| 摘要 |
1,219,789. Photographic exposure control. AGFA-GEVAERT A.G. April 26, 1968 [April 26, 1967(2)], No.19951/68. Headings G2A and G2C. In a method of photo-printing in which a predetermined density range is desired in the copies, although the originals have varying density ranges, a calibration curve 8 is first prepared for the particular copying material by making a series of test exposures in pairs upon the copying material each pair of exposures comprising one yellow light exposure and one blue light exposure in different colour proportions using a neutral density wedge as original to be printed, plotting for each exposure a density curve of print densities against the corresponding original densities of the neutral density wedge, determining from each curve the density range of an original corresponding to the desired predetermined density range of copies, and then interpolating the calibration curve by plotting the so determined original density ranges against the printing light colour proportions of the corresponding test exposures. This curve is then used to read off the proportions of the two colours of the printing light corresponding to the maximum and minimum density values and/or the density range of the original to be printed. In apparatus 1 for controlling the exposure of a photographic printer, an electronic timer is provided, the timer having one setting member 5 for setting the total exposure time and a second setting member 4 for setting the ratio of partial exposures in light of different colours; the member 5 is coupled to a scale 6 of density values movable with reference to a fixed index and the member 4 is coupled to a movable scale bearing the curve 8 and co-operating with the scale 6, the arrangement being such that the maximum density value of the original to be printed as indicated on the scale 6 is set against the fixed index, and the member 4 is adjusted so that the curve 8 cuts the scale 6 at the value corresponding to the minimum density of the original. A plurality of inter-changeable density scales are provided for use with copying materials having different Schwarzschild exponents. |
