[Intel-gfx] HDMI colour space and depth questions (YCbCr, xvYCC, Deep Colour)

Paul Owen paul at starstreak.net
Tue Feb 28 14:53:20 CET 2012

On 16 January 2012 22:12, Jesse Barnes <jbarnes at virtuousgeek.org> wrote:
> On Mon, 16 Jan 2012 21:50:22 +0000
> Andy Burns <xorg.lists at burns.me.uk> wrote:
> > Jesse Barnes <jbarnes at virtuousgeek.org> wrote:
> >
> > > Andy Burns <xorg.lists at burns.me.uk> wrote:
> > >
> > > There is a way to configure the gamut to be compressed (default) or
> > > expanded (up to 255).  But that's not exposed either.
> >
> > I see the following from the man page
> >
> > "DVI/HDMI outputs. Avaliable common properties include:
> > BROADCAST_RGB - method used to set RGB color range(full range 0-255,
> > not full range 16-235)
> > Adjusting this propertie allows you to set RGB color range on each
> > channel in order to match HDTV requirment(default 0 for full range).
> > Setting 1 means RGB color range is 16-235, 0 means RGB color range is
> > 0-255 on each channel.
> > SDVO and DVO TV outputs are not supported by the driver at this time."
> >
> > Does that mean I *can* toggle the studio colour range on the fly, or
> > is the doc wrong?
> Ah maybe we do expose it; I'm out of date.  Yeah that should change the
> color range handling...

Hi - I just wanted to revisit this particular topic. Firstly I should
say I'm subscribed to the list to try and stay up to date with the
cutting edge you guys are working on. I'm not a developer or anything,
just an interested user.

Okay so back to this question of broadcast rgb/limited/full range
colour. I'm not so sure it is working at all under Sandybridge. I use
XBMC under Linux (Ubuntu) and do not see any difference in the picture
when I do either of the following:

1) Set BROADCAST_RGB = 1 (or 0) in the xorg.conf - in fact the X log
shows the setting is ignored seemingly wherever I put it
2) type on the command line, xrandr -d :0 --output <OUTPUT HERE> --set
"Broadcast RGB" "Limited 16:235"


3) type on the command line, xrandr -d :0 --output <OUTPUT HERE> --set
"BROADCAST_RGB" 1 - this just errors as previously noted here and in
other related topics

It seems to me it outputs full range colour regardless of this setting
- are the above methods "potentially" correct? As such it limits the
usefulness of the platform to htpc users - under Linux that is. Under
Windows it seems to automatically detect that a TV is connected and
switch to 16-235 (using EDID info and manufacturer data maybe?). Is it
at all possible to manage this under Linux in a similar way maybe, any
future plans perhaps? This is, aside from the fractional framerate
issue probably the last major issue limiting the platform under Linux
and in my case XBMC.

For reference I've tried this on various kernels from 3.0 through to
the 3.3 RC's. The hardware in question is a Pentium G620T on an Intel
DH67CF motherboard. Also for reference in case you guys are interested
the following topic at XBMC's forum details setting up the platform
under Linux, http://forum.xbmc.org/showthread.php?t=114368 including
my comments about full/limited range colour.

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