Replace imshow_det_bboxes visualization backend

[hhaAndroid]

Replace imshow_det_bboxes visualization backend

[codecov]

Codecov Report

Merging #4389 (a358224) into master (103a4dd) will increase coverage by 0.22%.
The diff coverage is 67.50%.

@@            Coverage Diff             @@
##           master    #4389      +/-   ##
==========================================
+ Coverage   61.78%   62.01%   +0.22%     
==========================================
  Files         239      241       +2     
  Lines       18269    18335      +66     
  Branches     3060     3071      +11     
==========================================
+ Hits        11288    11370      +82     
+ Misses       6433     6409      -24     
- Partials      548      556       +8     

Flag	Coverage Δ
unittests	61.97% <67.50%> (+0.21%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mmdet/apis/inference.py	19.51% <0.00%> (-0.03%)	⬇️
mmdet/models/detectors/base.py	55.30% <16.66%> (+3.12%)	⬆️
mmdet/core/visualization/image.py	72.85% <72.85%> (ø)
mmdet/core/visualization/__init__.py	100.00% <100.00%> (ø)
mmdet/models/detectors/cornernet.py	94.87% <0.00%> (-5.13%)	⬇️
mmdet/models/dense_heads/corner_head.py	74.45% <0.00%> (-2.32%)	⬇️
mmdet/core/bbox/samplers/sampling_result.py	73.01% <0.00%> (-1.59%)	⬇️
mmdet/models/dense_heads/cascade_rpn_head.py	28.07% <0.00%> (-0.20%)	⬇️
... and 6 more

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[hhaAndroid]

opencv backend (old):

matplotlib backend(new):

[hhaAndroid]

opencv backend (old):

matplotlib backend(new):

also you can specify the mask color

[hiyyg]

@hhaAndroid How about putting the text inside the bbox? Otherwise if the bbox is on the top of the image, the text might not be shown.

[hhaAndroid]

@hiyyg
I try it

Doesn't seem to work very well，due to the size and the distance of the object, the y coordinate of the text is not easy to set

[hiyyg]

@hhaAndroid Try a strategy similar to this? https://github.com/facebookresearch/detectron2/blob/master/detectron2/utils/visualizer.py#L702

[hhaAndroid]

@hiyyg Thank you，Let me see

[hhaAndroid]

@hiyyg I found that it can be achieved by
verticalalignment="top" horizontalalignment="left"

[ZwwWayne]

Also involves @MeowZheng to review

[hellock]

Better to add a filling color for text regions.

[hhaAndroid]

Better to add a filling color for text regions.