[Bug 744395] New: Quality issue in video-blend

bugzilla at gnome.org bugzilla at gnome.org
Thu Feb 12 05:26:18 PST 2015


            Bug ID: 744395
           Summary: Quality issue in video-blend
    Classification: Platform
           Product: GStreamer
           Version: 1.4.5
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: gst-plugins-base
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: p_e_muthu at yahoo.com
        QA Contact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---

While overlaying a logo in video, I have used the following pipeline

gst-launch-1.0 videotestsrc ! gdkpixbufoverlay location=<logo_1240x1900.png>
overlay-width=100 overlay-height=152 ! autovideosink

The quality of logo was not upto the mark and I have observed staircase effect.
While digging into this, found that the issue was in video-blend.c module

1. Chroma sub-sampling is not performed before packing in video-blend.c. Chroma
sub-sampling while 4:4:4 to 4:2:0 format conversion should be done before
packing. Because this is not done, chroma pixels are directly dropped that led
to aliasing. 
2. The coefficients used in RGB to YUV conversion are not same mentioned for
Studio swing for BT.601 or Full swing for BT.601 in
http://en.wikipedia.org/wiki/YUV. Use of coefficients from
http://en.wikipedia.org/wiki/YUV improves the visual quality in Cb and Cr
components. The Y coefficients are not summing to 256. So there seems to be
some error.

Other than this, also found resizing by different filters may be added along
with bilinear which is already existing. Lanczos2 gives better visual quality.
Bilinear doesn’t give good quality though.

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