New VQVAE

8 files changed, 319 insertions, 308 deletions

diff --git a/text_recognizer/models/vqvae.py b/text_recognizer/models/vqvae.py
index 22da018..5890fd9 100644
--- a/text_recognizer/models/vqvae.py
+++ b/text_recognizer/models/vqvae.py
@@ -14,31 +14,33 @@ from text_recognizer.models.base import BaseLitModel
 class VQVAELitModel(BaseLitModel):
     """A PyTorch Lightning model for transformer networks."""
 
+    latent_loss_weight: float = attr.ib(default=0.25)
+
     def forward(self, data: Tensor) -> Tensor:
         """Forward pass with the transformer network."""
-        return self.network.predict(data)
+        return self.network(data)
 
     def training_step(self, batch: Tuple[Tensor, Tensor], batch_idx: int) -> Tensor:
         """Training step."""
         data, _ = batch
-        reconstructions, vq_loss = self.network(data)
+        reconstructions, vq_loss = self(data)
         loss = self.loss_fn(reconstructions, data)
-        loss += vq_loss
+        loss += self.latent_loss_weight * vq_loss
         self.log("train/loss", loss)
         return loss
 
     def validation_step(self, batch: Tuple[Tensor, Tensor], batch_idx: int) -> None:
         """Validation step."""
         data, _ = batch
-        reconstructions, vq_loss = self.network(data)
+        reconstructions, vq_loss = self(data)
         loss = self.loss_fn(reconstructions, data)
-        loss += vq_loss
+        loss += self.latent_loss_weight * vq_loss
         self.log("val/loss", loss, prog_bar=True)
 
     def test_step(self, batch: Tuple[Tensor, Tensor], batch_idx: int) -> None:
         """Test step."""
         data, _ = batch
-        reconstructions, vq_loss = self.network(data)
+        reconstructions, vq_loss = self(data)
         loss = self.loss_fn(reconstructions, data)
-        loss += vq_loss
+        loss += self.latent_loss_weight * vq_loss
         self.log("test/loss", loss)
diff --git a/text_recognizer/networks/vq_transformer.py b/text_recognizer/networks/vq_transformer.py
new file mode 100644
index 0000000..a972565
--- /dev/null
+++ b/text_recognizer/networks/vq_transformer.py
@@ -0,0 +1,77 @@
+"""Vector quantized encoder, transformer decoder."""
+import math
+from typing import Tuple
+
+from torch import nn, Tensor
+
+from text_recognizer.networks.encoders.efficientnet import EfficientNet
+from text_recognizer.networks.conv_transformer import ConvTransformer
+from text_recognizer.networks.transformer.layers import Decoder
+from text_recognizer.networks.transformer.positional_encodings import (
+    PositionalEncoding,
+    PositionalEncoding2D,
+)
+
+
+class VqTransformer(ConvTransformer):
+    """Convolutional encoder and transformer decoder network."""
+
+    def __init__(
+        self,
+        input_dims: Tuple[int, int, int],
+        hidden_dim: int,
+        dropout_rate: float,
+        num_classes: int,
+        pad_index: Tensor,
+        encoder: EfficientNet,
+        decoder: Decoder,
+    ) -> None:
+        # TODO: Load pretrained vqvae encoder.
+        super().__init__(
+            input_dims=input_dims,
+            hidden_dim=hidden_dim,
+            dropout_rate=dropout_rate,
+            num_classes=num_classes,
+            pad_index=pad_index,
+            encoder=encoder,
+            decoder=decoder,
+        )
+        # Latent projector for down sampling number of filters and 2d
+        # positional encoding.
+        self.latent_encoder = nn.Sequential(
+            nn.Conv2d(
+                in_channels=self.encoder.out_channels,
+                out_channels=self.hidden_dim,
+                kernel_size=1,
+            ),
+            PositionalEncoding2D(
+                hidden_dim=self.hidden_dim,
+                max_h=self.input_dims[1],
+                max_w=self.input_dims[2],
+            ),
+            nn.Flatten(start_dim=2),
+        )
+
+    def encode(self, x: Tensor) -> Tensor:
+        """Encodes an image into a latent feature vector.
+
+        Args:
+            x (Tensor): Image tensor.
+
+        Shape:
+            - x: :math: `(B, C, H, W)`
+            - z: :math: `(B, Sx, E)`
+
+            where Sx is the length of the flattened feature maps projected from
+            the encoder. E latent dimension for each pixel in the projected
+            feature maps.
+
+        Returns:
+            Tensor: A Latent embedding of the image.
+        """
+        z = self.encoder(x)
+        z = self.latent_encoder(z)
+
+        # Permute tensor from [B, E, Ho * Wo] to [B, Sx, E]
+        z = z.permute(0, 2, 1)
+        return z
diff --git a/text_recognizer/networks/vqvae/__init__.py b/text_recognizer/networks/vqvae/__init__.py
index 763953c..7d56bdb 100644
--- a/text_recognizer/networks/vqvae/__init__.py
+++ b/text_recognizer/networks/vqvae/__init__.py
@@ -1,5 +1,2 @@
 """VQ-VAE module."""
-from .decoder import Decoder
-from .encoder import Encoder
-from .vector_quantizer import VectorQuantizer
 from .vqvae import VQVAE
diff --git a/text_recognizer/networks/vqvae/decoder.py b/text_recognizer/networks/vqvae/decoder.py
index 32de912..3f59f0d 100644
--- a/text_recognizer/networks/vqvae/decoder.py
+++ b/text_recognizer/networks/vqvae/decoder.py
@@ -1,133 +1,65 @@
 """CNN decoder for the VQ-VAE."""
-
-from typing import List, Optional, Tuple, Type
-
-import torch
+import attr
 from torch import nn
 from torch import Tensor
 
