JP2008083439A - Liquid crystal display device and method for adjusting white balance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To keep a uniform white balance even when brightness of back-light changes. <P>SOLUTION: A variable n=0, and max=32 are set (S1), and the light control level of the back-light is set to n=1 (S2). Then, white balance adjustment is carried out at the light control level (S3), and an adjustment value is stored as the adjustment value for the light control level n (S4). Then, it is discriminated whether the present light control level setting n is n=Max (32) (S5). When the setting is not n=Max, the white balance adjustment is carried out again (S3) with the light control level set to n+1 (S6). When the present light control level setting n is equal to Max, processing is finished since the white balance adjustment is carried out for all the light control levels. When the light control level is changed when a user actually views, a video signal is corrected using the white level adjustment value stored according to the light control levels. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device and a white balance adjustment method, and more particularly to a technique for performing white balance adjustment in accordance with the light emission luminance of a backlight in a liquid crystal display device capable of variably setting the light emission luminance of a backlight.

  In a display device such as a television receiver, white balance adjustment is performed in the manufacturing process. Here, the color development of each of the RGB colors is adjusted so that an appropriate white color can be displayed on the display screen.

  Regarding white balance adjustment technology, for example, Patent Document 1 discloses a color balance adjustment device in which white balance of a liquid crystal color display is determined in advance by the color tone of a backlight so that white balance can be easily adjusted. Here, a backlight system of RGB independent light sources is used, and white balance is achieved by changing the output of each RGB.

  In addition, in Patent Document 2, in the implementation of various adjustments of the display device, luminance variation caused by the light source at the time of light irradiation from the light source incorporated in the product toward the liquid crystal panel is canceled, and the light intensity from the light source is reduced. A technique for realizing a high-quality display device by accurately setting gamma correction even in an abnormal state is disclosed.

Patent Document 3 discloses a display device capable of displaying an image so that a good contrast can be obtained without increasing power consumption and bit accuracy for signal processing. In this display device, two LUTs are used for gamma correction.
JP-A-1-179913 Japanese Patent Laid-Open No. 11-316577 JP-A-2005-260329

  In a liquid crystal display device such as a liquid crystal television, a backlight for illuminating a liquid crystal panel is used. Then, image display is performed by modulating illumination light from the backlight with a liquid crystal panel. A fluorescent tube using a cold cathode tube is generally used for the backlight. In addition, a backlight using an LED and a hybrid type backlight using both a fluorescent tube and an LED are also known.

  In a liquid crystal display device having a backlight as described above, when adjusting the white balance during the production process, the optimal brightness is usually obtained with the backlight brightness set to the highest level. White balance adjustment is performed.

  On the other hand, in a liquid crystal display device such as a liquid crystal television, the light emission luminance of the backlight can be variably set according to user settings. For example, the user can adjust the luminance of the backlight so as to obtain an arbitrary brightness by using a dimming mode prepared for the liquid crystal television. In this case, for example, a plurality of levels of brightness are preset as the dimming level of the backlight, and an arbitrary level of brightness can be set by a user operation. Alternatively, a brightness sensor that detects the brightness around the liquid crystal display device may be used to automatically adjust the light emission luminance of the backlight according to the brightness around the device.

  As described above, in the production process, the white balance is adjusted with the backlight emission luminance set to the highest level, but when the backlight emission luminance changes according to user operations, etc., the backlight is adjusted. The color of itself changes. As a result, there is a problem that the white balance is changed and the optimum white chromaticity cannot be obtained, and the image display color is changed. Such a problem is not solved in each of the above patent documents.

  The present invention has been made in view of the above circumstances, and in a liquid crystal display device having a backlight, a uniform white balance is obtained even when the brightness of the backlight changes due to a change in the dimming level setting or the like. It is an object of the present invention to provide a liquid crystal display device and a white balance adjustment method that can be used.

