https://bugs.kde.org/show_bug.cgi?id=356462
Dmitry Kazakov <dimul...@gmail.com> changed:
What |Removed |Added
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CC| |dimul...@gmail.com
--- Comment #5 from Dmitry Kazakov <dimul...@gmail.com> ---
Short:
The solution for the original problem: "just use 51% opacity to avoid rounding,
or use another composite op"
Long:
The formula for Normal alpha blending looks like that:
newColor = dstColor + alpha * (srcColor - dstColor)
In our case:
dstColor = 1
srcColor = 0
alpha = 0.5
We do all the calculations in a floating point numbers, so we get:
newColor = 1.0 + 0.5 * (0.0 - 0.5) = 0.5
Then, we convert the floating-point number back to integers using rounding:
newColorInt = round(0.5) = 1
We cannot skip rounding, because if we do the effects will be drastic. The
image pixels will flip to different sides in a random way, creating artifacts
on the merged image.
So, speaking truly, I don't know if we can (or should) fix this bug. How do the
other applications work with this case?
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