KR970073039A - Image enhancement method and its circuit using average separation histogram equalization with brightness compensation function - Google Patents

Image enhancement method and its circuit using average separation histogram equalization with brightness compensation function Download PDF

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KR970073039A
KR970073039A KR1019960011624A KR19960011624A KR970073039A KR 970073039 A KR970073039 A KR 970073039A KR 1019960011624 A KR1019960011624 A KR 1019960011624A KR 19960011624 A KR19960011624 A KR 19960011624A KR 970073039 A KR970073039 A KR 970073039A
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average level
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image
density function
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KR100188679B1 (en
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김영택
조용훈
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김광호
삼성전자 주식회사
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Priority to JP09051871A priority patent/JP3130266B2/en
Priority to DE69717518T priority patent/DE69717518T2/en
Priority to ES97301554T priority patent/ES2188863T3/en
Priority to CN97102591A priority patent/CN1075917C/en
Priority to EP97301554A priority patent/EP0794514B1/en
Priority to US08/813,425 priority patent/US5963665A/en
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/44—Receiver circuitry for the reception of television signals according to analogue transmission standards
    • H04N5/57—Control of contrast or brightness
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T5/00—Image enhancement or restoration
    • G06T5/40—Image enhancement or restoration using histogram techniques
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T5/00—Image enhancement or restoration
    • G06T5/50—Image enhancement or restoration using two or more images, e.g. averaging or subtraction
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T7/00—Image analysis
    • G06T7/10—Segmentation; Edge detection
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2207/00—Indexing scheme for image analysis or image enhancement
    • G06T2207/20—Special algorithmic details
    • G06T2207/20021—Dividing image into blocks, subimages or windows
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2207/00—Indexing scheme for image analysis or image enhancement
    • G06T2207/20—Special algorithmic details
    • G06T2207/20212—Image combination
    • G06T2207/20216—Image averaging

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  • Signal Processing (AREA)
  • Image Processing (AREA)
  • Picture Signal Circuits (AREA)

Abstract

본 발명의 화질 개선 방법은 입력되는 영상신호를 화면단위로 평균레벨을 구하는 단계, 화면단위의 입력되는 영상신호의 그레이 레벨분포도를 구하는 단계, 구해진 화면단위의 그레이 레벨 분포도를 평균레벨에 따라 소정수의 서브영상으로 분할하는 단계, 구해진 화면단위의 그레이 레벨 분포도를 근거로하여 분할된 서브영상별로 확률밀도함수와 누적밀도함수를 구하는 단계, 입력영상이 평균밝기에 근거하여 소정의 보정함수에 따른 보정치를 평균레벨에 가산하여 보상된 평균레벨을 얻는 단계 및 서브영상별로 구해진 누적밀도함수와 보상된 평균레벨에 따라 각 서브영상의 샘플들을 그레이 레벨로 맵핑하여 등화된 신호를출력하는 단계를 포함하여 입력영상의 평균밝기에 따라 보정치가 부가된 보상된 평균레벨을 근거로 하여 등화된 신호의밝기를 조절함으로써 지나치게 어둡거나 밝은 입력영상신호의 콘트라스트를 개선하여 화질을 크게 개선시킨다.According to an aspect of the present invention, there is provided an image quality improvement method including: obtaining an average level of an input video signal on a screen basis; obtaining a gray level distribution diagram of an input video signal on a screen basis; Calculating a probability density function and a cumulative density function for each divided sub-image based on the obtained gray-level distribution of the screen unit, calculating a correction value according to a predetermined correction function based on the average brightness, To the average level to obtain a compensated average level, and outputting an equalized signal by mapping the samples of each sub-image to a gray level according to the accumulated density function and the compensated average level obtained for each sub-image, The brightness of the equalized signal based on the compensated average level with the correction value added according to the average brightness of the image Thereby improving the contrast of the input image signal, which is excessively dark or bright, and greatly improving the image quality.

Description

밝기보상기능을 가진 평균 분리 히스토그램 등화를 이용한 화질 개선방법과 그 회로Image enhancement method and its circuit using average separation histogram equalization with brightness compensation function

본 내용은 요부공개 건이므로 전문내용을 수록하지 않았음Since this is a trivial issue, I did not include the contents of the text.

