WIP: Add offset normalizer by phobson · Pull Request #3858 · matplotlib/matplotlib · GitHub

Trying to close #1806

Not currently on a good machine for development, but I think this pretty straight-forward, so hopefully Travis a test runner will suffice...

OffsetNorm: This let's you set vmin, vcenter, and vmax. The use case for this is when you have data ranging from e.g., -1, to +2, and you want the the white/gray part at 0, but would also like to use the full range of the red scale. So:

offset = mcolors.OffsetNorm(vmin=-1, vcenter=0, vmax=2)
offset([-1.0, -0.5, 0.0, 1.0, 2.,])

#prints
[0, 0.25, 0.5, 0.75, 1.0]

Next I'll add SymNorm, that will look at the absolute values of vmin and vmax to produce:

sym = mcolors.SymNorm(vmin=-1, vcenter=0, vmax=2)
sym([-1.0, -0.5, 0.0, 1.0, 2.,])

#prints
[0.25, 0.325, 0.5, 0.75, 1.0]

@tacaswell I based this off of a master that I pulled down last night. Is that ok?

Yes

On Thu, Nov 27, 2014, 11:35 Paul Hobson notifications@github.com wrote:

@tacaswell https://github.com/tacaswell I based this off of a master
that I pulled down last night. Is that ok?

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#3858 (comment)
.

You are right about my last comment, but i have still three points:
There is buggy behavior with all negative limits:

os = OffsetNorm(-5, -2, -1)
x = np.linspace(-6, 6, 100)
abs(x-os.inverse(os(x))).max()  #should be zero, but is two

This is why my stackoverflow answer (which you probably read before :)) divides by

 abs(vmax - midpoint) 
 abs(vmin - midpoint)

instead of vmax-vcenter.

Second point the class has no docstring.
Third is i don't think OffsetNorm is a very descriptive name, but the alternatives are also not
very good (MidpointNorm, CenteredNorm) .

Yeah. Good points all around. What you you think about BiasedNorm?

I think there is a code path that will end up with self.vcenter to be None? I think you need to also override autoscale_None to make sure it gets set.

@tacaswell yup. Got that written, Will default to half-way in the middle if not specified.

Thought about looking at the signs of vmax and vmin to see if 0 would be a good choice, but I think edge cases of -0.001 and 1000 make that more complicated than it means to be,

Needs documentation and tests that stress the code a bit more.

Hey @Tillsten

I really feel like your class you posted on SO is more robust. I don't feel right using it here without you on the commit log. Do you want to pull this branch down and overwrite what I have with your class?

@tacaswell

About the tests, happy to beef things about a bit. What do you think about the pattern I'm using with subclassing a base test case? I feel like the whole file could benefit from similar treatment (separate PR,of course).

Here's that SO solution from @Tillsten
http://stackoverflow.com/questions/7404116/defining-the-midpoint-of-a-colormap-in-matplotlib/7746125#7746125

@phobsen Just use it, i will hopefully get other commits anyway. If i ever find the free time ... :)

Borrows heavily from @Tillsen's solution found on StackOverflow here: http://goo.gl/RPXMYB Used with his permission dicussesd on Github here: https://github.com/matplotlib/matplotlib/pull/3858`

Should the default value be None ?

This looks pretty solid. Left a few picky comments.

I am a bit confused by the decorators working on 2.6 and a bit concerned about the test classes as I don't recall seeing them anyplace else in the test suite.

I did. It didn't change anything, though I was working on a janky dev installation of MPL, so I should probably give it another shot.

Looking back a existing source code, LogNorm does have an inverse method, so there's something to learn there I'm sure.

Just had an idea in terms of a name for the general case, GraduatedNorm, what do you think?

It sounds like all this is actually about using a continuous piece-wise linear curve (first-degree spline) as the mapping function. Is that correct? GraduatedNorm doesn't give me any picture of what it is supposed to be.

PiecewiseLinearNorm sounds good to me.

I like that name.

On Tue, Jun 30, 2015 at 11:17 PM, Till Stensitzki notifications@github.com
wrote:

PiecewiseLinearNorm sounds good to me.

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#3858 (comment)
.

👍

Closing in favor of #4666 @phobson ping to have this re-opened if you want to take over development again.

Borrows heavily from @Tillsen's solution found on StackOverflow here: http://goo.gl/RPXMYB Used with his permission dicussesd on Github here: https://github.com/matplotlib/matplotlib/pull/3858`

Borrows heavily from @Tillsen's solution found on StackOverflow here: http://goo.gl/RPXMYB Used with his permission dicussesd on Github here: https://github.com/matplotlib/matplotlib/pull/3858` TST: add tests for DivergingNorm DOC: add to colors_api.rst

Borrows heavily from @Tillsen's solution found on StackOverflow here: http://goo.gl/RPXMYB Used with his permission dicussesd on Github here: https://github.com/matplotlib/matplotlib/pull/3858` TST: add tests for DivergingNorm DOC: add to colors_api.rst DOC: add tutorial FIX: fix extend=both

Borrows heavily from @Tillsen's solution found on StackOverflow here: http://goo.gl/RPXMYB Used with his permission dicussesd on Github here: https://github.com/matplotlib/matplotlib/pull/3858` TST: add tests for DivergingNorm DOC: add to colors_api.rst DOC: add tutorial FIX: fix extend=both DOC: add new example

tacaswell added the status: needs review label Nov 27, 2014

phobson mentioned this pull request Nov 27, 2014

Add symmetric norm for colormaps #1806

Closed

phobson force-pushed the add-asym-norm branch 2 times, most recently from 60aaec1 to 37ff5a5 Compare November 27, 2014 21:32

tacaswell added status: needs revision and removed status: needs review labels Nov 29, 2014

tacaswell added this to the v1.5.x milestone Nov 29, 2014

tacaswell reviewed Nov 29, 2014
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phobson force-pushed the add-asym-norm branch from 2d41664 to 933626c Compare December 1, 2014 08:18

phobson force-pushed the add-asym-norm branch from 933626c to 0b17fcf Compare December 1, 2014 17:00

phobson force-pushed the add-asym-norm branch from 0b17fcf to 205e8b9 Compare December 1, 2014 18:28

tacaswell added status: needs review and removed status: needs revision labels Dec 12, 2014

tacaswell reviewed Dec 12, 2014
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dopplershift mentioned this pull request Jul 11, 2015

Add PiecewiseLinearNorm #4666

Closed

tacaswell closed this Jul 16, 2015

tacaswell removed the status: needs review label Jul 16, 2015

phobson deleted the add-asym-norm branch October 14, 2016 17:03

jklymak mentioned this pull request Oct 6, 2018

Add DivergingNorm (again, again, again) #12419

Merged

3 of 6 tasks

ImportanceOfBeingErnest mentioned this pull request Sep 26, 2019

DivergingNorm is a misleading name #15336

Closed

WIP: Add offset normalizer by phobson · Pull Request #3858 · matplotlib/matplotlib · GitHub

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