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# Copyright (c) Meta Platforms, Inc. and affiliates.
# All rights reserved.
# This source code is licensed under the license found in the
# LICENSE file in the root directory of this source tree.
import math
from typing import Tuple
import torch
import torch.nn as nn
import torch.nn.functional as F
from sam2.modeling.sam2_utils import DropPath, get_clones, LayerNorm2d
class MaskDownSampler(nn.Module):
"""
Progressively downsample a mask by total_stride, each time by stride.
Note that LayerNorm is applied per *token*, like in ViT.
With each downsample (by a factor stride**2), channel capacity increases by the same factor.
In the end, we linearly project to embed_dim channels.
"""
def __init__(
self,
embed_dim=256,
kernel_size=4,
stride=4,
padding=0,
total_stride=16,
activation=nn.GELU,
):
super().__init__()
num_layers = int(math.log2(total_stride) // math.log2(stride))
assert stride**num_layers == total_stride
self.encoder = nn.Sequential()
mask_in_chans, mask_out_chans = 1, 1
for _ in range(num_layers):
mask_out_chans = mask_in_chans * (stride**2)
self.encoder.append(
nn.Conv2d(
mask_in_chans,
mask_out_chans,
kernel_size=kernel_size,
stride=stride,
padding=padding,
)
)
self.encoder.append(LayerNorm2d(mask_out_chans))
self.encoder.append(activation())
mask_in_chans = mask_out_chans
self.encoder.append(nn.Conv2d(mask_out_chans, embed_dim, kernel_size=1))
def forward(self, x):
return self.encoder(x)
# Lightly adapted from ConvNext (https://github.com/facebookresearch/ConvNeXt)
class CXBlock(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,
kernel_size=7,
padding=3,
drop_path=0.0,
layer_scale_init_value=1e-6,
use_dwconv=True,
):
super().__init__()
self.dwconv = nn.Conv2d(
dim,
dim,
kernel_size=kernel_size,
padding=padding,
groups=dim if use_dwconv else 1,
) # depthwise conv
self.norm = LayerNorm2d(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 > 0.0 else nn.Identity()
def forward(self, x):
input = x
x = self.dwconv(x)
x = self.norm(x)
x = x.permute(0, 2, 3, 1) # (N, C, H, W) -> (N, H, W, C)
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 Fuser(nn.Module):
def __init__(self, layer, num_layers, dim=None, input_projection=False):
super().__init__()
self.proj = nn.Identity()
self.layers = get_clones(layer, num_layers)
if input_projection:
assert dim is not None
self.proj = nn.Conv2d(dim, dim, kernel_size=1)
def forward(self, x):
# normally x: (N, C, H, W)
x = self.proj(x)
for layer in self.layers:
x = layer(x)
return x
class MemoryEncoder(nn.Module):
def __init__(
self,
out_dim,
mask_downsampler,
fuser,
position_encoding,
in_dim=256, # in_dim of pix_feats
):
super().__init__()
self.mask_downsampler = mask_downsampler
self.pix_feat_proj = nn.Conv2d(in_dim, in_dim, kernel_size=1)
self.fuser = fuser
self.position_encoding = position_encoding
self.out_proj = nn.Identity()
if out_dim != in_dim:
self.out_proj = nn.Conv2d(in_dim, out_dim, kernel_size=1)
def forward(
self,
pix_feat: torch.Tensor,
masks: torch.Tensor,
skip_mask_sigmoid: bool = False,
) -> Tuple[torch.Tensor, torch.Tensor]:
## Process masks
# sigmoid, so that less domain shift from gt masks which are bool
if not skip_mask_sigmoid:
masks = F.sigmoid(masks)
masks = self.mask_downsampler(masks)
## Fuse pix_feats and downsampled masks
# in case the visual features are on CPU, cast them to CUDA
pix_feat = pix_feat.to(masks.device)
x = self.pix_feat_proj(pix_feat)
x = x + masks
x = self.fuser(x)
x = self.out_proj(x)
pos = self.position_encoding(x).to(x.dtype)
return {"vision_features": x, "vision_pos_enc": [pos]}
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