lib/net/FBNet.py

"""
Copyright (C) 2019 NVIDIA Corporation. Ting-Chun Wang, Ming-Yu Liu, Jun-Yan Zhu.
BSD License. All rights reserved. 

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright notice, this
  list of conditions and the following disclaimer.

* Redistributions in binary form must reproduce the above copyright notice,
  this list of conditions and the following disclaimer in the documentation
  and/or other materials provided with the distribution.

THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL 
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR ANY PARTICULAR PURPOSE. 
IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL 
DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, 
WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING 
OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
"""
import functools

import numpy as np
import pytorch_lightning as pl
import torch
import torch.nn as nn
import torch.nn.functional as F
from torchvision import models


###############################################################################
# Functions
###############################################################################
def weights_init(m):
    classname = m.__class__.__name__
    if classname.find("Conv") != -1:
        m.weight.data.normal_(0.0, 0.02)
    elif classname.find("BatchNorm2d") != -1:
        m.weight.data.normal_(1.0, 0.02)
        m.bias.data.fill_(0)


def get_norm_layer(norm_type="instance"):
    if norm_type == "batch":
        norm_layer = functools.partial(nn.BatchNorm2d, affine=True)
    elif norm_type == "instance":
        norm_layer = functools.partial(nn.InstanceNorm2d, affine=False)
    else:
        raise NotImplementedError("normalization layer [%s] is not found" % norm_type)
    return norm_layer


def define_G(
    input_nc,
    output_nc,
    ngf,
    netG,
    n_downsample_global=3,
    n_blocks_global=9,
    n_local_enhancers=1,
    n_blocks_local=3,
    norm="instance",
    gpu_ids=[],
    last_op=nn.Tanh(),
):
    norm_layer = get_norm_layer(norm_type=norm)
    if netG == "global":
        netG = GlobalGenerator(
            input_nc,
            output_nc,
            ngf,
            n_downsample_global,
            n_blocks_global,
            norm_layer,
            last_op=last_op,
        )
    elif netG == "local":
        netG = LocalEnhancer(
            input_nc,
            output_nc,
            ngf,
            n_downsample_global,
            n_blocks_global,
            n_local_enhancers,
            n_blocks_local,
            norm_layer,
        )
    elif netG == "encoder":
        netG = Encoder(input_nc, output_nc, ngf, n_downsample_global, norm_layer)
    else:
        raise ("generator not implemented!")
    # print(netG)
    if len(gpu_ids) > 0:
        assert torch.cuda.is_available()
        netG.cuda(gpu_ids[0])
    netG.apply(weights_init)
    return netG


def define_D(
    input_nc,
    ndf,
    n_layers_D,
    norm='instance',
    use_sigmoid=False,
    num_D=1,
    getIntermFeat=False,
    gpu_ids=[]
):
    norm_layer = get_norm_layer(norm_type=norm)
    netD = MultiscaleDiscriminator(
        input_nc, ndf, n_layers_D, norm_layer, use_sigmoid, num_D, getIntermFeat
    )
    if len(gpu_ids) > 0:
        assert (torch.cuda.is_available())
        netD.cuda(gpu_ids[0])
    netD.apply(weights_init)
    return netD


def print_network(net):
    if isinstance(net, list):
        net = net[0]
    num_params = 0
    for param in net.parameters():
        num_params += param.numel()
    print(net)
    print("Total number of parameters: %d" % num_params)


##############################################################################
# Generator
##############################################################################
class LocalEnhancer(pl.LightningModule):
    def __init__(
        self,
        input_nc,
        output_nc,
        ngf=32,
        n_downsample_global=3,
        n_blocks_global=9,
        n_local_enhancers=1,
        n_blocks_local=3,
        norm_layer=nn.BatchNorm2d,
        padding_type="reflect",
    ):
        super(LocalEnhancer, self).__init__()
        self.n_local_enhancers = n_local_enhancers

        ###### global generator model #####
        ngf_global = ngf * (2**n_local_enhancers)
        model_global = GlobalGenerator(
            input_nc,
            output_nc,
            ngf_global,
            n_downsample_global,
            n_blocks_global,
            norm_layer,
        ).model
        model_global = [
            model_global[i] for i in range(len(model_global) - 3)
        ]    # get rid of final convolution layers
        self.model = nn.Sequential(*model_global)

