[Bug 783267] jpegdec: Outputting garbled colors

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=783267

--- Comment #9 from Antonio Ospite <ao2 at ao2.it> ---
Created attachment 366500
  --> https://bugzilla.gnome.org/attachment.cgi?id=366500&action=edit
jpegdec: improve visual results for 4:2:2 and 4:4:4 sampled images

When decoding jpeg images try to use native formats when they match the
image subsampling scheme, this  allows to keep the chroma info intact
and pass it downstream, where it can be surely handled in better ways
than the current crude chroma subsampling approach.

Get also rig of the horizontal resampling function which is not needed
anymore.

The changes sacrifice one case which was working before but won't work
after, 4:4:0 images in one of the variants.

The following feature matrix shows the situation before and after the changes
for the most common sampling schemes:

4:1:0
  Before: wrong chroma rendering
  After: unsupported (lack of native format in GStreamer)

4:1:1
  Before: wrong chroma rendering
  After: OK, colors a little smudged, but this is to be expected

4:2:0
  Before: OK
  After: OK

4:2:2
  Before: chroma crudely subsampled, with off colors depending on the variant
  After: OK, with full sampling for all variants

4:4:0
  Before: OK, for the most common variant, chroma wrong for the other variant
  After: unsupported (lack of native format in GStreamer)

4:4:4
  Before: chroma crudely subsampled
  After: OK, with full sampling)

-- 
You are receiving this mail because:
You are the QA Contact for the bug.
You are the assignee for the bug.