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# reference: https://github.com/SHI-Labs/OneFormer/blob/main/oneformer/modeling/backbone/convnext.py
from functools import partial
import torch
import torch.nn as nn
import torch.nn.functional as F
from timm.models.layers import DropPath
from detectron2.modeling import BACKBONE_REGISTRY, Backbone, ShapeSpec
from torch.cuda.amp import autocast
class Block(nn.Module):
r""" ConvNeXt Block. There are two equivalent implementations:
(1) DwConv -> LayerNorm (channels_first) -> 1x1 Conv -> GELU -> 1x1 Conv; all in (N, C, H, W)
(2) DwConv -> Permute to (N, H, W, C); LayerNorm (channels_last) -> Linear -> GELU -> Linear; Permute back
We use (2) as we find it slightly faster in PyTorch
Args:
dim (int): Number of input channels.
drop_path (float): Stochastic depth rate. Default: 0.0
layer_scale_init_value (float): Init value for Layer Scale. Default: 1e-6.
"""
def __init__(self, dim, drop_path=0., layer_scale_init_value=1e-6):
super().__init__()
self.dwconv = nn.Conv2d(dim, dim, kernel_size=7, padding=3, groups=dim) # depthwise conv
self.norm = LayerNorm(dim, eps=1e-6)
self.pwconv1 = nn.Linear(dim, 4 * dim) # pointwise/1x1 convs, implemented with linear layers
self.act = nn.GELU()
self.pwconv2 = nn.Linear(4 * dim, dim)
self.gamma = nn.Parameter(layer_scale_init_value * torch.ones((dim)),
requires_grad=True) if layer_scale_init_value > 0 else None
self.drop_path = DropPath(drop_path) if drop_path > 0. else nn.Identity()
def forward(self, x):
input = x
x = self.dwconv(x)
x = x.permute(0, 2, 3, 1) # (N, C, H, W) -> (N, H, W, C)
x = self.norm(x)
x = self.pwconv1(x)
x = self.act(x)
x = self.pwconv2(x)
if self.gamma is not None:
x = self.gamma * x
x = x.permute(0, 3, 1, 2) # (N, H, W, C) -> (N, C, H, W)
x = input + self.drop_path(x)
return x
class LayerNorm(nn.Module):
r""" LayerNorm that supports two data formats: channels_last (default) or channels_first.
The ordering of the dimensions in the inputs. channels_last corresponds to inputs with
shape (batch_size, height, width, channels) while channels_first corresponds to inputs
with shape (batch_size, channels, height, width).
"""
def __init__(self, normalized_shape, eps=1e-6, data_format="channels_last"):
super().__init__()
self.weight = nn.Parameter(torch.ones(normalized_shape))
self.bias = nn.Parameter(torch.zeros(normalized_shape))
self.eps = eps
self.data_format = data_format
if self.data_format not in ["channels_last", "channels_first"]:
raise NotImplementedError
self.normalized_shape = (normalized_shape, )
def forward(self, x):
with autocast(enabled=False):
x = x.float()
if self.data_format == "channels_last":
return F.layer_norm(x, self.normalized_shape, self.weight, self.bias, self.eps)
elif self.data_format == "channels_first":
u = x.mean(1, keepdim=True)
s = (x - u).pow(2).mean(1, keepdim=True)
x = (x - u) / torch.sqrt(s + self.eps)
x = self.weight[:, None, None] * x + self.bias[:, None, None]
return x
class ConvNeXt(nn.Module):
r""" ConvNeXt
A PyTorch impl of : `A ConvNet for the 2020s` -
https://arxiv.org/pdf/2201.03545.pdf
Args:
in_chans (int): Number of input image channels. Default: 3
num_classes (int): Number of classes for classification head. Default: 1000
depths (tuple(int)): Number of blocks at each stage. Default: [3, 3, 9, 3]
dims (int): Feature dimension at each stage. Default: [96, 192, 384, 768]
drop_path_rate (float): Stochastic depth rate. Default: 0.
layer_scale_init_value (float): Init value for Layer Scale. Default: 1e-6.
head_init_scale (float): Init scaling value for classifier weights and biases. Default: 1.
