A live gradient's dither adds a fraction of a level of noise, but gradient
fill layers kept it in float. Color Dodge divides by 1 - cs, so under a
bright dodge layer that sub-level noise came out as speckle several levels
high, and channels at 0 were lifted off black (coloured fringes).
Dithered gradient pixels are now rounded to the document depth's levels
(8/16-bit; float documents unchanged), as a painted gradient stores them.
Same rounding in the GPU shader. Regression tests in compose and a GPU
parity case for stacked dithered gradients under Color Dodge.
Claude-Session: https://claude.ai/code/session_01Qpa5z8GksXAFiDavFkmh4R
Co-authored-by: Leel Wasanatha <260480244+kavishkashehan726-sudo@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
* fix(compose): Preserve native CMYK fills through PSD round trips
Share depth-quantized ink samples between rendering and PSD caches.
Use the document profile for RGB fill colours and preserve valid imported
caches. Uncached CMYK fills use CPU rendering.
Cover all sample depths, gradient styles and tiled renders. Fix the real
16-bit gradient round trip and raise the psd-tools floor from 307 to 308.
* perf(raster): Reuse exact 8-bit CMYK conversions within rows
Cache the previous ink bytes and ICC result per row, with alpha decoded
independently. Keep the 16/32-bit conversion loops unchanged.
Matched 1 MP reads improve by 77% for smooth ramps, 33% with dithering
and 10% for random colours. Bitwise regression coverage includes all
depths, alpha and tile boundaries.
