Issue is based on message
https://groups.google.com/a/webmproject.org/forum/#!topic/webp-discuss/hvw3_k6Tn
_8
What steps will reproduce the problem?
wget http://static.kupivip.ru/V0/00/97/87/59/1b.jpg
convert 1b.jpg -filter Lanczos -resize 240x360 -quality 100 resized_q100.jpg
cwebp -m 6 -resize 240 360 -q 90 1b.jpg -o internal_resize_q90.webp
cwebp -m 6 -q 90 resized_q100.jpg -o external_resize_q90.webp
cwebp -lossless resized_q100.jpg -o external_resize_lossless.webp
What is the expected output? What do you see instead?
There are two problems:
1. external_resize_q90.webp and even external_resize_lossless.webp differ from
original image. Both images has user visible artifacts. Artifacts appear as
white lines around man.
2. If internal resize is used than there is no artifacts, but quality is not so
good (seems like Lanczos resize algorithm is better for this image than one
used in cwebp).
What version of the product are you using? On what operating system?
I use official build libwebp-0.3.1-linux-x86-64. Operating system is Ubuntu
13.04.
Please provide any additional information below.
skal has found the reason of problem:
"""
Seems there's a mismatch between the IDCT used by 'convert' and the one used by
'cwebp'.
The problem disappears when commenting out line 235 of examples/jpegdec.c
("dinfo.dct_method = JDCT_IFAST;").
There also no problem when using PNG format instead of JPEG (resized_q100.jpg
-> resized_q100.png).
Not sure about the speed impact when not using JDCT_IFAST. Maybe that could be
a cwebp option...
"""
and created a patch to fix an issue:
> I already have the patch ready here:
https://gerrit.chromium.org/gerrit/#/c/67084
Please write if I need to create a separate issue to make possible to use
different resize algorithms in cwebp.
Original issue reported on code.google.com by M.Mikhu...@gmail.com on 2 Sep 2013 at 9:23
Original issue reported on code.google.com by
M.Mikhu...@gmail.com
on 2 Sep 2013 at 9:23