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Transformers in Vision: From Zero to Hero
- 1. Transformers In Vision From Zero to Hero! Davide Coccomini & Nicola Messina Davide Coccomini Nicola Messina PhD Candidate Italian National Research Council PhD Student Italian National Research Council Reach me on … Reach me on …
- 2. What do you think when you hear the word «Transformer»? Davide Coccomini & Nicola Messina | AICamp 2021
- 4. The Transformer «today» Input Output Multi-Head Attention Feed Forward Feed Forward Add & Norm Add & Norm Add & Norm Add & Norm Multi-Head Attention Multi-Head Attention + + Salta (90%) | Odia (9%) | Perchè (1%) The cat jumps the wall Il gatto Positional Encoding Positional Encoding V K Q Nx Mx Davide Coccomini & Nicola Messina | AICamp 2021 V K Q V K Q Encoder Decoder Add & Norm Linear + Softmax Memory
- 5. Outline Some history: from RNNs to Transformers Transformers’ attention and self-attention mechanisms The power of the Transformer Encoder From text to images: Vision Transformers Transformers: The beginnings From images to videos The scale and data problem Convolutional Neural Networks and Vision Transformers Some interesting real-world applications Transformers in Vision
- 6. Videos Images Text History Introduced transformers in NLP 2017 Vision Transformers 2020 2021 Transformers for video understanding Now Computer Vision Revolution! Transformers Davide Coccomini & Nicola Messina | AICamp 2021
- 7. A step back: Recurrent Networks (RNNs) E The cat jumps the wall h0 hstart E h1 E h2 E h3 E h4 D h5 D h6 D h7 D h8 D Il gatto salta il h9 D <end> Davide Coccomini & Nicola Messina | AICamp 2021 muro Encoder Final sentence embedding Decoder <s>
- 8. Problems 1. We forget tokens too far in the past 2. We need to wait the previous token to compute the next hidden-state E The cat jumps the wall h0 hstart E h1 E h2 E h3 E h4 D h5 D h6 D h7 D h8 D Il gatto salta il muro h9 D <end> <s> Davide Coccomini & Nicola Messina | AICamp 2021
- 9. Solving problem 1 "We forget tokens too far in the past" E The cat jumps the wall h0 hstar t E h1 E h2 E h3 E h4 D D D Il gatto salta + + + context = Attention Solution Add an attention mechanism + h5 h6 <s>
- 10. Solving problem 2 "We need to wait the previous token to compute the next hidden-state" 2017 paper "Attention Is All You Need" Solution Throw away recurrent connections E The cat jumps the wall h0 hstar t E h1 E h2 E h3 E h4 D D D Il gatto salta + + + context = Attention + h5 h6 <s> Davide Coccomini & Nicola Messina | AICamp 2021
- 11. Full Transformer Architecture Input Output Multi-Head Attention Feed Forward Feed Forward Add & Norm Add & Norm Add & Norm Add & Norm Multi-Head Attention Multi-Head Attention + + “Salta” (90%) | “Odia” (9%) | “Perchè” (1%) “The cat jumps the wall” “Il gatto” Positional Encoding Positional Encoding V K Q Nx Mx Davide Coccomini & Nicola Messina | AICamp 2021 V K Q V K Q Encoder Decoder Add & Norm Linear + Softmax Memory
- 12. Transformer's Attention Mechanism Target tokens “from the point of view” of the source sequence Queries Target Sequence Source Sequence FFN FFN FFN FFN Keys & Values FFN FFN ∙ ∙ ∙ ∙ Norm & Softmax Dot product Il gatto salta The cat jumps the … … FFN
- 13. Key Value “A4” “N9” “O7” “A4” “N2” Transformer's Attention Mechanism From a different perspective Query “N5” Weighted average “gatto” token, built by aggregating value vectors in the source dictionary Lookup Table Target Sequence Source Sequence Il gatto salta The cat jumps the … wall Soft-matching Davide Coccomini & Nicola Messina | AICamp 2021
- 14. Attention and Self-Attention Self-Attention • Source = Target • Key, Queries, Values obtained from the same sentence • Captures intra-sequence dependencies Attention • Source ≠ Target • Queries from Source • Key, Values from Target • Captures inter-sequence dependencies I gave my dog Charlie some food Ho dato da mangiare al mio cane Charlie I gave my dog Charlie some food To whom? What? Who? Multi-Head Attention V K Q Multi-Head Attention V K Q Target Source Davide Coccomini & Nicola Messina | AICamp 2021