제1도는 본 발명에 의한 화질 개선 회로의 일 실시예에 따른 블럭도이다. 제2A도 및 제2B도는 본 발명에 적용되는 밝기 보정함수의 예를 설명하기 위한 도면이다. 제3A도 및 제3B도 및 제2B도에 도시된 밝기 보정함수에 의해 보상된 평균레벨과 입력영상의 평균레벨의 관계의 예를 보인 도면이다.FIG. 1 is a block diagram of an image quality improvement circuit according to an embodiment of the present invention. 2A and 2B are views for explaining an example of a brightness correction function applied to the present invention. FIG. 3B is a diagram showing an example of a relationship between an average level compensated by the brightness correction functions shown in FIGS. 3A, 3B and 2B and an average level of an input image; FIG.

Claims (14)

소정수(L)의 그레이 레벨로 표현되는 영상신호를 히스토그램 등화하여 화질을 개선하는 방법에 있어서. (a)입력되는 영상신호를 화면단위로 평균레벨을 구하는 단계. (b) 화면단위의 입력되는 영상신호의 그레이 레벨 분포도를 구하는 단계; (c) 상기 구해진 화면단위의 그레이 레벨 분포도를 상기 평균레벨에 따라 소정수의 서브영상으로 분할하는 단계; (d) 상기 구해진 화면단위의 그레이 레벨 분포도를 근거로하여 상기 분할된 서브영상별로 확률밀도함수와 누적밀도함수를 구하는 단계; (e) 입력영상의 평균밝기에 근거하여 소정의 보정함수에 따른 보정치를 상기 평균레벨에 가산하여 보상된 평균레벨을 얻는 단계; 및 (f) 서브영상별로 구해진 누적밀도함수와 상기 보상된 평균레벨에 따라 각 서브영상의 샘플들을 그레이 레벨로 밉핑하여 등화된 신호를 출력하는 단계를 포함함을 특징으로 하는 화질 개선 방법.A method for enhancing image quality by histogram equalizing a video signal represented by a predetermined number (L) of gray levels. (a) obtaining an average level of an input video signal on a screen basis; (b) obtaining a gray level distribution diagram of an input video signal in a screen unit; (c) dividing the gray level distribution diagram of the obtained screen unit into a predetermined number of sub-images according to the average level; (d) obtaining a probability density function and an accumulated density function for each of the divided sub-images based on the obtained gray-level distribution diagram of the screen unit; (e) obtaining a corrected average level by adding a correction value according to a predetermined correction function to the average level based on an average brightness of the input image; And (f) outputting an equalized signal by dumping the samples of each sub-image to a gray level according to the cumulative density function obtained for each sub-image and the compensated average level. 제 1 항에 있어서, 상기 (c)단계에서는 상기 화면단위의 그레이 분포도를 상기 평균레벨에 따라 2개의 서브영상으로 분할함을 특징으로 하는 화질 개선 방법.The method of claim 1, wherein in step (c), the gray distribution of the screen unit is divided into two sub-images according to the average level. 제1항에 있어서, 상기 (f)단계는 (f1) 입력되는 영상신호 샘플이 상기 평균레벨 이하이면 이에 해당하는 서브영상의 누적밀도함수에 따라 최소 그레이레벨(X0)에서 보상된 평균레벨(Bm)까지의 그레입레베로 맵핑하는 단계; 및 (f2) 입력되는 영상신호 샘플이 상기 평균레벨 보다 크면 이에 해당하는 서브영상의 누적밀도함수에 따라 Bm'에서 최대 그레이레벨(XL-1)까지의 그레이레벨로 맵핑하되 여기서 Bm′=Bm+XL-1/(L-1)인 단계를 포함함을 특징으로 하는 화질 개선방법.The method of claim 1, wherein the step (f) is (f1) of the picture signal samples to be input compensation at least the gray level (X 0) in accordance with the cumulative density function of the sub video, which is the average level less than equivalent average level ( B m ); And (f2) B m according to the cumulative density function of the video signal samples to be input is large, corresponding than the average level of the sub image, but the mapping on to the gray level to the maximum gray level (X L-1), where B m ' = B m + X L-1 / (L-1). 