[FIX] db loss TF and PT also for training with rotated samples

[felixdittrich92]

This PR:

• change DB loss from Balanced BCE to Focal loss
• fix target building

Any feedback is welcome 🤗

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (a48b72a) 95.76% compared to head (0375ee8) 95.76%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
...s/detection/differentiable_binarization/pytorch.py	93.75%	1 Missing ⚠️
...etection/differentiable_binarization/tensorflow.py	94.11%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1396      +/-   ##
==========================================
- Coverage   95.76%   95.76%   -0.01%     
==========================================
  Files         155      155              
  Lines        6950     6941       -9     
==========================================
- Hits         6656     6647       -9     
  Misses        294      294              

Flag	Coverage Δ
unittests	95.76% <95.83%> (-0.01%)	⬇️

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[felixdittrich92]

@odulcy-mindee @charlesmindee Still some work in progress

target building needs to be checked again (especially for the shrunken masks) and the loss comp

[felixdittrich92]

norm input:

seg_target:

seg_mask: (should be empty / ones if there are no ignored polygons ?)

thresh_target:

thresh_mask:

[felixdittrich92]

The loss comp is mostly borrowed from mmocr to see wht's going wrong (and because of missing time xD)

[felixdittrich92]

@odulcy-mindee I think that's also fine now :)

[odulcy-mindee]

Thanks @felixdittrich92 ! 🚀