that is, high chroma) assigned to the W subpixel in the display area corresponding to the backlight, the effect of reducing the backlight power consumption is small and the luminance is high. There may be a case where the power consumption increases rather than the display method.

In the case where a liquid crystal panel having a white luminance ratio WR of 1 is used below, an example of setting a backlight value for two pixels having the same luminance and different saturation will be described.

First, in the case of the pixel A (luminance = 208, chroma = 0533) of (R, G, B) = (176, 240, 112), the backlight value is calculated as follows.

In the pixel A, the amount of light allocated to the W subpixel is (112). Subsequently, the light amounts of the R, G, and B subpixels obtained by subtracting the light amount allocated to the W subpixels are (64, 128, 0). As a result, the backlight value set in the pixel A becomes (128).

On the other hand, in the case of the pixel B (luminance = 208, saturation = 0.75) of (R, G, B) = (160, 256, 64), the backlight value is calculated as follows.

In the pixel B, the amount of light allocated to the W subpixel is (64). Then, the light amounts of the R, G, and B subpixels minus the light amounts allocated to the W subpixels are (96, 192, 0). As a result, the backlight value set in the pixel B becomes (192).

Thus, when comparing pixel A and pixel B, although the brightness | luminance is the same, it turns out that the backlight value is set large in the pixel B with high saturation, and the effect of reducing backlight power consumption is small.

Here, the output signal generation unit 12 can calculate the backlight value and the subpixel transmittance by the above processing also for the original image data (that is, the first input RGB signal) first input to the liquid crystal display. . In this case, however, the power consumption reduction effect cannot be obtained for all the images due to the above-described reasons. (In addition, in the case of a normal halftone display screen which is considered to have the greatest display opportunity, the power consumption can be achieved. The effect of the reduction is often obtained).

For this reason, in this liquid crystal display device, the chroma reduction part 11 is arrange | positioned in front of the output signal generation part 12, the chroma reduction process is performed on the 1st input RGB signal, and is converted into the 2nd input RGB signal. . Thereby, in the process by the output signal generation part 12, the effect of reducing backlight power consumption can be obtained more reliably. Hereinafter, the chroma reduction processing in the chroma reduction unit 11 will be described in detail.

6 is a block diagram showing a schematic configuration of the saturation reducing unit 11. As shown in FIG. 6, the chroma reduction unit 11 includes a backlight upper limit calculator 21 and a signal converter 22. The backlight upper limit calculator 21 calculates the backlight upper limit from the upper limit of the first input RGB signal, the white luminance ratio WR, and the backlight value setting rate, and outputs the backlight upper limit to the signal converter 22. The signal converter 22 calculates and outputs a second input RGB signal from the first input RGB signal and the backlight upper limit value output from the backlight upper limit calculator 21.

7 is a flowchart for explaining the operation of the saturation reducing unit 11.

First, in S11, the backlight upper limit value is calculated by the backlight upper limit calculator 21 (S11). In the saturation reduction unit 11, the saturation reduction process is performed only for pixels having a low amount of light (i.e., high saturation) and high luminance, which are allocated to the W subpixels as it is, but at least one of saturation or luminance The chroma reduction process is not performed on the low pixel. This is because, for example, pixels with low saturation can significantly reduce the backlight value by allocating a large amount of light to the W subpixel even if the luminance is high, and in the case of low luminance pixels, a high backlight value is not required in the first display. . The backlight upper limit value is used to determine a pixel to be subjected to saturation reduction processing. The calculation procedure of the backlight upper limit is explained in full detail as follows.

First, it is a case where saturation reduction processing is not performed on image data (that is, an input RGB signal), and the case where the backlight value becomes the largest is considered. This is a case where there is a pixel whose saturation is 1 (the amount of light cannot be shared among the W subpixels) and at least one of the RGB values is MAX (pointing to the upper limit of the input RGB signal). In addition, the backlight value at this time also becomes MAX.

Next, it is a case where saturation reduction processing is performed on image data (namely, an input RGB signal), and the case where the backlight value becomes largest is considered. In addition, the chroma reduction process here is a process which minimizes chroma without changing brightness before and after the process with respect to the pixel in which the process is performed. In this case, when the saturation is 0 (there is no way of lowering the saturation any more, the backlight value cannot be lowered), and when there are pixels in which all of the RGB values are MAX, the maximum backlight value is obtained. Here, since the W subpixel can shine brighter WR times than the RGB subpixel, in the pixel, WR / (1 + WR) of the amount of light in each of the RGB values is assigned to the W subpixel. Allocating 1 / (1 + WR) is the most efficient backlight. At this time, the backlight value becomes MAX / (1 + WR).

