JP2005227436A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve visual contrast in various video signals. <P>SOLUTION: The chromaticity of a light source is changed according to the information on RGB luminance in the video signals obtainable from an RGB luminance detection circuit and the RGB ratios of the video signals are changed in correspondence thereto in the liquid crystal display device with which the chromaticity of a display screen can be changed by changing the chromaticity of the light source. In the liquid crystal display device capable of changing the color temperature of the display screen by changing the color temperature of the light source, the color temperature of the light source is changed according to the characteristic quantity of the RGB luminance in the video signals obtainable from the RGB luminance detection circuit and the RGB ratios of the video signals are changed in correspondence thereto. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display device such as a liquid crystal television using a liquid crystal display panel having a light source capable of changing chromaticity.

  The liquid crystal display device is characterized by a flat structure and low power consumption, and its practical application is becoming widespread from an in-vehicle panel, a measurement display to an OA device, a television, etc. as well as a calculator and a clock. In particular, in recent years, the use of televisions has increased in screen size and image quality, and the replacement of televisions using CRTs with liquid crystal televisions has become conspicuous with the thin features. However, since a liquid crystal display device such as a liquid crystal television displays an image on a non-light-emitting light-receiving light modulator (for example, a liquid crystal panel), the screen becomes darker than a light-emitting display device such as a CRT. End up. For this reason, the normal light receiving type image display device is provided with a backlight or the like to increase the visual luminance. At this time, generally, the brightness of the backlight can be adjusted so that the contrast and the brightness can be adjusted. Basically, the contrast and the brightness of the light source are fixedly set to the contents that are manually adjusted by the user. However, in recent years, in order to make the image easier to see, the contrast and the light source are changed according to the input video signal that changes as needed. Various methods for dynamically adjusting the brightness of the light have been proposed.

As a method for dynamically adjusting the contrast and the backlight, for example, there is a method disclosed in JP-A-2002-41007. The conventional adjustment method disclosed in this publication detects the maximum luminance level (MAX) and the minimum luminance level (MIN) of the input video signal, and the contrast is increased when the difference between the maximum luminance level and the minimum luminance level is large. When the difference between the maximum luminance level and the minimum luminance level is small, the contrast is increased. Further, the average luminance level (APL) of the input video signal is detected, and when the average luminance level is higher than a predetermined reference luminance level, the luminance of the backlight is decreased, and when the average luminance level is low, the luminance of the backlight is increased. By performing the contrast adjustment and the backlight brightness adjustment in a correlated manner, the visual contrast feeling is improved.
JP 2002-41007 A

  However, in the past, visual contrast was improved by detecting feature quantities at the luminance level of the video signal, and performing video signal conversion and backlight luminance change in conjunction with each other. When the feature amount is detected with respect to the video signal at the luminance level, the optimum contrast cannot always be improved. For example, as shown in FIG. 2, when the range of the luminance level of the video signal is 0 to 1, conventionally, the maximum luminance level of the input video signal such as a is Y = 0.7 and the minimum luminance level is Y = 0. .2. When the APL level is Y = 0.6, in order to improve the contrast, the video signal is kept in the dynamic range as shown in b, and the backlight is changed so that the APL does not change as shown in c. The brightness is reduced and APL is restored to improve the contrast. However, if the luminance Y is separated into RGB colors to represent various video signals and expressed using Er, Eg, and Eb that change in the range of 0 to 1, the luminance Y is Y = 0.3Er + 0.59Eg + 0.11Eb. It can be expressed as. At this time, the maximum luminance of the video signal can be considered as follows. For example, if the Er, Eg, and Eb values of the respective colors of the first video signal are Er = Eg = Eb = 0.7, the maximum luminance is Y = 0.7. If the Er, Eg, and Eb of the second video signal are Er = 0.9, Eg = 0.6, and Eb = 0.69 as signals having different Er, Eg, and Eb ratios, The maximum luminance is Y = 0.7. When trying to increase the gain of these two types of video signals, the maximum luminance can be increased up to 43% in the case of the first signal, whereas in the case of the second signal, if the gain is increased, the R signal will be increased. Since this is the upper limit, the maximum luminance level can be raised only 11% at the maximum. Further, when the gain is increased further, the luminance ratio of RGB changes, so that the color tone changes. In other words, in order not to cause a change in color tone, if a signal close to 100% is included as each of the RGB signals, the ratio of applying the gain must be suppressed or signal conversion should not be performed. Goodbye. Therefore, it is a lie that improves a sufficient visual contrast feeling.

