Video can be found at http://youtu.be/lTUtw0onSCw and the issue is observed around 9-10 second mark.

(In reply to comment #1)
> Video can be found at http://youtu.be/lTUtw0onSCw and the issue is observed
> around 9-10 second mark.

That looks like some auto level thing like C.A.T.S - is that turned on on the Panny for that input?

Unlike Windows I don't think OSS Radeon will do anything other than full range RGB over HDMI - I would investigate the "dark" issue as perhaps setting XBMC not to scale to full range may be confusing something that's trying to automagically tweak things for you - Denon or TV - I don't know, but it's normal for 16 - 235 luma to have samples that are below/above which usually get corrected by the stretch to full range.

PS How did you add dither to xrandr?

Thanks for the feedback Andy. 

The Denon and the Panasonic are both in "Extended (0-255)" and it seems in the upcoming XBMC release you can adjust the levels. By default XBMC was set to 0-255 and I noticed the VERY dark scenes and settings so they suggesting changing XBMC to 16-235. Before I know about the XBMC setting I changed the Denon to 16-235 and it fixed the darkness issue. I have these same two machines with IDENTICAL hardware, etc. but the second unit which is upstairs in my Bedroom is attached to an LG 32" LCD TV and has the same issue. The ONLY common point between the two setups is a Griffin HDMI detective to prevent issues I've seen in the past when I shut off the TVs(and AVR) and leave the units running. The only thing I've changed in this equation was the leap to Linux from Windows with the OSS drivers for radeon. 

FYI I used "xrandr --output HDMI-0 --set dither On" in my startup script after X started. 

Any recommendations is welcome.

(In reply to comment #3)
> Thanks for the feedback Andy. 
> 
> The Denon and the Panasonic are both in "Extended (0-255)" and it seems in
> the upcoming XBMC release you can adjust the levels. By default XBMC was set
> to 0-255 and I noticed the VERY dark scenes and settings so they suggesting
> changing XBMC to 16-235. Before I know about the XBMC setting I changed the
> Denon to 16-235 and it fixed the darkness issue. I have these same two
> machines with IDENTICAL hardware, etc. but the second unit which is upstairs
> in my Bedroom is attached to an LG 32" LCD TV and has the same issue. The
> ONLY common point between the two setups is a Griffin HDMI detective to
> prevent issues I've seen in the past when I shut off the TVs(and AVR) and
> leave the units running. The only thing I've changed in this equation was
> the leap to Linux from Windows with the OSS drivers for radeon. 
> 
> FYI I used "xrandr --output HDMI-0 --set dither On" in my startup script
> after X started.

Thanks, though it doesn't work for me (throws an error) , not sure why.

> 
> Any recommendations is welcome.

Other than trying with direct connections to TV and/or a different player I am afraid I can't really think of anything else.

For me with an HD4890 directly into a 2010 Panasonic plasma I have no issues.

Today I tested out by removing the HDMI Detective between the bedroom HTPC and the LG 32" LCD TV. My dithering xrandr option is still enabled and the XBMC 16-235 levels are still configured. I tested a few videos and still was able to notice the "grey to normal" transition for the first few seconds of the video playback start. So now I have a STRAIGHT HDMI connection to the TV and still experiencing the same issues. Thoughts?

The dithering option has nothing to do with channel clamping, it's for dithering when displaying 8 or 10 bpc content on 6bpc panels for example.

(In reply to comment #5)
> Today I tested out by removing the HDMI Detective between the bedroom HTPC
> and the LG 32" LCD TV. My dithering xrandr option is still enabled and the
> XBMC 16-235 levels are still configured. I tested a few videos and still was
> able to notice the "grey to normal" transition for the first few seconds of
> the video playback start. So now I have a STRAIGHT HDMI connection to the TV
> and still experiencing the same issues. Thoughts?

I would try the direct connection without the dithering or 16-235 xbox setting to see if you still have the dark issue, and if not maybe the level issue will be gone also.

I would also try with another player like mplayer.

Do you have issues with this mpeg2 full range ramp?

I would try with current set up and normal settings/different player etc.

http://www.w6rz.net/ramp.zip

Of course normally (= player stretching 16-235 to full) the end 2 blocks will be the same, if xbmc is managing to use full range then they won't be.

What you see will also depend to some extent on the levels (brightness/contrast) set on the TV.

Pyrodex, Ubuntu 13.10 reached EOL on July 17, 2014. For more on this, please see https://wiki.ubuntu.com/Releases.

If this is reproducible with a supported release, it will help immensely if you filed a new report with Ubuntu by ensuring you have the package xdiagnose installed, and that you click the Yes button for attaching additional debugging information running the following from a terminal:
ubuntu-bug xorg

Also, please feel free to subscribe me to it.

For more on why this is helpful, please see https://wiki.ubuntu.com/ReportingBugs.