        ###### local enhancer layers #####
        for n in range(1, n_local_enhancers + 1):
            # downsample
            ngf_global = ngf * (2**(n_local_enhancers - n))
            model_downsample = [
                nn.ReflectionPad2d(3),
                nn.Conv2d(input_nc, ngf_global, kernel_size=7, padding=0),
                norm_layer(ngf_global),
                nn.ReLU(True),
                nn.Conv2d(ngf_global, ngf_global * 2, kernel_size=3, stride=2, padding=1),
                norm_layer(ngf_global * 2),
                nn.ReLU(True),
            ]
            # residual blocks
            model_upsample = []
            for i in range(n_blocks_local):
                model_upsample += [
                    ResnetBlock(ngf_global * 2, padding_type=padding_type, norm_layer=norm_layer)
                ]

            # upsample
            model_upsample += [
                nn.ConvTranspose2d(
                    ngf_global * 2,
                    ngf_global,
                    kernel_size=3,
                    stride=2,
                    padding=1,
                    output_padding=1,
                ),
                norm_layer(ngf_global),
                nn.ReLU(True),
            ]

            # final convolution
            if n == n_local_enhancers:
                model_upsample += [
                    nn.ReflectionPad2d(3),
                    nn.Conv2d(ngf, output_nc, kernel_size=7, padding=0),
                    nn.Tanh(),
                ]

            setattr(self, "model" + str(n) + "_1", nn.Sequential(*model_downsample))
            setattr(self, "model" + str(n) + "_2", nn.Sequential(*model_upsample))

        self.downsample = nn.AvgPool2d(3, stride=2, padding=[1, 1], count_include_pad=False)

    def forward(self, input):
        # create input pyramid
        input_downsampled = [input]
        for i in range(self.n_local_enhancers):
            input_downsampled.append(self.downsample(input_downsampled[-1]))

        # output at coarest level
        output_prev = self.model(input_downsampled[-1])
        # build up one layer at a time
        for n_local_enhancers in range(1, self.n_local_enhancers + 1):
            model_downsample = getattr(self, "model" + str(n_local_enhancers) + "_1")
            model_upsample = getattr(self, "model" + str(n_local_enhancers) + "_2")
            input_i = input_downsampled[self.n_local_enhancers - n_local_enhancers]
            output_prev = model_upsample(model_downsample(input_i) + output_prev)
        return output_prev


class GlobalGenerator(pl.LightningModule):
    def __init__(
        self,
        input_nc,
        output_nc,
        ngf=64,
        n_downsampling=3,
        n_blocks=9,
        norm_layer=nn.BatchNorm2d,
        padding_type="reflect",
        last_op=nn.Tanh(),
    ):
        assert n_blocks >= 0
        super(GlobalGenerator, self).__init__()
        activation = nn.ReLU(True)

        model = [
            nn.ReflectionPad2d(3),
            nn.Conv2d(input_nc, ngf, kernel_size=7, padding=0),
            norm_layer(ngf),
            activation,
        ]
        # downsample
        for i in range(n_downsampling):
            mult = 2**i
            model += [
                nn.Conv2d(ngf * mult, ngf * mult * 2, kernel_size=3, stride=2, padding=1),
                norm_layer(ngf * mult * 2),
                activation,
            ]

        # resnet blocks
        mult = 2**n_downsampling
        for i in range(n_blocks):
            model += [
                ResnetBlock(
                    ngf * mult,
                    padding_type=padding_type,
                    activation=activation,
                    norm_layer=norm_layer,
                )
            ]

        # upsample
        for i in range(n_downsampling):
            mult = 2**(n_downsampling - i)
            model += [
                nn.ConvTranspose2d(
                    ngf * mult,
                    int(ngf * mult / 2),
                    kernel_size=3,
                    stride=2,
                    padding=1,
                    output_padding=1,
                ),
                norm_layer(int(ngf * mult / 2)),
                activation,
            ]
        model += [
            nn.ReflectionPad2d(3),
            nn.Conv2d(ngf, output_nc, kernel_size=7, padding=0),
        ]
        if last_op is not None:
            model += [last_op]
        self.model = nn.Sequential(*model)

    def forward(self, input):
        return self.model(input)


