- 前置知识：PyTorch, MobileNetV2
- 作者：Mingxing Tan, Quoc V. Le
- 文章链接
- 代码链接
在深度神经网络设计的时候，一般我们会通过调整输入图像的大小、网络的深度和宽度（卷积通道数）来增强网络性能。但是，这三者调整的综合关系并没有人进行探究。在EfficientNet这篇论文中对这三者的相关关系进行了研究。
图1：Scaling对比
如图1所示，作者对比了将深度、宽度以及分辨率放缩后的效果。可以看到，固定三者之中的两个变量，增加深度、宽度和分辨率，都有助于提高模型的性能。
图1：Scaling对比
如图2所示，同时扩大三者之中的两个，也有助于提高模型的性能。同时可以看到，组合不同，效果也不同。
为了探究三者之间的关系，作者提出了Compound Scaling公式，如图3所示。复合系数$\phi$可以由人工确定。
图3：Compound Scaling
整体网络架构没有太多新奇的地方，我们也很难应用这个思想，毕竟我们没有这么多卡用于测试训练。Efficient提供了B0-B7八个模型，这里以B0为例，放上其架构。B0使用的是MobileNetV2的MBConv基础架构
图3：Efficient-B0
class MBConvBlock(nn.Module):
"""Mobile Inverted Residual Bottleneck Block.
Args:
block_args (namedtuple): BlockArgs, defined in utils.py.
global_params (namedtuple): GlobalParam, defined in utils.py.
image_size (tuple or list): [image_height, image_width].
References:
[1] https://arxiv.org/abs/1704.04861 (MobileNet v1)
[2] https://arxiv.org/abs/1801.04381 (MobileNet v2)
[3] https://arxiv.org/abs/1905.02244 (MobileNet v3)
"""
def __init__(self, block_args, global_params, image_size=None):
super().__init__()
self._block_args = block_args
self._bn_mom = 1 - global_params.batch_norm_momentum # pytorch's difference from tensorflow
self._bn_eps = global_params.batch_norm_epsilon
self.has_se = (self._block_args.se_ratio is not None) and (0 < self._block_args.se_ratio <= 1)
self.id_skip = block_args.id_skip # whether to use skip connection and drop connect
# Expansion phase (Inverted Bottleneck)
inp = self._block_args.input_filters # number of input channels
oup = self._block_args.input_filters * self._block_args.expand_ratio # number of output channels
if self._block_args.expand_ratio != 1:
Conv2d = get_same_padding_conv2d(image_size=image_size)
self._expand_conv = Conv2d(in_channels=inp, out_channels=oup, kernel_size=1, bias=False)
self._bn0 = nn.BatchNorm2d(num_features=oup, momentum=self._bn_mom, eps=self._bn_eps)
# image_size = calculate_output_image_size(image_size, 1) <-- this wouldn't modify image_size
# Depthwise convolution phase
k = self._block_args.kernel_size
s = self._block_args.stride
Conv2d = get_same_padding_conv2d(image_size=image_size)
self._depthwise_conv = Conv2d(
in_channels=oup, out_channels=oup, groups=oup, # groups makes it depthwise
kernel_size=k, stride=s, bias=False)
self._bn1 = nn.BatchNorm2d(num_features=oup, momentum=self._bn_mom, eps=self._bn_eps)
image_size = calculate_output_image_size(image_size, s)
# Squeeze and Excitation layer, if desired
if self.has_se:
Conv2d = get_same_padding_conv2d(image_size=(1, 1))
num_squeezed_channels = max(1, int(self._block_args.input_filters * self._block_args.se_ratio))
self._se_reduce = Conv2d(in_channels=oup, out_channels=num_squeezed_channels, kernel_size=1)
self._se_expand = Conv2d(in_channels=num_squeezed_channels, out_channels=oup, kernel_size=1)
# Pointwise convolution phase
final_oup = self._block_args.output_filters
Conv2d = get_same_padding_conv2d(image_size=image_size)
self._project_conv = Conv2d(in_channels=oup, out_channels=final_oup, kernel_size=1, bias=False)
self._bn2 = nn.BatchNorm2d(num_features=final_oup, momentum=self._bn_mom, eps=self._bn_eps)
self._swish = MemoryEfficientSwish()
def forward(self, inputs, drop_connect_rate=None):
"""MBConvBlock's forward function.
