JP4477020B2 - Transmission type liquid crystal display device - Google Patents

Description

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

  There are various types of color displays, each of which has been put to practical use. Thin displays can be broadly classified into self-luminous displays such as PDP (plasma display panel) and non-luminous displays typified by LCD (liquid crystal display). As an LCD that is a non-light-emitting display, a transmissive LCD in which a backlight is disposed on the back side of a liquid crystal panel is known.

  FIG. 13 is a cross-sectional view showing a general structure of a transmissive LCD. In this transmissive LCD, a backlight 110 is disposed on the back surface of the liquid crystal panel 100. The liquid crystal panel 100 has a configuration in which a liquid crystal layer 103 is disposed between a pair of transparent substrates 101 and 102, and polarizing plates 104 and 105 are provided outside the pair of transparent substrates 101 and 102. Further, by providing the color filter 106 in the liquid crystal panel 100, color display is possible.

  Although illustration is omitted, 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 by controlling the voltage applied to the liquid crystal layer 103. Are controlled for each pixel. In other words, the transmissive LCD performs display control by controlling the amount of light emitted from the backlight 110 through the liquid crystal panel 110.

  The backlight 110 irradiates light including the wavelengths of the three RGB colors necessary for a color display. By adjusting the transmittance of light of each color of RGB by combining with the color filter 106, the backlight 110 is used as a pixel. It is possible to arbitrarily set the brightness and hue of the image. For such a backlight 110, a white light source such as electroluminescence (EL), cold cathode fluorescent lamp (CCFL), light emitting diode (LED), or the like is generally used.

  In the liquid crystal panel 100, as shown in FIG. 14, a plurality of pixels are arranged in a matrix, and each pixel is generally composed of three sub-pixels. Each subpixel is arranged so that the red (R), green (G), and blue (B) filter layers in the color filter 106 correspond to each other. Hereinafter, the respective subpixels are referred to as an R subpixel, a G subpixel, and a B subpixel.

  Each of the R, G, and B sub-pixels selectively transmits light in a corresponding wavelength band (that is, red, green, and blue) among white light generated from the backlight 110, and transmits in other wavelength bands. Light absorbs.

  In the transmissive LCD configured as described above, the amount of light irradiated from the backlight 110 is controlled in the amount of transmission in each pixel of the liquid crystal panel 100, so that naturally light that is absorbed by the liquid crystal panel 100 is generated. Also in the color filter 106, the R, G, and B sub-pixels absorb light other than the corresponding wavelength band in the white light generated from the backlight 110. As described above, a general transmissive LCD has a problem that power consumption in the backlight increases because the amount of light absorbed by the liquid crystal panel and the color filter is large and the use efficiency of the irradiation light from the backlight is low.

  As a technique for reducing the power consumption of such a transmissive LCD, a method using an active backlight capable of adjusting the light emission luminance according to a display image is known (for example, Patent Document 1).

  In other words, Patent Document 1 uses an active backlight with adjustable brightness, and performs LCD display control (brightness control) by controlling the transmittance of the liquid crystal panel and the brightness of the active backlight, thereby reducing the power consumption of the backlight. Techniques for reducing are disclosed.

  In Patent Document 1, the brightness of the backlight is controlled to match the maximum brightness value in the input image (input signal). The transmittance of the liquid crystal panel is adjusted according to the luminance of the backlight at that time.

  At this time, the transmissivity of the subpixel that is the maximum value of the input signal is 100%, and the transmissivities of the other subpixels are also 100% or less calculated by the backlight value. Therefore, when the entire image is dark, the backlight is darkened, and the power consumption of the backlight can be reduced.

As described above, in Patent Document 1, since the brightness of the backlight is suppressed to the necessary minimum based on the input signal RGB of the input image and the backlight is darkened, the liquid crystal transmittance is increased. The amount of light absorbed by the light source can be reduced, and the power consumption of the backlight can be reduced.
JP 11-65531 A (published March 9, 1999)

  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 amount of light absorbed by the color filter can be reduced, an effect of further reducing power consumption can be obtained.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to reduce the amount of light absorbed by the color filter as well as the liquid crystal panel, and achieve a further reduction in power consumption. Is to realize.

  In the transmissive liquid crystal display device according to the present invention, one pixel is divided into four sub-pixels of red (R), green (G), blue (B), and white (W) in order to solve the above problems. Saturation reduction processing for pixel data with high luminance and saturation among pixel data included in the first input RGB signal that is the input image, a white active backlight that can control the emission luminance, and the input image By applying the saturation reduction unit that converts the first input RGB signal into the second input RGB signal, and the R, G, B, and W of each pixel of the liquid crystal panel from the second input RGB signal, Generates a transmittance signal for the sub-pixel and outputs an output signal generator for calculating a backlight value in the active backlight, and controls driving of the liquid crystal panel based on the transmittance signal generated by the output signal generator. A liquid crystal panel control section that, based on the backlight value calculated above, is characterized by comprising a backlight controller for controlling the emission luminance of the backlight.

  According to the above configuration, by using a liquid crystal panel in which one pixel is divided into four sub-pixels of R, G, B, and W, a part of each color component of R, G, and B is light quantity by filter absorption. It can be distributed to W sub-pixels with no loss (or little). Accordingly, it is possible to reduce power consumption in the transmissive liquid crystal display device by reducing light absorption by the color filter and lowering the backlight value accordingly.

  Further, saturation reduction processing is performed on the first input RGB signal which is the original input, and a backlight value and RGBW transmittance are calculated based on the second input RGB signal subjected to the saturation reduction processing. The backlight value can be reduced more reliably.

  Further, in the transmissive liquid crystal display device, the saturation reduction unit includes only saturation without changing luminance and hue before and after the saturation reduction processing in the pixel data subjected to the saturation reduction processing. It is preferable to adopt a configuration that reduces the above.

  According to the above-described configuration, only the saturation having a small influence on the visual characteristic is reduced without changing the luminance and the hue having a large influence on the human visual characteristic, thereby accompanying the saturation reduction process. Image quality degradation can be suppressed.

  In the transmissive liquid crystal display device, the saturation reduction unit is preferably configured to be able to change the degree of saturation reduction processing.

  Moreover, it is preferable that the range of the degree of saturation reduction processing is configured such that the range can be changed according to the characteristics of the liquid crystal panel to be used. 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 said structure, the user can selectively set the balance of the power consumption reduction effect by a saturation reduction process, and the image quality degradation accompanying a saturation reduction process.

Further, in the transmissive liquid crystal display device, the saturation reduction unit outputs pixel data having high luminance and saturation among the pixel data included in the first input RGB signal that is an input image as follows (A). The saturation reduction process can be performed by the following procedure (B) for the extracted pixel data.
(A) Backlight upper limit MAXw MAXw = MAX × BlRatio
Calculated by the formula
MAXw <maxRGB-minRGB
Pixel data satisfying the above is extracted as pixel data having high luminance and saturation.

However,
MAX: Upper limit value 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 target pixel in the first input RGB signal Np: Number of pixels of the input image max (A, B,...): A, B, . . . Maximum value min (A, B,...): A, B,. . . The minimum value of.
(B) For 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 saturation reduction processing is obtained by the following equation.

However,
Rsi, Gsi, Bsi (i = 1, 2,..., Np): RGB value Yi (i = 1, 2,..., Np) of the target pixel after saturation reduction processing in the second input RGB signal: Luminance α = MAXw / (maxRGB−minRGB)
And

Further, in the transmissive liquid crystal display device, the output signal generation means includes a W transmission amount calculation unit that calculates a transmission amount (Wtsi) of each W sub-pixel according to the following procedure (A), and the following ( The RGB transmission amount calculation unit that calculates the transmission amount (Rtsi, Gtsi, Btsi) of each RGB sub-pixel by the procedure of B), and the backlight that calculates the backlight value (Wbs) by the procedure of (C) below. The value calculating unit and the transmittance calculating means for calculating the transmittance (rsi, gsi, bsi, wsi) of each RGBW sub-pixel can be configured by the following procedure (D).
(A) W transmission amount (Wtsi)
Wtsi = min (maxRGBs / (1 + 1 / WR), minRGBs)
It is calculated by the following formula.

However,
maxRGBs = max (Rsi, Gsi, Bsi)
minRGBs = min (Rsi, Gsi, Bsi)
And
(B) RGB transmission amount (Rtsi, Gtsi, Btsi)
Rtsi = Rsi−Wtsi
Gtsi = Gsi-Wtsi
Btsi = Bsi−Wtsi
It is calculated by the following formula.
(C) Set the backlight value (Wbs)
Wbs = max (Rts1, Gts1, Bts1, Wts1 / WR,
. . .
RtsNp, GtsNp, BtsNp, WtsNp / WR)
It is calculated by the following formula. Or without using W sub-pixel transmission,
Wbs = max (Rts1, Gts1, Bts1,
. . .
RtsNp, GtsNp, BtsNp)
It is calculated by the following formula.
(D) RGBW transmittance (rsi, gsi, bsi, wsi)
rsi = Rtsi / Wbs
gsi = Gtsi / Wbs
bsi = Btsi / Wbs
wsi = Wtsi / Wbs / WR
It is calculated by the following formula.

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

  The transmissive liquid crystal display device includes a plurality of active backlights for the liquid crystal panel, and controls the transmittance of the liquid crystal panel and the backlight backlight value for each area corresponding to each active backlight. It can be set as the structure which performs.

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

  As described above, in the transmissive liquid crystal display device according to the present invention, one pixel is divided into four subpixels of red (R), green (G), blue (B), and white (W). Of the pixel data included in the panel, the white active backlight capable of controlling the light emission luminance, and the first input RGB signal that is the input image, the pixel data having high luminance and saturation is subjected to saturation reduction processing. Then, a saturation reduction unit that converts the first input RGB signal into a second input RGB signal, and the R, G, B, and W subpixels of each pixel of the liquid crystal panel from the second input RGB signal. An output signal generation unit that generates a transmittance signal and calculates a backlight value in the active backlight, and a liquid crystal panel that drives and controls the liquid crystal panel based on the transmittance signal generated by the output signal generation unit. A control unit, based on the backlight value calculated by the output signal generation unit, a configuration in which a backlight controller for controlling the emission luminance of the backlight.

  Therefore, by using a liquid crystal panel in which one pixel is divided into four subpixels of R, G, B, and W, there is no light loss due to filter absorption of a part of each color component of R, G, and B ( (Or fewer) W subpixels. Accordingly, it is possible to reduce power consumption in the transmissive liquid crystal display device by reducing light absorption by the color filter and lowering the backlight value accordingly.

  Further, saturation reduction processing is performed on the first input RGB signal which is the original input, and a backlight value and RGBW transmittance are calculated based on the second input RGB signal subjected to the saturation reduction processing. The backlight value can be reduced more reliably.

  Further, when the second input RGB signal is generated, a saturation reduction range corresponding to the characteristics of the liquid crystal panel is provided, and the saturation reduction degree can be freely set in the present invention. Therefore, when the saturation is reduced to the lowest level in the saturation reduction process of the present invention, the power consumption of the backlight can be reduced most efficiently.

  An embodiment of the present invention will be described below with reference to FIGS. First, a schematic configuration of a liquid crystal display device according to the present embodiment (hereinafter referred to as the present liquid crystal display device) will be described with reference to FIG.

  This liquid crystal display device includes a saturation 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 referred to as a liquid crystal panel). , Simply referred to as a backlight) 16.

  The liquid crystal panel 14 is formed by arranging Np pixels on a matrix. As shown in FIGS. 2A and 2B, each pixel has R (red), G (green), B (blue), It is composed of 4 sub-pixels of W (white). In addition, the shape and arrangement | positioning relationship of R, G, B, and W sub pixel in each pixel are not specifically limited. The backlight 16 uses a white light source such as a cold cathode fluorescent lamp (CCFL) or a white light emitting diode (white LED), and is an active backlight capable of controlling the brightness of the irradiated light.

  The R, G, and B sub-pixels in the liquid crystal panel 14 are arranged so that the R, G, and B filter layers in the color filter (not shown) correspond to each other. Accordingly, each of the R, G, and B subpixels selectively transmits light in the corresponding wavelength band among white light generated from the backlight 16, and absorbs light in other wavelength bands. Further, the W sub-pixel basically has no corresponding absorption filter layer in the color filter. That is, the light transmitted through the W sub-pixel is emitted from the liquid crystal panel 14 as white light without being absorbed by the color filter. However, the W sub-pixel may have a filter layer that absorbs less 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 transmittance of each RGB subpixel is 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 and the transmittance of the W subpixel are the same, the brightness of the white light output as the sum of the light from the RGB subpixel and the white light output from the W subpixel Is not necessarily the same brightness. This is because the brightness changes depending on the amount of light absorbed by the color filter of each subpixel and the size of the subpixel.

  At this time, the ratio of the intensity of the white light output from the W subpixel to the intensity of the white light output from the RGB subpixel is defined as a white luminance ratio WR. Specifically, the display luminance P1 when each transmittance of the RGB subpixel is x% and each transmittance of the W subpixel is 0%, and each transmittance of the RGB subpixel is 0%, A ratio P2 / P1 with the display luminance P2 when each transmittance is x% is defined as a white luminance ratio WR. Normally, in a single liquid crystal panel, the same white luminance ratio WR is obtained for the entire panel (that is, for all pixels).

  This liquid crystal display device receives image information to be displayed as an RGB signal (first input RGB signal) from the outside such as a personal computer or a TV tuner, and receives the RGB signal as input signals 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 then outputs the first input RGB signal to the output signal generation unit 12 as a second input RGB signal.

  The output signal generation unit 12 is a means for obtaining the transmittance of each subpixel 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 generation unit 12 obtains the backlight value Wbs from the input signals Rsi, Gsi, and Bsi that are the second input RGB signals, and transmits the input signals Rsi, Gsi, and Bsi to the backlight value Wbs. The signals rsi, gsi, bsi, and wsi are converted.

  The obtained backlight value Wbs is output to the backlight control unit 15, and the backlight control unit 15 adjusts the luminance 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 control unit 15 to a brightness proportional to the backlight value. The method for controlling the brightness of the backlight 16 differs depending on the type of light source used. For example, the brightness is controlled by applying a voltage proportional to the backlight value or passing a current proportional to the backlight value. be able to. Further, 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). Furthermore, when the brightness of the backlight light source has non-linear characteristics, the desired brightness can be obtained by controlling the brightness of the backlight by obtaining the applied voltage or applied current to the light source from the backlight value using a lookup table. There is also a method to control it.

  The 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 determines that the transmittance of each sub-pixel of the liquid crystal panel 14 is a desired transmittance based on the transmittance signal. Control to become. The liquid crystal panel control unit 13 includes a scanning line driving circuit, a signal line driving circuit, and the like, generates a scanning signal and a data signal, and drives the liquid crystal panel 14 by the panel control signal such as the scanning signal and the data signal. To do. The transmittance signals rsi, gsi, bsi, and wsi are used to generate data signals in the signal line driver circuit. For controlling the transmittance of the liquid crystal panel 14, a voltage proportional to the transmittance of the subpixel is applied to control the transmittance of the liquid crystal panel, and the linearity is changed from the transmittance of the subpixel to the liquid crystal panel. There is a method of controlling the liquid crystal panel to a desired transmittance by drawing a voltage to be applied from a lookup table.

  In the liquid crystal display device of the present invention, the input signal is not limited to the RGB signal as described above, and may be a color signal such as a YUV signal. When a color signal other than an RGB signal is input, the color signal may be converted into an RGB signal and then input to the output signal generation unit 12. Alternatively, the output signal generation unit 12 may input a color input other than the RGB signal. A configuration capable of converting a signal into an RGBW signal may be used.

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

  In the present embodiment, the term “backlight value” is used, but this backlight value has a proportional relationship with the brightness of the backlight. It is not the same value as the brightness of the light. Similarly, the transmission amount of the subpixel is proportional to the brightness of the subpixel and is not the same value. That is, the backlight value in the present embodiment is a signal sent to the backlight, and the actual brightness is merely in a proportional relationship.

  Specifically, in the present embodiment, the transmission amount can be obtained by multiplying the backlight value by the transmittance (further WR in the case of the W sub-pixel). On the other hand, 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 a ratio of (white luminance by RGB subpixel) :( white luminance by W subpixel), and is considered based on RGB. The white luminance ratio can also be obtained by (transmittance by W color filter) / (transmittance by RGB color filter).

  Here, the display principle and the power consumption reduction effect in the present liquid crystal display device will be described in detail below. In the present liquid crystal display device, the backlight value and the sub-pixel transmittance are obtained by the output signal generation unit 12. Therefore, the backlight value and subpixel transmittance calculation method described below is a process performed on the second input RGB signal input from the saturation reduction unit 11 to the output signal generation unit 12.

  In the method for determining the backlight value and the sub-pixel transmittance in the present liquid crystal display device, first, the minimum necessary backlight value is obtained for every pixel in the display area corresponding to the backlight. Next, the maximum value in one image is obtained from the minimum necessary backlight value obtained for each pixel, and that value is used as the backlight value. Here, when obtaining the minimum necessary backlight value for each pixel, there are two methods for obtaining the backlight value depending on the display data content of the pixel. Specifically, the backlight for the target pixel is determined by the relationship between the maximum luminance (that is, max (Rsi, Gsi, Bsi)) and the minimum luminance (that is, min (Rsi, Gsi, Bsi)) in the sub-pixel in the target pixel. The way to find the value is different.

