JP2003259153A - Contrast correcting circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a contrast correcting circuit which prevents a white less- gradation on a dark screen. <P>SOLUTION: The contrast correcting circuit has an integrating circuit 10 which calculates the total level of lightness of a video signal of the whole screen, a ROM 22 which stores table data showing a plurality of kinds of contrast conversion characteristics, a select signal generating circuit 20 which compares the integration output of the integrating circuit 10 with a reference value while regarding the total level of lightness of all pixels when the level of lightness of all the pixels of the screen is maximum as a temporary reference value and selectively outputs table data matching the brightness of the screen among the plurality of kinds of table data, a RAM 24 which stores a conversion table for correcting the contrast of an inputted video signal with table data outputted from the ROM 22, and a correcting means (12, 14, 16, 18) of correcting the reference value when the black level of the inputted video signal is continuously present by pixels and the number of the successive pixels is larger than a specified value. <P>COPYRIGHT: (C)2003,JPO

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. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a contrast correction circuit capable of preventing white crushing on a dark screen.

[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. The sum of the brightness levels of all pixels at a given time is used as a temporary reference value to compare the reference value with the integrated output of the integrator, and based on the comparison result, the screen brightness of the plurality of types of table data. Selection means for instructing the first storage means to selectively output table data suitable for the height, and table data output from the first storage means for the contrast of the input video signal. Second storage means for storing a correct conversion table, and the reference when the number of consecutive pixels is a predetermined value or more when the black level of the input video signal continuously exists in pixel units. When there is a correction input from the correction means, the selection means selects from the plurality of types of table data with the value corrected by the correction input as a reference value. It is characterized in that table data to be specified is specified.

The invention described in claim 2 is the same as claim 1
In the contrast correction circuit described in (1), the correction means detects the brightness level of the input video signal in pixel units, and determines that the brightness level of the video signal is a black level when the brightness level is equal to or lower than a predetermined value. The black level detection means for judging and the number of pixels of the black level detected by the black level detection means in one horizontal scanning period are the same as the number of pixels set for each number of pixels set from the outside, and only when they are continuous. First counting means for counting and outputting the count value of the number of pixels of the black level for each line in the row direction of the screen, and the count output of the first counting means is fetched, and the row of the screen set from the outside Second counting means for outputting to the selecting means the total value of the number of lines in the direction as the counted value when the counted values of the number of pixels of the black level are continuously input from the first counting means; Have However, the selecting means uses the reference value to be compared with the output of the integrating means in a calculation formula indicating a sum of brightness levels of all pixels when the brightness levels of all pixels of the screen are maximum. A value obtained by replacing the value indicating the total number of pixels of the screen with a value obtained by subtracting the count value of the number of black level pixels output from the second counting unit from the value indicating the total number of pixels of the screen. It is characterized by doing.

Further, 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. Is determined in consideration of a noise component for the video signal.

[0009]

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. In the figure,
The contrast correction circuit includes an integration circuit 10, a black level detection circuit 12, a horizontal counter 14, a determination circuit 16,
Vertical counter 18, selection signal generation circuit 20, and ROM
22 and RAM 24. The integrating circuit 10 is
The brightness levels of the input video signals are integrated to calculate the total brightness level of the video signals of the entire screen.

The black level detection circuit 12 has a function of detecting the brightness level of the input video signal in pixel units and determining the brightness level as a black level when the brightness level of the video signal is less than a predetermined value. That is, the input terminals 100, 101,
In the video signal input from 102, when R, G, and B are all less than a certain value, it is determined as a black level and the determination signal is output. 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 includes a black level detection circuit 1
The number of black level pixels detected from 2 is counted for each number of pixels set from the outside in one horizontal scanning period by the number of set pixels only when they continue, and for each line in the row direction of the screen The count value of the number of black level pixels is output. The number of pixels set from the outside by setting one screen to 852 (dots) × 480 (lines) is “4”, for example.

The determination circuit 16 outputs the count output of the horizontal counter 14 to the vertical counter 1 only when the number of black level pixels output from the horizontal counter 14 for each line is equal to or larger than a predetermined value.
Output to 8. Here, the predetermined value is set to “800”, for example. The determination circuit 16 may be omitted by incorporating the function of the determination circuit 16 into the horizontal counter 14.

