models/gan_loss.py

import torch
import torch.nn as nn
import torch.nn.functional as F


class GANLoss(nn.Module):
    def __init__(self, target_real_label=1.0, target_fake_label=0.0, tensor=torch.FloatTensor, opt=None):
        super(GANLoss, self).__init__()
        self.real_label = target_real_label
        self.fake_label = target_fake_label
        self.real_label_tensor = None
        self.fake_label_tensor = None
        self.zero_tensor = None
        self.Tensor = tensor
        self.opt = opt

    def get_target_tensor(self, input, target_is_real):
        if target_is_real:
            return torch.ones_like(input).detach()
        else:
            return torch.zeros_like(input).detach()

    def get_zero_tensor(self, input):
        return torch.zeros_like(input).detach()

    def loss(self, inputs, target_is_real, for_discriminator=True):
        target_tensor = self.get_target_tensor(inputs, target_is_real)
        loss = F.binary_cross_entropy_with_logits(inputs, target_tensor)
        return loss

    def __call__(self, inputs, target_is_real, for_discriminator=True):
        # computing loss is a bit complicated because |input| may not be
        # a tensor, but list of tensors in case of multiscale discriminator
        if isinstance(inputs, list):
            loss = 0
            for pred_i in inputs:
                if isinstance(pred_i, list):
                    pred_i = pred_i[-1]
                loss_tensor = self.loss(pred_i, target_is_real, for_discriminator)
                bs = 1 if len(loss_tensor.size()) == 0 else loss_tensor.size(0)
                new_loss = torch.mean(loss_tensor.view(bs, -1), dim=1)
                loss += new_loss
            return loss / len(inputs)
        else:
            return self.loss(inputs, target_is_real, for_discriminator)