Methods for enhancing images with increased efficiency include using a discriminative index tree to expedite image optimization processes. The discriminative index tree indexes patch-based image priors for modifying an image by using classifiers determined by exploiting a structure of the patch-based image priors. The discriminative index tree quickly and efficiently parses a space of patch-based image patches to determine approximate dominant patch-based image priors for the space of image patches. To further improve the efficiency of the discriminative index tree, one or more embodiments can limit a number of potential patch-based image priors from which a dominant patch-based image prior is selected.