KR100441527B1 - Contrast compensation circuit - Google Patents

Abstract

A contrast correction circuit is provided to prevent white distortion and the like on a dark screen. The integrating circuit 10 for calculating the total sum of the brightness levels of the video signals of the entire screen, the ROM 22 in which table data indicating the plurality of types of contrast conversion characteristics are stored, and the brightness levels of all the pixels on the screen are the maximum. Comparing the reference value with the integral output of the integrating circuit 10, with the total value of the brightness levels of all the pixels at the time as the provisional value, and selectively outputting the table data suitable for the brightness of the screen among the plurality of table data. RAM 24 having stored therein the selection signal generation circuit 20 instructing 22, a conversion table for correcting the contrast of the input video signal according to the table data output from the ROM 22, and the input video. Correction means 12, 14, 16, and 18 for correcting the reference value when the number of consecutive pixels is greater than or equal to a predetermined value when the black level of the signal is continuously present in units of pixels.

Description

Contrast correction circuit {CONTRAST COMPENSATION CIRCUIT}

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 plasma display panel (PDP).

In a display device with a narrow dynamic range, such as a PDP, in order to obtain a better image, a contrast correction circuit for emphasizing the contrast of a large amount of information in an image is used well.

In such a conventional contrast correction circuit, a plurality of lookup tables having different contrast conversion characteristics are usually used for contrast conversion for emphasizing the contrast of an image, and these tables are stored in a memory such as a ROM (Read Only Memory) or the like. Put in. The result of integrating image data for one screen, taking a histogram, or the like is used to select such a lookup table.

In the case of using a conventional contrast correction circuit that performs contrast conversion of image data using the plurality of lookup tables described above, very good images are obtained on most screens.

However, there are cases where it is better not to correct on a specific screen. Specifically, this corresponds to image data such as a dark screen of a movie. In the case where such a screen, i.e., an image having a large number of black level pixels has a relatively bright image having a small area, the area ratio (corresponding to the data amount) is used. Therefore, since there are many images of black level pixels, there is a conventional contrast correction circuit. In the dark scene, a lookup table having effective contrast conversion characteristics is likely to be selected.

However, in the case of a screen having a relatively bright image having a small area among the pixels having a large number of pixels in the black level, the important information is rather a portion of the small area, and for such a screen, a dark screen lookup table is selected and contrast correction is performed. In this case, there is a problem that it is easy to cause deterioration such as white distortion.

Accordingly, an object of the present invention is to solve the above problems, and to provide a contrast correction circuit capable of preventing white distortion and the like on a dark screen.

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

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

FIG. 3 is an explanatory diagram showing a screen in a case where most of the background is a gray level gray scale, and an image of a light gray scale partially close to white exists.

4 is an explanatory diagram showing a detection result by the black level detection circuit for each pixel in one screen.

<Description of Symbols for Major Parts of Drawings>

10 Integrating circuit (integrating means)

12 Black level detection circuit (black level detection means, correction means)

14 horizontal counter (first counting means, correction means)

16 judgment circuit (first counting means, correcting means)

18 vertical counter (second counting means, correction means)

20 Selection signal generating circuit (selection means)

22 ROM (first storage means)

24 RAM (second storage means)

In order to achieve the above object, the invention described in claim 1 includes an integration means for integrating a brightness level of an input video signal and calculating a total of brightness levels of the video signal of the entire screen, and a plurality of kinds of contrasts according to the brightness of the screen. First storage means storing table data indicating conversion characteristics, and an integral output value of the reference value and the integrating means, with the total value of the brightness levels of all the pixels when the brightness level of all the pixels on the screen is the maximum; And selecting means for instructing the first storage means to selectively output table data suitable for brightness of the screen among the plurality of table data based on the comparison result, and contrast of the input video signal. Second storage means for storing a conversion table for correcting according to table data output from the first storage means; And a correcting means for correcting the reference value when the number of consecutive pixels is greater than or equal to a predetermined value when the black level of the input video signal is continuously present in pixel units. The selecting means includes a correction input from the correcting means. If there is, the table data to be selected from the plurality of types of table data is specified based on the value corrected according to the correction input.

