https://bugs.kde.org/show_bug.cgi?id=502489
Bug ID: 502489
Summary: Brush build up mode - issue at low opacity - color
never reaches 1005
Classification: Applications
Product: krita
Version: 5.2.9
Platform: Other
OS: Microsoft Windows
Status: REPORTED
Severity: normal
Priority: NOR
Component: Brush engines
Assignee: krita-bugs-n...@kde.org
Reporter: i...@cgidesign.de
Target Milestone: ---
Created attachment 180044
--> https://bugs.kde.org/attachment.cgi?id=180044&action=edit
Buil up issue in 8bit document
SUMMARY
Tested with Krita 5.2.9 from Krita.org, 5.3 prealpha and 6.0 prealpha (Windows
10) - no pen, only touchpad of the notebook.
krita-artists.org thread:
https://krita-artists.org/t/brush-build-up-mode-issue-at-low-opacity-values/120242
Brush (pixel engine) is set to “Build up” in the settings (all pressure
settings are off). As I understand it, in this mode the “Flow” settings get
ignored (they don’t have an effect) and “Opacity” acts like the “Flow”
parameter.
This mode builds up color in a single stroke if I paint over the same area
multiple times (like with a real pencil on paper where you move it forth and
back without lifting it).
What I expexted:
Regardless of what “Opacity” value I set for the brush, if paint over the same
area often enough I will get 100% color.
But as shown in the screen shot, if the Opacity is at a low level (1% for
example) this does not work. I paint endlessly over the same area but don’t get
to 100%.
Additional information from Freyalupen posted in the above linked thread:
"Checking the color numbers, 16bit integer isn’t perfect either. With pure
green on black I go from 65535 green to 65486. On 8bit it’s 255 to 206.
Interestingly the difference in both cases is 49, suggesting they have the same
problem. On 16bit it’s a visually indistinguishable .07% difference, but on
8bit it’s huge 19% difference."
STEPS TO REPRODUCE
1. Make a new Krita document (in 8bit mode the issue is visually obvious, in
16bit integer it is there as well but not visually perceptible)
2. Set a pixel engine brush to use build up mode
3. Set brush opacity to 1%
4. Paint over the same area multiple times without lifting the brush
OBSERVED RESULT
Color does not get to 100%
EXPECTED RESULT
Color gets to 100%
SOFTWARE/OS VERSIONS
Windows: 10 but happens with other versions as well.
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