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# python3.7
"""Contains the implementation of discriminator described in PGGAN.
Paper: https://arxiv.org/pdf/1710.10196.pdf
Official TensorFlow implementation:
https://github.com/tkarras/progressive_growing_of_gans
"""
import numpy as np
import torch
import torch.nn as nn
import torch.nn.functional as F
__all__ = ['PGGANDiscriminator']
# Resolutions allowed.
_RESOLUTIONS_ALLOWED = [8, 16, 32, 64, 128, 256, 512, 1024]
# Initial resolution.
_INIT_RES = 4
# Default gain factor for weight scaling.
_WSCALE_GAIN = np.sqrt(2.0)
class PGGANDiscriminator(nn.Module):
"""Defines the discriminator network in PGGAN.
NOTE: The discriminator takes images with `RGB` channel order and pixel
range [-1, 1] as inputs.
Settings for the network:
(1) resolution: The resolution of the input image.
(2) image_channels: Number of channels of the input image. (default: 3)
(3) label_size: Size of the additional label for conditional generation.
(default: 0)
(4) fused_scale: Whether to fused `conv2d` and `downsample` together,
resulting in `conv2d` with strides. (default: False)
(5) use_wscale: Whether to use weight scaling. (default: True)
(6) minibatch_std_group_size: Group size for the minibatch standard
deviation layer. 0 means disable. (default: 16)
(7) fmaps_base: Factor to control number of feature maps for each layer.
(default: 16 << 10)
(8) fmaps_max: Maximum number of feature maps in each layer. (default: 512)
"""
def __init__(self,
resolution,
image_channels=3,
label_size=0,
fused_scale=False,
use_wscale=True,
minibatch_std_group_size=16,
fmaps_base=16 << 10,
fmaps_max=512):
"""Initializes with basic settings.
Raises:
ValueError: If the `resolution` is not supported.
"""
super().__init__()
if resolution not in _RESOLUTIONS_ALLOWED:
raise ValueError(f'Invalid resolution: `{resolution}`!\n'
f'Resolutions allowed: {_RESOLUTIONS_ALLOWED}.')
self.init_res = _INIT_RES
self.init_res_log2 = int(np.log2(self.init_res))
self.resolution = resolution
self.final_res_log2 = int(np.log2(self.resolution))
self.image_channels = image_channels
self.label_size = label_size
self.fused_scale = fused_scale
self.use_wscale = use_wscale
self.minibatch_std_group_size = minibatch_std_group_size
self.fmaps_base = fmaps_base
self.fmaps_max = fmaps_max
# Level of detail (used for progressive training).
self.register_buffer('lod', torch.zeros(()))
self.pth_to_tf_var_mapping = {'lod': 'lod'}
for res_log2 in range(self.final_res_log2, self.init_res_log2 - 1, -1):
res = 2 ** res_log2
block_idx = self.final_res_log2 - res_log2
# Input convolution layer for each resolution.
self.add_module(
f'input{block_idx}',
ConvBlock(in_channels=self.image_channels,
out_channels=self.get_nf(res),
kernel_size=1,
padding=0,
use_wscale=self.use_wscale))
self.pth_to_tf_var_mapping[f'input{block_idx}.weight'] = (
f'FromRGB_lod{block_idx}/weight')
self.pth_to_tf_var_mapping[f'input{block_idx}.bias'] = (
f'FromRGB_lod{block_idx}/bias')
# Convolution block for each resolution (except the last one).
if res != self.init_res:
self.add_module(
f'layer{2 * block_idx}',
ConvBlock(in_channels=self.get_nf(res),
out_channels=self.get_nf(res),
use_wscale=self.use_wscale))
tf_layer0_name = 'Conv0'
self.add_module(
f'layer{2 * block_idx + 1}',
ConvBlock(in_channels=self.get_nf(res),
out_channels=self.get_nf(res // 2),
downsample=True,
fused_scale=self.fused_scale,
use_wscale=self.use_wscale))
tf_layer1_name = 'Conv1_down' if self.fused_scale else 'Conv1'
# Convolution block for last resolution.
else:
self.add_module(
f'layer{2 * block_idx}',
ConvBlock(
in_channels=self.get_nf(res),
out_channels=self.get_nf(res),
use_wscale=self.use_wscale,
minibatch_std_group_size=self.minibatch_std_group_size))
tf_layer0_name = 'Conv'
self.add_module(
f'layer{2 * block_idx + 1}',
DenseBlock(in_channels=self.get_nf(res) * res * res,
out_channels=self.get_nf(res // 2),
use_wscale=self.use_wscale))
tf_layer1_name = 'Dense0'
self.pth_to_tf_var_mapping[f'layer{2 * block_idx}.weight'] = (
f'{res}x{res}/{tf_layer0_name}/weight')
self.pth_to_tf_var_mapping[f'layer{2 * block_idx}.bias'] = (
f'{res}x{res}/{tf_layer0_name}/bias')
self.pth_to_tf_var_mapping[f'layer{2 * block_idx + 1}.weight'] = (
f'{res}x{res}/{tf_layer1_name}/weight')
self.pth_to_tf_var_mapping[f'layer{2 * block_idx + 1}.bias'] = (
f'{res}x{res}/{tf_layer1_name}/bias')
