JP2003198984A - Contrast correction circuit - Google Patents

Abstract

(57) [Summary] [Problem] To appropriately correct the contrast of an image to be noticed when an image with a uniform gradation occupies most of the screen. SOLUTION: An integrating circuit 10 for accumulating the brightness levels of input video signals and calculating the sum of the brightness levels of the video signals of the entire screen, and table data indicating a plurality of types of contrast conversion characteristics are stored. ROM 16
And comparing the reference value with the integrated output of the integrating means using the sum of the brightness levels of all the pixels when the brightness level of all the pixels of the screen is the maximum as a reference value, and based on the comparison result. Or generation of a selection signal instructing the ROM 16 to selectively output the table data suitable for the brightness of the screen among the plurality of types of table data in consideration of the gradation of the video signal input to the comparison result. It has a circuit 14 and a RAM 18 in which a conversion table for correcting the contrast of an input video signal with table data output from the ROM 16 is stored.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contrast correction circuit, and more particularly to a contrast correction circuit suitable for use in a display device having a narrow dynamic range such as a PDP (Plasma Display Panel).

[0002]

2. Description of the Related Art In a display device having a narrow dynamic range such as a PDP, a contrast correction circuit for enhancing the contrast of a portion having a large amount of information in an image is preferable in order to obtain a visually better image. Used. In such a conventional contrast correction circuit, the contrast conversion for enhancing the contrast of the image is
Usually, a plurality of types of look-up tables having different contrast conversion characteristics are used, and these tables are stored in a memory such as a ROM. To select the lookup table, the result of integrating the image data for one screen, the result of taking a histogram, or the like is used.

[0003]

When using the conventional contrast correction circuit which performs the contrast conversion of the image data by using the above-mentioned plurality of look-up tables, a considerably good image can be obtained on most of the screens. .

However, in some cases, it may be better not to correct a particular screen. Specifically, this corresponds to image data such as a dark screen of a movie. Screen like this,
That is, when there is a relatively bright image with a small area in an image with a large number of black level pixels, the area ratio (corresponding to the amount of data) has more images with black level pixels. In the conventional contrast correction circuit, it is easy to select a look-up table having a contrast conversion characteristic effective on a dark screen.

However, in the case of a screen having a small area and a relatively bright image in an image having a large number of black level pixels, the important information is rather a small area portion, and a dark screen for such a screen. When a lookup table for the user is selected and the contrast is corrected, there is a problem that deterioration such as white crushing is likely to occur. In addition, when there is a partially dark image on the whole white surface of a snow scene, etc., there is a problem that it may be difficult to see important information due to black crushing contrary to the above case. . The present invention has been made in view of the above circumstances, and the contrast of an image to be noticed when an image with a uniform gradation occupies most of the screen and an image of interest occupies a small part of the screen It is an object of the present invention to provide a contrast correction circuit capable of appropriately correcting the above.

[0006]

In order to achieve the above object, the invention according to claim 1 integrates the brightness levels of the input video signals to obtain the brightness levels of the video signals of the entire screen. Integrating means for calculating the total sum, first storage means for storing table data showing a plurality of types of contrast conversion characteristics according to the brightness of the screen, and the brightness level of all pixels of the screen are maximum. Based on the sum of the brightness levels of all pixels at a given time as a reference value, the reference value is compared with the integrated output of the integrating means, and based on the result of the comparison, or in the comparison result, the floor of the input video signal. Selection means for instructing the first storage means to selectively output table data suitable for screen brightness among the plurality of types of table data in consideration of the tone, and the input video signal Contrast And having a second memory means for conversion table corrected by the table data output from the serial first storage means is stored.

