1. A computer-implemented range image generation method comprising: receiving, by a computer processor, data representing an input image and a reference image; computing, by the computer processor, a raw disparity-space correlation disparity result representing a non-optimized disparity between a first pixel in a reference image and a second pixel in the input image; computing, by the computer processor, an optimized disparity-space correlation disparity result representing a disparity between the first pixel and the second pixel; computing, by the computer processor, a raw sub-pixel disparity estimate for the first pixel and an optimized sub-pixel disparity estimate for the first pixel using the raw disparity-space correlation disparity result and the optimized disparity-space correlation disparity result, respectively; and generating, by the computer processor, a range image based at least in part on the raw and optimized sub-pixel disparity estimates.