  In order to solve the above problems, a first technical means of the present invention is a liquid crystal display device including a liquid crystal panel that displays an image by illumination light from a backlight, and the liquid crystal display device is preset in the liquid crystal display device. The adjustment value used for adjusting the white balance is changed in accordance with the light emission luminance level of the backlight, and the white balance is automatically adjusted based on the adjustment value.

  According to a second technical means, in the first technical means, the liquid crystal display device holds in advance adjustment values for a plurality of backlight emission luminance levels that can be set in the liquid crystal display device. When it changes, the white balance is automatically adjusted by extracting an adjustment value corresponding to the changed light emission luminance level.

  According to a third technical means, in the second technical means, the plurality of levels are all light emission luminance levels that can be set in the liquid crystal display device.

  According to a fourth technical means, in any one of the first to third technical means, the adjustment value described above includes a gain and a cutoff of a gamma correction characteristic that defines a gradation of the output video signal with respect to a gradation of the input video signal. This is an adjustment value obtained by adjusting.

  According to a fifth technical means, in any one of the first to third technical means, the adjustment value is an adjustment value of table data of a gamma table that defines a gradation of an output video signal with respect to a gradation of an input video signal. It is characterized by being.

  A sixth technical means is a method for adjusting white balance in a liquid crystal display device including a liquid crystal panel that displays an image by illumination light from a backlight, wherein the liquid crystal display device has a backlight set in advance in the liquid crystal display device. The adjustment value used for adjusting the white balance is changed in accordance with the light emission luminance level, and the white balance is automatically adjusted based on the adjustment value.

  According to the present invention, in a liquid crystal display device provided with a backlight, it is possible to obtain a uniform white balance even when the luminance of the backlight changes due to a change in the light control level setting or the like.

  The liquid crystal display device according to the present invention can achieve a uniform white balance at different light emission luminance levels that can be set by the liquid crystal display device by changing the white balance adjustment value according to the light emission luminance of the backlight. It becomes like this.

FIG. 1 is a block diagram for explaining a configuration example of a liquid crystal display according to the present invention, and shows an example in which the liquid crystal display device of the present invention is applied to a liquid crystal television. The liquid crystal display device 1 includes a device main body 10 and a display device 20. A remote control device 30 is provided as an accessory.
In the liquid crystal display device 1, the tuner 11 receives a video signal input from an RF input terminal. The A / D converter 12 A / D converts the video signal received by the tuner or the video signal input from the video input terminal. The video processing unit 13 executes video processing of the A / D converted video signal, for example, color correction processing, size change processing, FRC processing, synchronization detection processing, OSD display processing, and the like as necessary, and scaling 14 The scaling process is performed according to the resolution of the display device.

  The white balance adjustment unit 15 receives the scaled video signal and automatically adjusts the white balance of RGB using an adjustment value corresponding to the light emission luminance of the backlight 22. Thereby, even if the light emission luminance of the backlight 22 changes, a uniform white balance can be obtained. The white balance adjustment value is set in accordance with each emission luminance level of the backlight 22 in the production process of the liquid crystal display device, and is held in a nonvolatile memory, for example, the EEPROM 18.

  The microcomputer 17 is a control unit that controls the entire apparatus. The microcomputer 17 sets gamma correction data based on the adjustment value held in the EEPROM 18 in the white balance adjustment unit 15 according to the light emission luminance level of the backlight 22 included in the display device 20. The white balance adjustment unit 15 performs gamma correction on the RGB input video signal using the set data.

The display device 20 includes a display device 21 using a liquid crystal panel and a backlight 22. The display device 21 displays an image by driving the liquid crystal according to the image signal optimally gamma corrected by the white balance adjustment unit 15.
The backlight 22 includes a drive circuit and a light emitter, and the light emitter is driven by the drive circuit according to a command from the microcomputer 17. A general fluorescent tube (CCFL) or LED can be applied as the light emitter. Moreover, the hybrid type which used fluorescent tube and LED together may be used.