The invention described in claim 2 is the same as claim 1
In the contrast correction circuit described in (1), a histogram detecting unit that further divides the gradation of the input video signal into a plurality of areas and detects the frequency of the gradation belonging to each of the divided areas in pixel units, The detection output of the histogram detection means is taken in, and when there is a gradation whose frequency is equal to or higher than a preset threshold value, it is determined that the gradation is uniform,
And a control unit that outputs data indicating the gradation determined to be the uniform gradation and the frequency of the gradation.
When the control unit receives the gradation determined to be the uniform gradation and the data indicating the frequency of the gradation, the reference value to be compared with the output of the integrating unit is set to the brightness of all pixels of the screen. Is a value obtained by subtracting the product of the gradation determined as the uniform gradation and the frequency of the gradation from the sum of the brightness levels of all pixels when the level is maximum, and the reference value is one screen. The plurality of types based on the value divided by the sum of the brightness levels when the brightness levels of all pixels in the image area excluding the image area occupied by the gradation determined as In order to selectively output table data suitable for screen brightness among the table data
Is instructed to the storage means.

The invention described in claim 3 is the same as that of claim 2.
In the contrast correction circuit according to, the threshold is
The area ratio of the display area to be noted to the entire display screen is defined in advance, and when the background is a screen with a uniform gradation, it is set to the number of pixels corresponding to the area of the screen with a uniform gradation. It is characterized by

The invention according to claim 4 is the same as claim 2
Alternatively, in the contrast correction circuit according to the third aspect, the control unit determines whether or not the gradation is a uniform gradation. The feature is that the data indicating the frequency is not output.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows the configuration of the contrast correction circuit according to this embodiment. The contrast correction circuit according to the present embodiment detects the frequency of gradations that are uniform and abundant in the video signal, and when the amount exceeds a certain value, important information is transferred to other gradations. By determining that there is, and operating the selection signal of the table data indicating the contrast conversion characteristic, it is possible to improve the crushed white on the dark screen, the crushed black on the bright screen, and the like.

In FIG. 1, the contrast correction circuit is
It has an integration circuit 10, a histogram detection circuit 12, a selection signal generation circuit 14, a ROM 16, a RAM 18, and a control circuit 20. The integrating circuit 10 has an input terminal 1
The brightness levels of the video signal signals input from 00, 101, and 102 are integrated to calculate the total brightness level of the video signals of the entire screen.

The histogram detection circuit 12 has an input terminal 1
Video signals (R,
G, B) gradations are divided into a plurality of areas, and the frequency of gradations belonging to each of the divided areas is detected in pixel units and output. The selection signal generation circuit 14 compares the reference value and the integrated output of the integration circuit 10 with the sum of the brightness levels of all the pixels when the brightness level of all the pixels of the screen is the maximum as a reference value. Based on the comparison result, or based on the output of the control circuit 20, the input terminal 10 is added to the comparison result.
A function for instructing the ROM 16 to selectively output table data that matches screen brightness among a plurality of types of table data in consideration of the gradation of the input video signal input from 0, 101, and 102. Have.

Further, the ROM 16 stores table data indicating a plurality of types of contrast conversion characteristics selected according to the brightness of the screen, and the ROM 16 is responsive to a selection signal output from the selection signal generation circuit 14. The table data of the selected contrast conversion characteristic is output.
The RAM 18 stores a conversion table for correcting the contrast of the video signal input from the input terminals 100 to 102 with the table data output from the ROM 16. The video signals whose contrast is corrected by the conversion table stored in the RAM 18 are output terminals 200 to 2
It is output to 02.

The control circuit 20 includes a histogram detection circuit 1
The detection output of 2 is taken in, and when there is a gradation whose frequency is equal to or higher than a preset threshold value, it is determined to be a uniform gradation, and the gradation determined to be the uniform gradation and the gradation It has a function of outputting data indicating the frequency. Where the threshold is
The area ratio of the display area to be noted to the entire display screen is defined in advance, and when the background is a screen with a uniform gradation, it is set to the number of pixels corresponding to the area of the screen with a uniform gradation. .

Further, the selection signal generation circuit 14 receives the data indicating the gray scale determined to be uniform gray scale by the control circuit 20 and the frequency of the gray scale, and compares it with the output of the integration circuit 10 as a reference. The value is subtracted from the sum of the brightness levels of all the pixels when the brightness level of all the pixels on the screen is the maximum, the product of the gradation determined as the uniform gradation and the frequency of the gradation. And the reference value is the sum of the brightness levels when the brightness levels of all pixels in the image area excluding the image area occupied by the gradation determined to be the uniform gradation in one screen are maximum. It has a function of instructing the ROM 16 to selectively output table data that matches the brightness of the screen among a plurality of types of table data based on the value divided by.