Therefore, when the backlight upper limit MAXw is set to MAX / (1 + WR) to MAX, and the range of BlRatio is set to 1 / (1 + WR) to 1.0, the backlight upper limit MAXw is expressed by Equation 1 below. I can express it.

In addition, although MAX refers to the upper limit of an input RGB signal, a some value is considered not a unique value. In other words, the lower limit of MAX is the maximum value MAXi of all RGB values of the input RGB signal. This is because if MAX is set to a value smaller than MAXi, it cannot be guaranteed to achieve a desired backlight value. On the other hand, the upper limit of MAX becomes the maximum value MAXs of the value which an input RGB signal can take. This is because no backlight value greater than MAXs is required.

If the bit width of the input RGB signal is Bw, MAXs is

MAXs = 2 ^Bw -1

It is expressed as For example, when Bw is 8, MAXs is 2 ⁸ -1 = 255. Therefore, the valid range of MAX is

MAXi≤MAX≤MAXs

It is expressed as

As a setting value of MAX, as long as MAXi <= MAX <MAXs is satisfied, what kind of value may be sufficient. By setting MAX = MAXi, you can achieve the lowest backlight value. However, it is necessary to calculate the MAX for each image. On the other hand, when MAX = MAXs, the upper limit of the backlight value MAXw is higher than MAXi, but since MAX is a constant value that does not depend on the image, it is not necessary to recalculate the MAX for each image.

In Equation 1, BlRatio is a constant indicating the degree of saturation reduction processing. That is, when BlRatio is 1, it corresponds to the case where the said chroma reduction process is not performed, and when BlRatio is 1 / (1 + WR), it corresponds to the case where the process which minimizes saturation is performed. In the saturation reduction process, as the saturation is further reduced, the effect of reducing backlight power consumption increases, but of course, the degree of deterioration in image quality due to saturation reduction also increases. For this reason, BlRatio may be arbitrarily set within the range of 1 / (1 + WR) to 1 according to the required saturation reduction level in consideration of the balance between the power consumption reduction effect and image quality deterioration.

When the backlight upper limit value MAXw is determined in this way, next, in S12, it is determined for each pixel on the basis of the following equation (2) whether or not to perform the chroma reduction process.

However, in Equation 2,

maxRGB = max (Ri, Gi, Bi)

minRGB = min (Ri, Gi, Bi)

to be.

In any pixel of interest, when the RGB value satisfies the above expression (2), it is determined that the pixel of interest is a pixel with high luminance and saturation in which the backlight value directly exceeds the backlight upper limit value MAXw. Therefore, the saturation reduction process is performed in S13.

In addition, the saturation reduction process deteriorates the image quality of the input image in terms of the vividness of colors. However, in the general image, there are not many parts of high luminance and high saturation, and a portion of the saturation that is lowered is part of the image. It is often limited to. In addition, since human visual characteristics are not very sensitive to changes in color as compared to changes in brightness, image degradation due to saturation reduction is often difficult to be perceived by humans. On the other hand, in the human visual characteristic, the luminance change is recognized as a large image quality deterioration. Therefore, in this saturation reduction process, it is important to reduce only the saturation without changing the luminance.

On the other hand, in S12, the pixel that does not satisfy the above formula (2) is determined to be a low luminance or saturation pixel in which the backlight value does not exceed the backlight upper limit value MAXw. It is not necessary to perform saturation reduction processing for such pixels, and the flow proceeds to S14 where the pixel data in the first input RGB data is also used in the second input RGB data as it is.

Here, the reason why Equation 2 is used for determining whether the chroma reduction processing for the pixel of interest is necessary will be described.

First, the calculation formula of the W sub-pixel transmission amount Wti when saturation reduction is not carried out is as follows.

In addition, the transmission amounts Rti, Gti, and Bti of the RGB subpixels are represented by the following expressions (4) to (6).

In the equations (3) to (6), each of the RGBW transmittances does not exceed minRGB, so the value does not fall below zero.

Next, the condition that each of the RGB transmission amounts does not exceed MAXw is expressed by the following expressions (7) to (9).

On the other hand, the condition in which the W transmittance does not exceed MAXw is a condition that the value obtained by dividing Wti by WR does not exceed MAXw because the W subpixel shines by WR times with respect to the RGB subpixel. The following equation (10) is obtained.

 Wti / WR≤MAXw

therefore,

From the above equations (3) to (6) and (7) to (9), the condition that each of the RGB transmittances does not exceed MAXw is expressed by the following equation (11).

 max (Rti, Gti, Bti) ≤MAXw

 maxRGB-Wti≤MAXw

therefore,

here,

(A) when maxRGB / (1 + 1 / WR) ≤minRGB,

The condition that the W transmittance does not exceed MAXw is from the above equation (10),

 maxRGB / (1 + 1 / WR) ≤MAXw × WR

therefore,

It becomes Since MAXw is in the range of MAX / (1 + WR) ≦ MAXw ≦ MAX, maxRGB / (1 + WR) ≦ MAX / (1 + WR) ≦ MAXw, and the above expression (12) is always satisfied. .

