Re: [9fans] alg to make a good colour palette for a graph

Re: [9fans] alg to make a good colour palette for a graph

[Steve Simon]

Hi,

I picked up somecode from Graphics gems to do this,
it was good enough for me though I wouldn't vouch
the optimal-ness of its solution.

The file is colorquant.c, I cannot find which volume of
gems its from but I could send you the code if you like.

-Steve

[9fans] Re: alg to make a good colour palette for a graph

[Jim Choate]

On Fri, 21 Feb 2003, Steve Simon wrote:

> I picked up somecode from Graphics gems to do this,
> it was good enough for me though I wouldn't vouch
> the optimal-ness of its solution.
>
> The file is colorquant.c, I cannot find which volume of
> gems its from but I could send you the code if you like.

Google is your friend, all the code from all five volumes is available on
the web at the Graphics Gem homesite, which by the way will take you to
their e-zine on graphics related topics.


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Re: [9fans] alg to make a good colour palette for a graph

[Skip Tavakkolian]

> totally non Plan9 question but people here oftentimes have nice simple algs
> which work well across lots of contexts.

I agree. There is so much to be learned from people on this list,
just by observing/listening in.

On a somewhat related note, I wanted to share my pick for a new
book of algorithms; It is called "Hacker's Delight" by Henry S.
Warren Jr.

Re: [9fans] alg to make a good colour palette for a graph

[George Michaelson]

Many, many thanks. perfecto!

-George

Re: [9fans] alg to make a good colour palette for a graph

[Eric Grosse]

It depends on the monitor.  Take a look at
   http://plan9.bell-labs.com/cm/cs/doc/85/4-01.ps.gz
That solution (which used l2 optimization over a psychophysical
color difference metric) gave very good results, but is way too
complicated for awk.    You can run the computation once, build
a decent spline approximation to the hue curve, and use awk to
interpolate in the table, given <n>.   That's the approach of
   http://plan9.bell-labs.com/netlib/graphics/rainbow.c.gz

Eric

[9fans] alg to make a good colour palette for a graph

[George Michaelson]

totally non Plan9 question but people here oftentimes have nice simple algs
which work well across lots of contexts.

I need to make a set of <n> visually distinctive colours in rgb space such
that I can feed the rgb values into a tool (RRD) to graph with.

Microsloth picks colours for you. a very nasty muted set. Gnuplot repeats the
same palette of colours over and over again.

I read in the RRD list of a technique to map the <n> as equidistant points
distributed in HSV space, and then use them. But, no code.

N varies. Usually its less than 15. In those cases I think I can use an
Acronymic 'Richard Of York Gave Battle In Vain' selection. But for one case I
am looking at, I need 250+ reasonably distinctive colours.

I thought about just taking a 256colourmap, and randomizing it, and using the
entire palette that way. It should mean no two adjacent colours are very alike
which is fine for a stacked line chart.

Is there something simple and nice, which I can do in AWK? Something which
will go into the ff-space and pick good colour combos? The obvious things I
come up with make gray (for a stunningly obvious reason) It would be super
nice to have up to 25 or 30 colours which are all mutually equi-distant in
some sense.

clues? I've tried web browsing. its phenominal how few things seem remotely
relevant from keyword searches using colourspace, colourmap, palette, graph.

-George