  First, a description will be given of how to obtain the minimum necessary backlight value for the target pixel that satisfies min (Rsi, Gsi, Bsi) ≧ max (Rsi, Gsi, Bsi) / (1 + 1 / WR).

  The maximum value of the second RGB input signals Rsi, Gsi, Bsi to the output signal generation unit is maxRGBsi, and the minimum value is minRGBsi. Here, the case where the color component of the sub-pixel corresponding to the maximum value maxRGBsi is R (red) will be described, but the same can be considered when maxRGBsi is G (green) and B (blue). Note that maxRGBsi and minRGBsi are both values represented by the transmission amount of the sub-pixel.

  Here, if only the display light of the R component having the transmission amount maxRGBsi is considered, the backlight value can be most reduced with respect to this display light because both the transmittances of the R subpixel and the W subpixel are 100. When the transmission amount is allocated to the R sub-pixel and the W sub-pixel so as to be%.

  If the minimum necessary backlight value at this time is Blmin and the white luminance ratio WR is taken into account, the transmittances of the R sub-pixel and the W sub-pixel are both 100%. The luminance is B1min, and the luminance of the light emitted from the W subpixel is WR × B1min. The sum of the light emitted from the R subpixel and the W subpixel, that is, (1 + WR) × Blmin is the transmission amount of the R component. Since (1 + WR) × Blmin is equal to maxRGBsi, B1min is maxRGBsi / (1 + WR).

  However, the above idea is a case where only the R component display light is considered, and the G and B components are not considered. Actually, if minRGBsi <maxRGBsi / (1 + 1 / WR) and the backlight value is set to maxRGBsi / (1 + WR), the transmission amount of the color component corresponding to the minimum value minRGBsi is required as shown in the following equation. It will exceed the amount.

maxRGBsi / (1 + WR) × WR
= MaxRGBsi / (1 + 1 / WR)> minRGBsi
Therefore, only when minRGBsi ≧ maxRGBsi / (1 + 1 / WR) is established in a certain pixel of interest, the minimum necessary backlight value in the pixel of interest is set to maxRGBsi / (1 + WR) based on the above idea. The

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

  In this way, the minimum necessary backlight value in each pixel is obtained, and the maximum value of the required backlight value in all pixels of one image is set as the backlight value Wbs.

  From the backlight value Wbs, the transmittance of each sub-pixel is obtained as follows. That is, the transmittance of each RGB sub-pixel can be expressed by (transmission amount) / (backlight value). The transmittance of the W sub-pixel can be expressed as (transmission amount) / (backlight value) / (white luminance ratio). This is because the W subpixel is brighter than the RGB subpixels by a white luminance ratio WR, and the backlight value required for the output luminance value of the W subpixel is the backlight value required for the RGB subpixel. This is because the calculation can be performed at 1 / WR times the.

  Specific examples will be described below with reference to FIGS. 3, 4, and 15 to 18.

  First, in the case where a liquid crystal panel having a white luminance ratio WR of 1 is used, a backlight value of a pixel satisfying min (Rsi, Gsi, Bsi) ≧ max (Rsi, Gsi, Bsi) / (1 + 1 / WR) is set. A method of obtaining will be described with reference to FIGS. Here, FIG. 3A is a diagram showing how to obtain the backlight value in the present liquid crystal display device. FIG. 3B is a diagram showing how to obtain the backlight value in Patent Document 1 for comparison.

  3A and 3B, consider a case where the target panel output luminance of a pixel of interest is (R, G, B) = (50, 60, 40). 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, The relationship of Gsi, Bsi) / (1 + 1 / WR) is satisfied.

  In the display method in Patent Document 1, as shown in FIG. 3B, the backlight value is set to max (Rsi, Gsi, Bsi) = 60, and the transmittance of each sub-pixel is adjusted to this backlight value. Determined. That is, the respective transmittances of the R, G, and B sub-pixels are set to 83% (= 50/60), 100% (= 60/60), and 67% (= 40/60).

  On the other hand, in this liquid crystal display device, the R component, the G component, and the B component of the input signals Rsi, Gsi, and Bsi each transmit a value corresponding to max (Rsi, Gsi, Bsi) / (1 + 1 / WR). Sort into quantities. As a result, an input signal (R, G, B) = (50, 60, 40) represented by an RGB signal has a transmission amount (R, G, B, W) = (20, 60) represented by an RGBW signal. 30, 10, 30). In this target pixel, the backlight value is set to max (Rsi, Gsi, Bsi) / (1 + WR) = 30. Further, the respective transmittances of the R, G, B, and W sub-pixels are determined in accordance with the backlight value. That is, the transmittances of the R, G, B, and W sub-pixels are 67% (= 20/30), 100% (= 30/30), 33% (= 10/30), 100% ( = 30/30 / WR). However, the transmittance shown in FIG. 3A is the largest among the plurality of backlight values obtained for all the pixels, and the luminance value in the backlight. Is an example of the transmittance when it is adopted as.

  Further, in order to compare the above backlight value in the present liquid crystal display device with the backlight value obtained by the method of Patent Document 1, it is necessary to consider the area ratio of the subpixels. That is, in Patent Document 1, one pixel is divided into three subpixels, whereas in the present liquid crystal display device, one pixel is divided into four subpixels. For this reason, assuming that each subpixel is equally divided, in the present liquid crystal display device, the area of one subpixel is only 3/4 that of Patent Document 1, and the area of such a subpixel is as follows. In the present liquid crystal display device, the backlight value is multiplied by 4/3 to compensate for the decrease in the brightness, and can be compared on the same basis as the backlight value obtained by the method of Patent Document 1.

  As a result, if the backlight value in the example of FIG. 3A is corrected to the same standard as the backlight value of FIG. 3B, (4/3) × 60 / (1 + WR) = 40. In the example of FIG. 3B in which the same display is performed, the backlight value is 60. Therefore, it can be seen that the pixel of interest has the effect of reducing power consumption according to the present invention.

  Next, in the case where a liquid crystal panel having a white luminance ratio WR of 1 is used, the backlight value in a pixel satisfying min (Rsi, Gsi, Bsi) <max (Rsi, Gsi, Bsi) / (1 + 1 / WR) is obtained. This will be described with reference to FIGS. 4 (a) and 4 (b). Here, FIG. 4A is a diagram showing how to obtain the backlight value in the present liquid crystal display device. FIG. 4B is a diagram showing how to obtain the backlight value in Patent Document 1 for comparison.

  In FIGS. 4A and 4B, a case is considered where the target panel output luminance of a target pixel is (R, G, B) = (50, 60, 20). 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, The relationship of Gsi, Bsi) / (1 + 1 / WR) is satisfied.

  In the display method in Patent Document 1, as shown in FIG. 4B, the backlight value is set to max (Rsi, Gsi, Bsi) = 60, and the transmittance of each sub-pixel is adjusted to this backlight value. Determined. That is, the respective transmittances in the R, G, and B sub-pixels are set to 83% (= 50/60), 100% (= 60/60), and 33% (= 20/60).

  On the other hand, in the present liquid crystal display device, a value corresponding to min (Rsi, Gsi, Bsi) is distributed to the transmission amount of the W component in the R, G, B components of the input signals Rsi, Gsi, Bsi. As a result, the input signal (R, G, B) = (50, 60, 20) represented by the RGB signal has a transmission amount (R, G, B, W) = (30, 60) represented by the RGBW signal. 40, 0, 20). In this target pixel, the backlight value is set to (max (Rsi, Gsi, Bsi) −min (Rsi, Gsi, Bsi)) = 40. Further, the respective transmittances of the R, G, B, and W sub-pixels are determined in accordance with the backlight value. The transmittances of the R, G, B, and W sub-pixels are 75% (= 30/40), 100% (= 40/40), 0% (= 0/40), and 50% (= 20). / 40 / WR).

  However, the transmittance shown in FIG. 4 (a) is the largest among the plurality of backlight values obtained for all the pixels, and the luminance value in the backlight. Is an example of the transmittance when it is adopted as. In the example of FIG. 4A as well, by multiplying the backlight value by 4/3, comparison with the backlight value obtained by the method of Patent Document 1 becomes 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 in which the same display is performed, the backlight value is 60. Therefore, it can be seen that the pixel of interest has the effect of reducing power consumption according to the present invention.

  Next, when a liquid crystal panel having a white luminance ratio WR of 1.5 is used, a backlight value in a pixel satisfying min (Rsi, Gsi, Bsi) ≧ max (Rsi, Gsi, Bsi) / (1 + 1 / WR). The method of obtaining will be described with reference to FIGS. 15 (a) and 15 (b). Here, FIG. 15A is a diagram showing how to obtain the backlight value in the present liquid crystal display device. FIG. 15B is a diagram showing how to obtain the backlight value in Patent Document 1 for comparison.

