JPH05224641A - Video display device - Google Patents

Abstract

PURPOSE:To eliminate influence on a part different from a main video signal existing on a screen and to always realize optimum video control. CONSTITUTION:The peak level, the average level, the black level and the pedestal level of a brightness signal obtained from a video signal are detected in respective detection circuits 5, 6 and 7 in every specified period. In the case of detecting them, the screen is divided into two or more areas such as a central part and a peripheral part in a screen area setting circuit 4, and the detection is executed in the area except the peripheral part area or the detection is executed by making weighting in the central part area larger than in the peripheral part area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device suitable for controlling an image displayed on, for example, a liquid crystal display panel or a cathode ray tube (hereinafter abbreviated as CRT). ..

[0002]

2. Description of the Related Art Conventionally, a video display device in which a transmissive or projection type liquid crystal panel is used for video display can obtain a bright display. Therefore, as a display device replacing a CRT, a direct-view type liquid crystal television or a projection type liquid crystal display device. It is being used in projection devices and the like.

However, since the liquid crystal panel has a narrower range of input voltage capable of expressing gradation as compared with the CRT, there is a problem that the image display device is apt to cause blackout or whiteout. That is, the electro-optical characteristics of the liquid crystal are as shown in, for example, FIG. 4 in terms of the relationship of the relative transmittance with respect to the applied voltage. As shown in FIG. 4, the range in which the liquid crystal changes the relative transmittance with respect to the applied voltage, that is, the range of the applied voltage effective for changing the gradation is the maximum V _sat to the minimum V
_This is a voltage range indicated by a symbol ΔV between _th . As can be seen from the example of FIG. 4, the range ΔV of the input voltage is 2
Since the range of the number (V) such as (V) is narrow and it is difficult to control the gradation of each pixel in the liquid crystal panel as desired, the pixel tends to become black or white, which causes black. Crushing and whitening are likely to occur.

Conventionally, in order to deal with the above problems,
In a video display device having a liquid crystal panel, contrast control is performed on the brightness signal by automatic gain control (abbreviated as AGC), or gradation is controlled according to the brightness level of the brightness signal obtained from the input video signal. There are some that perform video control to improve the sex. Further, some image display devices having a CRT also perform image control in order to address the same problem as the liquid crystal.

[0005]

However, in the conventional image display device including the liquid crystal and the CRT, the image signal detected as the basis of the image control is not intended by limiting the screen area. A part different from the main image on the screen, such as a movie subtitle supermarket,
Character information such as telop or aspect ratio is 1
When a 6: 9 landscape screen is displayed on a television screen with a normal aspect ratio, the presence of a black solid portion at the top and bottom causes the image level (luminance level) of that portion to be the peak level or average of the main image. There was a problem that the level was affected and proper video control was not performed.

In addition, on a screen in which the change width of the image control values such as the contrast value, the bright value and the gamma value of the image is large, particularly, in the screen where the image contents are largely switched,
There has been a problem that the display screen looks unnatural.

The present invention has been made in view of the above-mentioned problems, and it is possible to eliminate the influence of a portion different from the main image existing on the screen so that the optimum image control is always performed. An object of the present invention is to provide a video display device that can be used.

[0008]

The present invention has been made in view of the above points, and obtains a luminance signal of an input video signal, and obtains a peak level, an average level and a black level of the obtained luminance signal. , And a detection unit for detecting the pedestal level for each predetermined period, and based on the data of each detected level, calculate a video control value such as a contrast value, a bright value, and a gamma value of the image. In a video display device having a video control value calculation means for outputting, when detecting the peak level, the average level, and the black level of the luminance signal by the detection unit,
The screen is divided into two or more areas of the central portion and the peripheral portion, and the detection is performed in an area excluding the peripheral area, or the weighting of the central area is made larger than that of the peripheral area to perform the detection. The above-mentioned problems are solved by providing means for carrying out the above.

