JP4171247B2 - Contrast correction circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a contrast correction circuit used in a display device such as a liquid crystal display device.
[0002]
[Prior art]
When the average value (average luminance) of the luminance signal of one entire screen is calculated for each screen, and the black level of the luminance signal is expanded when the average luminance of the entire one screen is low, the average luminance of the entire one screen is high Has already been developed for improving the contrast by extending the white level of the luminance signal (see Japanese Patent Application Laid-Open No. 4-229788).
[0003]
As described above, in the technique of expanding the luminance signal based on the average value of the luminance signal of the entire screen, the average is obtained when the video signal of the single screen is a video signal biased to both the black side and the white side. Since the brightness is recognized as intermediate, it is impossible to perform suitable contrast correction, and it is also impossible to perform suitable contrast correction even when the video signal of one screen is a video signal biased to an intermediate gradation. is there.
[0004]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide a contrast correction circuit that can reproduce an image with high contrast regardless of the content of the image.
[0005]
[Means for Solving the Problems]
According to the first aspect of the present invention, gradation correction means for correcting gradation of an input video signal, means for generating a luminance signal from the input video signal, and one screen is divided into a plurality of areas. Means for calculating an average value of the luminance signal for each area, means for generating luminance frequency distribution information based on the average luminance value for each area, and input of the gradation correction means based on the luminance frequency distribution information. Control means for controlling the output characteristics, the control means compares the frequency distribution information of the luminance acquired this time with the frequency distribution information of the luminance acquired last time, the frequency difference of the corresponding luminance section is a predetermined value If it does not exceed, the input / output characteristics are not changed.
[0006]
According to a second aspect of the present invention, in the contrast correction circuit according to the first aspect, the control means causes the input video signal in the luminance section having a high frequency to be expanded (the gradation change rate in the luminance section having a high frequency). The input / output characteristics of the gradation correction means are controlled so as to increase.
[0007]
According to a third aspect of the present invention, in the contrast correction circuit according to the first aspect, the input video signal is an RGB signal.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0009]
FIG. 1 shows the configuration of the contrast correction circuit.
[0010]
An input video signal composed of R, G, and B signals is input to the luminance signal generation unit 1 and to the gradation correction unit 15. The horizontal synchronizing signal H and the vertical synchronizing signal V of the input video signal are sent to the timing control unit 3.
[0011]
The luminance signal generation unit 1 converts an input video signal composed of R, G, and B signals into a luminance signal based on, for example, a conversion table created in advance. In this contrast correction circuit, as shown in FIG. 2, the average value of the luminance signal is calculated for each area obtained by dividing one screen into M in the horizontal direction and N in the vertical direction, and the average luminance obtained for each area is calculated. A luminance frequency distribution is created for each screen based on the value, and input / output characteristics of the gradation correction unit 15 are controlled based on the obtained luminance frequency distribution. Each area has a size of X pixels in the horizontal direction and Y pixels in the vertical direction.
[0012]
The addition circuit 2, the division circuit 5, the horizontal buffer 6, the vertical buffer 7, the addition circuit 8, the division circuit 9, and the area-specific luminance average value storage buffer 10 are used for calculating the luminance average value for each area of M × N. Is provided.
[0013]
That is, the luminance signal obtained by the luminance signal generation unit 1 is sent to the adding circuit 2. The addition circuit 2 adds the previous addition result to the input luminance signal. The adder circuit 2 is initialized every time such addition is performed X times by the control signal c <b> 1 output from the timing control unit 3.
[0014]
The division circuit 5 divides the addition result by X every time the addition circuit 2 adds X times. The division result is stored in the horizontal buffer 6 having M buffers [1] to [M]. When such an operation is performed M times, the horizontal buffer 6 stores data for one line.
[0015]
By the same operation, while the data for the next line is being stored in the horizontal buffer 6, the data for the previous line is sequentially read from the horizontal buffer 6 and sent to the adder circuit 8. The adder circuit 8 adds the data of the previous line for the same area stored in the vertical buffer 7 to the input data. The vertical buffer 7 has M buffers [1] to [M]. The addition result of the addition circuit 8 is stored in the vertical buffer 7. However, when the data sent to the adder circuit 8 is the first line, there is no previous line data, so the data sent to the adder circuit 8 is stored in the vertical buffer 7 as it is.
[0016]
The vertical buffer 7 is initialized every time the addition circuit 8 performs Y addition by the control signal c2 output from the timing control unit 3. The division circuit 9 divides the addition result by Y every time the addition circuit 8 adds Y times. As a result, the average luminance value for each area in FIG. 2 is obtained. The result of the division is stored in the luminance average value storage buffer 10 by area having M buffers [1] to [M] by the control signal c4 output from the timing control unit 3.
[0017]
In this way, when the average luminance value of each area for one row in FIG. 2 is stored in the area-specific luminance average value storage buffer 10, the luminance section determination unit 11 stores it in the area-specific luminance average value storage buffer 10. It is determined which of the eight luminance intervals A1 to A8 shown in FIG. 3 includes the average luminance value for each area, and data corresponding to the determination result is stored in the frequency distribution information storage buffer 12. .
[0018]
