Charles Poynton
-Color technology
Charles Poynton
-(updated 1997-02-27 - yes, this is stale!)
I have written answers to "Frequently Asked Questions" about Gamma and Color in video, computer graphics, and print. The documents are available in several formats.
Permanent, easy solutions to many of the problems in tone and color reproduction in computing require assistance - even leadership - from the developers and manufacturers of hardware and software. Solving that problem is the primary goal of the Gamma FAQ and Color FAQ documents.
I dedicated many weeks to developing the Gamma and Color FAQs, and I make efforts to keep them up to date and free of errors. The popularity of the documents is gratifying - they average several hundred accesses a day. However, I receive one or two unsolicited color or video queries each day. That may not seem like a lot, but that's 350 or 700 in a year. Owing to the requirement for me to work to pay my rent, I regret that I can't promise a response to unsolicited queries, particularly those related to specific combinations of devices. (I don't even own a Wintel machine!) For color science issues, you can try the newsgroup sci.engr.color; for computer graphics issues, try comp.graphics.algorithms; for video, try sci.engr.television.broadcast (for broadcast video) or rec.video (for consumer video).
I would appreciate comments, criticisms, corrections, and contributions. In particular, I am looking for a qualified volunteer to contribute a section on color management systems, and a qualified volunteer to write about UCR, GCR, and RGB-to-CMYK separation.
You may be interested in the companion Frequently-questioned answers about gamma, the GammaFQA.
James M. Palmer was upset, as I am, concerning misuse of the term intensity. See his note, Getting Intense on Intensity; also, you might be interested in his FAQ on Radiometry and Photometry. The most important thing for me to point out to the computer community is that intensity is, by definiton, proportional - that is, linearly related - to a physical measure of light power. A quantity isn't necessarily an intensity value just because you get more intensity as the quantity increases!
On 1998-02-25, Timo Autiokari published, in an open letter in a Usenet posting, some inflammatory remarks concerning my FAQs. These remarks are sufficiently grave that I feel obliged to respond. You can read about the Timo incident.
You can obtain data for the GretagMacbeth ColorChecker.
This note introduces the two main user adjustments of a video monitor, Brightness and Contrast (sometimes called Black Level and Picture). I explain the effect that these controls have on picture reproduction, and I explain how to set them. You can read the note online, or you can obtain a typographic-quality PDF version (69126 bytes).
This note is available online, or you can obtain a typographic-quality PDF version (101879 bytes).
I presented this paper at the SPIE/IS&T Conference in San Jose, Calif., Jan. 26 - 30, 1998. The paper is published in the Proceedings of that conference, B. E. Rogowitz and T. N. Pappas (eds.), Proceedings of SPIE 3299, 232-249 (Bellingham, Wash.: SPIE, 1998).
This article describes the theory of color reproduction in video, and some of the engineering compromises necessary to make practical cameras and practical coding systems. I presented this paper at the SMPTE Advanced Television and Electronic Imaging Conference, San Francisco, Feb. 1995. This is an edited version of the paper published in the proceedings of that conference, New Foundations for Video Technology (pages 167-180).
Proceedings of International Broadcasting Convention, 1994 (Amsterdam, 16-20 September 1994), IEE Conference Publication No. 397, pages 218-222.
The following two articles are dated now, but indicate the state of color management in 1992:
Color Management Technology for Workstations, Sun Expo '92, Manchester, U.K., Sepember 10, 1992.
RISC/UNIX Workstations in Desktop Color Prepress, Youngblood/IBEC's DeskTop PrePress Today - Colour Conference 92, Toronto, March 26, 1992.
The International Color Consortium has agreed on a standard for color device characterization. The standard, designated Specification ICC.1:2001-04, File Format for Color Profiles is available in Acrobat PDF format (1.7 MBytes).
Paul Haeberli has written an interesting set of notes, Graphica Obscura. In his Viewing Notes, Paul points out some problems with gamma on the web. Paul has written a note Matrix Operations for Image Processing that explains how certain image processing operations that people think have to use HSB, HSL and so on can actually be accomplished more efficiently in RGB space.
Charles © 2005-04-03(a)