Method for image enhancing using quantized mean-separate histogram equalization and a circuit therefor

A method for enhancing the image of histogram-equalizing image signals represented as a predetermined number of gray levels, said method comprising the steps of:

• (a) quantizing levels of input image signals and outputting quantized input image signals;
• (b) calculating a gray level distribution of the quantized input image signals by a unit of a picture;
• (c) quantizing the mean of the input image signals by the unit of a picture and outputting a quantized mean level;
• (d) splitting the gray level distribution into a predetermined number of quantized sub-images according to the quantized mean level;
• (e) obtaining a cumulative density function value for each of the quantized sub-images in said step (d) according to the gray level distribution;
• (f) interpolating the cumulative density function value of each of the quantized sub-images based on the input image signals and the cumulative density function value obtained for each of the quantized sub-images and outputting an interpolated cumulative density function value for each of the quantized sub-images;
• and
• (g) independently performing histogram-equalization for each of the quantized sub-images according to the interpolated cumulative density function value of each of the quantized sub-images and outputting an enhanced signal.

A circuit for enhancing an image of histogram-equalizing image signals represented as a predetermined number of gray levels, said circuit comprising:

• first quantizing means for quantizing levels of input image signals and outputting quantized input image signals;
• first calculating means for calculating a gray level distribution of the quantized input image signals by a unit of a picture;
• second calculating means for calculating the mean level of input image signals by the unit of a picture;
• second quantizing means for quantizing the mean level and outputting a quantized mean level;
• third calculating means for calculating a cumulative density function value for each quantized sub-image by splitting the gray level distribution calculated in said first calculating means into a predetermined number of quantized sub-images according to the quantized mean level;
• interpolating means for interpolating the cumulative density function value of each quantized sub-image based on the input image signals and the cumulative density function value for each quantized sub-image and outputting interpolated cumulative density function value for each quantized sub-image;
• mapping means for mapping the sample of each quantized sub-image to a gray level based on the interpolated cumulative density function value for each quantized sub-image;
• and
• outputting means for outputting one of the samples mapped to the gray level for each quantized sub-image according to a comparison result of the quantized mean level and input image signals.