I'm attending ECCV right now and must share this with you.
Great talk from Erik Learned-Miller on unsupervised learning using depth prediction as a surrogate task. The paper: https://t.co/BeaSLoQAPh
Improving detector's perfomance by unsupervised hard examples mining.
Paper: https://t.co/3P4NX2dds5
Great talk from Erik Learned-Miller on unsupervised learning using depth prediction as a surrogate task. The paper: https://t.co/BeaSLoQAPh
Improving detector's perfomance by unsupervised hard examples mining.
Paper: https://t.co/3P4NX2dds5
X2Face: A network for controlling face generation using images, audio, and pose codes
Olivia Wiles*, A. Sophia Koepke*, Andrew Zisserman
https://arxiv.org/abs/1807.10550
ECCV 2018
❓ Briefly
Authors proposed a model that can control a
✏️ Method:
The model consists of 2 networks: embedding net and driving net.
1. Given a source frame embedding net predicts a vector field which after applying to the source frame gives a so-called embedded face (which essentially is a frontalized face).
2. Given a
Driving net has an encoder-decoder architecture (U-Net and pix2pix based). The latent space (i.e. bottleneck features, called the driving vector) of this network encodes pose/expression/zoom/other factors of variation.
Note: The trick is to avoid translating an input image to output image directly on the pixel level (as for example CycleGAN does), but to predict a vector field which will transform the input image to something new. This allows training w/o a discriminator and explicit pose/expression labels.
◼️ Training is done in two steps:
First step:
Authors sample two random frames from the same video (same person). One is used as the source frame, another as the
Second step:
The new loss function is introduced: identity loss, which compares frames using features of the pre-trained network (VGG-11) for person identification.
Authors sample a source frame
For a pair
◼️ Inference step:
The pose and expression of the
Additionally, authors show that the transformation of the
Analogously authors train a mapping from 0.2 s sound excerpt to the driving vector (bottleneck features of the driving net). The resultant driving vector can be used to transform the source face in the same way as described before.
✔️ Experiments:
The model is trained on VoxCeleb dataset on cropped faces of size 256x256 pix.
The model is compared to CycleGAN and Averbuch-Elor et al. [1]. The proposed method obviously produces better results than CycleGAN. Compared to [1], X2Face makes fewer assumptions about the input data (e.g. the
Olivia Wiles*, A. Sophia Koepke*, Andrew Zisserman
https://arxiv.org/abs/1807.10550
ECCV 2018
❓ Briefly
Authors proposed a model that can control a
source face given a driving face to produce a generated frame with the same identity as the source face but the pose and expression from the driving face. The model is trained in a self-supervised manner on a large collection of video data. They also show that the generation process can be driven by audio (person speaking) or pose codes w/o further network training. No 3D models used, the method works on 2D frames.✏️ Method:
The model consists of 2 networks: embedding net and driving net.
1. Given a source frame embedding net predicts a vector field which after applying to the source frame gives a so-called embedded face (which essentially is a frontalized face).
2. Given a
driving frame driving net predicts a vector field (i.e. x,y shift for every pixel of the input image). This vector field transforms pixels from an embedded face to produce the generated frame.Driving net has an encoder-decoder architecture (U-Net and pix2pix based). The latent space (i.e. bottleneck features, called the driving vector) of this network encodes pose/expression/zoom/other factors of variation.
Note: The trick is to avoid translating an input image to output image directly on the pixel level (as for example CycleGAN does), but to predict a vector field which will transform the input image to something new. This allows training w/o a discriminator and explicit pose/expression labels.
◼️ Training is done in two steps:
First step:
Authors sample two random frames from the same video (same person). One is used as the source frame, another as the
driving frame. In this case, the loss function will be a photometric L1 loss between the driving frame and the generated frame (since the source frame has the same identity as the driving frame).Second step:
The new loss function is introduced: identity loss, which compares frames using features of the pre-trained network (VGG-11) for person identification.
