JP2009081647A - Image display device and image display method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To display an excellent color image by keeping white balance from when an image display device is started. <P>SOLUTION: Each of image signals of RGB is input to a gamma curve processing circuit (gamma correcting part) 14 and is subjected to gamma correction so as to adjust white balance. Then, each of the image signals of RGB subjected to the gamma correction is input to a liquid crystal panel control circuit 15 for driving a liquid crystal panel 11, and on the basis of the signal, the liquid crystal panel (display part) 11 is driven. A microcomputer 16 uses data of a plurality of gamma curves stored in a memory 17 to create a gamma curve to be applied at the present time in accordance with an elapsed time from when the power supply of a backlight being a constituent in the image display device 10 is turned on. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image display device that displays a color image and automatically performs white balance adjustment, and an image display method.

  In a color image display device typified by a liquid crystal display, white balance adjustment is important. In white balance, for example, the input RGB signal is not output to the display as it is, but is output after correcting (gamma correction) each of the RGB signals so that white is appropriately expressed. Here, for example, in the case of a liquid crystal display, this white balance is adjusted in accordance with a black body having a color temperature of 12000K. This makes it possible to display a color image that is appropriately reflected in the human eye. In gamma correction, the output luminance is determined according to the input level for each color of RGB, and this relationship (gamma curve) generally shows a characteristic deviating from a linear relationship. An example of the gamma curve is shown in FIG. In this figure, a solid line, a broken line, and a dotted line are gamma curves for the R component, G component, and B component image signals, respectively. By converting the input image signal in accordance with the gamma curve, white can be appropriately displayed, and a good color image can be displayed.

  Regarding the white balance adjustment method, the work of actually determining the characteristics of the gamma curve is the most important and laborious work. For this reason, for example, Patent Document 1 discloses an adjustment in which a test pattern is generated inside a liquid crystal display device, an image of the test pattern is visually confirmed by an adjustment operator, and a parameter (correction coefficient) for specifying a gamma curve is set. A method is described.

  Further, in Patent Document 2, the adjustment operator is made to input a correction coefficient until the chromaticity reaches a target value, and a gamma table is created using the correction coefficient when the chromaticity reaches the target value. An adjustment method for performing gamma correction using a gamma table is described.

As a result, white was properly displayed and a good color image could be displayed.
JP-A-10-133163 JP 2006-325014 A

  However, for example, the characteristics of the image display apparatus may fluctuate with time due to various factors. For example, in a liquid crystal display, the liquid crystal itself does not emit light, and a color image is formed by modulating light from the backlight with the liquid crystal. At this time, the characteristics of the backlight are not constant in time, and the luminance, chromaticity, and the like of the emitted light vary particularly during a certain period after startup.

  Therefore, it has been difficult to keep the white balance optimal from the start.

  The present invention has been made in view of such a situation, and an object thereof is to provide a television system capable of solving the above-described problems.

In order to solve the above problems, the present invention has the following configurations.
An image display device according to the present invention is an image display device in which white balance adjustment in a color image to be displayed is performed by gamma correction for an image signal for each color, and a process from power-on of components of the image display device A storage unit for storing data used in gamma correction for the image signal for each color according to time, and a gamma curve used for gamma correction for the image signal for each color according to the elapsed time are set based on the data. A control unit; a gamma correction unit that performs gamma correction on the image signal for each color using the gamma curve; and a display unit that displays the color image by the image signal after the gamma correction. It is characterized by that.
In the image display device of the present invention, a liquid crystal panel is used for the display unit.
In the image display device of the present invention, the component is a backlight used in the liquid crystal panel.
The image display method of the present invention is an image display method in which white balance adjustment in a color image to be displayed is performed by gamma correction for an image signal for each color, and the elapsed time from the power-on of the components of the image display device. A gamma curve setting step for setting a gamma curve used for gamma correction for the image signal for each color according to the elapsed time from data used in the gamma correction for the image signal for each color according to the gamma curve, and using the gamma curve A gamma correction step of performing gamma correction on the image signal for each color, and a display step of displaying the color image by the image signal after the gamma correction.
In the image display method of the present invention, a liquid crystal panel is used for the display unit for displaying the color image.
In the image display method of the present invention, the component is a backlight used in the liquid crystal panel.

