[matplotlib-devel] How to move beyond JET as the default matplotlib colormap

[Phil E. <pel...@gm...>]

Many of you will be aware of there has been an ongoing issue (#875,
http://goo.gl/xLZvuL) which recommends the removal of Jet as the default
colormap in matplotlib.

The argument against Jet is compelling and I think that as a group who care
about high quality visualisation we should be seriously discussing how
matplotlib can move beyond Jet.

There was recently an open letter to the climate science community
<http://www.climate-lab-book.ac.uk/2014/end-of-the-rainbow/> asking for
scientists to "pledge" against using rainbow like colormaps (such as Jet),
and there are similar initiatives in other scientific fields, as well as
there being a plethora of well researched literature on the subject.

As such, it's time to agree on a solution on how matplotlib can reach the
end of the rainbow.


The two major hurdles, AFAICS, to replacing the three little characters
which control the default colormap of matplotlib are:

 * We haven't had a clear (decisive) discussion about what we should
replace Jet with.
 * There are concerns about changing the default as it would change the
existing widespread behaviour.

To address the first point I'll start a new mailinglist thread (entitled
"Matplotlib's new default colormap") where new default colormap suggestions
can be made. The thread should strictly avoid "+1" type comments, and
generally try to stick to reference-able/demonstrable fact, rather than
opinion. There *will* be a difference of opinion, however the final
decision has to come down to the project lead (sorry Mike) who I know will
do whatever is necessary to make the best choice for matplotlib.

The second point is a reasonable response when we consider that matplotlib
as a project has no *clear* statement on backwards compatibility. As a
result, matplotlib is highly change averse between minor releases (to use
semantic versioning terms) and therefore changing the default colormap is
unpalatable in the v1.x release series. As a result I'd like to propose
that the next release of matplotlib be called 2.0, with the *only* major
backwards-incompatible change be the removal of Jet as the default colormap.

As a project matplotlib mustn't get caught up in the trap of shying away
from a major version release when the need arises, and in my opinion
helping our users to avoid using a misleading colormap is a worthy cause
for a v2.0.

Please try to keep this thread on the "how", and not on the "what" of the
replacement default colormap, for which there is a dedicated thread.

Thanks,

Phil

(#endrainbow)