Next, the condition that the RGB transmittance does not exceed MAXw, from the above formula (11),

 maxRGB-maxRGB / (1 + 1 / WR) ≤MAXw

therefore,

 maxRGB / (1 + WR) ≤MAXw

It becomes Since the equation is the same as the equation 12, it is always true.

Meanwhile,

The condition that the W transmittance does not exceed MAXw is from the above equation (10),

 minRGB≤MAXw × WR

It becomes In this case, from MAX / (1 + WR) ≦ MAXw ≦ MAX, and minRGB <maxRGB / (1 + 1 / WR), minRGB <maxRGB / (1 + 1 / WR) = WR × maxRGB / (1 + WR) ≤ WR x MAX / (1 + WR) ≤ MAXw x WR, and the above equation is always true.

Next, the condition that the RGB transmittance does not exceed MAXw, from the equation (11),

It becomes

Since Equation 13 is not always satisfied, the condition that all of the RGBW transmittance does not exceed MAXw is expressed by Equation 13 when (B) minRGB <maxRGB / (1 + 1 / WR). .

On the contrary, the condition under which at least one of the RGBW transmission amounts exceeds MAXw becomes the above expression (2) when (B) minRGB <maxRGB / (1 + 1 / WR).

When the above expression (2) holds, from MAX / (1 + WR) ≦ MAXw ≦ MAX,

 maxRGB / (1 + 1 / WR) ≤MAX / (1 + 1 / WR)

= WR x MAX / (1 + WR) ≤ MAXw x WR

<(maxRGB-minRGB) × WR

 maxRGB / (1 + 1 / WR) <(maxRGB-minRGB) × WR

therefore,

minRGB <maxRGB / (1 + 1 / WR)

That is, (B) minRGB <maxRGB / (1 + 1 / WR) always holds.

Therefore, the condition that at least one of the RGBW transmittances exceeds MAXw becomes the above expression (2) unconditionally.

That is, when Ri, Gi, and Bi satisfy the above expression (2), the chroma reduction process is performed so that the backlight value does not exceed MAXw.

Subsequently, the saturation reduction processing performed on the pixel determined that both the saturation and the luminance are high based on Equation 2 will be described in detail.

For pixels with high luminance and saturation that require saturation reduction processing, the signal conversion unit 22 performs saturation reduction processing using the following equations (16) to (19), and the first RGB signal Ri before the process (Ri). , Gi, and Bi are converted into second RGB signals Rsi, Gsi, and Bsi.

However, in the above equations (16) to (18), Yi is the luminance of the input RGB signals Ri, Gi, and Bi (for example, Yi = (2 × Ri + 5 × Gi + Bi) / 8).

Here, the derivation process of the equations (16) to (19), which is the calculation formula of the saturation reduction process, will be described.

First, the conversion equation of the RGB signal in which the luminance and the hue are invariant and only the saturation is reduced is the same as the above expressions (16) to (18) when the following expression (20) is satisfied.

Proof that the equations (16) to (18) do not change the luminance and color of the RGB signal before and after the chroma reduction process is as follows.

First, if the formula for calculating luminance when the RGB value is (R, G, B) is (2 × R + 5 × G + B) / 8, the luminance Ysi after the chroma reduction is as follows for the luminance Yi before the chroma reduction. Is represented by Equation 21.

Substituting Equation 16 to Equation 18 into Equation 21 results in Equation 22 below.

From Equation 22, it can be seen that the chroma reduction process using Equations 16 to 18 does not change the brightness before and after the process.

On the other hand, regarding the color, first, consider the case where the R value is maximum. The color Hi before the saturation reduction process when the R value is maximum is expressed by the following expression (23).

only,

 Cb = (maxRGB-Bi) / (maxRGB-minRGB)

 Cg = (maxRGB-Gi) / (maxRGB-minRGB)

to be.

Next, the hue Hsi after the saturation reduction process is expressed by the following expression (24).

only,

Cbs = (maxRGBs-Bsi) / (maxRGBs-minRGBs)

Cgs = (maxRGBs-Gsi) / (maxRGBs-minRGBs)

maxRGBs = max (Rsi, Gsi, Bsi)

minRGBs = min (Rsi, Gsi, Bsi)

to be.

If the above equation (24) is modified and equations (16) to (18) are substituted, the following equation (25) is obtained.

From Equation 25, it can be seen that the saturation reduction process using Equations 16 to 18 does not change color before and after the process. The same applies when the G value or the B value is maximum.

Next, in the above formulas (16) to (18), α is derived so that the backlight value becomes the backlight upper limit value MAXw.

