Created attachment 122835 [details] layerstyle-alpha-bug.kra SUMMARY Some (all?) layer styles seem to compute RGB values of translucent pixels incorrectly (they are multiplied by alpha in the result). I've attached a simple test case that demonstrates the issue. The "Circle" layer contains an anti-aliased circle with translucent edges. The "Disable translucency" filter layer makes all pixels fully opaque to conveniently display their color values. The "Circle" layer has an "Inner Glow" layer style configured in such a way that should add pure red to every pixel. STEPS TO REPRODUCE See attached test case OBSERVED RESULT The circle's edges are darkened due to bogus alpha-multiplication. EXPECTED RESULT The circle should appear completely yellow. SOFTWARE/OS VERSIONS Linux distro: openSUSE Tumbleweed 20190920 KDE Plasma Version: 5.16.5 KDE Frameworks Version: 5.61.0 Qt Version: 5.13.1 ADDITIONAL INFORMATION I don't know if this behavior is consistent with Photoshop or not. However, I believe it's broken and not useful.
Yeah, Krita has no concept of premultiplied alpha, so this shouldn't happen.
Dmitry is working on this.
*** Bug 373336 has been marked as a duplicate of this bug. ***
*** Bug 409282 has been marked as a duplicate of this bug. ***
*** Bug 382269 has been marked as a duplicate of this bug. ***
Git commit 227bd473709b1332f2b52346bb651489b3b5478d by Dmitry Kazakov. Committed on 02/10/2019 at 19:41. Pushed by dkazakov into branch 'master'. Fix blending of layer styles with transparent pixels Overlay-like layer styles (overlay, inner shadow, inner glow and satin) seem to be applied in a complicated way: 1) Firstly the copy of the layer-stack projection is created 2) Then a copy of original layer alpha channel is extracted into a selection 3) Alpha channel of the layer itself is maxed-out to 1.0 4) The layer and all the layer overlay-like styles are merged into the projection 5) The the copy of the original projection from step 1) is copied onto the projection again using selection from step 2). This weird technique is used to ensure that color mixing happens exactly in full opacity, as if the colors would have no alpha-channel. M +4 -3 libs/image/kis_layer.cc M +3 -1 libs/image/kis_layer.h M +33 -1 libs/image/kis_layer_projection_plane.cpp M +8 -0 libs/image/kis_layer_projection_plane.h M +5 -0 libs/image/layerstyles/kis_layer_style_filter_projection_plane.cpp M +7 -0 libs/image/layerstyles/kis_layer_style_filter_projection_plane.h M +97 -64 libs/image/layerstyles/kis_layer_style_projection_plane.cpp M +2 -15 libs/image/layerstyles/kis_ls_overlay_filter.cpp M +0 -2 libs/image/layerstyles/kis_ls_overlay_filter.h M +9 -27 libs/image/layerstyles/kis_ls_satin_filter.cpp M +3 -2 libs/image/layerstyles/kis_ls_utils.h M +5 -0 libs/image/layerstyles/kis_multiple_projection.cpp M +2 -0 libs/image/layerstyles/kis_multiple_projection.h M +117 -0 libs/image/tests/kis_layer_style_projection_plane_test.cpp M +2 -0 libs/image/tests/kis_layer_style_projection_plane_test.h M +2 -1 libs/psd/psd.h https://invent.kde.org/kde/krita/commit/227bd473709b1332f2b52346bb651489b3b5478d