mmdet.models.backbones.pvt 源代码
# Copyright (c) OpenMMLab. All rights reserved.
import math
import warnings
import numpy as np
import torch
import torch.nn as nn
import torch.nn.functional as F
from mmcv.cnn import (Conv2d, build_activation_layer, build_norm_layer,
constant_init, normal_init, trunc_normal_init)
from mmcv.cnn.bricks.drop import build_dropout
from mmcv.cnn.bricks.transformer import MultiheadAttention
from mmcv.cnn.utils.weight_init import trunc_normal_
from mmcv.runner import (BaseModule, ModuleList, Sequential, _load_checkpoint,
load_state_dict)
from torch.nn.modules.utils import _pair as to_2tuple
from ...utils import get_root_logger
from ..builder import BACKBONES
from ..utils import PatchEmbed, nchw_to_nlc, nlc_to_nchw, pvt_convert
class MixFFN(BaseModule):
"""An implementation of MixFFN of PVT.
The differences between MixFFN & FFN:
1. Use 1X1 Conv to replace Linear layer.
2. Introduce 3X3 Depth-wise Conv to encode positional information.
Args:
embed_dims (int): The feature dimension. Same as
`MultiheadAttention`.
feedforward_channels (int): The hidden dimension of FFNs.
act_cfg (dict, optional): The activation config for FFNs.
Default: dict(type='GELU').
ffn_drop (float, optional): Probability of an element to be
zeroed in FFN. Default 0.0.
dropout_layer (obj:`ConfigDict`): The dropout_layer used
when adding the shortcut.
Default: None.
use_conv (bool): If True, add 3x3 DWConv between two Linear layers.
Defaults: False.
init_cfg (obj:`mmcv.ConfigDict`): The Config for initialization.
Default: None.
"""
def __init__(self,
embed_dims,
feedforward_channels,
act_cfg=dict(type='GELU'),
ffn_drop=0.,
dropout_layer=None,
use_conv=False,
init_cfg=None):
super(MixFFN, self).__init__(init_cfg=init_cfg)
self.embed_dims = embed_dims
self.feedforward_channels = feedforward_channels
self.act_cfg = act_cfg
activate = build_activation_layer(act_cfg)
in_channels = embed_dims
fc1 = Conv2d(
in_channels=in_channels,
out_channels=feedforward_channels,
kernel_size=1,
stride=1,
bias=True)
if use_conv:
# 3x3 depth wise conv to provide positional encode information
dw_conv = Conv2d(
in_channels=feedforward_channels,
out_channels=feedforward_channels,
kernel_size=3,
stride=1,
padding=(3 - 1) // 2,
bias=True,
groups=feedforward_channels)
fc2 = Conv2d(
in_channels=feedforward_channels,
out_channels=in_channels,
kernel_size=1,
stride=1,
bias=True)
drop = nn.Dropout(ffn_drop)
layers = [fc1, activate, drop, fc2, drop]
if use_conv:
layers.insert(1, dw_conv)
self.layers = Sequential(*layers)
self.dropout_layer = build_dropout(
dropout_layer) if dropout_layer else torch.nn.Identity()
def forward(self, x, hw_shape, identity=None):
out = nlc_to_nchw(x, hw_shape)
out = self.layers(out)
out = nchw_to_nlc(out)
if identity is None:
identity = x
return identity + self.dropout_layer(out)
class SpatialReductionAttention(MultiheadAttention):
"""An implementation of Spatial Reduction Attention of PVT.
This module is modified from MultiheadAttention which is a module from
mmcv.cnn.bricks.transformer.
Args:
embed_dims (int): The embedding dimension.
num_heads (int): Parallel attention heads.
attn_drop (float): A Dropout layer on attn_output_weights.
Default: 0.0.
proj_drop (float): A Dropout layer after `nn.MultiheadAttention`.
Default: 0.0.
dropout_layer (obj:`ConfigDict`): The dropout_layer used
when adding the shortcut. Default: None.
batch_first (bool): Key, Query and Value are shape of
(batch, n, embed_dim)
or (n, batch, embed_dim). Default: False.
qkv_bias (bool): enable bias for qkv if True. Default: True.
norm_cfg (dict): Config dict for normalization layer.
