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# Copyright (c) Facebook, Inc. and its affiliates.
# Modified by Bowen Cheng from: https://github.com/facebookresearch/detr/blob/master/models/detr.py
import fvcore.nn.weight_init as weight_init
from typing import Optional
import torch
from torch import nn, Tensor
from torch.nn import functional as F
from .position_encoding import PositionEmbeddingSine
class SelfAttentionLayer(nn.Module):
def __init__(self, d_model, nhead, dropout=0.0,
activation="relu", normalize_before=False):
super().__init__()
self.self_attn = nn.MultiheadAttention(d_model, nhead, dropout=dropout)
self.norm = nn.LayerNorm(d_model)
self.dropout = nn.Dropout(dropout)
self.activation = _get_activation_fn(activation)
self.normalize_before = normalize_before
self._reset_parameters()
def _reset_parameters(self):
for p in self.parameters():
if p.dim() > 1:
nn.init.xavier_uniform_(p)
def with_pos_embed(self, tensor, pos: Optional[Tensor]):
return tensor if pos is None else tensor + pos
def forward_post(self, tgt,
tgt_mask: Optional[Tensor] = None,
tgt_key_padding_mask: Optional[Tensor] = None,
query_pos: Optional[Tensor] = None):
q = k = self.with_pos_embed(tgt, query_pos)
tgt2 = self.self_attn(q, k, value=tgt, attn_mask=tgt_mask,
key_padding_mask=tgt_key_padding_mask)[0]
tgt = tgt + self.dropout(tgt2)
tgt = self.norm(tgt)
return tgt
def forward_pre(self, tgt,
tgt_mask: Optional[Tensor] = None,
tgt_key_padding_mask: Optional[Tensor] = None,
query_pos: Optional[Tensor] = None):
tgt2 = self.norm(tgt)
q = k = self.with_pos_embed(tgt2, query_pos)
tgt2 = self.self_attn(q, k, value=tgt2, attn_mask=tgt_mask,
key_padding_mask=tgt_key_padding_mask)[0]
tgt = tgt + self.dropout(tgt2)
return tgt
def forward(self, tgt,
tgt_mask: Optional[Tensor] = None,
tgt_key_padding_mask: Optional[Tensor] = None,
query_pos: Optional[Tensor] = None):
if self.normalize_before:
return self.forward_pre(tgt, tgt_mask,
tgt_key_padding_mask, query_pos)
return self.forward_post(tgt, tgt_mask,
tgt_key_padding_mask, query_pos)
class CrossAttentionLayer(nn.Module):
def __init__(self, d_model, nhead, dropout=0.0,
activation="relu", normalize_before=False):
super().__init__()
self.multihead_attn = nn.MultiheadAttention(d_model, nhead, dropout=dropout)
self.norm = nn.LayerNorm(d_model)
self.dropout = nn.Dropout(dropout)
self.activation = _get_activation_fn(activation)
self.normalize_before = normalize_before
self._reset_parameters()
def _reset_parameters(self):
for p in self.parameters():
if p.dim() > 1:
nn.init.xavier_uniform_(p)
def with_pos_embed(self, tensor, pos: Optional[Tensor]):
return tensor if pos is None else tensor + pos
def forward_post(self, tgt, memory,
memory_mask: Optional[Tensor] = None,
memory_key_padding_mask: Optional[Tensor] = None,
pos: Optional[Tensor] = None,
query_pos: Optional[Tensor] = None):
tgt2 = self.multihead_attn(query=self.with_pos_embed(tgt, query_pos),
key=self.with_pos_embed(memory, pos),
value=memory, attn_mask=memory_mask,
key_padding_mask=memory_key_padding_mask)[0]
tgt = tgt + self.dropout(tgt2)
tgt = self.norm(tgt)
return tgt
def forward_pre(self, tgt, memory,
memory_mask: Optional[Tensor] = None,
memory_key_padding_mask: Optional[Tensor] = None,
pos: Optional[Tensor] = None,
query_pos: Optional[Tensor] = None):
tgt2 = self.norm(tgt)
tgt2 = self.multihead_attn(query=self.with_pos_embed(tgt2, query_pos),
key=self.with_pos_embed(memory, pos),
value=memory, attn_mask=memory_mask,
key_padding_mask=memory_key_padding_mask)[0]
tgt = tgt + self.dropout(tgt2)
return tgt
def forward(self, tgt, memory,
memory_mask: Optional[Tensor] = None,
memory_key_padding_mask: Optional[Tensor] = None,
pos: Optional[Tensor] = None,
query_pos: Optional[Tensor] = None):
if self.normalize_before:
return self.forward_pre(tgt, memory, memory_mask,
memory_key_padding_mask, pos, query_pos)
return self.forward_post(tgt, memory, memory_mask,
memory_key_padding_mask, pos, query_pos)
class FFNLayer(nn.Module):
