pngenc producing strange colours for certain devices

[anno domini]

Hi All,

I am using gstreamer bindings within a python script to generate an
individual snapshot of the display from various video capture devices.

I had been using pngenc to produce the snapshots with success with easycap
cards and decklink/intensity pro cards.

However, when we tried it on a different video capture device (bt878 card)
i noticed all the snapshots had strange colors.

This is the pipeline i was using:

*v4l2src device=/dev/video1 norm=PAL ! ffmpegcolorspace ! valve
name=video_capture_valve drop=true ! videoscale ! video/x-raw-rgb,
width=720, height=576, pixel-aspect-ratio=1/1 ! pngenc snapshot=true
compression-level=1 ! filesink location="myimage.png"*

(In case you are wondering, the valve is used to delay capture for a few
seconds because the intensity pro card seemed to produce several poor
frames at the start).

I couldn't figure out what the problem was so i opted to use the jpegenc
instead which appeared to work for all the cards i.e. no funny colors with
the BT878 card. However, unfortunately this wasn't a valid solution because
this was producing very poor quality snapshots.

Can anyone suggest what may be causing the funny colors with the pngenc and
the BT878 video capture card??

Thanks!
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