  In addition, the liquid crystal panel has a problem that the color changes depending on the viewing angle because of the liquid crystal molecular arrangement of the liquid crystal. This is because the input gradation-luminance characteristics vary depending on the viewing angle because of the molecular arrangement of the liquid crystal. When a specific color is displayed, the luminance ratio of RGB of that color varies greatly depending on the viewing angle, so the color tone changes, and there is a problem that the color when viewed from the front and the viewing color are different. . This will be described with reference to FIG. FIG. 3 is a diagram showing the characteristics of relative luminance with respect to the input gradation when the viewing angle of the VA mode that is generally widely used is changed. FIG. 3 shows the luminance when the input gradation is 255 as 1. It is. It can be seen that the input gradation-luminance characteristics in the halftone are greatly changed in the characteristics at the viewing angle of 60 ° compared to the front. As shown in the figure, the RGB input gradation is (255, 200, 140) at the front and the RGB input gradation at the viewing angle of 60 ° is (255, 200, 140). It can be seen that the luminance ratio changes. For this reason, a color tone changes with viewing angles. For example, a phenomenon that the skin color becomes light when the visual field of the skin color is shaken.

  In order to solve this problem, the present invention provides a signal conversion unit that generates an RGB signal from an input video signal, a liquid crystal panel that displays a screen based on the RGB signal generated by the signal conversion unit, and chromaticity A backlight that illuminates the liquid crystal panel, an RGB luminance detecting unit that detects luminance information of RGB from the RGB signal, and a value generated by the RGB luminance detecting unit And a control means for controlling each of the signal conversion means and the backlight.

  The control means is a liquid crystal display device that changes the chromaticity of the backlight and the RGB signal values in conjunction with each other based on the values detected by the RGB luminance detecting means.

  With the liquid crystal display device according to the present invention, it is possible to control the chromaticity of the backlight and the video signal in association with various video signals, and to provide a sufficient visual contrast feeling with respect to the various video signals. A certain video can be displayed.

  In addition, when the liquid crystal panel is in the VA mode, it is possible to control the chromaticity of the backlight and the video signal in association with various video signals, and suppress changes in color tone depending on the field of view for various video signals. be able to.

  In addition, when the LCD panel is in the TN mode, it is possible to control the chromaticity of the backlight and the video signal in conjunction with various video signals, and suppress changes in color tone depending on the field of view for various video signals. be able to.

  In addition, in the case of a signal that contains a certain proportion or more of a specific color in the video signal, a control signal for controlling the chromaticity of the backlight and the video signal in accordance with the proportion can be obtained. Change in color tone due to visual field can be suppressed. In addition, the circuit configuration can be simplified by detecting only a specific color by the detection circuit.

  According to the first aspect of the present invention, there is provided a signal conversion unit that generates an RGB signal from an input video signal, a liquid crystal panel that displays a screen based on the RGB signal generated by the signal conversion unit, and chromaticity A backlight that illuminates the liquid crystal panel, an RGB luminance detecting unit that detects luminance information of RGB from the RGB signal, and a value generated by the RGB luminance detecting unit And a control means for controlling each of the signal conversion means and the backlight.

  The control means is a liquid crystal display device that changes the chromaticity of the backlight and the RGB signal values in conjunction with each other based on the values detected by the RGB luminance detecting means.

(Embodiment 1)
Hereinafter, an embodiment of the invention described in the first invention of the present application will be described with reference to FIG.

  The liquid crystal display device 100 shown in FIG. 1 is sent to the liquid crystal panel 2 based on the video signal conversion circuit 1 to which the video signal I is supplied, the liquid crystal panel 2 to which the output of the signal conversion circuit 1 is supplied, and the video signal I. An RGB luminance detection circuit 3 for detecting information of each luminance from the RGB signal, a CPU 4 to which an output from the RGB luminance detection circuit 3 is supplied, a backlight control circuit 5 to which an output from the CPU 4 is supplied, and a backlight A backlight 6 capable of changing chromaticity as disclosed in, for example, Japanese Patent Application Laid-Open No. 2000-81605 is provided by an output from the control circuit 5.

