KR970071239A - Image quality improvement method using average-matching histogram equalization and its circuit - Google Patents

Abstract

A method for improving an image quality using an average-matching histogram equalization according to the present invention includes the steps of: obtaining a gray level distribution diagram of an input image signal on a screen basis and obtaining a probability density function on the basis of a gray level distribution of the obtained screen unit; Calculating an average level of the input video signal on a screen basis and mapping the input video signal to a gray level according to the obtained cumulative density function, The histogram equalization is performed according to the cumulative density function of a given image signal, and the average signal of a given image is mapped to an average signal of the output image to improve the contrast and the average brightness of a given image is constant There is an effect to maintain.

Description

Image quality improvement method using average-matching histogram equalization and its circuit

Since this is a trivial issue, I did not include the contents of the text.

FIG. 1 is a block diagram according to an embodiment of an image quality improvement circuit using an average-matching histogram equalization according to the present invention. FIG. 2 is a block diagram according to another embodiment of an image quality improvement circuit using an average- FIG.

Claims (9)

A method for enhancing image quality by histogram equalization of a video signal represented by a predetermined number of gray levels, the method comprising: (a) obtaining a gray level distribution diagram of an input video signal on a screen basis, and obtaining a probability density function on the basis of a gray level distribution diagram of the obtained screen unit; (b) obtaining an accumulated density function on a screen basis on the basis of the obtained probability density function; (c) calculating an average level of an input video signal on a screen basis; And (d) mapping the input video signal to the gray level according to the obtained cumulative density function, and adjusting the conversion function such that the average level obtained in the step (c) is directly mapped to the average level. How to improve. The method of claim 1, further comprising: (e) delaying the input video signal by a unit of a picture and outputting the delayed video signal to the step (d). A method for enhancing image quality by histogram equalization of a video signal represented by a predetermined number of gray levels, the method comprising: (a) obtaining a gray level distribution diagram of an input video signal on a screen basis, and obtaining a probability density function on the basis of a gray level distribution diagram of the obtained screen unit; (b) calculating an average level of an input video signal on a screen basis; (c) obtaining a cumulative density function and a cumulative density function value for the average level on a screen basis on the basis of the obtained probability density function; And (d) mapping a cumulative density function value corresponding to an image signal input from the cumulative density function of the screen unit to a gray level according to an accumulated density function value for an average level, wherein the average level obtained in step (c) And adjusting the changed function to be mapped to the average level as it is. The method of claim 3, further comprising: (e) delaying the input video signal by a unit of a picture and outputting the delayed video signal to the step (d). A circuit for enhancing picture quality by histogram equalizing a video signal represented by a predetermined number of gray levels, the circuit comprising: A first calculation means for calculating a probability density function based on a gray level distribution diagram of a screen unit calculated by calculating a gray level distribution diagram on a screen basis of an input video signal; Second calculation means for calculating a cumulative density function based on the probability density function calculated by the first calculation means; Third calculation means for calculating an average level of the input video signal on a screen basis; And mapping the accumulated density function value corresponding to the input image signal to the gray level according to the cumulative density function value for the average level, wherein the average level obtained by the third calculation means is an average level as it is And an output means for outputting an equalized signal by adjusting a conversion function to be mapped. 6. The apparatus of claim 5, further comprising a screen memory for delaying the inputted video signal in units of one screen so as to input the video signal of the same frame as the cumulative density function calculated by the second calculation means to the mapping means A picture quality improvement circuit characterized by. The apparatus of claim 5, further comprising: a buffer for updating the cumulative density function calculated by the second calculation unit on a screen basis, and outputting an accumulated cumulative density function during updating and an accumulated cumulative density function value for the average level And an image quality improving circuit. The image processing apparatus according to claim 5, wherein the output means maps the average level calculated by the third calculation means to an average level, and outputs the input image signal having an average level or lower to the cumulative density function value corresponding thereto and the cumulative density A first mapper for mapping a first range of gray levels according to a function value; A second mapper for mapping an input image signal having an average level higher than the average level calculated by the third calculation unit to a gray level of a second range according to a cumulative density function value corresponding thereto and an accumulated density function value for the average level; A comparator for comparing the input video signal with the average level to generate a selection control signal; And a selector for selecting the first mapper if the input video signal is equal to or lower than the average level according to the selection control signal, and selecting the second mapper otherwise. The image processing apparatus according to claim 6, wherein the output means maps the average level calculated by the third calculation means to an average level, and the image signal output from the screen memory below the average level corresponds to the cumulative density function value and the average A first mapper mapping the first range of gray levels according to an accumulated density function value for the level; Wherein the image signal output from the picture memory, which is greater than the average level calculated by the third calculation means, is mapped to a gray level of the second range according to the cumulative density function value corresponding thereto and the cumulative density function value of the average level. 2 mapper; A comparator for comparing a video signal output from the picture memory with the average level to generate a selection control signal; And a selector for selecting the first mapper if the video signal output from the screen memory is equal to or lower than the average level according to the selection control signal, and if not, selecting the second mapper. ※ Note: It is disclosed by the contents of the first application.