KR100606740B1 - Method for controlling dynamic contrast - Google Patents

Abstract

 An object of the present invention is to provide a dynamic contrast adjustment method for determining an optimal contrast value in which a screen is not saturated by including spatial information in histogram information used for contrast adjustment.

To this end, the present invention comprises the steps of (a) calculating the luminance difference between the previous pixel and the current input pixel based on the data enable signal when the video signal input; (b) if the luminance difference is less than a reference value, storing a position of a previous pixel and assuming a start position of a horizontal line region having similar luminance values; calculating a luminance difference between pixels assumed to be the start position of the horizontal line region and pixels sequentially input; (d) storing positions of the sequentially input pixels as horizontal line regions having similar luminance values when the luminance difference is less than a reference value; And (e) comparing the luminance value of the pixel input to the previous horizontal line with the luminance value of the input pixel to the next horizontal line and storing the vertical line region having similar luminance values. To provide.

Histogram, Contrast

Description

Dynamic Contrast Adjustment Method

1 is a diagram illustrating a region in which luminance values between adjacent pixels are similar.

 2 is a diagram illustrating a method of finding a region having a similar luminance value between adjacent pixels.

3 is a flowchart illustrating a method of finding an area having a similar luminance value between adjacent pixels.

4 is a diagram illustrating a contrast adjustment method using a change in inclination.

5 is a diagram illustrating a contrast adjustment method using an S-curve.

Explanation of symbols for main parts of the drawings

10: zone 1 20: zone 2

40: horizontal line area 50: vertical line area

60: input signal curve 80, 90: output signal curve

The present invention relates to a dynamic contrast adjustment method, and more particularly, to a dynamic contrast adjustment method of determining an optimal contrast value that does not saturate a screen by including spatial information in a histogram information used for contrast adjustment. It is about.

Image processing methods for improving image quality include contrast control, noise reduction, edge restoration, edge enhancement, gamma correction, and the like.

Among such image processing methods, the contrast adjustment method is widely used because it enables the image quality to be improved without increasing the amount of information by using a histogram indicating the luminance level distribution of each pixel.

In more detail, the contrast adjustment method adjusts the contrast based on the luminance distribution of the pixels. In other words, the luminance of each pixel is changed by using a Cumulative Density Function (CDF) of an input luminance signal as a transfer function, and is used in various image processing, capture, and transmission / reception apparatuses.

When the distribution of the histogram is concentrated around a part of the luminance level, it means that the pixels have similar luminance values. Therefore, the image is not clearly seen. That is, the image looks low in contrast.

On the contrary, when the histogram is spread out widely, each pixel has a different luminance value, so the image is clearly visible. In other words, the image looks very high in contrast.

Therefore, in order to adjust the contrast high, the histogram should be spread as widely as possible by modifying the luminance value of each pixel based on the information shown in the histogram.

As such, when the contrast is adjusted high, pixels of higher luminance level have higher values after contrast adjustment in the case of dark images as a whole, and those of lower luminance level have lower values in bright images. The picture becomes clearer.

However, as a result of the experiment, it was found that the distortion of the screen occurs even if the contrast is slightly increased in some cases.

This is because the histogram provides only information on the luminance level distribution of each pixel, not the spatial information of each pixel. That is, the histogram provides only information about a distribution state of pixels having a predetermined luminance value, and does not provide information on which position of a screen a pixel having a predetermined luminance value exists.

Therefore, even when the image has similar histogram information, when the luminance difference is similar between adjacent pixels, even if the contrast is slightly adjusted, the luminance values of the adjacent pixels become the same, that is, saturation occurs and the screen is distorted.

However, in the case of a screen having a large luminance difference between spatially adjacent pixels, the distortion of the screen does not occur well even if contrast adjustment is performed. This is because even if the contrast adjustment is performed and the luminance value of each pixel changes, the difference in luminance value exists between neighboring pixels unless the contrast is extremely adjusted.

As such, the dynamic contrast adjustment method according to the related art has a problem in that a part of the screen is often saturated when uniform contrast adjustment is performed based only on the histogram distribution without spatial information of each pixel.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to include a spatial information in histogram information used for contrast adjustment to determine an optimal contrast value that does not saturate a screen. To provide.