With respect to all the pixels satisfying Equation 2, if the chroma is reduced to satisfy the following Equation, the backlight value is necessarily MAXw or less.

MAXw = maxRGBs-minRGBs

From the equations (16) to (18), and the above equation,

α × max RGB + (1-α) × Yi-α × min RGB- (1-α) × Yi = MAXw

α × (maxRGB-minRGB) = MAXw

therefore,

α = MAXw / (maxRGB-minRGB)

In this way, the saturation reducing unit 11 converts the first input RGB signal into a second input RGB signal for inputting to the output signal generator 12 at the rear stage by the processing according to the above description. That is, the second input RGB signal is obtained by converting pixel data having high luminance and saturation in the first input RGB signal into pixel data with reduced saturation. In addition, pixel data having low luminance or saturation in the first input RGB signal is not converted, and the same data is used in the second input RGB signal.

Next, a schematic configuration of the output signal generator 12 will be described with reference to FIG. 8. As illustrated in FIG. 8, the output signal generator 12 includes a W transmittance calculator 31, an RGB transmittance calculator 32, a backlight value calculator 33, and a transmittance calculator 34. Consists of. 9 is a flowchart for explaining the operation of the output signal generator 12.

The W transmittance calculating unit 31 calculates the W transmittance from the second input RGB signal input from the saturation reducing unit 11 by using the following expression (26) (S21).

The W transmittance is output to the RGB transmittance calculator 32, the backlight value calculator 33, and the transmittance calculator 34. The RGB transmission amount calculation unit 32 calculates the RGB transmission amount from the second input RGB signal and the W transmission amount using the following equations (27) to (29) (S22).

This RGB transmission amount is output to a backlight value calculation part. The processing of S21 and S22 is repeated by the number of pixels in the input RGB signal.

The backlight value calculator 33 uses the following formula 33 to calculate the backlight of the backlight from the W transmittance calculator 31 and the RGB transmittance calculator 32. The value Wbs is calculated (S23).

Alternatively, from the RGB transmission amount excluding the W transmission amount among the RGBW transmission amounts of all the pixels in the image output from the W transmission amount calculation unit 31 and the RGB transmission amount calculation unit 32 in the backlight value calculation unit 33, It is also possible to calculate the backlight value Wbs in the image using equation (34). This is because when W transmission amount Wts is obtained by the above-described method, max (Rts, Gts, Bts) ≧ Wts / WR is necessarily obtained for each RGB transmission amount Rts, Gts, and Bts.

This backlight value Wbs is output to the transmittance | permeability calculation part 34. FIG. The transmittance calculator 34 calculates the following equation from the W transmittance calculator 31, the RGBW transmittance output from the RGB transmittance calculator 32, and the backlight value Wbs output from the backlight value calculator 33. The transmittance of each subpixel is calculated using Equations 35 to 38 (S24). The process of S24 is repeated by the number of pixels in the input RGB signal.

As described above, in the liquid crystal display device according to the present embodiment, before the output signal generation unit 12 calculates the backlight value and the RGBW transmittance, the saturation reduction process is performed on the input RGB signal as the original input, thereby ensuring the backlight value. Can be reduced.

For example, when a liquid crystal panel having a white luminance ratio WR = 1 is used, when the pixel B of (R, G, B) = (160, 256, 64) illustrated above is considered, a saturation reduction process is not performed. The backlight value of is 192.

On the other hand, similarly, when the chroma reduction process is performed on the pixel B with MAX = 256 and BlRatio = 1 / (1 + WR) = 0.5, the pixel value after the chroma reduction of the pixel B in the second input RGB signal is as follows. Is derived as follows.

MAXw = MAX × BlRatio = 256 × 0.5 = 128 (from Equation 1)

α = 128 / (256-64) = 2/3 (from equation 19)

Y1 = (2 × R1 + 5 × G1 + B1) / 8

  = (2 × 160 + 5 × 256 + 64) / 8 = 208

Rs1 = α × R1 + (1-α) × Y1

   = (2/3) × 160 + (1-2 / 3) × 208 = 176 (from Equation 16)

Gs1 = α × G1 + (1-α) × Y1

    = (2/3) × 256 + (1-2 / 3) × 208 = 240 (from Equation 17)

Bs1 = α × B1 + (1-α) × Y1

    = (2/3) × 64 + (1-2 / 3) × 208 = 112 (from Equation 18)

Therefore, the input RGB value after saturation reduction in the pixel B is (176, 240, 112), and the backlight value at this time is 128.

That is, by the saturation reduction process, the backlight value can be reduced from 192 to 128 (a reduction of about 33%).

