[BC-breaking] Fix initialisation bug on FeaturePyramidNetwork by datumbox · Pull Request #2954 · pytorch/vision

datumbox · 2020-11-03T10:59:46Z

The FeaturePyramidNetwork intended to initialize all the Conv2d layer weights using the following distribution:

vision/torchvision/ops/feature_pyramid_network.py

Lines 89 to 92 in 971c3e4

    
           for m in self.children(): 
        
               if isinstance(m, nn.Conv2d): 
        
                   nn.init.kaiming_uniform_(m.weight, a=1) 
        
                   nn.init.constant_(m.bias, 0)

Unfortunately due to the use of children() instead of modules() we only initialize the direct blocks of the FPN and not the ones of its nested modules. This means that those nested modules use the default distribution from PyTorch:

init.kaiming_uniform_(self.weight, a=math.sqrt(5))
if self.bias is not None:
    fan_in, _ = init._calculate_fan_in_and_fan_out(self.weight)
    bound = 1 / math.sqrt(fan_in)
    init.uniform_(self.bias, -bound, bound)

This PR changes the use of children() to modules() to ensure that the weight initialization is consistent across all nested blocks of FeaturePyramidNetwork.

The above change, though trivial in terms of coding it has side-effects:

It increases the instability of unit-tests.
It affects the validation metrics of the Detection pre-trained models.

The first issue is addressed on two separate PRs. See #2965 and #2966 from more information. To address the second, I retrained the Detection models on master and on this branch and compared their stats. Overall we see that fixing the bug and applying initialization correctly in all blocks leads to small improvements for all models except keypointrcnn.

Master

fasterrcnn_resnet50_fpn: boxAP=37.6

0: IoU metric: bbox
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=   all | maxDets=100 ] = 0.376
0:  Average Precision  (AP) @[ IoU=0.50      | area=   all | maxDets=100 ] = 0.583
0:  Average Precision  (AP) @[ IoU=0.75      | area=   all | maxDets=100 ] = 0.405
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= small | maxDets=100 ] = 0.212
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=medium | maxDets=100 ] = 0.413
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= large | maxDets=100 ] = 0.489
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets=  1 ] = 0.313
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets= 10 ] = 0.495
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets=100 ] = 0.518
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= small | maxDets=100 ] = 0.317
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=medium | maxDets=100 ] = 0.556
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= large | maxDets=100 ] = 0.669

retinanet_resnet50_fpn: boxAP=36.3

0: IoU metric: bbox
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=   all | maxDets=100 ] = 0.363
0:  Average Precision  (AP) @[ IoU=0.50      | area=   all | maxDets=100 ] = 0.555
0:  Average Precision  (AP) @[ IoU=0.75      | area=   all | maxDets=100 ] = 0.384
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= small | maxDets=100 ] = 0.191
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=medium | maxDets=100 ] = 0.400
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= large | maxDets=100 ] = 0.492
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets=  1 ] = 0.313
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets= 10 ] = 0.501
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets=100 ] = 0.539
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= small | maxDets=100 ] = 0.329
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=medium | maxDets=100 ] = 0.581
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= large | maxDets=100 ] = 0.692

maskrcnn_resnet50_fpn: boxAP=38.5, maskAP=34.5

0: IoU metric: bbox
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=   all | maxDets=100 ] = 0.385
0:  Average Precision  (AP) @[ IoU=0.50      | area=   all | maxDets=100 ] = 0.592
0:  Average Precision  (AP) @[ IoU=0.75      | area=   all | maxDets=100 ] = 0.415
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= small | maxDets=100 ] = 0.219
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=medium | maxDets=100 ] = 0.420
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= large | maxDets=100 ] = 0.508
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets=  1 ] = 0.319
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets= 10 ] = 0.506
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets=100 ] = 0.529
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= small | maxDets=100 ] = 0.335
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=medium | maxDets=100 ] = 0.569
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= large | maxDets=100 ] = 0.677
0: IoU metric: segm
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=   all | maxDets=100 ] = 0.345
0:  Average Precision  (AP) @[ IoU=0.50      | area=   all | maxDets=100 ] = 0.559
0:  Average Precision  (AP) @[ IoU=0.75      | area=   all | maxDets=100 ] = 0.366
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= small | maxDets=100 ] = 0.159
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=medium | maxDets=100 ] = 0.372
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= large | maxDets=100 ] = 0.517
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets=  1 ] = 0.295
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets= 10 ] = 0.457
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets=100 ] = 0.476
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= small | maxDets=100 ] = 0.280
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=medium | maxDets=100 ] = 0.514
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= large | maxDets=100 ] = 0.637