The vertical counter 18 takes in the count output of the horizontal counter 14 and judges from the horizontal counter 14 the number of lines in the row direction of the screen set from the outside.
When the count value of the number of pixels at the black level (a non-zero value) is continuously input via, the total value thereof is output to the selection signal generation circuit 20 as the count value. Here, the number of lines set from the outside is, for example, “4”. 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 with respect to the non-video signal. The horizontal counter 14 and the determination circuit 1
6 corresponds 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 uses the integrated output of the integration circuit 10 and the sum of the brightness levels of all the pixels when the brightness level of all the pixels on the screen is maximum as a temporary reference value. The ROM 16 is configured to compare the value with the integrated output of the integrator circuit 10 and selectively output table data matching the screen brightness among the plurality of types of table data stored in the ROM 16 based on the comparison result. It has a function to instruct.

Further, the selection signal generating circuit 20 is an integrating circuit 1
A reference value that is compared with the output of 0 is a value that indicates the total number of pixels of the screen in a calculation formula that indicates the sum of the brightness levels of all the pixels when the brightness level of all the pixels of the screen is maximum. , The vertical counter 1 from the value showing the total number of pixels of the screen
The value obtained by replacing the count value of the number of black level pixels output from 8 with the subtracted value.

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 is selected by the selection signal output from the selection signal generation circuit 20. The table data of the contrast conversion characteristic is output.

Further, the RAM 24 has input terminals 100 to 100.
ROM of the contrast of the video signal input from 102
A conversion table for correcting the table data output from the table 22 is stored. The video signal whose contrast is corrected by the conversion table stored in the RAM 24 is output to the output terminals 200 to 202. The selection signal generating circuit 20 corresponds to the selecting means of the present invention, the ROM 22 corresponds to the first storing means of the present invention, and the RAM 24 corresponds to the second storing means of the present invention.

Next, table data showing a plurality of types of contrast conversion characteristics stored in the ROM 22 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, 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 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 20 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 from 0 to 1, but each of the contrast conversion characteristics Q1 to Q16. Are evenly allocated according to the number of contrast conversion tables formed 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 2 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 22 as follows according to the calculation result of 0. 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, a selection signal for selecting each of the contrast conversion tables Q16 is output to the ROM 22.

As a result, in the ROM 22, the table data having the contrast conversion characteristic selected by the selection signal output from the selection signal generation circuit 20 is stored in the RAM 24.
Output to. In the RAM 24, the conversion table RO
Based on the table data received from M22, 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, when the entire screen is dark, an image in which the contrast of the dark part is emphasized is obtained, and when the entire screen is bright, an image in which the contrast of the bright part is emphasized is obtained. In most cases, the desired contrast can be corrected by this method, but as described above, it may cause adverse effects. A specific example will be described with reference to FIG.

FIG. 3 shows a screen when there is an image B in which most of the background A has a black level gradation, and a part of which has a bright gradation close to white. In case of the screen as shown in FIG.
Since the output of the integrating circuit 10, that is, the sum (average value) of the brightness levels of the video signals of the entire screen is a low value, the black level detection circuit 12, the horizontal counter 14, the determination circuit 16, the vertical circuit in the configuration of FIG. When the counter 18 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, since the important video signal is located in the bright portion, the contrast in that portion is reduced, which causes a phenomenon such as white crushing. 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 black level detection circuit 12 causes the input terminals 100, 101, 1
Of the brightness levels of the video signal input from 02,
When R, G, and B are all less than a certain value, it is determined to be a black level.

Here, the reason why the black level detection circuit 12 determines the black level to be a certain value or less is that the video signal detected by the black level detection circuit 12 contains noise components. This is because even if the brightness level is actually the black level, the brightness level of the video signal does not always become zero. In the present embodiment, for example, when the gradation of the video signal is 0 to 5, it is determined to be the black level and the gradation is 6 to 2.
In 55, it is determined that the color is other than black.