The frequency distribution information storage buffer 12 includes eight buffers [A1] to [A8] corresponding to the eight luminance sections A1 to A8. The frequency is stored in each of the buffers [A1] to [A8]. Therefore, when the luminance section determining unit 11 determines that the average luminance value of a certain area is included in the luminance section A1, for example, the data in the buffer [A1] in the frequency distribution information storage buffer 12 is only one. Increment.
[0019]
By repeating the above operation, the luminance frequency distribution information (information indicating the frequency for each of the luminance distribution areas A1 to A8, the histogram shown in FIG. 3) based on the average luminance for each area in FIG. It is stored in the information storage buffer 12. The luminance frequency distribution information stored in the frequency distribution information storage buffer 12 is cleared by the control signal c3 output from the timing control unit 3.
[0020]
The CPU 13 acquires the luminance frequency distribution information for each V from the frequency distribution information storage buffer 12, determines the input / output characteristic data of the gradation correction unit 15 based on the acquired luminance frequency distribution information, and the gradation correction unit Give to 15. The gradation correction unit 15 corrects the gradation of the input video signals R, G, and B based on the input / output characteristic data given from the CPU 13.
[0021]
3A, 3B, and 3C show specific examples of luminance frequency distribution information acquired by the CPU 13 from the frequency distribution information storage buffer 12. FIG.
[0022]
FIG. 3A shows a luminance frequency distribution for a relatively bright scene, and the frequencies in the luminance sections A1 and A2 are larger than a predetermined threshold value. That is, on this screen, the amount of information in the luminance sections A1 and A2 is large. In such a screen, the CPU 13 expands the luminance sections A1 and A2 having a large amount of information as shown by the solid line in FIG. (Enlarge)
[0023]
In FIG. 3B, the frequencies of the luminance sections A3 and A6 that are intermediate gradations are larger than a predetermined threshold. In such a screen, the CPU 13 sets the input / output characteristics of the gradation correction unit 15 to extend the luminance sections A3 and A6 having a large amount of information as indicated by the solid line in FIG.
[0024]
FIG. 3C shows a luminance frequency distribution for a relatively dark scene, and the frequencies in the luminance sections A7 and A8 are larger than a predetermined threshold value. In such a screen, the CPU 13 sets the input / output characteristics of the gradation correction unit 15 to extend the luminance sections A7 and A8 having a large amount of information as indicated by the solid line in FIG.
[0025]
As described above, by changing the input / output characteristics of the gradation correction unit 15 according to the luminance frequency distribution, it is possible to extend a luminance section with a large amount of information, and limit the contrast reproducibility like a liquid crystal panel or the like. Even some devices can reproduce high-contrast images.
[0026]
When the above operation is performed in real time, it may cause flickering of the screen depending on the content of the video. For example, when a luminance section in which the frequency is determined to be greater than the threshold with a slight change in the image content currently displayed is determined to have a frequency that is less than the threshold, a gradation correction unit is provided for each screen. If the input / output correction is performed by changing the input / output characteristics of 15, the screen may flicker.
[0027]
In order to solve such a problem, the CPU compares the luminance frequency distribution information acquired this time with the luminance frequency distribution information acquired last time, and if the corresponding luminance interval does not exceed a predetermined value, The input / output characteristics should not be changed.
[0028]
By taking such measures, flickering of the screen can be prevented, but when the brightness of the screen changes slowly, the input / output characteristics of the gradation correction unit 15 are not changed, and the current video content However, there is a possibility that a preferable input / output characteristic cannot be realized. Therefore, as a result of comparing the luminance frequency distribution information acquired by the CPU this time with the luminance frequency distribution information acquired last time, the difference between the corresponding luminance intervals does not exceed a predetermined value, but the luminance frequency distribution information acquired this time and the previous acquisition When the brightness frequency distribution information is different and the preferred input / output characteristics are different, the input / output characteristics may be changed slowly.
[0029]
【The invention's effect】
According to the present invention, a high-contrast video can be reproduced regardless of the video content.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a contrast correction circuit.
FIG. 2 is a schematic diagram showing an area for calculating an average luminance set in one screen.
FIG. 3 is a histogram showing a specific example of a luminance frequency distribution.
4 is a graph showing an example of input / output characteristics set by the CPU for each specific example of FIG. 3;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Luminance signal production | generation part 2, 8 Addition circuit 3 Timing control part 5, 9 Dividing circuit 6 Horizontal buffer 7 Vertical buffer 10 Brightness average value storage buffer 11 by area Brightness area determination part 12 Frequency distribution information storage buffer 13 CPU
15 Tone correction part

Claims (3)

Gradation correction means for correcting the gradation of the input video signal, means for generating a luminance signal from the input video signal, and dividing one screen into a plurality of areas, and calculating the average value of the luminance signal for each area Means for generating luminance frequency distribution information based on the average luminance value for each area, and control means for controlling the input / output characteristics of the tone correction means based on the luminance frequency distribution information. The control means compares the frequency distribution information of the luminance acquired this time with the frequency distribution information of the luminance acquired last time, and if the frequency difference of the corresponding luminance section does not exceed a predetermined value, the input / output characteristics A contrast correction circuit characterized by not changing the frequency.   2. The contrast correction circuit according to claim 1, wherein the control means controls input / output characteristics of the gradation correction means so that an input video signal in a luminance section having a high frequency is expanded.   The contrast correction circuit according to claim 1, wherein the input video signal is an RGB signal.

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