In the liquid crystal display device, the light emission luminance of the backlight 22 can be changed according to an operation signal received from the remote control light receiving unit 16 or a predetermined operation input to a hardware key group or a touch panel of the main body (not shown). .
In the case where the backlight emission luminance is changed according to the brightness around the apparatus, the microcomputer 17 controls the emission luminance of the backlight 22 according to the brightness detection result by a brightness sensor (not shown).
When the light emission luminance of the backlight 22 is changed by these processes, the microcomputer 17 reads an adjustment value corresponding to the light emission luminance level at this time from the EEPROM 18 and sets it in the white balance adjustment unit 15.

  FIG. 2 is a diagram for explaining white balance adjustment processing in the display device of the present invention. In the present invention, as described above, an adjustment value for adjusting the white balance of the video signal is set in accordance with the light emission luminance level of the backlight that can be set by the liquid crystal display device. As a white balance adjustment method applied to the present invention, an R / G / B gain and a cutoff value are set for each dimming level, and these values are stored and retained in a nonvolatile memory as white balance adjustment values. To.

  For example, it is assumed that the light control level of the backlight of the liquid crystal display device has 33 levels (+16 to −16). In an embodiment according to the present invention, white balance adjustment values are set for all 33 stages. In this example, the gamma correction characteristic (A) for each RGB is held by default in the white balance adjustment device. Then, with respect to the default gamma correction characteristic (A), the gain and the cut-off value are adjusted so that the white balance is optimal, and the adjusted gamma correction characteristic (B) is obtained. The white balance adjustment at this time is performed for each of the RGB colors, and the RGB output balance is set.

  Then, the adjusted cutoff and gain values are stored in a non-volatile memory (eg, EEPROM 18) of the liquid crystal display device in association with the luminance setting level of the backlight at that time. Such white balance adjustment is performed for each dimming level, and white balance adjustment values at all dimming levels are stored in the nonvolatile memory of the liquid crystal display device.

  At the time of actual user viewing, the microcomputer 17 of the liquid crystal display device of FIG. 1 reads the cutoff and gain values corresponding to the dimming level of the backlight 22 at that time from the EEPROM 18, and gamma correction characteristics based on these data Is set in the white balance adjustment unit 15. In accordance with the set gamma correction characteristic, the white balance adjusting unit 15 applies gamma correction to the input video signal and outputs it. The gamma correction characteristic defines the gradation of the output video signal relative to the gradation of the input video signal, and is determined for each of RGB.

FIG. 3 is a diagram for explaining another example of white balance adjustment processing in the display device of the present invention. As the white balance adjustment method shown in FIG. 3, the data of the gamma table provided independently by R / G / B is adjusted for each light control level, and the gamma table data is stored and held as a white balance adjustment value. To do.
In this example, the device for adjusting white balance stores gamma table data for each RGB by default. Then, the table data is adjusted with respect to the gamma correction characteristic (A) obtained from the default gamma table data, and the adjusted gamma correction characteristic (B) is obtained. The adjusted gamma table data is stored and held in the nonvolatile memory of the liquid crystal display device in association with the light control level of the backlight at that time. Such white balance adjustment is performed for each dimming level of the backlight, white balance adjustment is performed for all dimming levels, and the adjustment value is stored.

  In the actual white balance adjustment during viewing, the microcomputer 17 of the liquid crystal display device in FIG. 1 reads the adjustment value of the gamma table data corresponding to the backlight luminance setting level at that time from the EEPROM 18 and uses it from these data. Power gamma table data is generated and set in the white balance adjustment unit 15. The white balance adjustment unit 15 adds the gamma correction to the input video signal using the set gamma table data and outputs it.

