- From: Gregg Vanderheiden <gv@trace.wisc.edu>
- Date: Fri, 30 Apr 2004 10:13:07 -0500
- To: <w3c-wai-gl@w3.org>
- Message-ID: <auto-000022898091@spamarrest.com>
From materials I got from Jim Thatcher. Gregg -- ------------------------------ Gregg C Vanderheiden Ph.D. Professor - Ind. Engr. & BioMed Engr. Director - Trace R & D Center University of Wisconsin-Madison _____ From: Jim Thatcher [mailto:jim@jimthatcher.com] Sent: Thursday, April 29, 2004 8:39 PM To: 'Gregg Vanderheiden'; 'Piper, Ian'; 'Whitney Quesenbery'; 'David Aragon (E-mail)'; 'Josephine (Josie) Scott (E-mail)' Subject: RE: Docs for reference to comfortable to reach - easy to read. Group . Sorry, here is some grayscale rambling! Here is a different grayscale test - it works well (I think). http://colorfilter.wickline.org/. The test page is awkward - but you can select grayscale from the combo box and paste in a url. I would like a definition of grayscale. Here it is from w3.org: An image representation in which each pixel is represented by a single sample value representing overall luminance (on a scale from black to white). PNG also permits an alpha sample to be stored for each pixel of a grayscale image. <http://www.w3.org/TR/PNG-Glossary.html> www.w3.org/TR/PNG-Glossary.html So now how do you go from rgb to luminance? The first google hit on that was: There is no one "correct" conversion from RGB to grayscale, since it depends on the sensitivity response curve of your detector to light as a function of wavelength. A common one in use is: Y = 0.3*R + 0.59*G + 0.11*B And another: (red + green * 2 + blue) >> 6 (http://www.directfb.org/mailinglists/directfb-dev/2003/01-2003/msg00032.htm l) And another: Photoshop uses a standard mix of the RGB channels for their grayscale conversion: RED=30%, GREEN=59% and BLUE=11%. (http://gimpguru.org/Tutorials/Color2BW/#grayscale) Looks like it's Y = 0.3*R + 0.59*G + 0.11*B Jim Accessibility, What Not to do: http://jimthatcher.com/whatnot.htm. Web Accessibility Tutorial: http://jimthatcher.com/webcourse1.htm. -----Original Message----- From: Jim Thatcher [mailto:jim@jimthatcher.com] Sent: Thursday, April 29, 2004 1:42 PM To: 'Gregg Vanderheiden'; 'Piper, Ian'; 'Whitney Quesenbery'; 'David Aragon (E-mail)'; 'John O'Hara (E-mail)'; 'Josephine (Josie) Scott (E-mail)'; 'Shari Little (E-mail)'; 'Sharon Laskowski (E-mail)'; 'Ted Selker (E-mail)' Subject: RE: Docs for reference to comfortable to reach - easy to read. http://www.q42.nl/demos/colorblindnesssimulator/ http://www.nils.org.au/ais/web/resources/toolbar/index.html#ins Jim Accessibility, What Not to do: http://jimthatcher.com/whatnot.htm. Web Accessibility Tutorial: http://jimthatcher.com/webcourse1.htm. -----Original Message----- From: Gregg Vanderheiden [mailto:gv@trace.wisc.edu] Sent: Thursday, April 29, 2004 1:13 PM To: 'Piper, Ian'; 'Whitney Quesenbery'; 'David Aragon (E-mail)'; 'Jim Thatcher (E-mail)'; 'John O'Hara (E-mail)'; 'Josephine (Josie) Scott (E-mail)'; 'Shari Little (E-mail)'; 'Sharon Laskowski (E-mail)'; 'Ted Selker (E-mail)' Subject: Docs for reference to comfortable to reach - easy to read. Gregg -- ------------------------------ Gregg C Vanderheiden Ph.D. Professor - Ind. Engr. & BioMed Engr. Director - Trace R & D Center University of Wisconsin-Madison
Received on Friday, 30 April 2004 11:14:59 UTC