Next, table data showing a plurality of types of contrast conversion characteristics stored in the ROM 16 will be described with reference to FIG. FIG. 2 shows the contrast conversion characteristic of the image. In the figure, the contrast conversion characteristic indicated by the curve Q1 is a characteristic that is selected for an image whose input video signal has a small average brightness level and is entirely dark, and is indicated by a curve Q16. The contrast conversion characteristic is a characteristic that is selected for an image in which the brightness value of the input video signal has a large average value and the whole is bright. In the figure, the characteristic is such that the contrast of the image data in the area surrounded by the broken line is emphasized.

In this embodiment, the curves Q1 and Q16 are used.
16 of curves Q1 to Q16 obtained by evenly dividing
Table data (numerical value data) indicating the contrast conversion characteristic of (1) is stored in the ROM 16, and predetermined table data is selected according to the average value of the brightness levels of the input video signal. The operation of the contrast correction circuit according to this embodiment having the above configuration will be described.

In FIG. 1, when R, G, B video signals (digital signals) are input from the input terminals 100 to 102, the integrating circuit 10 integrates the brightness levels of the input video signals and displays the screen. The sum (average value) S0 of the brightness levels of the entire video signal is calculated. Here, the size of one screen is 852 (dots) x 480 (lines), one pixel is R,
Assuming that G and B are displayed with 8 bits, the sum Sm of the brightness levels of all pixels when the brightness level of all pixels on the screen is the maximum is: Sm = 852 (dots) × 480 (lines) × 255 (8 bits: maximum value) x 3 (RGB) = 312854400.

The sum (average value) S0 of the brightness levels of the video signals of the entire screen calculated by the integration circuit 10 is converted by the selection signal generation circuit 14 into a selection signal for selecting table data as follows. Is replaced by That is, the selection signal is a value obtained by dividing the output S0 of the integrating circuit 10 by the total sum Sm (output of the integrator (total sum) / 312854400), and takes a value of 0 to 1, but each contrast conversion characteristic Q1.
To Q16 are evenly allocated according to the number of contrast conversion tables made up of table data. here,
A set of table data showing each contrast conversion characteristic will be referred to as a contrast conversion table.

As described above, the selection signal generation circuit 1 selects the selection signal when there are 16 types of contrast conversion tables.
A selection signal for selecting the contrast conversion table is output to the ROM 16 as described below according to the calculation result in 4. That is, when S0 / Sm = 0 to 0.0625, the contrast conversion table Q1 is set to S0 / Sm = 0.0.
If it is 625 to 0.125, the contrast conversion table Q
2 is S0 / Sm = 0.875 to 0.9375, the contrast conversion table Q15 is S0 / Sm = 0.9375-1
If so, selection signals for selecting the respective contrast conversion tables Q16 are output to the ROM 16.

As a result, in the ROM 16, the table data having the contrast conversion characteristic selected by the selection signal output from the selection signal generation circuit 14 is stored in the RAM 18.
Output to. In the RAM 18, the conversion table is used for RO
Based on the table data received from M16, the video signals (R, G,
B) the contrast is corrected, and the video signals (R, G, B) with the corrected contrast are output terminals 200 to 20.
Output from 2.

In this way, an image in which the contrast of the dark portion is emphasized when the entire screen is dark and an image in which the contrast of the bright portion is emphasized when the entire screen is bright are obtained. In most cases, the desired contrast can be corrected by this method, but as described above, it may cause adverse effects. Specific examples thereof are shown in FIGS.
Will be described with reference to.

FIG. 3 shows a screen when there is an image B1 in which most of the background A1 has a gradation of black level and a gradation of which is partially close to white. In the case of the screen as shown in FIG. 3, the output of the integrating circuit 10, that is, the sum total (average value) of the brightness levels of the video signals of the entire screen has a low value, so that the histogram detection circuit 12 and the histogram detection circuit 12 in the configuration of FIG. When the control circuit 20 is not provided, the contrast conversion table suitable for the dark screen is selected, and the contrast of the dark part is emphasized at the expense of the contrast of the bright part in the screen.

