Re: [matplotlib-devel] RFC: candidates for a new default colormap

[Joe K. <jof...@gm...>]

>
> I'm not sure what I'm looking at in that picture exactly, or how to
> distinguish a good result from a poor one -- could you elaborate?
>
It an nutshell, it's whether shading can be distinguished from value
changes.

> FYI I should also note that we're planning on additionally providing
> isoluminant (or approximately isoluminant) variants for whatever colormaps
> we end up contributing, exactly for cases where you want to preserve the
> lightness channel for shading effects. So in any case you'll have a choice
> between "mapA" and "mapA-isoluminant", etc.
>
> -n
>
It's essentially isoluminance, but also the absolute value of the
luninance. (Ideally, you'd want a more-or-less isoluminant colormap with an
average luminance near 0.5.)

A colormap with all dark colors or all light colors can be isoluminant, but
is largely useless for this application, as it will be difficult to
distinguish shaded slopes from low areas or highlighted slopes from high
areas.

Also, from a purely subjective level for this example, it's how effectively
the shading tricks your brain into seeing a topographic surface.  The
colormap has a good bit of influence on this, but I have no idea how to
quantify it.

At any rate, including an isoluminant version solves a large amount of the
problem. Thanks!

Also, to illustrate the exact issue I was referring to a touch more
clearly, here's a zoomed-in version of the previous example:


P.S. Sorry, Nathaniel, you're going to get this twice.  I didn't look
closely enough when I hit reply. I seem to be rather bad at the whole
"e-mail" thing today.