  In the liquid crystal display device configured as described above, for example, the video signal I has a maximum luminance level of Y = 0.7, a minimum luminance level of Y = 0.2, and an APL level of Y = 0.6. Suppose that is entered. Further, as described above, to represent various input video signals I, the luminance Y is decomposed into RGB and Er, Eg, and Eb that change in the range of 0 to 1 are used, and Y = 0.3Er + 0.59Eg + 0. .11Eb. The Er, Eg, Eb values of the first signal having the same Er, Eg, Eb ratio are set to Er = Eg = Eb = 0.7, and the Er, Eg, Eb ratios of the second video signal having different Er, Eg, Eb ratios are set. , Eb values are Er = 0.9, Eg = 0.6, and Eb = 0.69. Assume that a characteristic video signal is input in which the ratio of each color is different as in the second signal compared to the first signal and one of the colors is close to 100%. Signal conversion at that time will be described with reference to FIG. FIG. 4 is a diagram showing signal intensities of RGB colors. First, a method for improving the contrast by detecting only the luminance feature amount as in the past and changing the luminance of the backlight in conjunction with the value will be described. If signals such as the first and second signals are input, the luminance information is both the same value as Y = 0.7, and it is assumed that the signal is multiplied by 1.2 in order to improve contrast. As shown in (a), with the first signal, the luminance can be increased by 1.2 without changing the luminance ratio of RGB (without changing the color tone). The contrast can be improved by controlling the backlight so that the APL becomes the original value. However, as shown in FIG. 4B, in the case of the second signal, if an attempt is made to multiply by 1.2 without changing the RGB luminance ratio, R is the upper limit because Er = 0.9. Therefore, the luminance cannot be increased by 1.2 without changing the luminance ratio of RGB. Therefore, when the second signal is input, the RGB luminance detection circuit first detects the luminance information of each RGB. The CPU 4 outputs control signals c and d for controlling the video signal conversion circuit 1 and the backlight control circuit 5 according to the detected value b. At this time, the control signals c and d are controlled so as to improve the contrast. This will be described with reference to FIG. Here, a description will be given using a diagram showing luminance of each color of RGB. As shown in FIG. 4, for G and B, Eg and Eb can be multiplied by 1.2 as in the conventional case, but Er cannot take a value of 1 or more, so Er = 1. In this state, the luminance of R is not 1.2 times. Therefore, the amount that is not enough to increase the luminance by 1.2 is corrected by increasing the luminance of the R backlight so that the luminance becomes 1.2 times. To. Finally, the luminance of each color backlight is controlled so that the entire APL is the same as the beginning. As a result, conventionally, when various video signals include characteristic signals with different RGB signal ratios as in the second signal and any of the colors being close to 100%, the color tone changes. It is possible to improve the problems such as the need to suppress the contrast improvement effect so as not to cause a change in color tone, and there is sufficient visual contrast for any type of signal. An image can be displayed.

(Embodiment 2)
A second invention of the present application is a liquid crystal display device in which the liquid crystal panel is in a VA mode.

  In the second embodiment of the present invention described below, the liquid crystal panel of the liquid crystal display device 100 according to the first embodiment shown in FIG. 1 is a liquid crystal display device exhibiting VA mode characteristics. Since other configurations are the same as those of the liquid crystal display device 100 described in the first embodiment, detailed description thereof is omitted.

  In the liquid crystal display device configured as described above, consider a case where a video signal I including a signal as shown in FIG. 6 having an RGB luminance ratio of R100%, G50%, and B20% is input. The RGB signals in this case are (r1, g1, b1). As described above, in the case of colors with different RGB luminance ratios in the VA mode liquid crystal, when the viewing angle is 60 °, G and B are Bup and Gup proportions increase with respect to R, so the RGB luminance ratio is R100%. G60% and B45%. Therefore, the RGB luminance ratio changes depending on the viewing angle, and the color tone changes. When such a video signal I is input, the RGB luminance detection circuit 3 first detects RGB luminance information in the video signal I. The CPU 4 outputs control signals c and d for controlling the video signal conversion circuit 1 and the backlight control signal conversion circuit 5 in accordance with the detected value b. At this time, the control signals c and d are controlled so as to be control signals that suppress a change in color tone depending on the viewing angle. As a specific example of control, as shown in the graph of G80% and B60% in FIG. 6, the RGB luminance ratio of the backlight is changed to be, for example, R100%, G80%, B60%, and the input gradation-luminance. A control signal c is output so that the characteristics are different for each color of RGB. In this case, since the control signal d output to the video signal conversion circuit 1 first changes the RGB ratio of the backlight, it must output a control signal for controlling the RGB signal so that the color tone in front view does not change. Don't be. Therefore, the control signal d for changing the input gradation of the RGB signal is output so that the RGB luminance ratio of the backlight becomes the RGB luminance ratio of the front view at R100%, G100%, and B100%. In this case, as shown in FIG. 6, a control signal d is output so that the RGB input gradation is (r2, g2, b2). Based on the control signals c and d, the backlight control signal conversion circuit 5 controls the backlight 6, and the video signal conversion circuit 1 controls the liquid crystal panel 2. As a result, the RGB luminance ratio at the front does not change, and as shown in Bup2 and Gup2 in FIG. 7, the RGB luminance ratio is suppressed to R100%, G53%, and B32% depending on the viewing angle, and the color tone depending on the visual field Change can be suppressed. As described above, by using the circuit according to the present invention, it is possible to suppress a change in color tone depending on the visual field.

(Embodiment 3)
A third invention of the present application is a liquid crystal display device characterized in that the liquid crystal panel is in a TN mode.