제1항에 있어서, 상기 (e)단계에서는 상기 평균레벨이 아주 작으면 즉, 아주 어두운 영상이면 제로보다 큰 보정치를 상기 평균레벨에 가산하고, 상기 평균레벨이 아주 크면 아주 밝은 영상이면 제로보다 작은 보정치를 상기 평균레벨에 가산하여 보상된 평균레벨을 얻고 이 보상된 평균레벨에 따라 등화된 신호의 밝기가 조절됨을 특징으로 하는 화질 개선 방법.The method of claim 1, wherein in step (e), if the average level is very small, that is, if the image is a very dark image, a correction value larger than zero is added to the average level, The correction value is added to the average level to obtain the compensated average level, and the brightness of the equalized signal is adjusted according to the compensated average level. 소정수(L)의 그레이 레벨로 표현되는 영상신호를 히스토그램 등화하여 화질 개선하는 회로에 있어서 입력되는 영상신호를 화면단위로 그레이 레벨 분포도를 계산하는 제1계산수단; 입력되는 영상신호를 화면단위로 평균레벨을 계산하는 제2계산수단; 입력영상의 평균밝기에 근거하여 소정의 보정함수에 따른 보정치를 상기 평균레벨에 가산하여 보상된 평균레벨을 출력하는 밝기 보상수단; 상기 계산된 화면단위의 그레이 레벨 분포도를 상기 평균레벨에 따라 소정수의 서브영상으로 분할하고 서브영상별로 확률밀도함수를 출력하는 분할수단; 상기 서브영상별로 출력되는 확률밀도함수를 근거로하여 서브영상별로 누적밀도함수를 계산하는 제3계산수단; 입력되는 영상신호를 화면 단위로 지연하는 화면 메모리; 상기 화면 메모리로부터 출력되는 각 서브영상의 샘플들을 상기 서브영상별로 계산된 누적밀도함수와 상기 보상된 평균레벨에 따라 그레이레벨로 맵핑하는 맵핑수단; 및 상기 화면 메모리로부터 출력되는 영상신호와 상기 평균레벨을 비교한 결과에 따라 상기 맵핑수단에서 출려되는 서브영상별로 그레이 레벨로 맵핑된 출력중 하나를 선택해서 등화된 신호를 출력하는 출력수단을 포함함을 특징으로 하는 화질 개선 회로.A first calculation means for calculating a gray level distribution diagram of an input video signal on a screen basis in a circuit for improving a picture quality by histogram equalizing a video signal represented by a predetermined number (L) of gray levels; Second calculation means for calculating an average level of an input video signal on a screen basis; Brightness compensation means for adding a correction value according to a predetermined correction function to the average level based on an average brightness of an input image to output a compensated average level; Dividing means for dividing the gray level distribution diagram of the calculated screen unit into a predetermined number of sub-images according to the average level and outputting a probability density function for each sub-image; Third calculation means for calculating an accumulated density function for each sub-image based on a probability density function output for each sub-image; A screen memory for delaying an input video signal in picture units; Mapping means for mapping the samples of each sub-image output from the screen memory to a gray level according to the accumulated density function calculated for each sub-image and the compensated average level; And output means for outputting an equalized signal by selecting one of gray level mapped outputs of the sub-images output from the mapping means according to a result of comparing the video signal outputted from the picture memory with the average level And an image quality improving circuit. 제5항에 있어서, 상기 출력수단은 상기 평균레벨과 상기 화면 메모리의 출력신호를 비교해서 선택제어신호를 출력을 비교기; 및 상기 맵핑수단으로부터 출려되는 서브영상별로 그레이레벨로 맵핑된 출력중 하나를 상기 선택제어신호에 따라 선택하는 선택기를 포함함을 특징으로 하는 화질 개선 회로.6. The apparatus of claim 5, wherein the output means comprises: a comparator for comparing the average level with an output signal of the screen memory and outputting a selection control signal; And a selector for selecting one of the outputs mapped to the gray level for each of the sub images output from the mapping unit according to the selection control signal. 