# coding=utf-8
# Copyright 2021 NVIDIA The HuggingFace Inc. team. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
""" PyTorch SegFormer model. """
import collections
import math
import torch
import torch.utils.checkpoint
from torch import nn
from torch.nn import CrossEntropyLoss, MSELoss
from ...activations import ACT2FN
from ...file_utils import add_start_docstrings, add_start_docstrings_to_model_forward, replace_return_docstrings
from ...modeling_outputs import BaseModelOutput, SequenceClassifierOutput
from ...modeling_utils import PreTrainedModel, find_pruneable_heads_and_indices, prune_linear_layer
from ...utils import logging
from .configuration_segformer import SegformerConfig
logger = logging.get_logger(__name__)
_CHECKPOINT_FOR_DOC = "nvidia/segformer-b0-finetuned-ade-512-512"
_CONFIG_FOR_DOC = "SegformerConfig"
SEGFORMER_PRETRAINED_MODEL_ARCHIVE_LIST = [
"nvidia/segformer-b0-finetuned-ade-512-512",
# See all SegFormer models at https://huggingface.co/models?filter=segformer
]
# Inspired by
# https://github.com/rwightman/pytorch-image-models/blob/b9bd960a032c75ca6b808ddeed76bee5f3ed4972/timm/models/layers/helpers.py
# From PyTorch internals
def to_2tuple(x):
if isinstance(x, collections.abc.Iterable):
return x
return (x, x)
# Stochastic depth implementation
# Taken from https://github.com/rwightman/pytorch-image-models/blob/master/timm/models/layers/drop.py
def drop_path(x, drop_prob: float = 0.0, training: bool = False):
"""
Drop paths (Stochastic Depth) per sample (when applied in main path of residual blocks). This is the same as the
DropConnect impl I created for EfficientNet, etc networks, however, the original name is misleading as 'Drop
Connect' is a different form of dropout in a separate paper... See discussion:
https://github.com/tensorflow/tpu/issues/494#issuecomment-532968956 ... I've opted for changing the layer and
argument names to 'drop path' rather than mix DropConnect as a layer name and use 'survival rate' as the argument.
"""
if drop_prob == 0.0 or not training:
return x
keep_prob = 1 - drop_prob
shape = (x.shape[0],) + (1,) * (x.ndim - 1) # work with diff dim tensors, not just 2D ConvNets
random_tensor = keep_prob + torch.rand(shape, dtype=x.dtype, device=x.device)
random_tensor.floor_() # binarize
output = x.div(keep_prob) * random_tensor
return output
class DropPath(nn.Module):
"""Drop paths (Stochastic Depth) per sample (when applied in main path of residual blocks)."""
def __init__(self, drop_prob=None):
super().__init__()
self.drop_prob = drop_prob
def forward(self, x):
return drop_path(x, self.drop_prob, self.training)
class SegformerOverlapPatchEmbeddings(nn.Module):
"""Construct the patch embeddings from an image."""
def __init__(self, image_size, patch_size, stride, num_channels, hidden_size):
super().__init__()
image_size = to_2tuple(image_size)
patch_size = to_2tuple(patch_size)
self.height, self.width = image_size[0] // patch_size[0], image_size[1] // patch_size[1]
self.num_patches = self.height * self.width
self.proj = nn.Conv2d(
num_channels,
hidden_size,
kernel_size=patch_size,
stride=stride,
padding=(patch_size[0] // 2, patch_size[1] // 2),
)
self.layer_norm = nn.LayerNorm(hidden_size)
def forward(self, pixel_values):
x = self.proj(pixel_values)
_, _, height, width = x.shape
x = x.flatten(2).transpose(1, 2)
x = self.layer_norm(x)
return x, height, width
class SegformerEfficientSelfAttention(nn.Module):
def __init__(self, config, hidden_size, num_attention_heads, sr_ratio):
super().__init__()
self.hidden_size = hidden_size
self.num_attention_heads = num_attention_heads
if self.hidden_size % self.num_attention_heads != 0:
raise ValueError(
f"The hidden size ({self.hidden_size}) is not a multiple of the number of attention "
f"heads ({self.num_attention_heads})"
)
self.attention_head_size = int(self.hidden_size / self.num_attention_heads)
self.all_head_size = self.num_attention_heads * self.attention_head_size
