KR101238249B1 - Method of Improving Contrast and Apparatus using the method - Google Patents

Abstract

The present invention discloses a method and apparatus for improving image contrast ratio.
The image contrast ratio improvement method of the present invention includes: setting an effective area that is a region of interest based on motion information and brightness information in an input original image; Improving the image quality of the effective area; And synthesizing the original image and the effective area having the improved image quality.

Description

Method and apparatus for improving image contrast ratio {Method of Improving Contrast and Apparatus using the method}

An apparatus and method for improving an image contrast ratio used in a video system.

In the related art, an image contrast ratio is improved by applying an image quality improvement algorithm to an entire image, or by manually specifying a region that a user wants to improve image quality, the image contrast ratio is improved by using an image quality improvement algorithm only for a specific part.

When the method of collectively improving the image contrast ratio for the entire image is applied to the purpose of video surveillance, the image contrast ratio may be improved even for a portion that is not desired by the user, and thus it may be difficult to distinguish the object of interest in the entire image, and the pixel brightness may be difficult. When the image contrast ratio is improved for a low region (dark region), noise may be amplified together, and there is a possibility of unwanted noise amplification.

If the method that improves the contrast ratio only for the set area by manually setting the specific area where the event is expected to occur is applied to the purpose of video surveillance, it may be difficult to detect the event when the event occurs in the part other than the effective area set by the user. In addition, when the selected effective area includes a low pixel area (dark area), there is a possibility that noise components are amplified and image quality deterioration occurs.

The present invention provides an apparatus and method for improving an image contrast ratio that can automatically set an effective area for improving image quality and prevent amplification of noise components in an area where pixel brightness is low (dark area).

In accordance with another aspect of the present invention, there is provided a method for improving an image contrast ratio, comprising: setting an effective area, which is a region of interest, based on motion information and brightness information in an input original image; Improving the image quality of the effective area; And synthesizing the original image and the effective area having the improved image quality.

The setting of the effective area may include detecting a background area in the original image; Detecting a movement area in the original image based on the background area; Detecting overall brightness information of the original image; And determining the pixel of the effective area among the pixels of the moving area by using the pixel value obtained from the brightness information.

The detecting of brightness information may include: down sampling the original image; And upsampling the downsampled image.

The detecting of the motion area may include detecting the motion area by using a difference between the image information of the original image and the image information of the background area.

The determining of the pixel of the effective area may include determining, as a pixel of the effective area, a pixel whose pixel value of a corresponding pixel of the upsampled image is greater than or equal to a threshold value among the pixels of the moving area. have.

The synthesizing of the original image and the effective area may include synthesizing the original image by applying a weight to the pixels of the original area and the effective area, respectively, wherein the weight is determined based on brightness information of the original image. Can be.

In accordance with another aspect of the present invention, an apparatus for improving an image contrast ratio includes: an effective area setting unit configured to set an effective area that is a region of interest based on motion information and brightness information in an input original image; An image quality improving unit which improves the image quality of the effective area; And a fusion unit configured to synthesize the original image and the effective area having the improved image quality.

The effective area setting unit may include a background area detection unit detecting a background area in the original image; A motion region detector for detecting a motion region in the original image based on the background region; A brightness information detector for detecting overall brightness information of the original image; And an effective area extractor configured to determine a pixel of the effective area among the pixels of the moving area by using the pixel value obtained from the brightness information.

The brightness information detector may downsample the original image and upsample the downsampled image.

The effective area extractor may determine, as a pixel of the effective area, a pixel whose pixel value of a corresponding pixel of the upsampled image is greater than or equal to a threshold value among the pixels of the movement area.

The motion region detector may detect the motion region by using a difference between the image information of the original image and the image information of the background region.

The fusion unit may be synthesized by applying weights to the pixels of the original image and the effective area, respectively, and the weight may be determined based on brightness information of the original image.

The apparatus and method for improving the image contrast ratio of the present invention can automatically set the effective area to increase the contrast ratio of the effective area, prevent amplification of noise components in a low pixel brightness (dark area), and facilitate subject recognition. Do.

