Abstract: A signal produced by a telecine suffers from losses and defects caused by differences in response to incident light between different areas of the screen area scanned. These differences may arise from burning of the screen, blemishes, dirt in the system, differences in grain size of phosphor particles, missing particles, and losses in the internal optical system of the machine. The invention divides the scanning area into a correction map and devises for each area a correction factor based on the response of that area to incident illumination. When a defect is detected, video data from an adjacent area is substituted. Correction factors are held in a look-up RAM and output to a multiplier where they are multiplied with video data. The video data input to the multiplier may be suppressed and a test pattern may be loaded into the multiplier.