Args:
inputs (tensor): Input tensor.
drop_connect_rate (bool): Drop connect rate (float, between 0 and 1).
Returns:
Output of this block after processing.
"""
# Expansion and Depthwise Convolution
x = inputs
if self._block_args.expand_ratio != 1:
x = self._expand_conv(inputs)
x = self._bn0(x)
x = self._swish(x)
x = self._depthwise_conv(x)
x = self._bn1(x)
x = self._swish(x)
# Squeeze and Excitation
if self.has_se:
x_squeezed = F.adaptive_avg_pool2d(x, 1)
x_squeezed = self._se_reduce(x_squeezed)
x_squeezed = self._swish(x_squeezed)
x_squeezed = self._se_expand(x_squeezed)
x = torch.sigmoid(x_squeezed) * x
# Pointwise Convolution
x = self._project_conv(x)
x = self._bn2(x)
# Skip connection and drop connect
input_filters, output_filters = self._block_args.input_filters, self._block_args.output_filters
if self.id_skip and self._block_args.stride == 1 and input_filters == output_filters:
# The combination of skip connection and drop connect brings about stochastic depth.
if drop_connect_rate:
x = drop_connect(x, p=drop_connect_rate, training=self.training)
x = x + inputs # skip connection
return x
def set_swish(self, memory_efficient=True):
"""Sets swish function as memory efficient (for training) or standard (for export).
Args:
memory_efficient (bool): Whether to use memory-efficient version of swish.
"""
self._swish = MemoryEfficientSwish() if memory_efficient else Swish()MBConv架构。
class EfficientNet(nn.Module):
"""EfficientNet model.
Most easily loaded with the .from_name or .from_pretrained methods.
Args:
blocks_args (list[namedtuple]): A list of BlockArgs to construct blocks.
global_params (namedtuple): A set of GlobalParams shared between blocks.
References:
[1] https://arxiv.org/abs/1905.11946 (EfficientNet)
Example:
>>> import torch
>>> from efficientnet.model import EfficientNet
>>> inputs = torch.rand(1, 3, 224, 224)
>>> model = EfficientNet.from_pretrained('efficientnet-b0')
>>> model.eval()
>>> outputs = model(inputs)
"""
def __init__(self, blocks_args=None, global_params=None):
super().__init__()
assert isinstance(blocks_args, list), 'blocks_args should be a list'
assert len(blocks_args) > 0, 'block args must be greater than 0'
self._global_params = global_params
self._blocks_args = blocks_args
# Batch norm parameters
bn_mom = 1 - self._global_params.batch_norm_momentum
bn_eps = self._global_params.batch_norm_epsilon
# Get stem static or dynamic convolution depending on image size
image_size = global_params.image_size
Conv2d = get_same_padding_conv2d(image_size=image_size)
# Stem
in_channels = 3 # rgb
out_channels = round_filters(32, self._global_params) # number of output channels
self._conv_stem = Conv2d(in_channels, out_channels, kernel_size=3, stride=2, bias=False)
self._bn0 = nn.BatchNorm2d(num_features=out_channels, momentum=bn_mom, eps=bn_eps)
image_size = calculate_output_image_size(image_size, 2)
# Build blocks
self._blocks = nn.ModuleList([])
for block_args in self._blocks_args:
# Update block input and output filters based on depth multiplier.
block_args = block_args._replace(
input_filters=round_filters(block_args.input_filters, self._global_params),
output_filters=round_filters(block_args.output_filters, self._global_params),
num_repeat=round_repeats(block_args.num_repeat, self._global_params)
)