Default: dict(type='LN').
sr_ratio (int): The ratio of spatial reduction of Spatial Reduction
Attention of PVT. Default: 1.
init_cfg (obj:`mmcv.ConfigDict`): The Config for initialization.
Default: None.
"""
def __init__(self,
embed_dims,
num_heads,
attn_drop=0.,
proj_drop=0.,
dropout_layer=None,
batch_first=True,
qkv_bias=True,
norm_cfg=dict(type='LN'),
sr_ratio=1,
init_cfg=None):
super().__init__(
embed_dims,
num_heads,
attn_drop,
proj_drop,
batch_first=batch_first,
dropout_layer=dropout_layer,
bias=qkv_bias,
init_cfg=init_cfg)
self.sr_ratio = sr_ratio
if sr_ratio > 1:
self.sr = Conv2d(
in_channels=embed_dims,
out_channels=embed_dims,
kernel_size=sr_ratio,
stride=sr_ratio)
# The ret[0] of build_norm_layer is norm name.
self.norm = build_norm_layer(norm_cfg, embed_dims)[1]
# handle the BC-breaking from https://github.com/open-mmlab/mmcv/pull/1418 # noqa
from mmdet import digit_version, mmcv_version
if mmcv_version < digit_version('1.3.17'):
warnings.warn('The legacy version of forward function in'
'SpatialReductionAttention is deprecated in'
'mmcv>=1.3.17 and will no longer support in the'
'future. Please upgrade your mmcv.')
self.forward = self.legacy_forward
def forward(self, x, hw_shape, identity=None):
x_q = x
if self.sr_ratio > 1:
x_kv = nlc_to_nchw(x, hw_shape)
x_kv = self.sr(x_kv)
x_kv = nchw_to_nlc(x_kv)
x_kv = self.norm(x_kv)
else:
x_kv = x
if identity is None:
identity = x_q
# Because the dataflow('key', 'query', 'value') of
# ``torch.nn.MultiheadAttention`` is (num_query, batch,
# embed_dims), We should adjust the shape of dataflow from
# batch_first (batch, num_query, embed_dims) to num_query_first
# (num_query ,batch, embed_dims), and recover ``attn_output``
# from num_query_first to batch_first.
if self.batch_first:
x_q = x_q.transpose(0, 1)
x_kv = x_kv.transpose(0, 1)
out = self.attn(query=x_q, key=x_kv, value=x_kv)[0]
if self.batch_first:
out = out.transpose(0, 1)
return identity + self.dropout_layer(self.proj_drop(out))
def legacy_forward(self, x, hw_shape, identity=None):
"""multi head attention forward in mmcv version < 1.3.17."""
x_q = x
if self.sr_ratio > 1:
x_kv = nlc_to_nchw(x, hw_shape)
x_kv = self.sr(x_kv)
x_kv = nchw_to_nlc(x_kv)
x_kv = self.norm(x_kv)
else:
x_kv = x
if identity is None:
identity = x_q
out = self.attn(query=x_q, key=x_kv, value=x_kv)[0]
return identity + self.dropout_layer(self.proj_drop(out))
class PVTEncoderLayer(BaseModule):
"""Implements one encoder layer in PVT.
Args:
embed_dims (int): The feature dimension.
num_heads (int): Parallel attention heads.
feedforward_channels (int): The hidden dimension for FFNs.
drop_rate (float): Probability of an element to be zeroed.
after the feed forward layer. Default: 0.0.
attn_drop_rate (float): The drop out rate for attention layer.
Default: 0.0.
drop_path_rate (float): stochastic depth rate. Default: 0.0.
qkv_bias (bool): enable bias for qkv if True.
Default: True.
act_cfg (dict): The activation config for FFNs.
Default: dict(type='GELU').
norm_cfg (dict): Config dict for normalization layer.
Default: dict(type='LN').
sr_ratio (int): The ratio of spatial reduction of Spatial Reduction
Attention of PVT. Default: 1.
use_conv_ffn (bool): If True, use Convolutional FFN to replace FFN.
Default: False.
init_cfg (dict, optional): Initialization config dict.
Default: None.