  In FIGS. 15A and 15B, consider the case where the target panel output luminance of a certain pixel of interest is (R, G, B) = (100, 120, 80). 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, The relationship of Gsi, 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 the backlight value. It is decided according to. That is, the respective transmittances in the R, G, and B subpixels are set to 83% (= 100/120), 100% (= 120/120), and 67% (= 80/120).

  On the other hand, in this liquid crystal display device, the R component, the G component, and the B component of the input signals Rsi, Gsi, and Bsi each transmit a value corresponding to max (Rsi, Gsi, Bsi) / (1 + 1 / WR). Sort into quantities. As a result, the input signal (R, G, B) = (100, 120, 80) represented by the RGB signal has a transmission amount (R, G, B, W) = (28, 48, 8, 72). In this target pixel, the backlight value is set to max (Rsi, Gsi, Bsi) / (1 + WR) = 48.

  Further, the respective transmittances in the R, G, B, and W sub-pixels are determined in accordance with the brightness of the backlight produced from the backlight value. Since the W subpixel is WR times brighter than the RGB subpixel, the backlight value required for the transmission amount of the W subpixel is 1 / WR times the backlight value required for the RGB subpixel. It can be calculated with That is, the respective transmittances in the R, G, B, and W sub-pixels are 58% (= 28/48), 100% (= 48/48), 16.7% (= 8/48), 100, respectively. % (= 72/48 / WR).

  However, the transmittance shown in FIG. 15A is the largest among the plurality of backlight values obtained for all the pixels, and the luminance value in the backlight. Is an example of the transmittance when it is adopted as. Also, in the example of FIG. 15A, the backlight luminance value is multiplied by 4/3, so that comparison can be made based on the same standard as the backlight value obtained by the method of Patent Document 1.

  As a result, if the backlight value in the example of FIG. 15A is corrected to the same standard as the backlight value of FIG. 15B, (4/3) × 48 = 64. In the example of FIG. 15B in which the same display is performed, the backlight value is 120. Therefore, it can be seen that the pixel of interest has the effect of reducing power consumption according to the present invention.

  Next, in the case where a liquid crystal panel having a white luminance ratio WR of 1.5 is used, a backlight value in a pixel satisfying min (Rsi, Gsi, Bsi) <max (Rsi, Gsi, Bsi) / (1 + 1 / WR). The method of obtaining will be described with reference to FIGS. 16 (a) and 16 (b). Here, FIG. 16A is a diagram showing how to obtain the backlight value in the present liquid crystal display device. FIG. 16B is a diagram showing how to obtain the backlight value in Patent Document 1 for comparison.

  In FIGS. 16A and 16B, a case where the target panel output luminance of a target pixel 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, The relationship of Gsi, Bsi) / (1 + 1 / WR) is satisfied.

  In the display method in 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 the backlight value. It is decided according to. That is, the respective transmittances in the R, G, and B subpixels are set to 83% (= 100/120), 100% (= 120/120), and 58% (= 70/120).

  On the other hand, in the present liquid crystal display device, a value corresponding to min (Rsi, Gsi, Bsi) is distributed to the transmission amount of the W component in the R, G, B components of the input signals Rsi, Gsi, Bsi. As a result, the input signal (R, G, B) = (100, 120, 70) represented by the RGB signal has a transmission amount (R, G, B, W) = (30, 50, 0, 70). In this target pixel, the backlight value is set to (max (Rsi, Gsi, Bsi) −min (Rsi, Gsi, Bsi)) = 50. Further, the transmittances of the R, G, B, and W sub-pixels are 60% (= 30/50), 100% (= 50/50), 0% (= 0/50), and 93% ( = 70/50 / WR).

  However, the transmittance shown in FIG. 16 (a) is the largest among the plurality of backlight values obtained for all the pixels, and the luminance value in the backlight. Is an example of the transmittance when it is adopted as. Also, in the example of FIG. 16A, the backlight luminance value is multiplied by 4/3, so that the comparison can be made based on the same standard as the backlight value obtained by the method of Patent Document 1.

  As a result, in the example of FIG. 16A, the backlight value is (4/3) × (120−70) = 66.7. In the example of FIG. 16B in which the same display is performed, the backlight value is 120. Therefore, it can be seen that the pixel of interest has the effect of reducing power consumption according to the present invention.

  Next, when a liquid crystal panel having a white luminance ratio WR of 0.6 is used, a backlight value in a pixel satisfying min (Rsi, Gsi, Bsi) ≧ max (Rsi, Gsi, Bsi) / (1 + 1 / WR). The method of obtaining will be described with reference to FIGS. 17 (a) and 17 (b). Here, FIG. 17A is a diagram showing how to obtain the backlight value in the present liquid crystal display device. FIG. 17B is a diagram showing how to obtain the backlight value in Patent Document 1 for comparison.

  In FIGS. 17A and 17B, consider a case where the target panel output luminance of a certain pixel of interest is (R, G, B) = (100, 120, 50). 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, The relationship of 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 the backlight value. It is decided according to. That is, the respective transmittances of the R, G, and B subpixels are set to 83% (= 100/120), 100% (= 120/120), and 42% (= 50/120).

  On the other hand, in this liquid crystal display device, the R component, the G component, and the B component of the input signals Rsi, Gsi, and Bsi each transmit a value corresponding to max (Rsi, Gsi, Bsi) / (1 + 1 / WR). Sort into quantities. As a result, the input signal (R, G, B) = (100, 120, 50) represented by the RGB signal has a transmission amount (R, G, B, W) = (55, 75, 5, 45). In this target pixel, the backlight value is set to max (Rsi, Gsi, Bsi) / (1 + WR) = 75. Further, the transmittances of the R, G, B, and W sub-pixels are 73% (= 55/75), 100% (= 75/75), 6.7% (= 5/75), 100, respectively. % (= 45/75 / WR).

  However, the transmittance shown in FIG. 17 (a) is the largest among the plurality of backlight values obtained for all the pixels, and the luminance value in the backlight. Is an example of the transmittance when it is adopted as. Also, in the example of FIG. 17A, the backlight luminance value is multiplied by 4/3, so that the comparison can be made based on the same standard as the backlight value obtained by the method of Patent Document 1.

  As a result, if the backlight value in the example of FIG. 17A is corrected to the same standard as the backlight value of FIG. 17B, (4/3) × 75 = 100. In the example of FIG. 17B in which the same display is performed, the backlight value is 120. Therefore, it can be seen that the pixel of interest has the effect of reducing power consumption according to the present invention.

  Next, when a liquid crystal panel having a white luminance ratio WR of 0.6 is used, a backlight value in a pixel satisfying min (Rsi, Gsi, Bsi) <max (Rsi, Gsi, Bsi) / (1 + 1 / WR). The method of obtaining will be described with reference to FIGS. 18 (a) and 18 (b). Here, FIG. 18A is a diagram showing how to obtain the backlight value in the present liquid crystal display device. FIG. 18B is a diagram showing how to obtain the backlight value in Patent Document 1 for comparison.

  In FIGS. 18A and 18B, consider a case where the target panel output luminance of a certain pixel of interest is (R, G, B) = (100, 120, 40). 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, The relationship of Gsi, Bsi) / (1 + 1 / WR) is satisfied.

  In the display method in Patent Document 1, as shown in FIG. 18B, the backlight value is set to max (Rsi, Gsi, Bsi) = 120, and the transmittance of each sub-pixel is adjusted to this backlight value. Determined. That is, the respective transmittances in the R, G, and B subpixels are set to 83% (= 100/120), 100% (= 120/120), and 33% (= 40/120).

  On the other hand, in the present liquid crystal display device, a value corresponding to min (Rsi, Gsi, Bsi) is distributed to the transmission amount of the W component in the R, G, B components of the input signals Rsi, Gsi, Bsi. As a result, an input signal (R, G, B) = (100, 120, 40) represented by an RGB signal is an output signal (R, G, B, W) = (60, 80, 0, 40). In this target pixel, the backlight value is set to (max (Rsi, Gsi, Bsi) −min (Rsi, Gsi, Bsi)) = 80. Further, the transmittances of the R, G, B, and W sub-pixels are 75% (= 60/80), 100% (= 80/80), 0% (= 0/80), 83% ( = 40/80 / WR).

  However, the transmittance shown in FIG. 18A is the largest among the plurality of backlight values obtained for all pixels, and the backlight value obtained for this pixel of interest is the largest. It illustrates the transmittance when it is adopted as a value. In the example of FIG. 18A as well, by multiplying the backlight luminance value by 4/3, the comparison can be made based on the same standard as the backlight value obtained by the method of Patent Document 1.