In order to achieve the above object, the present invention comprises the steps of (a) calculating the luminance difference between the previous pixel and the current input pixel based on the data enable signal when the video signal input; (b) if the luminance difference is less than a reference value, storing a position of a previous pixel and assuming a start position of a horizontal line region having similar luminance values; calculating a luminance difference between pixels assumed to be the start position of the horizontal line region and pixels sequentially input; (d) storing positions of the sequentially input pixels as horizontal line regions having similar luminance values when the luminance difference is less than a reference value; And (e) comparing the luminance value of the pixel input to the previous horizontal line with the luminance value of the input pixel to the next horizontal line and storing the vertical line region having similar luminance values. To provide.

If the luminance difference calculated in step (c) is greater than or equal to the reference value, steps (a) and (b) are repeated based on the current time point.

The present invention may further include finding only an area in which the vertical line region and the horizontal line region cross each other.

The method may further include determining a contrast value using information on the maximum and minimum values of the luminance of the crossing area and the histogram.

Hereinafter, preferred embodiments of the present invention, in which the above object can be specifically realized, are described with reference to the accompanying drawings. In describing the present embodiment, the same name and the same reference numerals are used for the same configuration and additional description thereof will be omitted below.

1 is a diagram illustrating a region in which luminance values between adjacent pixels are similar.

As shown in FIG. 1, there are regions 1 (10) and regions 2 (20) having similar luminance differences between two adjacent pixels in the entire screen, and maximum and minimum values of luminance of the regions 1, 2 (10, 20). Suppose you know the value.

In addition, it is assumed that the maximum value of the luminance of the region 2 (20) is greater than the maximum value of the luminance of the region 1 (10).

In this situation, when the contrast is adjusted, the luminance value of each pixel in the histogram is changed. At this time, when the luminance value of the saturated pixel according to the contrast adjustment is smaller than the maximum value of the luminance of the region 2 (20), each pixel of the region 2 (20) having a similar luminance value is also saturated and eventually, the region The entirety of 2 (20) is saturated, resulting in distortion of the screen in region 2 (20).

Therefore, in order to prevent distortion of the screen that may occur due to the contrast adjustment, it may be understood that the luminance value of the saturated pixel during the contrast adjustment should be larger than the maximum value of the luminance of the region 2 20.

As a result, if the regions having similar luminance differences between two adjacent pixels in the entire screen can be known, distortion of the screen can be prevented during contrast adjustment.

2 is a diagram illustrating a method of finding regions having similar luminance values between adjacent pixels, and FIG. 3 is a flowchart illustrating a method of finding regions having similar luminance values between adjacent pixels.

Referring to FIGS. 2 and 3, when a video signal is input, first, an area in which pixels having similar luminance values exist in the horizontal direction is started. At the same time, a line buffer or the like is used to find an area in which pixels having similar luminance values exist in the vertical direction.

This process starts at the rising edge of the vertical synchronization signal of the input video signal. In detail, the luminance values of the previous pixel and the current input pixel are compared based on the data enabler signal.

Here, when the difference between the luminance values is less than the predetermined reference value, the position of the previous pixel is stored and it is assumed as the start position of a horizontal line having similar luminance differences.

Of course, when the difference between the luminance values is greater than or equal to a predetermined reference value, the process of comparing the luminance values of the previous pixel and the current input pixel is continued.

The luminance values of the pixels sequentially input and the luminance values of the pixels assumed as starting positions are compared with each other, and when the luminance difference is less than the reference value, the luminance value is stored in the horizontal line region 40 having similar luminance differences.

At this time, if the difference between the luminance values of the pixels sequentially input and the luminance values of the pixels assumed as the start position is greater than or equal to the reference value, the process of searching for the horizontal line region 40 is repeated by comparing the luminance values of the pixels sequentially input again.

This process is performed sequentially for each horizontal line.

Meanwhile, in the process as described above, the luminance value of the pixel of the previous horizontal line and the luminance value of the pixel of the current horizontal line are compared with each other to find a vertical line region 50 having a similar luminance difference.