1 is a block diagram schematically illustrating a configuration of an apparatus for improving an image contrast ratio according to an embodiment of the present invention.
FIG. 2 is a block diagram schematically illustrating a configuration of an effective area setting unit of FIG. 1.
3 is a block diagram schematically illustrating a configuration of the brightness information detector of FIG. 2.
4 is a flowchart illustrating a method of improving an image contrast ratio according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the same elements among the drawings are denoted by the same reference numerals and symbols as much as possible even though they are shown in different drawings. In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

1 is a block diagram schematically illustrating a configuration of an apparatus for improving an image contrast ratio according to an embodiment of the present invention. FIG. 2 is a block diagram schematically illustrating a configuration of an effective area setting unit of FIG. 1. 3 is a block diagram schematically illustrating a configuration of the brightness information detector of FIG. 2.

Referring to FIG. 1, the image contrast ratio improving apparatus 10 of the present invention includes an input unit 101, an effective area setting unit 103, an image quality improving unit 105, a fusion unit 107, and an output unit 109. do.

The image contrast ratio improvement apparatus 10 is a device that makes it possible to more clearly distinguish a subject of a region of interest from an original image. Contrast ratio refers to the difference in color tone between the lightest and darkest parts of a television, facsimile or computer display. If the contrast ratio is small, the image quality of the image as a whole is not clear and it is difficult to identify the object. Therefore, the image quality should be improved to make observation easier by improving the contrast ratio as much as possible.

The image contrast ratio improvement apparatus 10 is an apparatus that outputs an original image as it is to a background region, and applies an image quality improvement algorithm only to a portion determined to be an effective region, thereby improving the image quality as a whole. The image contrast ratio improvement apparatus 10 is a digital imaging apparatus that displays a video such as a visual camera that performs digital image processing, a thermal camera, a surveillance camera such as a special purpose camera, a mobile phone camera, a camcorder, a mobile device for playing a video, and the like. Can be applied to

The input unit 101 receives an original image in a frame cycle from a camera or an external device.

The effective area setting unit 103 automatically detects an area of interest, that is, an effective area, to improve image quality in the original image. The effective area setting unit 103 sets an effective area based on the motion information and the brightness information in the original image. Referring to FIG. 2, the effective area setting unit 103 includes a background area detector 202, a motion area detector 204, a brightness information detector 206, and an effective area extractor 208.

The background region detector 202 detects the background region from the original image input from the input unit 101. The background region detector 202 may detect a background region by applying various known techniques.

As an example, the background region detector 202 may detect the background region by generating a background image using an IIR filter (infinite impulse response filter) on the original image. The IIR filter is a digital filter in which filtering is performed by applying a value of an input signal and a value of an output signal recursively. Various background image generation techniques, including a background image generation method using an IIR filter, are well known and thus will not be described in detail. As another example, the background region detector 202 may use an average sum between image frames to detect the background region.

The motion region detector 204 detects a motion region (motion information) from the original image by using the background region of the background image. The motion region detector 204 may generate a motion image by using the difference between the original image and the background image, and extract the motion information. That is, the motion region detector 204 may detect the motion region by using the difference between the image information of the original image and the image information of the background region.

The brightness information detector 206 generates a blur image from the original image, and detects overall screen brightness distribution information (hereinafter referred to as 'screen brightness information') for the original image. Referring to FIG. 3, the brightness information detector 206 includes a down sampling unit 302 and an up sampling unit 304. The downsampling unit 302 downsamples the original image input from the input unit 101 to a predetermined size. The upsampling unit 304 generates a blur image by up-sampling the down-sampled image to the original image size. In this case, a bilinear interpolation algorithm may be used during upsampling, and the present invention is not limited thereto. The brightness information detector 206 may generate a blur image like a low pass filter (LPF) while reducing the burden on hardware.

As another example, the brightness information detector 206 may blur the entire original image horizontally / vertically through a low pass filter (LPF) having a large number of taps, thereby obtaining a full screen brightness distribution of the image.

