fix(anchors): allow flexible anchor size specification across feature maps (issue #2135) - #9596
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jlaportebot wants to merge 1 commit into
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fix(anchors): allow flexible anchor size specification across feature maps (issue #2135)#9596jlaportebot wants to merge 1 commit into
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… maps (issue pytorch#2135) - Modified AnchorGenerator to accept flat sizes/aspect_ratios tuples that apply to all feature maps - New API: AnchorGenerator(sizes=(32, 64, 128), aspect_ratios=(0.5, 1.0, 2.0)) applies all sizes to all feature maps - Legacy API: AnchorGenerator(sizes=((32,), (64,), (128,)), aspect_ratios=((0.5, 1.0, 2.0),) * 3) unchanged - Updated RPN, RetinaNet, and FCOS to handle new anchor format (list of lists per image/feature level) - Added comprehensive tests for new flexible API and backward compatibility Closes pytorch#2135
🔗 Helpful Links🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/vision/9596
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Summary
This PR addresses issue #2135 by allowing users to specify anchor sizes and aspect ratios that apply to ALL feature maps, rather than requiring one sizes tuple per feature map.
Problem
The original AnchorGenerator API required users to specify sizes as a tuple of tuples, where each inner tuple corresponds to a specific feature map:
This was confusing because users expected to specify sizes that apply to all feature maps (as stated in the docs: "sizes[i] and aspect_ratios[i] can have an arbitrary number of elements").
Solution
Added a new flexible API that accepts flat tuples:
The module auto-detects which API is being used and expands flat tuples to all feature maps in the forward pass.
Changes
anchor_utils.py: Modified AnchorGenerator to support both APIs:
rpn.py: Updated RPN to handle new anchor format (list of lists per image/feature level)
retinanet.py: Updated RetinaNet to handle new anchor format
fcos.py: Updated FCOS to handle new anchor format
test_anchor_distribution.py: New comprehensive test suite (10 tests)
test_models_detection_anchor_utils.py: Updated existing tests for compatibility
Testing
Backward Compatibility
Fully backward compatible - existing code using tuple-of-tuples syntax continues to work unchanged.
Closes #2135