  As a result, in the example of FIG. 18A, the backlight value is (4/3) × (120−40) = 107. In the example of FIG. 18B in which the same display is performed, since the backlight value is 120, it can be seen that the pixel of interest has the effect of reducing power consumption according to the present invention.

  FIGS. 3, 4, and 15 to 18 explain how to obtain the minimum backlight value for each pixel. In accordance with the above method, the display area corresponding to the backlight is displayed. The minimum necessary backlight value is obtained for every pixel in the. Of the plurality of backlight values thus obtained, the maximum value is set as the luminance value of 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 method described above, will be described with reference to FIGS.

  FIG. 5A shows an input signal (Rsi, Gsi, Bsi) of a display area corresponding to a certain backlight. Here, to simplify the description, it is assumed that the white luminance ratio WR is 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 common value for all pixels, and is a value greater than zero.

  For these pixels A to D, the result of converting the input signal (Rsi, Gsi, Bsi) into the output signal (Rtsi, Gtsi, Btsi, Wtsi) represented by the RGBW signal is as shown in FIG. Become. Further, the backlight value obtained for each pixel is as shown in FIG. Thereby, the backlight value is set to the maximum value among the plurality of backlight values obtained for each pixel, that is, 100.

  The transmittance (rsi, gsi, bsi, wsi) of each pixel with respect to the backlight value 100 thus obtained is obtained based on the values of the output signals (Rtsi, Gtsi, Btsi, Wtsi) shown in FIG. The result is as shown in FIG. The final display brightness in each pixel is the result shown in FIG. 5E, and it can be confirmed that the display brightness matches the brightness value of the input signal (Rsi, Gsi, Bsi) shown in FIG. .

  As described above, in the calculation process of the backlight value and the sub-pixel transmittance in the output signal generation unit 12 described above, the light absorption by the color filter is suppressed by sharing the light amount of the white component in the W sub-pixel, and the backlight. 16 can reduce power consumption. For this reason, in the display image data, it is an indispensable condition for obtaining the effect of reducing the backlight power consumption that the white component light amount can be distributed to the W sub-pixel.

  That is, in the calculation process of the backlight value and the sub-pixel transmittance in the output signal generation unit 12, a large amount of white component is distributed to the W sub-pixel in all the pixels in the display area corresponding to the backlight (that is, saturation) The power consumption of the backlight is greatly reduced. On the other hand, if there is a pixel with a small amount of white component light distributed to the W sub-pixel in the display area corresponding to the backlight (that is, the saturation is high), the effect of reducing the backlight power consumption is small, and the luminance is high. As compared with the display method of Patent Document 1, the power consumption may rather increase.

  In the following, when a liquid crystal panel having a white luminance ratio WR of 1 is used, a backlight value setting example is shown for two pixels having the same luminance and different saturation.

  First, in the case of pixel A (luminance = 208, saturation = 0.533) with (R, G, B) = (176, 240, 112), the backlight value is calculated as follows.

  In the pixel A, the amount of light distributed to the W sub-pixel is (112). Then, the respective light amounts of the R, G, and B sub-pixels after subtracting the distribution light amount to the W sub-pixel are (64, 128, 0). As a result, the backlight value set in the pixel A is (128).

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

  In the pixel B, the amount of light distributed to the W sub-pixel is (64). Then, the respective light amounts of the R, G, and B sub-pixels after subtracting the distribution light amount to the W sub-pixel are (96, 192, 0). As a result, the backlight value set in the pixel B is (192).

  As described above, when comparing the pixel A and the pixel B, the backlight value of the pixel B having higher saturation is set to be larger although the luminance is the same, and the effect of reducing the backlight power consumption can be obtained. I understand that it is small.

  Here, the output signal generation unit 12 also performs the backlight value and the sub-pixel transmittance by the above processing on the original image data (that is, the first input RGB signal) that is first input to the liquid crystal display device. Can be calculated. However, in this case, the power consumption reduction effect is not always obtained for all the images for the reasons described above (in practice, in a normal halftone display screen that is considered to have the most display opportunities) In many cases, an effect of reducing power consumption can be obtained).

  For this reason, in the present liquid crystal display device, the saturation reduction unit 11 is disposed in front of the output signal generation unit 12, and the first input RGB signal is subjected to saturation reduction processing to be converted into the second input RGB signal. . Thereby, in the process in the output signal generation part 12, the reduction effect of backlight power consumption can be acquired more reliably. Below, the saturation reduction process in the saturation reduction part 11 is demonstrated in detail.

  FIG. 6 is a block diagram illustrating a schematic configuration of the saturation reduction unit 11. As shown in FIG. 6, the saturation reduction unit 11 includes a backlight upper limit calculation unit 21 and a signal conversion unit 22. The backlight upper limit calculation unit 21 calculates a backlight upper limit value from the upper limit value of the first input RGB signal, the white luminance ratio WR, and the backlight value setting rate, and outputs the backlight upper limit value to the signal conversion unit 22. To do. 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.

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

  First, in S11, the backlight upper limit value calculation unit 21 calculates the backlight upper limit value (S11). The saturation reduction unit 11 performs the saturation reduction processing only on a pixel with a small amount of light that is distributed to the W sub-pixel as it is (that is, the saturation is high) and a high luminance, but at least one of the saturation or the luminance is Saturation reduction processing is not performed for low pixels. This is because, for pixels with low saturation, the backlight value can be greatly reduced by allocating a large amount of light to the W sub-pixel even if the luminance is high. This is because no write value is required. The backlight upper limit value is used for determining a pixel to be subjected to saturation reduction processing. The procedure for calculating the backlight upper limit value will be described in detail as follows.

  First, consider a case where saturation reduction processing is not performed on image data (that is, input RGB signals) and the backlight value is the largest. This is a case where there is a pixel whose saturation is 1 (the amount of light cannot be shared by the W sub-pixel) and at least one of the RGB values is MAX (which indicates the upper limit value of the input RGB signal). The backlight value at this time is also MAX.

  Next, consider a case where saturation reduction processing is performed on image data (that is, input RGB signals) and the backlight value is the largest. Note that the saturation reduction processing here is processing that minimizes the saturation without changing the luminance before and after the processing on the pixel to which the processing is applied. In this case, when there is a pixel whose saturation is 0 (the backlight value cannot be lowered because there is no attempt to lower the saturation any more), and there are pixels whose RGB values are all MAX, the maximum This is the backlight value. Here, since the W sub-pixel can emit light WR times brighter than the RGB sub-pixel, in the pixel, WR / (1 + WR) of the light amount in each of the RGB values is distributed to the W sub-pixel, and the RGB sub-pixel is assigned to each RGB sub-pixel. Allocating 1 / (1 + WR) is the most efficient backlight. The backlight value at this time is MAX / (1 + WR).

  Therefore, the range of the backlight upper limit MAXw is MAX / (1 + WR) to MAX, and when the range of BlRatio is 1 / (1 + WR) to 1.0, the backlight upper limit MAXw is the following (1) It can be expressed by a formula.

MAXw = MAX × BlRatio (1)
Here, MAX indicates the upper limit value of the input RGB signal, but a plurality of values are conceivable instead of a unique value. That is, the lower limit value 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 ensured that the desired backlight value is obtained. On the other hand, the upper limit value of MAX is the maximum value (MAXs) that the input RGB signal can take. This is because it is meaningless to make MAX larger than MAXs.

When the bit width of the input RGB signal is Bw, MAXs is
MAXs = 2 ^Bw −1
It is represented by For example, when Bw is 8, MAXs is 2 ⁸ −1 = 255. Therefore, the effective range of MAX is
MAXi ≦ MAX ≦ MAXs
It is represented by

  Basically, any set value of MAX may be used as long as MAXi ≦ MAX ≦ MAXs is satisfied. If MAX = MAXi is set, the backlight value can be lowered most. However, it is necessary to calculate MAX for each image. On the other hand, if MAX = MAXs is set, the backlight upper limit (MAXw) is higher than MAXi, but MAX is a constant value that does not depend on the image, so there is no need to recalculate MAX for each image.

  In the above 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 saturation reduction process is not performed, and when BlRatio is 1 / (1 + WR), it corresponds to the case where the process for minimizing the saturation is performed. In the saturation reduction process, the effect of reducing the backlight power consumption increases as the saturation is further reduced, but naturally the degree of image quality deterioration due to the saturation reduction also increases. For this reason, in consideration of the balance between the power consumption reduction effect and the image quality degradation, the BlRatio may be arbitrarily set in the range of 1 / (1 + WR) to 1 according to the required saturation reduction level.

  If the backlight upper limit MAXw is determined in this way, next, in S12, it is determined for each pixel based on the following equation (2) whether or not the saturation reduction processing is performed.

MAXw <maxRGB−minRGB (2)
However, in the above equation (2),
maxRGB = max (Ri, Gi, Bi)
minRGB = min (Ri, Gi, Bi)
It is.

