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From: lisa seeman <seeman@netvision.net.il>
Date: Mon, 15 Mar 2004 07:32:52 +0200
To: w3c-wai-gl@w3.org
Message-id: <004101c40a4e$f9925460$340aa8c0@patirsrv.patir.com>
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 work

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  <http://www.ubaccess.com/> Access website

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Received on Monday, 15 March 2004 00:44:57 UTC

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