Patent GB-639142-A (GB)
Title: Improvements in or relating to a method and apparatus for making photographic colourprints
IPC: G03B27/73
Filed: 1947-05-09
Abstract: 639,142. Colour photography. KODAK, Ltd. May 9, 1947, No. 12636. Convention date, May 10, 1946. [Class 98 (ii)] [Also in Group XL (b)] In a colour-printing apparatus of the type described in Specification 660,099 in which light from a source 10 is passed through a colour negative 14 on to multilayer colour sensitive printing material 13, red, green and blue filters being successively interposed between the negative and the print and the light from each filter being measured by a photo-cell 16 which controls the intensity of the printing beam, a unit is provided which compensates for variations in the printing paper, response of the photo-cell, and the action of the controlling mechanism. A sample of the printing paper to be used is given an exposure with red, green, and blue light so that subsequent processing results in separate areas of cyan, magenta, and yellow. This print is then placed on the table 129 and the areas are each illuminated with their complementary colours by means of filters 126. A further photo-cell 131 receives diffused light from each of the areas in turn at the same time as the corresponding area is being printed by the lamp 10. This photo-cell with photo-cell 16 controls the input to the amplifier 103 which in turn controls the intensity of the lamp so that print sensitivity variations are compensated for. In order to compensate for variations in the behaviour of the printer as well, however, the compensating chart is made on the same machine. The printer is initially adjusted by inserting a gray reflector in the compensator and adjusting the printer until a satisfactory print results. A print is then made through a set of negatives, the transmittances of which are so adjusted that the print may be substituted for the gray filter. This print is then used in the compensator unit until a change occurs in the type of paper being used or in the action of the printer when the gray filter is again inserted in the compensator so that subsequent prints are always returned to the original colour level. In a further embodiment (Fig. 3, not shown), barrier layer type photo-cells are used, a different photo-cell being used to view each colour in the printer and in the compensator chart. This chart is made by the same process as in the previous embodiments, each pair of photo-cells being successively switched in the circuit by a cam. The construction of the compensator unit comprises three similar elements side by side which are shown in Figure 5. The compensator chart 138 is of rectangular form and is wrapped around the semi-cylindrical end of the unit, light being passed from sources L through appropriate filters on to compensating areas prepared by the method already indicated. The barrier layer cells B B  are inclined at an angle to receive only diffused light from the chart areas which may be of different sizes. A circuit is described (Fig. 7, not shown) for dimming all the printing lamps together by inserting resistance in the primary of a transformer from the secondary of which they are fed, or individually by inserting resistance in series with each lamp.