Further, according to the present invention, the image control value output from the image control value calculating means is used for averaging the output image control value before the previous time and the output image control value this time. Means may be provided to reduce the range of change in the image control value.

[0010]

In the present invention, the peak level of the luminance signal,
When detecting the average level and the black level, the screen is divided into two or more regions of the central portion and the peripheral portion, and the detection is performed in the region excluding the peripheral region, or The weighting is made larger than that in the peripheral area to perform the detection. Therefore, it is possible to remove the influence of a portion different from the main image existing on the screen (character information such as movie subtitles and text telops, or a black and white solid portion of a landscape screen with an aspect ratio of 16: 9, etc.). Therefore, optimum video control is always possible.

Further, in the present invention, the variation range of the video control value is calculated by averaging the output video control value of 1 or more before the previous time and the current output video control value with respect to the output video control value. If alleviated, the output value at the time of switching the output of each image control value is alleviated, so that smooth image control becomes possible.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a video display device according to an embodiment of the present invention. This image display device displays an image based on an input image signal (also referred to as a video signal) on the liquid crystal panel 21, and eliminates the influence of a part different from the main image on the screen to perform optimum image control. It was something that I was supposed to do.

In the video display device shown in FIG. 1, a video signal of an analog signal input to a video input terminal is transmitted to an analog / digital (A / D) converter 1. The A / D converter 1 converts the transmitted video signal into a digital signal of, for example, 8 bits by sampling and quantizing the transmitted video signal, and the digital video signal is converted into a luminance signal Y /
It is input to the color signal C separation circuit (Y / C separation circuit) 2. The Y / C separation circuit 2 separates the input digital video signal into a digital luminance signal Y and a digital color signal C. The separated luminance signal Y and color signal C are input to the video signal processing circuit 3, and the video signal processing circuit 3 inputs the input luminance signal Y and color signal C into red (R), green (G), and blue. The signal of (B) is demodulated and the R, G, B signals are input to the R, G, B control circuit 20. Also, the video signal processing circuit 3
The horizontal sync signal H · SYNC and the vertical sync signal V · SYNC are obtained based on the input luminance signal Y and the color signal C and input to the screen area setting circuit 4.

On the other hand, the digital luminance signal Y is input to the peak value detection circuit 5, the average value detection circuit 6 and the black value detection circuit 7 via the screen area setting circuit 4. Each of the detection circuits 5, 6 and 7 detects the peak level, the average level and the black level (or the black peak level) of the input luminance signal Y, and inputs the detected value data to the correction calculation circuit 9. The luminance signal Y output from the Y / C separation circuit 2 is input to the pedestal level detection circuit 8 as it is, and the pedestal level detection circuit 8 detects the pedestal level from the input luminance signal Y to detect detected pedestal data. Is input to the correction calculation circuit 9. Based on the input pedestal level data, the correction calculation circuit 9 performs a correction calculation to remove the sync signal component from the peak level, average level, and black level data to obtain a true video signal level, and corrects each level data to each data. It is stored in the registers 10, 11, and 12.

Here, the screen area setting circuit 4 determines a brightness signal within a preset screen area range based on the horizontal synchronizing signal H.SYNC and the vertical synchronizing signal V.SYNC, a peak level detecting circuit 5, and an average level. Input to the detection circuit 6 and the black level detection circuit 7. Therefore, the peak level, the average level, and the black level of the luminance signal are detected in the setting screen area.

Although various areas to be detected can be considered, as shown in FIG. 2A, a screen (effective area input as a video signal) 25 is divided into a peripheral portion 25B and other areas 25A. Then, the area 25A is set as the detection area.
Further, as shown in FIG. 2B, the predetermined detection area 26 is divided into a central portion 26A and a peripheral portion 26B, and these respective portions are weighted for detection. This weighting is for example in the center:
The peripheral part can be a ratio of 8: 2.