 from text_recognizer.networks.util import activation_function
-from text_recognizer.networks.vqvae.encoder import _ResidualBlock
+from text_recognizer.networks.vqvae.residual import Residual
 
 
+@attr.s(eq=False)
 class Decoder(nn.Module):
     """A CNN encoder network."""
 
-    def __init__(
-        self,
-        channels: List[int],
-        kernel_sizes: List[int],
-        strides: List[int],
-        num_residual_layers: int,
-        embedding_dim: int,
-        upsampling: Optional[List[List[int]]] = None,
-        activation: str = "leaky_relu",
-        dropout_rate: float = 0.0,
-    ) -> None:
-        super().__init__()
-
-        if dropout_rate:
-            if activation == "selu":
-                dropout = nn.AlphaDropout(p=dropout_rate)
-            else:
-                dropout = nn.Dropout(p=dropout_rate)
-        else:
-            dropout = None
-
-        self.upsampling = upsampling
-
-        self.res_block = nn.ModuleList([])
-        self.upsampling_block = nn.ModuleList([])
-
-        self.embedding_dim = embedding_dim
-        activation = activation_function(activation)
-
-        # Configure encoder.
-        self.decoder = self._build_decoder(
-            channels, kernel_sizes, strides, num_residual_layers, activation, dropout,
-        )
-
-    def _build_decompression_block(
-        self,
-        in_channels: int,
-        channels: int,
-        kernel_sizes: List[int],
-        strides: List[int],
-        activation: Type[nn.Module],
-        dropout: Optional[Type[nn.Module]],
-    ) -> nn.ModuleList:
-        modules = nn.ModuleList([])
-        configuration = zip(channels, kernel_sizes, strides)
-        for i, (out_channels, kernel_size, stride) in enumerate(configuration):
-            modules.append(
-                nn.Sequential(
-                    nn.ConvTranspose2d(
-                        in_channels,
-                        out_channels,
-                        kernel_size,
-                        stride=stride,
-                        padding=1,
-                    ),
-                    activation,
-                )
-            )
-
-            if self.upsampling and i < len(self.upsampling):
-                modules.append(nn.Upsample(size=self.upsampling[i]),)
+    in_channels: int = attr.ib()
+    embedding_dim: int = attr.ib()
+    out_channels: int = attr.ib()
+    res_channels: int = attr.ib()
+    num_residual_layers: int = attr.ib()
+    activation: str = attr.ib()
+    decoder: nn.Sequential = attr.ib(init=False)
 