# Final dense block.
self.add_module(
f'layer{2 * block_idx + 2}',
DenseBlock(in_channels=self.get_nf(res // 2),
out_channels=1 + self.label_size,
use_wscale=self.use_wscale,
wscale_gain=1.0,
activation_type='linear'))
self.pth_to_tf_var_mapping[f'layer{2 * block_idx + 2}.weight'] = (
f'{res}x{res}/Dense1/weight')
self.pth_to_tf_var_mapping[f'layer{2 * block_idx + 2}.bias'] = (
f'{res}x{res}/Dense1/bias')
self.downsample = DownsamplingLayer()
def get_nf(self, res):
"""Gets number of feature maps according to current resolution."""
return min(self.fmaps_base // res, self.fmaps_max)
def forward(self, image, lod=None, **_unused_kwargs):
expected_shape = (self.image_channels, self.resolution, self.resolution)
if image.ndim != 4 or image.shape[1:] != expected_shape:
raise ValueError(f'The input tensor should be with shape '
f'[batch_size, channel, height, width], where '
f'`channel` equals to {self.image_channels}, '
f'`height`, `width` equal to {self.resolution}!\n'
f'But `{image.shape}` is received!')
lod = self.lod.cpu().tolist() if lod is None else lod
if lod + self.init_res_log2 > self.final_res_log2:
raise ValueError(f'Maximum level-of-detail (lod) is '
f'{self.final_res_log2 - self.init_res_log2}, '
f'but `{lod}` is received!')
lod = self.lod.cpu().tolist()
for res_log2 in range(self.final_res_log2, self.init_res_log2 - 1, -1):
block_idx = current_lod = self.final_res_log2 - res_log2
if current_lod <= lod < current_lod + 1:
x = self.__getattr__(f'input{block_idx}')(image)
elif current_lod - 1 < lod < current_lod:
alpha = lod - np.floor(lod)
x = (self.__getattr__(f'input{block_idx}')(image) * alpha +
x * (1 - alpha))
if lod < current_lod + 1:
x = self.__getattr__(f'layer{2 * block_idx}')(x)
x = self.__getattr__(f'layer{2 * block_idx + 1}')(x)
if lod > current_lod:
image = self.downsample(image)
x = self.__getattr__(f'layer{2 * block_idx + 2}')(x)
return x
class MiniBatchSTDLayer(nn.Module):
"""Implements the minibatch standard deviation layer."""
def __init__(self, group_size=16, epsilon=1e-8):
super().__init__()
self.group_size = group_size
self.epsilon = epsilon
def forward(self, x):
if self.group_size <= 1:
return x
group_size = min(self.group_size, x.shape[0]) # [NCHW]
y = x.view(group_size, -1, x.shape[1], x.shape[2], x.shape[3]) # [GMCHW]
y = y - torch.mean(y, dim=0, keepdim=True) # [GMCHW]
y = torch.mean(y ** 2, dim=0) # [MCHW]
y = torch.sqrt(y + self.epsilon) # [MCHW]
y = torch.mean(y, dim=[1, 2, 3], keepdim=True) # [M111]
y = y.repeat(group_size, 1, x.shape[2], x.shape[3]) # [N1HW]
return torch.cat([x, y], dim=1)
class DownsamplingLayer(nn.Module):
"""Implements the downsampling layer.
Basically, this layer can be used to downsample feature maps with average
pooling.
"""
def __init__(self, scale_factor=2):
super().__init__()
self.scale_factor = scale_factor
def forward(self, x):
if self.scale_factor <= 1:
return x
return F.avg_pool2d(x,
kernel_size=self.scale_factor,
stride=self.scale_factor,
padding=0)
class ConvBlock(nn.Module):
"""Implements the convolutional block.
Basically, this block executes minibatch standard deviation layer (if
needed), convolutional layer, activation layer, and downsampling layer (
if needed) in sequence.
"""
def __init__(self,
in_channels,
out_channels,
kernel_size=3,
stride=1,
padding=1,
add_bias=True,
downsample=False,
fused_scale=False,
use_wscale=True,
wscale_gain=_WSCALE_GAIN,
activation_type='lrelu',
minibatch_std_group_size=0):
"""Initializes with block settings.