In the contrast correction circuit according to claim 1, in the contrast correction circuit according to claim 1, the correction means detects the brightness level of the input video signal in units of pixels, and blacks when the brightness level of the video signal is equal to or less than a predetermined value. The black level detecting means for determining the level and the number of pixels of the black level detected by the black level detecting means are counted only when the set number of pixels is continued for each pixel number set from the outside in one horizontal scanning period, and the A first counting means for outputting a count value of the number of pixels of a black level with respect to each line in the row direction of the screen; and a first counting means for receiving the count output of the first counting means, and the number of lines in the row direction of the screen set from the outside. 1, in the case where the count value of the number of pixels of the black level is continuously input from the counting means, And a second counting means for outputting to the selecting means, wherein the selecting means is configured to calculate the total value of the brightness levels of all the pixels when the brightness level of all the pixels on the screen is maximum compared with the output of the integrating means. It is obtained by substituting a value representing the total number of pixels of the screen by a value obtained by subtracting a coefficient value of the number of pixels of the black level output from the second counting means from a value representing the total number of pixels of the screen in the formula shown It is characterized by setting it as a value.

In the invention according to claim 3, in the contrast correction circuit according to claim 2, the number of pixels set in the first counting means and the number of lines set in the second counting means take into account the noise component of the video signal. Characterized in that it is determined.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

The configuration of the contrast correction circuit according to the present embodiment is shown in FIG. In this figure, the contrast correction circuit includes an integrating circuit 10, a black level detection circuit 12, a horizontal counter 14, a determination circuit 16, a vertical counter 18, and a selection signal generating circuit. 20, ROM 22, and RAM 24.

The integrating circuit 10 integrates the brightness levels of the input video signals and calculates the total of the brightness levels of the video signals of the entire screen.

The black level detecting circuit 12 has a function of detecting the brightness level of the input video signal in pixel units and determining that the black level is when the brightness level of the video signal is equal to or less than a predetermined value. That is, it is a circuit which determines that it is black level, when R, G, and B are below a certain value among the video signals input from the input terminals 100, 101, and 102, and outputs the determination signal. The integrating circuit 10 corresponds to the integrating means of the present invention, and the black level detecting circuit 12 corresponds to the black level detecting means of the present invention.

The horizontal counter 14 counts the number of pixels of the black level detected by the black level detection circuit 12 only in the horizontal scanning period for each set number of pixels by the set number of pixels from the outside, only when the number of pixels is continuous. The count value of the number of pixels of the black level is output for each line in the row direction. The number of pixels set from the outside with one screen as 852 (dots) x 480 (lines) is "4", for example.

The determination circuit 16 outputs the counting output of the horizontal counter 14 to the vertical counter 18 only when the number of pixels of the black level for each line output from the horizontal counter 14 is equal to or larger than a predetermined value. Here, the predetermined value is set to "800", for example. In addition, the determination circuit 16 may be omitted by combining the function of the determination circuit 16 with the horizontal counter 14.

The vertical counter 18 receives the count output of the horizontal counter 14, and counts the number of pixels of the black level through the determination circuit 16 from the horizontal counter 14 with respect to the number of lines in the row direction of the screen set from the outside. In the case where (non-zero values) are continuously inputted, their total values are outputted to the selection signal generating circuit 20 as count values. Here, the number of lines set from the outside is "4", for example. In addition, each value set in the horizontal counter 14, the determination circuit 16, and the vertical counter 18 is determined in consideration of the noise component of the non-image signal.

The horizontal counter 14 and the determination circuit 16 correspond to the first counting means of the present invention, and the vertical counter 18 corresponds to the second counting means of the present invention.