The effective area extractor 208 extracts the effective area in units of pixels based on the motion area information from the motion area detector 204 and the brightness information from the brightness information detector 206. The effective area extractor 208 determines the pixel of the effective area among the pixels of the moving area by using the pixel value obtained from the brightness information. The effective area extractor 208 determines, as a pixel of the effective area, a pixel whose pixel value of the corresponding pixel of the blur image is greater than or equal to a threshold value among the pixels of the moving area. The blur image may be an upsampled image after down sampling or an image generated by LPF.

If the contrast ratio is improved after determining the effective area using only the motion information, noise may be amplified together in an area where the pixel brightness is low (dark area) to deteriorate image quality. Therefore, the effective area extraction unit 208 of the present embodiment excludes an area where the pixel brightness is below a certain level from the effective area and sets it as an effective area only when the pixel brightness is above a certain level. The effective area extraction unit 208 extracts a pixel whose pixel brightness (pixel value) of the pixel included in the moving area is equal to or greater than a specific level (threshold value) and sets the effective area. In the present exemplary embodiment, the effective area is set in pixel units, but the effective area may be set in block units instead of pixel units.

The threshold value may be set in various ways. For example, after analyzing the entire pixel brightness information using a histogram, the threshold value may be set to an optimal brightness value determined, or the user may set the threshold value using an external control register. You can select the values manually, or you can set the threshold by applying both methods.

The image quality improvement unit 105 improves the image quality of the effective area set by the effective area setting unit 103. The image quality improving unit 105 may improve the image quality by adjusting the brightness, contrast, color amount, contrast ratio, sharpness, and the like of the image data in the effective area. Accordingly, the image quality of the effective area is output as an improved image. In this case, each parameter value for improving image quality may be fixed to an initial value or adjusted and preset by a user. The image quality improvement unit 105 may include various edge enhancement algorithms such as an edge enhancement algorithm, a histogram-based image enhancement algorithm such as histogram equalization or histogram stretching, and a color control (HUE control) algorithm. The method can be applied, and the image quality improvement techniques are well known, and thus detailed description will be omitted.

The fusion unit 107 synthesizes the original image input from the input unit 101 and the effective area having improved image quality. The fusion unit 107 may generate a composite image by fusing (synthesizing) the original image and the improved image having improved image quality of the effective region. The fusion unit 107 fuses the pixels of the original image and the enhancement image by applying weights. In the dark areas, weights are set to refer to more of the original image, and in light areas to refer to more contrast-enhanced images. In the present embodiment, by fusion of the improved image with the original image, it is possible to minimize unnaturalness of the synthesized image and to suppress noise amplification in the dark region.

For example, when the pixel value of the image is represented by 8 bits (0 to 255), the weight value of (255-A) is applied to the pixel value B of the original image, and to the pixel value C of the enhancement image. When the weight of A is applied, the corresponding pixel value of the synthesized image is calculated by Equation 1 below.

(B x (255-A) + C x A} / 255 ..... (1)

Here, the weight A is a value determined based on the brightness information of the original image and may be a pixel value of the blur image. The fusion unit 107 may obtain brightness information of the original image from the brightness information detector 206.

The output unit 109 outputs the synthesized image to a display device such as a monitor. The synthesized image is an image having an improved image contrast ratio by improving image quality of an effective area.

4 is a flowchart illustrating a method of improving an image contrast ratio according to an embodiment of the present invention.

Referring to FIG. 4, in the image contrast ratio improvement method of the present embodiment, a background region is detected from an original image, a motion region (motion information) is detected using the extracted background region, and brightness obtained from the motion region information and the original image is detected. An effective area for image quality improvement is extracted based on the information. The method generates an improved image by applying an image quality improvement algorithm to the extracted effective area, and generates a final composite image by fusing the original image and the improved image.

First, the apparatus for improving image contrast ratio receives an image (S420) and automatically sets an effective area from the input original image (S440).

In order to set an effective area, the image contrast ratio improvement apparatus detects a background area from the original image (S441). The background area detection may be performed using an IIR filter or an average sum method among image frames.