However, while the important video signal is located in the bright part, the contrast in that part is reduced, so that a phenomenon such as white crushing occurs. Also, as shown in FIG. 4, contrary to FIG. 3, the background A2 is bright on the screen when there is an image B2 with a gray level of most of the white and a dark gray level partially close to black. The contrast conversion table suitable for the screen is selected, and the contrast of the dark part is emphasized at the expense of the contrast of the dark part. Therefore, in the case of the screen shown in FIG. 4, a phenomenon such as blackout occurs.

Further, as shown in FIG. 5, the screen in the case where the background A3 is gray, and there is an image B31 having a bright gradation partially close to white and an image B32 having a dark gradation partially close to black. Then, the contrast conversion table suitable for the gray of the background A3 is selected, and the contrast of the gray background A3 is emphasized at the expense of the contrast of the white portion and the black portion in the screen. Therefore, in the case of the screen shown in FIG. 5, both white and black crushing may occur.

When a video signal representing the screen shown in FIGS. 3 to 5 is input from the input terminals 100, 101 and 102, the histogram detection circuit 12 causes the gray scale represented by the histograms shown in FIGS. 6 to 8. And data indicating the frequency are output. 6 corresponds to the screen shown in FIG. 3, FIG. 7 corresponds to the screen shown in FIG. 4, and FIG. 8 corresponds to the screen shown in FIG. In the present embodiment, the control circuit 20
Is a black level when the gradation of the video signal is 0 to 5,
When the gradation is 125 to 1130, the gray level is recognized, and when the gradation is 250 to 255, the white level is recognized.

In the case of the screens shown in FIGS. 3 to 5, the sum of the brightness levels of the video signals of the entire screen calculated by the integrating circuit 10 is determined by the gradations occupying most of the area in the screen. Therefore, the above-mentioned phenomenon occurs. In order to avoid such a phenomenon, in the present invention, first, the integration circuit 10 integrates the sum of the video signals, and at the same time, the histogram detection circuit 12 inputs the video signals (R, R) input from the input terminals 100, 101, 102. G and B) gradations are divided into a plurality of areas, and the frequency of gradations belonging to each of the divided areas is detected and output.

The control circuit 20 includes the histogram detection circuit 1
When there is a gray scale having a frequency exceeding the threshold value set from the outside based on the output of 2, the frequency for each gray scale is output to the selection signal generation circuit 14. That is, the control circuit 20
Outputs data indicating the gradation D and its frequency H for correcting the calculation of the selection signal calculated by the selection signal generation circuit 14. The threshold value is a criterion for determining the degree of frequency (area) in the histogram before determining a uniform gradation.

At this time, when the gradation range to be ignored, that is, the gradation range which is not the target of contrast correction is designated from the outside to the control circuit 20, the control circuit 20 is specified.
Does not output the frequency data of the specified gradation.
The threshold value has a predetermined area ratio of the display area to be watched with respect to the entire display screen, and corresponds to the area of the black screen when the background has a uniform gradation, for example, a black screen. The number of pixels to be set may be set. For example, a small screen display with a black background and a bright gradation close to white (1 / the full screen)
4 display area), the set value as the threshold value set in the control circuit 20 is 3/8 of the 852 × 480 display screen.
When 4 is a black screen, 852 × 480 × 3/4 = 306720.

On the other hand, the selection signal generation circuit 14 calculates the selection signal by the following equation based on the gradation D and the frequency H output from the control circuit 20 when the gradation having the frequency exceeding the threshold value exists. . S0 ′ = (output of integrating circuit 10 (sum) −D × H) (1) Sm ′ = {852 (dots) × 480 (row) −H} × 255 (8-bit maximum value) × 3 (RGB) (2 ) Selection signal = S0 '/ Sm' (3)

Here, D × H is the total number of pixels (the number of dots) of the image area occupied by the image of uniform gradation, which is desired to eliminate the effect on the image to be noticed when the contrast is corrected on the screen. It is the sum of the brightness levels, and S0 'is the sum of the brightness levels in the image area of interest on the screen. Further, Sm ′ is the sum of the brightness levels of all the pixels in the image area of interest, that is, the image of interest when the brightness level of each pixel in the image area of interest is the maximum on the screen. It is the total sum (maximum value) of the brightness levels that can be taken in the area.