def __init__(self, d_model, dim_feedforward=2048, dropout=0.0,
activation="relu", normalize_before=False):
super().__init__()
# Implementation of Feedforward model
self.linear1 = nn.Linear(d_model, dim_feedforward)
self.dropout = nn.Dropout(dropout)
self.linear2 = nn.Linear(dim_feedforward, d_model)
self.norm = nn.LayerNorm(d_model)
self.activation = _get_activation_fn(activation)
self.normalize_before = normalize_before
self._reset_parameters()
def _reset_parameters(self):
for p in self.parameters():
if p.dim() > 1:
nn.init.xavier_uniform_(p)
def with_pos_embed(self, tensor, pos: Optional[Tensor]):
return tensor if pos is None else tensor + pos
def forward_post(self, tgt):
tgt2 = self.linear2(self.dropout(self.activation(self.linear1(tgt))))
tgt = tgt + self.dropout(tgt2)
tgt = self.norm(tgt)
return tgt
def forward_pre(self, tgt):
tgt2 = self.norm(tgt)
tgt2 = self.linear2(self.dropout(self.activation(self.linear1(tgt2))))
tgt = tgt + self.dropout(tgt2)
return tgt
def forward(self, tgt):
if self.normalize_before:
return self.forward_pre(tgt)
return self.forward_post(tgt)
def _get_activation_fn(activation):
"""Return an activation function given a string"""
if activation == "relu":
return F.relu
if activation == "gelu":
return F.gelu
if activation == "glu":
return F.glu
raise RuntimeError(F"activation should be relu/gelu, not {activation}.")
class MLP(nn.Module):
""" Very simple multi-layer perceptron (also called FFN)"""
def __init__(self, input_dim, hidden_dim, output_dim, num_layers):
super().__init__()
self.num_layers = num_layers
h = [hidden_dim] * (num_layers - 1)
self.layers = nn.ModuleList(nn.Linear(n, k) for n, k in zip([input_dim] + h, h + [output_dim]))
def forward(self, x):
for i, layer in enumerate(self.layers):
x = F.relu(layer(x)) if i < self.num_layers - 1 else layer(x)
return x
class MultiScaleMaskedTransformerDecoder(nn.Module):
def __init__(
self,
in_channels,
num_classes,
mask_classification=True,
hidden_dim=256,
num_queries=100,
nheads=8,
dim_feedforward=2048,
dec_layers=10,
pre_norm=False,
mask_dim=256,
enforce_input_project=False
):
super().__init__()
assert mask_classification, "Only support mask classification model"
self.mask_classification = mask_classification
# positional encoding
N_steps = hidden_dim // 2
self.pe_layer = PositionEmbeddingSine(N_steps, normalize=True)
# define Transformer decoder here
self.num_heads = nheads
self.num_layers = dec_layers
self.transformer_self_attention_layers = nn.ModuleList()
self.transformer_cross_attention_layers = nn.ModuleList()
self.transformer_ffn_layers = nn.ModuleList()
for _ in range(self.num_layers):
self.transformer_self_attention_layers.append(
SelfAttentionLayer(
d_model=hidden_dim,
nhead=nheads,
dropout=0.0,
normalize_before=pre_norm,
)
)
self.transformer_cross_attention_layers.append(
CrossAttentionLayer(
d_model=hidden_dim,
nhead=nheads,
dropout=0.0,
normalize_before=pre_norm,
)
)
self.transformer_ffn_layers.append(
FFNLayer(
d_model=hidden_dim,
dim_feedforward=dim_feedforward,
dropout=0.0,
normalize_before=pre_norm,
)
)
self.decoder_norm = nn.LayerNorm(hidden_dim)
self.num_queries = num_queries
# learnable query features
self.query_feat = nn.Embedding(num_queries, hidden_dim)
# learnable query p.e.
self.query_embed = nn.Embedding(num_queries, hidden_dim)
# level embedding (we always use 3 scales)
self.num_feature_levels = 3
self.level_embed = nn.Embedding(self.num_feature_levels, hidden_dim)
self.input_proj = nn.ModuleList()
for _ in range(self.num_feature_levels):
if in_channels != hidden_dim or enforce_input_project:
self.input_proj.append(nn.Conv2d(in_channels, hidden_dim, kernel_size=1))
weight_init.c2_xavier_fill(self.input_proj[-1])
else:
self.input_proj.append(nn.Sequential())
# output FFNs
if self.mask_classification:
self.class_embed = nn.Linear(hidden_dim, num_classes + 1)
self.mask_embed = MLP(hidden_dim, hidden_dim, mask_dim, 3)
def forward(self, x, mask_features, mask = None):
#print(mask_features.shape, "!!")
