GB1244495A - Photographic colour printing apparatus - Google Patents

Abstract

1,244,495. Photographic colour printing control. AGFA-GEVAERT A.G. Oct. 22, 1968 [Oct. 27, 1967], No. 50110/68. Heading G2A. In a photographic colour printing apparatus which includes a photo-electric exposure regulating device for separately terminating simultaneously commenced exposures to light of each primary colour, the termination of the shortest and/or intermediate exposure shortens the period of the remainder of the or each continuing exposure relatively to the period that would have been determined by the exposure regulating device in the absence of a prior termination, in order to take account of colour dominants in the original in an approximation of the so-called under-correction method. Photo-sensitive secondary electron multiplier tubes 5, 6, 7 charge capacitors, e.g. 23, so that the potential thereof changes at a rate corresponding to the intensity of illumination in the corresponding primary colour. The potential is compared in a threshold device 32 with a potential derived from a voltage generator 27, and when a certain ratio between the potentials is reached a relay 11, 12 or 13 is energized. Associated contacts 11a, 12a, 13a are closed to short variable resistances 8, 9, 10 in the primary circuits of the feed transformers 2, 3, 4, thus increasing the speed of voltage rise on the capacitors still being charged. Alternatively, the energization of the relays may bridge resistors in the generator 27 to lower the value of the comparison potentials. Exposure for each primary colour is terminated by switching off the current supply to a lamp or by pivotting a subtractive filter into the printing light beam.