WIP NEW histogram backprojection

[sciunto]

Description

This PR replaces and enhances #979

TODO list

• Move code to correct location
• improve example
• add unitests
• Fix API & docstring
• suppress specific code for uint8, use our histogram function

Checklist

[It's fine to submit PRs which are a work in progress! But before they are merged, all PRs should provide:]

• Clean style in the spirit of PEP8
• Docstrings for all functions
• Gallery example in ./doc/examples (new features only)
• Benchmark in ./benchmarks, if your changes aren't covered by an
  existing benchmark
• Unit tests

[For detailed information on these and other aspects see scikit-image contribution guidelines]

References

[If this is a bug-fix or enhancement, it closes issue # ]
[If this is a new feature, it implements the following paper: ]

For reviewers

(Don't remove the checklist below.)

• Check that the PR title is short, concise, and will make sense 1 year
  later.
• Check that new functions are imported in corresponding __init__.py.
• Check that new features, API changes, and deprecations are mentioned in
  doc/release/release_dev.rst.
• Consider backporting the PR with @meeseeksdev backport to v0.14.x

[pep8speaks]

Hello @sciunto! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file doc/examples/segmentation/plot_backprojection.py:

Line 13:80: E501 line too long (81 > 79 characters)

• In the file skimage/segmentation/backproject.py:

Line 112:80: E501 line too long (81 > 79 characters)
Line 115:80: E501 line too long (81 > 79 characters)

Comment last updated at 2020-01-15 06:18:06 UTC

[jni]

@sciunto looking good! A few PEP8 issues (e.g. camelCase). Let us know when you think the WIP can come down and we can do a full review.

[sciunto]

This is not ready yet imho. I just fixed something that crossed a grep on my repository. :)

[emmanuelle]

@sciunto what else did you want to do for this PR? I noticed that some variable names (B, R...) did not correspond to our conventions of using meaningful names. But apart from that it looks good. Happy to take over with your guidance, if you prefer.

[sciunto]

@emmanuelle I do not like the way the color detection is done. I believe that we consider this as "magic" (ie guess from dimensions). Instead, kwarg is the function's signature would be better.

Also, I do not like that images are forced to be with a 8 bits precision. This must be generalized as well.

I agree also for some cleanup on the variable names. Unitests are missing as well.

Still a significant effort to do, if you would like to help, I'll be happy of it :)