JP2969408B2 - Video display device - Google Patents

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, an image display device using a transmission type or projection type liquid crystal panel for image display can provide a bright display. Therefore, as a display device instead of a CRT, a direct-view type liquid crystal television or a projection type liquid crystal panel is used. It is being used for projection devices.

However, since the liquid crystal panel has a narrower input voltage range in which gradation can be expressed than a CRT, there is a problem in that the above-mentioned video display device tends to cause underexposure and underexposure. That is, the electro-optical characteristics of the liquid crystal are, for example, as shown in FIG. 4 in the relation of the relative transmittance 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 from the maximum V _sat to the minimum V _sat.
The voltage range is represented by the symbol ΔV between _th . As understood from the example of FIG. 4, the range ΔV of the input voltage is 2
(V) and the like, and the range of the number (V) is narrow, and it is difficult to control the gradation of each pixel in the liquid crystal panel as desired. The crushing and white crushing are apt to occur.

Conventionally, in order to address the above-mentioned problems,
2. Description of the Related Art In a video display device having a liquid crystal panel, contrast is controlled by an automatic gain control (abbreviated as AGC) on a luminance signal according to a luminance level of a luminance signal obtained from an input video signal, or gradation is controlled. Some of them perform video control to improve the performance. Some video display devices having a CRT perform video control in order to deal with the same problem as that of the liquid crystal.

[0005]

However, in a conventional video display device equipped with a liquid crystal or a CRT, the video signal detected as a basis of video control is not limited to a screen area and is not targeted. Different parts of the screen from the main video, for example, movie subtitles,
Character information such as telops or an aspect ratio of 1
When a 6: 9 landscape screen is displayed on a television screen having a normal aspect ratio, the presence of the lower solid black portion causes the video level (luminance level) of the portion to be reduced to the peak level or average of the main video. There has been a problem that the level is affected and proper video control is not performed.

Further, in a screen in which a change width of a video control value such as a contrast value, a brightness value, and a gamma value of a video is large, particularly in a screen in which video contents are largely switched,
There has been a problem that the display screen looks unnatural.

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

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has been described in which a luminance signal of an input video signal is obtained, and the luminance signal is set in advance at predetermined intervals based on a vertical synchronizing signal. A detector for detecting a luminance signal level from a luminance signal within a range of a screen area, and calculating and outputting an optimal video control value for each input video signal based on the detected luminance signal level data. A video control value calculating means, wherein when the detection unit detects the luminance signal level, the screen is divided into two or more areas of a central part and a peripheral part of a screen, and the peripheral part area Means for performing the detection in the region excluding the above, or performing the detection by making the weight of the central region larger than that of the peripheral region.

In addition, means for storing a video control value obtained based on the luminance signal level detected at predetermined intervals, and a video control value output from the video control value calculating means based on the luminance signal level detected this time. Means are provided for averaging the output video control value before the stored value and the previous output video control value, so that the change width of the video control value is reduced.

[0010]

In the present invention, when detecting the luminance signal level, the screen is divided into two or more regions, that is, a central portion and a peripheral portion of the screen, and the detection is performed in the region excluding the peripheral region. The weighting of the central region is made larger than that of the peripheral region to perform the detection. Accordingly, a portion different from the main video existing on the screen (information such as superimposed subtitles and character telops of a movie, or an aspect ratio of 16:
9) can be removed, so that optimal video control is always possible.

Further, in the present invention, the output video control value is averaged by one or more previous output video control values and the present output video control value, so that the variation range of the video control value can be reduced. If it is relaxed, the output value at the time of output switching of each video control value is relaxed, so that smooth video control can be achieved.

[0012]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an image display device according to one 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 removes the influence of a portion different from the main image on the screen to perform optimal image control. It is something 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 converts the digital video signal into a luminance signal Y / D.
It is input to a color signal C separation circuit (Y / C separation circuit) 2. The Y / C separation circuit 2 separates an input digital video signal into a digital luminance signal Y and a digital chrominance 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 converts 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, and B signals are input to the R, G, and B control circuit 20. The video signal processing circuit 3
Calculates a horizontal synchronizing signal H.SYNC and a vertical synchronizing signal V.SYNC based on the input luminance signal Y and the color signal C, and inputs them to the screen area setting circuit 4.

