| 摘要 |
A system for a photographic color printer which sets its exposure control device (lamphouse/shutter) to provide the illumination intensity of each color component (red, blue and green -- RBG) and the exposure time to produce test prints of the same print density from negatives having different exposures and therefore different densities. The printer is calibrated by means which calibrate a densitometer which can scan and read density over a matrix of pixels of the negative, and by means which calibrate the printing system including all components of the exposure control device; i.e. its lamps, filters, light leakage characteristics, printing medium (the photosensitive paper), and the parameters of the print developing process (the photochemistry which converts the exposed print into a print having a permanent image). The densitometer calibration and the photographic calibration is accomplished on a statistical basis by the use of a set of calibration film negative patches which are scanned during calibration of the printer by the densitometer and used to make a gamut of calibration prints on the printing medium after exposure by the exposure control device. The patches include sets of patches having different density (exposed at different f-stops) for each of several colors and neutral. Thus, the patches provide a plurality of density levels of a plurality of color and neutral variations. In the course of calibrating the photographic system of the printer a plurality of exposure variations (a set of deltas) is used so as to obtain the calibration prints, the number of which is equal to the number of calibration patches multiplied by the number of exposure variations in the set. A computer controlled system carries out a regression computation to derive models with matrices of coefficients and offsets, which when applied to density readings of production negatives, allows for complete compensation for the scanner, exposure device, photographic print media and processing system response characteristics and makes the control of the exposure device independent of such characteristics. |
