KR0145624B1 - Image compensation by local block histogram - Google Patents

Abstract

The present invention relates to a device for compensating a histogram by local block simplification. In a conventional video camera, when an image is taken in a room with low illumination, the entire image appears dark, and the beach or the sunlight exhibiting high illumination In outdoor scenes, we tried to solve the problem by using functions such as AUTO GAIN CONTROL, WHITE BALANCE, or AUTO KNEE to prevent the picture from appearing bright overall. For the locally weak image, the effect of it is weak, and in case of image compensation by normal histogram, it is difficult to process in real time when applying the histogram, and the hardware volume becomes large due to the hardware implementation for real time processing. Full spirit Divide the pixel level of the input image by the pixel level of the specific size for a simplified representation of the histogram, and divide the histogram with the local block of the specific size. The histogram for each level is expressed in binary, and then the correction is performed for each block by the probability distribution that each pixel number occupies in the whole image, and the local image compensation as well as the overall low contrast image compensation is performed. The present invention also relates to an image compensating apparatus using a histogram simplification for each local block.

Description

Image compensation device by histogram for each local block

1 is a block diagram of an image compensation apparatus using a histogram for each local block according to an exemplary embodiment of the present invention.

2 is a characteristic diagram showing regression of input levels for histograms for each local block according to an embodiment of the present invention;

3 is a binary representation of the histogram for each local block according to a specific threshold according to an embodiment of the present invention.

4 is a characteristic diagram showing a guard zone (GUARD ZONE) which is proportionally compensated for eliminating an intervector between the blocks on a histogram represented by a binary number for each pixel number according to an embodiment of the present invention.

* Explanation of symbols for main parts of the drawings

1: Requantization part (REQUANTIZAION)

2: Local Histogram Counter

3: Reference Generator (Bottom High Peak Low)

4: Parameter Memory

5: Parameter Interpolation

6: Histogram Modification

7: Timing Control Generator

The present invention relates to an image compensator using histograms for each local block. More specifically, a histogram for each local block is obtained for an input video signal. In this case, for the sake of simplicity, the histogram of the input level is recalculated and thresholded. The present invention relates to an image correction apparatus using a histogram for each local block for local image compensation of a video camera input image using a parameter obtained from binary information.

In general, in the video camera, the external illuminance has a great influence on the video image. When the image is taken in a low-light interior, the entire image appears dark. The picture is bright overall.

Conventionally, in case of a video camera, in order to prepare for such a case, a problem such as AUTO GAIN CONTROL, WHITE BALANCE, or AUTO KNEE has been tried to solve the problem, but these functions perform the same compensation for the entire image. As a result, the effects of local weak images were weak. In addition, even in the image compensation by the histogram, the real-time processing is difficult to apply the histogram, and the hardware volume due to the implementation of the hardware for the real-time processing is not commercialized.

Therefore, an object of the present invention is to solve the disadvantages of the prior art by using a histogram equalization method or a histogram modulation method. The histogram is obtained and the histogram is corrected for each block to improve not only the local image but also the overall low contrast image compensation.

The configuration of the present invention to achieve the above object,

A requantization unit (REQUANTIZATION) for simplifying a digitally inputted video signal (Y signal) according to local block processing;

A local histogram counter unit (LOCAL HISTOGRAM COUNTER) for receiving the simplified result as an input and determining the number of pixels for each level for each local block;

A reference generator section (BH PL GENERATOR) for determining two parameter values (BHM, PLM) from the histogram generated for each block;

A parameter memory unit (PLM) for storing the two parameter values (BHM, PLM) for compensation to the next field;

A parameter interpolator (PAI) for interpolating interblock parameters to prevent sudden changes in two parameter values (FDBHM, FDPLM) that delay a field between adjacent local blocks and artifacts between blocks;

A local histogram modulating unit (HM) for obtaining a final compensated signal (CY) by multiplying a parameter value using the interpolation method with a video signal (Y signal) input after one field delay;

It consists of a time control generator section (TCG) which controls the operation at each section in time and creates a delay adjustment time for one field delay of the parameter.

