CORRECTION OF SHADING EFFECTS IN VIDEO IMAGES

摘要

YO9-82-O4OX CORRECTION OF SHADING EFFECTS IN VIDEO IMAGES Video images are corrected for shading effects by generating a histogram of picture element (pel) gray scale intensity values and calculating the median and the black and white extremes thereof. A range of permitted background gray scale values is empirically selected. A background image is then created by sampling the intensity values of the original image pels and using a look-up table to remap the image. In one embodiment, pel intensity values are compared with the median value and only corrections lying within the range are carried out. A duplicate image is created from the remapped image and the intensity values of a number of pels in a predetermined region about a first pel in this image are sampled and the value of the corresponding pel in the background image is changed to the largest value among those of the first pel and the sampled pels. This is continued using a look-up table with a 7 bit output until all of the pels in the background image have been changed accordingly. The duplicate image is then changed to conform to the changed background image and the sampling procedure is carried out over a larger surrounding region.