Smooth Ramps: Walking the Straight and Narrow Path through Color Space

Smoothly shaded color ramps, important for presentation graphics and computer imaging, are difficult for color managed systems utilizing device profiles. The causes for disruptive artifacts such as contours and banding are examined and a set of visual limits are established that, if met will avoid them. Based on these visual thresholds, an analysis of the numeric representation and processing of color data in an ICC profile-based environment yields some requirements for device profiles and their use. Specifically, we find that 8-bit precision and inadequate table indexing resolution cause contour artifacts. Banding is caused indirectly from the inversion of noisy and nonlinear printer color data when the profile was created. The noise is not instrument noise, but rather due to the inconsistency of printer output. Some proposals for improving this stage of profile making are suggested. Examples are provided to illustrate the sources of difficulties in rendering smooth and uniform color ramps.