From Spectra to Perceptual Color: Visualization Tools for the Dimensional Reduction Achieved by the Human Color Sense

Abstract

Physical colors, defined as unique combinations of photon populations whose wavelengths lie in the visible range, occupy an infinite-dimensional real Hilbert space. Any number of photon populations from the continuous spectrum of monochromatic wavelengths may be present to any positive amount. For normal vision, this space collapses to three dimensions at the retina, with any physical color eliciting just three sensor values corresponding to the excitations of the three classes of cone photoreceptor cells. While there are many mappings and visualizations of three-dimensional perceptual color space, attempts to visualize the relationship between infinite-dimensional physical color space and perceptual space are lacking. We present a visualization framework to illustrate this mathematical relation, using animation and transparency to map multiple physical colors to locations in perceptual space, revealing how the perceptual color solid can be understood as intersecting surfaces and volumes. This framework provides a clear and intuitive illustration of color metamerism.