Transformers and Vision Transformer (ViT)

Transformers are a class of deep learning models that have achieved remarkable success in natural language processing (NLP) tasks. The transformer architecture, introduced in the seminal paper "Attention is All You Need" by Vaswani et al., revolutionized NLP by eliminating the need for recurrent or convolutional layers.

Recently, transformers have also been applied to computer vision tasks, giving rise to the Vision Transformer (ViT) model. ViT extends the transformer architecture to handle image data, allowing it to achieve state-of-the-art performance on various vision tasks.

Key Components of Transformers

Transformers consist of several key components:

Self-Attention Mechanism: This mechanism allows the model to weigh the importance of different parts of the input sequence when making predictions. It computes attention scores between all pairs of positions in the input sequence and uses them to construct context-aware representations.
Multi-Head Attention: To capture different types of information, transformers employ multiple attention heads, each responsible for learning different attention patterns. These heads operate in parallel, allowing the model to attend to different parts of the input simultaneously.
Positional Encoding: Since transformers don't have recurrent layers, they need a way to incorporate positional information into the input. Positional encoding vectors are added to the input embeddings, providing the model with positional context.
Feed-Forward Neural Networks: Transformers utilize fully connected feed-forward networks to process the outputs of the attention mechanism and produce the final representations.
Residual Connections and Layer Normalization: Residual connections enable the gradient flow during training, preventing the vanishing gradient problem. Layer normalization helps stabilize the training process by normalizing the inputs of each layer.

Vision Transformer (ViT)

The Vision Transformer (ViT) extends the transformer architecture to handle image data. It treats the image as a sequence of patches and reshapes them into a linear sequence, similar to text.

ViT consists of the following steps:

Patch Embedding: The input image is divided into patches, which are then linearly projected into embedding vectors. These patch embeddings serve as the initial input to the transformer.
Positional Encoding: Similar to NLP transformers, ViT incorporates positional encoding to introduce spatial information into the input sequence.
Transformer Encoder: The patch embeddings, along with the positional encoding, are passed through multiple transformer encoder layers. Each encoder layer consists of self-attention mechanisms and feed-forward neural networks.
Classification Head: After the transformer encoder, a classification head is added on top of the final embeddings. It can be a simple linear layer followed by softmax to predict class probabilities.

Training ViT

To train a ViT model, a large labeled dataset is required. The model is trained using a supervised learning approach, where the model learns to minimize a loss function such as cross-entropy loss between its predictions and the ground truth labels.

The training process involves initializing the model with random weights and iteratively updating the weights using backpropagation and gradient descent optimization.

Conclusion

Transformers, including the Vision Transformer (ViT), have revolutionized both natural language processing and computer vision. Their ability to capture long-range dependencies and process input sequences in parallel has made them highly effective for a wide range of tasks. With ongoing research, transformers continue to push the boundaries of AI in various domains.