Originally Posted by tbrunet
Y= 16-235 with a offset of "16" and an excursion of 219
CbCr= 16-240 with an offset of 128 and an excursion +/- 112
I'm with you so far. Those are the reference ranges. The encoded levels are allowed to stray outside those ranges. That's why there are more codes.
|There are 256 discrete levels of "Chroma" , and NOT 256 levels of luminance!
I agree. There are 254 discrete levels of luma because codes 0 and 255 are reserved. How this is relevant is beyond me.
|Also headroom was built into the digital payload, it's called "Peak White" and it's bound at 235.
601 calls it "peak white" but Poynton does not. I'm going to go with Poynton:
Digital Video and HDTV, Charles Poynton, pg. 22:
"Headroom allows code values that exceed reference white; therefore you should distinguish between reference
white and peak
white." (italics in original)
|According to you theres NO offset?
Huh? When did I say this?
|I have read Poynton and I'm going to quote him when he states!
"The headroom and toeroom are NOT PICTURE INFORMATION"
I've searched through Poynton and can't find anything remotely resembling this quote. Could you provide a cite, please? Book? Page number? Web site?
All this doesn't really matter - I've looked at hundreds of DVDs at this point. I'm confident in saying that ALL DVDs contain information coded above 235. And ALL DVDs contain information coded below 16. You can scream and shout about how it's wrong (and I disagree, as I've made clear), but that's the way it is.
As for the codes below 16, many of them are invisible and were invisible on the BVM, and aren't supposed to be seen. I would still like to keep that range, partially to allow proper calibration and partially because some of them were visible on the BVM.
I have had it demonstrated to me that clipping below 16 is visible on real-world DVDs. It's subtle, but it's there. So all the theory about "why" is kind of immaterial. It actually does change the picture to clip the below-reference values.
The stuff above 235 is much simpler - ALL of it is visible. ALL of it was visible on the BVM. The director approved it. It shouldn't be clipped off.