GB1109381A - Photographic printing - Google Patents

Abstract

1,109,381. Classifying transparencies. ILFORD Ltd. Jan.12, 1966 [Jan. 13, 1965; April 21, 1965; May 12, 1965], Nos. 1526/65, 16787/65 and 20076/65. Heading G2A. In an apparatus for producing prints from photographic transparencies there is provided means for classifying the transparencies according to their optical density ranges prior to printing so as to determine an exposure correction factor which varies the value the integral against time of image forming light has to reach before the exposure is terminated. A negative is scanned by a flying spot on a cathode-ray tube CRT, and light transmitted by the negative is directed on to the photo-multiplier PM1. A semi-reflecting mirror SM, a photo-multiplier PM2 and a constant input voltage control the intensity of the electron beam of the CRT, and hence of the light received by the negative. The collector current drawn by PM1 causes a voltage to develop across semi-conductor diodes LD, and the variations in this voltage are amplified in A. C. amplifiers VA1, VA2, connected to meters M1, M2. The deflection of the meter M1 indicates the optical density range D r between the highest and lowest densities in the area of the transparency. The deflection of the meter M2 is proportional to a subject key factor S which is related to a quantity B, the quantity S being the proportional change in probability frequency through the range D r . Alternatively, or in addition to, finding the value of D r for a transparency being classified, at least 10 area-elements of the transparency are scanned and the proportion B by which the number of such area-elements of density greater than the average density D z of the transparency exceeds the number of such area elements of density below D z is calculated. The value of D r and/or the value of B are used to calculate a quantity A which in turn is used to calculate the correction factor which is a function of A and D z .