From: rob@alegria.com (Rob Lingelbach) Date: Wed, 4 Nov 1998 18:12:03 -0600 To: telecine internet group Subject: [TIG] 1080i color space? What is the difference in colorspace between 1080i and 601? What is done to convert from one colorspace to the other? --Rob Lingelbach Senior Colorist, FWC Dallas From: Hans Lehmann To: "'telecine@alegria.com'" Subject: RE: [TIG] 1080i color space? Date: Wed, 4 Nov 1998 16:22:27 -0800 The expert on this subject? Why Charles Poynton, of course, who has been spreading the gospel across the land about the evils of using two different color spaces. Check out: http://www.inforamp.net/~poynton/notes/video/Luma_coefficients/index.html From: "John Sprung" To: Rob Lingelbach Date: Wed, 4 Nov 1998 18:55:48 -0800 Subject: Re: [TIG] 1080i color space? Rob asks what the difference between 601 and 1080i color is. There are two differences, one of which I can simulate on your computer if you want. First, they use slightly different primaries on the CIE x-y plane -- that theoretical graph that looks like a shark fin. Second, they use different luminance equations, and consequently, different color difference matrices in converting between RGB color and luminance/color difference. (Actually, from gamma corrected RGB to gamma corrected Y Cr Cb. Poynton proposes using luminance for the linear version and luma for its gamma corrected counterpart.) The proposed color standard for 1080i and 720p is called ITU Rec 709, while ITU Rec 601 is proposed for all the 480 line formats. There's little if any 709 implemented yet. There are two guys on the planet who really grok this stuff, LeRoy DeMarsh, and Charles Poynton. I've talked to both, and I can summarize their positions on this quite simply: They both say that 709 is a mistake. We'd do better to use 601 for everything. The little program takes any 24 bit .BMP file, and spits out two modified copies: One showing what happens if you encode as 601 and decode as 709, and the other what happens if you encode as 709 and decode as 601. The biggest numerical differences are in green. Some pictures from last halloween of kids in costume show this, since they contain saturated green and orange. Nature shots with lots of grass and trees don't show as much of a problem. Faces, though the numerical differences are fairly small, do have more of a problem, because we're quite sensitive to errors in that specific subject matter. I sent the sample pictures and the source and executable to Craig Birkmaier, who posted them on his web site. They're probably still there, www.pcube.com. If not, I can send them to you (Rob) if you want. The hell of it is, the errors are of the worst possible magnitude: a little less than the difference between TV sets at Circuit City. They're big enough to aggrivate the artists, but small enough that the bean counters will resist paying to fix it. -- J.S. ------- From: DBClrst@aol.com Date: Fri, 6 Nov 1998 03:37:28 EST To: telecine@alegria.com Subject: Re: [TIG] 1080i color space?/ C-Reality demo In a message dated 11/4/98 4:15:37 PM Pacific Standard Time, rob@alegria.com writes: << What is the difference in colorspace between 1080i and 601? What is done to convert from one colorspace to the other? >> I work with a 601 SDTV monitor and a 709 HDTV monitor side by side, and when both monitors are carefully calibrated, the color difference between them is very slight. The HDTV signal tends to exhibit slightly more red, especially in the skin tones. Of course, keeping an HDTV monitor in careful calibration is no small task, as anyone using one can tell you. I am definitely ready for a more stable display than a huge CRT that can't hold it's color values when there is too much white in the frame. In regard to the C-Reality demo recently, I too was duly impressed. I viewed an I.P. reel on the HD machine, and the picture was very crisp and natural, with no noticeable video noise, only the film grain structure was visible. The resolution was amazing. Color control was a bit crude, as only the local panel was able to operate the machine at that time, the communication bugs between the CR and the daVinci 2K are still being worked out. I liked what I saw, and I'm anxious for a more in depth evaluation. These opinions are my own, I receive no compensation, blah blah...although I did get a nice pen from daVinci. David Bernstein Senior Colorist High Definition Telecine Center, Universal Studios From: "John Sprung" To: DBClrst@aol.com Date: Fri, 6 Nov 1998 13:00:35 -0800 Subject: Re: [TIG] 1080i color space?/ C-Reality demo David Bernstein wrote: >> >I work with a 601 SDTV monitor and a 709 HDTV monitor side by side, and when >both monitors are carefully calibrated, the color difference between them is >very slight. That's absolutely right, but it's not the problem. The issue is that stuff you time as 601 could get upconverted by a cheap box without a color conversion, and played back as if it were 709, and vice versa. Does anyone think that 709 looks so very much better than 601 that it's worth keeping track of two different standards? We've had drop and non-drop, dolby and non-dolby, and now we'll have 601 and 709 stickers.... Is it worth it? If you want, I can show you simulations of the possible mistakes as .BMP files. -- J.S. ------- Date: Fri, 6 Nov 1998 13:29:00 -0500 From: "Dewolde, Jeff" To: "John Sprung" , "DBClrst" Subject: RE: [TIG] 1080i color space?/ C-Reality demo > >I work with a 601 SDTV monitor and a 709 HDTV monitor side by side, and > when > >both monitors are carefully calibrated, the color difference between them > is > >very slight. > > That's absolutely right, but it's not the problem. The issue is that stuff > you time as 601 could get upconverted by a cheap box without a color > conversion, It strikes me as rather odd that we have lived for many years with programming being color corrected on SMPTE phosphor monitors and then delivered as a PAL product for viewing on EBU phosphor monitors. The differences can be very striking, especially when the program in question has been made to look "warm". This "warmth" typically manifests itself as a "very red show" when viewed with a EBU phosphor monitor. What sort of phosphors will the new 1080P/24 monitors have? Assuming that this standard proves to be a truly universal post production format, how will it look beside a standard definition SMPTE and EBU phosphor monitor? Will we have 1080P/24 SMPTE and EBU phosphor monitors? Will the upconverters address whether or not the 601 signal was timed on a EBU or SMPTE monitor? Then again, maybe I'm missing something and there is no issue here! Jeff Dewolde