Hereinafter, with reference to the accompanying drawings, the most preferred embodiment that can easily implement the image compensation apparatus by the histogram for each local block according to the configuration as follows.

1 is a block diagram illustrating a locally adaptive histogram modulation.

As shown in Figure 1 above, the locally adaptive histogram requantization is

A reordering unit 1 which simplifies the digital input video signal (Y signal) composed of 256 levels to 16 kinds of levels to easily obtain a histogram while performing local block processing;

A local histogram counter unit 2 that calculates a local histogram by taking the simplified result as an input, calculating the number of pixels for each level for each local block, and then expressing it as a 16-bit binary number based on a threshold. Wow;

From the local histogram expressed as a 16-bit binary number based on the threshold, the value is lowered to 0, and the value is lowered to 0 from the level BH and 255 level where the binary 1 first starts. A reference generator section 3 for determining the level value PL at which the decimal number 1 starts and then for determining two parameter values BHM and PLM for BH and PL values for eliminating the ARTIFACT in the block;

A parameter memory unit (4) for storing parameter (FDBHM, FDPLM) values for storing two parameters per block to compensate the two parameter values (BHM, PLM) by one field and compensate for the video signal of the next field;

Block artifacts occur when two parameter values (FDBHM, FDPLM) that delay one field between adjacent local blocks have a large gap between adjacent blocks. Therefore, interblock parameters can be interpolated using 2-D INTERPOLATION to prevent this. A parameter interpolator 5 for obtaining final parameters NBHM and NPLM;

A local histogram modulating section (6) which multiplies one field delayed tooth type parameter (NBHM, NPLM) by a Y signal to obtain a final compensated CY signal;

It is made up of a time adjusting generator section 7 which controls the operation in each section in time and controls the delay time for the delay of one field in the parameter memory section PLM.

Using the last two parameters (NBHM, NPLM) passed through the parameter interpolator (5), the value for the input image signal (Y signal) is calculated in the histogram modulation unit (6). In this case, local histogram modulation is performed by multiplying the field input video signal (Y signal) of the extracted field by the parameter, and a final compensated CY signal is generated by the following equation.

The IRE value is a value determined according to the video signal format (FORMAT).

2 is a characteristic diagram showing a locally adaptive histogram regression.

As shown in FIG. 2, the Y-signal input to the digital signal composed of 256 levels for local block processing is simplified to 16 smaller levels in the requantization unit 1, and then at each level. It is represented by the histogram according to the probability distribution of the number of image pixels.

Figure 3 shows the representation of the local adaptive histogram 1 and 0 in binary.

As shown in FIG. 3, when the level of the histogram of each level is greater than the threshold value based on the threshold 8, the requantized level is represented as 1; otherwise, 0 is represented. Represented by. According to this method, the histogram is expressed as 1 and 0 without representing the number of pixels, thereby facilitating real-time processing.

4 is a characteristic diagram showing a guard zone (GUARD ZONE) proportionally compensated on a histogram represented in binary in an embodiment of the present invention.

As shown in FIG. 4, ARTIFACT occurs when a parameter value in the local block is too large. To eliminate this, the BH and PL values are modified according to parameters to modify the parameter value (BHM, PLM).

Equation related to the generation method of the guard zone parameter (GUARD ZONE PARAMETER) using a specific ratio (Ratio) for removing the above-described fact is as follows.

The ratio here has a value from 0 to 1.

Operation of the locally adaptive histogram modulation according to the embodiment of the present invention by the above configuration is as follows.

First, when power is applied to the color video camera, the solid-state image sensor (CCD) in the camera is separated into three video signals, Y, RY, and BY, from the output base color RGB, and then only the video signal (Y signal). We divide the entire video into 64 * 64 local blocks.

In addition, after dividing the entire image into local blocks, the quantization unit 1 simplifies the digital input image signal (Y signal) composed of 256 levels to 16 kinds of levels.

For the simplified level, the local histogram counter unit 2 calculates the number of pixels for each level, and then calculates the local histogram by expressing it in 16-bit binary numbers based on a threshold.

