In the application of machine vision

it is implicitly assumed that the pixel grey level out of from CCD reflects the feature of object. So

in almost all cases

a correction of pixel grey level is neglected. But due to the occurrence of dark current and non-uniformity in CCD

the grey level of different pixel has deviation for same irradiance

for this reason

in optics precision measurement

the grey level of each pixel on CCD should be corrected

in order to accurately characters object feature. After analyzing the cases which ware related to the pixel non-uniformity

an algorithm based on least square method is introduced for correcting pixel non-uniformity. Simulation shows that the method presented is effective to correct CCD non-uniformity grey level.