[Matplotlib-users] Automatic selection of different colormaps for anomaly & intensity data

[George Nurser]

Hi,
I've been following the discussions about the new default colormaps.
I think it might be really helpful if the default behaviour were that
matplotlib simply examined your data (Z, say), and if
(1) Z.max() & Z.min() had the same sign then used a sequential colormap
whereas if
(2) Z.max() & Z.min() had opposite signs then it used a diverging colormap,
centered on zero.
Keywords e.g. Anomaly=True & centre = 10. could be extra arguments to
override this behaviour.

I realise that
a) this really only requires a user to write a simple helper application.
But 99% of users will never do this.

b) it may not always be desired; but again 99% of the time it probably is.

This would enable people just starting to use matplotlib perhaps to see
that it can give 'better' plots than matlab

Anyway, just a thought.

George Nurser.

[Thomas Caswell]

This has been discussed and the consensus was that getting the heuristics
right is probably impossible (I work with dark-current subtracted image
data so it can have negative values, but using a diverging color map is
_very_ wrong, taking 0 as the center only makes sense some of the time).
Defaulting to a linear norm and sequential color map is in the worst case
not helpful, where as using the wrong center (or incorrectly using a
diverging color map) can be misleading. We are prioritizing not being
misleading over being slightly more convenient in the core library.

A function with a call signature like you describe should definitely be in
the examples.

Also see PR https://github.com/matplotlib/matplotlib/pull/3858 which is
adding a new normalizer to make setting up non-symmetric diverging color
maps easier.

Tom

Post by George Nurser
Hi,
I've been following the discussions about the new default colormaps.
I think it might be really helpful if the default behaviour were that
matplotlib simply examined your data (Z, say), and if
(1) Z.max() & Z.min() had the same sign then used a sequential colormap
whereas if
(2) Z.max() & Z.min() had opposite signs then it used a diverging
colormap, centered on zero.
Keywords e.g. Anomaly=True & centre = 10. could be extra arguments to
override this behaviour.
I realise that
a) this really only requires a user to write a simple helper application.
But 99% of users will never do this.
b) it may not always be desired; but again 99% of the time it probably is.
This would enable people just starting to use matplotlib perhaps to see
that it can give 'better' plots than matlab
Anyway, just a thought.
George Nurser.
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