keypointrcnn_resnet50_fpn: boxAP=55.7, kpAP=65.1

0: IoU metric: bbox
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=   all | maxDets=100 ] = 0.557
0:  Average Precision  (AP) @[ IoU=0.50      | area=   all | maxDets=100 ] = 0.831
0:  Average Precision  (AP) @[ IoU=0.75      | area=   all | maxDets=100 ] = 0.606
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= small | maxDets=100 ] = 0.382
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=medium | maxDets=100 ] = 0.637
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= large | maxDets=100 ] = 0.721
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets=  1 ] = 0.190
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets= 10 ] = 0.565
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets=100 ] = 0.646
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= small | maxDets=100 ] = 0.497
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=medium | maxDets=100 ] = 0.710
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= large | maxDets=100 ] = 0.795
0: IoU metric: keypoints
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=   all | maxDets= 20 ] = 0.651
0:  Average Precision  (AP) @[ IoU=0.50      | area=   all | maxDets= 20 ] = 0.862
0:  Average Precision  (AP) @[ IoU=0.75      | area=   all | maxDets= 20 ] = 0.711
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=medium | maxDets= 20 ] = 0.602
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= large | maxDets= 20 ] = 0.732
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets= 20 ] = 0.718
0:  Average Recall     (AR) @[ IoU=0.50      | area=   all | maxDets= 20 ] = 0.907
0:  Average Recall     (AR) @[ IoU=0.75      | area=   all | maxDets= 20 ] = 0.771
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=medium | maxDets= 20 ] = 0.669
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= large | maxDets= 20 ] = 0.788

Branch

fasterrcnn_resnet50_fpn: boxAP=38.0

0: IoU metric: bbox
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=   all | maxDets=100 ] = 0.380
0:  Average Precision  (AP) @[ IoU=0.50      | area=   all | maxDets=100 ] = 0.587
0:  Average Precision  (AP) @[ IoU=0.75      | area=   all | maxDets=100 ] = 0.411
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= small | maxDets=100 ] = 0.214
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=medium | maxDets=100 ] = 0.413
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= large | maxDets=100 ] = 0.500
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets=  1 ] = 0.316
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets= 10 ] = 0.496
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets=100 ] = 0.521
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= small | maxDets=100 ] = 0.327
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=medium | maxDets=100 ] = 0.557
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= large | maxDets=100 ] = 0.664

retinanet_resnet50_fpn: boxAP=36.4

0: IoU metric: bbox
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=   all | maxDets=100 ] = 0.364
0:  Average Precision  (AP) @[ IoU=0.50      | area=   all | maxDets=100 ] = 0.558
0:  Average Precision  (AP) @[ IoU=0.75      | area=   all | maxDets=100 ] = 0.381
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= small | maxDets=100 ] = 0.193
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=medium | maxDets=100 ] = 0.400
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= large | maxDets=100 ] = 0.489
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets=  1 ] = 0.314
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets= 10 ] = 0.502
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets=100 ] = 0.541
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= small | maxDets=100 ] = 0.334
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=medium | maxDets=100 ] = 0.584
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= large | maxDets=100 ] = 0.692

maskrcnn_resnet50_fpn: boxAP=38.7, maskAP=34.7

0: IoU metric: bbox
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=   all | maxDets=100 ] = 0.387
0:  Average Precision  (AP) @[ IoU=0.50      | area=   all | maxDets=100 ] = 0.592
0:  Average Precision  (AP) @[ IoU=0.75      | area=   all | maxDets=100 ] = 0.420
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= small | maxDets=100 ] = 0.216
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=medium | maxDets=100 ] = 0.421
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= large | maxDets=100 ] = 0.512
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets=  1 ] = 0.321
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets= 10 ] = 0.506
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets=100 ] = 0.531
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= small | maxDets=100 ] = 0.333
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=medium | maxDets=100 ] = 0.569
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= large | maxDets=100 ] = 0.683
0: IoU metric: segm
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=   all | maxDets=100 ] = 0.347
0:  Average Precision  (AP) @[ IoU=0.50      | area=   all | maxDets=100 ] = 0.559
0:  Average Precision  (AP) @[ IoU=0.75      | area=   all | maxDets=100 ] = 0.371
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= small | maxDets=100 ] = 0.152
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=medium | maxDets=100 ] = 0.373
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= large | maxDets=100 ] = 0.519
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets=  1 ] = 0.297
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets= 10 ] = 0.458
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets=100 ] = 0.478
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= small | maxDets=100 ] = 0.278
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=medium | maxDets=100 ] = 0.514
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= large | maxDets=100 ] = 0.642

