1. A method of generating an index tree for identifying patch-based image priors for patch-based image enhancement, comprising: determining a plurality of patch-based image priors from a plurality of natural image training patches; calculating, by at least one processor, a plurality of informed candidate linear classifiers based on a structure of the plurality of patch-based image priors; selecting a linear classifier from the plurality of informed candidate linear classifiers for each non-leaf node of a discriminative index tree; and generating, by the at least one processor, an enhanced output digital image by applying the discriminative index tree to an input digital image.