  If the RGB value of the pixel of interest satisfies the above equation (2), it is determined that the pixel of interest is a pixel with high luminance and saturation that causes the backlight value to exceed the backlight upper limit MAXw. Is done. Therefore, the saturation reduction process is performed in S13 for such pixels.

  This saturation reduction processing degrades the image quality of the input image in terms of color vividness. However, in a general image, there are not so many high-brightness and high-saturation portions, and the saturation is reduced. In many cases, the portion is limited to a part of the image. Furthermore, human visual characteristics are less sensitive to color changes than brightness changes, and image quality degradation due to saturation reduction is often difficult for humans to recognize. On the other hand, in human visual characteristics, a 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 expression (2) is determined to be a pixel with low luminance or saturation that does not exceed the backlight upper limit value MAXw even if it is used as it is. It is not necessary to perform saturation reduction processing for such pixels, and the process proceeds to S14, and the pixel data in the first input RGB data is used as it is in the second input RGB data.

  Here, the reason why the equation (2) is used for determining whether or not the saturation reduction process is necessary for the pixel of interest will be described.

  First, for a pixel that is not subjected to saturation reduction processing, if the W transmission amount (white component) distributed to the W sub-pixel is Wti, the RGB transmission amounts Rti, Gti, and Bti after the white component distribution is It is calculated by the following formulas (3) to (5).

Rti = Ri-Wti (3)
Gti = Gi-Wti (4)
Bti = Bi-Wti (5)
The RGBW transmission amounts Rti, Gti, Bti, and Wti can take a range of 0 or more in the case of RGB transmission amounts and less than or equal to the backlight upper limit value MAXw. Therefore, it becomes 0 or more and WR times or less of the backlight upper limit value, and the following expressions (6) to (9) are obtained.

0 ≦ Rti ≦ MAXw (6)
0 ≦ Gti ≦ MAXw (7)
0 ≦ Bti ≦ MAXw (8)
0 ≦ Wti ≦ MAXw × WR (9)
Here, the condition that all of RGB transmission amounts Rti, Gti, and Bti are 0 or more, that is,
0 ≦ min (Rti, Gti, Bti)
Consider the conditions that become. When the above equation is transformed using equations (3) to (5),
0 ≦ min (Rti, Gti, Bti)
= Min (Ri-Wti, Gi-Wti, Bi-Wti)
= MinRGB-Wti
It becomes. Accordingly, the condition that all of the RGB transmission amounts Rti, Gti, and Bti are 0 or more is expressed by the following equation (10).

Wti ≦ minRGB (10)
Next, a condition that all of RGB transmission amounts Rti, Gti, and Bti do not exceed MAXw, that is,
max (Rti, Gti, Bti) ≦ MAXw
Consider the conditions that become. When the above equation is transformed using equations (3) to (5),
max (Rti, Gti, Bti)
= Max (Ri-Wti, Gi-Wti, Bi-Wti)
= MaxRGB-Wti ≦ MAXw
It becomes. Accordingly, the condition that all of the RGB transmission amounts Rti, Gti, and Bti do not exceed MAXw is the following expression (11).

maxRGB-MAXw ≦ Wti (11)
From the above equations (10) and (11), the conditions under which all of the RGB transmission amounts Rti, Gti, Bti are 0 or more and MAXw or less are as follows:
maxRGB-MAXw ≦ Wti ≦ minRGB (12)
Furthermore, from the above formulas (9) and (12), the conditions that the RGB transmission amount is 0 or more and MAXw or less and the W transmission amount Wti is 0 or more and MAXw × WR or less are as follows: Become.

max (maxRGB-MAXw, 0) ≦ Wti
≦ min (minRGB, MAXw × WR) (13)
In order for Wti to exist from the above equation (13), the following equation (14) must be satisfied.

max (maxRGB-MAXw, 0)
≦ min (minRGB, MAXw × WR) (14)
The above equation (14) is considered separately for the cases a) to d) as follows.
a) When maxRGB-MAXw ≧ 0 and minRGB ≧ MAXw × WR In this case, the above (14) is
maxRGB-MAXw ≦ MAXw × WR
maxRGB ≦ (1 + WR) × MAXw
It becomes. Since this expression always holds, in the case of a), the above (14) always holds.
b) When maxRGB-MAXw ≧ 0 and minRGB <MAXw × WR In this case, (14) is
maxRGB-MAXw ≦ minRGB
It becomes. For this reason, in case of b)
MAXw ≧ maxRGB−minRGB (15)
However, this is a condition for satisfying the above expression (14).
c) When maxRGB-MAXw <0 and minRGB ≧ MAXw × WR In this case, the above (14) is
0 ≦ MAXw × WR
It becomes. Since this equation always holds, the above (14) is always satisfied in the case of c).
d) When maxRGB-MAXw <0 and minRGB <MAXw × WR In this case, (14) is
0 ≦ minRGB
It becomes. Since this equation always holds, in the case of d), the above (14) always holds.

  From the above a) to d), the expression (14) always holds if the expression (15) in the case of b) is satisfied. That is, equation (14) can be simplified to equation (15) (equation (14) and equation (15) are equivalent).

  That is, when Ri, Gi, Bi satisfies the above equation (15), since Rti, Gti, Bti, and Wti do not exceed MAXw, the backlight value does not exceed MAXw at the target pixel. Therefore, the condition that the backlight value of a certain target pixel exceeds MAXw is the above expression (2) which is the opposite condition to the above expression (15).

  Next, a saturation reduction process that is performed on a pixel that is determined to have both high saturation and luminance based on the above equation (2) will be described in detail.

  For pixels with high luminance and high 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 before processing is performed. The signal (Ri, Gi, Bi) is converted into a second RGB signal (Rsi, Gsi, Bsi).

Rsi = α × Ri + (1−α) × Yi (16)
Gsi = α × Gi + (1−α) × Yi (17)
Bsi = α × Bi + (1−α) × Yi (18)
α = MAXw / (maxRGB−minRGB) (19)
However, in the above equations (16) to (18), Yi is the luminance of the input RGB signal (Ri, Gi, Bi) (for example, Yi = (2 × Ri + 5 × Gi + Bi) / 8).

  Here, the derivation process of the equations (16) to (19), which are the equations for calculating the saturation reduction process, will be described.

  First, the RGB signal conversion formulas for reducing only the saturation with the luminance and hue unchanged are as shown in the above formulas (16) to (18) when the following formula (20) is satisfied.

0 <α <1 (20)
The proof that the above equations (16) to (18) do not change the luminance and hue of the RGB signal before and after the saturation reduction processing is as follows.

  First, assuming that the formula for calculating the luminance when the RGB value is (R, G, B) is (2 × R + 5 × G + B) / 8, the luminance Ysi after saturation reduction is equal to the luminance Yi before saturation reduction. It is represented by the following formula (21).

Ysi = (2 × Rsi + 5 × Gsi + Bsi) / 8 (21)
Substituting the above equations (16) to (18) into the above equation (21) yields the following (22).

Ysi = α × (2 × Ri + 5 × Gi + Bi) / 8 + (1−α) × Yi
= Α × Yi + (1−α) × Yi
= Yi (22)
From the above equation (22), it can be seen that the saturation reduction processing using the above equations (16) to (18) does not change the luminance before and after the processing.

  On the other hand, regarding the hue, first, consider the case where the R value is the maximum. The hue Hi before saturation reduction processing when the R value is the maximum is as shown in (23) below.

Hi = (Cb−Cg) × 60 (23)
However,
Cb = (maxRGB−Bi) / (maxRGB−minRGB)
Cg = (maxRGB−Gi) / (maxRGB−minRGB)
It is.

  Next, the hue Hsi after the saturation reduction process is as shown in (24) below.

Hsi = (Cbs−Cgs) × 60 (24)
However,
Cbs = (maxRGBs−Bsi) / (maxRGBs−minRGBs)
Cgs = (maxRGBs−Gsi) / (maxRGBs−minRGBs)
maxRGBs = max (Rsi, Gsi, Bsi)
minRGBs = min (Rsi, Gsi, Bsi)
It is.

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

Hsi = {(maxRGBs−Bsi) − (maxRGBs−Gsi)} /
(MaxRGBs−minRGBs) × 60
= {(Gsi-Bsi) / (maxRGBs-minRGBs)} * 60
= Α × (Gi−Bi) / {α × (maxRGB−minRGB)} × 60
= {(Gi-Bi) / (maxRGB-minRGB)} * 60
= {(MaxRGB-Bi)-(maxRGB-Gi)} /
(MaxRGB-minRGB) × 60
= (Cb-Cg) x 60
= Hi (25)
From the above equation (25), it can be seen that the saturation reduction processing using the above equations (16) to (18) does not change the hue before and after the processing. The same applies when the G value or B value is maximum.