Authors sample a source frame
sA of identity A, and two driving frames dA, dR. dA is of identity A and dR a random identity. sA, dA, dR are used as training inputs. This gives two generated frames g_dA and g_dR respectively which should both be of identity A.For a pair
(dA, g_dA) photometric L1 loss + identity loss is used; for a pair (dA, g_dR) only identity loss is used.◼️ Inference step:
The pose and expression of the
source face can be changed by feeding to the model a driving frame with the face of any other person.Additionally, authors show that the transformation of the
source face can be done using a pose code (encodes face attributes such as pitch/yaw/roll angles, for which the ground truth is provided in the dataset). They train a 1-layer neural network to convert pose code into a driving vector (bottleneck features of the driving net) and use the driving net to generate a corresponding driving vector field from the driving vector.Analogously authors train a mapping from 0.2 s sound excerpt to the driving vector (bottleneck features of the driving net). The resultant driving vector can be used to transform the source face in the same way as described before.
✔️ Experiments:
The model is trained on VoxCeleb dataset on cropped faces of size 256x256 pix.
The model is compared to CycleGAN and Averbuch-Elor et al. [1]. The proposed method obviously produces better results than CycleGAN. Compared to [1], X2Face makes fewer assumptions about the input data (e.g. the
source face should not necessarily be in a frontal pose with the neutral expression, etc.) and can handle larger pose changes. In contrary to [1], X2Face can work with a single driving frame and does not require a driving video.⛔ Criticism:
- The resolution of the generated face is only 256x256.
- Generated frames appear to be blurred (not sharp), due to missing fine details on the face. Adding a discriminator might help to get more realistic renderings.
💬 Conclusion:
I talked to Olivia (the first author) and overall it is a very nice work. They propose an interesting self-supervised method, which produces vector fields to transform a source face into a generated face with new pose and expression but the same appearance.
Links:
[1] Bringing Portraits to Life, SIGGRAPH Asia 2017, http://cs.tau.ac.il/~averbuch1/portraitslife/elor2017_bringingPortraits.pdf
- The resolution of the generated face is only 256x256.
- Generated frames appear to be blurred (not sharp), due to missing fine details on the face. Adding a discriminator might help to get more realistic renderings.
💬 Conclusion:
I talked to Olivia (the first author) and overall it is a very nice work. They propose an interesting self-supervised method, which produces vector fields to transform a source face into a generated face with new pose and expression but the same appearance.
Links:
[1] Bringing Portraits to Life, SIGGRAPH Asia 2017, http://cs.tau.ac.il/~averbuch1/portraitslife/elor2017_bringingPortraits.pdf
Transferring Dense Pose to Proximal Animal Classes
Artsiom Sanakoyeu, Vasil Khalidov, Maureen S. McCarthy, Andrea Vedaldi, Natalia Neverova (Facebook AI Research)
In CVPR 2020.
🌐https://asanakoy.github.io/densepose-evolution/
▶️youtu.be/OU3Ayg_l4QM
📝https://arxiv.org/pdf/2003.00080.pdf
❓ What?
DensePose approach predicts the pose of humans densely and accurately given a large dataset of poses annotated in detail.
We want to extend the same approach to animals but without annotations. Because it's super expensive to collect DensePose annotations for all different classes of animals. So we show that, at least for proximal animal classes such as chimpanzees, it is possible to transfer the knowledge existing in DensePose for humans. We propose to utilize the existing annotations of humans and do self-training on unlabeled images of animals.
In a nutshell, we first pretrain the DensePose on the existing human annotations. Then we predict DensePose on unlabeled images, select the most confident predictions and throw them in the augmented training set for retraining the model. To be able to select point-wise the most confident DensePose predictions we introduce a novel Auto-Calibrated version of DensePose-RCNN which can estimate the uncertainty of its predictions for every pixel.
We tested several techniques for sampling pseudo-labels and concluded that sampling based on confidence estimates from fine-grained tasks (24-Body-part estimation and DensePose UV-maps) results in the best performance.
We introduced a novel DensePose-Chimps dataset with Dense Pose ground truth annotations for chimps and tested our models on it, obtaining significant performance improvement over the baseline.
In this paper, we conducted thorough experiments only for chimps, but the method can be extended to other animals like cats and dogs as well.
✏️ More details:
1. To transfer DensePose from humans to animals we need a reference 3D model of an animal. Let's suppose we got an artist-created 3D model of the desired animal. The next step is to establish a dense mapping between the 3D model of animal and 3D model of a human. This is necessary to unify the evaluation protocols between humans and animals and allows to transfer of knowledge and annotations between different species. The matching between 3D models is done by matching semantic descriptors of the vertices on the meshes.