# Defines the PatchGAN discriminator with the specified arguments.
class NLayerDiscriminator(nn.Module):
    def __init__(
        self,
        input_nc,
        ndf=64,
        n_layers=3,
        norm_layer=nn.BatchNorm2d,
        use_sigmoid=False,
        getIntermFeat=False
    ):
        super(NLayerDiscriminator, self).__init__()
        self.getIntermFeat = getIntermFeat
        self.n_layers = n_layers

        kw = 4
        padw = int(np.ceil((kw - 1.0) / 2))
        sequence = [[
            nn.Conv2d(input_nc, ndf, kernel_size=kw, stride=2, padding=padw),
            nn.LeakyReLU(0.2, True)
        ]]

        nf = ndf
        for n in range(1, n_layers):
            nf_prev = nf
            nf = min(nf * 2, 512)
            sequence += [[
                nn.Conv2d(nf_prev, nf, kernel_size=kw, stride=2, padding=padw),
                norm_layer(nf),
                nn.LeakyReLU(0.2, True)
            ]]

        nf_prev = nf
        nf = min(nf * 2, 512)
        sequence += [[
            nn.Conv2d(nf_prev, nf, kernel_size=kw, stride=1, padding=padw),
            norm_layer(nf),
            nn.LeakyReLU(0.2, True)
        ]]

        sequence += [[nn.Conv2d(nf, 1, kernel_size=kw, stride=1, padding=padw)]]

        if use_sigmoid:
            sequence += [[nn.Sigmoid()]]

        if getIntermFeat:
            for n in range(len(sequence)):
                setattr(self, 'model' + str(n), nn.Sequential(*sequence[n]))
        else:
            sequence_stream = []
            for n in range(len(sequence)):
                sequence_stream += sequence[n]
            self.model = nn.Sequential(*sequence_stream)

    def forward(self, input):
        if self.getIntermFeat:
            res = [input]
            for n in range(self.n_layers + 2):
                model = getattr(self, 'model' + str(n))
                res.append(model(res[-1]))
            return res[1:]
        else:
            return self.model(input)


class MultiscaleDiscriminator(pl.LightningModule):
    def __init__(
        self,
        input_nc,
        ndf=64,
        n_layers=3,
        norm_layer=nn.BatchNorm2d,
        use_sigmoid=False,
        num_D=3,
        getIntermFeat=False
    ):
        super(MultiscaleDiscriminator, self).__init__()
        self.num_D = num_D
        self.n_layers = n_layers
        self.getIntermFeat = getIntermFeat

        for i in range(num_D):
            netD = NLayerDiscriminator(
                input_nc, ndf, n_layers, norm_layer, use_sigmoid, getIntermFeat
            )
            if getIntermFeat:
                for j in range(n_layers + 2):
                    setattr(
                        self, 'scale' + str(i) + '_layer' + str(j), getattr(netD, 'model' + str(j))
                    )
            else:
                setattr(self, 'layer' + str(i), netD.model)

        self.downsample = nn.AvgPool2d(3, stride=2, padding=[1, 1], count_include_pad=False)

    def singleD_forward(self, model, input):
        if self.getIntermFeat:
            result = [input]
            for i in range(len(model)):
                result.append(model[i](result[-1]))
            return result[1:]
        else:
            return [model(input)]

    def forward(self, input):
        num_D = self.num_D
        result = []
        input_downsampled = input.clone()
        for i in range(num_D):
            if self.getIntermFeat:
                model = [
                    getattr(self, 'scale' + str(num_D - 1 - i) + '_layer' + str(j))
                    for j in range(self.n_layers + 2)
                ]
            else:
                model = getattr(self, 'layer' + str(num_D - 1 - i))
            result.append(self.singleD_forward(model, input_downsampled))
            if i != (num_D - 1):
                input_downsampled = self.downsample(input_downsampled)
        return result


