GB884251A - A process and photographic material for the production of photographic records and copies which are corrected for tone valne - Google Patents

Abstract

884,251. Photographic materials and processes for tone value correction. AGFA A.G. Feb. 12, 1958 [Feb. 12, 1957], No. 4629/58. Drawings to Specification. Class 98(2). A photographic material comprises an image-forming (described in the Specification as "continuous tone") silver halide emulsion and a less sensitive silver halide emulsion for producing a tone value mask, these emulsions being sensitive in the same regions of the spectrum but the ratio of the sensitivities of these emulsions not being constant over the entire common sensitivity range. The emulsions may be in separate layers on a support, or may be in the form of a mixed emulsion, the gradation and sensitivity of the two emulsions responding separately to light of different wave lengths. The emulsions may be sensitive to the blue and green parts of the spectrum. Exposure may be to an object or image and processing to silver, dye or silver-containing dye, and in the latter two cases the processed material may be copied with two types of light simultaneously or successively on to material sensitive to both types of light, such as the same type of material originally used for the exposure, to result in a picture corrected as regards both shadow and highlight definition. Example 1 describes somewhat mathematically with reference to drawings (not shown), a continuous tone gelatino-silver bromoiodide layer and a masking gelatinosilver chlorobromide layer of 1 /30 sensitivity of the continuous tone layer, both layers being orthochromatic but the continuous tone layer having pronounced sensitivity in the green region and the masking layer having pronounced sensitivity in the blue region; and describes exposure of these with unfiltered light, and with blue and yellow lights which latter affect respectively masking and continuous tone layers more strongly. In Example 2 the continuous tone layer has 4 times sensitivity to green light than to blue and the masking layer of lower inherent sensitivity has equal sensitivity to blue and green, and such is stated to have advantages when used as exposure material as by arc light to a black and white continuous tone original via a reproduction camera, and additional advantages when used as copying material with coloured light. Example 3 specifies emulsions for the two layers, indicates exposure and processing as in Example 2 to produce a tone-value corrected image in silver, and continues with description of bleaching and colour developing this image to one of yellow dye and silver, which latter is printed by green and blue light on to the same two-layer material to give a result corrected for tone value in high lights and shadows. Specifications 799,590, 819,041, 845,217 and 878,487 are referred to.