"""
def __init__(self, in_chans=3, depths=[3, 3, 9, 3], dims=[96, 192, 384, 768],
drop_path_rate=0., layer_scale_init_value=1e-6, out_indices=[0, 1, 2, 3],
):
super().__init__()
self.num_features = dims
self.downsample_layers = nn.ModuleList() # stem and 3 intermediate downsampling conv layers
stem = nn.Sequential(
nn.Conv2d(in_chans, dims[0], kernel_size=4, stride=4),
LayerNorm(dims[0], eps=1e-6, data_format="channels_first")
)
self.downsample_layers.append(stem)
for i in range(3):
downsample_layer = nn.Sequential(
LayerNorm(dims[i], eps=1e-6, data_format="channels_first"),
nn.Conv2d(dims[i], dims[i+1], kernel_size=2, stride=2),
)
self.downsample_layers.append(downsample_layer)
self.stages = nn.ModuleList() # 4 feature resolution stages, each consisting of multiple residual blocks
dp_rates=[x.item() for x in torch.linspace(0, drop_path_rate, sum(depths))]
cur = 0
for i in range(4):
stage = nn.Sequential(
*[Block(dim=dims[i], drop_path=dp_rates[cur + j],
layer_scale_init_value=layer_scale_init_value) for j in range(depths[i])]
)
self.stages.append(stage)
cur += depths[i]
self.out_indices = out_indices
def forward_features(self, x):
outs = {}
for i in range(4):
# We add zero padding here for downstream tasks.
# ref: https://github.com/google-research/deeplab2/blob/main/model/pixel_encoder/convnext.py#L128
if i == 0:
x = F.pad(x, (1, 2, 1, 2, 0, 0, 0, 0), "constant", 0)
else:
x = F.pad(x, (0, 1, 0, 1, 0, 0, 0, 0), "constant", 0)
x = self.downsample_layers[i](x)
x = self.stages[i](x)
if i in self.out_indices:
outs["res{}".format(i + 2)] = x
return outs
def forward(self, x):
x = self.forward_features(x)
return x
@BACKBONE_REGISTRY.register()
class D2ConvNeXt(ConvNeXt, Backbone):
def __init__(self, cfg, input_shape):
in_chans = cfg.MODEL.CONVNEXT.IN_CHANNELS
depths = cfg.MODEL.CONVNEXT.DEPTHS
dims = cfg.MODEL.CONVNEXT.DIMS
drop_path_rate = cfg.MODEL.CONVNEXT.DROP_PATH_RATE
layer_scale_init_value = cfg.MODEL.CONVNEXT.LSIT
out_indices = cfg.MODEL.CONVNEXT.OUT_INDICES
super().__init__(
in_chans=in_chans,
depths=depths,
dims=dims,
drop_path_rate=drop_path_rate,
layer_scale_init_value=layer_scale_init_value,
out_indices=out_indices,
)
self._out_features = cfg.MODEL.CONVNEXT.OUT_FEATURES
self._out_feature_strides = {
"res2": 4,
"res3": 8,
"res4": 16,
"res5": 32,
}
self._out_feature_channels = {
"res2": self.num_features[0],
"res3": self.num_features[1],
"res4": self.num_features[2],
"res5": self.num_features[3],
}
def forward(self, x):
"""
Args:
x: Tensor of shape (N,C,H,W). H, W must be a multiple of ``self.size_divisibility``.
Returns:
dict[str->Tensor]: names and the corresponding features
"""
assert (
x.dim() == 4
), f"ConvNeXt takes an input of shape (N, C, H, W). Got {x.shape} instead!"
outputs = {}
y = super().forward(x)
for k in y.keys():
if k in self._out_features:
outputs[k] = y[k]
return outputs
def output_shape(self):
return {
name: ShapeSpec(
channels=self._out_feature_channels[name], stride=self._out_feature_strides[name]
)
for name in self._out_features
}
@property
def size_divisibility(self):
return -1 |