Next, each of the registers 10, 11 and 12
Inputs the accumulated peak level, average level, and black level data to the video control arithmetic circuit 13.
The arithmetic circuit 13 calculates an optimum video control value (contrast value, bright value, gamma value in the embodiment) for each input video signal from each input data, and averages these control values. , 19 to the R, G, B control circuit 20. The R, G, B control circuit 20 controls the R, G, B luminance signals in accordance with the input control value signal to display an image of the video signal on the liquid crystal panel 21.

The video control values output from the averaging circuits 17, 18 and 19 are output value registers 14 and 1, respectively.
5 and 16 are stored and averaged with the next video control values of the output of the arithmetic circuit 13. That is, each video control value of the present output of the arithmetic circuit 13 is averaged with the video control signal previously input to the R, G, B control circuit 20 before, and is input to the control circuit 20. .. By repeating this averaging process every time the video control value is calculated, the person who sees the change in the video control value when the output is changed (when the output screen is switched, etc.) is shown by the broken line in FIG. It is naturally relieved to the level that the eye feels naturally.
In FIG. 3, an output example of the averaging processing circuits 17, 18 and 19 when the video control value changes from 0 to FFH is shown by a broken line, and for comparison, each of the registers 14 and 1 is used.
5, 16 and the averaging processing circuits 17, 18, and 19 are not provided and the output values are not relaxed.

In the above embodiment, the image control values of the previous time and the present time are averaged in order to relax the image control values, but in the present invention, the averaging process is performed by such a method. It is not limited to. For example, the video control values of the previous time and the time before the last time (two times before) and this time are averaged, or three times before and this time, or before n.
The number of times (n is an arbitrary natural number) and the current image control value can be averaged.

[0021]

As described above, according to the image display device of the present invention, when the peak level, the average level, and the black level of the luminance signal are detected, two or more areas of the central portion and the peripheral portion of the screen are displayed. Divided into, the detection is performed in a region excluding the peripheral region, or by performing the detection by increasing the weight of the central region compared to the peripheral region, a portion different from the main image, for example, The effects of subtitles in movies, text telops for TV broadcasts, and black solid areas above and below the landscape screen can be eliminated, and optimal video control can always be performed. Further, by mitigating the output switching of each control value, an excellent effect that the video control can be performed in a more natural form can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a video display device according to an embodiment of the present invention.

FIG. 2 is a plan view showing a screen area for detecting the level of a video signal in the video display device of FIG.

FIG. 3 is a diagram showing an example of changes in a video control value of the video display device of FIG.

FIG. 4 is a diagram showing an example of electro-optical characteristics of the liquid crystal panel of FIG.

[Explanation of symbols]

 1 analog / digital converter 2 luminance signal Y / color signal C separation circuit 3 video signal processing circuit 4 screen area setting circuit 5 peak level detection circuit 6 average level detection circuit 7 black level detection circuit 8 pedestal level detection circuit 9 correction calculation circuit 10 Peak level data register 11 Average level data register 12 Black level data register 13 Video control arithmetic circuit 14 Previous contrast output value register 15 Previous bright output value register 16 Previous gamma output value register 17, 18, 19 Averaging circuit 20 Red (R ), Green (G), blue (B) control circuit 21 LCD panel

Claims (2)

[Claims] 1. Obtaining a luminance signal of an input video signal,
The detection unit for detecting the peak level, the average level, the black level, and the pedestal level of the obtained luminance signal for each predetermined period, and the contrast value and the bright value of the image based on the data of each detected level. , And a video control value calculating means for calculating and outputting a video control value such as a gamma value, wherein a peak level, an average level, and a black level of the luminance signal by the detection unit are detected. When the detection is performed, the screen is divided into two or more areas of the central portion and the peripheral portion, and the detection is performed in an area excluding the peripheral area, or the weighting of the central area is compared with the peripheral area. A video display device comprising means for increasing the size and performing the detection. 2. The method according to claim 1, further comprising: for averaging the video control value output from the video control value calculation means, the output video control value before the previous time and the output video control value this time. An image display device, characterized in that it is provided with means to reduce the range of change of the image control value.