Filters for Color Images

Abstract

Color images are everywhere and filtering them is such a common task that it does not seem to require much attention at all. In this chapter, we describe how classical linear and nonlinear filters, which we covered before in the context of grayscale images (see Ch. 5), can be either used directly or adapted for the processing of color images. Often color images are treated as stacks of intensity images and existing monochromatic filters are simply applied independently to the individual color channels. While this is straightforward and performs satisfactorily in many situations, it does not take into account the vector-valued nature of color pixels as samples taken in a specific, multi-dimensional color space. As we show in this chapter, the outcome of filter operations depends strongly on the working color space and the variations between different color spaces may be substantial. Although this may not be apparent in many situations, it should be of concern if high-quality color imaging is an issue.