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diff --git a/src/text_recognizer/networks/vqvae/vector_quantizer.py b/src/text_recognizer/networks/vqvae/vector_quantizer.py
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-"""Implementation of a Vector Quantized Variational AutoEncoder.
-
-Reference:
-https://github.com/AntixK/PyTorch-VAE/blob/master/models/vq_vae.py
-
-"""
-
-from einops import rearrange
-import torch
-from torch import nn
-from torch import Tensor
-from torch.nn import functional as F
-
-
-class VectorQuantizer(nn.Module):
- """The codebook that contains quantized vectors."""
-
- def __init__(
- self, num_embeddings: int, embedding_dim: int, beta: float = 0.25
- ) -> None:
- super().__init__()
- self.K = num_embeddings
- self.D = embedding_dim
- self.beta = beta
-
- self.embedding = nn.Embedding(self.K, self.D)
-
- # Initialize the codebook.
- nn.init.uniform_(self.embedding.weight, -1 / self.K, 1 / self.K)
-
- def discretization_bottleneck(self, latent: Tensor) -> Tensor:
- """Computes the code nearest to the latent representation.
-
- First we compute the posterior categorical distribution, and then map
- the latent representation to the nearest element of the embedding.
-
- Args:
- latent (Tensor): The latent representation.
-
- Shape:
- - latent :math:`(B x H x W, D)`
-
- Returns:
- Tensor: The quantized embedding vector.
-
- """
- # Store latent shape.
- b, h, w, d = latent.shape
-
- # Flatten the latent representation to 2D.
- latent = rearrange(latent, "b h w d -> (b h w) d")
-
- # Compute the L2 distance between the latents and the embeddings.
- l2_distance = (
- torch.sum(latent ** 2, dim=1, keepdim=True)
- + torch.sum(self.embedding.weight ** 2, dim=1)
- - 2 * latent @ self.embedding.weight.t()
- ) # [BHW x K]
-
- # Find the embedding k nearest to each latent.
- encoding_indices = torch.argmin(l2_distance, dim=1).unsqueeze(1) # [BHW, 1]
-
- # Convert to one-hot encodings, aka discrete bottleneck.
- one_hot_encoding = torch.zeros(
- encoding_indices.shape[0], self.K, device=latent.device
- )
- one_hot_encoding.scatter_(1, encoding_indices, 1) # [BHW x K]
-
- # Embedding quantization.
- quantized_latent = one_hot_encoding @ self.embedding.weight # [BHW, D]
- quantized_latent = rearrange(
- quantized_latent, "(b h w) d -> b h w d", b=b, h=h, w=w
- )
-
- return quantized_latent
-
- def vq_loss(self, latent: Tensor, quantized_latent: Tensor) -> Tensor:
- """Vector Quantization loss.
-
- The vector quantization algorithm allows us to create a codebook. The VQ
- algorithm works by moving the embedding vectors towards the encoder outputs.
-
- The embedding loss moves the embedding vector towards the encoder outputs. The
- .detach() works as the stop gradient (sg) described in the paper.
-
- Because the volume of the embedding space is dimensionless, it can arbitarily
- grow if the embeddings are not trained as fast as the encoder parameters. To
- mitigate this, a commitment loss is added in the second term which makes sure
- that the encoder commits to an embedding and that its output does not grow.
-
- Args:
- latent (Tensor): The encoder output.
- quantized_latent (Tensor): The quantized latent.
-
- Returns:
- Tensor: The combinded VQ loss.
-
- """
- embedding_loss = F.mse_loss(quantized_latent, latent.detach())
- commitment_loss = F.mse_loss(quantized_latent.detach(), latent)
- return embedding_loss + self.beta * commitment_loss
-
- def forward(self, latent: Tensor) -> Tensor:
- """Forward pass that returns the quantized vector and the vq loss."""
- # Rearrange latent representation s.t. the hidden dim is at the end.
- latent = rearrange(latent, "b d h w -> b h w d")
-
- # Maps latent to the nearest code in the codebook.
- quantized_latent = self.discretization_bottleneck(latent)
-
- loss = self.vq_loss(latent, quantized_latent)
-
- # Add residue to the quantized latent.
- quantized_latent = latent + (quantized_latent - latent).detach()
-
- # Rearrange the quantized shape back to the original shape.
- quantized_latent = rearrange(quantized_latent, "b h w d -> b d h w")
-
- return quantized_latent, loss