"""
def __init__(self,
embed_dims,
num_heads,
feedforward_channels,
drop_rate=0.,
attn_drop_rate=0.,
drop_path_rate=0.,
qkv_bias=True,
act_cfg=dict(type='GELU'),
norm_cfg=dict(type='LN'),
sr_ratio=1,
use_conv_ffn=False,
init_cfg=None):
super(PVTEncoderLayer, self).__init__(init_cfg=init_cfg)
# The ret[0] of build_norm_layer is norm name.
self.norm1 = build_norm_layer(norm_cfg, embed_dims)[1]
self.attn = SpatialReductionAttention(
embed_dims=embed_dims,
num_heads=num_heads,
attn_drop=attn_drop_rate,
proj_drop=drop_rate,
dropout_layer=dict(type='DropPath', drop_prob=drop_path_rate),
qkv_bias=qkv_bias,
norm_cfg=norm_cfg,
sr_ratio=sr_ratio)
# The ret[0] of build_norm_layer is norm name.
self.norm2 = build_norm_layer(norm_cfg, embed_dims)[1]
self.ffn = MixFFN(
embed_dims=embed_dims,
feedforward_channels=feedforward_channels,
ffn_drop=drop_rate,
dropout_layer=dict(type='DropPath', drop_prob=drop_path_rate),
use_conv=use_conv_ffn,
act_cfg=act_cfg)
def forward(self, x, hw_shape):
x = self.attn(self.norm1(x), hw_shape, identity=x)
x = self.ffn(self.norm2(x), hw_shape, identity=x)
return x
class AbsolutePositionEmbedding(BaseModule):
"""An implementation of the absolute position embedding in PVT.
Args:
pos_shape (int): The shape of the absolute position embedding.
pos_dim (int): The dimension of the absolute position embedding.
drop_rate (float): Probability of an element to be zeroed.
Default: 0.0.
"""
def __init__(self, pos_shape, pos_dim, drop_rate=0., init_cfg=None):
super().__init__(init_cfg=init_cfg)
if isinstance(pos_shape, int):
pos_shape = to_2tuple(pos_shape)
elif isinstance(pos_shape, tuple):
if len(pos_shape) == 1:
pos_shape = to_2tuple(pos_shape[0])
assert len(pos_shape) == 2, \
f'The size of image should have length 1 or 2, ' \
f'but got {len(pos_shape)}'
self.pos_shape = pos_shape
self.pos_dim = pos_dim
self.pos_embed = nn.Parameter(
torch.zeros(1, pos_shape[0] * pos_shape[1], pos_dim))
self.drop = nn.Dropout(p=drop_rate)
def init_weights(self):
trunc_normal_(self.pos_embed, std=0.02)
def resize_pos_embed(self, pos_embed, input_shape, mode='bilinear'):
"""Resize pos_embed weights.
Resize pos_embed using bilinear interpolate method.
Args:
pos_embed (torch.Tensor): Position embedding weights.
input_shape (tuple): Tuple for (downsampled input image height,
downsampled input image width).
mode (str): Algorithm used for upsampling:
``'nearest'`` | ``'linear'`` | ``'bilinear'`` | ``'bicubic'`` |
``'trilinear'``. Default: ``'bilinear'``.
Return:
torch.Tensor: The resized pos_embed of shape [B, L_new, C].
"""
assert pos_embed.ndim == 3, 'shape of pos_embed must be [B, L, C]'
pos_h, pos_w = self.pos_shape
pos_embed_weight = pos_embed[:, (-1 * pos_h * pos_w):]
pos_embed_weight = pos_embed_weight.reshape(
1, pos_h, pos_w, self.pos_dim).permute(0, 3, 1, 2).contiguous()
pos_embed_weight = F.interpolate(
pos_embed_weight, size=input_shape, mode=mode)
pos_embed_weight = torch.flatten(pos_embed_weight,
2).transpose(1, 2).contiguous()
pos_embed = pos_embed_weight
return pos_embed
def forward(self, x, hw_shape, mode='bilinear'):
pos_embed = self.resize_pos_embed(self.pos_embed, hw_shape, mode)
return self.drop(x + pos_embed)
[文档]@BACKBONES.register_module()
class PyramidVisionTransformer(BaseModule):
"""Pyramid Vision Transformer (PVT)
Implementation of `Pyramid Vision Transformer: A Versatile Backbone for
Dense Prediction without Convolutions
<https://arxiv.org/pdf/2102.12122.pdf>`_.