The process of finding the vertical line region is the same as the process of finding the horizontal line region 40 described above, except that the luminance difference between the pixels adjacent up and down is compared.

When all the video signals for the entire screen are input through this process, all regions in which pixels having similar luminance values exist in the horizontal direction or the vertical direction are found.

At this time, the regions 40 and 50 in which pixels adjacent in the horizontal or vertical direction have similar luminance values are removed. This is because the distortion of the screen does not occur even if all of the areas in which adjacent pixels have similar luminance values in one line are saturated.

As such, when the regions 40 and 50 found in the vertical direction or the horizontal direction are removed in turn, the regions found in the horizontal and vertical directions such as the regions 1 (10) and 2 (20) cross each other. To be found.

If such regions 1 and 2 (10 and 20) are found, as described above, the luminance value of the saturated pixel during contrast adjustment is determined based on the maximum value of the luminance of the region 2 (20).

That is, after the falling edge of the vertical synchronization signal, the information obtained through the above processes is compared with the histogram information to determine and apply a contrast that does not cause distortion of the screen.

4 is a diagram illustrating a contrast adjustment method using a change in inclination, and FIG. 5 is a diagram illustrating a contrast adjustment method using an S-shaped curve.

First, as shown in FIG. 4, the contrast adjustment may be performed by determining a luminance value of the output signal by giving a weight to the luminance value of the input signal. That is, when a certain weight is applied to the input signal curve 60, the slope of the output signal curve 80 is determined, and the contrast value to be adjusted is determined accordingly.

At this time, the slope of the output signal curve 80 determined by the weighting is determined based on the maximum luminance value 70 of the region 2 20 (see FIG. 2), which is a reference of the contrast value to be adjusted.

That is, when the slope of the output signal curve 80 becomes larger than that shown in FIG. 4, the luminance value of the pixel of the region 2 20 is saturated to cause distortion of the screen. Therefore, the range of contrast determined by the weighting becomes the area between the input signal curve 60 and the output signal curve 80.

On the other hand, as shown in Figure 5, when the contrast is adjusted using the output signal curve consisting of the S-shaped curve, the minimum value 110 of the luminance of each pixel obtained in the region 1 (10) and region 2 (20) also It must be considered together.

That is, the method of adjusting the contrast using the S-shaped curve increases the contrast of the screen in such a manner that a higher luminance value is made higher and a lower luminance value is made smaller, so that the contrast is obtained in the areas 1, 2 (10, 20). This is because saturation may occur in a direction in which the luminance is low unless the minimum value 110 of the luminance is also considered.

Therefore, when the output signal curve forms an S curve, the output signal curve 90 may determine the luminance maximum value 100 of the region 2 (20) and the minimum value 110 of the luminance of the regions 1, 2 (10, 20). It should not have excessively strong curvature.

As a result, when the S-curve is used, the range of contrast becomes the area between the input signal curve 60 and the output signal 90 curve.

The dynamic contrast adjustment method according to the present invention determines the contrast value by using histogram information together with information on regions in which pixels having similar luminance values exist. Can be prevented in advance.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (4)

calculating a luminance difference between a previous pixel and a current input pixel based on the data enable signal when the video signal is input; (b) if the luminance difference is less than a reference value, storing a position of a previous pixel and assuming a start position of a horizontal line region having similar luminance values; calculating a luminance difference between pixels assumed to be the start position of the horizontal line region and pixels sequentially input; (d) storing positions of the sequentially input pixels as horizontal line regions having similar luminance values when the luminance difference is less than a reference value; And, and (e) comparing the luminance value of the pixel input in the previous horizontal line with the luminance value of the input pixel in the next horizontal line and storing the vertical line region having similar luminance values. The method of claim 1, And repeating steps (a) and (b) based on the current time point if the luminance difference calculated in step (c) is greater than or equal to the reference value. The method of claim 1, And only finding an area in which the vertical line region and the horizontal line region cross each other. The method of claim 3, wherein And determining a contrast value using information on the maximum and minimum values of the luminance and the histogram of the intersecting region.

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