In addition, in the saturation reduction process performed in the present liquid crystal display device, the degree can be changed by adjusting the value of BlRatio in the formula (1) in the range of 1 / (1 + WR) to 1. In other words, the present liquid crystal display device has a function of changing the value of BlRatio, so that the user can arbitrarily select whether the image quality priority (larger value of BlRatio) or power saving priority (reduced value of BlRatio) is selected. can do. In this case, when the value of BlRatio is set to 1, the saturation reduction process is not performed. Therefore, it is possible to select whether or not to execute the saturation reduction process.

In the liquid crystal display device, one backlight 16 is basically provided for a plurality of pixels. For this reason, for example, the liquid crystal display device shown in FIG. 1 exemplifies a configuration in which one white backlight 16 is associated with the entire display screen of the liquid crystal panel 14. However, the present invention is not limited to this, and the display screen of the liquid crystal panel 14 may be divided into a plurality of regions, and a plurality of backlights may be provided so that backlight luminance can be adjusted for each region.

FIG. 10 shows an example of having two white backlights for one display area, but the number of backlights is not limited.

In the liquid crystal display shown in FIG. 10, the chroma reduction unit 11, the input signal division unit 41, the output signal generation units 12a and 12b, the liquid crystal panel control units 13a and 13b, the liquid crystal panel 14, The backlight control parts 15a and 15b and the white backlights 16a and 16b are provided.

The input signal dividing unit 41 allocates the second input RGB signal for one screen input from the saturation reducing unit 11 to the signals for the two areas, and outputs the input RGB signal for each area. Input to 12a and 12b. The output signal generators 12a and 12b perform processing equivalent to the output signal generator 12 in FIG. 1 for each corresponding area.

Although the liquid crystal panel control parts 13a and 13b perform the process similar to the liquid crystal panel control part 13 in FIG. 1 about each corresponding area, each control part corresponds to the area which the liquid crystal panel 14 corresponds to. Control the pixel transmittance of the position.

The backlight control units 15a and 15b perform processing equivalent to the backlight control unit 15 in FIG. 1 for each corresponding area. The white backlights 16a and 16b each have the same structure as the backlight 16, but each backlight illuminates a corresponding area.

In this way, by dividing one screen into a plurality of areas and controlling the area units, the backlight value can be further lowered. In this embodiment, one screen is divided into two areas, but it is also possible to divide and control the screen into three or more areas.

In a general image, a similar color is continuous in the vicinity of the image. For this reason, as shown in FIG. 10, by dividing the backlight region, the backlight of the backlight region in which dark pixels are collected can be made darker. As a result, dividing the backlight can lower the overall backlight power consumption than when the backlight is not divided.

The processing of the chroma reduction unit 11 and the output signal generation unit 12 can be realized by software that can be operated on a personal computer. The procedure in the case of realizing the above process in software is explained below.

Fig. 11 is a diagram showing a system configuration in the case where the above process is implemented by software. The system is composed of a personal computer body 51 and an input / output device 55. In addition, the personal computer main body 51 includes a CPU 52, a memory 53, and an input / output interface 54. The input / output device 55 includes a storage medium 56.

First, the CPU 52 controls the input / output device 55 through the input / output interface 54, and stores the chroma reduction / output signal generation program, the parameter file (the upper limit value of the input RGB signal, and the backlight value) from the storage medium 56. Setting rate, area information used when dividing one screen into a plurality of areas), and input image data are read out and stored in the memory 53.

In addition, the CPU 52 reads the chroma reduction / output signal generation program, the parameter file, and the input image data from the memory 53, and inputs the input image data according to each instruction of the chroma reduction / output signal generation program. After the saturation reduction and output signal generation are performed, the input / output device 55 is controlled through the input / output interface 54, and the backlight value and the RGBW transmittance after the output signal are generated are output to the storage medium 56. do.

Alternatively, as illustrated in FIG. 12, the white backlight 16 is output by outputting the backlight value and the RGBW transmittance after the output signal is generated to the backlight controller 15 and the liquid crystal panel controller 13, respectively, through the input / output interface 54. And the liquid crystal panel 14 may be controlled to actually display an image.

In this manner, the above-described saturation reduction and output signal generation can be performed on the personal computer. This makes it possible to confirm the feasibility of the chroma reduction method and the output signal generation method and the effect of the backlight value reduction before actually starting the chroma reduction unit or the output signal generation unit.

As described above, the transmissive liquid crystal display device according to the present invention includes a liquid crystal panel in which one pixel is divided into four subpixels of red (R), green (G), blue (B), and white (W), A saturation reduction process is performed on the white active backlight capable of controlling the emission luminance and the pixel data having high luminance and saturation among the pixel data included in the first input RGB signal as the input image, thereby converting the first input RGB signal to the second input RGB signal. A saturation reduction unit for converting into an input RGB signal and a transmittance signal of each subpixel of R, G, B, and W in each pixel of the liquid crystal panel from the second input RGB signal; An output signal generation unit for calculating a backlight value at s, a liquid crystal panel control unit for driving control of a liquid crystal panel based on the transmittance signal generated at the output signal generation unit, and based on the backlight value calculated above, And a backlight control unit for controlling the light emission luminance in the tree.

