Originally Posted by xgalaxy
A little bit more information.
Okay well I've partially solved the issue.
For some reason, only when in THX Cinema certain sources show the green 'snow' (I guess dithering).
All other display modes are fine.
The only two sources I've tested so far are the Xbox 360 and my HTPC.
Now, the gotcha is, if I change the color output of my HTPC from YCbCr (4:4:4) to RGB FULL (4:4:4) then the green 'snow' effect disappears completely.
But this only works for my HTPC. I haven't seen any option like this for the Xbox.
My GT50 does the exact same thing. I posted about it 3-4 weeks ago.
I wrote in post #4299
that I found the setting that causes it. It's the panel brightness setting which you can change in the Custom mode. You get very little noise when set to low, a little bit on mid and a lot of noise on high. The other modes uses various settings, Cinema uses low, THX I believe uses mid and vivid uses high.
It only occurs in very dark grey areas but not in black. That's why you don't see it when your HTPC is booting as the screen is black. Changing the HTPC from YCbCr to RGB Full changes the video level from 16-235 to 0-255. If you didn't change the HDMI/DVI RGB Range to Nonstandard then you've shifted the grey levels and all the dark grey areas are now being displayed as black. The best way to test is to use the 8 step grey scale test pattern.
The Xbox has this setting. It's called Reference Levels. Expanded is RGB Full (0-255) and Normal is RGB Standard (16-235). There is also a Color Space setting that lets you pick Auto, Source, RGB, YCbCr709 and YCbCr601. Games run RGB, HiDef video uses YCbCr709. YCbCr always uses 16-235.
The GT50's auto setting for HDMI/DVI RGB Range doesn't work and acts like Standard. This means you should have all your devices set to the same levels, 0-255 or 16-235. On the Xbox that means if you're set to Auto or Source you should leave the Reference levels on Normal.
I had my TV calibrated when set on low panel brightness. Since I have a dark room this works quite nicely. For my Xbox I bypass my AVR and run it to another HDMI input on the TV. I have that input set to Game mode and Nonstandard range. Game mode uses mid panel brightness but I'm usually to busy dealing with the game action to care about noise.
BTW, do not use the Xbox picture viewer to display a grey scale test chart. It's has a bug where it messes up the levels when in Expanded mode. It probably messes up mapping the level in normal mode as well.