2. Our goal is to develop a DensePose predictor for a new class. Such a predictor must detect the object via a bounding box, segment it from the background, and obtain the Dense-Pose chart and UV-map coordinates for each foreground pixel. To do this we introduce a multi-head R-CNN architecture that combines multiple recognition tasks within a single model.
The first head refines the coordinates of the bounding box. The second head computes a foreground-background segmentation mask in the same way as MaskR-CNN. The third and the final head computes a part segmentation mask I, assigning each pixel to one of the 24-body parts charts, and the UV-map values for each foreground pixel.
3. We have a few existing instance-segmentation and detection annotations for some animals in the COCO dataset. Let's use them! Given a target animal class, let's say chimps. We want to find an optimal support domain: We find such classes from the COCO dataset pretraining on which gives the best detection (or segmentation) performance on the holdout set of chimps.
4. We jointly train DensePose prediction for people and detection, segmentation for other classes in the support domain. The goal is always to only build a model for the final target class — we found that merging classes is an effective way of integrating information. So all support domain categories are merged in one and the training is done in a class-agnostic manner.
5. Now we have our baseline network which knows a lot about humans and a bit about the detection and segmentation of animals. We run this model over ~5Tb of videos from camera traps in the wild and select around 100k video frames with good detections. N
Artsiom Sanakoyeu, Vasil Khalidov, Maureen S. McCarthy, Andrea Vedaldi, Natalia Neverova (Facebook AI Research)
In CVPR 2020.
🌐https://asanakoy.github.io/densepose-evolution/
▶️youtu.be/OU3Ayg_l4QM
📝https://arxiv.org/pdf/2003.00080.pdf
❓ What?
DensePose approach predicts the pose of humans densely and accurately given a large dataset of poses annotated in detail.
We want to extend the same approach to animals but without annotations. Because it's super expensive to collect DensePose annotations for all different classes of animals. So we show that, at least for proximal animal classes such as chimpanzees, it is possible to transfer the knowledge existing in DensePose for humans. We propose to utilize the existing annotations of humans and do self-training on unlabeled images of animals.
In a nutshell, we first pretrain the DensePose on the existing human annotations. Then we predict DensePose on unlabeled images, select the most confident predictions and throw them in the augmented training set for retraining the model. To be able to select point-wise the most confident DensePose predictions we introduce a novel Auto-Calibrated version of DensePose-RCNN which can estimate the uncertainty of its predictions for every pixel.
We tested several techniques for sampling pseudo-labels and concluded that sampling based on confidence estimates from fine-grained tasks (24-Body-part estimation and DensePose UV-maps) results in the best performance.
We introduced a novel DensePose-Chimps dataset with Dense Pose ground truth annotations for chimps and tested our models on it, obtaining significant performance improvement over the baseline.
In this paper, we conducted thorough experiments only for chimps, but the method can be extended to other animals like cats and dogs as well.
✏️ More details:
1. To transfer DensePose from humans to animals we need a reference 3D model of an animal. Let's suppose we got an artist-created 3D model of the desired animal. The next step is to establish a dense mapping between the 3D model of animal and 3D model of a human. This is necessary to unify the evaluation protocols between humans and animals and allows to transfer of knowledge and annotations between different species. The matching between 3D models is done by matching semantic descriptors of the vertices on the meshes.
2. Our goal is to develop a DensePose predictor for a new class. Such a predictor must detect the object via a bounding box, segment it from the background, and obtain the Dense-Pose chart and UV-map coordinates for each foreground pixel. To do this we introduce a multi-head R-CNN architecture that combines multiple recognition tasks within a single model.
The first head refines the coordinates of the bounding box. The second head computes a foreground-background segmentation mask in the same way as MaskR-CNN. The third and the final head computes a part segmentation mask I, assigning each pixel to one of the 24-body parts charts, and the UV-map values for each foreground pixel.
3. We have a few existing instance-segmentation and detection annotations for some animals in the COCO dataset. Let's use them! Given a target animal class, let's say chimps. We want to find an optimal support domain: We find such classes from the COCO dataset pretraining on which gives the best detection (or segmentation) performance on the holdout set of chimps.
4. We jointly train DensePose prediction for people and detection, segmentation for other classes in the support domain. The goal is always to only build a model for the final target class — we found that merging classes is an effective way of integrating information. So all support domain categories are merged in one and the training is done in a class-agnostic manner.