In the above example, R / G / B white balance adjustment values are performed for every dimming level, and these adjustment values are stored in the nonvolatile memory of the liquid crystal display device. Instead of the light level, white balance adjustment values may be stored and held for a plurality of light control levels that can be set in the liquid crystal display device.
When the dimming level is set during actual user viewing, if there is an adjustment value corresponding to the dimming level, the white balance can be adjusted using the adjustment value. If there is no adjustment value corresponding to the set dimming level, white adjustment is performed using the adjustment value corresponding to the dimming level closest to the current dimming level. Adjust the balance.

  In the above example, the example in which the adjustment value of the white balance is stored according to the dimming level that changes stepwise has been described. However, the dimming level can be changed (dimming) steplessly within a predetermined range. You may comprise as follows. In this case, the stepless dimming level is divided into a plurality of dimming levels at a predetermined interval, and the above example is applied to the multistage dimming levels to adjust the white balance for each dimming level. Can be done.

Next, an example of a white balance adjustment method applicable to the above embodiment will be described. In the production process of the liquid crystal display device, the dimming level of the first backlight among the dimming levels of the backlight of the plurality of stages of the liquid crystal display device is set.
Then, an image of a predetermined gradation is displayed on the screen of the liquid crystal display device, the display screen is detected by a sensor, and coordinates x, y on the CIE chromaticity diagram are measured. An operator who performs white balance adjustment in the process adjusts the image quality based on the measured coordinate value so that the coordinate value becomes a predetermined target value.

  A target chromaticity is determined for the liquid crystal display device. That is, the target coordinate values x and y are determined for the video of the predetermined gradation. At the time of white balance adjustment at this time, cut-off and gain adjustment are performed for each of RGB so as to obtain target coordinate values x and y in an image of a predetermined gradation.

For example, as an example, a slightly dark gray (for example, 128 gradation when the image gradation is 8 bit 256 gradation) and a light gray (for example, 200 gradation) are displayed on the adjustment screen, and a slightly dark gray display screen is displayed. Adjust the cutoff value at. Next, the light gray is displayed and the gain value is adjusted. When the cutoff is adjusted, the output value of the default gamma characteristic at that gradation moves, the gradient of the gamma characteristic changes at gradations 128 and below, and the output value translates at gradations above 128. A predetermined upper limit is set for the output value.
When the gain is adjusted, the output value of the gamma characteristic at that gradation moves, and the slope of the gamma characteristic changes accordingly. At this time, the cutoff value already set does not change, and the slope changes between the gradations 128 and 200. In this way, the gamma correction characteristic can be adjusted by adjusting the cutoff and the gain.

  Further, when adjusting the gamma table data, the gamma table data is adjusted for each of the slightly dark gray and the light gray. Here, the output gradation with respect to the input gradation is adjusted for each RGB at each dimming level. For example, when the light control level is +16, the R output gradation for the input gradation 128 is set to 120, the G output gradation is set to 128, the B output gradation is set to 125, and the R for the input gradation 200 is set. The output gradation of 195 can be determined such as 195, the output gradation of G is 200, the output gradation of B is 200, and so on. For example, the target gamma correction characteristics can be obtained by linearly interpolating these two points of gamma table data. Such adjustment processing is similarly performed for other dimming levels.

  The above example is an example of white balance adjustment. The present invention is characterized by having white balance adjustment value data for each of a plurality of dimming levels of the backlight, and does not limit the white balance adjustment method itself, but a conventionally known method or novel adjustment. The method can be applied as appropriate.

FIG. 4 is a flow chart for explaining an example of the white balance adjustment method according to the present invention, and shows an example of white balance adjustment value setting processing for each light control level. Here, it is assumed that the dimming level of the backlight that can be set in the liquid crystal display device is 33 levels from 0 to 32.
First, variables n = 0 and max = 32 are set (step S1). Then, the backlight dimming level setting n = 1 is set (step S2), and the white balance is adjusted at the dimming level (step S3). As described above, the white balance adjustment can be executed by the cutoff with respect to the default gamma correction characteristic, the gain adjustment, the gamma table data adjustment, and the like.