# The first block needs to take care of stride and filter size increase.
self._blocks.append(MBConvBlock(block_args, self._global_params, image_size=image_size))
image_size = calculate_output_image_size(image_size, block_args.stride)
if block_args.num_repeat > 1: # modify block_args to keep same output size
block_args = block_args._replace(input_filters=block_args.output_filters, stride=1)
for _ in range(block_args.num_repeat - 1):
self._blocks.append(MBConvBlock(block_args, self._global_params, image_size=image_size))
# image_size = calculate_output_image_size(image_size, block_args.stride) # stride = 1
# Head
in_channels = block_args.output_filters # output of final block
out_channels = round_filters(1280, self._global_params)
Conv2d = get_same_padding_conv2d(image_size=image_size)
self._conv_head = Conv2d(in_channels, out_channels, kernel_size=1, bias=False)
self._bn1 = nn.BatchNorm2d(num_features=out_channels, momentum=bn_mom, eps=bn_eps)
# Final linear layer
self._avg_pooling = nn.AdaptiveAvgPool2d(1)
if self._global_params.include_top:
self._dropout = nn.Dropout(self._global_params.dropout_rate)
self._fc = nn.Linear(out_channels, self._global_params.num_classes)
# set activation to memory efficient swish by default
self._swish = MemoryEfficientSwish()
def set_swish(self, memory_efficient=True):
"""Sets swish function as memory efficient (for training) or standard (for export).
Args:
memory_efficient (bool): Whether to use memory-efficient version of swish.
"""
self._swish = MemoryEfficientSwish() if memory_efficient else Swish()
for block in self._blocks:
block.set_swish(memory_efficient)
def extract_endpoints(self, inputs):
"""Use convolution layer to extract features
from reduction levels i in [1, 2, 3, 4, 5].
Args:
inputs (tensor): Input tensor.
Returns:
Dictionary of last intermediate features
with reduction levels i in [1, 2, 3, 4, 5].
Example:
>>> import torch
>>> from efficientnet.model import EfficientNet
>>> inputs = torch.rand(1, 3, 224, 224)
>>> model = EfficientNet.from_pretrained('efficientnet-b0')
>>> endpoints = model.extract_endpoints(inputs)
>>> print(endpoints['reduction_1'].shape) # torch.Size([1, 16, 112, 112])
>>> print(endpoints['reduction_2'].shape) # torch.Size([1, 24, 56, 56])
>>> print(endpoints['reduction_3'].shape) # torch.Size([1, 40, 28, 28])
>>> print(endpoints['reduction_4'].shape) # torch.Size([1, 112, 14, 14])
>>> print(endpoints['reduction_5'].shape) # torch.Size([1, 320, 7, 7])
>>> print(endpoints['reduction_6'].shape) # torch.Size([1, 1280, 7, 7])
"""
endpoints = dict()
# Stem
x = self._swish(self._bn0(self._conv_stem(inputs)))
prev_x = x
# Blocks
for idx, block in enumerate(self._blocks):
drop_connect_rate = self._global_params.drop_connect_rate
if drop_connect_rate:
drop_connect_rate *= float(idx) / len(self._blocks) # scale drop connect_rate
x = block(x, drop_connect_rate=drop_connect_rate)
if prev_x.size(2) > x.size(2):
endpoints['reduction_{}'.format(len(endpoints) + 1)] = prev_x
elif idx == len(self._blocks) - 1:
endpoints['reduction_{}'.format(len(endpoints) + 1)] = x
prev_x = x
# Head
x = self._swish(self._bn1(self._conv_head(x)))
endpoints['reduction_{}'.format(len(endpoints) + 1)] = x
return endpoints
def extract_features(self, inputs):
"""use convolution layer to extract feature .
Args:
inputs (tensor): Input tensor.
Returns:
Output of the final convolution
layer in the efficientnet model.