5. Now we have our baseline network which knows a lot about humans and a bit about the detection and segmentation of animals. We run this model over ~5Tb of videos from camera traps in the wild and select around 100k video frames with good detections. N
ow we aim to utilize DensePose pseudo-labels obtained on the unlabeled frames for retraining the network.
6. To be able to select good point-wise predictions our model has to know how to estimate it's uncertainty for every pixel and for every task which we are solving. We introduce a novel Auto-Calibrated version of DensePose-RCNN which can estimate the uncertainty of its predictions for every pixel and every task. We propose to model: (a) Classification uncertainty (for object classification and segmentation) using temperature scaling in the softmax layer and; (b) regression uncertainty (for bounding box proposals and DensePose UV-maps) by prediction of a Gaussian distribution instead of a single target value. The higher the predicted variance the higher the uncertainty.
7. Now given pixel-wise uncertainties we can sample for the second round of training only those foreground points from the selected 100k points which have the highest confidence. We have experimented with different sampling strategies and show that sampling based on the confidences from fine-grained tasks (24-way body part segmentation, UV-maps) results in the bests performance.
8. The network retrained on the augmented data (existing human annotations + pseudo-labeled animals) show a significant performance boost on the hold out manually annotated DensePose-Chimps dataset.
The video demonstration of the self-trained model: youtu.be/OU3Ayg_l4QM
9. We also show that the proposed Auto-Calibrated RCNN improves over the baseline even without self-training on standard DensePose-Human, detection and segmentation tasks. This is due to the higher robustness of the proposed model to unseen data distributions at test time.
✔️Conclusion:
- Studied the problem of extending dense body pose recognition to animal species and suggested that doing this at scale requires learning from unlabelled data;
- demonstrated that existing detection, segmentation, and dense pose labeling models can transfer very well to a proximal animal class such as chimpanzee despite significant inter-class differences;
- introduced Auto-Calibrated DensePose-RCNN which can estimate the uncertainty of its predictions;
- introduced novel DensePose-Chips dataset for benchmarking dense pose prediction for Chimpanzees;
- showed that substantial improvements can be obtained by carefully selecting which categories to use to pre-train the model, by using a class-agnostic architecture to integrate different sources of information;
- and by modeling labeling uncertainty to grade pseudo-labels for self-training;
- achieved excellent performance without using a single labeled image of the target class for training.
6. To be able to select good point-wise predictions our model has to know how to estimate it's uncertainty for every pixel and for every task which we are solving. We introduce a novel Auto-Calibrated version of DensePose-RCNN which can estimate the uncertainty of its predictions for every pixel and every task. We propose to model: (a) Classification uncertainty (for object classification and segmentation) using temperature scaling in the softmax layer and; (b) regression uncertainty (for bounding box proposals and DensePose UV-maps) by prediction of a Gaussian distribution instead of a single target value. The higher the predicted variance the higher the uncertainty.
7. Now given pixel-wise uncertainties we can sample for the second round of training only those foreground points from the selected 100k points which have the highest confidence. We have experimented with different sampling strategies and show that sampling based on the confidences from fine-grained tasks (24-way body part segmentation, UV-maps) results in the bests performance.
8. The network retrained on the augmented data (existing human annotations + pseudo-labeled animals) show a significant performance boost on the hold out manually annotated DensePose-Chimps dataset.
The video demonstration of the self-trained model: youtu.be/OU3Ayg_l4QM
9. We also show that the proposed Auto-Calibrated RCNN improves over the baseline even without self-training on standard DensePose-Human, detection and segmentation tasks. This is due to the higher robustness of the proposed model to unseen data distributions at test time.
✔️Conclusion:
- Studied the problem of extending dense body pose recognition to animal species and suggested that doing this at scale requires learning from unlabelled data;
- demonstrated that existing detection, segmentation, and dense pose labeling models can transfer very well to a proximal animal class such as chimpanzee despite significant inter-class differences;
- introduced Auto-Calibrated DensePose-RCNN which can estimate the uncertainty of its predictions;
- introduced novel DensePose-Chips dataset for benchmarking dense pose prediction for Chimpanzees;
- showed that substantial improvements can be obtained by carefully selecting which categories to use to pre-train the model, by using a class-agnostic architecture to integrate different sources of information;
- and by modeling labeling uncertainty to grade pseudo-labels for self-training;
- achieved excellent performance without using a single labeled image of the target class for training.
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