Args:
pretrain_img_size (int | tuple[int]): The size of input image when
pretrain. Defaults: 224.
in_channels (int): Number of input channels. Default: 3.
embed_dims (int): Embedding dimension. Default: 64.
num_stags (int): The num of stages. Default: 4.
num_layers (Sequence[int]): The layer number of each transformer encode
layer. Default: [3, 4, 6, 3].
num_heads (Sequence[int]): The attention heads of each transformer
encode layer. Default: [1, 2, 5, 8].
patch_sizes (Sequence[int]): The patch_size of each patch embedding.
Default: [4, 2, 2, 2].
strides (Sequence[int]): The stride of each patch embedding.
Default: [4, 2, 2, 2].
paddings (Sequence[int]): The padding of each patch embedding.
Default: [0, 0, 0, 0].
sr_ratios (Sequence[int]): The spatial reduction rate of each
transformer encode layer. Default: [8, 4, 2, 1].
out_indices (Sequence[int] | int): Output from which stages.
Default: (0, 1, 2, 3).
mlp_ratios (Sequence[int]): The ratio of the mlp hidden dim to the
embedding dim of each transformer encode layer.
Default: [8, 8, 4, 4].
qkv_bias (bool): Enable bias for qkv if True. Default: True.
drop_rate (float): Probability of an element to be zeroed.
Default 0.0.
attn_drop_rate (float): The drop out rate for attention layer.
Default 0.0.
drop_path_rate (float): stochastic depth rate. Default 0.1.
use_abs_pos_embed (bool): If True, add absolute position embedding to
the patch embedding. Defaults: True.
use_conv_ffn (bool): If True, use Convolutional FFN to replace FFN.
Default: False.
act_cfg (dict): The activation config for FFNs.
Default: dict(type='GELU').
norm_cfg (dict): Config dict for normalization layer.
Default: dict(type='LN').
pretrained (str, optional): model pretrained path. Default: None.
convert_weights (bool): The flag indicates whether the
pre-trained model is from the original repo. We may need
to convert some keys to make it compatible.
Default: True.
init_cfg (dict or list[dict], optional): Initialization config dict.
Default: None.
"""
def __init__(self,
pretrain_img_size=224,
in_channels=3,
embed_dims=64,
num_stages=4,
num_layers=[3, 4, 6, 3],
num_heads=[1, 2, 5, 8],
patch_sizes=[4, 2, 2, 2],
strides=[4, 2, 2, 2],
paddings=[0, 0, 0, 0],
sr_ratios=[8, 4, 2, 1],
out_indices=(0, 1, 2, 3),
mlp_ratios=[8, 8, 4, 4],
qkv_bias=True,
drop_rate=0.,
attn_drop_rate=0.,
drop_path_rate=0.1,
use_abs_pos_embed=True,
norm_after_stage=False,
use_conv_ffn=False,
act_cfg=dict(type='GELU'),
norm_cfg=dict(type='LN', eps=1e-6),
pretrained=None,
convert_weights=True,
init_cfg=None):
super().__init__(init_cfg=init_cfg)
self.convert_weights = convert_weights
if isinstance(pretrain_img_size, int):
pretrain_img_size = to_2tuple(pretrain_img_size)
elif isinstance(pretrain_img_size, tuple):
if len(pretrain_img_size) == 1:
pretrain_img_size = to_2tuple(pretrain_img_size[0])
assert len(pretrain_img_size) == 2, \
f'The size of image should have length 1 or 2, ' \
f'but got {len(pretrain_img_size)}'
assert not (init_cfg and pretrained), \
'init_cfg and pretrained cannot be setting at the same time'
if isinstance(pretrained, str):
warnings.warn('DeprecationWarning: pretrained is deprecated, '
'please use "init_cfg" instead')
self.init_cfg = dict(type='Pretrained', checkpoint=pretrained)
elif pretrained is None:
self.init_cfg = init_cfg
else:
raise TypeError('pretrained must be a str or None')
self.embed_dims = embed_dims
self.num_stages = num_stages
self.num_layers = num_layers
self.num_heads = num_heads
self.patch_sizes = patch_sizes
