GB1450797A - Photographic colour printing apparatus and method for its adjustment - Google Patents

Abstract

1450797 Photographic colour printers AGFAGEVAERT AG 21 Sept 1973 [22 Sept 1972] 44342/73 Heading G2A In a printer having at least one photo-cell for each primary colour arranged to receive light transmitted through an original (a) data is stored in the printer before exposure, the density of the original to be printed is measured in each colour and corresponding reference signals are computed from the data and densities (b) the photo-cell outputs are integrated during exposure and compared with the reference signals to determine the exposure of the print material to each colour; the data being stored in step (a) by setting data in temporary stores and transferring it to permanent stores by using meters to balance the signals on the stores. The printer has three channels, one for each primary colour; only one channel being shown. Each channel has input stores 41, 42, permanent stores 36, 60, 61 and a meter 67. A store 50 is common to all three channels. In operation (a) correction values are set on potentiometers 41, 42, a potentiometer 49 is adjusted until meter 67 reads zero, pots 41, 42 are reset to zero, and pot 36 is adjusted until the meter again reads zero pot 36 stores the print material sensitivity. (b) each meter 67 (67', 67") is connected between a photo-cell 10 measuring the density of a calibrating original in one colour and the pot 50 which is adjusted until one meter 67 (67', 67") reads zero. Colour filters are inserted in the printing beam to obtain zero readings on the other meters. This provides equal exposure times in each channel for a calibrating original. (c) further correction values are set on potentiometers 41, 42 and with the photo-cells 10 &c. measuring calibrating originals, pots 60, 61 are adjusted to give zero meter readings. Pots 60, 61 compensate respectively for under and over exposure. A pot 29 is set according to the format of the original. In each channel, an amplifier 51 subtracts the setting of potentiometer 50 from the original density as measured by the photo-cell 10, components 54-56 compute from this difference signal and the difference signals from the other channels, an under correction signal for the channel shown, components 58-61, 66 compute a slope correction signal for correcting under or over-exposure and a summing amplifier 40 in each channel receives these signals and generates a corresponding reference signal. At the start of exposure an integrating capacitor 27 is switched in and its output compared by an amplifier 39 with that of summing amplifier 40 to terminate exposure in the channel shown.