arcface_model.py

from torch.nn import Linear, Conv2d, BatchNorm1d, BatchNorm2d, PReLU, ReLU, Sigmoid, Dropout2d, Dropout, AvgPool2d, MaxPool2d, AdaptiveAvgPool2d, Sequential, Module, Parameter, ModuleList
import torch.nn.functional as F
import torch
from collections import namedtuple
import math
import pdb
import numpy as np
import time
import re
import collections
##################################  Original Arcface Model #############################################################

class Flatten(Module):
    def forward(self, input):
        return input.view(input.size(0), -1)

def l2_norm(input,axis=1):
    norm = torch.norm(input,2,axis,True)
    output = torch.div(input, norm)
    return output

class SEModule(Module):
    def __init__(self, channels, reduction):
        super(SEModule, self).__init__()
        self.avg_pool = AdaptiveAvgPool2d(1)
        self.fc1 = Conv2d(
            channels, channels // reduction, kernel_size=1, padding=0 ,bias=False)
        self.relu = ReLU(inplace=True)
        self.fc2 = Conv2d(
            channels // reduction, channels, kernel_size=1, padding=0 ,bias=False)
        self.sigmoid = Sigmoid()

    def forward(self, x):
        module_input = x
        x = self.avg_pool(x)
        x = self.fc1(x)
        x = self.relu(x)
        x = self.fc2(x)
        x = self.sigmoid(x)
        return module_input * x

class bottleneck_IR(Module):
    def __init__(self, in_channel, depth, stride):
        super(bottleneck_IR, self).__init__()
        #if in_channel == depth:
        if stride == 1:
            self.shortcut_layer = MaxPool2d(1, stride)
        else:
            self.shortcut_layer = Sequential(
                Conv2d(in_channel, depth, (1, 1), stride ,bias=False), BatchNorm2d(depth))
        self.res_layer = Sequential(
            BatchNorm2d(in_channel),
            Conv2d(in_channel, depth, (3, 3), (1, 1), 1 ,bias=False),
            BatchNorm2d(depth),
            PReLU(depth),
            Conv2d(depth, depth, (3, 3), stride, 1 ,bias=False),
            BatchNorm2d(depth))

    def forward(self, x):
        shortcut = self.shortcut_layer(x)
        res = self.res_layer(x)
        return res + shortcut

class bottleneck_IR_SE(Module):
    def __init__(self, in_channel, depth, stride):
        super(bottleneck_IR_SE, self).__init__()
        #if in_channel == depth:
        if stride == 1:
            self.shortcut_layer = MaxPool2d(1, stride)
        else:
            self.shortcut_layer = Sequential(
                Conv2d(in_channel, depth, (1, 1), stride ,bias=False), 
                BatchNorm2d(depth))
        self.res_layer = Sequential(
            BatchNorm2d(in_channel),
            Conv2d(in_channel, depth, (3,3), (1,1),1 ,bias=False),
            BatchNorm2d(depth),
            PReLU(depth),
            Conv2d(depth, depth, (3,3), stride, 1 ,bias=False),
            BatchNorm2d(depth),
            SEModule(depth,16)
            )
    def forward(self,x):
        shortcut = self.shortcut_layer(x)
        res = self.res_layer(x)
        return res + shortcut

class Bottleneck(namedtuple('Block', ['in_channel', 'depth', 'stride'])):
    '''A named tuple describing a ResNet block.'''
    