In FIG. 4, in one screen (852 (dots) × 480 (lines)), the pixel determined by the black level detection circuit to be the black level is “0”, and the other level, that is, “there is a signal”. A detection result in which a pixel determined to be “1” is marked as “1” is shown. Horizontal counter 1 in this example
4, the operation of the determination circuit 16 and the vertical counter 18 will be described.

The horizontal counter 14 includes the black level detection circuit 1
The number of black level pixels detected in 2 is set to 1 horizontal scanning period (1
In H), for each number of pixels set from the outside, the set number of pixels is counted only when they are continuous, and the count value of the number of pixels at 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 causes "0000" for the first 4 pixels and "0000" for the next 4 pixels in the row (H) direction on the line L1 of the first row of the screen. 0000 ”, and when the next four pixels are detected as“ 0100 ”, the horizontal counter 14
Line 4 is counted as "4", "4", "0" for every 4 pixels.
As the count value of 1, “808”, which is the total value of the count values of these four pixels, is output. Similarly, line L
As for 2, L3, and L4, "812", "814", and "816" are output as the count output of the horizontal counter 14.

On the other hand, the determination circuit 16 outputs the count output of the horizontal counter 14 to the vertical counter 18 only when the number of black level pixels output from the horizontal counter 14 for each line is equal to or larger than a predetermined value. Here, the predetermined value serving as the criterion for determination is set to "800" as described above. Therefore, in this example, the determination circuit 16 outputs "808", "812", "81" for the lines L1 to L4.
4 ”and“ 816 ”are output to the vertical counter 18. However, when the number of black level pixels in each line is less than 800, the determination circuit 16 outputs "0" for that line.

The vertical counter 18 takes in the count output of the horizontal counter 14 and indicates the black level from the horizontal counter 14 via the determination circuit 16 for the number of lines in the row direction of the screen (4 in this embodiment) set from the outside. When the count values (non-zero values) of the number of pixels are continuously input, the total value is output to the selection signal generation circuit 20 as the count value.

In this example, the determination circuit 16 outputs the line L1.
~ L4, "808", "812", "81"
Since "4" and "816" are input, the vertical counter has a total value of "325" for the first four lines.
"0" is output. Where at least one of the four lines
When “0” is output from the determination circuit 16 for the lines, the output of the vertical counter 18 for these four lines becomes “0”.

Next, the selection signal generating circuit 20 is integrated circuit 1
A value indicating the total number of pixels of the screen in a calculation formula indicating the sum Sm of the brightness levels of all the pixels when the brightness level of all the pixels of the screen is maximum Is a value obtained by replacing the value indicating the total number of pixels on the screen with a value obtained by subtracting the count value of the number of black level pixels output from the vertical counter 18. That is, Sm 'obtained by the following equation is used instead of Sm to calculate the selection signal (S0 / Sm'). Sm '= {852 (dots) x 480 (rows)-(value counted as black level (count output of vertical counter 18))} x 255 (8
bit maximum value) x 3 (RGB)

In this way, according to the contrast correction circuit of the present embodiment, table data having more appropriate contrast conversion characteristics is selected even in a screen with a lot of black-level pixel data, so that the background It is possible to prevent an adverse effect such as white crushing on a screen that is mostly occupied by black level pixels.

[0036]

According to the present invention, the integrating means for accumulating the brightness levels of the input video signals to calculate the sum of the brightness levels of the video signals of the entire screen, and a plurality of integrating means corresponding to the brightness of the screen. First storage means for storing table data indicating the contrast conversion characteristics of the seeds, and a provisional reference for the sum of the brightness levels of all pixels when the brightness level of all pixels of the screen is the maximum. As a value, the reference value is compared with the integrated output of the integrating means, and based on the comparison result, the table data that matches the screen brightness is selectively output from among the plurality of types of table data. Selection means for instructing the first storage means, and second storage means for storing a conversion table for correcting the contrast of the input video signal by the table data output from the first storage means. A correction unit that corrects the reference value when the number of consecutive pixels is equal to or more than a predetermined value when the black level of the input video signal continuously exists in pixel units. When there is a correction input from the correction means, the table data to be selected from the plurality of types of table data is specified using the value corrected by the correction input as a reference value.

