Fast R-CNNweb.cs.ucdavis.edu/~yjlee/teaching/ecs289g-winter2018/Fast_RCNN.… · confidence Produce...
Transcript of Fast R-CNNweb.cs.ucdavis.edu/~yjlee/teaching/ecs289g-winter2018/Fast_RCNN.… · confidence Produce...
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Fast R-CNNRoss Girshick
Facebook AI Research (FAIR)Work done at Microsoft Research
Presented by: Nick Joodi ⎸ Doug Sherman
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Fast Region-based ConvNets (R-CNNs)
Fast Sorry about the black BG, Girshick’s slides were all black. 2
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The Pascal Visual Object Classes Challenge● Overview
○ Classification, Detection, Segmentation○ For each image:
■ Does it contain the class? → classification■ Where is it? → detection via bounding box
● Evaluation○ Mean Average Precision (mAP)
■ Participants submitted results in the form of confidence
■ Produce Precision Recall curves● Average precision for each class - ● Take mean to get mAP
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Object detection renaissance (2013-Present)
Adapted from Fast R-CNN [R. Girshick (2015)]4
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Object detection renaissance (2013-Present)
Adapted from Fast R-CNN [R. Girshick (2015)]5
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Object detection renaissance (2013-Present)
Adapted from Fast R-CNN [R. Girshick (2015)]6
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1. Pre-existing Modelsa. “Slow” R-CNNb. SPP-net
2. Ways to improvea. SGD Mini-Batchb. New Loss Function
3. Fast R-CNNa. Architectureb. Results & Future Work
Agenda
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● R-CNN (aka “slow R-CNN”) [Girshick et al. CVPR14]● SPP-net [He et al. ECCV14]
Region-based convnets (R-CNNs)
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Adapted from Fast R-CNN [R. Girshick (2015)]Adapted from Fast R-CNN [R. Girshick (2015)]9
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Adapted from Fast R-CNN [R. Girshick (2015)]10
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Adapted from Fast R-CNN [R. Girshick (2015)]11
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Adapted from Fast R-CNN [R. Girshick (2015)]12
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Adapted from Fast R-CNN [R. Girshick (2015)]13
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Adapted from Fast R-CNN [R. Girshick (2015)]14
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What’s wrong with slow R-CNN?● Ad hoc training objectives
○ Fine-tune network with softmax classifier (log loss)○ Train post-hoc linear SVMs (hinge loss)○ Train post-hoc bounding-box regressors (L2 loss)
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What’s wrong with slow R-CNN?● Ad hoc training objectives
○ Fine-tune network with softmax classifier (log loss)○ Train post-hoc linear SVMs (hinge loss)○ Train post-hoc bounding-box regressors (L2 loss)
● Training is slow (84h), takes a lot of disk space
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What’s wrong with slow R-CNN?● Ad hoc training objectives
○ Fine-tune network with softmax classifier (log loss)○ Train post-hoc linear SVMs (hinge loss)○ Train post-hoc bounding-box regressors (L2 loss)
● Training is slow (84h), takes a lot of disk space● Inference (detection) is slow
○ 47s / image with VGG16 [Simonyan & Zisserman. ICLR15]○ Fixed by SPP-net [He et al. ECCV14]
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1. Pre-existing Modelsa. “Slow” R-CNNb. SPP-net
2. Ways to improvea. SGD Mini-Batchb. New Loss Function
3. Fast R-CNNa. Architectureb. Results & Future Work
Agenda
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Adapted from Fast R-CNN [R. Girshick (2015)]19
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Adapted from Fast R-CNN [R. Girshick (2015)]20
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Adapted from Fast R-CNN [R. Girshick (2015)]21
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Adapted from Fast R-CNN [R. Girshick (2015)]22
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Adapted from Fast R-CNN [R. Girshick (2015)]23
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Adapted from Fast R-CNN [R. Girshick (2015)]24
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Pyramid Pooling Layer
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1 2
3 4
RegionOutput of Pooling Concatenated
(w/2 x h/2)(4 x 2)
(w/4 x h/4)(2 x 1)
(w/1 x h/1)(8 x 2)
To FC
Stride/Window Size
8
4
1
2
3
4
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Adapted from Fast R-CNN [R. Girshick (2015)]26
