Image optimization in mobile capture and editing applications

A method for tensor-product B-Spline (TPB) based image reshaping of high dynamic range (HDR) input images, the method comprising:

• building sampled HDR color space points distributed throughout an HDR color space, wherein sampling the HDR color space points comprises sampling each color primary of the color space by a defined number of units to obtain a sampled data set of color patches representing a subset of the HDR color space, wherein the subset of the HDR color space is delineated as a triangle formed by the color primaries in a color coordinate system and is parameterized by a color primary scaling parameter with a candidate value iteratively selected from among a plurality of candidate values, the color primary scaling parameter serving as an input parameter for executing a reshaping operation optimization algorithm for TPB based image reshaping, wherein the color primary scaling parameter is indicative of the size of the subset of the HDR color space;
• generating from the sampled HDR color space points in the HDR color space:
• (a) reference standard dynamic range (SDR) color space points represented in a reference SDR color space, (b) input HDR color space points represented in an input HDR color space, and (c) reference HDR color space points represented in a reference HDR color space;
• and
• executing the reshaping operation optimization algorithm to optimize, in a pipeline of chained reshaping functions comprising a forward reshaping mapping and a corresponding backward reshaping mapping, forward and backward TPB predictors, wherein the reshaping operation optimization algorithm uses the reference SDR color space points, the input HDR color space points and the reference HDR color space points as input to generate an optimized forward reshaping mapping and a corresponding optimized backward reshaping mapping based on a candidate value of the color primary scaling parameter that corresponds to the largest subset of the HDR color space that can achieve minimized HDR prediction errors,
• wherein the optimized forward reshaping mapping is used to forward reshape input HDR images in the input HDR color space into forward reshaped SDR images in a forward reshaped SDR color space, wherein the optimized backward reshaping mapping is used to backward reshape the forward reshaped SDR images in the forward reshaped SDR color space into backward reshaped HDR images.