src/modules/appearance_feature_extractor.py

# coding: utf-8

"""
Appearance extractor(F) defined in paper, which maps the source image s to a 3D appearance feature volume.
"""

import torch
from torch import nn
from .util import SameBlock2d, DownBlock2d, ResBlock3d


class AppearanceFeatureExtractor(nn.Module):

    def __init__(self, image_channel, block_expansion, num_down_blocks, max_features, reshape_channel, reshape_depth, num_resblocks):
        super(AppearanceFeatureExtractor, self).__init__()
        self.image_channel = image_channel
        self.block_expansion = block_expansion
        self.num_down_blocks = num_down_blocks
        self.max_features = max_features
        self.reshape_channel = reshape_channel
        self.reshape_depth = reshape_depth
    #  image_channel: 3
    # block_expansion: 64
    # num_down_blocks: 2
    # max_features: 512
    # reshape_channel: 32
    # reshape_depth: 16
    # num_resblocks: 6
        self.first = SameBlock2d(image_channel, block_expansion, kernel_size=(3, 3), padding=(1, 1))

        down_blocks = []
        for i in range(num_down_blocks):
            in_features = min(max_features, block_expansion * (2 ** i))
            out_features = min(max_features, block_expansion * (2 ** (i + 1)))
            down_blocks.append(DownBlock2d(in_features, out_features, kernel_size=(3, 3), padding=(1, 1)))
        self.down_blocks = nn.ModuleList(down_blocks)

        self.second = nn.Conv2d(in_channels=out_features, out_channels=max_features, kernel_size=1, stride=1)

        self.resblocks_3d = torch.nn.Sequential()
        for i in range(num_resblocks):
            self.resblocks_3d.add_module('3dr' + str(i), ResBlock3d(reshape_channel, kernel_size=3, padding=1))

    def forward(self, source_image):
        out = self.first(source_image)  # Bx3x256x256 -> Bx64x256x256

        for i in range(len(self.down_blocks)):
            out = self.down_blocks[i](out)
        out = self.second(out)
        bs, c, h, w = out.shape  # ->Bx512x64x64

        f_s = out.view(bs, self.reshape_channel, self.reshape_depth, h, w)  # ->Bx32x16x64x64
        f_s = self.resblocks_3d(f_s)  # ->Bx32x16x64x64
        return f_s