hardnet.py

import numpy as np
import torch
import torch.nn as nn
import torch.nn.functional as F


class ConvLayer(nn.Sequential):
    def __init__(self, in_channels, out_channels, kernel=3, stride=1, dropout=0.1):
        super().__init__()
        self.add_module('conv', nn.Conv2d(in_channels, out_channels, kernel_size=kernel,
                                          stride=stride, padding=kernel//2, bias = False))
        self.add_module('norm', nn.BatchNorm2d(out_channels))
        self.add_module('relu', nn.ReLU(inplace=True))

    def forward(self, x):
        return super().forward(x)
        


class HarDBlock(nn.Module):
    def get_link(self, layer, base_ch, growth_rate, grmul):
        if layer == 0:
          return base_ch, 0, []
        out_channels = growth_rate
        link = []
        for i in range(10):
          dv = 2 ** i
          if layer % dv == 0:
            k = layer - dv
            link.append(k)
            if i > 0:
                out_channels *= grmul
        out_channels = int(int(out_channels + 1) / 2) * 2
        in_channels = 0
        for i in link:
          ch,_,_ = self.get_link(i, base_ch, growth_rate, grmul)
          in_channels += ch
        return out_channels, in_channels, link

    def get_out_ch(self):
        return self.out_channels
 
    def __init__(self, in_channels, growth_rate, grmul, n_layers, keepBase=False, residual_out=False):
        super().__init__()
        self.keepBase = keepBase
        self.links = []
        layers_ = []
        self.out_channels = 0 # if upsample else in_channels
        for i in range(n_layers):
          outch, inch, link = self.get_link(i+1, in_channels, growth_rate, grmul)
          self.links.append(link)
          use_relu = residual_out
          layers_.append(ConvLayer(inch, outch))
          if (i % 2 == 0) or (i == n_layers - 1):
            self.out_channels += outch
        #print("Blk out =",self.out_channels)
        self.layers = nn.ModuleList(layers_)


    def forward(self, x):
        layers_ = [x]
        for layer in range(len(self.layers)):
            link = self.links[layer]
            tin = []
            for i in link:
                tin.append(layers_[i])
            if len(tin) > 1:
                x = torch.cat(tin, 1)
            else:
                x = tin[0]
            out = self.layers[layer](x)
            layers_.append(out)
        t = len(layers_)
        out_ = []
        for i in range(t):
          if (i == 0 and self.keepBase) or \
             (i == t-1) or (i%2 == 1):
              out_.append(layers_[i])
        out = torch.cat(out_, 1)
        return out



class TransitionUp(nn.Module):
    def __init__(self, in_channels, out_channels):
        super().__init__()
        #print("upsample",in_channels, out_channels)

    def forward(self, x, skip, concat=True):
        out = F.interpolate(
                x,
                size=(skip.size(2), skip.size(3)),
                mode="bilinear",
                align_corners=True,
                            )
        if concat:                            
          out = torch.cat([out, skip], 1)
          
        return out

class hardnet(nn.Module):
    def __init__(self):
        super(hardnet, self).__init__()

        first_ch  = [16,24,32,48]
        ch_list = [  64, 96, 160, 224, 320]
        grmul = 1.7
        gr       = [  10,16,18,24,32]
        n_layers = [   4, 4, 8, 8, 8]

        blks = len(n_layers) 
        self.shortcut_layers = []

        self.base = nn.ModuleList([])
        self.base.append (
             ConvLayer(in_channels=3, out_channels=first_ch[0], kernel=3,
                       stride=2) )
        self.base.append ( ConvLayer(first_ch[0], first_ch[1],  kernel=3) )
        self.base.append ( ConvLayer(first_ch[1], first_ch[2],  kernel=3, stride=2) )
        self.base.append ( ConvLayer(first_ch[2], first_ch[3],  kernel=3) )

        skip_connection_channel_counts = []
        ch = first_ch[3]
        for i in range(blks):
            blk = HarDBlock(ch, gr[i], grmul, n_layers[i])
            ch = blk.get_out_ch()
            skip_connection_channel_counts.append(ch)
            self.base.append ( blk )
            if i < blks-1:
              self.shortcut_layers.append(len(self.base)-1)

            self.base.append ( ConvLayer(ch, ch_list[i], kernel=1) )
            ch = ch_list[i]
            
            if i < blks-1:            
              self.base.append ( nn.AvgPool2d(kernel_size=2, stride=2) )


        cur_channels_count = ch
        prev_block_channels = ch
        n_blocks = blks-1
        self.n_blocks =  n_blocks

        #######################
        #   Upsampling path   #
        #######################

        self.transUpBlocks = nn.ModuleList([])
        self.denseBlocksUp = nn.ModuleList([])
        self.conv1x1_up    = nn.ModuleList([])
        
        for i in range(n_blocks-1,-1,-1):
            self.transUpBlocks.append(TransitionUp(prev_block_channels, prev_block_channels))
            cur_channels_count = prev_block_channels + skip_connection_channel_counts[i]
            self.conv1x1_up.append(ConvLayer(cur_channels_count, cur_channels_count//2, kernel=1))
            cur_channels_count = cur_channels_count//2

            blk = HarDBlock(cur_channels_count, gr[i], grmul, n_layers[i])
            
            self.denseBlocksUp.append(blk)
            prev_block_channels = blk.get_out_ch()
            cur_channels_count = prev_block_channels


    def forward(self, x):
        
        skip_connections = []
        size_in = x.size()
        
        
        for i in range(len(self.base)):
            x = self.base[i](x)
            if i in self.shortcut_layers:
                skip_connections.append(x)
        out = x
        
        for i in range(self.n_blocks):
            skip = skip_connections.pop()
            out = self.transUpBlocks[i](out, skip, True)
            out = self.conv1x1_up[i](out)
            out = self.denseBlocksUp[i](out)
        
        return out


def get_hard_net(num_layers, cfg):
  model = hardnet()
  return model