models/vae.py

import os, sys
sys.path.append(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
import torch
from torch import nn
from torch.nn import functional as F
# from .types_ import *


class VanillaVAE(nn.Module):
    def __init__(self,args,
                 in_channels: int,
                 latent_dim: int,
                 hidden_dims = None,
                 **kwargs) -> None:
        super(VanillaVAE, self).__init__()

        self.latent_dim = latent_dim

        modules = []
        if hidden_dims is None:
            hidden_dims = [32, 64, 128, 256, 512]
        
        if latent_dim is None:
            latent_dim = 512

        # Build Encoder
        for h_dim in hidden_dims:
            modules.append(
                nn.Sequential(
                    nn.Conv2d(in_channels, out_channels=h_dim,
                              kernel_size= 3, stride= 2, padding  = 1),
                    nn.BatchNorm2d(h_dim),
                    nn.LeakyReLU())
            )
            in_channels = h_dim

        self.encoder = nn.Sequential(*modules)
        self.fc_mu = nn.Linear(hidden_dims[-1]*4, latent_dim)
        self.fc_var = nn.Linear(hidden_dims[-1]*4, latent_dim)


        # Build Decoder
        modules = []

        self.decoder_input = nn.Linear(latent_dim, hidden_dims[-1] * 4)

        hidden_dims.reverse()

        for i in range(len(hidden_dims) - 1):
            modules.append(
                nn.Sequential(
                    nn.ConvTranspose2d(hidden_dims[i],
                                       hidden_dims[i + 1],
                                       kernel_size=3,
                                       stride = 2,
                                       padding=1,
                                       output_padding=1),
                    nn.BatchNorm2d(hidden_dims[i + 1]),
                    nn.LeakyReLU())
            )



        self.decoder = nn.Sequential(*modules)

        self.final_layer = nn.Sequential(
                            nn.ConvTranspose2d(hidden_dims[-1],
                                               hidden_dims[-1],
                                               kernel_size=3,
                                               stride=2,
                                               padding=1,
                                               output_padding=1),
                            nn.BatchNorm2d(hidden_dims[-1]),
                            nn.LeakyReLU(),
                            nn.Conv2d(hidden_dims[-1], out_channels= 3,
                                      kernel_size= 3, padding= 1),
                            nn.Tanh())

    def encode(self, input):
        """
        Encodes the input by passing through the encoder network
        and returns the latent codes.
        :param input: (Tensor) Input tensor to encoder [N x C x H x W]
        :return: (Tensor) List of latent codes
        """
        result = self.encoder(input)
        result = torch.flatten(result, start_dim=1)

        # Split the result into mu and var components
        # of the latent Gaussian distribution
        mu = self.fc_mu(result)
        # log_var = self.fc_var(result)

        return mu

    def decode(self, z):
        """
        Maps the given latent codes
        onto the image space.
        :param z: (Tensor) [B x D]
        :return: (Tensor) [B x C x H x W]
        """
        result = self.decoder_input(z)
        result = result.view(-1, 512, 2, 2)
        result = self.decoder(result)
        result = self.final_layer(result)
        return result

    # def reparameterize(self, mu, logvar):
    #     """
    #     Reparameterization trick to sample from N(mu, var) from
    #     N(0,1).
    #     :param mu: (Tensor) Mean of the latent Gaussian [B x D]
    #     :param logvar: (Tensor) Standard deviation of the latent Gaussian [B x D]
    #     :return: (Tensor) [B x D]
    #     """
    #     std = torch.exp(0.5 * logvar)
    #     eps = torch.randn_like(std)
    #     return eps * std + mu

    def forward(self, input, **kwargs):
        mu = self.encode(input)
        # z = self.reparameterize(mu, log_var)
        return  self.decode(mu)

    def loss_function(self,
                      *args,
                      **kwargs) -> dict:
        """
        Computes the VAE loss function.
        KL(N(\mu, \sigma), N(0, 1)) = \log \frac{1}{\sigma} + \frac{\sigma^2 + \mu^2}{2} - \frac{1}{2}
        :param args:
        :param kwargs:
        :return:
        """
        recons = args[0]
        input = args[1]
        # mu = args[2]
        # log_var = args[3]

        # kld_weight = kwargs['M_N'] # Account for the minibatch samples from the dataset
        recons_loss =F.mse_loss(recons, input)


        # kld_loss = torch.mean(-0.5 * torch.sum(1 + log_var - mu ** 2 - log_var.exp(), dim = 1), dim = 0)

        loss = recons_loss
        return loss
        # {'loss': loss, 'Reconstruction_Loss':recons_loss.detach(), 'KLD':recons_loss.detach()}


    def generate(self, x, **kwargs):
        """
        Given an input image x, returns the reconstructed image
        :param x: (Tensor) [B x C x H x W]
        :return: (Tensor) [B x C x H x W]
        """

        return self.forward(x)[0]