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Full Bandwidth Color Difference



To All on the TIG,

I have to say that when doing FX with blue or green screen traveling
mattes, you need and want, full bandwidth color signals. You can not get
full bandwidth color difference signals from a machine that adds detail
(high frequencies) from a luminace channel to pose as full bandwidth RGB. 
Anything that is added equally to the RGB has no color difference, its
black and white. Color difference FX will not work as well on these type of
signals. This means is that you can't cheat if you want the best! 

Spirit with it's "2k" luminace CCD sensor and half resolution color sensors
cheats but will work great if you could use the HiDef for down conversion
to Rec-601 SDTV projects. ("1k" sampling is still higher than 480 or 702
pixels) It also might work okay for the HDTV projects but the Data projects
might be somewhat marginal. Can we get some feedbak from the "2k" CGI folks
on this? Does "4k" make it better? Certainly, "4k" is sharper than "2k" and
full bandwitdth RGB is certainly better than YUV no matter what your
working on.

I think that at NAB'98 if everyone asks for and demands FULL bandwidth RGB
the manufactures will listen. The confusion, I think, is that MPEG and
other transmission systems CAN and DO reduce chroma information. To do that
at the telecine is a waste. If you have to take an "off air" or MPEG
bitstream recording to work with you will have trouble. These type of
recordings will not give you the razor's edge. Only full bandwidth RGB will
suffice. (Note: HDTV has YUV bandwidths of 30/15/15 MHz per SMPTE 274M
standard. (Up from the original  20/10/10 MHz. SMPTE 240M) In the UNIHI
HDTV recorder, it prefilters the luminance down from 30 MHz to 20 MHz. and
the chrominance from 15 MHz down to 7 MHz.) 

Jim Mendrala
Real Image Technology, Inc.
(805) 294-1049
mailto:J_Mendrala at compuserve.com

---
Thanks to Peter Stansfield for supporting the TIG in 1998..
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945 subscribers in 36 countries on Wed Mar 25 01:12:06 PST 1998
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