AVS Forum Special Member
Join Date: Mar 2000
Location: Kirkland, WA, USA
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Let's back up a bit here. Stacey and I work in the digital media group at Microsoft. We have all the relevant specs at our disposal. I can tell you with 100% confidence that there exists a standard called Studio RGB which keeps black at 16 and reference white at 235. (Peak white is 254, so there really doesn't exist an "above white," but that's a whole other can of worms.)
Not only does this standard exist, it is the appropriate standard to use when outputting video, and we have spent a tremendous amount of time and energy getting computer engineers to understand this - something that video engineers have understood for a long time. Windows Media Center uses this spec. NVidia will in the next version or so of their drivers be using this spec for all YCbCr conversion, as will ATI. Get ready, because this is the future of video output on computers. Read the references that Stacey provided. Poynton is the expert on digital video, and just quoting randomly from his "Digital Video and HDTV", page 309:
"In studio equipment, 8-bit R'G'B' components usually have the same 219 excursion as the luma component of Y'CbCr..."
Yes, it is true that in computing we have generally defined 0 as reference black and 255 as reference white, but when outputting video it makes much more sense to use the studio RGB standard of 16 and 235.
As for FSOne's comment that below 7.5 IRE is "illegal" in analog NTSC, that's just completely wrong. First off, 7.5 IRE setup is not used in all flavors of NTSC. In Japan and a few other countries, black is set at 0 IRE. But even in this country, below-black is perfectly legal - it's fundamental to all video interfaces. TV stations broadcast color bars with PLUGE patterns that go below black, and VCRs record below black. DVD players that are properly made produce below black just fine.
Every DVD I have ever examined has had significant below-black and above-reference-white information, often in every frame. On a real CRT, the above-reference-white information is absolutely visible, and the below-black is often visible because of the variations in black level retention.
Believe me, I'm not just smoking crack here, and neither is Stacey. I realize that for many people familiar with standard computer practice it's jarring to hear that RGB is not always 0-255 nominal range, but it's true.