# x is a list of multi-scale feature
assert len(x) == self.num_feature_levels
src = []
pos = []
size_list = []
# disable mask, it does not affect performance
del mask
for i in range(self.num_feature_levels):
size_list.append(x[i].shape[-2:])
pos.append(self.pe_layer(x[i], None).flatten(2))
src.append(self.input_proj[i](x[i]).flatten(2) + self.level_embed.weight[i][None, :, None])
# flatten NxCxHxW to HWxNxC
pos[-1] = pos[-1].permute(2, 0, 1)
src[-1] = src[-1].permute(2, 0, 1)
_, bs, _ = src[0].shape
# QxNxC
query_embed = self.query_embed.weight.unsqueeze(1).repeat(1, bs, 1)
output = self.query_feat.weight.unsqueeze(1).repeat(1, bs, 1)
predictions_class = []
predictions_mask = []
# prediction heads on learnable query features
outputs_class, outputs_mask, attn_mask = self.forward_prediction_heads(output, mask_features, attn_mask_target_size=size_list[0])
predictions_class.append(outputs_class)
predictions_mask.append(outputs_mask)
for i in range(self.num_layers):
level_index = i % self.num_feature_levels
attn_mask[torch.where(attn_mask.sum(-1) == attn_mask.shape[-1])] = False
# attention: cross-attention first
output = self.transformer_cross_attention_layers[i](
output, src[level_index],
memory_mask=attn_mask,
memory_key_padding_mask=None, # here we do not apply masking on padded region
pos=pos[level_index], query_pos=query_embed
)
output = self.transformer_self_attention_layers[i](
output, tgt_mask=None,
tgt_key_padding_mask=None,
query_pos=query_embed
)
# FFN
output = self.transformer_ffn_layers[i](
output
)
#print(output.shape, "??")
outputs_class, outputs_mask, attn_mask = self.forward_prediction_heads(output, mask_features, attn_mask_target_size=size_list[(i + 1) % self.num_feature_levels])
predictions_class.append(outputs_class)
predictions_mask.append(outputs_mask)
assert len(predictions_class) == self.num_layers + 1
out = {
'pred_logits': predictions_class[-1],
'pred_masks': predictions_mask[-1],
'aux_outputs': self._set_aux_loss(
predictions_class if self.mask_classification else None, predictions_mask
)
}
return out
def forward_prediction_heads(self, output, mask_features, attn_mask_target_size):
decoder_output = self.decoder_norm(output)
decoder_output = decoder_output.transpose(0, 1)
outputs_class = self.class_embed(decoder_output)
mask_embed = self.mask_embed(decoder_output)
outputs_mask = torch.einsum("bqc,bchw->bqhw", mask_embed, mask_features)
# NOTE: prediction is of higher-resolution
# [B, Q, H, W] -> [B, Q, H*W] -> [B, h, Q, H*W] -> [B*h, Q, HW]
attn_mask = F.interpolate(outputs_mask, size=attn_mask_target_size, mode="bilinear", align_corners=False)
# must use bool type
# If a BoolTensor is provided, positions with ``True`` are not allowed to attend while ``False`` values will be unchanged.
#print('before', attn_mask.shape)
#print(self.num_heads)
attn_mask = (attn_mask.sigmoid().flatten(2).unsqueeze(1).repeat(1, self.num_heads, 1, 1).flatten(0, 1) < 0.5).bool()
#print('after', attn_mask.shape)
attn_mask = attn_mask.detach()
return outputs_class, outputs_mask, attn_mask
@torch.jit.unused
def _set_aux_loss(self, outputs_class, outputs_seg_masks):
# this is a workaround to make torchscript happy, as torchscript
# doesn't support dictionary with non-homogeneous values, such
# as a dict having both a Tensor and a list.
if self.mask_classification:
return [
{"pred_logits": a, "pred_masks": b}
for a, b in zip(outputs_class[:-1], outputs_seg_masks[:-1])
]
else:
return [{"pred_masks": b} for b in outputs_seg_masks[:-1]]
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