The apparatus for improving image contrast ratio detects a motion region from the difference between the image information of the original image and the image information of the background region (S443).

The image contrast ratio improvement apparatus detects overall screen brightness information of the original image (S445). The screen brightness information of the original image may be detected from a blurred image of the original image blurred through the LPF, or a blurred image by down-sampling the original image after upsampling.

The image contrast ratio improvement apparatus sets an effective region in the original image based on the movement region information and the brightness information (S447). The image contrast ratio improvement apparatus compares the pixel brightness value (pixel value) and the threshold value of each of the pixels detected as the moving region. Herein, the pixel value of the pixel in the motion area is the pixel value of the blur image. As a result of the comparison, except that the pixel value is smaller than the threshold value, the pixel whose pixel value is larger than the threshold value is determined as a pixel of the effective area. Pixels having the same pixel value as the threshold may be set to be excluded from or included in the effective area.

The apparatus for improving image contrast ratio performs image quality improvement by applying an appropriate image quality improvement algorithm to an effective area (S460).

The image contrast ratio improvement apparatus fuses the original image and the improved image having improved image quality of the effective area (S480). In this case, a weight is applied to each pixel of the original image and the corresponding pixel of the enhancement image. The weight is determined from the brightness value (pixel value) of the pixel of the blur image.

So far I looked at the center of the preferred embodiment for the present invention. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

Claims (14)

delete Setting an effective area, which is a region of interest, based on motion information and brightness information in the input original image;
Improving the image quality of the effective area; And
And synthesizing the original area and the effective area having the improved image quality.
The effective area setting step,
Detecting a background area from the original image;
Detecting a movement area in the original image based on the background area;
Detecting overall brightness information of the original image; And
And determining the pixel of the effective area among the pixels of the moving area by using the pixel value obtained from the brightness information. The method of claim 2, wherein the detecting of the brightness information comprises:
Downsampling the original image; And
Upsampling the downsampled image; and improving the image contrast ratio. Claim 4 has been abandoned due to the setting registration fee. The method of claim 2, wherein the detecting of the motion area comprises:
And detecting the motion region by using a difference between the image information of the original image and the image information of the background region. The method of claim 3, wherein the determining of the pixel of the effective area comprises:
And determining a pixel having a pixel value of a corresponding pixel of the upsampled image among the pixels of the moving area equal to or greater than a threshold value as a pixel of the effective area. The method of claim 2, wherein the synthesizing the original image and the effective area comprises:
And synthesizing the original image by applying weights to the pixels of the effective area, respectively. Claim 7 has been abandoned due to the setting registration fee. The method according to claim 6,
And the weight is determined based on brightness information of the original image. delete An effective area setting unit configured to set an effective area which is a region of interest on the basis of motion information and brightness information in the input original image;
An image quality improving unit which improves the image quality of the effective area; And
And a fusion unit configured to synthesize the original image and the effective area having the improved image quality.
The effective area setting unit,
A background area detector for detecting a background area from the original image;
A motion region detector for detecting a motion region in the original image based on the background region;
A brightness information detector for detecting overall brightness information of the original image; And
And an effective area extractor configured to determine a pixel of the effective area among the pixels of the moving area by using the pixel value obtained from the brightness information. The method of claim 9, wherein the brightness information detection unit,
And down-samples the original image and up-samples the down-sampled image. Claim 11 was abandoned upon payment of a setup registration fee. The method of claim 9, wherein the motion area detection unit,
And an image contrast ratio improvement device using the difference between the image information of the original image and the image information of the background region. The method of claim 10, wherein the effective area extraction unit,
And determining a pixel having a pixel value of a corresponding pixel of the upsampled image among the pixels of the moving area as a pixel of the effective area. The method of claim 9, wherein the fusion unit,
And an image contrast ratio improving device configured to apply weights to the original image and the pixels of the effective area, respectively. Claim 14 has been abandoned due to the setting registration fee. The method of claim 13,
And the weight is determined based on brightness information of the original image.

Images