# Define a resnet block
class ResnetBlock(pl.LightningModule):
    def __init__(self, dim, padding_type, norm_layer, activation=nn.ReLU(True), use_dropout=False):
        super(ResnetBlock, self).__init__()
        self.conv_block = self.build_conv_block(
            dim, padding_type, norm_layer, activation, use_dropout
        )

    def build_conv_block(self, dim, padding_type, norm_layer, activation, use_dropout):
        conv_block = []
        p = 0
        if padding_type == "reflect":
            conv_block += [nn.ReflectionPad2d(1)]
        elif padding_type == "replicate":
            conv_block += [nn.ReplicationPad2d(1)]
        elif padding_type == "zero":
            p = 1
        else:
            raise NotImplementedError("padding [%s] is not implemented" % padding_type)

        conv_block += [
            nn.Conv2d(dim, dim, kernel_size=3, padding=p),
            norm_layer(dim),
            activation,
        ]
        if use_dropout:
            conv_block += [nn.Dropout(0.5)]

        p = 0
        if padding_type == "reflect":
            conv_block += [nn.ReflectionPad2d(1)]
        elif padding_type == "replicate":
            conv_block += [nn.ReplicationPad2d(1)]
        elif padding_type == "zero":
            p = 1
        else:
            raise NotImplementedError("padding [%s] is not implemented" % padding_type)
        conv_block += [nn.Conv2d(dim, dim, kernel_size=3, padding=p), norm_layer(dim)]

        return nn.Sequential(*conv_block)

    def forward(self, x):
        out = x + self.conv_block(x)
        return out


class Encoder(pl.LightningModule):
    def __init__(self, input_nc, output_nc, ngf=32, n_downsampling=4, norm_layer=nn.BatchNorm2d):
        super(Encoder, self).__init__()
        self.output_nc = output_nc

        model = [
            nn.ReflectionPad2d(3),
            nn.Conv2d(input_nc, ngf, kernel_size=7, padding=0),
            norm_layer(ngf),
            nn.ReLU(True),
        ]
        # downsample
        for i in range(n_downsampling):
            mult = 2**i
            model += [
                nn.Conv2d(ngf * mult, ngf * mult * 2, kernel_size=3, stride=2, padding=1),
                norm_layer(ngf * mult * 2),
                nn.ReLU(True),
            ]

        # upsample
        for i in range(n_downsampling):
            mult = 2**(n_downsampling - i)
            model += [
                nn.ConvTranspose2d(
                    ngf * mult,
                    int(ngf * mult / 2),
                    kernel_size=3,
                    stride=2,
                    padding=1,
                    output_padding=1,
                ),
                norm_layer(int(ngf * mult / 2)),
                nn.ReLU(True),
            ]

        model += [
            nn.ReflectionPad2d(3),
            nn.Conv2d(ngf, output_nc, kernel_size=7, padding=0),
            nn.Tanh(),
        ]
        self.model = nn.Sequential(*model)

    def forward(self, input, inst):
        outputs = self.model(input)

        # instance-wise average pooling
        outputs_mean = outputs.clone()
        inst_list = np.unique(inst.cpu().numpy().astype(int))
        for i in inst_list:
            for b in range(input.size()[0]):
                indices = (inst[b:b + 1] == int(i)).nonzero()    # n x 4
                for j in range(self.output_nc):
                    output_ins = outputs[indices[:, 0] + b, indices[:, 1] + j, indices[:, 2],
                                         indices[:, 3], ]
                    mean_feat = torch.mean(output_ins).expand_as(output_ins)
                    outputs_mean[indices[:, 0] + b, indices[:, 1] + j, indices[:, 2],
                                 indices[:, 3], ] = mean_feat
        return outputs_mean


class Vgg19(nn.Module):
    def __init__(self, requires_grad=False):
        super(Vgg19, self).__init__()
        vgg_pretrained_features = models.vgg19(weights=models.VGG19_Weights.DEFAULT).features
        self.slice1 = torch.nn.Sequential()
        self.slice2 = torch.nn.Sequential()
        self.slice3 = torch.nn.Sequential()
        self.slice4 = torch.nn.Sequential()
        self.slice5 = torch.nn.Sequential()
        for x in range(2):
            self.slice1.add_module(str(x), vgg_pretrained_features[x])
        for x in range(2, 7):
            self.slice2.add_module(str(x), vgg_pretrained_features[x])
        for x in range(7, 12):
            self.slice3.add_module(str(x), vgg_pretrained_features[x])
        for x in range(12, 21):
            self.slice4.add_module(str(x), vgg_pretrained_features[x])
        for x in range(21, 30):
            self.slice5.add_module(str(x), vgg_pretrained_features[x])
        if not requires_grad:
            for param in self.parameters():
                param.requires_grad = False