-            if dropout is not None:
-                modules.append(dropout)
-
-            in_channels = out_channels
-
-        modules.extend(
-            nn.Sequential(
-                nn.ConvTranspose2d(
-                    in_channels, 1, kernel_size=kernel_size, stride=stride, padding=1
-                ),
-                nn.Tanh(),
-            )
-        )
-
-        return modules
-
-    def _build_decoder(
-        self,
-        channels: int,
-        kernel_sizes: List[int],
-        strides: List[int],
-        num_residual_layers: int,
-        activation: Type[nn.Module],
-        dropout: Optional[Type[nn.Module]],
-    ) -> nn.Sequential:
-
-        self.res_block.append(
-            nn.Conv2d(self.embedding_dim, channels[0], kernel_size=1, stride=1,)
-        )
+    def __attrs_pre_init__(self) -> None:
+        super().__init__()
 
-        # Bottleneck module.
-        self.res_block.extend(
-            nn.ModuleList(
-                [
-                    _ResidualBlock(channels[0], channels[0], dropout)
-                    for i in range(num_residual_layers)
-                ]
+    def __attrs_post_init__(self) -> None:
+        """Post init configuration."""
+        self.decoder = self._build_decompression_block()
+
+    def _build_decompression_block(self,) -> nn.Sequential:
+        activation_fn = activation_function(self.activation)
+        blocks = [
+            nn.Conv2d(
+                in_channels=self.in_channels,
+                out_channels=self.embedding_dim,
+                kernel_size=3,
+                padding=1,
             )
-        )
-
-        # Decompression module
-        self.upsampling_block.extend(
-            self._build_decompression_block(
-                channels[0], channels[1:], kernel_sizes, strides, activation, dropout
+        ]
+        for _ in range(self.num_residual_layers):
+            blocks.append(
+                Residual(in_channels=self.embedding_dim, out_channels=self.res_channels)
             )
-        )
-
-        self.res_block = nn.Sequential(*self.res_block)
-        self.upsampling_block = nn.Sequential(*self.upsampling_block)
-
-        return nn.Sequential(self.res_block, self.upsampling_block)
+        blocks.append(activation_fn)
+        blocks += [
+            nn.ConvTranspose2d(
+                in_channels=self.embedding_dim,
+                out_channels=self.embedding_dim // 2,
+                kernel_size=4,
+                stride=2,
+                padding=1,
+            ),
+            activation_fn,
+            nn.ConvTranspose2d(
+                in_channels=self.embedding_dim // 2,
+                out_channels=self.out_channels,
+                kernel_size=4,
+                stride=2,
+                padding=1,
+            ),
+        ]
+        return nn.Sequential(*blocks)
 
     def forward(self, z_q: Tensor) -> Tensor:
         """Reconstruct input from given codes."""
-        x_reconstruction = self.decoder(z_q)
-        return x_reconstruction
+        return self.decoder(z_q)
diff --git a/text_recognizer/networks/vqvae/encoder.py b/text_recognizer/networks/vqvae/encoder.py
index 65801df..e480545 100644
--- a/text_recognizer/networks/vqvae/encoder.py
+++ b/text_recognizer/networks/vqvae/encoder.py
@@ -1,147 +1,75 @@
 """CNN encoder for the VQ-VAE."""
 from typing import Sequence, Optional, Tuple, Type
 
-import torch
+import attr
 from torch import nn
 from torch import Tensor
 
 from text_recognizer.networks.util import activation_function
-from text_recognizer.networks.vqvae.vector_quantizer import VectorQuantizer
-
-
-class _ResidualBlock(nn.Module):
-    def __init__(
-        self, in_channels: int, out_channels: int, dropout: Optional[Type[nn.Module]],
-    ) -> None:
-        super().__init__()
-        self.block = [
-            nn.Conv2d(in_channels, out_channels, kernel_size=3, padding=1, bias=False),
-            nn.ReLU(inplace=True),
-            nn.Conv2d(out_channels, out_channels, kernel_size=1, bias=False),
-        ]
-
-        if dropout is not None:
-            self.block.append(dropout)
-
-        self.block = nn.Sequential(*self.block)
-
-    def forward(self, x: Tensor) -> Tensor:
-        """Apply the residual forward pass."""
-        return x + self.block(x)
+from text_recognizer.networks.vqvae.residual import Residual
 
 
+@attr.s(eq=False)
 class Encoder(nn.Module):
     """A CNN encoder network."""
 
