[lmyllari]

Remember, no two devices have the same color/black level output on your TV, they all need tweaking to some extent.

Hi Boris,

I mostly agree with your post, but the above is incorrect. The NUC (at least using OpenELEC) is very well behaved and will match other (digital) video sources with correct output levels.

There are three variables and if you understand these, finding the right settings should be pretty easy. If you don't want to go into the details, there are two basic setups that should work on any standards compliant TV (and at least one should work on the rest..)

1. Everything at default. XBMC will output full range, GPU will scale full range signal to limited range and signal to the TV that signal is limited range. This should work on any TV using the standard 1080p modes. Blacker-than-black and whiter-than-white will be clipped and there will be some banding.
   
2. Full range output. This is set up using xrandr. XBMC will output full range and GPU will pass it through and signal to the TV that signal is full range. (Some TVs and receivers will happily ignore this and crush blacks and whites.) Blacker-than-black and whiter-than-white will be clipped and there will be some banding. (Banding can be fixed by adding dithering to XBMC, I have a proof of concept patch for this.)
   

If you just want a setting that works, pick one of the above and use avshd709 to verify. Note that both will clip BtB and WtW (video signal levels below 16 and above 235).

If you want to go a little further, here are the three variables you should consider:

1. Scaling applied by XBMC. By default XBMC takes the original 16-235 levels and expands them to 0-255. This clips BtB and WtW and introduces banding. To avoid this, XBMC can be set to 16-235 levels and it will pass the video through with BtB and WtW intact.
   
2. Scaling applied by GPU. If the output range is set to full, GPU passes the signal through unmodified. If the output range is set to limited, GPU will take the XBMC output and scale 0-255 to 16-235 levels; if XBMC is outputting full range, original levels are restored, but the clipping and banding caused by the previous 16-235 -> 0-255 are not fixed. If the output range is set to auto, limited range will be used for standard video modes.
   
3. Signaling to the TV. The GPU sends AVI infoframes along with the video, and they include a bit that specifies the signal level. This bit is set according to the output range set using xrandr.
   

From these you can see how the two settings I suggested above work (and why they should work on any TV). If your TV ignores the infoframes and assumes limited range, setting XBMC to 16-235 and GPU to full range gives the best quality.

You can also see why setting both XBMC and GPU to limited range gives you incorrect levels.

It is possible to patch the driver to allow untouched output with infoframes telling it is limited range. This should work on all TVs and matches what a standalone player typically does.

While checking the levels, it's important to keep in mind whether the BtB/WtW are passed through the whole chain (XBMC, GPU and whatever other devices may be between your PC and TV - a receiver, signal processor, splitter or anything else). It doesn't matter much for real content, but may cause loss of hair while checking the levels.

edit: Be sure to have XBMC contrast/brightness neutral when looking for the correct settings. No adjustment on the NUC is needed to get correct levels.

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Can someone remind me if there is a way to send the test pattern to the OpenElec display through the shell? I recall there was a way to do that but can't remember it now.

Why not download the mp4 version of avshd709 and play the files with XBMC as you would any other video files? This gives you the exact same video path that you're trying to verify.