According to the above-described configuration, by using a liquid crystal panel in which one pixel is divided into four subpixels of R, G, B, and W, a loss of light amount due to filter absorption is achieved by a part of each color component of R, G, and B. Can be assigned to missing (or few) W subpixels. This reduces the amount of light absorbed by the color filter, thereby lowering the backlight value, thereby realizing a reduction in power consumption in the transmissive liquid crystal display device.

Further, by performing a chroma reduction process on the first input RGB signal which is the original input, and calculating the backlight value and the RGBW transmittance based on the second input RGB signal subjected to the chroma reduction process, the backlight value can be reduced more reliably. Can be.

In the transmissive liquid crystal display device, it is preferable that the saturation reduction unit is configured to reduce saturation only without changing luminance and color in the pixel data subjected to the saturation reduction processing before and after the saturation reduction processing.

According to the above configuration, the image quality deterioration associated with the saturation reduction process can be suppressed by reducing only the saturation having a small influence on the visual characteristic without changing the luminance and hue having a large influence on the human visual characteristics.

Moreover, in the said transmissive liquid crystal display device, it is preferable to set it as the structure which can change the degree of chroma reduction processing.

Moreover, it is preferable to set it as the structure which can change a range according to the characteristic of the liquid crystal panel to be used for the range of the grade of chroma reduction processing. One of the characteristics of the liquid crystal panel is the white luminance ratio WR indicating the ratio of the white brightness of the W subpixel to the white brightness produced from the RGB subpixel when the transmittance of each RGBW subpixel is the same.

According to the above configuration, the user can selectively set the balance between the power consumption reduction effect by the saturation reduction process and the image quality deterioration accompanying the saturation reduction process.

In the transmissive liquid crystal display device, the saturation reduction unit extracts pixel data having high luminance and saturation among pixel data included in the first input RGB signal as the input image by the following procedure (A), The extracted pixel data can be configured to perform a saturation reduction process by the following procedure (B).

(A) Backlight upper limit MAXw

 MAXw = MAX × BlRatio

Calculated by the formula,

MAXw <maxRGB-minRGB

Pixel data of interest that satisfies? Is extracted as pixel data having high luminance and saturation.

only,

MAX: Upper limit of backlight value when saturation reduction processing is not performed

WR: White luminance ratio

BlRatio: Backlight value setting rate (1 / (1 + WR) ≤ BlRatio ≤ 1.0)

maxRGB = max (Ri, Gi, Bi)

minRGB = min (Ri, Gi, Bi)

Ri, Gi, Bi (i = 1, 2, ..., Np): RGB value of the pixel of interest in the first input RGB signal

Np: Number of pixels in the input image

max (A, B, ...): The maximum value of A, B, ...

min (A, B, ...): Minimum value of A, B, ...

It is done.

(B) About the extracted pixel data,

Rsi = α × Ri + (1-α) × Yi

Gsi = α × Gi + (1-α) × Yi

Bsi = α × Bi + (1-α) × Yi

The pixel data after the chroma reduction process is obtained by the following equation.

only,

Rsi, Gsi, Bsi (i = 1, 2, ..., Np): RGB value of the pixel of interest after saturation reduction processing in the second input RGB signal

Yi (i = 1, 2, ..., Np): luminance of the main pixel

α = MAXw / (maxRGB-minRGB)

Shall be.

In the transmissive liquid crystal display device, the output signal generating means includes a W transmittance calculator for calculating a transmittance Wtsi of each W subpixel according to the following procedure (A), and the following (B). An RGB transmittance calculator for calculating the transmittances (Rtsi, Gtsi, Btsi) of each RGB sub-pixel in accordance with the procedure; a backlight value calculator for calculating the backlight value (Wbs) by the following procedure (C); According to the following procedure (D), it can be set as the structure provided with the transmittance calculation means which calculates the transmittance | permeability (rsi, gsi, bsi, wsi) of each RGBW subpixel.

(A) W transmittance (Wtsi),

It calculates by the formula Wtsi = min (maxRGBs / (1 + 1 / WR), minRGBs).

only,

maxRGBs = max (Rsi, Gsi, Bsi)

minRGBs = min (Rsi, Gsi, Bsi)

Shall be.