-    def __init__(
-        self,
-        in_channels: int,
-        channels: Sequence[int],
-        kernel_sizes: Sequence[int],
-        strides: Sequence[int],
-        num_residual_layers: int,
-        embedding_dim: int,
-        num_embeddings: int,
-        beta: float = 0.25,
-        activation: str = "leaky_relu",
-        dropout_rate: float = 0.0,
-    ) -> None:
-        super().__init__()
-
-        if dropout_rate:
-            if activation == "selu":
-                dropout = nn.AlphaDropout(p=dropout_rate)
-            else:
-                dropout = nn.Dropout(p=dropout_rate)
-        else:
-            dropout = None
-
-        self.embedding_dim = embedding_dim
-        self.num_embeddings = num_embeddings
-        self.beta = beta
-        activation = activation_function(activation)
-
-        # Configure encoder.
-        self.encoder = self._build_encoder(
-            in_channels,
-            channels,
-            kernel_sizes,
-            strides,
-            num_residual_layers,
-            activation,
-            dropout,
-        )
+    in_channels: int = attr.ib()
+    out_channels: int = attr.ib()
+    res_channels: int = attr.ib()
+    num_residual_layers: int = attr.ib()
+    embedding_dim: int = attr.ib()
+    activation: str = attr.ib()
+    encoder: nn.Sequential = attr.ib(init=False)
 
-        # Configure Vector Quantizer.
-        self.vector_quantizer = VectorQuantizer(
-            self.num_embeddings, self.embedding_dim, self.beta
-        )
-
-    @staticmethod
-    def _build_compression_block(
-        in_channels: int,
-        channels: int,
-        kernel_sizes: Sequence[int],
-        strides: Sequence[int],
-        activation: Type[nn.Module],
-        dropout: Optional[Type[nn.Module]],
-    ) -> nn.ModuleList:
-        modules = nn.ModuleList([])
-        configuration = zip(channels, kernel_sizes, strides)
-        for out_channels, kernel_size, stride in configuration:
-            modules.append(
-                nn.Sequential(
-                    nn.Conv2d(
-                        in_channels, out_channels, kernel_size, stride=stride, padding=1
-                    ),
-                    activation,
-                )
-            )
-
-            if dropout is not None:
-                modules.append(dropout)
-
-            in_channels = out_channels
-
-        return modules
+    def __attrs_pre_init__(self) -> None:
+        super().__init__()
 
-    def _build_encoder(
-        self,
-        in_channels: int,
-        channels: int,
-        kernel_sizes: Sequence[int],
-        strides: Sequence[int],
-        num_residual_layers: int,
-        activation: Type[nn.Module],
-        dropout: Optional[Type[nn.Module]],
-    ) -> nn.Sequential:
-        encoder = nn.ModuleList([])
+    def __attrs_post_init__(self) -> None:
+        """Post init configuration."""
+        self.encoder = self._build_compression_block()
+
+    def _build_compression_block(self) -> nn.Sequential:
+        activation_fn = activation_function(self.activation)
+        block = [
+            nn.Conv2d(
+                in_channels=self.in_channels,
+                out_channels=self.out_channels // 2,
+                kernel_size=4,
+                stride=2,
+                padding=1,
+            ),
+            activation_fn,
+            nn.Conv2d(
+                in_channels=self.out_channels // 2,
+                out_channels=self.out_channels,
+                kernel_size=4,
+                stride=2,
+                padding=1,
+            ),
+            activation_fn,
+            nn.Conv2d(
+                in_channels=self.out_channels,
+                out_channels=self.out_channels,
+                kernel_size=3,
+                padding=1,
+            ),
+        ]
 