On the other hand, the digital luminance signal Y is input to a peak value detection circuit 5, an average value detection circuit 6, and a black value detection circuit 7 via a screen area setting circuit 4. Each of the detection circuits 5, 6, and 7 detects the peak level, average level, and black level (or black peak level) of the input luminance signal Y, and inputs data of the detected values to the correction operation circuit 9. The luminance signal Y output from the Y / C separation circuit 2 is directly input to a pedestal level detection circuit 8. The pedestal level detection circuit 8 detects a pedestal level from the input luminance signal Y, and outputs the detected pedestal data. Is input to the correction operation circuit 9. The correction operation circuit 9 performs a correction operation on the input pedestal level data to remove the synchronizing signal component from the peak level, average level, and black level data to a true video signal level, and converts the corrected level data to each data. The data is stored in the registers 10, 11, and 12.

Here, the screen area setting circuit 4 detects a luminance signal within a predetermined screen area based on the horizontal synchronizing signal H.SYNC and the vertical synchronizing signal V.SYNC. It is input to the detection circuit 6 and the black level detection circuit 7. Therefore, the peak level, average level, and black level of the luminance signal target the setting screen area.

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

Next, each of the registers 10, 11, 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 optimal video control value (contrast value, bright value, gamma value in this embodiment) for each input video signal from each input data by calculation, and averages these control values. , 19 to the R, G, B control circuit 20. The R, G, B control circuit 20 controls the luminance signals of R, G, B in accordance with the input control value signal to display an image of a video signal on the liquid crystal panel 21.

The video control values output from the averaging circuits 17, 18, 19 are stored in the output value registers 14, 1 respectively.
5 and 16 and averaged with each video control value of the output of the arithmetic circuit 13 at the next time. That is, each video control value output this time from the arithmetic circuit 13 is averaged with the video control signal previously input to the R, G, B control circuit 20 and input to the control circuit 20. . By repeating this averaging process every time the video control value is calculated, as shown by a broken line in FIG. Naturally relaxed to a level that feels natural to the eyes.
In FIG. 3, the output examples of the averaging circuits 17, 18, and 19 when the video control value changes from 0 to FFH are shown by broken lines, and the registers 14, 1 are used for comparison.
Output examples in the case where the output values are not relaxed without providing the averaging processing circuits 17, 18, 19 are shown by solid lines.

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

[0021]

As described above, according to the video display apparatus of the present invention, when detecting the luminance signal level, the screen is divided into two or more regions, that is, the central portion and the peripheral portion of the screen. By performing the above-described detection in the region excluding the above, or by performing the above-described detection by increasing the weight of the central region as compared with the peripheral region, so that a portion different from the main video, for example, a subtitle of a movie or a TV broadcast. This eliminates the effects of character telops and black solid areas at the top and bottom of the landscape screen, making it possible to always perform optimal video control. Further, by alleviating the switching of the output of each control value, an excellent effect that the video control can be performed in a more natural manner can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating 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 a level of a video signal in the video display device of FIG. 1;

FIG. 3 is a diagram illustrating an example of a change in a video control value of the video display device in FIG. 1;

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 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 operation circuit Reference Signs List 10 Peak level data register 11 Average level data register 12 Black level data register 13 Image control operation 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 liquid crystal panel

Continuation of the front page (56) References JP-A-4-34594 (JP, A) JP-A-62-110369 (JP, A) JP-A-4-40170 (JP, A) JP-A-4-29473 (JP) JP-A-62-269475 (JP, A) JP-A-2-29077 (JP, A) JP-A-2-253770 (JP, A) JP-A-3-80672 (JP, A) 4-88168 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) G09G 5/36 G09G 3/20 H04N 5/66

Claims (1)

(57) [Claims] 1. Obtaining a luminance signal of an input video signal,
Screen preset for each predetermined period based on the vertical synchronization signal
A detecting unit for detecting a luminance signal level from a luminance signal within the range of the area, and calculating and outputting an optimal video control value for each input video signal based on the detected luminance signal level data. a video display device and a video control value calculating means, when performing detection of the luminance signal level by the detection unit is divided into two or more regions of the central portion and the peripheral portion of the screen, the peripheral region The detection is performed in the excluded region, or the weighting of the central region is made larger than that of the peripheral region to perform the detection, and the detection is performed based on the luminance signal level detected every predetermined period.
And means for storing the video control values, the image control value outputted from the video control value calculating means based on the luminance signal level of the detection current, storage
Averaging the previous previous output video control values
And means for, the image display device being characterized in that so as to mitigate the variation width of the video control values.