- 15. LINEAR LINEAR LINEAR LINEAR LINEAR LINEAR LINEAR LINEAR LINEAR DOT NORMALIZE MATMUL CONCAT + DENSE VALUES KEYS QUERIES Multi-Head Self-Attention Multiple instantiations of the attention mechanism h h h Davide Coccomini & Nicola Messina | AICamp 2021 The cat is running h slices
- 16. Full Transformer Architecture Input Output Feed Forward Feed Forward Add & Norm Add & Norm Add & Norm Add & Norm Multi-Head Attention Multi-Head Attention + + Salta (90%) | Odia (9%) | Perchè (1%) The cat jumps the wall Il gatto Positional Encoding Positional Encoding V K Q Nx Mx Davide Coccomini & Nicola Messina | AICamp 2021 V K Q V K Q Encoder Decoder Add & Norm Linear + Softmax Memory Key Value “A4” “N9” “O7” “A4” “N2” Lookup Table (source sequence) Multi-Head Self Attention Multi-Head Attention
- 17. Is there any problem with Transformers? Attention calculation is O(n2) Self-Attention I gave my dog Charlie some food I gave my dog Charlie some food I gave my dog Charlie some food . . . . . . . . . . Davide Coccomini & Nicola Messina | AICamp 2021
- 18. I gave my dog Charlie some food I gave my dog Charlie some food Attention calculation is O(n2) Self-Attention Davide Coccomini & Nicola Messina | AICamp 2021
- 19. The Power of the Transformer Encoder • Many achievements using only the Encoder • BERT (Devlin et al., 2018) Next Sentence Prediction {0, 1} Transformer Encoder (N layers) I gave my dog Charlie some food <CLS> <SEP> He ate it Positional Encoding Embedding Layer Masked Language Modelling «ate» Memory
- 20. Transformers in Computer Vision Can we use the self-attention mechanism in images? Davide Coccomini & Nicola Messina | AICamp 2021
- 21. Transformers in Computer Vision 256px 256px 3906250000 calculations Impossible! 62500 pixels • The transformer works with a set of tokens • What are tokens in images? Davide Coccomini & Nicola Messina | AICamp 2021
- 22. • Tokens as the features from an object detector Transformers in Computer Vision Tokens! ROI Pooling ROI Pooling ROI Pooling Davide Coccomini & Nicola Messina | AICamp 2021
- 23. “An image is worth 16x16 words” Image to Patches Tokens! Linear Projection 256px 256px 16px 16px Vision Transformers (ViTs) Davide Coccomini & Nicola Messina | AICamp 2021 “An image is worth 16x16 words” | Dosovitskiy et al., 2020
- 24. Vision Transformers (ViTs) 0 * 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 MLP Head CLASS Linear Projection of Flattened Patches Transformer Encoder Davide Coccomini & Nicola Messina | AICamp 2021
- 25. Image Classification on ImageNet Davide Coccomini & Nicola Messina | AICamp 2021
- 26. What about video? Davide Coccomini & Nicola Messina | AICamp 2021
- 27. TimeSformers Combine space and time attention with Divided Space-Time Attention! frame t - δ frame t frame t + δ Space Time Time Davide Coccomini & Nicola Messina | AICamp 2021 Is Space-Time Attention All You Need for Video Understanding? | Gedas Bertasius et al.
- 28. TimeSformers Up to several minutes of analysis! Davide Coccomini & Nicola Messina | AICamp 2021
- 29. Wait… Can I use different types of attention???
- 31. Transformers use a lot of memory! Attention Feed Forward Feed Forward . . . . 2 GB 2 GB 2 GB Davide Coccomini & Nicola Messina | AICamp 2021 USED MEMORY 2 GB 4 GB A LOT!
- 32. Efficient Transformers Attention + FeedForward + - - Attention FeedForward Davide Coccomini & Nicola Messina | AICamp 2021 A new efficient Transformer variant | Lukasz Kaiser USED MEMORY 2 GB 4 GB Rev Attention!
- 33. Patch Partition Davide Coccomini & Nicola Messina | AICamp 2021 Linear Embedding x2 Stage 1 Swin Transformer Block Patch Merging Swin Transformer Block x2 Stage 2 Patch Merging Swin Transformer Block x6 Stage 3 Patch Merging Swin Transformer Block x2 Stage 4 𝑯 × 𝑾 × 𝟑 𝑯 𝟒 × 𝑾 𝟒 × 𝟒𝟖 𝑯 𝟒 × 𝑾 𝟒 × 𝑪 𝑯 𝟖 × 𝑾 𝟖 × 𝟐𝑪 𝑯 𝟏𝟔 × 𝑾 𝟏𝟔 × 𝟒𝑪 𝑯 𝟑𝟐 × 𝑾 𝟑𝟐 × 𝟖𝑪 Swin Transformers Swin Transformer: Hierarchical Vision Transformer using Shifted Windows | Ze Liu et al.
- 34. 16x 4x 8x 16x Swin Transformers Swin Transformer Vision Transformer 16x 16x Davide Coccomini & Nicola Messina | AICamp 2021 Shifted Window based Self-Attention
- 35. Self-Attention Layer l Self-Attention Layer l+1 Davide Coccomini & Nicola Messina | AICamp 2021 Swin Transformers
- 36. Source: Swin Transformer Object Detection Demo – By DeepReader https://www.youtube.com/watch?v=FQVS_0Bja6o
- 37. Can we do without Self-Attention?