-        # compression module
-        encoder.extend(
-            self._build_compression_block(
-                in_channels, channels, kernel_sizes, strides, activation, dropout
+        for _ in range(self.num_residual_layers):
+            block.append(
+                Residual(in_channels=self.out_channels, out_channels=self.res_channels)
             )
-        )
 
-        # Bottleneck module.
-        encoder.extend(
-            nn.ModuleList(
-                [
-                    _ResidualBlock(channels[-1], channels[-1], dropout)
-                    for i in range(num_residual_layers)
-                ]
+        block.append(
+            nn.Conv2d(
+                in_channels=self.out_channels,
+                out_channels=self.embedding_dim,
+                kernel_size=1,
             )
         )
 
-        encoder.append(
-            nn.Conv2d(channels[-1], self.embedding_dim, kernel_size=1, stride=1,)
-        )
-
-        return nn.Sequential(*encoder)
+        return nn.Sequential(*block)
 
     def forward(self, x: Tensor) -> Tuple[Tensor, Tensor]:
         """Encodes input into a discrete representation."""
-        z_e = self.encoder(x)
-        z_q, vq_loss = self.vector_quantizer(z_e)
-        return z_q, vq_loss
+        return self.encoder(x)
diff --git a/text_recognizer/networks/vqvae/vector_quantizer.py b/text_recognizer/networks/vqvae/quantizer.py
index f92c7ee..5e0b602 100644
--- a/text_recognizer/networks/vqvae/vector_quantizer.py
+++ b/text_recognizer/networks/vqvae/quantizer.py
@@ -2,9 +2,7 @@
 
 Reference:
 https://github.com/AntixK/PyTorch-VAE/blob/master/models/vq_vae.py
-
 """
-
 from einops import rearrange
 import torch
 from torch import nn
@@ -12,21 +10,27 @@ from torch import Tensor
 from torch.nn import functional as F
 
 
+class EmbeddingEMA(nn.Module):
+    def __init__(self, num_embeddings: int, embedding_dim: int) -> None:
+        super().__init__()
+        weight = torch.zeros(num_embeddings, embedding_dim)
+        nn.init.kaiming_uniform_(weight, nonlinearity="linear")
+        self.register_buffer("weight", weight)
+        self.register_buffer("_cluster_size", torch.zeros(num_embeddings))
+        self.register_buffer("_weight_avg", weight)
+
+
 class VectorQuantizer(nn.Module):
     """The codebook that contains quantized vectors."""
 
     def __init__(
-        self, num_embeddings: int, embedding_dim: int, beta: float = 0.25
+        self, num_embeddings: int, embedding_dim: int, decay: float = 0.99
     ) -> 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)
+        self.num_embeddings = num_embeddings
+        self.embedding_dim = embedding_dim
+        self.decay = decay
+        self.embedding = EmbeddingEMA(self.num_embeddings, self.embedding_dim)
 
     def discretization_bottleneck(self, latent: Tensor) -> Tensor:
         """Computes the code nearest to the latent representation.
@@ -62,7 +66,7 @@ class VectorQuantizer(nn.Module):
 
         # Convert to one-hot encodings, aka discrete bottleneck.
         one_hot_encoding = torch.zeros(
-            encoding_indices.shape[0], self.K, device=latent.device
+            encoding_indices.shape[0], self.num_embeddings, device=latent.device
         )
         one_hot_encoding.scatter_(1, encoding_indices, 1)  # [BHW x K]
 