After calculating the local histogram, the BN and PL values are obtained from the local histogram expressed in 16-bit binary number based on the threshold value in the reference generator section 3, and two parameter values (BHM, PLM) are obtained from the values. Determine.

The two parameter values BHM and PLM determined by the reference generator 3 are delayed by one field in the parameter memory 4 under the control of the time control generator 7 and the two delayed parameters FOBHM and FDPLM. The values are read into the parameter memory section 4 in the next field.

The two parameter values FDBHM and FDPLM read in the parameter memory section 4 are interpolated in the parameter interpolation section 5 to prevent artifacts caused by large parameter differences between blocks. Find (NBHM, NPLM).

By using the final parameters (NBHM, NPLM) obtained from the parameter interpolator 5, the local histogram modulation unit 6 multiplies with the Y signal to generate a final compensated signal CY, thereby generating an image by histogram for each local block. The compensation device is operated.

The effect of the present invention is not only to improve the overall image quality deterioration of the image, but also to obtain a better image quality through the simplified histogram correction for local image degradation, and to perform histogram correction for each local block instead of the whole, and to reduce the threshold and threshold. By performing histogram modulation through binary representation of histogram by threshold and block parameter interpolation, real-time processing is easy and hardware volume can be reduced.

Claims (7)

A requantization unit (REQUANTIZATION) for simplifying a digital input image signal (Y signal) to simplify local block processing; a local according to calculation of the number of pixels for each level for each local block by receiving the simplified result as an input; A LOCAL HISTORGRAM COUNTER; a binary generator of the histogram by the threshold in the histogram and a reference generator section (BH PL GENERATOR) for determining two parameter values (BHM, PLM) from these values; A parameter memory unit (RAM) for storing the two parameter values (BHM, PLM); and two parameter values (FDBHM, FDPLM) between adjacent ones delayed by one field, using parameter interpolation to prevent sudden changes. A parametric interpolation unit (PAI) for interpolating the local histogram modulating unit (HM) for multiplying a parameter value using the interpolation method with an image signal of another field to obtain a final compensated signal (CY); A time compensation generator (TCG) for controlling the operation in time and generating a control signal for delay of one field, the image compensation device by simplifying the number of pixels per local block. The method of claim 1, wherein the reordering unit simplifies the Y signal among the Y, RY, and BY video signals of the digital input color video camera composed of 256 levels to simplify the local block processing to 16 kinds of levels. Image compensation device by histogram simplification for each local block. The method of claim 1, wherein the local histogram counter unit receives the requantized result as an input, calculates the number of pixels for each level for each local block, and then uses a 16-bit binary number based on a threshold 8. Representation level is represented as 1 when the number of pixels more than the threshold value is input, otherwise it is represented by 0 to represent the histogram to represent a histogram for each local block. The method of claim 1, wherein the reference generator unit determines a histogram difference at 0 and a histogram difference at 255 of a local histogram expressed in 16-bit binary numbers based on a threshold, and then removes artifacts according to the histogram distribution. And an image compensation device according to a histogram simplification for each local block, wherein two parameter values (BHM and PLM) are determined according to a guard zone method. The method of claim 1, wherein the parameter interpolator is two-dimensional to prevent a block artifact from changing a large window between blocks in which two field delayed values (FDBHM, FDPLM) of one field delay between adjacent local blocks according to a timing generator are changed. And a final parameter (NBHM, NPLM) obtained by performing interpolation (2-D INTERPOLATION). 2. The method of claim 1, wherein the local histogram modulation unit is finally compensated by multiplying the last two parameters (NBHM, NPLM) with one field delay through the parameter interpolator by the current input image signal (Y signal). An image compensation device by simplifying a histogram for each local block, the CY signal being calculated. The method of claim 1, wherein a specific ratio (Ratio) having a value of 0 to 1 is used to remove the ARTIFACT generated by the parameter difference in the local block for the two parameter values obtained by the reference generator. An image compensation device using a histogram simplification for each local block, which uses a guard zone parameter generator technique.