RE: YCbCr
RE: YCbCr
- Subject: RE: YCbCr
- From: <email@hidden>
- Date: Wed, 27 Jun 2007 08:28:00 -0700
- Importance: Normal
------- email@hidden wrote ---------
> [snip] the "diagonal shoe-box shape of the YCbCr
> space" with opposite corners touching the (1) max-black and (2) max-white points in the
> centers of the faces of the R'G'B' cube, is "relative" to the gamut of the particular
RGB
> Color Space. It will be smaller in <sRGB> and larger in <ProPhoto RGB>. [snip]
Seems I got it wrong... I saw what I wanted to see.
* The "shoebox" is sitting in Lab color space, not RGB, let alone R'B'G' [gamma corrected]
space.
* The "shoebox" has nothing to do with an ICC Working Space; it's not even "broadcast
legal" ITU 601 video color.
* The Y'CbCr space "shoebox" shown is a subset of an RGB cube, resting on its "black"
corner, sitting in Lab space.
* There is no RGB or R'G'B' cube depicted in the image; the cube depicted is a small
section of theoretical Lab space.
* The Y'CbCr "shoebox" shows the black point scaled to 0 RGB; this does not allow for
video blanking; it should be sitting on a "floor" of 7.5 IRE, or 17-RGB-steps.
* The Y'CbCr "shoebox's" white point is shown at 219 RGB; the ITU 601 "Y axis" does have
only 220 steps (of 24-but RGB), but the white point is also mis-scaled down 17-RGB-steps
from 235 RGB (24-bit).
* The Y'CbCr space shown is not depicted as "broadcast legal" ITU 601 color.
* The ITU 601 black point should be 16 RGB (24-bit).
* The ITU 601 white point should be 235 RGB (24-bit).
See:
(1) Keith Jack, "Video Demystified" Ch 3, pp 15-34, 2001, 3rd ed., LLH Technology Pub.
(Now in 5th ed. see http://www.video-demystified.com/)
(2) RGB Color Model in http://en.wikipedia.org/wiki/RGB_color_model.
(3) Bruce Lindbloom website
There are undoubtedly other problems, but those are the ones I've caught so far.
Tim Vitale
Paper, Photographs &
Electronic Media Conservator
Film Migration to Digital Format
Digital Imaging & Facsimiles
Preservation & Imaging Consulting
Preservation Associates
1500 Park Avenue
Suite 132
Emeryville, CA 94608
510-594-8277
510-594-8799 fax
email@hidden <http://briefcase.yahoo.com/email@hidden>
[use of the above URL may require a "Yahoo! ID" to download files]
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