제5항에 있어서, 상기 제3계산수단에서 서브영상별로 계산된 누적밀도함수를 화면단위로 갱신함과 동시에 이전에 저장된 누적밀도함수를 상기 맵핑수단에 공급하는 버퍼를 더 포함함을 특징으로 하는 화질 개선 회로.The image processing apparatus according to claim 5, further comprising a buffer for updating the cumulative density function calculated for each sub-image in the third calculation unit on a screen basis and for supplying the previously stored cumulative density function to the mapping unit Image quality improvement circuit. 제5항에 있어서, 상기 밝기 보상수단은 상기 평균레벨이 아주 작으면 즉, 아주 어두운 영상이면 제로보다 큰 보정치를 상기 평균레벨에 가산하고, 상기 평균레벨이 아주 크면 즉, 아주 밝은 영상이면 제로보다 작은 보정치를 평균레벨에 가산하여 보상된 평균레벨을 출력함으로써 등화된 신호의 밝기가 조절됨을 특징으로 하는 화질 개선 회로.6. The apparatus of claim 5, wherein the brightness compensating means adds a correction value greater than zero to the average level if the average level is very small, that is, if the average level is very dark, and if the average level is very large, And the brightness of the equalized signal is adjusted by adding a small correction value to the average level and outputting the compensated average level. 제5항에 있어서, 상기 맵핑수단은 입력되는 영상신호 샘플이 상기 평균레벨 이하이면 이에 해당하는 서브영상의 누적밀도함수에 따라 최소 그레이레벨(X0)에서 보상된 평균레벨(Bm)까지의 그레이레벨로 맵핑하는 제1맵퍼; 및 입력되는 영상신호 샘플리 평균레벨 보다 크면 이에 해당하는 서브영상의 누적밀도함수에 따라 Bm에서 최대 그레이 레벨(XL-1)까지의 그레이 레벨로 맵핑하되 여기서 Bm′=Bm+X|L-1/(L-1)인 제2맵퍼를 포함함을 특징으로 하는 화질 개선 회로.The method of claim 5, wherein the mapping means is a video signal samples to be input to the mean level (B m) compensating for at least the gray level (X 0) in accordance with the cumulative density function of the sub video, which is the average level than corresponding A first mapper for mapping to a gray level; And that the input video signal sample is greater than Li mean level according to the cumulative density function of the sub-images corresponding thereto, but the mapping from B m to the gray level to the maximum gray level (X L-1) wherein B m '= B m + X | L-1 / (L-1). 소정수(L)의 그레이 레벨로 표현되는 영상신호를 히스토그램 등화하여 화질 개선하는 회로에 있어서; 입력되는 영상신호를 화면단위로 그레이 레벨 분포도를 계산하는 제1계산수단; 입력되는 영상신호를 화면단위로 평균레벨을 계산하는 제2계산수단; 입력영상의 평균밝기에 근거하여 소정의 보정함수에 따른 보정치를 상기 평균레벨에 가산하여 보상된 평균레벨을 출력하는 밝기 보상수단; 상기 화면단위의 그레이 레벨 분포도를 상기 평균레벨에 따라 소정수의 서브영상으로 분할하고 분할된 서브영상의 확률밀도함수를 출력하는 분할수단; 상기 서브영상별로 출력되는 확률밀도함수를 근거로하여 서브영상별로 누적밀도함수를 계산하는 제3계산수단; 입력되는 각 서브영상의 샘플들을 상기 서브영상별로 계산된 누적밀도함수와 상기 보상된 평균레벨에 따라 그레이레벨로 맵핑하는 맵핑수단; 및 입력되는 영상신호와 상기 평균레벨을 비교한 결과에 따라 상기 맵핑수단으로부터 출력되는 서브영상별로 그레이 레벨로 맵핑된 출력중 하나를 선택해서 등화된 신호를 출력하는 출력수단을 포함함을 특징으로 하는 화질 개선 회로.A circuit for enhancing image quality by histogram equalizing a video signal represented by a predetermined number (L) of gray levels, the circuit comprising: A first calculation means for calculating a gray level distribution diagram on a screen basis of an input video signal; Second calculation means for calculating an average level of an input video signal on a screen basis; Brightness compensation means for adding a correction value according to a predetermined correction function to the average level based on an average brightness of an input image to output a compensated average level; Dividing means for dividing a gray level distribution diagram of the screen unit into a predetermined number of sub-images according to the average level and outputting a probability density