  The basic operation of the liquid crystal display device of the present invention is the same as that described in the second embodiment, and is omitted when the liquid crystal panel exhibits TN mode characteristics. Here, only the method of signal conversion will be described. FIG. 8 is a diagram showing the input gradation-luminance characteristics in the front of the TN mode and an upper visual field of 60 °. In the case of the TN mode, when the upper visual field is 60 °, the reversal of luminance occurs at a higher gradation than the front. For example, consider a case in which a signal having RGB luminance ratios of R44%, G0%, and B100% shown in FIG. The RGB input gradation at this time is (r, 0, g1). The RGB luminance ratio is R120%, G0%, and B100% at the upper visual field of 60 °, and the luminance is lower than B when R is in front, but the luminance is higher than B at the upper visual field of 60 °. As a result, the color tone changes. When such a signal is detected by the RGB luminance detection circuit 3, for example, as shown by B130% in FIG. 8, only the backlight of B is changed to increase to the original 130%, and the input gradation-luminance characteristic of only B is changed. Let us consider a case where a control signal c is output that changes. In this case, since the RGB luminance ratio of the backlight is changed, the control signal d output to the video signal conversion circuit must output an RGB signal so that the color tone in front view does not change. Here, since only the backlight of B is 130%, the input signal of B is changed so as to be the same as the luminance at the input gradation b1 when the backlight is 100%. In this case, a control signal d for changing the input gradation of B so as to be b2 shown in FIG. 8 is output. As a result, the RGB luminance ratio is R44%, G0%, and B100% as in the front, and the upper visual field of 60 ° is R120% and G0 from the B waveform at the backlight of 130% and the upper 60 ° in FIG. %, B174%. The luminance of R with respect to B is 69%, and the change in color tone can be suppressed. In this way, the use of the circuit according to the present invention can suppress a change in color tone depending on the visual field.

(Embodiment 4)
A fourth invention of the present application is the liquid crystal display device in which the RGB luminance detecting means detects a specific color having a specific RGB luminance ratio.

  The fourth embodiment of the present invention will be described below with reference to FIG.

  The liquid crystal display device 101 shown in FIG. 9 is obtained by replacing the RGB luminance detection circuit of the liquid crystal display device 100 described in the first embodiment with a specific color detection circuit, and the other configuration is the liquid crystal display device 100 described in the first embodiment. It is the same.

  Since the detailed description is the same as that described in the second embodiment and the RGB luminance detecting means detects only a specific color, the description of other operations is omitted. The specific color detection circuit detects, for example, a video signal containing a color that is sensitive to human eyes, such as skin color, in a certain ratio or more, and according to the ratio, the second embodiment As shown in Fig. 4, the color is prevented from changing depending on the visual field. With this liquid crystal display device, it is possible to suppress a change in color tone due to the field of view of a specific color with respect to a signal of a certain ratio or more. Further, the circuit configuration can be simplified by limiting the color to be detected to a specific color.

The liquid crystal display device according to the present invention can control the backlight chromaticity and the video signal in association with various video signals, and as a result, has a sufficient visual contrast feeling with respect to the various video signals. It is effective as a liquid crystal display device such as a liquid crystal television using a liquid crystal display panel having a light source capable of displaying a certain image and having a light source capable of changing chromaticity.

The figure explaining operation | movement of the circuit for improving the visual contrast in Embodiment 1 of this invention Conventional contrast improvement graph The figure which shows the viewing angle characteristic of VA mode The figure which shows operation | movement of Embodiment 1 of this invention. The figure which shows operation | movement of Embodiment 1 of this invention. The figure which shows operation | movement of Embodiment 2 of this invention. The figure which shows operation | movement of Embodiment 2 of this invention. The figure which shows operation | movement of Embodiment 3 of this invention. The figure explaining the operation | movement of the circuit for performing the viewing angle improvement in Embodiment 2 of this invention.

Explanation of symbols

1 Video signal conversion circuit 2 Liquid crystal panel 3 RGB luminance detection circuit 4 CPU
5 Backlight control circuit 6 Backlight

Claims (4)

A signal conversion unit that generates an RGB signal from an input video signal, a liquid crystal panel that displays a screen based on the RGB signal generated by the signal conversion unit, and a structure capable of changing chromaticity A backlight for illuminating the liquid crystal panel, an RGB luminance detecting means for detecting information on the luminance of each RGB from the RGB signal, and the signal converting means and the backlight based on values generated by the RGB luminance detecting means, respectively. Control means for controlling,
The liquid crystal display device characterized in that the control means changes the chromaticity of the backlight and the value of the RGB signal in conjunction with each other based on the value detected by the RGB luminance detecting means. The liquid crystal display device according to claim 1, wherein the liquid crystal panel is in a VA mode. The liquid crystal display device according to claim 1, wherein the liquid crystal panel is in a TN mode. 2. The liquid crystal display device according to claim 1, wherein the RGB luminance detecting means detects a specific color having a specific RGB luminance ratio.

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