self.strides = strides
self.sr_ratios = sr_ratios
assert num_stages == len(num_layers) == len(num_heads) \
== len(patch_sizes) == len(strides) == len(sr_ratios)
self.out_indices = out_indices
assert max(out_indices) < self.num_stages
self.pretrained = pretrained
# transformer encoder
dpr = [
x.item()
for x in torch.linspace(0, drop_path_rate, sum(num_layers))
] # stochastic num_layer decay rule
cur = 0
self.layers = ModuleList()
for i, num_layer in enumerate(num_layers):
embed_dims_i = embed_dims * num_heads[i]
patch_embed = PatchEmbed(
in_channels=in_channels,
embed_dims=embed_dims_i,
kernel_size=patch_sizes[i],
stride=strides[i],
padding=paddings[i],
bias=True,
norm_cfg=norm_cfg)
layers = ModuleList()
if use_abs_pos_embed:
pos_shape = pretrain_img_size // np.prod(patch_sizes[:i + 1])
pos_embed = AbsolutePositionEmbedding(
pos_shape=pos_shape,
pos_dim=embed_dims_i,
drop_rate=drop_rate)
layers.append(pos_embed)
layers.extend([
PVTEncoderLayer(
embed_dims=embed_dims_i,
num_heads=num_heads[i],
feedforward_channels=mlp_ratios[i] * embed_dims_i,
drop_rate=drop_rate,
attn_drop_rate=attn_drop_rate,
drop_path_rate=dpr[cur + idx],
qkv_bias=qkv_bias,
act_cfg=act_cfg,
norm_cfg=norm_cfg,
sr_ratio=sr_ratios[i],
use_conv_ffn=use_conv_ffn) for idx in range(num_layer)
])
in_channels = embed_dims_i
# The ret[0] of build_norm_layer is norm name.
if norm_after_stage:
norm = build_norm_layer(norm_cfg, embed_dims_i)[1]
else:
norm = nn.Identity()
self.layers.append(ModuleList([patch_embed, layers, norm]))
cur += num_layer
[文档] def init_weights(self):
logger = get_root_logger()
if self.init_cfg is None:
logger.warn(f'No pre-trained weights for '
f'{self.__class__.__name__}, '
f'training start from scratch')
for m in self.modules():
if isinstance(m, nn.Linear):
trunc_normal_init(m, std=.02, bias=0.)
elif isinstance(m, nn.LayerNorm):
constant_init(m, 1.0)
elif isinstance(m, nn.Conv2d):
fan_out = m.kernel_size[0] * m.kernel_size[
1] * m.out_channels
fan_out //= m.groups
normal_init(m, 0, math.sqrt(2.0 / fan_out))
elif isinstance(m, AbsolutePositionEmbedding):
m.init_weights()
else:
assert 'checkpoint' in self.init_cfg, f'Only support ' \
f'specify `Pretrained` in ' \
f'`init_cfg` in ' \
f'{self.__class__.__name__} '
checkpoint = _load_checkpoint(
self.init_cfg.checkpoint, logger=logger, map_location='cpu')
logger.warn(f'Load pre-trained model for '
f'{self.__class__.__name__} from original repo')
if 'state_dict' in checkpoint:
state_dict = checkpoint['state_dict']
elif 'model' in checkpoint:
state_dict = checkpoint['model']
else:
state_dict = checkpoint
if self.convert_weights:
# Because pvt backbones are not supported by mmcls,
# so we need to convert pre-trained weights to match this
# implementation.
state_dict = pvt_convert(state_dict)
load_state_dict(self, state_dict, strict=False, logger=logger)
[文档] def forward(self, x):
outs = []
for i, layer in enumerate(self.layers):
x, hw_shape = layer[0](x)
for block in layer[1]:
x = block(x, hw_shape)
x = layer[2](x)
x = nlc_to_nchw(x, hw_shape)
if i in self.out_indices:
outs.append(x)
return outs
[文档]@BACKBONES.register_module()
class PyramidVisionTransformerV2(PyramidVisionTransformer):
"""Implementation of `PVTv2: Improved Baselines with Pyramid Vision
Transformer <https://arxiv.org/pdf/2106.13797.pdf>`_."""
def __init__(self, **kwargs):
super(PyramidVisionTransformerV2, self).__init__(
patch_sizes=[7, 3, 3, 3],
paddings=[3, 1, 1, 1],
use_abs_pos_embed=False,
norm_after_stage=True,
use_conv_ffn=True,
**kwargs)