(B) RGB transmission amount (Rtsi, Gtsi, Btsi)

Rtsi = Rsi-Wtsi

Gtsi = Gsi-Wtsi

Btsi = Bsi-Wtsi

Calculated by the formula

(C) the backlight value (Wbs),

Wbs = max (Rts1, Gts1, Bts1, Wts1 / WR,

       …

       RtsNp, GtsNp, BtsNp, WtsNp / WR)

Calculated by the formula Or without using the W subpixel transmission amount,

Wbs = max (Rts1, Gts1, Bts1,

        …

        RtsNp, GtsNp, BtsNp)

Calculated by the formula

(D) RGBW transmittance (rsi, gsi, bsi, wsi),

rsi = Rtsi / Wbs

gsi = Gtsi / Wbs

bsi = Btsi / Wbs

wsi = Wtsi / Wbs / WR

Calculated by the formula

However, when Wbs = 0, rsi = gsi = bsi = wsi = 0.

In the transmissive liquid crystal display device, a plurality of active backlights may be provided for the liquid crystal panel, and the transmittance control of the liquid crystal panel and the backlight value control of the backlight may be performed for each region corresponding to the active backlight.

According to the above configuration, by dividing the backlight, it is possible to optimally set the backlight value for each divided backlight region, thereby lowering the overall backlight power consumption.

Specific embodiments or examples made in the description of the present invention are intended to clarify the technical contents of the present invention to the last, and are not to be construed as limited only to such specific embodiments, but are described in the spirit and the following. Within the scope of claims, various modifications can be made.

BRIEF DESCRIPTION OF THE DRAWINGS The block diagram which shows embodiment of this invention, and shows the principal part structure of a liquid crystal display device.

2A and 2B show an arrangement example of sub-pixels in the transmissive liquid crystal display device.

FIG. 3A is a diagram showing a method for obtaining a backlight value in the present liquid crystal display, and FIG. 3B is a diagram showing a method for obtaining a backlight value in Patent Document 1 for comparison.

4A is a diagram showing a method for obtaining a backlight value in the present liquid crystal display, and FIG. 4B is a diagram showing a method for obtaining a backlight value in Patent Document 1 for comparison.

5A to 5E are diagrams showing the procedure for determining the backlight value and the subpixel transmittance in the liquid crystal display device.

6 is a block diagram showing an example of a configuration of a saturation reducing unit in the liquid crystal display device.

7 is a flowchart showing an operation procedure of the saturation reduction unit.

8 is a block diagram showing an example of a configuration of an output signal generation unit in the liquid crystal display device.

9 is a flowchart showing an operation procedure of the output signal generator.

Fig. 10 is a block diagram showing another embodiment of the present invention and showing the main part configuration of a transmissive liquid crystal display device.

Fig. 11 is a diagram showing a system configuration in the case of realizing the display control process of the present invention in software.

Fig. 12 is a diagram showing a modification of the system configuration when the display control processing of the present invention is realized by software.

Fig. 13 is a sectional view showing a general configuration of a transmissive liquid crystal display device.

Fig. 14 is a diagram showing a general arrangement example of sub pixels in a transmissive liquid crystal display device.

FIG. 15A is a diagram illustrating a method of obtaining a backlight value in the present liquid crystal display, and FIG. 15B is a diagram illustrating a method of obtaining a backlight value in Patent Document 1 for comparison.

FIG. 16A is a diagram illustrating a method of obtaining a backlight value in the present liquid crystal display, and FIG. 16B is a diagram illustrating a method of obtaining a backlight value in Patent Document 1 for comparison.

17A is a diagram showing a method of obtaining a backlight value in the present liquid crystal display, and FIG. 17B is a diagram showing a method of obtaining a backlight value in Patent Document 1 for comparison.

18A is a diagram showing a method of obtaining a backlight value in the present liquid crystal display, and FIG. 18B is a diagram showing a method of obtaining a backlight value in Patent Document 1 for comparison.

<Explanation of symbols for the main parts of the drawings>

11: Saturation Reduction Part

12: output signal generator

13: liquid crystal panel control unit

14: RGBW liquid crystal panel

15: backlight control unit

16: white backlight

21: backlight upper limit calculation unit

22: signal conversion unit

31: W transmittance calculation unit

32: RGB transmission amount calculation unit

33: backlight value calculation unit

34: transmittance calculation unit

41: input signal divider

51: the personal computer body

52: CPU

53: memory

54: I / O interface

56: storage medium

55: input / output device

Claims (9)

