Patent GB-592270-A (GB)
Title: Improvements in and relating to photographic printing processes employing image masks
IPC: G03C5/02
Filed: 1944-01-21
Abstract: 592,270. Photographic reproduction processes. KODAK, Ltd. (Eastman Kodak Co., and Yule, J. A. C.). Jan. 21, 1944, Nos. 449/45 (divided out of Complete Specification of 579,239) and 1122/45. Drawings to Specification. [Class 98 (ii)] An outline image, or an image of enhanced outline, is made by contact or projection printing from a continuous-tone photographic record while it is in register with an image mask of complementary density thereto (i.e. a positive if the record is a negative, and vice versa), the mask having an absorption gamma (as defined in Specification 553,196) between 70 per cent and 130 per cent that of the record, and being unsharp and used sharply or unsharply (i.e. in or out of exact printing relation with the sensitive surface). The print simulates an engraving, the outlines occurring wherever there is an abrupt density change in the record. The outlines alone are printed if the mask is within 5 per cent of 100 per cent, but a residual amount of the continuous-tone record also is printed if the mask differs otherwise, within the extent stated, from 100 per cent and the exposure is sufficient. This residual amount may be varied, if desired, after the record and mask have been made, by colouring, e.g. one of them, and using a printing light of selected colour ; a similar result may be achieved, after an outline negative has been made, by making a composite print from the outline negative and the continuous-tone record. If the record is made so that the shadows exhibit higher contrast than the high-lights (by using the toe of the characteristic curve when making a positive record, or the shoulder of the curve when making a negative record), the masked print from the record has outlines which are broader in the shadows than in the highlights. By selecting the gamma of the mask and varying the exposure, the print may be made to exhibit black or white outlines, with possibly outlines of both kinds in the shadows. If the record is of a subject against an out-offocus background, the latter does not print at all since it does not exhibit abrupt density changes, so that the result is an outline print of the subject only. Any of the ways of masking described in Specification 579,239 may be used ; preference is given to printing with parallel light through an unsharp negative mask as nearly as possible in contact with a sharp positive record which is in contact with the sensitive material. For photo-mechanical half-tone work, a positive or negative may be made by printing the record on to the same sensitive film in two stages, using in one a mask as described above for producing outlines, and in the other a half-tone screen ; and in this case also, in order if desired to adjust the contrasts of the final print, any pair of the three elements, record, mask, and half-tone screen may be coloured differently, with appropriate selection of the colour of the printing lights. The Specification describes in detail the production of outline prints in the preferred way above-mentioned, and also the production of a composite outline and half-tone screened print, using where required either parallel light, or a uniformly extended printing source, or a ring source (or its equivalent produced by illuminating the printing zone by light falling thereon at a constant obliquity while effecting relative rotation between the source and the combination of elements being printed). For carrying out the invention, an integral masking sensitive film may be used whereon a sharp continuous-tone positive (or negative) record is first made in a blue-sensitive emulsion layer, which may also be sensitive to green but not to red, on a support backed by a black antihalation dye layer, the dye of which is removed or bleached in the bath used to develop the record, over which dye layer is coated a red-sensitive emulsion layer in which the unsharp negative (or positive) mask is printed during the development of the record by exposing the material to a beam of diffuse red light. The antihalation dye may be contained in the red-sensitive layer, and if the record sensitive layer is blue-sensitive only, the mask sensitive layer may be sensitive to red or green or to both, printing being effected with light of corresponding colour or colours. An outline negative may be used for the grey key record in multi-colour work. The invention is distinguished from known methods of producing relief or cameo effects by printing from the combination of a positive and negative placed slightly out of register, but may, if desired, be combined with such methods. U.S.A. Specification 2,304,988 is referred to in connection with the use of coloured photo-mechanical halftone screens. Specifications 411,718, 544,034 and 592,296 also are referred to.