Method and apparatus for automatically generating single-channel critical color transformations

摘要

The invention described herein uses minimization techniques to find a good single-channel transformation that preserves the accuracy of critical colors. The invention takes as inputs a set of critical colors and from these colors determines a set of constraints on the output device and simulated device colorants that is used for the minimization. The constraints are selected to allow the minimization step to determine a consistent single-channel transformation. Then, the color characteristics of a simulated and an output printer are used to find a transformation that minimizes color distance, given the constraints. The invention takes into account certain critical colors during the generation of the single-channel transformation. The invention consists first selecting a set of colorant values in the simulated device color space that are critical to render accurately. The requirements of the critical colors are that they lie on a set of curves in space with the following properties: each curve is smooth and non-intersecting; each curve has at least one coordinate that goes from no ink to full ink; and the set of all curves has the property that for each colorant cs, ms, ys, and ks, there is a curve that has no ink at one endpoint and full ink at the other endpoint. Once the selection of the set of critical colors is made, the functions fc, fm, fy, and fk are calculated by finding the output colorant values that minimize a colorimetric distance (i.e. CIELAB DELTAE) between the input simulated colorant values and the output colorant values.