Fast Gray Calibration for Digital Photographic Printers

摘要

Gray calibration of a photographic printer is usually an iterative process of printing and measuring test prints with the goal to produce a gray wedge from paper white (D_(min)) to the maximal reachable dark gray (D_(max)). The iterative nature is due to the lack of an appropriate color reproduction model, in particular for colors not on the gray axis. A calibration method is presented based on two main elements. One element is a color reproduction model using the spectral properties of the color dyes of the photographic paper. This model was originally developed to facilitate color management for photographic printing but turned out to be very useful also for paper calibration. The other element is an analytical model for the saturation curves of the three dyes. Special attention is paid to the handling of the colors close to (D_(max)) and (D_(min)). The presented method drastically reduces the number of iterations needed for the calibration process and even allows one step calibrations in many cases. A first successful implementation of this method was realized in GRETAG's CYRA FastPrint.