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Bug 72879 - Incorrect RGBA resampling in Smudge tool
Incorrect RGBA resampling in Smudge tool
Status: VERIFIED FIXED
Product: GIMP
Classification: Other
Component: Tools
1.x
Other All
: Normal major
: 2.0
Assigned To: GIMP Bugs
GIMP Bugs
Depends on:
Blocks: 70335
 
 
Reported: 2002-02-27 17:42 UTC by Raphaël Quinet
Modified: 2009-08-15 18:40 UTC
See Also:
GNOME target: ---
GNOME version: ---


Description Raphaël Quinet 2002-02-27 17:42:36 UTC 
If two pixels have different opacity values (alpha channel), then their
colors are not averaged correctly by the Smudge tool.
It looks like the RGB channels are resampled without taking the opacity
into account.  As a result, the (invisible) color of a transparent pixel
can bleed into an opaque pixel.  The resulting image is incorrect.

See bug #70335 for some test images and a longer description of the
problem.  This problem affects many other tools and plug-ins.
Comment 1 Sven Neumann 2003-06-08 12:01:42 UTC 
The problem is caused by the wrong algorithm being used in
app/paint-funcs/paint-funcs.c:blend_pixels(). This functions needs to
weight the pixels by its alpha value.
Comment 2 Sven Neumann 2003-06-09 15:12:38 UTC 
Fixed in CVS (both branches):

2003-06-09  Sven Neumann  <sven@gimp.org>

  * app/paint-funcs/paint-funcs-generic.h (blend_pixels): weight
  pixels by their alpha value. Fixes the smudge tool (bug #72879).
Comment 3 Raphaël Quinet 2003-06-20 17:40:22 UTC 
The fix is part of the stable release 1.2.5.  Closing this bug.