aglnet.py

"""
Paper:      AGLNet: Towards real-time semantic segmentation of self-driving images 
                    via attention-guided lightweight network
Url:        https://www.sciencedirect.com/science/article/abs/pii/S1568494620306207
Create by:  zh320
Date:       2023/08/27
"""

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

from .modules import conv1x1, ConvBNAct, Activation, channel_shuffle
from .enet import InitialBlock as DownsamplingUnit
from .lednet import SSnbtUnit


class AGLNet(nn.Module):
    def __init__(self, num_class=1, n_channel=3, act_type='relu'):
        super(AGLNet, self).__init__()
        self.layer1 = DownsamplingUnit(n_channel, 32, act_type=act_type)
        self.layer2_4 = build_blocks(SSnbtUnit, 32, 3, act_type=act_type)
        self.layer5 = DownsamplingUnit(32, 64, act_type=act_type)
        self.layer6_7 = build_blocks(SSnbtUnit, 64, 2, act_type=act_type)
        self.layer8 = DownsamplingUnit(64, 128, act_type=act_type)
        self.layer9_16 = build_blocks(SSnbtUnit, 128, 8, dilations=[1,2,5,9,2,5,9,17], act_type=act_type)
        self.layer17 = FAPM(128, act_type=act_type)
        self.layer18 = GAUM(64, 128, 64, act_type=act_type)
        self.layer19 = GAUM(32, 64, 32, act_type=act_type)
        self.layer20 = conv1x1(32, num_class)

    def forward(self, x):
        size = x.size()[2:]
        
        # Stage 1
        x = self.layer1(x)
        x = self.layer2_4(x)
        x_s1 = x

        # Stage 2
        x = self.layer5(x)
        x = self.layer6_7(x)
        x_s2 = x

        # Stage 3
        x = self.layer8(x)
        x = self.layer9_16(x)
        
        x = self.layer17(x)
        x = self.layer18(x, x_s2)
        x = self.layer19(x, x_s1)
        
        x = self.layer20(x)
        x = F.interpolate(x, size, mode='bilinear', align_corners=True)
        
        return x


def build_blocks(block, channels, num_block, dilations=[], act_type='relu'):
    if len(dilations) == 0:
        dilations = [1 for _ in range(num_block)]
    else:
        if len(dilations) != num_block:
            raise ValueError(f'Number of dilation should be equal to number of blocks')

    layers = []
    for i in range(num_block):
        layers.append(block(channels, dilation=dilations[i], act_type=act_type))
    return  nn.Sequential(*layers)


class FAPM(nn.Module):
    def __init__(self, channels, act_type):
        super(FAPM, self).__init__()
        self.pfa = PyramidFeatureAttention(channels, act_type)
        self.conv = conv1x1(1, channels)
        self.gp = nn.Sequential(
                            nn.AdaptiveAvgPool2d(1),
                            conv1x1(channels, channels),
                        )
        
    def forward(self, x):
        size = x.size()[2:]
        x_pfa = self.pfa(x)
        x_pfa = self.conv(x_pfa)

        x_gp = self.gp(x)
        x_gp = F.interpolate(x_gp, size, mode='bilinear', align_corners=True)

        x = x * x_pfa
        x += x_gp

        return x


class PyramidFeatureAttention(nn.Module):
    def __init__(self, channels, act_type):
        super(PyramidFeatureAttention, self).__init__()
        self.conv11 = ConvBNAct(channels, 1, (1,7), 2, act_type=act_type)
        self.conv12 = ConvBNAct(1, 1, (7,1), 1, act_type=act_type)
        self.conv21 = ConvBNAct(1, 1, (1,5), 2, act_type=act_type)
        self.conv22 = ConvBNAct(1, 1, (5,1), 1, act_type=act_type)
        self.conv31 = ConvBNAct(1, 1, (1,3), 2, act_type=act_type)
        self.conv32 = ConvBNAct(1, 1, (3,1), 1, act_type=act_type)

    def forward(self, x):
        size0 = x.size()[2:]

        x = self.conv11(x)
        size1 = x.size()[2:]
        x1 = self.conv12(x)
        
        x = self.conv21(x)
        size2 = x.size()[2:]
        x2 = self.conv22(x)
        
        x = self.conv31(x)
        x = self.conv32(x)
        x = F.interpolate(x, size2, mode='bilinear', align_corners=True)

        x += x2
        x = F.interpolate(x, size1, mode='bilinear', align_corners=True)
        
        x += x1
        x = F.interpolate(x, size0, mode='bilinear', align_corners=True)
        
        return x


class GAUM(nn.Module):
    def __init__(self, low_channels, high_channels, out_channels, act_type):
        super(GAUM, self).__init__()
        self.up_conv = nn.Sequential(
                                nn.ConvTranspose2d(high_channels, low_channels, 3, 2, 1, 1),
                                nn.BatchNorm2d(low_channels),
                                Activation(act_type)
                        )
        self.sab = SpatialAttentionBlock(low_channels)
        self.cab = ChannelAttentionBlock(low_channels, out_channels)

    def forward(self, x_high, x_low):
        x_low = self.sab(x_low)
        x_high = self.up_conv(x_high)
        x_skip = x_high
        
        x_high = x_high * x_low
        x_skip2 = x_high
        
        x_high = self.cab(x_high)
        x_high = x_high * x_skip2
        
        x_high += x_skip
        return x_high


class SpatialAttentionBlock(nn.Module):
    def __init__(self, channels):
        super(SpatialAttentionBlock, self).__init__()
        self.conv = conv1x1(channels, 1)
        
    def forward(self, x):
        x_s = self.conv(x)
        x_s = torch.sigmoid(x_s)
        x = x * x_s
        return x


class ChannelAttentionBlock(nn.Module):
    def __init__(self, in_channels, out_channels):
        super(ChannelAttentionBlock, self).__init__()
        self.pool = nn.AdaptiveAvgPool2d(1)
        self.conv = conv1x1(in_channels, out_channels)
        
    def forward(self, x):
        x_c = self.pool(x)
        x_c = self.conv(x_c)
        x_c = torch.sigmoid(x_c)
        x = x * x_c
        return x