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Bug 72848 - Incorrect RGBA resampling in Gaussian Blur (IIR) plug-in
Incorrect RGBA resampling in Gaussian Blur (IIR) 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 16:21 UTC by Raphaël Quinet
Modified: 2005-01-01 21:56 UTC
See Also:
GNOME target: ---
GNOME version: ---

Attachments
Proposed patch (3.53 KB, patch)
2003-02-05 16:10 UTC, Yeti 		none Details | Review

Description Raphaël Quinet 2002-02-27 16:21:15 UTC 
If two pixels have different opacity values (alpha channel), then their
colors are not averaged correctly by the Gaussian Blur (IIR) 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 2003-02-05 16:10:04 UTC 
Created attachment 14129 [details] [review]
Proposed patch
Comment 2 Yeti 2003-02-05 16:18:12 UTC 
Attached a patch against HEAD.

It uses alpha premultiplication and separation functions already
present in the code, but used in a pointless manner. They premultiply
alpha in guchar domain, so color precission is considerably damaged in
low-opacity areas. But at least it works.

Beside that, it removes some completely bogus stuff, looking like
,,optimizations`` done by someone who read about optimization in
Sunday Times...
Comment 3 Sven Neumann 2003-02-18 17:53:43 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.