    def forward(self, X):
        h_relu1 = self.slice1(X)
        h_relu2 = self.slice2(h_relu1)
        h_relu3 = self.slice3(h_relu2)
        h_relu4 = self.slice4(h_relu3)
        h_relu5 = self.slice5(h_relu4)
        out = [h_relu1, h_relu2, h_relu3, h_relu4, h_relu5]
        return out


class VGG19FeatLayer(nn.Module):
    def __init__(self):
        super(VGG19FeatLayer, self).__init__()
        self.vgg19 = models.vgg19(weights=models.VGG19_Weights.DEFAULT).features.eval()

        self.register_buffer("mean", torch.tensor([0.485, 0.456, 0.406]).view(1, 3, 1, 1))
        self.register_buffer("std", torch.tensor([0.229, 0.224, 0.225]).view(1, 3, 1, 1))

    def forward(self, x):

        out = {}
        x = x - self.mean
        x = x / self.std
        ci = 1
        ri = 0
        for layer in self.vgg19.children():
            if isinstance(layer, nn.Conv2d):
                ri += 1
                name = 'conv{}_{}'.format(ci, ri)
            elif isinstance(layer, nn.ReLU):
                ri += 1
                name = 'relu{}_{}'.format(ci, ri)
                layer = nn.ReLU(inplace=False)
            elif isinstance(layer, nn.MaxPool2d):
                ri = 0
                name = 'pool_{}'.format(ci)
                ci += 1
            elif isinstance(layer, nn.BatchNorm2d):
                name = 'bn_{}'.format(ci)
            else:
                raise RuntimeError('Unrecognized layer: {}'.format(layer.__class__.__name__))
            x = layer(x)
            out[name] = x
        # print([x for x in out])
        return out


class VGGLoss(pl.LightningModule):
    def __init__(self):
        super(VGGLoss, self).__init__()
        self.vgg = Vgg19().eval()
        self.criterion = nn.L1Loss()
        self.weights = [1.0 / 32, 1.0 / 16, 1.0 / 8, 1.0 / 4, 1.0]

    def forward(self, x, y):
        x_vgg, y_vgg = self.vgg(x), self.vgg(y)
        loss = 0
        for i in range(len(x_vgg)):
            loss += self.weights[i] * self.criterion(x_vgg[i], y_vgg[i].detach())
        return loss


class GANLoss(pl.LightningModule):
    def __init__(self, use_lsgan=True, target_real_label=1.0, target_fake_label=0.0):
        super(GANLoss, self).__init__()
        self.real_label = target_real_label
        self.fake_label = target_fake_label
        self.real_label_var = None
        self.fake_label_var = None
        self.tensor = torch.cuda.FloatTensor
        if use_lsgan:
            self.loss = nn.MSELoss()
        else:
            self.loss = nn.BCELoss()

    def get_target_tensor(self, input, target_is_real):
        target_tensor = None
        if target_is_real:
            create_label = ((self.real_label_var is None) or
                            (self.real_label_var.numel() != input.numel()))
            if create_label:
                real_tensor = self.tensor(input.size()).fill_(self.real_label)
                self.real_label_var = real_tensor
                self.real_label_var.requires_grad = False
            target_tensor = self.real_label_var
        else:
            create_label = ((self.fake_label_var is None) or
                            (self.fake_label_var.numel() != input.numel()))
            if create_label:
                fake_tensor = self.tensor(input.size()).fill_(self.fake_label)
                self.fake_label_var = fake_tensor
                self.fake_label_var.requires_grad = False
            target_tensor = self.fake_label_var
        return target_tensor

    def __call__(self, input, target_is_real):
        if isinstance(input[0], list):
            loss = 0
            for input_i in input:
                pred = input_i[-1]
                target_tensor = self.get_target_tensor(pred, target_is_real)
                loss += self.loss(pred, target_tensor)
            return loss
        else:
            target_tensor = self.get_target_tensor(input[-1], target_is_real)
            return self.loss(input[-1], target_tensor)


