Online video object segmentation via convolutional trident network
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발표자: 장원동 (고려대 박사과정) 발표일: 2017.8. 개요: A semi-supervised online video object segmentation algorithm, which accepts user annotations about a target object at the first frame, will be presented. It propagates the segmentation labels at the previous frame to the current frame using optical flow vectors. However, the propagation is error-prone. Therefore, I’ve developed the convolutional trident network, which has three decoding branches: separative, definite foreground, and definite background decoders. Then, the algorithm performs Markov random field optimization based on outputs of the three decoders. These process is sequentially carried out from the second to the last frames to extract a segment track of the target object. Experimental results will demonstrate that this algorithm significantly outperforms the state-of-the-art conventional algorithms on the DAVIS benchmark dataset.
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Online video object segmentation via convolutional trident network
- 1. Online Video Object Segmentation via Convolutional Trident Network Seminar at Naver Won-Dong Jang Korea University 2017-08-22
- 2. Introduction & related works
- 3. Video object segmentation • Clustering pixels in videos into objects or background • Unsupervised • Supervised • Semi-supervised Segment track
- 4. Video object segmentation • Unsupervised video object segmentation • Discover and segment a primary object in a video • Without user annotations Input videos Ground-truth segmentation labels
- 5. Video object segmentation • Unsupervised video object segmentation • Saliency detection-based approach • Visual saliency • Motion saliency Examples of saliency detection
- 6. Video object segmentation • Supervised video object segmentation • User can annotate mislabeled pixels in any frames • Interaction between an algorithm and a user Annotation at the first frame Segmentation results after adding the annotation Segmentation results Additional user annotation
- 7. Video object segmentation • Semi-supervised video object segmentation • Discover and segment a primary object in a video • With user annotations in the first frame Annotated target object in the first frame Segmentation results
- 8. Related works • Object proposal-based algorithm • Generate object proposals in each frame • Select object proposals that are similar to the target object [2015][ICCV][Perazzi] Fully Connected Object Proposals for Video Segmentation Generated object proposals Segment track
- 9. Related works • Superpixel-based algorithm • Over-segment each frame into superpixels • Trace the target object based on the inter-frame matching [2015][CVPR][Wen] Joint Online Tracking and Segmentation Inter-frame matching Segment track
- 11. In this presentation • A semi-supervised online segmentation algorithm • Online method • Offline techniques require a huge memory space for a long video • Deep learning-based approach • Connection between a convolutional neural network and an MRF optimization strategy • Remarkable performance on the DAVIS benchmark dataset
- 12. Overview • Framework • Inter-frame propagation • Inference via convolutional trident network (CTN) • Yields three tailored probability maps for the MRF optimization • MRF optimization
- 13. Inter-frame propagation • Propagation from the previous frame • To roughly locate the target object in the current frame • Using backward optical flow • From 𝑡 to 𝑡 − 1 Segmentation label map for frame 𝑡 − 1 Backward motion (optical flow) Propagation map for frame 𝑡