The selection signal generation circuit 20 integrates this reference value and the integrating circuit 10 by setting the integrated output of the integrating circuit 10 and the total of the brightness levels of the telephone station when the brightness level of the telephone station on the screen is the maximum. The outputs are compared and the ROM 16 is instructed to selectively output table data suitable for the brightness of the screen from among a plurality of types of table data stored in the ROM 16.

Further, the selection signal generating circuit 20 calculates a reference value compared with the output of the integrating circuit 10, and calculates the total value of the brightness level of the telephone station when the brightness level of the telephone station of the screen is maximum. The value representing the telephone number is set to a value obtained by subtracting the coefficient value of the number of pixels of the black level output from the vertical counter 18 from the value representing the telephone number on the screen.

The ROM 22 stores table data indicating a plurality of types of contrast conversion characteristics selected according to the brightness of the screen, and the ROM 22 converts the contrast conversion selected in accordance with the selection signal output from the selection signal generation circuit 20. Outputs table data of a property.

The RAM 24 also stores a conversion table for correcting the contrast of the video signal input from the input terminals 100 to 102 in accordance with the table data output from the ROM 22. The video signal whose contrast is corrected according to the conversion table stored in the RAM 24 is output to the output terminals 200 to 202.

The selection signal generation circuit 20 corresponds to the selection means of the present invention, the ROM 22 corresponds to the first storage means of the present invention, and the RAM 24 corresponds to the second storage means of the present invention.

Next, table data indicating the plurality of types of contrast conversion characteristics stored in the ROM 22 will be described with reference to FIG. 2. 2 shows the contrast conversion characteristic of an image. In this figure, the contrast conversion characteristic represented by the curve Q1 is a characteristic that is selected for an image having a small average value of the brightness levels of the input video signal and the whole dark, and the contrast conversion characteristic represented by the curve Q16 is an input. It is a characteristic that is selected for an image having a large average value of brightness levels of a video signal to be bright and the whole bright. In this figure, the contrast of the image data of the area | region enclosed by the dotted line is emphasized.

In the present embodiment, table data (numerical data) indicating 16 contrast conversion characteristics of curves Q1 to Q16 obtained by equally dividing the curves between the curves Q1 and Q16 are stored in the ROM 16. The 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 the present embodiment having the above configuration will be described.

In FIG. 1, when R, G, and 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 the image of the entire screen is displayed. The total (average value) SO of the brightness levels of the signals is calculated. Here, the size of one screen is set to 852 (dots) x 480 (line), and one pixel is displayed with 8 bits for R, G, and B, and the brightness level of the telephone station when the brightness level of the telephone station of the screen is the maximum. The total (Sm) of

Sm = 852 (dots) × 480 (lines) × 255 (8 bits: maximum) × 3 (RGB) = 312 2854 400

Becomes

The total (average value) SO of the brightness levels of the video signals of the entire screen calculated by the integrating circuit 10 is replaced by the selection signal generation circuit 20 with a selection signal for selecting table data as follows. That is, the selection signal is a value obtained by dividing the output S0 of the integrating circuit 10 by the total Sm (the output of the integrator (total) ÷ 312,854,400) and taking a value from 0 to 1, but each contrast conversion characteristic ( According to the number of contrast conversion tables composed of table data indicating Q1 to Q16), the allocation is evenly performed. Here, a set of table data representing each contrast conversion characteristic is called a contrast conversion characteristic.

As described above, in the case where there are 16 kinds of contrast conversion tables, the selection signal for selecting the contrast conversion table is output to the ROM 22 in accordance with the calculation result of the selection signal generation circuit 20 as follows. . In other words,

When S0 / Sm = 0 to 0.0625, the contrast conversion table Q1 is

When S0 / Sm = 0.0625 ~ 0.125, contrast conversion table Q2 is

When S0 / Sm = 0.875 to 0.9375, contrast conversion table Q15 is

When S0 / Sm is 0.9375 to 1, a selection signal for selecting the contrast conversion table Q16 is output to the ROM 22, respectively.

