[Datumaro] Image control in converters

[zhiltsov-max]

Motivation and context

• Added an option to specify image extension when exporting datasets.
• Added image copying when exporting datasets, if possible.
• Updated Converter class interface. Now it should be invoked with Converter.convert(...). Converter definition simplified.
• Annotation-less files are not generated anymore in COCO format, unless target tasks explicitly requested.

How has this been tested?

Unit tests.

How to test:

datum project export -f <any format> -- [--image-ext '.png'] --save-images

Checklist

• I submit my changes into the develop branch
• I have added description of my changes into CHANGELOG file
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues (read github docs)
• I have increased versions of npm packages if it is necessary (cvat-canvas,
  cvat-core, cvat-data and cvat-ui)

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.
• I have updated the license header for each file (see an example below)

# Copyright (C) 2020 Intel Corporation
#
# SPDX-License-Identifier: MIT

[zhiltsov-max]

@nmanovic, how do you think, should we add an option of making symlinks instead of copying?

[coveralls]

Pull Request Test Coverage Report for Build 6199

• 196 of 233 (84.12%) changed or added relevant lines in 23 files are covered.
• 6 unchanged lines in 4 files lost coverage.
• Overall coverage increased (+0.02%) to 65.124%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
cvat/apps/dataset_manager/formats/mask.py	3	4	75.0%
datumaro/datumaro/components/project.py	1	2	50.0%
datumaro/datumaro/plugins/labelme_format.py	10	11	90.91%
datumaro/datumaro/plugins/mot_format.py	7	8	87.5%
datumaro/datumaro/plugins/tf_detection_api_format/converter.py	21	22	95.45%
datumaro/datumaro/plugins/image_dir.py	12	14	85.71%
datumaro/datumaro/cli/contexts/project/init.py	0	3	0.0%
datumaro/datumaro/components/converter.py	40	45	88.89%
datumaro/datumaro/plugins/coco_format/converter.py	33	40	82.5%
datumaro/datumaro/plugins/voc_format/converter.py	33	48	68.75%

Files with Coverage Reduction	New Missed Lines	%
datumaro/datumaro/components/project.py	1	77.69%
datumaro/datumaro/plugins/coco_format/converter.py	1	89.03%
datumaro/datumaro/plugins/image_dir.py	1	87.72%
datumaro/datumaro/plugins/coco_format/importer.py	3	79.49%

Totals
Change from base Build 6185:	0.02%
Covered Lines:	10979
Relevant Lines:	16448

---

💛 - Coveralls

[azhavoro]

@zhiltsov-max could you fix conflicts?

[zhiltsov-max]

@azhavoro, done. Is there a way to obtain really original images? I mean, a path to the raw image. The problem is that once read, jpeg images can't be saved with original quality, even if saving with 100% quality. PNG images are likely to lose their compression. So, since we've learned to just copy images on export, it makes sense to support it in CVAT too. Also, it potentially should give a significant performance boost for export.

An example - an original (raw) PNG was 43 kb, exported became 60.

[nmanovic]

@zhiltsov-max , could you please resolve conflicts?

[nmanovic]

Here is an overview of what got changed by this pull request:

Complexity increasing per file
==============================
- datumaro/datumaro/components/converter.py  2
         

Complexity decreasing per file
==============================
+ datumaro/datumaro/plugins/tf_detection_api_format/extractor.py  -1
         

See the complete overview on Codacy