Args:
in_channels: Number of channels of the input tensor.
out_channels: Number of channels of the output tensor.
kernel_size: Size of the convolutional kernels. (default: 3)
stride: Stride parameter for convolution operation. (default: 1)
padding: Padding parameter for convolution operation. (default: 1)
add_bias: Whether to add bias onto the convolutional result.
(default: True)
downsample: Whether to downsample the result after convolution.
(default: False)
fused_scale: Whether to fused `conv2d` and `downsample` together,
resulting in `conv2d` with strides. (default: False)
use_wscale: Whether to use weight scaling. (default: True)
wscale_gain: Gain factor for weight scaling. (default: _WSCALE_GAIN)
activation_type: Type of activation. Support `linear` and `lrelu`.
(default: `lrelu`)
minibatch_std_group_size: Group size for the minibatch standard
deviation layer. 0 means disable. (default: 0)
Raises:
NotImplementedError: If the `activation_type` is not supported.
"""
super().__init__()
if minibatch_std_group_size > 1:
in_channels = in_channels + 1
self.mbstd = MiniBatchSTDLayer(group_size=minibatch_std_group_size)
else:
self.mbstd = nn.Identity()
if downsample and not fused_scale:
self.downsample = DownsamplingLayer()
else:
self.downsample = nn.Identity()
if downsample and fused_scale:
self.use_stride = True
self.stride = 2
self.padding = 1
else:
self.use_stride = False
self.stride = stride
self.padding = padding
weight_shape = (out_channels, in_channels, kernel_size, kernel_size)
fan_in = kernel_size * kernel_size * in_channels
wscale = wscale_gain / np.sqrt(fan_in)
if use_wscale:
self.weight = nn.Parameter(torch.randn(*weight_shape))
self.wscale = wscale
else:
self.weight = nn.Parameter(torch.randn(*weight_shape) * wscale)
self.wscale = 1.0
if add_bias:
self.bias = nn.Parameter(torch.zeros(out_channels))
else:
self.bias = None
if activation_type == 'linear':
self.activate = nn.Identity()
elif activation_type == 'lrelu':
self.activate = nn.LeakyReLU(negative_slope=0.2, inplace=True)
else:
raise NotImplementedError(f'Not implemented activation function: '
f'`{activation_type}`!')
def forward(self, x):
x = self.mbstd(x)
weight = self.weight * self.wscale
if self.use_stride:
weight = F.pad(weight, (1, 1, 1, 1, 0, 0, 0, 0), 'constant', 0.0)
weight = (weight[:, :, 1:, 1:] + weight[:, :, :-1, 1:] +
weight[:, :, 1:, :-1] + weight[:, :, :-1, :-1]) * 0.25
x = F.conv2d(x,
weight=weight,
bias=self.bias,
stride=self.stride,
padding=self.padding)
x = self.activate(x)
x = self.downsample(x)
return x
class DenseBlock(nn.Module):
"""Implements the dense block.
Basically, this block executes fully-connected layer, and activation layer.
"""
def __init__(self,
in_channels,
out_channels,
add_bias=True,
use_wscale=True,
wscale_gain=_WSCALE_GAIN,
activation_type='lrelu'):
"""Initializes with block settings.
Args:
in_channels: Number of channels of the input tensor.
out_channels: Number of channels of the output tensor.
add_bias: Whether to add bias onto the fully-connected result.
(default: True)
use_wscale: Whether to use weight scaling. (default: True)
wscale_gain: Gain factor for weight scaling. (default: _WSCALE_GAIN)
activation_type: Type of activation. Support `linear` and `lrelu`.
(default: `lrelu`)
Raises:
NotImplementedError: If the `activation_type` is not supported.
"""
super().__init__()
weight_shape = (out_channels, in_channels)
wscale = wscale_gain / np.sqrt(in_channels)
if use_wscale:
self.weight = nn.Parameter(torch.randn(*weight_shape))
self.wscale = wscale
else:
self.weight = nn.Parameter(torch.randn(*weight_shape) * wscale)
self.wscale = 1.0
if add_bias:
self.bias = nn.Parameter(torch.zeros(out_channels))
else:
self.bias = None
if activation_type == 'linear':
self.activate = nn.Identity()
elif activation_type == 'lrelu':
self.activate = nn.LeakyReLU(negative_slope=0.2, inplace=True)
else:
raise NotImplementedError(f'Not implemented activation function: '
f'`{activation_type}`!')
def forward(self, x):
if x.ndim != 2:
x = x.view(x.shape[0], -1)
x = F.linear(x, weight=self.weight * self.wscale, bias=self.bias)
x = self.activate(x)
return x
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