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bachphuc / webp

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Red Color bleed regardless of quality settings #125

Closed GoogleCodeExporter closed 9 years ago

GoogleCodeExporter commented 9 years ago 
What steps will reproduce the problem?
1. Use testcase image nuremberg-test2k.tif 
(https://docs.google.com/file/d/0B_PoCfoFzhyUTmZraEVfMWx3VzQ/edit)
2. convert it to webp with cwebp with any quality measure, for example in the 
60ies, 80ies or even with -q 100
3. other parameters such as -m or -pass seem to have little or no effect

What is the expected output? What do you see instead?

Regardless of the quality setting, there a noticable color bleed when looking 
at the rooftops of the test image. Details and other quality indicators appear 
fine along expectations for different quality settings, the noticeable less red 
roofs are an unusual degradation of sebjective encoding quality.

What version of the product are you using? On what operating system?
cwebp from git. 0.1.3 on cygwin

Please provide any additional information below.

Original issue reported on code.google.com by mathias.schindler on 16 Jul 2012 at 6:03

GoogleCodeExporter commented 9 years ago 
Seems this behaviour is similar to what's mentioned in Issue 98 - 
http://code.google.com/p/webp/issues/detail?id=125. Though I'm not the one to 
tell the priority for fixing this.

Original comment by kjetilb...@gmail.com on 17 Jul 2012 at 8:57

GoogleCodeExporter commented 9 years ago 
@Kjetil When I opened this bug, I did not see any option to specify Type and 
Priority.

If this bug is indeed similar to 98 (and it certainly appears that way), I 
suggest we close it with DUPLICATE.

Original comment by mathias.schindler on 17 Jul 2012 at 9:24

GoogleCodeExporter commented 9 years ago 
The problem is indeed inherent to YUV 4:2:0 subsampling of U/V planes.

See the attached simple case of patterns.png, which contains lines of various 
colors
and width. You can see how the decimation operates on the U/V place, even when
using quality 95 (while compressing patterns.webp).

Original comment by pascal.m...@gmail.com on 6 Sep 2012 at 8:31

Attachments:

GoogleCodeExporter commented 9 years ago 
the latest RGB->YUV conversion (-pre 4) greatly with the color edge smearing.

See output of 'cwebp -pre 4 patterns.png' attached

Also attached for reference, some roof example extracted from 
nuremberg-test2k.tif

Original comment by pascal.m...@gmail.com on 18 Aug 2014 at 10:11

Attachments: