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Change in custom norm colour map display #20581
Description
Compare https://matplotlib.org/stable/tutorials/colors/colormapnorms.html
vs https://matplotlib.org/devdocs/tutorials/colors/colormapnorms.html
The same thing happens with the custom norm at the end of the tutorial. I'm not sure about TwoSlopeNorm, but at least for the custom one, the 0 is definitely not supposed to be in the middle. This half broke when merging #20054, with the 0 tick at the old place but the 0 colour in the middle. Then with d1c5a6a, the 0 tick also moved to the middle.
Activity
jklymak commentedon Jul 6, 2021
The tick moving to the middle is expected - colorbars are supposed to space equally in colourspace (i.e. consider log norm).
The -1000 is more problematic, as that is simply incorrect I believe. Part of the issue here is that two-slope norm doesn't have a scale, and hence doesn't have good ticking.
jklymak commentedon Jul 6, 2021
... the Custom norm is in even worse shape ;-)
jklymak commentedon Jul 6, 2021
OK, the -1000 is because TwoSlopeNorm didn't extrapolate at all, and so -1000 == -500. Adding extrapolation fixes that.
The
MidpointNormalizeexample was broken becauseMidpointNormalizedid not define an inverse. Defining an inverse also fixes this.