- 38. It is «just» a transformation! What essentially is the attention mechanism? Davide Coccomini & Nicola Messina | AICamp 2021 Attention Mechanism
- 39. Input Attention Calculation Embeddings Feed Forward Add & Normalize Dense Output Prediction Add & Normalize Embeddings Fourier Network Fourier Transformation Davide Coccomini & Nicola Messina | AICamp 2021
- 40. Why Fourier? It’s just a transformation! Image from mriquestion.com Fourier Transform Davide Coccomini & Nicola Messina | AICamp 2021
- 41. Fourier Transform Fourier Transform Transforming over the hidden domain Transforming over the sequence domain Fourier Network What does it transform? Input Vectors Davide Coccomini & Nicola Messina | AICamp 2021 FNet: Mixing Tokens with Fourier Transforms | James Lee-Thorp et al.
- 42. MLP Mixer 1 2 3 4 5 6 7 8 9 Per-patch Fully Connected N x (Mixer Layer) Davide Coccomini & Nicola Messina | AICamp 2021 Global Average Pooling Fully-Connected CLASS MLP-Mixer: An all-MLP Architecture for Vision | Ilya Tolstikhin et al.
- 43. Layer Norm MLP MLP MLP MLP Layer Norm MLP MLP MLP MLP Mixer Layer Davide Coccomini & Nicola Messina | AICamp 2021 Transforming over the sequence domain Transforming over the hidden domain
- 45. Convolutional Neural Network Vision Transformer Not Improving Anymore Still Improving Learned Knowledge What happens during training? Davide Coccomini & Nicola Messina | AICamp 2021
- 46. Why are they different? Able to find long-term dependencies Learns inductive biases Need very large dataset for training Lack of global understanding Locality Sensitive Translation Invariant Davide Coccomini & Nicola Messina | AICamp 2021 Convolutional Neural Network Vision Transformers
- 47. A different point of view ViTs are both local and global! The ViT learns only global information with low amount of data 0.7 0.01 Davide Coccomini & Nicola Messina | AICamp 2021 Heads focus on farther patches
- 48. A different point of view ViTs are both local and global! The ViT learns also local information with more data Davide Coccomini & Nicola Messina | AICamp 2021 0.7 0.01 Higher layers heads still focus on farther patches 0.01 0.4 0.3 Lower layers heads focus on both farther and closer patches 0.6 0.06
- 49. A different point of view They learn different representations! Similar representations through the layers Different representations through the layers Davide Coccomini & Nicola Messina | AICamp 2021 Do Vision Transformers See Like Convolutional Neural Networks? | Maithra Raghu et al.
- 50. A different point of view Vision Transformers are very robust! Davide Coccomini & Nicola Messina | AICamp 2021 Occlusion Distribution Shift Adversarial Perturbation Permutation Intriguing Properties of Vision Transformers | Muzammal Naseer et al.
- 51. Can we obtain the best of the two architectures?
- 53. 28 x 28 24 x 24 8 x 8 12 x 12 4 x 4 Davide Coccomini & Nicola Messina | AICamp 2021 What happens in CNNs? Hey! They are patches!
- 54. Convolutional Neural Network Transformer Encoder CLASS MLP Davide Coccomini & Nicola Messina | AICamp 2021 Hybrids A possible configuration! Combining EfficientNet and Vision Transformers for Video Deepfake Detection | Coccomini et al.
- 56. Recap Use a pure Vision Transformer Improve the internal attention mechanism Use an alternative transformation Combine CNNs with Vision Transformers How can we use Transformers in Vision?
- 57. ViT-G/14 CoAtNet-7 ViT-MoE-15B 1° 2° 3° 90.45% top-1 accuracy Vision Transformer Pretrained on JFT 1843M parameters 90.88% top-1 accuracy Conv + Vision Transformer Pretrained on JFT 2440M parameters 90.35% top-1 accuracy Vision Transformer Pretrained on JFT 14700M parameters ImageNet Ranking
- 58. APPLICATIONS!!!
- 59. Video Supervised Learning DINO Source: Advancing the state of the art in computer vision with self-supervised Transformers and 10x more efficient training – Facebook AI
- 60. Source: Advancing the state of the art in computer vision with self-supervised Transformers and 10x more efficient training – Facebook AI
- 61. Source: Paint Transformer: Feed Forward Neural Painting with Stroke Prediction
- 62. Source: Image GPT – By OpenAI
- 64. Thank You for the Attention! Any question?
Notes de l'éditeur
- - They plot CKA similarities between all pairs of layers across different model architectures. We observe that ViTs have relatively uniform layer similarity structure, with a clear grid-like pattern and large similarity between lower and higher layers. By contrast, the ResNet models show clear stages in similarity structure, with smaller similarity scores between lower and higher layers.