As described above, the selection signal generation circuit 14
The selection signal is calculated by
As a result of being output to M16, table data having a contrast conversion characteristic suitable for an image to be noted when correcting the contrast of the video signal is selected.
The influence of the gradation image area which is uniform and occupies a large area in the screen is eliminated, and the adverse effects described with reference to FIGS. 3 to 5 can be prevented.

According to the contrast correction circuit according to the present embodiment, when the contrast of the video signal is corrected, if there is a gradation image occupying a uniform and large area in the screen, its influence is eliminated. As described above, table data having a more appropriate contrast conversion characteristic for an image to be noticed is selected, and thus white crushing on a dark screen or black crushing on a bright screen occurs when the contrast is corrected. The harmful effect can be prevented. In addition, even if the contrast of the video signal is intentionally processed, it is possible to prevent the adverse effect.

[0034]

According to the first aspect of the invention, the brightness level of the screen and the integrating means for integrating the brightness levels of the input video signals to calculate the sum of the brightness levels of the video signals of the entire screen. First storage means for storing table data showing a plurality of types of contrast conversion characteristics according to the brightness, and brightness levels of all pixels when the brightness level of all pixels of the screen is maximum. The plurality of types of table data are compared on the basis of the comparison result by comparing the reference value with the integrated output of the integrator using the sum as a reference value, or in consideration of the gradation of the input video signal in the comparison result. Selection means for instructing the first storage means to selectively output table data matching the screen brightness, and the contrast of the input video signal is output from the first storage means. Rute And a second storage means for translation table correction is stored by Rudeta.

According to the second aspect of the invention, the gradation of the input video signal is further divided into a plurality of areas,
Histogram detection means for detecting the frequency of the gradation belonging to each of the divided regions in pixel units, and the detection output of the histogram detection means is fetched, and when there is a gradation whose frequency is equal to or greater than a preset threshold value. And a control means for determining that the gradation is uniform and outputting data indicating the gradation determined to be the uniform gradation and the frequency of the gradation. When the data showing the gradation determined to be uniform gradation and the frequency of the gradation is received,
The reference value to be compared with the output of the integrator is a gradation determined to be the uniform gradation from the sum of the brightness levels of all the pixels when the brightness level of all the pixels of the screen is maximum, and A value obtained by subtracting the product of the frequencies of the gradations is used, and the reference value is
Based on the value divided by the sum of the brightness levels when the brightness levels of all pixels in the image area excluding the image area occupied by the gradation determined to be the uniform gradation in one screen are the maximum, The first storage unit is instructed to selectively output table data that matches the screen brightness among a plurality of types of table data.

Therefore, when correcting the contrast of the video signal, if there is a uniform and large-area gradation image in the screen, it is better to focus on the image to be noticed so as to eliminate the influence. Since the table data having an appropriate contrast conversion characteristic is selected, it is possible to prevent the adverse effects such as white crushing on a dark screen and black crushing on a bright screen when the contrast is corrected. In addition, even if the contrast of the video signal is intentionally processed, it is possible to prevent the adverse effect.

According to the third aspect of the present invention, the threshold is such that the area ratio of the display area of interest to the entire display screen is defined in advance, and the background is a screen with a uniform gradation. Is set to the number of pixels corresponding to the area of the screen of uniform gradation. Therefore, even on a screen with a uniform gradation, table data having a more appropriate contrast conversion characteristic for an image to be noticed is selected, so that the influence of the background having a uniform gradation when the contrast is corrected is selected. Can be eliminated.

According to the invention described in claim 4, the control means determines whether or not the gradation is uniform.
If the gradation not to be determined is set in advance, the data indicating the frequency of this gradation is not output, so the amount of data for contrast correction can be reduced and the processing load can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a contrast correction circuit according to the present embodiment.

