Electronic reproduction colour contrast increasing circuit - corrects colour signals exceeding threshold to threshold value and varies other signals to maintain constant colour relationship

摘要

Colour signal (ROR'GOR'BOR) representing the pixel colour distribution are obtained by pixel and line-wise optoelectronic scanning of a master picture. Field signals (RTP'GTP'BTP) are generated which represent the colour distribution of the pixel surroundings. Colour difference signals (r', G', B') are formed from differences between the original signals and the field signals. The difference signals are weighted and added to the original signals to obtain contrast corrected signals (RST'GST'BST). To reduce errors in improving contrast the corrected signals of individual channels (1,2,3) are checked to see if they exceed a given threshold (14). If at least one signal exceeds the threshold (14) permissible difference signals are set as the distance between the original signal and the threshold (14). New difference signals (ARneuAGneuABneu) are provided from the permissible and the normal difference signals to maintain the ratio between the latter and the new difference signals. The latter and the original signals (ROR,..) are combined to provide new corrected colour signals (RK,GK,BK). ADVANTAGE - Allows optimal contrast correction without interfering colour errors.