Re: [matplotlib-devel] release strategy and the color revolution

[Michael W. <mw...@st...>]

On Wed, Feb 18, 2015 at 5:23 PM, Eric Firing <ef...@ha...> wrote:

>
> Do you think there is a way to make a sequential map that is more pleasing
> to those of us who are more comfortable with blues and greens than with the
> slightly muddy purples and browns in the initial attempt at HCL?


Just to be clear, Hcl is just a color space; you could in principle make
any number of colormaps using it. My particular proposal is to do something
cubehelix-like in Hcl space while aiming for around .5-.75 of a rotation
around the color wheel. What motivated the particular parameters in the
original proposal was two things:

a) Starting with blue and ending with yellow makes sense, because you can
get good saturation out of dark blues and light yellows
b) Once you have those endpoints, you can either go through green (this is
what matlab does with parula) or through purple and red. the latter has the
functional advantage of getting a bit more hue variation, and it also
distinguishes the colormap from parula. I think this was the argument
Nathaniel originally made.

Tastes differ, but I find the blue-purple-red-yellow colormap quite
attractive, (perhaps because it reminds me of the sunset. Actually, as an
aside, your speculation that your aesthetic preferences are driven by
positive associations by things that have those colors has some support in
the psych literature: http://www.pnas.org/content/107/19/8877.full)

Anyway, within the constraints of the "increase lightness and chroma
linearly while circling around the hue wheel", it's easy to create a
blue-green-yellow colormap:



​


And also more generally, once you have a way of making a colormap from a
few parameters, and some objective function for what makes a colormap
"good", you can optimize in more principled ways than just playing around
with the knobs of a widget. I believe this is what Nathaniel was proposing,
and it sounds like a good idea.

I would suggest that you folks (i.e. the matplotlib core developers) figure
out earlier, rather than later, how the actual decision is going to be
made. I think you can get pretty far with principled arguments, but
ultimately there's going to be an aesthetic aspect and the decision will
easily devolve some people thinking option A is "ugly" and other people
thinking option B is "ugly". And that will be annoying for everyone
involved, but particularly for the people who put time into developing
candidates.