splat.py

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# encoding: utf-8
"""
@author:  xingyu liao
@contact: sherlockliao01@gmail.com
"""
 
import torch
import torch.nn.functional as F
from torch import nn
from torch.nn import Conv2d, ReLU
from torch.nn.modules.utils import _pair
from fastreid.layers import get_norm
 
 
class SplAtConv2d(nn.Module):
    """Split-Attention Conv2d
    """
 
    def __init__(self, in_channels, channels, kernel_size, stride=(1, 1), padding=(0, 0),
                 dilation=(1, 1), groups=1, bias=True,
                 radix=2, reduction_factor=4,
                 rectify=False, rectify_avg=False, norm_layer=None, num_splits=1,
                 dropblock_prob=0.0, **kwargs):
        super(SplAtConv2d, self).__init__()
        padding = _pair(padding)
        self.rectify = rectify and (padding[0] > 0 or padding[1] > 0)
        self.rectify_avg = rectify_avg
        inter_channels = max(in_channels * radix // reduction_factor, 32)
        self.radix = radix
        self.cardinality = groups
        self.channels = channels
        self.dropblock_prob = dropblock_prob
        if self.rectify:
            from rfconv import RFConv2d
            self.conv = RFConv2d(in_channels, channels * radix, kernel_size, stride, padding, dilation,
                                 groups=groups * radix, bias=bias, average_mode=rectify_avg, **kwargs)
        else:
            self.conv = Conv2d(in_channels, channels * radix, kernel_size, stride, padding, dilation,
                               groups=groups * radix, bias=bias, **kwargs)
        self.use_bn = norm_layer is not None
        if self.use_bn:
            self.bn0 = get_norm(norm_layer, channels * radix)
        self.relu = ReLU(inplace=True)
        self.fc1 = Conv2d(channels, inter_channels, 1, groups=self.cardinality)
        if self.use_bn:
            self.bn1 = get_norm(norm_layer, inter_channels)
        self.fc2 = Conv2d(inter_channels, channels * radix, 1, groups=self.cardinality)
 
        self.rsoftmax = rSoftMax(radix, groups)
 
    def forward(self, x):
        x = self.conv(x)
        if self.use_bn:
            x = self.bn0(x)
        if self.dropblock_prob > 0.0:
            x = self.dropblock(x)
        x = self.relu(x)
 
        batch, rchannel = x.shape[:2]
        if self.radix > 1:
            splited = torch.split(x, rchannel // self.radix, dim=1)
            gap = sum(splited)
        else:
            gap = x
        gap = F.adaptive_avg_pool2d(gap, 1)
        gap = self.fc1(gap)
 
        if self.use_bn:
            gap = self.bn1(gap)
        gap = self.relu(gap)
 
        atten = self.fc2(gap)
        atten = self.rsoftmax(atten).view(batch, -1, 1, 1)
 
        if self.radix > 1:
            attens = torch.split(atten, rchannel // self.radix, dim=1)
            out = sum([att * split for (att, split) in zip(attens, splited)])
        else:
            out = atten * x
        return out.contiguous()
 
 
class rSoftMax(nn.Module):
    def __init__(self, radix, cardinality):
        super().__init__()
        self.radix = radix
        self.cardinality = cardinality
 
    def forward(self, x):
        batch = x.size(0)
        if self.radix > 1:
            x = x.view(batch, self.cardinality, self.radix, -1).transpose(1, 2)
            x = F.softmax(x, dim=1)
            x = x.reshape(batch, -1)
        else:
            x = torch.sigmoid(x)
        return x