  Then, the white balance adjustment value at that time is stored as a dimming level n adjustment value (step S4). Then, it is determined whether or not n = Max (= 32) for the current dimming level setting n (step S5). If n is not Max, the dimming level is set to n + 1 (Step S6), and white balance adjustment is performed again (Step S3). If the current dimming level setting n is equal to Max, the white balance adjustment has been executed for all the dimming levels, and the process ends.

  In this way, the white balance is adjusted for all the light control levels that can be set by the liquid crystal display device, and the adjustment value is stored in the liquid crystal display device. Here, when white balance adjustment is performed for a plurality of light control levels instead of all light control levels, the light control level is set to “n + 2” in step S6, for example, for every other light control level. White balance adjustment is possible.

FIG. 5 is a flowchart for explaining another example of the white balance adjustment method according to the present invention, and shows an example of processing when the dimming level setting is changed while the user is actually viewing.
First, when the dimming level setting of the backlight is changed from n to n ′ by processing based on a predetermined user operation or brightness sensor (step S11), the microcomputer of the liquid crystal display device uses the dimming level setting n ′. The white balance adjustment value is acquired from a non-volatile memory (EEPROM, etc.) (step S12).
Then, the microcomputer reflects the acquired adjustment value on the actual white balance adjustment value (step S13). Here, as in the above example, the cutoff value, gain value, and gamma table data stored in association with the light control level are acquired as adjustment values, and the gamma correction characteristics based on these adjustment values are stored in the white balance adjustment unit. Set to have the video signal corrected. Then, the dimming setting of the backlight is set to the level n ′ (step S14).

It is a block diagram for demonstrating the structural example of the liquid crystal display which concerns on this invention. It is a figure for demonstrating the white balance adjustment process in the display apparatus of this invention. It is a figure for demonstrating the other example of the white balance adjustment process in the display apparatus of this invention. It is a flowchart for demonstrating an example of the white balance adjustment method by this invention. It is a flowchart for demonstrating the other example of the white balance adjustment method by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device, 10 ... Apparatus main body part, 11 ... Tuner, 12 ... A / D converter, 13 ... Image processing part, 14 ... Scaling, 15 ... White balance adjustment part, 16 ... Remote control light-receiving part, 17 ... Microcomputer, 18 ... EEPROM, 20 ... display device, 21 ... display device, 22 ... backlight, 30 ... remote control device.

Claims (6)

  In a liquid crystal display device including a liquid crystal panel that displays an image by illumination light from a backlight, the liquid crystal display device adjusts a white balance according to a light emission luminance level preset in the liquid crystal display device. A liquid crystal display device characterized by changing an adjustment value used for the adjustment and automatically adjusting the white balance based on the adjustment value.   2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device holds the adjustment values in advance for a plurality of levels of light emission luminance levels of a backlight that can be set in the liquid crystal display device, and the light emission luminance level. A liquid crystal display device that automatically adjusts the white balance by extracting an adjustment value corresponding to the changed light emission luminance level when the brightness changes.   3. The liquid crystal display device according to claim 2, wherein the plurality of levels are all light emission luminance levels that can be set in the liquid crystal display device.   4. The liquid crystal display device according to claim 1, wherein the adjustment value is an adjustment obtained by adjusting a gain and a cutoff of a gamma correction characteristic that defines a gradation of an output video signal with respect to a gradation of an input video signal. A liquid crystal display device characterized by having a value.   4. The liquid crystal display device according to claim 1, wherein the adjustment value is an adjustment value of table data of a gamma table that defines a gradation of an output video signal with respect to a gradation of an input video signal. A characteristic liquid crystal display device.   A method for adjusting white balance in a liquid crystal display device including a liquid crystal panel that displays an image by illumination light from a backlight, the liquid crystal display device having a light emission luminance level set in advance in the liquid crystal display device A white balance adjustment method, wherein an adjustment value used for adjusting the white balance is changed according to the white balance, and the white balance is automatically adjusted based on the adjustment value.

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