FIG. 2 is a ROM of the contrast correction circuit shown in FIG.
Explanatory diagram showing the contrast conversion characteristics indicated by the table data stored in FIG.

FIG. 3 is an explanatory diagram showing a screen when most of the background has a gradation of black level and there is an image of a bright gradation that is partially close to white.

FIG. 4 is an explanatory diagram showing a screen in the case where most of the background has a gradation of a white level and there is an image of a dark gradation that is partially close to black.

FIG. 5 is an explanatory diagram showing a screen in the case where there is an image with a light gray tone whose background is gray and is partially close to white, and an image with a dark tone close to partially black.

6 is a histogram showing the relationship between the gradation and the frequency of the video signal representing the screen shown in FIG.

7 is a histogram showing the relationship between the gradation and the frequency of a video signal representing the screen shown in FIG.

8 is a histogram showing the relationship between the gradation and the frequency of a video signal representing the screen shown in FIG.

[Explanation of symbols]

10 ... Integrator circuit 12 ... Black level detection circuit 14 ... Selection signal generation circuit 16 ... ROM 18 ... RAM 20 ... Control circuit

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 5/14 H04N 5/66 A 5/66 G09G 3/28 K (72) Inventor Ryutaro Okamoto Yokohama, Kanagawa 2-7 Sugawasawa-cho, Tsurumi-ku, Ltd. Samsung Electronics Yokohama Research Co., Ltd. Electronic Research Laboratory F-term (reference) 5B057 AA20 CA08 CA12 CA16 CB08 CB12 CB16 CC01 CE11 DA17 DB02 DB09 DC23 5C021 PA61 PA76 PA77 PA80 RB03 XA35 5C026 CA02 CA13 CA20 5C058 AA11 BA BB14 5C080 AA05 BB05 CC03 DD03 EE19 EE29 GG07 GG08 GG12 JJ01 JJ02 JJ05

Claims (4)

[Claims] 1. An integrating means for integrating the brightness levels of input video signals to calculate the sum of the brightness levels of the video signals of the entire screen, and a plurality of types of contrast conversion according to the brightness of the screen. A first storage unit in which table data indicating characteristics is stored; and a sum of brightness levels of all pixels when the brightness level of all pixels of the screen is maximum, and the reference value as a reference value. The integrated output of the integrator is compared and based on the comparison result, or in consideration of the gradation of the input video signal, the comparison result is adapted to the screen brightness of the plurality of types of table data. Selecting means for instructing the first storage means to selectively output table data; and a change means for correcting the contrast of the input video signal by the table data output from the first storage means. A second storage means in which a replacement table is stored; and a contrast correction circuit. 2. A histogram detecting unit that further divides the gradation of the input video signal into a plurality of regions and detects the frequency of the gradation belonging to each of the divided regions in pixel units, and the histogram detecting unit. Is detected, the gradation is determined to be uniform when there is a gradation whose frequency is equal to or greater than a preset threshold, and the gradation determined to be the uniform gradation and the frequency of the gradation. And a controller for outputting data indicating the gradation, the selector selects the integral when the data indicating the gradation determined by the controller as the uniform gradation and the frequency of the gradation is received. The reference value to be compared with the output of the means, the gradation determined to be the uniform gradation from the sum of the brightness levels of all the pixels when the brightness level of all the pixels of the screen is maximum, and the floor The reference value is the value obtained by subtracting the product of the key frequencies. Based on a value divided by the sum of the brightness levels when the brightness levels of all pixels in the image area excluding the image area occupied by the gradation determined to be the uniform gradation in one screen are the maximum 2. The contrast correction circuit according to claim 1, wherein the first storage means is instructed to selectively output table data that matches screen brightness among the plurality of types of table data. 3. The threshold has a predetermined area ratio of a display area to be noted with respect to the entire display screen, and when the background has a uniform gradation, the area of the uniform gradation screen is defined. The contrast correction circuit according to claim 2, wherein the number of pixels corresponding to is set. 4. The control means determines whether or not the gradation is uniform, and if the gradation not to be judged is set in advance, the data indicating the frequency of the gradation is The contrast correction circuit according to claim 2, wherein the contrast correction circuit does not output.