In the present invention, the invention according to claim 2 is the contrast correction circuit according to claim 1, wherein the correction means sets the brightness level of the input video signal in pixel units. The black level detection means that determines the black level when the brightness level of the video signal is less than or equal to a predetermined value, and the number of black level pixels detected by the black level detection means in one horizontal scanning period A first counting means for counting the set number of pixels for each set number of pixels only when they are continuous, and outputting the count value of the number of black level pixels for each line in the row direction of the screen; A case where the count output of the first counting means is fetched and 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 from the outside. To those Second counting means for outputting the total value as a count value to the selecting means, wherein the selecting means compares the reference value to be compared with the output of the integrating means with the brightness level of all pixels of the screen. A value indicating the total number of pixels on the screen in the calculation formula indicating the sum of the brightness levels of all the pixels when is maximum is output from the second counting means from the value indicating the total number of pixels on the screen. The value obtained by replacing the count value of the number of pixels of the black level with the subtracted value. Therefore, it is possible to prevent white crushing when correcting the contrast of a screen in which an image with a large number of black level pixels includes a relatively bright image with a small area.

Further, in the present invention, 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 with respect to the video signal. Therefore, even in a screen with a lot of black level pixel data by eliminating the noise component of the video signal, table data having a more appropriate contrast conversion characteristic for a desired image of interest is selected, and most of the background is selected. It is possible to prevent an adverse effect such as white crushing on a screen occupied by black level pixels.

[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 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 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 detection result of each pixel on one screen by a black level detection circuit.

[Explanation of symbols]

10 ... Integrating circuit (integrating means) 12 ... Black level detecting circuit (black level detecting means, correcting means) 14 ... Horizontal counter (first counting means, correcting means) 16 ... Judgment circuit (first counting means, correcting means) 18 ... Vertical counter (second counting means, correcting means) 20 ... Selection signal generating circuit (selecting means) 22 ... ROM (first storage means) 24 ... RAM (second storage means)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Ryutaro Okamoto             2-7 Sugasawa-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Stock             Samsung Electronics Research Laboratories Electronics Research Institute F-term (reference) 5C021 PA17 PA58 PA61 PA76 PA80                       XA35 XA61                 5C026 CA02 CA13                 5C080 AA05 BB05 DD30 EE28 FF12                       GG12 JJ01 JJ02 JJ05                 5C082 BB51 CA11 CA81 CB01 DA71                       MM10

Claims (3)

[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 that stores table data indicating characteristics; and a sum of brightness levels of all pixels when the brightness level of all pixels of the screen is maximum as a temporary reference value. The first storage means is configured to compare a value with an integrated output of the integration means, and selectively output table data suitable for screen brightness among the plurality of types of table data based on the comparison result. And a second storage unit that stores a conversion table that corrects the contrast of the input video signal with the table data output from the first storage unit, The black level of the video signal continuously exists in pixel units, the correction unit corrects the reference value when the number of continuous pixels is a predetermined value or more, and the selection unit includes the correction unit. If there is a correction input from the means, the contrast correction circuit is characterized in that table data to be selected from the plurality of types of table data is specified using the value corrected by the correction input as a reference value. 2. The black level detection, wherein the correction means detects the brightness level of the input video signal in pixel units, and determines the black level when the brightness level of the video signal is a predetermined value or less. Means and the number of black level pixels detected by the black level detection means
In the horizontal scanning period, the number of pixels set for each of the number of pixels set from the outside is counted only when they are continuous, and the count value of the number of pixels of the black level is output for each line in the row direction of the screen. The counting value of the first counting means and the counting output of the first counting means are taken in, and the count value of the number of pixels of the black level is continuously output from the first counting means with respect to the line number in the row direction of the screen set from the outside And a second counting unit that outputs the total value to the selecting unit as a count value when the input value is input, the selecting unit compares the reference value with the output of the integrating unit, From the value indicating the total number of pixels of the screen, the value indicating the total number of pixels of the screen in the calculation formula indicating the sum of the brightness levels of all the pixels when the brightness level of all the pixels of the screen is the maximum. From the second counting means Contrast correction circuit according to claim 1, characterized in that a value obtained by replacing the force value obtained by subtracting the count value of the number of pixels of the black level. 3. 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 a noise component with respect to a video signal. 2. The contrast correction circuit according to item 2.