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xceptionnet.py
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"""
Creates an Xception Model as defined in:
Francois Chollet
Xception: Deep Learning with Depthwise Separable Convolutions
https://arxiv.org/pdf/1610.02357.pdf
This weights ported from the Keras implementation. Achieves the following performance on the validation set:
Loss:0.9173 Prec@1:78.892 Prec@5:94.292
REMEMBER to set your image size to 3x299x299 for both test and validation
normalize = transforms.Normalize(mean=[0.5, 0.5, 0.5],
std=[0.5, 0.5, 0.5])
The resize parameter of the validation transform should be 333, and make sure to center crop at 299x299
"""
import math
import torch.nn as nn
import torch.nn.functional as F
import torch.utils.model_zoo as model_zoo
from torch.nn import init
import torch
__all__ = ['xception']
model_urls = {
'xception': 'https://www.dropbox.com/s/1hplpzet9d7dv29/xception-c0a72b38.pth.tar?dl=1'
}
class SeparableConv2d(nn.Module):
def __init__(self, in_channels, out_channels, kernel_size=1, stride=1, padding=0, dilation=1, bias=False):
super(SeparableConv2d, self).__init__()
self.conv1 = nn.Conv2d(in_channels, in_channels, kernel_size, stride, padding, dilation, groups=in_channels,
bias=bias)
self.pointwise = nn.Conv2d(in_channels, out_channels, 1, 1, 0, 1, 1, bias=bias)
def forward(self, x):
x = self.conv1(x)
x = self.pointwise(x)
return x
class Block(nn.Module):
def __init__(self, in_filters, out_filters, reps, strides=1, start_with_relu=True, grow_first=True):
super(Block, self).__init__()
if out_filters != in_filters or strides != 1:
self.skip = nn.Conv2d(in_filters, out_filters, 1, stride=strides, bias=False)
self.skipbn = nn.BatchNorm2d(out_filters)
else:
self.skip = None
self.relu = nn.ReLU(inplace=True)
rep = []
filters = in_filters
if grow_first:
rep.append(self.relu)
rep.append(SeparableConv2d(in_filters, out_filters, 3, stride=1, padding=1, bias=False))
rep.append(nn.BatchNorm2d(out_filters))
filters = out_filters
for i in range(reps - 1):
rep.append(self.relu)
rep.append(SeparableConv2d(filters, filters, 3, stride=1, padding=1, bias=False))
rep.append(nn.BatchNorm2d(filters))
if not grow_first:
rep.append(self.relu)
rep.append(SeparableConv2d(in_filters, out_filters, 3, stride=1, padding=1, bias=False))
rep.append(nn.BatchNorm2d(out_filters))
if not start_with_relu:
rep = rep[1:]
else:
rep[0] = nn.ReLU(inplace=False)
if strides != 1:
rep.append(nn.MaxPool2d(3, strides, 1))
self.rep = nn.Sequential(*rep)
def forward(self, inp):
x = self.rep(inp)
if self.skip is not None:
skip = self.skip(inp)
skip = self.skipbn(skip)
else:
skip = inp
x += skip
return x
class Xception(nn.Module):
"""
Xception optimized for the ImageNet dataset, as specified in
https://arxiv.org/pdf/1610.02357.pdf
"""
def __init__(self, num_classes=1000):
""" Constructor
Args:
num_classes: number of classes
"""
super(Xception, self).__init__()
self.num_classes = num_classes
self.conv1 = nn.Conv2d(3, 32, 3, 2, 0, bias=False)
self.bn1 = nn.BatchNorm2d(32)
self.relu = nn.ReLU(inplace=True)
self.conv2 = nn.Conv2d(32, 64, 3, bias=False)
self.bn2 = nn.BatchNorm2d(64)
# do relu here
self.block1 = Block(64, 128, 2, 2, start_with_relu=False, grow_first=True)
self.block2 = Block(128, 256, 2, 2, start_with_relu=True, grow_first=True)
self.block3 = Block(256, 728, 2, 2, start_with_relu=True, grow_first=True)
self.block4 = Block(728, 728, 3, 1, start_with_relu=True, grow_first=True)
self.block5 = Block(728, 728, 3, 1, start_with_relu=True, grow_first=True)
self.block6 = Block(728, 728, 3, 1, start_with_relu=True, grow_first=True)
self.block7 = Block(728, 728, 3, 1, start_with_relu=True, grow_first=True)
self.block8 = Block(728, 728, 3, 1, start_with_relu=True, grow_first=True)
self.block9 = Block(728, 728, 3, 1, start_with_relu=True, grow_first=True)
self.block10 = Block(728, 728, 3, 1, start_with_relu=True, grow_first=True)
self.block11 = Block(728, 728, 3, 1, start_with_relu=True, grow_first=True)
self.block12 = Block(728, 1024, 2, 2, start_with_relu=True, grow_first=False)
self.conv3 = SeparableConv2d(1024, 1536, 3, 1, 1)
self.bn3 = nn.BatchNorm2d(1536)
# do relu here
self.conv4 = SeparableConv2d(1536, 2048, 3, 1, 1)
self.bn4 = nn.BatchNorm2d(2048)
self.fc = nn.Linear(2048, num_classes)
# ------- init weights --------
for m in self.modules():
if isinstance(m, nn.Conv2d):
n = m.kernel_size[0] * m.kernel_size[1] * m.out_channels
m.weight.data.normal_(0, math.sqrt(2. / n))
elif isinstance(m, nn.BatchNorm2d):
m.weight.data.fill_(1)
m.bias.data.zero_()
# -----------------------------
def forward(self, x):
x = self.conv1(x)
x = self.bn1(x)
x = self.relu(x)
x = self.conv2(x)
x = self.bn2(x)
x = self.relu(x)
x = self.block1(x)
x = self.block2(x)
x = self.block3(x)
x = self.block4(x)
x = self.block5(x)
x = self.block6(x)
x = self.block7(x)
x = self.block8(x)
x = self.block9(x)
x = self.block10(x)
x = self.block11(x)
x = self.block12(x)
x = self.conv3(x)
x = self.bn3(x)
x = self.relu(x)
x = self.conv4(x)
x = self.bn4(x)
x = self.relu(x)
x = F.adaptive_avg_pool2d(x, (1, 1))
x = x.view(x.size(0), -1)
x = self.fc(x)
return x
def xception(pretrained=False, **kwargs):
"""
Construct Xception.
"""
model = Xception(**kwargs)
if pretrained:
model.load_state_dict(model_zoo.load_url(model_urls['xception']))
return model