GB1173565A - Colour Photography - Google Patents

Abstract

1,173,565. Photographic colour printing. ILFORD Ltd. July 20, 1967 [July 21, 1966; Dec. 6, 1966], Nos. 32885/66 and 54585/66. Heading G2A. In a method of colour printing, the print material is exposed through the negative to light having at least two colour components controlled as regards either intensity or exposure time, such that printing is effected either with fixed colour correction or with colour correction in inverse proportion to the ratio of integrated transmissions to light of the said colours, fixed colour correction being used when said ratio departs by more than a predetermined proportion from a predetermined value, and in said inverse proportion when the ratio does not so depart. By "fixed colour correction" is meant that the ratios of the integrals against the time of the products of the light intensity incident on the negative and light attenuation be - tween negative and print material are in constant proportion. The method is of especial advantage in printing from negatives representing so-called "colour subject failures", i.e. representing a subject containing an abnormally high proportion of one colour. The colour printer itself may be basically of the known form shown in Fig.6, in which light from three lamps 1, 2, 3 passes through filters 11, 12, 13 of the three primary colours, and an integrating box 15, and projects an image of a negative 7 on to photo-sensitive print material 9. A proportion of the light is reflected into a box 17 containing a photo-cell which controls shutters 18, 19, 20 to terminate exposure to each of the three coloured lights. The usual exposure control circuit is modified by the addition of a time ratio controller, to provide required limitation of the ratios of printing exposure times for red, green, and blue light. Thus there is comprised, in addition to the integrator, voltage reference, voltage adder, and trigger circuit whose output is fed to an "OR" gate which controls the shutter Figs. 7 and 8 (not shown) the time ratio controller of Fig. 9 (not shown). This is responsive to the output of the trigger circuit in a first photo-electric control circuit corresponding to one of the three primary colours, and its output is connected as input to the "OR" gate of a second photo-electric control circuit corresponding to a second of the three primary colours. The time ratio controller produces, in response to a first and a second impulse, a third impulse which follows the second impulse at a time in controlled proportion to the time elapsing between the first and second impulses. Thus the exposure time of the two primary colours (e.g. red and green) is held to the required limitations as set out above.