stretch histogram support multi-select

[kecnry]

Description

This pull request generalizes and approves the stretch histogram's support for the new separate multiselect modes introduced in #2574 - the stretch curve and colorbar now works correctly regardless of whether the viewer and/or layer are in multiselect mode, supports multiple viewers selected (in which case vmin/vmax lines are currently shown based on the first entry - we could eventually somehow represent mixed state here somehow, but it isn't clear if that is necessary yet). Note that the entire histogram is hidden if the select layer is a subset OR if multiple layers are chosen.

Change log entry

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  list the proposed change log here for review and add to CHANGES.rst before merge. If no, maintainer
  should add a no-changelog-entry-needed label.

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• Do the proposed changes actually accomplish desired goals? Also manually run the affected example notebooks, if necessary.
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[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (2746b72) 91.47% compared to head (f672ea3) 91.48%.

Files	Patch %	Lines
...nfigs/default/plugins/plot_options/plot_options.py	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2582      +/-   ##
==========================================
+ Coverage   91.47%   91.48%   +0.01%     
==========================================
  Files         160      160              
  Lines       19514    19517       +3     
==========================================
+ Hits        17851    17856       +5     
+ Misses       1663     1661       -2     

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[javerbukh]

If I change the color of a layer in Imviz while multiple layers are selected and then turn multiselect off, the histogram color is still the previous color.

[javerbukh]

Looks good to me! Only question I had is what is the expected histogram behavior when a layer is selected in multiple viewers if it also has different colors? Currently the histogram just picks one of the colors and that's fine, just making sure that is on our radar.

[kecnry]

Only question I had is what is the expected histogram behavior when a layer is selected in multiple viewers if it also has different colors? Currently the histogram just picks one of the colors and that's fine, just making sure that is on our radar.

Let's kick that down the road a bit (🐱), I think the colorbar still provides some helpful information. It would be nice if all aspects (the stretch curve, vmin/vmax, colorbar, etc) would have some way of representing when they're in mixed state. The alternative would be to not show the histogram at all (or at least disable the curve, vmin/vmax, colorbar) if any of them are mixed.

[rosteen]

Seems to work as advertised. I do think it would be useful to enable the histogram for multiple layers, in case a user wants to compare two different images on the same scale. In that case we could do the auto-scaling based on the min across all images and the max across all images. That can be a future discussion/enhancement though.

[kecnry]

Yep, but then we'd need multiple histograms/colorscales and need to figure out what to do with stretch inputs/representation 🤔

[rosteen]

I meant a single histogram, where the stretch parameters get applied to multiple layers. I guess there's an additional complication of which layer to use for the histogram bars themselves (or maybe combine all data to generate the histogram). Anyway, discussion for elsewhere.