def get_block(in_channel, depth, num_units, stride = 2):
  return [Bottleneck(in_channel, depth, stride)] + [Bottleneck(depth, depth, 1) for i in range(num_units-1)]

def get_blocks(num_layers):
    if num_layers == 50:
        blocks = [
            get_block(in_channel=64, depth=64, num_units = 3),
            get_block(in_channel=64, depth=128, num_units=4),
            get_block(in_channel=128, depth=256, num_units=14),
            get_block(in_channel=256, depth=512, num_units=3)
        ]
    elif num_layers == 100:
        blocks = [
            get_block(in_channel=64, depth=64, num_units=3),
            get_block(in_channel=64, depth=128, num_units=13),
            get_block(in_channel=128, depth=256, num_units=30),
            get_block(in_channel=256, depth=512, num_units=3)
        ]
    elif num_layers == 152:
        blocks = [
            get_block(in_channel=64, depth=64, num_units=3),
            get_block(in_channel=64, depth=128, num_units=8),
            get_block(in_channel=128, depth=256, num_units=36),
            get_block(in_channel=256, depth=512, num_units=3)
        ]
    return blocks

class Backbone(Module):
    def __init__(self, num_layers, drop_ratio, mode='ir'):
        super(Backbone, self).__init__()
        assert num_layers in [50, 100, 152], 'num_layers should be 50,100, or 152'
        assert mode in ['ir', 'ir_se'], 'mode should be ir or ir_se'
        blocks = get_blocks(num_layers)
        if mode == 'ir':
            unit_module = bottleneck_IR
        elif mode == 'ir_se':
            unit_module = bottleneck_IR_SE
        self.input_layer = Sequential(Conv2d(3, 64, (3, 3), 1, 1 ,bias=False), 
                                      BatchNorm2d(64), 
                                      PReLU(64))
        self.output_layer = Sequential(BatchNorm2d(512), 
                                       Dropout(drop_ratio),
                                       Flatten(),
                                       Linear(512 * 7 * 7, 512),
                                       BatchNorm1d(512))
        modules = []
        for block in blocks:
            for bottleneck in block:
                modules.append(
                    unit_module(bottleneck.in_channel,
                                bottleneck.depth,
                                bottleneck.stride))
        self.body = Sequential(*modules)
    
    def forward(self, x):
        x = self.input_layer(x)
        x = self.body(x)
        x = self.output_layer(x)
        return l2_norm(x)

##################################  Arcface head #############################################################

class Arcface(Module):
    # implementation of additive margin softmax loss in https://arxiv.org/abs/1801.05599    
    def __init__(self, embedding_size=512, classnum=51332,  s=64., m=0.5):
        super(Arcface, self).__init__()
        self.classnum = classnum
        self.kernel = Parameter(torch.Tensor(embedding_size,classnum))
        # initial kernel
        self.kernel.data.uniform_(-1, 1).renorm_(2,1,1e-5).mul_(1e5)
        self.m = m # the margin value, default is 0.5
        self.s = s # scalar value default is 64, see normface https://arxiv.org/abs/1704.06369
        self.cos_m = math.cos(m)
        self.sin_m = math.sin(m)
        self.mm = self.sin_m * m
        self.threshold = math.cos(math.pi - m)
    def forward(self, embbedings, label):
        # weights norm
        nB = len(embbedings)
        kernel_norm = l2_norm(self.kernel,axis=0)
        # cos(theta+m)
        cos_theta = torch.mm(embbedings,kernel_norm)
        cos_theta = cos_theta.clamp(-1,1) # for numerical stability
        cos_theta_2 = torch.pow(cos_theta, 2)
        sin_theta_2 = 1 - cos_theta_2
        sin_theta = torch.sqrt(sin_theta_2)
        cos_theta_m = (cos_theta * self.cos_m - sin_theta * self.sin_m)
        # this condition controls the theta+m should in range [0, pi]
        #      0<=theta+m<=pi
        #     -m<=theta<=pi-m
        cond_v = cos_theta - self.threshold
        cond_mask = cond_v <= 0
        keep_val = (cos_theta - self.mm) # when theta not in [0,pi], use cosface instead
        cos_theta_m[cond_mask] = keep_val[cond_mask]
        output = cos_theta * 1.0 # a little bit hacky way to prevent in_place operation on cos_theta
        idx_ = torch.arange(0, nB, dtype=torch.long)
        output[idx_, label] = cos_theta_m[idx_, label]
        output *= self.s # scale up in order to make softmax work, first introduced in normface
        return output