[winswitch] Reducing the colour depth (client side)

Antoine Martin antoine at nagafix.co.uk
Mon Mar 4 09:00:41 GMT 2013

Hi Nick,

xpra is a compositing window manager, and AFAIK this requires 24bpp or
higher. I've tried launching Xvfb/Xdummy with 8bpp and Composite gets
turned off. The -pixdepths switch does not help here. FYI: xpra seems to
crash rather than exit gracefully, but that's another problem.

As for achieving bandwidth savings by reducing the colour depth, x264
and vpx encodings use colour subsampling when the quality is lowered
(switching from 4:4:4 to 4:2:2 and 4:2:0), this is in the chroma+luma
space rather than plain RGB, but it does save about 50% on image size.
Also note that newer encodings (x264, webp, etc) are vastly superior to
the encodings found in VNC, so the bandwidth usage should already be
much lower (even without colour subsampling).

If you find that the quality/bandwidth/framerate/latency isn't good
enough for you use case, let me know - it is quite possible that recent
versions have focused a little bit too much on the LAN usage scenario..


On 03/03/2013 07:26 PM, Nick Burrett wrote:
> Hi,
> Is it possible to reduce the colour depth client side when performing
> xpra attach?
> I'm attempting to use xpra over a 3G modem link where the X server is
> 140ms away.  For a while, I've been using a VNC setup in exactly this
> way and found that reducing the colour from 24bits to 8bits had a
> considerable impact on usability.
> Xvfb has a -pixdepths option, which appears to be a list of supported
> colour depths.  I just would like to get the client to allow the
> choice to be determined at connection time.
> Regards,
> Nick.
> _______________________________________________
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> shifter-users at lists.devloop.org.uk
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