- 14. Convolutional trident network • Infer segmentation information • The propagation map may be inaccurate • The inferred information is effectively used to solve a binary labeling problem
- 15. Network architecture • Encoder-decoder architecture • Single encoder • VGG encoder • Three decoders • Separative decoder • Definite foreground decoder • Definite background decoder
- 16. Network architecture • Encoder-decoder architecture • Single encoder • VGG encoder • Three decoders • Separative decoder • Definite foreground decoder • Definite background decoder
- 17. Network architecture • VGG encoder • Trained for image classification • Using ImageNet dataset 22K categories 14M images
- 18. Network architecture • VGG encoder • Trained for image classification • Using ImageNet dataset Convolutional layers Fully connected layers Fox Cat Lion Dog Zebra Umbrella Tank Lamp Desk Orange Kite …
- 19. Network architecture • Separative decoder (SD) • Separate a target object from the background • Using a down-sampled foreground propagation patch Conv1_1 Conv1_2 Pooling Conv2_1 Conv2_2 Pooling Conv3_1 Conv3_2 Conv3_3 Pooling Conv4_1 Conv4_2 Conv4_3 Pooling Conv5_1 Conv5_2 Conv5_3 SD-Dec2 SD-Dec3 SD-Dec4 SD-Dec5 SD-Pred SD-Dec1 Unpooling Unpooling Unpooling Unpooling Skip connections Image patch Separative probability patch Foreground propagation patch
- 20. Network architecture • Definite foreground and background decoders • Definite pixels indicate locations that should be labeled as the foreground or the background indubitably • Fixing labels in definite pixels improves labeling accuracies • Inspired by the image matting problem Input image Tri-map Matting result
- 21. Network architecture • Definite foreground decoder (DFD) • Identifies definite foreground pixels Conv1_1 Conv1_2 Pooling Conv2_1 Conv2_2 Pooling Conv3_1 Conv3_2 Conv3_3 Pooling Conv4_1 Conv4_2 Conv4_3 Pooling Conv5_1 Conv5_2 Conv5_3 DFD-Dec2 DFD-Dec3 DFD-Dec4 DFD-Dec5 DFD-Pred DFD-Dec1 Unpooling Unpooling Unpooling Unpooling Image patch Definite foreground probability patch Foreground propagation patch
- 22. Network architecture • Definite background decoder (DBD) • Finds definite background pixels Conv1_1 Conv1_2 Pooling Conv2_1 Conv2_2 Pooling Conv3_1 Conv3_2 Conv3_3 Pooling Conv4_1 Conv4_2 Conv4_3 Pooling Conv5_1 Conv5_2 Conv5_3 DBD-Dec2 DBD-Dec3 DBD-Dec4 DBD-Dec5 DBD-Pred DBD-Dec1 Unpooling Unpooling Unpooling Unpooling Image patch Definite background probability patch Background propagation patch
- 23. Network architecture • Implementation issues in decoders • Prediction layer • Sigmoid layer is used to yield normalized outputs within [0, 1] • Rectified linear unit (ReLU) + Batch normalization • Kernel size • 3 ×3 kernels are used in the prediction layers • 5 × 5 kernels are used in the other convolution layers
- 24. Training phase • Lack of video object segmentation dataset • There are several datasets for video object segmentation • However, each of them consists of a small number of videos from 12 to 59 • Instead, • We use the PASCAL VOC 2012 dataset • Object segmentation • 26,844 object masks • 11,355 images
- 25. Training phase • Preprocessing of training data • Ground-truth masks for the DFD and DBD are not available • Hence, we generate them through simple image processing
- 26. Training phase • Preprocessing of training data • Degrade the objet mask to imitate propagation errors • By performing suppression and noise addition • Synthesize the ground-truth masks for the DFD and DBD • By applying erosion and dilation
- 27. Training phase • Implementation issues • Caffe library • Cross-entropy losses − 1 𝑛 𝑛=1 𝑁 𝑝 𝑛 log Ƹ𝑝 𝑛 + 1 − 𝑝 𝑛 log 1 − Ƹ𝑝 𝑛 • Minibatch • with eight training data • Learning rate • 1e-3 for the first 55 epochs • 1e-4 for the next 35 epochs • Stochastic gradient descent