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

  First, the backlight value calculation algorithm using only Rsi, Gsi, and Bsi (one pixel) is as follows.

  First, the W transmission amount Wtsi is calculated by the following equation (26).

Wtsi = min (maxRGBs / (1 + 1 / WR), minRGBs) (26)
Next, the RGB transmission amount (Rtsi, Gtsi, Btsi) is calculated by the following equations (27) to (29).

Rtsi = Rsi−Wtsi (27)
Gtsi = Gsi−Wtsi (28)
Btsi = Bsi−Wtsi (29)
The backlight value Wbs is calculated by the following equation (30).

Wbs = max (Rtsi, Gtsi, Btsi, Wtsi / WR) (30)
In the above algorithm, consider a case where A) maxRGBs / (1 + 1 / WR) ≦ minRGBs and B) a case where minRGBs <maxRGBs / (1 + 1 / WR).
A) When maxRGBs / (1 + 1 / WR) ≦ minRGBs In this case, (26) above is
Wtsi = maxRGBs / (1 + 1 / WR)
It becomes. However, from condition A), maxRGBs−minRGBs ≦ maxRGBs / (1 + WR) ≦ MAXw, and equation (15) always holds. That is, when the saturation reduction process is performed in which the luminance and hue are unchanged and only the saturation is reduced, A) maxRGBs / (1 + 1 / WR) ≦ minRGBs is not satisfied.
B) When minRGBs <maxRGBs / (1 + 1 / WR) In this case, (26) above is
Wtsi = minRGBs
It becomes. Therefore, the above equations (27) to (29) are
Rtsi = Rsi-minRGBs (≦ maxRGBs−minRGBs)
Gtsi = Gsi−minRGBs (≦ maxRGBs−minRGBs)
Btsi = Bsi−minRGBs (≦ maxRGBs−minRGBs)
It becomes. Further, from condition B) minRGBs <maxRGBs / (1 + 1 / WR), since minRGBs <(maxRGBs−minRGBs) × WR, the above equation (30) is
Wbs = maxRGBs−minRGBs (31)
It becomes.

At this time, in order to obtain α at which Wbs becomes MAXw,
Wbs = MAXw
And substituting equation (31) for this,
maxRGBs-minRGBs = MAXw
It becomes. Applying equations (16) to (18) to this,
α × maxRGB + (1−α) × Yi−α × minRGB− (1−α) × Yi
= MAXw
α × maxRGB−α × minRGB = MAXw
α × (maxRGB−minRGB) = MAXw
It becomes. Therefore, the following equation (32) is derived.

α = MAXw / (maxRGB−minRGB) (32)
Here, since there is a relationship of the expression (2), the expression (32) matches the condition (0 <α <1) of the expression (20). That is, in the case of B) minRGBs <maxRGBs / (1 + 1 / WR), the luminance and hue are unchanged, and it is possible to perform saturation reduction processing that reduces only saturation, so that the backlight value becomes MAXw. Α is expressed by the above equation (32).

  Incidentally, from the results of A) and B), Rsi, Gsi, and Bsi subjected to the saturation reduction process always satisfy minRGBs <maxRGBs / (1 + 1 / WR), which is the condition of B).

  As described above, the saturation reduction unit 11 converts the first input RGB signal into the second input RGB signal to be input to the output signal generation unit 12 at the subsequent stage by the processing according to the above description. That is, the second input RGB signal is obtained by converting pixel data with high luminance and saturation in the first input RGB signal into pixel data with reduced saturation. Also, pixel data with low luminance or saturation in the first input RGB signal is not converted, and the data is used as it is in the second input RGB signal.

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

  The W transmission amount calculation unit 31 calculates the W transmission amount from the second input RGB signal input from the saturation reduction unit 11 using the above equation (26) (S21). This W transmission amount is output to the RGB transmission amount calculation unit 32, the backlight value calculation unit 33, and the transmittance calculation unit 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 equations (27) to (29) (S22). This RGB transmission amount is output to the backlight value calculation unit. The processes of S21 and S22 are repeated for the number of pixels in the input RGB signal.

  The backlight value calculation unit 33 calculates the backlight in the image using the following equation (33) from the RGBW transmission amount of all the pixels in the image output from the W transmission amount calculation unit 31 and the RGB transmission amount calculation unit 32. The write value Wbs is calculated (S23).

Wbs = max (Rts1, Gts1, Bts1, Wts1 / WR,
. . .
RtsNp, GtsNp, BtsNp, WtsNp / WR) (33)
Alternatively, in the backlight value calculation unit 33, among the RGBW transmission amounts of all pixels in the image output from the W transmission amount calculation unit 31 and the RGB transmission amount calculation unit 32, from the RGB transmission amount excluding the W transmission amount, It is also possible to calculate the backlight value Wbs in the image using the following equation (34). This is because when the W transmission amount Wts is obtained by the above-described method, max (Rts, Gts, Bts) ≧ Wts / WR for each RGB transmission amount Rts, Gts, and Bts.

Wbs = max (Rts1, Gts1, Bts1,
. . .
RtsNp, GtsNp, BtsNp) (34)
The backlight value Wbs is output to the transmittance calculation unit 34. The transmittance calculation unit 34 calculates the following (35) from the RGBW transmission amount output from the W transmission amount calculation unit 31, the RGB transmission amount calculation unit 32, and the backlight value Wbs output from the backlight value calculation unit 33. ) To (38) to calculate the transmittance of each sub-pixel (S24). The process of S24 is repeated for the number of pixels in the input RGB signal.

rsi = Rtsi / Wbs (35)
gsi = Gtsi / Wbs (36)
bsi = Btsi / Wbs (37)
wsi = Wtsi / Wbs / WR (38)
Thus, in the liquid crystal display device according to the present embodiment, the saturation reduction process is performed on the input RGB signal that is the original input before the output signal generation unit 12 calculates the backlight value and the RGBW transmittance. Thus, the backlight value can be reliably reduced.

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

  On the other hand, when the saturation reduction process is performed on the pixel B with MAX = 256, BlRatio = 1 / (1 + WR) = 0.5, the pixel after saturation reduction of the pixel B in the second input RGB signal The value 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) x 160 + (1-2 / 3) x 208 = 176 (from equation (16))
Gs1 = α × G1 + (1−α) × Y1
= (2/3) x 256 + (1-2 / 3) x 208 = 240 (from equation (17))
Bs1 = α × B1 + (1−α) × Y1
= (2/3) x 64 + (1-2 / 3) x 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, the backlight value can be reduced from 192 to 128 (a reduction of about 33%) by the saturation reduction process.

  In addition, the degree of saturation reduction processing performed in the present liquid crystal display device can be changed by adjusting the value of BlRatio in the equation (1) in the range of 1 / (1 + WR) to 1. . In other words, in this liquid crystal display device, by providing a function to change the value of BlRatio, the user can arbitrarily set whether to give priority to image quality (increase the value of BlRatio) or prioritize power saving (to reduce the value of BlRatio) Can be selectable. In this case, if the value of BlRatio is set to 1, the saturation reduction process is not performed, so execution / non-execution of the saturation reduction process can be selected.

  In the present liquid crystal display device, basically, one backlight 16 is provided for a plurality of pixels. For this reason, for example, the liquid crystal display device illustrated in FIG. 1 illustrates 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 is divided into a plurality of regions, and a plurality of backlights are provided so that the backlight luminance can be adjusted for each region. It is good also as a structure.

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

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

  The input signal dividing unit 41 distributes the second input RGB signal for one screen input from the saturation reduction unit 11 into signals for two areas, and outputs the input RGB signals of the respective areas to the output signal generation units 12a and 12b. To enter. The output signal generation units 12a and 12b perform the same processing as the output signal generation unit 12 in FIG. 1 for each corresponding area.

  The liquid crystal panel control units 13a and 13b perform the same processing as the liquid crystal panel control unit 13 in FIG. 1 for each corresponding area, but each control unit is located at a position corresponding to the corresponding area of the liquid crystal panel 14. Control the pixel transmittance.

  The backlight control units 15a and 15b perform the same processing as 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.

  Thus, the backlight value can be further lowered by dividing one screen into a plurality of areas and performing control in units of areas. In the present embodiment, one screen is divided into two areas, but it is also possible to control by dividing it into three or more areas.

  A general image has a property that colors similar to those in a neighboring region continue. For this reason, as in the configuration shown in FIG. 10, by dividing the backlight region, the backlight of the backlight region where dark pixels are gathered can be made darker. As a result, it is possible to reduce the overall backlight power consumption when the backlight is divided rather than when the backlight is not divided.

  The processing of the saturation reduction unit 11 and the output signal generation unit 11 can be realized by software operable on a personal computer. The procedure for realizing the above processing by software will be described below.

