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RE: colors

From: Gregg Vanderheiden <gv@trace.wisc.edu>
Date: Mon, 15 Mar 2004 10:07:31 -0600
To: 'lisa seeman' <seeman@netvision.net.il>, w3c-wai-gl@w3.org
Message-id: <0HUM00C80KW7ED@smtp3.doit.wisc.edu>
Around color, we have two different problems as I understand it


1 - information that is CODED in color.    (e.g.  please correct the field
below that is shown in red.) or ( the numbers in green are to your credit,
the red must be addressed) or ( the items in the picture that are red must
be fixed). 




2 - places where color is used to separate figure from background (e.g. red
letters on a green background). 



The first one requires that some other form of coding is provided as well so
that the person does not need to understand color in order to understand
which items are marked as such-and-such a category.    Sometimes the color
coding can be deciphered from text formatting - but the coding may be lines
or embedded in a picture such that it is not easy to do this.     Also, many
people who are color blind do not know how to query the color coding of


The second requires that contrast be maintained even if one does not know
for sure which cones are weak or inoperative.  Some are more common than
others, but the easiest way to avoid all this is to look at darkness - not
color.   If you use  dark color A   over light color B it doesn't matter
what the colors (hues) are.  They can in fact be the SAME color (hue).
Using a black and white test  is NOT to see how it would look to people with
no color perception.   It is an easy way to test for DARKNESS and LIGHTNESS
irrespective of color.    If a person doesn't have some cone - the black and
white test would not be an accurate picture of what they would see (unless
they had no cones).  But it would give you a pretty good test of darkness
and lightness.   


We need however to 


1 - come up with some specific tests

2 -  determine their affect / benefit on the different types of color


I do not like the idea of just picking the highest frequency color blindness
though and addressing it in isolation - forgetting the rest.  Yes we want to
start there.  Yes we want to keep it simple.  But if we can keep it simple
and address the problem generically then we should.  I don't want to only
solve it for some unless we can show that it is a lot of work to address it
generically and only a little to solve it for most.


I think the darkness/lightness approach may help us here.  





 -- ------------------------------ 
Gregg C Vanderheiden Ph.D. 
Professor - Ind. Engr. & BioMed Engr.
Director - Trace R & D Center 
University of Wisconsin-Madison 


From: w3c-wai-gl-request@w3.org [mailto:w3c-wai-gl-request@w3.org] On Behalf
Of lisa seeman
Sent: Sunday, March 14, 2004 11:33 PM
To: w3c-wai-gl@w3.org
Subject: colors


re - forwarding some of my old emails / action item to the list on color 




Note: It does not look like the algorithms  currently proposed will help a
lot of these user groups


If someone twists my arm I could work on a formula...



Important bits from past emails (just incase someone does not follow through
the links..):



The conclusion must be that we do not know enough about what are real
disorders to write them off as a continuum. What we should do is inlist help
from people who do know what they are talking about. I wrote of to
Achromatopsia.org. If anyone knows more people to write to, please do.

However that said, I will give you the fruits of my labor.

Two types of photoreceptors in the eye: rods and cones. Rods, which provide
vision in dim light, have no ability to distinguish between colors. Cones
are responsible for color vision
Color vision deficiencies result from either a lack of one or more cone
types, or cones that behave differently from average

To have rod monochromacy, or congenital achromatopsia is totally colorblind
or almost totally colorblind, and they have poor visual acuity. This is very
rare.  Without normal cone vision, their eyes are not able to adapt normally
to higher levels of illumination. There are many variations in the severity
of these symptoms. There are complete rod monochromats, incomplete rod
monochromats, and blue cone monochromats. Complete rod monochromats have the
most severely impaired vision of all achromats

They cannot distinguish any hues (e.g., blue, green, yellow and red. They
also have poor visual acuity, aversion to bright light and nystagmus (an
involuntary, rapid movement of the eyes).

Cerebral achromatopsia (unlike other  achromatopsia ) report that they see a
monochromatic world, all in shades of gray. (not accompanied by severely
impaired vision, extreme light sensitivity, or any abnormality in the
photoreceptors of the retina)

Dichromacy is a less severe form of color defect than monochromacy It is
much much more common. Dichromats can tell some hues apart. Dichromacy is
divided into three types: protanopia, deuteranopia and tritanopia. 

Protanopia and deuteranopia are red-green defects. Persons with red-green
defects have difficulty distinguishing between reds, greens and yellows but
can discriminate between blues and yellows. Protanopes often can name red
and green correctly because green looks lighter to them than red.

Hereditary tritanopia is a blue-yellow defect. Persons with blue-yellow
defects cannot see the difference between blues and yellows but can
distinguish between reds and greens. (Less common.) 

Anomalous Trichromacy-The ability of anomalous trichromats to distinguish
between hues is better than dichromats but still not normal. Red-green
anomalous trichromacy is subdivided into protanomaly and deuteranomaly. A
third type of anomalous trichromacy is tritanomaly. In fact, those suffering
from any of these conditions do experience color, but not in the sense that
a color "normal" observer does.

Some sites claim (and seem reputable) that with color deficits, ability to
discriminate colors on the basis of all three attributes - hue, lightness
and saturation - is reduced. Designers can help to compensate for these
deficits by making colors differ more dramatically in all three attributes

To conclude with an opinion ( It is not ready for a proposal but could be
the basis for one) 

For Dichromacy:
Avoid colors that depend on being able to differentiate:
    a.. Red-green 
    b.. blues and yellows
    c.. reds, greens and yellows 

So using colors that mix a blue with a red and a green with a yellow would

Or hand control over to the user (so this is more important in an image then
as a text color scheme) or provide alternative renderings...

For achromatopsia: 
Maintain high contrast in all color schemes.(Especially were control is not
handed over to the user.)
Hand control over to the user.

How does that sound?

Needs more work..


All the best

Lisa Seeman


Visit us at the UB Access <http://www.ubaccess.com/>  website

UB Access - Moving internet accessibility


Received on Monday, 15 March 2004 11:12:11 UTC

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