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What’s wrong with SPP-net?● Inherits the rest of R-CNN’s problems
○ Ad hoc training objective○ Training is slow (25h), takes a lot of disk space
● Introduces a new problem: cannot update parameters below SPP layer during training
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Adapted from Fast R-CNN [R. Girshick (2015)]28
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Agenda1. Pre-existing Models
a. “Slow” R-CNNb. SPP-net
2. Ways to improvea. SGD Mini-Batchb. New Loss Function
3. Fast R-CNNa. Architectureb. Results & Future Work
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SGD Mini-Batch Method for RoIs
Adapted from Fast R-CNN [R. Girshick (2015)]30
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SGD Mini-Batch Method for RoIs
Adapted from Fast R-CNN [R. Girshick (2015)]31
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SGD Mini-Batch Method for RoIs
Adapted from Fast R-CNN [R. Girshick (2015)]32
Input size for SPP-net
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SGD Mini-Batch Method for RoIs
Adapted from Fast R-CNN [R. Girshick (2015)]33
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SGD Mini-Batch Method for RoIs
Adapted from Fast R-CNN [R. Girshick (2015)]34
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SGD Mini-Batch Method for RoIs
Adapted from Fast R-CNN [R. Girshick (2015)]35
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SGD Mini-Batch Method for RoIs
Adapted from Fast R-CNN [R. Girshick (2015)]36
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SGD Mini-Batch Method for RoIs
Adapted from Fast R-CNN [R. Girshick (2015)]37
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Agenda1. Pre-existing Models
a. “Slow” R-CNNb. SPP-net
2. Ways to improvea. SGD Mini-Batchb. New Loss Function
3. Fast R-CNNa. Architectureb. Resultsc. Future Work
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Revised loss function For the classification For the bounding box
p: Predicted RoI Classificationu: True RoI Classification
tu = (tx,ty,tw,th): Predicted Bounding Boxv = (vx,vy,vw,vh): True Bounding Box
ƛ : Controls the balance between the two losses
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Revised loss function
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Revised loss function
Smooth: Continuously Differentiable41
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1. Pre-existing Modelsa. “Slow” R-CNNb. SPP-net
2. Ways to improvea. SGD Mini-Batchb. New Loss Function
3. Fast R-CNNa. Architectureb. Results & Future Work
Agenda
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Fast R-CNN● Fast test-time, like SPP-net● One network, trained in one stage● Higher mean average precision than slow R-CNN and SPP-net
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Adapted from Fast R-CNN [R. Girshick (2015)]44
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Adapted from Fast R-CNN [R. Girshick (2015)]45
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Adapted from Fast R-CNN [R. Girshick (2015)]46
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Adapted from Fast R-CNN [R. Girshick (2015)]47
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Adapted from Fast R-CNN [R. Girshick (2015)]48
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Adapted from Fast R-CNN [R. Girshick (2015)]49
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Adapted from Fast R-CNN [R. Girshick (2015)]50
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Agenda1. Pre-existing Models
a. “Slow” R-CNNb. SPP-net
2. Ways to improvea. SGD Mini-Batchb. New Loss Function
3. Fast R-CNNa. Architectureb. Results & Future Work
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Adapted from Fast R-CNN [R. Girshick (2015)]52
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Adapted from Fast R-CNN [R. Girshick (2015)]53
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Adapted from Fast R-CNN [R. Girshick (2015)]54
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● Out-of-network region proposals○ Selective search: 2s / img; EdgeBoxes: 0.2s / img
● Fortunately, this has already been solved
S. Ren, K. He, R. Girshick & J. Sun. “Faster R'CNN: Towards Real'Time Object Detection with Region Proposal Networks.” NIPS (2015).
What’s still wrong?
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Fast R-CNN take-aways● End-to-end training of deep ConvNets for object detection● Fast training times● Open source for easy experimentation● A large number of ImageNet detection and COCO detection methods are
built on Fast R-CNN
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