@@ -71,9 +75,27 @@ class VectorQuantizer(nn.Module):
         quantized_latent = rearrange(
             quantized_latent, "(b h w) d -> b h w d", b=b, h=h, w=w
         )
+        if self.training:
+            self.compute_ema(one_hot_encoding=one_hot_encoding, latent=latent)
 
         return quantized_latent
 
+    def compute_ema(self, one_hot_encoding: Tensor, latent: Tensor) -> None:
+        batch_cluster_size = one_hot_encoding.sum(axis=0)
+        batch_embedding_avg = (latent.t() @ one_hot_encoding).t()
+        print(batch_cluster_size.shape)
+        print(self.embedding._cluster_size.shape)
+        self.embedding._cluster_size.data.mul_(self.decay).add_(
+            batch_cluster_size, alpha=1 - self.decay
+        )
+        self.embedding._weight_avg.data.mul_(self.decay).add_(
+            batch_embedding_avg, alpha=1 - self.decay
+        )
+        new_embedding = self.embedding._weight_avg / (
+            self.embedding._cluster_size + 1.0e-5
+        ).unsqueeze(1)
+        self.embedding.weight.data.copy_(new_embedding)
+
     def vq_loss(self, latent: Tensor, quantized_latent: Tensor) -> Tensor:
         """Vector Quantization loss.
 
@@ -96,9 +118,10 @@ class VectorQuantizer(nn.Module):
             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
+        # embedding_loss = F.mse_loss(quantized_latent, latent.detach())
+        # return embedding_loss + self.beta * commitment_loss
+        return commitment_loss
 
     def forward(self, latent: Tensor) -> Tensor:
         """Forward pass that returns the quantized vector and the vq loss."""
diff --git a/text_recognizer/networks/vqvae/residual.py b/text_recognizer/networks/vqvae/residual.py
new file mode 100644
index 0000000..98109b8
--- /dev/null
+++ b/text_recognizer/networks/vqvae/residual.py
@@ -0,0 +1,18 @@
+"""Residual block."""
+from torch import nn
+from torch import Tensor
+
+
+class Residual(nn.Module):
+    def __init__(self, in_channels: int, out_channels: int,) -> None:
+        super().__init__()
+        self.block = nn.Sequential(
+            nn.Mish(inplace=True),
+            nn.Conv2d(in_channels, out_channels, kernel_size=3, padding=1, bias=False),
+            nn.Mish(inplace=True),
+            nn.Conv2d(out_channels, in_channels, kernel_size=1, bias=False),
+        )
+
+    def forward(self, x: Tensor) -> Tensor:
+        """Apply the residual forward pass."""
+        return x + self.block(x)
diff --git a/text_recognizer/networks/vqvae/vqvae.py b/text_recognizer/networks/vqvae/vqvae.py
index 5aa929b..1585d40 100644
--- a/text_recognizer/networks/vqvae/vqvae.py
+++ b/text_recognizer/networks/vqvae/vqvae.py
@@ -1,10 +1,14 @@
 """The VQ-VAE."""
-from typing import Any, Dict, List, Optional, Tuple
+from typing import Tuple
 
+import torch
 from torch import nn
 from torch import Tensor
+import torch.nn.functional as F
 
-from text_recognizer.networks.vqvae import Decoder, Encoder
+from text_recognizer.networks.vqvae.decoder import Decoder
+from text_recognizer.networks.vqvae.encoder import Encoder
+from text_recognizer.networks.vqvae.quantizer import VectorQuantizer
 
 
 class VQVAE(nn.Module):
@@ -13,62 +17,92 @@ class VQVAE(nn.Module):
     def __init__(
         self,
         in_channels: int,
-        channels: List[int],
-        kernel_sizes: List[int],
-        strides: List[int],
+        res_channels: int,
         num_residual_layers: int,
         embedding_dim: int,
         num_embeddings: int,
-        upsampling: Optional[List[List[int]]] = None,
-        beta: float = 0.25,
-        activation: str = "leaky_relu",
-        dropout_rate: float = 0.0,
-        *args: Any,
-        **kwargs: Dict,
+        decay: float = 0.99,
+        activation: str = "mish",
     ) -> None:
         super().__init__()
+        # Encoders
+        self.btm_encoder = Encoder(
+            in_channels=1,
+            out_channels=embedding_dim,
+            res_channels=res_channels,
+            num_residual_layers=num_residual_layers,
+            embedding_dim=embedding_dim,
+            activation=activation,
+        )
+
+        self.top_encoder = Encoder(
+            in_channels=embedding_dim,
+            out_channels=embedding_dim,
+            res_channels=res_channels,
+            num_residual_layers=num_residual_layers,
+            embedding_dim=embedding_dim,
+            activation=activation,
+        )
+
+        # Quantizers
+        self.btm_quantizer = VectorQuantizer(
+            num_embeddings=num_embeddings, embedding_dim=embedding_dim, decay=decay,
+        )
 
