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USM Renderer

The Unsharp Mask Renderer is a built-in post-processing step based on the unsharp mask technique, which has been used to enhance high frequencies since the days of photographic plate processing (see, for example, this page). This renderer acts after all other rendering steps have completed, except for Irani-Peleg rendering, which occurs afterward.

Properties

Given a sequence of images that satisfy all predicates for merging (or drizzling) except point sampling; given a known linear PSF; and given only translations between frames, the result of merging (or drizzling) will be an acceptable approximation of T convolved with the PSF. This does not imply that deconvolution of this result will be an acceptable approximation of T, however, since frequencies with low response may be reconstructed with poor fidelity due to reduced precision. We use the low-response approximation to ignore these frequencies. Assuming the USM approximation, the remaining frequencies are reconstructed to form an acceptable approximation of T. (Since this doesn't really constitute a proof, the results should be considered unreliable.)

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