class IDMRFLoss(pl.LightningModule):
    def __init__(self, featlayer=VGG19FeatLayer):
        super(IDMRFLoss, self).__init__()
        self.featlayer = featlayer()
        self.feat_style_layers = {'relu3_2': 1.0, 'relu4_2': 1.0}
        self.feat_content_layers = {'relu4_2': 1.0}
        self.bias = 1.0
        self.nn_stretch_sigma = 0.5
        self.lambda_style = 1.0
        self.lambda_content = 1.0

    def sum_normalize(self, featmaps):
        reduce_sum = torch.sum(featmaps, dim=1, keepdim=True)
        return featmaps / reduce_sum

    def patch_extraction(self, featmaps):
        patch_size = 1
        patch_stride = 1
        patches_as_depth_vectors = featmaps.unfold(2, patch_size, patch_stride).unfold(
            3, patch_size, patch_stride
        )
        self.patches_OIHW = patches_as_depth_vectors.permute(0, 2, 3, 1, 4, 5)
        dims = self.patches_OIHW.size()
        self.patches_OIHW = self.patches_OIHW.view(-1, dims[3], dims[4], dims[5])
        return self.patches_OIHW

    def compute_relative_distances(self, cdist):
        epsilon = 1e-5
        div = torch.min(cdist, dim=1, keepdim=True)[0]
        relative_dist = cdist / (div + epsilon)
        return relative_dist

    def exp_norm_relative_dist(self, relative_dist):
        scaled_dist = relative_dist
        dist_before_norm = torch.exp((self.bias - scaled_dist) / self.nn_stretch_sigma)
        self.cs_NCHW = self.sum_normalize(dist_before_norm)
        return self.cs_NCHW

    def mrf_loss(self, gen, tar):
        meanT = torch.mean(tar, 1, keepdim=True)
        gen_feats, tar_feats = gen - meanT, tar - meanT

        gen_feats_norm = torch.norm(gen_feats, p=2, dim=1, keepdim=True)
        tar_feats_norm = torch.norm(tar_feats, p=2, dim=1, keepdim=True)

        gen_normalized = gen_feats / gen_feats_norm
        tar_normalized = tar_feats / tar_feats_norm

        cosine_dist_l = []
        BatchSize = tar.size(0)

        for i in range(BatchSize):
            tar_feat_i = tar_normalized[i:i + 1, :, :, :]
            gen_feat_i = gen_normalized[i:i + 1, :, :, :]
            patches_OIHW = self.patch_extraction(tar_feat_i)

            cosine_dist_i = F.conv2d(gen_feat_i, patches_OIHW)
            cosine_dist_l.append(cosine_dist_i)
        cosine_dist = torch.cat(cosine_dist_l, dim=0)
        cosine_dist_zero_2_one = -(cosine_dist - 1) / 2
        relative_dist = self.compute_relative_distances(cosine_dist_zero_2_one)
        rela_dist = self.exp_norm_relative_dist(relative_dist)
        dims_div_mrf = rela_dist.size()
        k_max_nc = torch.max(rela_dist.view(dims_div_mrf[0], dims_div_mrf[1], -1), dim=2)[0]
        div_mrf = torch.mean(k_max_nc, dim=1)
        div_mrf_sum = -torch.log(div_mrf)
        div_mrf_sum = torch.sum(div_mrf_sum)
        return div_mrf_sum

    def forward(self, gen, tar):
        ## gen: [bz,3,h,w] rgb [0,1]
        gen_vgg_feats = self.featlayer(gen)
        tar_vgg_feats = self.featlayer(tar)
        style_loss_list = [
            self.feat_style_layers[layer] *
            self.mrf_loss(gen_vgg_feats[layer], tar_vgg_feats[layer])
            for layer in self.feat_style_layers
        ]
        self.style_loss = functools.reduce(lambda x, y: x + y, style_loss_list) * self.lambda_style

        content_loss_list = [
            self.feat_content_layers[layer] *
            self.mrf_loss(gen_vgg_feats[layer], tar_vgg_feats[layer])
            for layer in self.feat_content_layers
        ]
        self.content_loss = functools.reduce(
            lambda x, y: x + y, content_loss_list
        ) * self.lambda_content

        return self.style_loss + self.content_loss