[Pkg-gmagick-im-team] Bug#912777: imagemagick: webp options are ignored due to wrong cwebp flags - including lossless

[beuc at debian.org]

Package: imagemagick
Version: 8:6.9.10.14+dfsg-4
Severity: important

Hi,

'convert' delegates conversion to webp format to the 'cwebp' utility.
(possibly due to #806425, as there seem to also be native support in
coders/webp.c)

However the tool is invoked incorrectly.


1) "-quiet" is used instead of "-q", hence quality is ignored

www/source/delegates.xml:  <delegate decode="png" encode="webp"
command=""cwebp" -quiet %Q "%i" -o "%o""/>


2) lossless parameter is not taken into account, resulting in LOSSY
encoding even when stating the opposite:

$ convert -verbose large.png -quality 100 -define webp:lossless=true
large.webp
'cwebp' -quiet 100 '/tmp/magick-17343sNKIc5bM2Kkg' -o
'/tmp/magick-173430j5VYMgDbQcg'

$ webpinfo large.webp
  Format: Lossy (1)

Valid command line would be:
$ cwebp -lossless large.png -o large.webp
$ webpinfo large.webp
  Format: Lossless (2)


Using another source format (such as bmp or ppm) results in an
intermediate automatic conversion to .png, hence does not avoid the bug.


Setting severity as "important" because there is silent loss of information.


Cheers!
Sylvain