A liquid crystal panel in which one pixel is divided into four subpixels of red (R), green (G), blue (B), and white (W); White active backlight which can control emission brightness, A saturation reduction unit that converts the first input RGB signal into a second input RGB signal by performing a chroma reduction process on the pixel data having high luminance and saturation among the pixel data included in the first input RGB signal as the input image; , An output signal generator for generating transmittance signals of R, G, B, and W subpixels of each pixel of the liquid crystal panel from the second input RGB signal, and calculating a backlight value of the active backlight; Wow, A liquid crystal panel controller which controls driving of a liquid crystal panel based on the transmittance signal generated by the output signal generator; And a backlight controller which controls the light emission luminance of the backlight based on the backlight value calculated by the output signal generator. The method of claim 1, The saturation reduction unit is a pixel type of the saturation reduction process, wherein the transmissive liquid crystal display reduces saturation only without changing luminance and color before and after the saturation reduction process. The method of claim 1, The saturation reduction unit is a transmissive liquid crystal display device which can change the degree of saturation reduction processing. The method of claim 3, Display luminance P1 when each transmittance of RGB subpixels is x% and each transmittance of W subpixels is 0%, each transmittance of RGB subpixels is 0%, and each transmittance of W subpixels is x% When the ratio P2 / P1 of the display luminance P2 in one case is set to the white luminance ratio WR, The saturation reduction unit sets the range of change of the degree of saturation reduction processing based on the white luminance ratio WR. The method of claim 1, The saturation reduction unit, Among the pixel data included in the first input RGB signal as the input image, the pixel data having high luminance and saturation is converted into the following procedure (A), (A) Backlight upper limit MAXw MAXw = MAX × BlRatio Calculated by the formula, MAXw <maxRGB-minRGB Extracting the pixel data of interest that satisfies? As pixel data having high luminance and saturation, only, WR: White luminance ratio (display luminance P1 when each transmittance of RGB subpixels is x% and each transmittance of W subpixels is 0%, and each transmittance of RGB subpixels is 0% and the W subpixel Ratio P2 / P1 of display luminance P2 when each transmittance is x%) MAX: Upper limit of backlight value when saturation reduction processing is not performed BlRatio: Backlight value setting rate (1 / (1 + WR) ≤ BlRatio ≤ 1.0) maxRGB = max (Ri, Gi, Bi) minRGB = min (Ri, Gi, Bi) Ri, Gi, Bi (i = 1, 2, ..., Np): RGB value of the pixel of interest in the first input RGB signal Np: Number of pixels in the input image max (A, B, ...): The maximum value of A, B, ... min (A, B, ...): Minimum value of A, B, ... Should be Extracted by Regarding the extracted pixel data, the procedure of the following (B) (B) About the extracted pixel data, Rsi = α × Ri + (1-α) × Yi Gsi = α × Gi + (1-α) × Yi Bsi = α × Bi + (1-α) × Yi Find the pixel data after the chroma reduction process by only, Rsi, Gsi, Bsi (i = 1, 2, ..., Np): RGB value of the pixel of interest after saturation reduction processing in the second input RGB signal Yi (i = 1, 2, ..., Np): luminance of the main pixel α = MAXw / (maxRGB-minRGB) The transmissive liquid crystal display device which performs a chroma reduction process by The method of claim 5, The output signal generating means, The procedure of the following (A) (A) W transmittance (Wtsi), Wtsi = min (maxRGBs / (1 + 1 / WR), minRGBs) Calculated by only, maxRGBs = max (Rsi, Gsi, Bsi) minRGBs = min (Rsi, Gsi, Bsi) By, W transmission amount calculating unit for calculating the transmission amount (Wtsi) of each W sub-pixel by, The procedure of the following (B) (B) RGB transmission amount (Rtsi, Gtsi, Btsi) Rtsi = Rsi-Wtsi Gtsi = Gsi-Wtsi Btsi = Bsi-Wtsi Calculated by An RGB transmission amount calculating section that calculates transmission amounts (Rtsi, Gtsi, Btsi) of each RGB sub-pixel, The procedure of the following (C) (C) the backlight value (Wbs), Wbs = max (Rts1, Gts1, Bts1, Wts1 / WR,         …         RtsNp, GtsNp, BtsNp, WtsNp / WR) Calculated by A backlight value calculator for calculating a backlight value Wbs by The procedure of the following (D) (D) RGBW transmittance (rsi, gsi, bsi, wsi), rsi = Rtsi / Wbs gsi = Gtsi / Wbs bsi = Btsi / Wbs wsi = Wtsi / Wbs / WR Calculated by However, when Wbs = 0, rsi = gsi = bsi = wsi = 0, The transmissive liquid crystal display device provided with the transmittance | permeability calculation means which calculates the transmittance | permeability (rsi, gsi, bsi, wsi) of each RGBW subpixel by this. The method of claim 1, A plurality of active backlights are provided for the liquid crystal panel, A transmissive liquid crystal display device which performs transmittance control of a liquid crystal panel and backlight value control of a backlight for each area corresponding to each active backlight. A control program for causing a computer to perform the processing of each of the functional units of claim 5. A computer program which causes a computer to process each of the functional units according to claim 6.

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