https://bugs.kde.org/show_bug.cgi?id=412756
Bug ID: 412756
Summary: Artifacts on 8 bit brushes that get composted at low
transparencies.
Product: krita
Version: git master
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: Brush engines
Assignee: krita-bugs-n...@kde.org
Reporter: griffinval...@gmail.com
Target Milestone: ---
Created attachment 123099
--> https://bugs.kde.org/attachment.cgi?id=123099&action=edit
On the left there's a stroke with the airbrush preset on an 16bit layer, on the
right it's on the 8bit layer. Observe the weird pattern on the right at full
brightness.
SUMMARY
8bit brush compositing has artifacts compared to 16bit brush compositing. This
is most clear when using a soft low slow brush, as the artifacts compound.
STEPS TO REPRODUCE
1. Make an 8bit canvas and a 16bit canvas
2. Take brush with a soft or gaussian mask at low flow and low spacing.
3. Draw a few strokes on both.
OBSERVED RESULT
At full brightness, there's clear artifacts on the 8bit image and not on the
16bit image.
EXPECTED RESULT
Minimal difference between the 8 and 16bit images. Preferably full smoothness.
ADDITIONAL INFORMATION
Ok, so we actually discussed this one thoroughly in the IRC:
There's three places we can do something:
1. The compositing in the brush engine. This is how a similar problem was
solved with the color smudge brush. However, this will only work for wash mode,
and not for the build-up mode.
2. it can be fixed at the level of sse-compositions and mask processors. They
already have floating point representations, so we can just make rounding more
fuzzy. This is the most likely candidate, and right now there's discussion in
the IRC on the fastest dithering method(or rather, the fastest randomness
method) we can think of)
3. 16bit(or higher) brush masks. This is something no other program seems to
have and will require a lot of time, so this is more a feature. This will make
the 16bit example smoother too.
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