"""
# Stem
x = self._swish(self._bn0(self._conv_stem(inputs)))
# Blocks
for idx, block in enumerate(self._blocks):
drop_connect_rate = self._global_params.drop_connect_rate
if drop_connect_rate:
drop_connect_rate *= float(idx) / len(self._blocks) # scale drop connect_rate
x = block(x, drop_connect_rate=drop_connect_rate)
# Head
x = self._swish(self._bn1(self._conv_head(x)))
return x
def forward(self, inputs):
"""EfficientNet's forward function.
Calls extract_features to extract features, applies final linear layer, and returns logits.
Args:
inputs (tensor): Input tensor.
Returns:
Output of this model after processing.
"""
# Convolution layers
x = self.extract_features(inputs)
# Pooling and final linear layer
x = self._avg_pooling(x)
if self._global_params.include_top:
x = x.flatten(start_dim=1)
x = self._dropout(x)
x = self._fc(x)
return x
@classmethod
def from_name(cls, model_name, in_channels=3, **override_params):
"""Create an efficientnet model according to name.
Args:
model_name (str): Name for efficientnet.
in_channels (int): Input data's channel number.
override_params (other key word params):
Params to override model's global_params.
Optional key:
'width_coefficient', 'depth_coefficient',
'image_size', 'dropout_rate',
'num_classes', 'batch_norm_momentum',
'batch_norm_epsilon', 'drop_connect_rate',
'depth_divisor', 'min_depth'
Returns:
An efficientnet model.
"""
cls._check_model_name_is_valid(model_name)
blocks_args, global_params = get_model_params(model_name, override_params)
model = cls(blocks_args, global_params)
model._change_in_channels(in_channels)
return model
@classmethod
def from_pretrained(cls, model_name, weights_path=None, advprop=False,
in_channels=3, num_classes=1000, **override_params):
"""Create an efficientnet model according to name.
Args:
model_name (str): Name for efficientnet.
weights_path (None or str):
str: path to pretrained weights file on the local disk.
None: use pretrained weights downloaded from the Internet.
advprop (bool):
Whether to load pretrained weights
trained with advprop (valid when weights_path is None).
in_channels (int): Input data's channel number.
num_classes (int):
Number of categories for classification.
It controls the output size for final linear layer.
override_params (other key word params):
Params to override model's global_params.
Optional key:
'width_coefficient', 'depth_coefficient',
'image_size', 'dropout_rate',
'batch_norm_momentum',
'batch_norm_epsilon', 'drop_connect_rate',
'depth_divisor', 'min_depth'
Returns:
A pretrained efficientnet model.
"""
model = cls.from_name(model_name, num_classes=num_classes, **override_params)
load_pretrained_weights(model, model_name, weights_path=weights_path,
load_fc=(num_classes == 1000), advprop=advprop)
model._change_in_channels(in_channels)
return model
@classmethod
def get_image_size(cls, model_name):
"""Get the input image size for a given efficientnet model.
Args:
model_name (str): Name for efficientnet.
Returns:
Input image size (resolution).
"""
cls._check_model_name_is_valid(model_name)
_, _, res, _ = efficientnet_params(model_name)
return res
@classmethod
def _check_model_name_is_valid(cls, model_name):
"""Validates model name.
Args:
model_name (str): Name for efficientnet.
Returns:
bool: Is a valid name or not.
"""
if model_name not in VALID_MODELS:
raise ValueError('model_name should be one of: ' + ', '.join(VALID_MODELS))
def _change_in_channels(self, in_channels):
"""Adjust model's first convolution layer to in_channels, if in_channels not equals 3.
Args:
in_channels (int): Input data's channel number.
"""
if in_channels != 3:
Conv2d = get_same_padding_conv2d(image_size=self._global_params.image_size)
out_channels = round_filters(32, self._global_params)
self._conv_stem = Conv2d(in_channels, out_channels, kernel_size=3, stride=2, bias=False)EfficientNet主体架构。
EfficientNet主要创新点是探究了深度、宽度以及分辨率对性能的影响。