On Histogram-preserving Blending for Randomized Texture Tiling

To support interactive authoring of high-resolution randomly tiled textures, we modify the histogram-preserving tiling algorithm of Heitz and Neyret to avoid any lengthy preprocessing. Instead of calculating a 3D histogram transformation by optimal transport, which can take minutes even at low resolution, the input texture is transformed using per-channel 1D lookup tables, constructed trivially from the input histogram on texture load. Three sources of clipping are described. Modifying the algorithm to use a truncated Gaussian distribution and a novel soft-clipping contrast operator avoids clipping artifacts while retaining very high rendering performance. Per-channel histogram preservation is sufficient for most textures, but some will produce unwanted colorations; these can often be avoided by performing histogram preservation only on luminance. Exponentiating the blending weights can reduce ghosting artifacts and better preserve structured texture details.