[R] palettes for the color-blind

[Ken Knoblauch]

Max Kuhn <mxkuhn <at> gmail.com> writes:

> 
> Yes, I was aware of the different type and their respective 
prevalences.
> 
> The dichromat package helped me find what I needed.
> 
> Thanks,
> 
> Max
> 
> On Wed, Nov 2, 2011 at 6:38 PM, Thomas Lumley 
<tlumley <at> uw.edu> wrote:
> > On Thu, Nov 3, 2011 at 11:04 AM, Carl Witthoft 
<carl <at> witthoft.com> wrote:
> >>
> >> Before you pick out a palette:  you are aware that their are several
> >> different types of color-blindness, aren't you?
> >
> > Yes, but to first approximation there are only two, and they have
> > broadly similar, though not identical impact on choice of color
> > palettes.  The dichromat package knows about them, and so does
> > Professor Brewer.
> >
> > More people will be unable to read your graphs due to some kind of
> > gross visual impairment (cataracts, uncorrected focusing problems,
> > macular degeneration, etc) than will have tritanopia or 
monochromacy.
> >
> >   -thomas
> >

Sorry to come into this late, but I was travelling.

As indicated, the dichromat package will give you an excellent first
order approximation as to what works or doesn't for the 3 types
of congenital dichromacies, As indicated by THomas, the two most
prevalent varieties, protanopia and deuteranopia, result in similar
confusion axes and the third, tritanopia, is relatively rare, except
in eye disease.  That said, the most prevalent color deficiencies
are not the dichromacies but the anomalous trichromacies.  These
will not necessarily lead to losses in chromatic discrimination but
just shifts (i.e., one might see as orange or green what 
a normal trichromat sees as yellow).  About 20 years ago, I was
involved in an attempt to develop guidelines (or rules of thumb,
at least) for display design for color deficient observers, that did
not require any deep understanding of colorimetry.  The distillation
of this effort can be found here, for what it is worth;:

http://www.lighthouse.org/accessibility/design/
accessible-print-design/effective-color-contrast

The most important point, I think, was to make sure that there
was a sufficient luminance contrast difference, so that in the
absence of the capacity to make a chromatic discrimination,
the differences would still be detectable.  
The principles necessary for optimizing color choices in a 
scatterplot will certainly be more complex, however.
In this light (no pun intended), I would draw your attention
to the seminal work of Berniece Rogowitz at IBM:

http://www.research.ibm.com/people/l/lloydt/
color/color.HTM

http://www.research.ibm.com/dx/proceedings/
pravda/truevis.htm

who was (is) quite concerned with this issue, as well,
as the excellent article by Zeileis, Hornik and Murrell

http://statmath.wu.ac.at/~zeileis/papers/
Zeileis+Hornik+Murrell-2009.pdf

HTH,

Ken

-- 
Ken Knoblauch
Inserm U846
Stem-cell and Brain Research Institute
Department of Integrative Neurosciences
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