  According to the image display device and the image display method of the present invention, it is possible to maintain white balance from the start-up and display a good color image.

  An image display device according to an embodiment of the present invention is a liquid crystal display device (display). In this liquid crystal display device, video signals for each color of RGB are used, and a color image is displayed by outputting the video signals.

  FIG. 1 is a diagram showing the configuration of the image display apparatus. In the image display device 10, an output signal from the TV tuner, a video signal, and a YPBPR signal (HDTV signal) are input and displayed on the liquid crystal panel 11 as a color image. The input signal is input to the input switching circuit 12, selected and output. This signal is input to the image conversion circuit 13, and images such as yc separation processing (separation of luminance signal and color signal), color space conversion processing, interlace / progressive conversion processing, sharpness, color, contrast, brightness, tint, etc. Processing is performed, and an image signal for each RGB is created.

  The RGB image signals are input to a gamma curve processing circuit (gamma correction unit) 14 where gamma correction is performed so that white balance is adjusted. Thereafter, the RGB image signals subjected to gamma correction are input to a liquid crystal panel control circuit 15 that drives the liquid crystal panel 11, and the liquid crystal panel (display unit) 11 is driven based on the signals. Therefore, a color image based on the RGB image signals is displayed. The liquid crystal panel 11 modulates and displays light from a backlight (not shown) with this signal using liquid crystal.

  Here, the microcomputer (control unit) 16 controls each unit in the above configuration. In particular, the gamma curve used in the gamma curve processing circuit 14 is appropriately set. For this reason, the memory (storage unit) 17 stores a plurality of data used in gamma correction for each color, and the microcomputer 16 sets a gamma curve to be applied to the gamma curve processing circuit 14 from the data. Since the memory 17 needs to store gamma curve data even when the power is turned off, the memory 17 is configured by a non-volatile memory such as a flash memory or a hard disk.

  Hereinafter, an image display method used in the image display device 10, particularly a white balance adjustment method, will be described. First, a white balance adjustment method in a conventional image display method will be described for comparison.

  FIG. 2 is a diagram illustrating a change in white balance (chromaticity of a point to be recognized as white) when the luminance of the backlight varies in a conventional image display device, where the horizontal axis is chromaticity x and the vertical axis is Indicates chromaticity y. Here, each point fluctuates in the direction of the dashed arrow in the figure as the luminance increases. The broken line in the figure shows the locus of white balance when the temperature of the black body fluctuates, the dotted line shows the isothermal line in the black body and the equal deviation line from the black body, and the black body temperature (color temperature) and chromaticity The deviation is shown in the figure. From this result, it can be seen that as the luminance of the backlight fluctuates, the white balance is greatly lost, that is, the color in the color image fluctuates.

  FIG. 3 is a diagram showing the change in white balance when the brightness of the backlight fluctuates when white balance is adjusted at six points in the characteristics of the image display apparatus similar to the data in FIG. It is. Here, changing the luminance of the backlight is performed by controlling the power of the backlight. The white balance adjustment means that gamma correction has been performed to match a 12000K black body at six luminance points. Compared to the case of unadjusted (FIG. 2), the overall fluctuation is small, and the fluctuation is particularly small in the vicinity of the adjusted point. Obviously, if the number of adjustment points is larger than 6, this variation can be further reduced.

  On the other hand, in general, the characteristics of the backlight are not constant for a certain period after the power is turned on, in addition to the fact that the luminance varies by changing the power. FIG. 4 shows the results of measuring the dependence of the luminance of the backlight on the elapsed time after the power is turned on when a cold cathode tube CCFL (Cold Cathode Fluorescent Lamp) is used for the backlight. Similarly, the results of measuring chromaticity x and y are shown in FIG. It takes a considerable amount of time to stabilize both luminance and chromaticity. Further, the luminance is stable in about 5 minutes, while the chromaticity is not yet stable even in about 30 minutes.

  FIG. 6 is a diagram showing changes in white balance during a certain period after power-on when white balance adjustment is performed at six luminance points as shown in FIG. . Dashed arrows in the figure correspond to the passage of time. Here, since the white balance is adjusted in a state in which the characteristics are stable after a lapse of a certain period, the white balance is taken after the lapse of a certain period, and even if the luminance of the backlight is changed in that state, FIG. A constant characteristic is exhibited when the color temperature is around 12000K. In other words, since the backlight characteristics are not stable for a certain period after the backlight is turned on, there is also a deviation in the white balance. White balance. The characteristics of the backlight during this fixed period are different from the stable characteristics after the fixed period has elapsed, as shown in FIGS. For this reason, it is not possible to cope with the problem by simply increasing the number of white balance adjustment points as in the case of FIG.

