[Bug 677114] New: [pitivi] VideoScale lanczos downscaling is not pretty

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=677114
  GStreamer | gst-plugins-base | 0.10.36

           Summary: [pitivi] VideoScale lanczos downscaling is not pretty
    Classification: Platform
           Product: GStreamer
           Version: 0.10.36
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: gst-plugins-base
        AssignedTo: gstreamer-bugs at lists.freedesktop.org
        ReportedBy: nekohayo at gmail.com
         QAContact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---


Created an attachment (id=215267)
 --> (https://bugzilla.gnome.org/attachment.cgi?id=215267)
comparing VideoScale bilinear, VideoScale Lanczos and gimp GIMP Lanczos3

Pitivi uses VideoScale's method #3 (GST_VIDEO_SCALE_LANCZOS) for thumbnailing
(height = 50 pixels). It seems there is a slight improvement over the default
method (bilinear), but the difference is very minor and I can't help but to
compare with gimp's bicubic or lanczos3 scaling that looks much better (because
it's smoothed, somehow).

Attached is a screenshot comparing
- pitivi 0.15 (videoscale bilinear)
- pitivi GES (videoscale lanczos)
- the same images (from a 2K source) resized by GIMP's Lanczos

Perhaps there is something suboptimal going on with VideoScale when downscaling
to small sizes? Or is it something that is done incorrectly in Pitivi's code? I
tried playing with various values of the "sharpen", "shapness" and "envelope"
properties, no luck.

Code:
http://git.gnome.org/browse/pitivi/tree/pitivi/timeline/thumbnailer.py#n457
(the bus-handler sets the element's props.method = 3)

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