function of the divided sub-images; Third calculation means for calculating an accumulated density function for each sub-image based on a probability density function output for each sub-image; Mapping means for mapping the input samples of each sub-image into a gray level according to the accumulated density function calculated for each sub-image and the compensated average level; And output means for outputting an equalized signal by selecting one of the outputs mapped to the gray level for each of the sub images output from the mapping means according to a result of comparing the input video signal and the average level, Image quality improvement circuit. 제10항에 있어서, 상기 출력수단은 입력되는 영상신호의 레벨과 상기 평균레벨을 비교해서 선택제어신호를 출력하는 비교기; 및 상기 맵핑수단으로부터 출력되는 서브영상별로 그레이레벨로 맵핑된 출력중 하나를 상기 선택제어신호에 따라 선택하는 선택기를 포함함을 특징으로 하는 화질 개선 회로.11. The apparatus of claim 10, wherein the output means comprises: a comparator for comparing a level of an input video signal with the average level and outputting a selection control signal; And a selector for selecting one of outputs mapped to the gray level for each sub video output from the mapping means according to the selection control signal. 제10항에 있어서, 상기 제3계산수단에서 서브영상별로 계산된 누적밀도함수를 화면단위로 갱신함과 동시에 미리 저장된 누적밀도함수를 상기 맵핑수단에 공급하는 버퍼를 더 포함함을 특징으로 하는 화질 개선 회로.11. The image processing apparatus according to claim 10, further comprising a buffer for updating the cumulative density function calculated for each sub-image in the third calculation unit on a screen basis and for supplying a previously stored cumulative density function to the mapping unit Improvement circuit. 제10항에 있어서, 상기 밝기 보상수단은 상기 평균레벨이 아주 작으면 즉, 아주 어두운 영상이면 제로보다 큰 보정치를 상기 평균레벨에 가산하고, 상기 평균레벨이 아주 크면 즉, 아주 밝은 영상이면 제로보다 작은 보정치를 평균레벨에 가산하여 보상된 평균레벨을 출력함으로써 등화된 신호의 밝기가 조절됨을 특징으로 하는 화질 개선 회로.11. The apparatus of claim 10, wherein the brightness compensating means adds a correction value greater than zero to the average level if the average level is very small, that is, if the average level is very dark, and if the average level is very large, And the brightness of the equalized signal is adjusted by adding a small correction value to the average level and outputting the compensated average level. 제10항에 있어서, 상기 맵핑수단은 입력되는 영상신호 샘플이 상기 평균레벨 이하이면 이에 해당하는 서브영상의 누적밀도함수에 따라 최소 그레이레벨(X0)에서 보상된 평균레벨(Bm)까지의 그레이 레벨로 맵핑하는 제1맵퍼; 및 입력되는 영상신호 샘플이 평균레벨 보다 크면 이에 해당하는 서브영상의 누적밀도함수에 따라 Bm′에서 최대 그레이 레벨(XL-1)까지의 그레이 레벨로 맵핑하되 여기서 Bm′=Bm+X|L-1/(L-1)인 제2맵퍼를 포함함을 특징으로 하는 화질 개선 회로.11. The method of claim 10, wherein the mapping means of the video signal samples to be input to the mean level (B m) compensating for at least the gray level (X 0) in accordance with the cumulative density function of the sub video, which is the average level than corresponding A first mapper for mapping to a gray level; And mapping the gray level from Bm 'to the maximum gray level (X L-1 ) according to the cumulative density function of the corresponding sub-image if the input video signal samples are larger than the average level, wherein B m ' = B m + X | L-1 / (L-1). ※ 참고사항 : 최초출원 내용에 의하여 공개하는 것임.※ Note: It is disclosed by the contents of the first application.
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