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

[Sourish Basu]

On 06/05/2015 12:22 PM, Jody Klymak wrote: Hi, On 5 Jun 2015, at  11:17 AM, Sourish Basu <sourish.b...@gmail.com> wrote: On 06/05/2015 10:17 AM, Jody Klymak wrote: Anyways, I guess I am advocating trying to find a colormap with a very obvious central hue to represent zero.  Anomaly data sets are *very* common, so having a default colormap that doesn’t do something reasonable with them may be a turn off to new users.  I agree that jet does a bad job with anomaly data, but I disagree that having a diverging colormap as default (or even a "diverging" argument to anything that takes a cmap value) would solve that. Very often the "zero" of an anomaly is not at the center of the extrema, and requires creating a custom diverging colormap anyway (see attached example). Well, I *strongly* disagree with that attached example!  It makes it look like -0.5 is equivalent to +1.5!  Unless there is a really strong reason to do that, I think that is poor practice as it makes your negative anomalies look far stronger than your positive, and that is not the case in the underlying numbers. Yes, that is indeed a problem. However, if I want to plot a field which is mostly zeros, then I prefer to use a colormap which is white at zero. I could just extend the smaller absolute value (-0.5) to the same absolute value as the larger one, and plot -1.5 to 1.5. But in that case, I'd only be using a third of the possible dynamical range of the negative (blue) part, which IMO is a waste. If I have a field which has a zero median (which I want mapped to white), goes from -0.5 to +1.5, and I actually want to show the difference between (say) -0.3 and -0.4, what other option do I have? This problem is reasonably common for me, BTW. I can have a carbon monoxide field with an average/background of 60 ppb, but variations from 30 to 550 ppb. So I need a color scale which (a) is white at 60, and (b) shows small variations below 60 and large variations above 60 with equal "clarity". Cheers, Sourish Cheers,   Jody OT, I recently found a nice alternative to jet here: https://mycarta.wordpress.com/2014/11/13/new-rainbow-colormap-sawthoot-shaped-lightness-profile/ It takes care of my biggest crib with jet, which is that there is not enough perceptual variation in the middle of the range. Cheers, Sourish Basu <ff_adjustment_winter.png>------------------------------------------------------------------------------ _______________________________________________ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users -- Jody Klymak     http://web.uvic.ca/~jklymak/ ------------------------------------------------------------------------------ _______________________________________________ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users -- Q: What if you strapped C4 to a boomerang? Could this be an effective weapon, or would it be as stupid as it sounds? A: Aerodynamics aside, I’m curious what tactical advantage you’re expecting to gain by having the high explosive fly back at you if it misses the target.

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