  FIG. 11 is a diagram showing a system configuration when the above processing is realized by software. The system includes a personal computer main body 51 and an input / output device 55. 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 via the input / output interface 54, and from the storage medium 56, the saturation reduction / output signal generation program, the parameter file (the upper limit value of the input RGB signal, the backlight value setting rate, The area information used when dividing one screen into a plurality of areas) and input image data are read and stored in the memory 53.

  Further, the CPU 52 reads the saturation reduction / output signal generation program, the parameter file, and the input image data from the memory 53, and in accordance with each command of the saturation reduction / output signal generation program, After performing saturation reduction and output signal generation, the input / output device 55 is controlled via the input / output interface 54 to output the backlight value and RGBW transmittance after the output signal generation to the storage medium 56.

  Alternatively, as shown in FIG. 12, by outputting the backlight value after generation of the output signal and the RGBW transmittance to the backlight control unit 15 and the liquid crystal panel control unit 13 via the input / output interface 54, respectively. It is also possible to actually display an image by controlling the white backlight 16 and the liquid crystal panel 14.

  Thus, in the above system, the above-described saturation reduction and output signal generation can be performed on a personal computer. This makes it possible to confirm the validity of the saturation reduction method and the output signal generation method and the effect of reducing the backlight value before actually producing a prototype of the saturation reduction unit and the output signal generation unit.

1, showing an embodiment of the present invention, is a block diagram illustrating a main configuration of a liquid crystal display device. FIG. FIGS. 2A and 2B are diagrams showing examples of subpixel arrangement in the transmissive liquid crystal display device. FIG. 3A is a diagram showing how to obtain the backlight value in the present liquid crystal display device, and FIG. 3B is a diagram showing how to obtain the backlight value in Patent Document 1 for comparison. . FIG. 4A is a diagram showing how to obtain the backlight value in the present liquid crystal display device, and FIG. 4B is a diagram showing how to obtain the backlight value in Patent Document 1 for comparison. . FIGS. 5A to 5E are diagrams showing a procedure for determining a backlight value and subpixel transmittance in the liquid crystal display device. FIG. 3 is a block diagram illustrating a configuration example of a saturation reduction unit in the liquid crystal display device. It is a flowchart which shows the operation | movement procedure of the said saturation reduction part. FIG. 3 is a block diagram illustrating a configuration example of an output signal generation unit in the liquid crystal display device. It is a flowchart which shows the operation | movement procedure of the said output signal generation part. FIG. 24, showing another embodiment of the present invention, is a block diagram illustrating a configuration of a main part of a transmissive liquid crystal display device. It is a figure which shows the system configuration | structure in the case of implement | achieving the display control processing of this invention with software. It is a figure which shows the modification of a system configuration in the case of implement | achieving the display control processing of this invention with software. It is sectional drawing which shows the general structure of a transmissive liquid crystal display device. It is a figure which shows the general example of arrangement | positioning of the sub pixel in a transmissive liquid crystal display device. FIG. 15A is a diagram showing how to obtain the backlight value in the present liquid crystal display device, and FIG. 15B is a diagram showing how to obtain the backlight value in Patent Document 1 for comparison. . FIG. 16A is a diagram showing how to obtain the backlight value in the present liquid crystal display device, and FIG. 16B is a diagram showing how to obtain the backlight value in Patent Document 1 for comparison. . FIG. 17A is a diagram showing how to obtain the backlight value in the present liquid crystal display device, and FIG. 17B is a diagram showing how to obtain the backlight value in Patent Document 1 for comparison. . FIG. 18A is a diagram showing how to obtain the backlight value in the present liquid crystal display device, and FIG. 18B is a diagram showing how to obtain the backlight value in Patent Document 1 for comparison. .

Explanation of symbols

11 Saturation reduction unit 12, 12a, 12b Output signal generation unit 13, 13a, 13b Liquid crystal panel control unit 14 RGBW liquid crystal panel (liquid crystal panel)
15, 15a, 15b Backlight controller 16, 16a, 16b White backlight (active backlight)
21 Backlight upper limit calculation unit 22 Signal conversion unit 31 W transmission amount calculation unit 32 RGB transmission amount calculation unit 33 Backlight value calculation unit 34 Transmittance calculation unit 41 Input signal division unit 51 PC main body 52 CPU
53 Memory 54 I / O Interface 55 I / O Device 56 Storage Medium

Claims (6)

A liquid crystal panel in which one pixel is divided into four sub-pixels of red (R), green (G), blue (B), and white (W);
A white active backlight with controllable brightness,
Of the pixel data included in the first input RGB signal that is an input image, the pixel data having high luminance and saturation is subjected to saturation reduction processing that reduces only the saturation without changing the luminance and hue. A saturation reduction unit for converting the first input RGB signal into a second input RGB signal;
From the second input RGB signal, the transmittance signals of the R, G, B, and W sub-pixels in each pixel of the liquid crystal panel are generated without changing the luminance and saturation for all the pixels. An output signal generator for calculating a backlight value in the active backlight;
A liquid crystal panel control unit that drives and controls the liquid crystal panel based on the transmittance signal generated by the output signal generation unit;
A backlight control unit that controls the luminance of the backlight based on the backlight value calculated by the output signal generation unit ;
The saturation reduction unit
Among the pixel data included in the first input RGB signal that is an input image, pixel data having high luminance and saturation are extracted by the following procedure (A):
A transmissive liquid crystal display device, wherein the extracted pixel data is subjected to saturation reduction processing according to the following procedure (B).
(A) Backlight upper limit MAXw
MAXw = MAX × BlRatio
Calculated by the formula
MAXw <maxRGB-minRGB
Pixel data satisfying the above is extracted as pixel data having high luminance and saturation.
However,
WR: White luminance ratio (display luminance P1 when each transmittance of the RGB sub-pixel is x% and each transmittance of the W sub-pixel is 0%, and each transmittance of the RGB sub-pixel is 0% and the W sub-pixel The ratio P2 / P1 with the display luminance P2 when each transmittance of x 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 of the input image
max (A, B,...): A, B,. . . Maximum value of
min (A, B,...): A, B,. . . Minimum of
And
(B) For 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 saturation reduction processing is obtained by the following equation.
However,
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 target pixel
α = MAXw / (maxRGB−minRGB)   The transmissive liquid crystal display device according to claim 1, wherein the saturation reduction unit can change a degree of saturation reduction processing. Display luminance P1 when each transmittance of the RGB subpixel is x% and each transmittance of the W subpixel is 0%, and each transmittance of the W subpixel is x when each transmittance of the RGB subpixel is 0% %, When the ratio P2 / P1 with the display brightness P2 is the white brightness ratio WR,
The transmissive liquid crystal display device according to claim 2, wherein the saturation reduction unit sets a change range of the degree of saturation reduction processing based on the white luminance ratio WR. The output signal generator is
A W transmission amount calculation unit that calculates a transmission amount (Wtsi) of each W sub-pixel by the following procedure (A);
An RGB transmission amount calculation unit that calculates the transmission amount (Rtsi, Gtsi, Btsi) of each RGB sub-pixel according to the following procedure (B);
A backlight value calculation unit for calculating a backlight value (Wbs) by the following procedure (C);
The transmission type according to claim 1 , further comprising transmittance calculation means for calculating the transmittance (rsi, gsi, bsi, wsi) of each RGBW sub-pixel by the following procedure (D). Liquid crystal display device.
(A) W transmission amount (Wtsi)
Wtsi = min (maxRGBs / (1 + 1 / WR), minRGBs)
It is calculated by the following formula.
However,
maxRGBs = max (Rsi, Gsi, Bsi)
minRGBs = min (Rsi, Gsi, Bsi)
And
(B) RGB transmission amount (Rtsi, Gtsi, Btsi)
Rtsi = Rsi−Wtsi
Gtsi = Gsi-Wtsi
Btsi = Bsi−Wtsi
It is calculated by the following formula.
(C) Set the backlight value (Wbs)
Wbs = max (Rts1, Gts1, Bts1, Wts1 / WR,
. . .
RtsNp, GtsNp, BtsNp, WtsNp / WR)
It is calculated by the following formula.
(D) RGBW transmittance (rsi, gsi, bsi, wsi)
rsi = Rtsi / Wbs
gsi = Gtsi / Wbs
bsi = Btsi / Wbs
wsi = Wtsi / Wbs / WR
It is calculated by the following formula.
However, when Wbs = 0, rsi = gsi = bsi = wsi = 0. A plurality of active backlights for the liquid crystal panel,
For each region corresponding to each active backlight, transmissive liquid crystal display device according to any one of claims 1 to 4, characterized in that the backlight value control of the transmission ratio control and a back light of a liquid crystal panel. A control program for causing a computer to perform processing of each functional unit according to claim 1 or 4 .

Images