As a result, the ROM 22 outputs the table data having the contrast conversion characteristic selected in accordance with the selection signal output from the selection signal generation circuit 20 to the RAM 24. The RAM 24 corrects the contrast of the video signals R, G, and B input from the input terminals 100 to 102 based on the table data received from the ROM 22 in accordance with the conversion table, and corrects this contrast. The video signals R, G, and B are output from the output terminals 200 to 202.

In this way, when the entire screen is dark, an image which emphasizes the contrast of the dark portion is obtained, and when the entire screen is bright, an image which emphasizes the contrast of the bright portion is obtained.

In most cases, the desired contrast correction is possible with this method, but as described above, there may be adverse effects. The specific example is demonstrated with reference to FIG.

FIG. 3 shows a screen in the case where most of the background A is a gray level of gray level, and an image B of bright gray level, which is partially close to white, is present. In the case of the screen as shown in Fig. 3, the output of the integrating circuit 10, i.e., the total (average value) of the brightness levels of the video signal of the entire screen becomes a low value, and therefore the black level detection circuit 12 in the configuration of Fig. ), The horizontal counter 14, the judging circuit 16, and the vertical counter 18 are not provided, the contrast conversion table corresponding to the dark screen is selected, and at the expense of the contrast of the bright part of the screen, Contrast is emphasized.

By the way, the important video signal is in the bright part, whereas the contrast of the part is reduced, causing a phenomenon such as white distortion.

In order to avoid such a phenomenon, the present invention first integrates the total of the video signals by the integrating circuit 10 and is input from the input terminals 100, 101, and 102 by the black level detection circuit 12. Among the brightness levels of the video signal, if R, G, and B are all below a certain value, it is determined as the black level.

In the black level detection circuit 12, the determination of the black level is below a certain value. Since the video signal includes noise components, the brightness level of the video signal detected by the black level detection circuit 12 is This is because the brightness level of the video signal cannot be all zero even in the black level. In the present embodiment, for example, when the gradation of the video signal is 0 to 5, it is determined that it is a black level, and when the gradation is 6 to 255, it is determined that it is a color other than black.

In one screen 852 (dots) x 480 (lines) in Fig. 4, the pixels determined as black level with respect to each pixel by the black level detection circuit 12 are &quot; 0 &quot; The detection result which recorded the pixel determined as "with signal" as "1" is shown. In this example, operations of the horizontal counter 14, the determination circuit 16, and the vertical counter 18 will be described.

The horizontal counter 14 counts the number of pixels of the black level detected by the black level detecting circuit 12 only in the case of one horizontal scanning period 1H, for each of the number of pixels set from the outside by the set number of pixels. The count value of the number of pixels of the black level is output for each line in the row direction of the screen.

That is, for example, as shown in Fig. 4, the black level detection circuit 12 in the direction of the line H from the line L1 of the first row of the screen to &quot; 0000 &quot; When "0000" is detected with respect to the four pixels of "0100", and "0100" is detected by the next four pixels, the horizontal counter 14 counts "4", "4", "0" every four pixels, and the line (L1). As a count value of?), &Quot; 808 &quot; which is the sum of count values of these four pixels is output.

Similarly, "812", "814", and "816" are output as counting outputs of the horizontal counter 14 with respect to the lines L2, L3, and L4.

In contrast, the determination circuit 16 outputs the counting output of the horizontal counter 14 to the vertical counter 18 only when the number of pixels of the black level for each line output from the horizontal counter 14 is equal to or larger than a predetermined value. Here, the predetermined value used as a criterion of determination is set to "800" as described above. Therefore, in this example, "808", "812", "814", and "816" are output from the determination circuit 16 to the vertical counter 18 with respect to the lines L1 to L4. However, when the number of pixels of the black level of each line is less than 800, the judgment circuit 16 outputs "0" with respect to the line.

The vertical counter 18 receives the counting output of the horizontal counter 14 and tests the horizontal counter 14 from the horizontal counter 14 via the determination circuit 16 with respect to the number of lines in the row direction of the screen (4 in this embodiment). When count values (non-zero values) of the number of pixels in the level are continuously input, their sum values are output as the count values to the selection signal generation circuit 20.

