Image contrast intensifying method

This invention relates to image contrast intensifying method, comprising the following steps: first, scanning a piece of image to sequentially calculate brightness variance of two adjacent pixels; then, comparing the variance to pre-setting threshold value, if large, generating a positive force sequence, if smaller, generating a negative force sequence; third, repeatedly operating the generation and accumulating calculation of the positive and negative ones to get a net positive force sequence and a net negative one until judging termination; fourth, forming a net force sequence by net positive one minus added-weight factor net negative one, and integrating and normalizing it to get a spreading force function; fifth, linear combining the spreading force function and original brightness switching function to get a new switching function for adjusting original brightness to intensify image contrast.