Grain under the new process V3 is drawn from a simulated emulsion of crystal
layers, after Aurélien Pierre's crystallographic grain model (implemented from
the article's description). It fades out towards black and white as on a print,
is applied symmetrically in the display-encoded domain (no shadow darkening, no
grey specks in blown highlights), and matches Lightroom Classic's strength and
grain width at mid grey.
The emulsion is drawn once per Size / Roughness / seed on two periodic tiles in
frame coordinates and kept as summed-area tables, so each output pixel takes
the exact mean of the emulsion under its footprint: a preview is the export's
grain box-downscaled. CPU and GPU read the same tables (the GPU from the finish
kernel's aux buffer). V1 and V2 keep their value-noise grain exactly.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
