[R] Creating a vector of colours that are as different from

[Spencer Graves]

      There should be a caveat with psycho-visual experimentation:  
Tufte (1983, p. 183) says that 5-10 percent of viewers are color 
deficient or color blind.  He (pp. 153-154) argues strongly against 
"color puzzles" that look pretty but are extremely difficult to decode.  
He says, "Shades of gray provide an easily comprehended order to the 
data measures", in some cases better than "the visually more spectacular 
color".  Cleveland (1993, pp. 264-265) suggests color encoding he calls 
THVL (two hues, varying lightness).  His example ranges from 100% cyan 
(red) in steps of 20% to 20% cyan then switches to 20% magenta (blue) in 
steps of 20% to 100% magenta.  These are selected in part because they 
are fairly distinct even for people with modest color blindness. 

      Perhaps others can comment on more recent research and how this 
relates to the color brewer. 

      In a related area, I learned years ago that substantial portions 
of the public (especially those over 40) do not have eyesight corrected 
to 20-20 and can't read PowerPoint slides with type smaller than 25-28 
point, unless they are in a very small room or are otherwise right on 
top of the slides.  The painful part for me was that they would rarely 
tell me they couldn't read my slides.  I had to guess from the questions 
they asked or didn't ask. 

      hope this helps.  spencer graves

REFERENCES: 

Edward R. Tufte (1983) The Display of Quantitative Information (Chesire, 
CT:  Graphics Press) 

William S. Cleveland (1993) Visualizing Data (Murray Hill, NJ:  AT&T 
Bell Labs)

(Ted Harding) wrote:

>On 21-Dec-04 michael watson \(IAH-C\) wrote:
>  
>
>>Hi
>>
>>I want to create a vector of colors that are as different
>>from one another as possible.  ?rainbow states "Conceptually,
>>all of these functions actually use (parts of) a line cut out
>>of the 3-dimensional color space...".  This suggests to me
>>that the resulting colors are all placed on this "line" and
>>are equi-distant along it.  The resulting color palette is
>>a range of colours where adjacent colours are actually quite
>>similar, especially when n (the number of colours) is high.
>>
>>Conceptually I guess what I want is colors from a 3D polygon
>>in 3D colour space, where the number of vertices in the polygon
>>is n, resulting in a color palette where the colors are all
>>quite different from one another.  Is this possible or am I
>>talking crap? (I've only had one coffee this morning)
>>    
>>
>
>One is not enough, by a long way, in my experience ...
>
>How large is n? It's not easy to select more than a few clearly
>distinct colours. Also, "distinct" is context-dependent, because:
>
>What will be the spatial relationships of the different colours
>in your output? You can successfully have fairly similar
>colours adjacent to each other, since the contrast is more
>obvious when they're adjacent. However, if you want to use
>colours to track identity and difference across scttered points
>or patches, then you need bigger separations between colours,
>since you want to be able to see easily that patch "A" here is
>of the same kind as patch "A" there and different from patch "B"
>somwehere else, when mingled with patches of other kinds.
>
>And size matters. Big patches of similar colour (as on a map)
>can look quite distinct, while the same colours used to plot
>filled circular blobs on a graph might be barely distinguishable,
>and totally undistinguishable if used to plot coloured "."s
>or "+"s.
>
>It depends too on what you will be using to render the colours.
>Monitor screens vary in their aility to render different
>colours distinctly, and so do colour printers.
>
>It's all very psycho-visual and success usually requires
>experimentation!
>
>Cheers,
>Ted.
>
>
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>Date: 21-Dec-04                                       Time: 13:02:10
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-- 
Spencer Graves, PhD, Senior Development Engineer
O:  (408)938-4420;  mobile:  (408)655-4567