- 28. Inference phase • Set input data • By cropping the frame and propagation map • CTN outputs three probability patches • Separative probability map 𝑅S • Definite foreground probability map 𝑅F • Definite background probability map 𝑅B Frame 𝑡 Segmentation label at frame 𝑡 − 1 Optical flow Inter-frame propagationInput at frame 𝑡 Propagation map at frame 𝑡 Inference via convolutional encoder-decoder network Encoder Background propagation patch Foreground propagation patch Image patch Definite background decoder Definite foreground decoder Separative decoder Definite background probability patch Definite foreground probability patch Separative probability patch
- 29. Inference phase • Classification • Separative probability map 𝑅S • If 𝑅S(𝐩) > 𝜃sep, pixel 𝐩 is classified as the foreground • ℒ be the coordinate set for such foreground pixels • Definite foreground probability map 𝑅F • If 𝑅F(𝐩) > 𝜃def, pixel 𝐩 is classified as the definite foreground • ℱ denotes the set of the definite foreground pixels • Definite background probability map 𝑅B • If 𝑅B(𝐩) > 𝜃def, pixel 𝐩 is classified as the definite background • ℬ indicates the set of the definite background pixels
- 30. MRF optimization • Solve two-class MRF optimization problem • To improve the segmentation quality further • Define a graph 𝐺 = (𝑁, 𝐸) • Nodes are pixels in the current frame • Each node is connected to its four neighbors by edges
- 31. MRF optimization • MRF energy function ℰ 𝑆 = 𝐩∈𝑁 𝒟 𝐩, 𝑆 + 𝛾 × 𝐩,𝐪 ∈𝐸 𝒵 𝐩, 𝐪, 𝑆 Definite background probability patch Definite foreground probability patch Image patch Separative probability patch Unary cost 𝒟 - Returns extremely high costs on DF and DB pixels when they have background and foreground labels Pairwise cost 𝒵 - Encourage neighboring pixels to have the same label
- 32. MRF optimization • Unary cost computation • Build the RGB color Gaussian mixture models (GMMs) of the foreground and the background, respectively • 𝐾 = 10 for both GMMs • Use pixels in ℒ to construct the foreground GMMs • Use pixels in ℒ 𝑐 to construct the background GMMs • Gaussian cost 𝜓 𝐩, 𝑠 = min 𝑘 − log 𝑓 𝐩; ℳ𝑠,𝑘 • Unary cost 𝒟 𝐩, 𝑆 = ൞ ∞ if 𝑝 ∈ ℱ and 𝑆 𝑝 = 0 ∞ if 𝑝 ∈ ℱ and 𝑆 𝑝 = 0 𝜓 𝐩, 𝑆(𝐩) otherwise
- 33. MRF optimization • Pairwise cost computation • Pairwise cost 𝒵 𝐩, 𝐪, 𝑆 = ቊ exp −𝑑 𝐩, 𝐪 if 𝑆 𝐩 ≠ 𝑆 𝐪 0 otherwise • Graph-cut optimization ℰ 𝑆 = 𝐩∈𝑁 𝒟 𝐩, 𝑆 + 𝛾 × 𝐩,𝐪 ∈𝐸 𝒵 𝐩, 𝐪, 𝑆
- 34. Reappearing object detection • Identification of reappearing parts • A target object may disappear and be occluded by other objects • Use backward-forward motion consistency
- 36. Experimental results • The DAVIS benchmark dataset • 50 videos • 854 × 480 resolution • Number of frames • From 25 to 104 • Difficulties • Fast motion • Occlusion • Object deformation
- 37. Experimental results • Performance measures • Region similarity • Jaccard index • Contour accuracy • F-measure • Statistics • Mean • Recall • Decay
- 38. Experimental results • Performance comparison
- 39. Experimental results • Qualitative results
- 40. Experimental results • The SegTrack dataset • 5 videos • Performance comparison • Jaccard index
- 41. Experimental results • Ablation studies • Effectiveness of each decoder • Efficacy of MRF optimization
- 42. Experimental results • Running time analysis • Prop-Q • Uses the state-of-the-art optical flow technique • Prop-F • Adopts a much faster optical flow technique • Parameter selection
- 43. Conclusions • A semi-supervised online video object segmentation algorithm is introduced in this presentation • Deep learning-based semi-supervised video object segmentation algorithm • Tailored network for MRF optimization • Remarkable performance on the DAVIS dataset • Q&A • Thank you