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Bug 72865 - Incorrect RGBA resampling in IWarp plug-in
Incorrect RGBA resampling in IWarp plug-in
Status: RESOLVED FIXED
Product: GIMP
Classification: Other
Component: Plugins
1.x
Other All
: Normal normal
: ---
Assigned To: GIMP Bugs
Daniel Egger
Depends on:
Blocks: 70335
 
 
Reported: 2002-02-27 17:17 UTC by Raphaël Quinet
Modified: 2005-01-01 21:56 UTC
See Also:
GNOME target: ---
GNOME version: ---

Attachments
Proposed patch (3.14 KB, patch)
2003-02-06 23:41 UTC, Yeti 		none Details | Review

Description Raphaël Quinet 2002-02-27 17:17:02 UTC 
If two pixels have different opacity values (alpha channel), then their
colors are not averaged correctly by the Distorts->IWarp plug-in.
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 Yeti 2003-02-06 22:47:28 UTC 
Currently IWarp does nothing. This prevents correct alpha handling, so
I'm adding dependency to bug #105442.

What I don't understand is, how you was able to make it handle alpha
incorrectly (i.e. do anything at all).
Comment 2 Yeti 2003-02-06 23:41:52 UTC 
Created attachment 14174 [details] [review]
Proposed patch
Comment 3 Yeti 2003-02-06 23:46:28 UTC 
Please forget my first comment, it's bogus.

Attached a patch against CVS HEAD.

It fixes alpha in the image but doesn't fix preview -- the preview
alpha handling is strange so it's better to wait for GimpPreview with
a fix.
Comment 4 Sven Neumann 2003-02-18 17:53:45 UTC 
2003-02-18  Sven Neumann  <sven@gimp.org>

	Applied patches from David Necas <yeti@physics.muni.cz> that fix
	incorrect RGBA resampling in a number of plug-ins:

	* libgimpcolor/gimpbilinear.c (gimp_bilinear_rgba): fixes RGBA
	resampling in Map Object and Lighting Effects plug-ins (#72876 and
	#105496).

	* plug-ins/common/curve_bend.c: fixes bug #72863.
	* plug-ins/common/deinterlace.c: fixes bug #72856.
	* plug-ins/common/gauss_iir.c: fixes bug #72848.
	* plug-ins/common/gauss_rle.c: fixes bug #72849.
	* plug-ins/common/iwarp.c: fixes bug #72865 (except preview, see
	comment).
	* plug-ins/common/mblur.c: fixes bug #72850.
	* plug-ins/common/pixelize.c: fixes bug #72851.
	* plug-ins/common/polar.c: fixes bug #72866.
	* plug-ins/common/ripple.c: fixes bug #72868.