Image sharpening by coupled nonlinear - Diffusion on the chromaticity - Brightness color representation

Previously we presented a selective image sharpening method with a coupled nonlinear diffusion process, and it sharpens only blurred edges without enhancing noise. Our prototypal color-image sharpening methods were formulated on the linear color models, namely, the channel-by-channel model and the 3D vector model. Our prototypal methods sharpen blurred color edges, but they do not necessarily enhance contrasts of signal variations in complex texture regions so well as in simple step-edge regions. To remedy the drawback, we extend our coupled nonlinear-diffusion sharpening method to the nonlinear non-flat color model, namely, the chromaticity-brightness model, which is known to be closely relating to human color perception. We modify our time-evolution PDE's for the non-flat space of the chromaticity vector, and present its digital implementations.