GB905600A - Improvements in or relating to colour or tone correction in printing processes - Google Patents

Abstract

905,600. Copying by scanning. CROSFIELD ELECTRONICS Ltd. March 31, 1959 [April 3, 1958], No. 10836/58. Class 40 (3). Images to be reproduced by a printing process using an electro-optical scanner, are first examined point-by-point by a separate televisiontype system which incorporates circuits having adjustable characteristics corresponding to those of electronic correction circuits incorporated in the electro-optical scanner, a reproduced image being examined and the circuits adjusted until it is satisfactory. Corrections derived from the settings of the circuits are then transferred to the correction circuits of the electro-optical scanner used in the reproduction process. The invention is described as applied to the examination of a coloured transparency 20 by means of a cathode-ray tube flying-spot scanner 14 and photo-electric cells 32, 38, 40 with associated colour component filters 30, 34, 36. The resulting signals pass through tone-compensating circuits 42 which modify the gamma or contrast in correspondence with the modification which takes in the preparation of separation negatives from a transparency, circuits 43 and 44 which by cross-coupling between the three channels simulate the effect of errors in printing inks due to overlap in their colour ranges, and non-linear circuits 46 which simulate distortions due to additivity failure in ink absorptions. The signals then pass to circuits 48 and 50 whose characteristics are adjustable and which introduce respectively the kind of colour and tone correction which can be achieved by the electronic correction circuits incorporated in the electro-optical scanner used in the reproduction process. Finally the signals pass to a display device comprising cathode-ray tubes 52, 54 and 56. From the settings of circuits 48 and 50 required to produce a satisfactory final display corresponding corrections are introduced into the actual reproduction process. A hinged mirror 16 may be moved into the optical path in front of cathode-ray tube 14 in order to direct light to a second scanning station, Fig. 2 (not shown), intended to accommodate three colour separation negatives of an original. The signals produced are applied to the alternative inputs of a switch 88 so as to bypass the circuits 42. Reference is made to the use of a black printer negative in addition to the three separation negatives. The invention may be applied to black-and-white reproduction processes.