In this example, since "808", "812", "814", and "816" are input to the lines L1 to L4 from the determination circuit 16, the vertical counter is the sum of these values with respect to the first four lines. "3250" is outputted.

Here, when "0" is output from the determination circuit 16 for at least one of the four lines, the output of the vertical counter 18 for these four lines is "0".

Subsequently, the selection signal generating circuit 20 calculates the reference value compared with the output of the integrating circuit 10 in the calculation formula representing the total value Sm of the brightness level of the telephone station when the brightness level of the telephone station of the screen is the maximum. The value indicating the telephone number of the screen is replaced with the value obtained by subtracting the coefficient value of the number of pixels of the black level output from the vertical counter 18 from the value indicating the telephone number of the screen.

That is, the selection signal S0 / Sm 'is calculated by using Sm' obtained by the following equation instead of Sm.

Sm '= {852 (dots) × 480 (rows)-(value counted by the black level (counting output of the vertical counter 18))} x 255 (8-bit maximum) x 3 (RGB)

In this manner, according to the contrast correction circuit according to the present embodiment, even in a screen having many black level pixel data, table data having a more suitable contrast conversion characteristic is selected, so that a screen in which most of the background is occupied by black level pixels is selected. It is possible to prevent the harmful effects such as the occurrence of white distortion.

According to the present invention, white distortion can be prevented when correcting the contrast of a screen having a relatively bright image of a small area among images having a large number of black level pixels.

In addition, since noise components of the video signal are eliminated and table data having a more suitable contrast conversion characteristic is selected for a desired noteworthy image even on a screen having many black level pixel data, most of the background is occupied by black level pixels. Harm such as white distortion on the screen can be prevented.

Claims (3)

Integrating means for integrating the brightness levels of the input video signals to calculate the total of the brightness levels of the video signals throughout the screen; First storage means for storing table data representing a plurality of types of contrast conversion characteristics according to the brightness of the screen; The total value of the brightness levels of the telephone stations when the brightness level of the telephone station of the screen is the maximum is a temporary reference value, and the reference value is compared with the integral output of the integrating means, and the screen among the plurality of kinds of table data is based on the comparison result. Selecting means for instructing the first storage means to selectively output table data suitable for the brightness of the apparatus; Second storage means for storing a conversion table for correcting the contrast of the input video signal according to the table data output from the first storage means; And correcting means for correcting the reference value when the number of consecutive pixels is greater than or equal to a predetermined value when the black level of the input video signal is continuously present in a pixel unit. The selection means, when there is a correction input from the correction means, specifies the table data to be selected from the plurality of types of table data, using the value corrected according to the correction input as a reference value. Contrast correction circuit, characterized in that. The method of claim 1, The correction means, Black level detection means for detecting the brightness level of the input video signal in units of pixels and determining the black level when the brightness level of the video signal is equal to or less than a predetermined value; The number of pixels of the black level detected by the black level detecting means is counted only when the set number of pixels is continuous for each of the number of pixels set from the outside in one horizontal scanning period, and the angle in the row direction of the screen is determined. First counting means for outputting a coefficient value of the number of pixels of the black level with respect to the line; The total value is obtained when the count value of the number of pixels of the black level is continuously input from the first counting means with respect to the number of lines in the row direction of the screen set externally by receiving the count output of the first counting means. Having a second counting means for outputting to said selecting means as a counting value, The selection means, The reference value to be compared with the output of the integrating means is a value representing the total number of pixels of the screen in a calculation formula representing the total of the brightness levels of the telephone stations when the brightness level of the telephone station of the screen is maximum. A value obtained by subtracting the coefficient value of the number of pixels of the black level outputted from the second counting means from the value representing the total number of pixels is obtained. Contrast correction circuit, characterized in that. The method of claim 2, And the number of pixels set in the first counting means and the number of lines set in the second counting means are determined in consideration of the noise component of the video signal.