The ColorFAQ clarifies aspects of colour specification and image coding that are important to computer graphics, image processing, video, and the transfer of digital images to print.
I discuss the mapping from physical spectral power distributions to perceived colour. I outline the CIE system, CIE XYZ, xyY, L*u*v* and L*a*b* color systems, linear and nonlinear R'G'B', Y'CBCR, Y'PBPR, Y'UV, Y'IQ and PhotoYCC, including the standards established by SMPTE, EBU and ITU-R (formerly CCIR). I explain why HLS (HSL) and HSI are useless for the specification of accurate color. I give a brief introduction to the CMY system used in photography and CMYK system used in printing.
The Color FAQ is distributed in several formats, listed in the table below. If you would like to view this document in typographic quality, or if you would like to print it, I recommend that you obtain the Acrobat PDF version.
|Acrobat PDF format||ColorFAQ.pdf|
|Hypertext (.html) format, with poor typesetting and low-resolution GIF graphics||ColorFAQ.html|
|ASCII text-only format, devoid of all graphics||ColorFAQ.txt|
A translation to Belorussian is available, thanks to Paul Bukhovko.
You may be interested in the companion GammaFAQ.
Adrian Ford and Alan Roberts wrote a document, Colour Space Conversions. It documents methods that have been used to transform among colour spaces such as RGB, HSI, HSL, CMY, and video. Adrian Ford has left the University of Westminster, and that organization no longer hosts the document. I have obtained permission to post the document here, in its Acrobat PDF version (184198 bytes). The front matter of this document contains incorrect information concerning places where the document can be obtained. I am awaiting the source files for the document so as to correct this information, and I am awaiting the files containing other versions (e.g., HTM).
Another source of information concerning color is the document Frequently asked questions about colour physics, by Steve Westland <email@example.com>.
For information about radiometry and photometry, see Radiometry and photometry FAQ, by the late James M. Palmer. Dr. Palmer had, for some time, been conducting a campaign to correct widespread improper usage of the term intensity. I confess that I had fallen victim to some errors that he pointed out, and I am in the process of correcting my documents to conform to his recommendations. Read Getting intense on intensity.
Other Color links ...
Charles - Color technology