  Therefore, in the conventional image display method, it is difficult to obtain a good color image during the period until the backlight characteristics are stabilized.

  Here, in the image display method used in the image display device 10, the microcomputer 16 has the memory 17 in accordance with the elapsed time since the power of the backlight, which is a component in the image display device 10, is turned on. A gamma curve to be applied at present is created using data of a plurality of stored gamma curves. That is, a gamma curve setting process for selecting or creating a gamma curve having a characteristic for canceling the white balance deviation in the liquid crystal panel shown in FIG.

  Actually, gamma curves used for canceling the characteristics shown in FIG. 6 are shown in FIGS. Here, FIG. 7A is an R component, (b) is a G component, and (c) is a gamma curve for an image signal of a B component. In each characteristic, the solid line is immediately after power-on, and the broken line is 10 minutes later. A dash-dot line is a gamma curve used after 20 minutes and a dotted line is used after 30 minutes. Although these data are memorize | stored in the memory 17, the aspect is arbitrary, You may memorize | store as a parameter expressing these characteristics. In this characteristic, the gamma curve is set for each RGB image signal and for each elapsed time since the backup power is turned on. Further, in the above characteristics, when the input level is fixed at 24, FIGS. 8A to 8C show the elapsed time dependence of the output luminance of each RGB image signal. The change according to the elapsed time changes in the direction of increasing output luminance for the same input level in the R component (a) and the B component (c), whereas in the G component (b). Conversely, the output luminance decreases. Thus, the gamma curve is set for each color of RGB and for each elapsed time.

  In this case, the microcomputer 16 sets the gamma curve used in the gamma curve processing circuit 14 according to the elapsed time in the stored gamma curve. When the gamma curve data is used, the gamma curve data may be switched to the data shown in FIG. 7 when 0 minutes, 10 minutes, 20 minutes, and 30 minutes have elapsed. For example, the memory 17 stores gamma curve data at intervals of 10 minutes, but the gamma curve data used in the gamma curve processing circuit 14 can be set every minute. In this case, the data of the gamma curve after 0 to 10 minutes (1 minute, 2 minutes, 3 minutes, etc.) is calculated by the microcomputer 16 interpolating from the data after 0 minutes and the data after 10 minutes. And can be output to the gamma curve processing circuit 14.

Thereafter, the gamma curve processing circuit 14 applies gamma correction for each RGB to each RGB image signal to perform gamma correction (gamma correction step). The corrected RGB image signal is input to a liquid crystal panel control circuit 15 that drives the liquid crystal panel 11, and the liquid crystal panel 11 displays the color image as an output (display process). In this color image, an appropriate white balance is maintained even when the backlight characteristics are not stable immediately after the power is turned on.
Therefore, a good color image can be obtained.

  Note that the gamma curve shown in FIG. 7 is after 0 minutes, 10 minutes, 20 minutes, and 30 minutes, but actually stores data at intervals of 1 minute, for example. The data corresponding to the elapsed time can be selected. Thereby, white balance adjustment with higher accuracy can be performed. However, when this interval is short, the memory 17 needs to store a large amount of data, so a large capacity memory is required as the memory 17. Therefore, it is only necessary to store gamma data at an appropriate time interval according to the capacity of the memory 17.

  Further, the data interval of the gamma curve does not need to be equal, and the interval can be shortened at a portion where the variation rate with respect to the elapsed time is large, and the interval can be increased at a portion where the variation rate is small. Thereby, the amount of data stored in the memory 17 can be reduced, and white balance adjustment with high accuracy can be performed. Even when the fluctuation rate is large, if the fluctuation is linear, an appropriate gamma curve can be accurately calculated by the above-described interpolation. And storage area can be saved.

  The gamma curve data for each elapsed time can be stored in the memory 17 by any method. For example, the user measures the change in chromaticity from when the backlight is turned on using a chromaticity system, and in this case, the user creates gamma curve data necessary to maintain white balance. May be input to the image display device 10 using a keyboard or the like, and the microcomputer 16 may store this in the memory 17.