keypointrcnn_resnet50_fpn: boxAP=55.5, kpAP=65.1

0: IoU metric: bbox
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=   all | maxDets=100 ] = 0.555
0:  Average Precision  (AP) @[ IoU=0.50      | area=   all | maxDets=100 ] = 0.833
0:  Average Precision  (AP) @[ IoU=0.75      | area=   all | maxDets=100 ] = 0.603
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= small | maxDets=100 ] = 0.381
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=medium | maxDets=100 ] = 0.634
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= large | maxDets=100 ] = 0.719
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets=  1 ] = 0.190
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets= 10 ] = 0.564
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets=100 ] = 0.647
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= small | maxDets=100 ] = 0.499
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=medium | maxDets=100 ] = 0.709
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= large | maxDets=100 ] = 0.796
0: IoU metric: keypoints
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=   all | maxDets= 20 ] = 0.651
0:  Average Precision  (AP) @[ IoU=0.50      | area=   all | maxDets= 20 ] = 0.865
0:  Average Precision  (AP) @[ IoU=0.75      | area=   all | maxDets= 20 ] = 0.706
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area=medium | maxDets= 20 ] = 0.605
0:  Average Precision  (AP) @[ IoU=0.50:0.95 | area= large | maxDets= 20 ] = 0.730
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=   all | maxDets= 20 ] = 0.719
0:  Average Recall     (AR) @[ IoU=0.50      | area=   all | maxDets= 20 ] = 0.911
0:  Average Recall     (AR) @[ IoU=0.75      | area=   all | maxDets= 20 ] = 0.768
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area=medium | maxDets= 20 ] = 0.670
0:  Average Recall     (AR) @[ IoU=0.50:0.95 | area= large | maxDets= 20 ] = 0.787

The deterioration in accuracy might be because of:

Random effects: Let's assume that sampling from distribution X is a better initialization scheme than sampling from distribution Y. On average we expect that applying scheme X yields better results than Y. This does not mean that every instantiation of the sampling from X will yield better results than instantiations from Y. Using different seeds can yield different results.
Changing the initialization is not beneficial: Initializing from the same distribution X in all blocks is not beneficial for all models. Thus for some models, it might be beneficial to keep the old scheme Y.

To fully investigate the situation, we would need to do multiple runs using different seeds for each initialization scheme and then conduct a statistical test to assess if our change has statistically significant effects on the accuracy. If the change turns out to have statistically significant negative results, we might want to support different init schemes per model.

I believe that the above is not worth the effort because:

The suggested change does not seem to hurt overall the performance in most cases.
Training multiple models is costly and time consuming and the use of similar init schemes is unlikely in this case to lead to significant improvements.
Our goal is to provide a clean and consistent implementation rather than apply hacks to achieve SOTA performance.

Based on the above, I recommend merging the change into master.

This reverts commit 050b64a

codecov · 2020-11-06T12:20:38Z

Codecov Report

Merging #2954 into master will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2954      +/-   ##
==========================================
+ Coverage   73.41%   73.44%   +0.03%     
==========================================
  Files          99       99              
  Lines        8812     8812              
  Branches     1389     1389              
==========================================
+ Hits         6469     6472       +3     
+ Misses       1917     1915       -2     
+ Partials      426      425       -1

Impacted Files	Coverage Δ
torchvision/ops/feature_pyramid_network.py	`94.50% <100.00%> (+3.29%)`	⬆️

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fmassa

Thanks a lot for the PR and the investigation Vasilis!

I agree with all your points, I think it's not necessary for now to run more tests for keypoint rcnn.

We should at some point though consider uploading newer weights, but we will need to handle versioning before.

* Change children() to modules() to ensure init happens in all blocks. * Update expected values of all detection models. * Revert "Update expected values of all detection models." This reverts commit 050b64a * Update expecting values.

Change children() to modules() to ensure init happens in all blocks.

d3a6dac

facebook-github-bot added the cla signed label Nov 3, 2020

Update expected values of all detection models.

050b64a

datumbox changed the title ~~[WIP] Change children() to modules() to ensure init happens in all blocks.~~ [WIP] Fix initialisation bug on FeaturePyramidNetwork Nov 3, 2020

Merge branch 'master' into bugfix/pyramidnet_init

f042027

datumbox force-pushed the bugfix/pyramidnet_init branch from 639d06f to f042027 Compare November 5, 2020 11:19

datumbox mentioned this pull request Nov 5, 2020

Fix flakiness on detection tests #2966

Merged

datumbox added 3 commits November 5, 2020 18:11

Revert "Update expected values of all detection models."

033c218

This reverts commit 050b64a

Merge branch 'master' into bugfix/pyramidnet_init

a9b81b3

Update expecting values.

f344366

datumbox requested a review from fmassa November 8, 2020 14:04

fmassa approved these changes Nov 9, 2020

View reviewed changes

fmassa merged commit 8fe0b15 into pytorch:master Nov 9, 2020

fmassa changed the title ~~[WIP] Fix initialisation bug on FeaturePyramidNetwork~~ [BC-breaking] Fix initialisation bug on FeaturePyramidNetwork Nov 9, 2020

datumbox deleted the bugfix/pyramidnet_init branch November 9, 2020 11:07

datumbox mentioned this pull request Nov 21, 2020

Support for image with no annotations in RetinaNet #3032

Merged

datumbox mentioned this pull request Jan 4, 2021

Improve speed/accuracy of *RCNN models by introducing a score threshold on RPN #3205

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datumbox mentioned this pull request May 13, 2021

Unify onnx and JIT resize implementations #3654

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[BC-breaking] Fix initialisation bug on FeaturePyramidNetwork#2954

[BC-breaking] Fix initialisation bug on FeaturePyramidNetwork#2954
fmassa merged 6 commits intopytorch:masterfrom
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	for m in self.children():
	if isinstance(m, nn.Conv2d):
	nn.init.kaiming_uniform_(m.weight, a=1)
	nn.init.constant_(m.bias, 0)

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