-        # configure encoder.
-        self.encoder = Encoder(
-            in_channels,
-            channels,
-            kernel_sizes,
-            strides,
-            num_residual_layers,
-            embedding_dim,
-            num_embeddings,
-            beta,
-            activation,
-            dropout_rate,
+        self.top_quantizer = VectorQuantizer(
+            num_embeddings=num_embeddings, embedding_dim=embedding_dim, decay=decay,
         )
 
-        # Configure decoder.
-        channels.reverse()
-        kernel_sizes.reverse()
-        strides.reverse()
-        self.decoder = Decoder(
-            channels,
-            kernel_sizes,
-            strides,
-            num_residual_layers,
-            embedding_dim,
-            upsampling,
-            activation,
-            dropout_rate,
+        # Decoders
+        self.top_decoder = Decoder(
+            in_channels=embedding_dim,
+            out_channels=embedding_dim,
+            embedding_dim=embedding_dim,
+            res_channels=res_channels,
+            num_residual_layers=num_residual_layers,
+            activation=activation,
+        )
+
+        self.btm_decoder = Decoder(
+            in_channels=2 * embedding_dim,
+            out_channels=in_channels,
+            embedding_dim=embedding_dim,
+            res_channels=res_channels,
+            num_residual_layers=num_residual_layers,
+            activation=activation,
         )
 
     def encode(self, x: Tensor) -> Tuple[Tensor, Tensor]:
         """Encodes input to a latent code."""
-        return self.encoder(x)
+        z_btm = self.btm_encoder(x)
+        z_top = self.top_encoder(z_btm)
+        return z_btm, z_top
+
+    def quantize(
+        self, z_btm: Tensor, z_top: Tensor
+    ) -> Tuple[Tensor, Tensor, Tensor, Tensor]:
+        q_btm, vq_btm_loss = self.top_quantizer(z_btm)
+        q_top, vq_top_loss = self.top_quantizer(z_top)
+        return q_btm, vq_btm_loss, q_top, vq_top_loss
 
-    def decode(self, z_q: Tensor) -> Tensor:
+    def decode(self, q_btm: Tensor, q_top: Tensor) -> Tuple[Tensor, Tensor]:
         """Reconstructs input from latent codes."""
-        return self.decoder(z_q)
+        d_top = self.top_decoder(q_top)
+        x_hat = self.btm_decoder(torch.cat((d_top, q_btm), dim=1))
+        return d_top, x_hat
+
+    def loss_fn(
+        self, vq_btm_loss: Tensor, vq_top_loss: Tensor, d_top: Tensor, z_btm: Tensor
+    ) -> Tensor:
+        """Calculates the latent loss."""
+        return 0.5 * (vq_top_loss + vq_btm_loss) + F.mse_loss(d_top, z_btm)
 
     def forward(self, x: Tensor) -> Tuple[Tensor, Tensor]:
         """Compresses and decompresses input."""
-        if len(x.shape) < 4:
-            x = x[(None,) * (4 - len(x.shape))]
-        z_q, vq_loss = self.encode(x)
-        x_reconstruction = self.decode(z_q)
-        return x_reconstruction, vq_loss
+        z_btm, z_top = self.encode(x)
+        q_btm, vq_btm_loss, q_top, vq_top_loss = self.quantize(z_btm=z_btm, z_top=z_top)
+        d_top, x_hat = self.decode(q_btm=q_btm, q_top=q_top)
+        vq_loss = self.loss_fn(
+            vq_btm_loss=vq_btm_loss, vq_top_loss=vq_top_loss, d_top=d_top, z_btm=z_btm
+        )
+        return x_hat, vq_loss