  Further, it is necessary for the user to input chromaticity variation data from when the backlight is turned on to the image display device 10 in the same manner as described above, and to automatically maintain the white balance using this data. Gamma curve data can also be calculated and stored in the memory 17.

  In addition, when the characteristics of chromaticity variation from when the backlight is turned on are known in advance, the gamma curve data can be set in the memory 17 in advance. In this case, the memory 17 may be a ROM (Read Only Memory).

  As described above, the microcomputer 16 can cause the gamma curve processing circuit 14 to perform appropriate white balance adjustment immediately after the backlight is turned on by referring to the memory 17.

  Therefore, in the image display device 10 and the image display method, the white balance is appropriately adjusted immediately after the backlight is turned on, and a good color image can be displayed.

  In the above example, the case where the image display device is a liquid crystal display has been described. However, the present invention is not limited to this, and in an image display device that requires a certain time from the power-on to the stabilization of the characteristics in the color image. Similarly, the present invention can be applied. In the above example, the case where the characteristics of the backlight are not stabilized within the predetermined period is described. However, the present invention can also be applied to the case where the characteristics of the color image are not stable because the characteristics of other components are not stable. For example, in a CRT (Cathode Ray Tube), the characteristics of the CRT tube itself may not be stable. If the characteristics of the component that affects the characteristics of the color image are not stable immediately after the power is turned on, the same processing as described above can be performed according to the elapsed time from the time when the power of the component is turned on.

  In addition, although an example in which gamma correction is performed for RGB three-color signals has been described, the same applies when other color systems such as CMY are used.

It is a figure which shows the structure of the image display apparatus which is embodiment of this invention. It is a figure which shows the fluctuation | variation of the chromaticity of the point which should be recognized as white when a brightness | luminance changes when white balance adjustment is not performed appropriately. It is a figure which shows the fluctuation | variation of the chromaticity of the point which should be recognized as white when a brightness | luminance changes when white balance adjustment is performed in 6 points | pieces of a brightness | luminance. It is a figure which shows the fluctuation | variation of the brightness | luminance in a liquid crystal panel after the power supply of a backlight is turned on. It is a figure which shows the fluctuation | variation of chromaticity in the liquid crystal panel after the power supply of a backlight is turned on. It is a figure which shows the fluctuation | variation of the white balance from the time of power-on of a backlight. It is an example of the gamma curve according to the elapsed time after the power supply of a backlight was turned on. It is a figure which shows the elapsed time dependence of an output voltage when an input level is fixed in a gamma curve. It is an example of a gamma curve used for gamma correction in order to maintain white balance.

Explanation of symbols

10 Image display device 11 Liquid crystal panel (display unit)
12 Input switching circuit 13 Image conversion circuit 14 Gamma curve processing circuit (gamma correction unit)
15 LCD panel control circuit 16 Microcomputer (control unit)
17 Memory (storage unit)

Claims (6)

An image display device in which white balance adjustment in a color image to be displayed is performed by gamma correction for an image signal for each color,
A storage unit for storing data used in gamma correction for the image signal for each color according to the elapsed time from the power-on of the components of the image display device;
From the data, a control unit for setting a gamma curve used for gamma correction for an image signal for each color according to the elapsed time;
A gamma correction unit that performs gamma correction on the image signal for each color using the gamma curve;
A display unit for displaying the color image by the image signal after the gamma correction;
An image display device comprising:   The image display apparatus according to claim 1, wherein a liquid crystal panel is used for the display unit.   The image display device according to claim 2, wherein the component is a backlight used in the liquid crystal panel. An image display method for performing white balance adjustment in a color image to be displayed by gamma correction for an image signal for each color,
A gamma curve used for gamma correction for the image signal for each color according to the elapsed time from data used in the gamma correction for the image signal for each color according to the elapsed time since the power-on of the components of the image display device Gamma curve setting process,
A gamma correction step for performing gamma correction on the image signal for each color using the gamma curve;
A display step of displaying the color image by the image signal after the gamma correction;
An image display method comprising:   The image display method according to claim 4, wherein a liquid crystal panel is used for the display unit that displays the color image. The image display method according to claim 5, wherein the component is a backlight used in the liquid crystal panel.