Colour space setting (16-235) - video output good, XBMC menus washed out
#1
After comparing the two colour space settings on my HTPC (Intel 4600 graphics), HD material looks a bit more vibrant with the 16-235 setting in XBMC Gotham (windows, recent nightly). I don’t know much about colour space settings but my understanding is that there will be less conversion going on with this setting as most blu rays are encoded as YCbCr 16-235.

A side effect of switching the 16-235 setting is that XBMC menus now look all washed out which is annoying (I assume because they are calibrated to be presented in 0-255 RGB?).

My question is, why does the 16-235 setting have to be applied globally and not just to the video output? Alternatively, am I missing something here and is there a better way to set up my system?
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#2
I have set the color space to 16-235 in the videocard output config (ATI CCC - YCbCr4:4:4) and all the rest is configured for full/0-255. That way there's only one conversion taking place, it keeps things simple to configure and remember and everything looks right.
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#3
Will there only be one conversion taking place? If you have XBMC set to 0-255, won't it convert the video to that format from the blu ray's YCbCr 16-235 and then back again in your video card?
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#4
Gotham has a known issue with the 16-235 setting within XBMC on Windows. It's semi-fixed and I'm not sure if it's been merged into the latest nightly builds. You can find all the information you need from this thread.

The bottom line, more or less, is that colour conversion is performed twice when using DXVA in certain conditions, but only when you have the setting turned on.

Also there's no reason not to use full RGB on your card (unless you never use it for anything other than XBMC) and let XBMC handle the colours.
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#5
Thanks, but I'm not using DXVA in my set up and I have no issues with video reproduction. It's the presentaion of the XBMC menu screen that's the issue. With the 0-255 setting it looks normal but when I engage 16-235 it appears washed out. I think I need to do some more investigation on the colour space management chain in my system
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#6
Are you also switching the display to 16-235? If not, then it's expected that it would appear washed out. PC Levels are 0-255, for which 0 is black, and 16 is a shade of gray. If you send a display at PC Levels images that are at Video Levels, for which 16 is black, then black is going to appear gray in those images, and they're going to appear washed out. That's assuming the card and any other entities in the display chain are acting as simple passthrough devices and not manipulating the images.

Both UI and video look fine on my Panasonic plasma when XBMC and TV are configured for Video Levels, 16-235. See my post in the thread Piers linked to for my configuration and settings:

http://forum.xbmc.org/showthread.php?tid...pid1673929

As I described, the bug that's being discussed in that thread does not occur with my Nvidia card and display for the settings I use.

To better assess what's happening, instead of looking for "vibrancy in HD material", download the free AVS HD 709 pattern suite in MP4 format, and look at the various clipping patterns, Black, White, APL, and Color. They will reveal what is going on for video WRT levels; to determine which pixel format works best, you would need something like the Color Space Evaluation pattern from Spears and Munsil 2nd ed. For non-video output, you would need picture files done at the normal PC Levels, 0-255.
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#7
Thanks, that's useful info and advice.
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