Introduce mosaic augmentation

[potipot]

Fixes #587

• figure out how to attach mosaic as batch_tfms
• implement bbox unaware mosaic
• implement bbox safe crop mosaic with scaling
• implement bbox safe crop without scaling (requires new Albumentation transform)
• add tests (especially for negative samples - what happens if there is no bbox to "safely crop"?)

[potipot]

some early results for bbox unaware mosaic

[codecov]

Codecov Report

Merging #1007 (e4b74db) into master (4050e0e) will decrease coverage by 0.28%.
The diff coverage is 54.00%.

❗ Current head e4b74db differs from pull request most recent head b7e64f1. Consider uploading reports for the commit b7e64f1 to get more accurate results

@@            Coverage Diff             @@
##           master    #1007      +/-   ##
==========================================
- Coverage   85.88%   85.59%   -0.29%     
==========================================
  Files         255      256       +1     
  Lines        5631     5679      +48     
==========================================
+ Hits         4836     4861      +25     
- Misses        795      818      +23     

Flag	Coverage Δ
unittests	85.59% <54.00%> (-0.29%)	⬇️

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Impacted Files	Coverage Δ
icevision/tfms/batch/mosaic.py	48.88% <48.88%> (ø)
icevision/data/record_collection.py	100.00% <100.00%> (ø)
...sion/tfms/albumentations/albumentations_adapter.py	96.25% <100.00%> (ø)
icevision/tfms/batch/__init__.py	100.00% <100.00%> (ø)

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[potipot]

bbox aware mosaic with enforced scaling

[potipot]

what I want to achieve with non-scaling mosaic is keeping the original size of objects. The current scaled mosaic tries to encircle all of the bboxes in an image and make such crop, that will include all of the objects.

Another, smarter approach is to select exclusive areas in an image that can be cropped out and used as "pieces" in the mosaic.

[dav-ell]

Can this be merged? It looks fantastic, and I've been struggling trying to implement one myself.

[potipot]

@dav-ell Oh wow! I completely forgot about this one. Yeah I'll sync master changes and try to merge it as is. (the non-scaling mosaic aug is still TBD but if you find it useful as is then I'd say let's merge!)

[dav-ell]

Thanks @potipot!

What a shame that I just finished my own custom implementation that I referenced here: albumentations-team/albumentations#677 (comment)

The good news is that this one has more features than mine, so I'll almost definitely be switching over once it's in.

[Modius22]

This looks great. I am also looking for a similar functionality for object detection.
I hope it can be merged soon =)

[mikel-brostrom]

Any update on this?

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[potipot]

Hi @mikel-brostrom, it's been a while since I worked on this. I just checked and it should be working. Do you mind giving it a try? you can install this PR in your venv by

pip install git+https://github.com/potipot/icevision@add_mosaic#egg=icevision[all]

here is the notebook showcasing how to use the mosaic tfm:
https://github.com/potipot/icevision/blob/add_mosaic/notebooks/mosaic.ipynb

if it works for you I could put some more time into it and try to merge it.