self.query = nn.Linear(self.hidden_size, self.all_head_size)
self.key = nn.Linear(self.hidden_size, self.all_head_size)
self.value = nn.Linear(self.hidden_size, self.all_head_size)
self.dropout = nn.Dropout(config.attention_probs_dropout_prob)
self.sr_ratio = sr_ratio
if sr_ratio > 1:
self.sr = nn.Conv2d(hidden_size, hidden_size, kernel_size=sr_ratio, stride=sr_ratio)
self.layer_norm = nn.LayerNorm(hidden_size)
def transpose_for_scores(self, x):
new_x_shape = x.size()[:-1] + (self.num_attention_heads, self.attention_head_size)
x = x.view(*new_x_shape)
return x.permute(0, 2, 1, 3)
def forward(
self,
hidden_states,
height,
width,
output_attentions=False,
):
query_layer = self.transpose_for_scores(self.query(hidden_states))
if self.sr_ratio > 1:
batch_size, seq_len, num_channels = hidden_states.shape
hidden_states = hidden_states.permute(0, 2, 1).reshape(batch_size, num_channels, height, width)
hidden_states = self.sr(hidden_states)
hidden_states = hidden_states.reshape(batch_size, num_channels, -1).permute(0, 2, 1)
hidden_states = self.layer_norm(hidden_states)
key_layer = self.transpose_for_scores(self.key(hidden_states))
value_layer = self.transpose_for_scores(self.value(hidden_states))
# Take the dot product between "query" and "key" to get the raw attention scores.
attention_scores = torch.matmul(query_layer, key_layer.transpose(-1, -2))
attention_scores = attention_scores / math.sqrt(self.attention_head_size)
# Normalize the attention scores to probabilities.
attention_probs = nn.Softmax(dim=-1)(attention_scores)
# This is actually dropping out entire tokens to attend to, which might
# seem a bit unusual, but is taken from the original Transformer paper.
attention_probs = self.dropout(attention_probs)
context_layer = torch.matmul(attention_probs, value_layer)
context_layer = context_layer.permute(0, 2, 1, 3).contiguous()
new_context_layer_shape = context_layer.size()[:-2] + (self.all_head_size,)
context_layer = context_layer.view(*new_context_layer_shape)
outputs = (context_layer, attention_probs) if output_attentions else (context_layer,)
return outputs
class SegformerSelfOutput(nn.Module):
def __init__(self, config, hidden_size):
super().__init__()
self.dense = nn.Linear(hidden_size, hidden_size)
self.dropout = nn.Dropout(config.hidden_dropout_prob)
def forward(self, hidden_states, input_tensor):
hidden_states = self.dense(hidden_states)
hidden_states = self.dropout(hidden_states)
return hidden_states
class SegformerAttention(nn.Module):
def __init__(self, config, hidden_size, num_attention_heads, sr_ratio):
super().__init__()
self.self = SegformerEfficientSelfAttention(
config=config, hidden_size=hidden_size, num_attention_heads=num_attention_heads, sr_ratio=sr_ratio
)
self.output = SegformerSelfOutput(config, hidden_size=hidden_size)
self.pruned_heads = set()
def prune_heads(self, heads):
if len(heads) == 0:
return
heads, index = find_pruneable_heads_and_indices(
heads, self.self.num_attention_heads, self.self.attention_head_size, self.pruned_heads
)
# Prune linear layers
self.self.query = prune_linear_layer(self.self.query, index)
self.self.key = prune_linear_layer(self.self.key, index)
self.self.value = prune_linear_layer(self.self.value, index)
self.output.dense = prune_linear_layer(self.output.dense, index, dim=1)
# Update hyper params and store pruned heads
self.self.num_attention_heads = self.self.num_attention_heads - len(heads)
self.self.all_head_size = self.self.attention_head_size * self.self.num_attention_heads
self.pruned_heads = self.pruned_heads.union(heads)
def forward(self, hidden_states, height, width, output_attentions=False):
self_outputs = self.self(hidden_states, height, width, output_attentions)
attention_output = self.output(self_outputs[0], hidden_states)
outputs = (attention_output,) + self_outputs[1:] # add attentions if we output them
return outputs
class SegformerDWConv(nn.Module):
def __init__(self, dim=768):
super().__init__()
self.dwconv = nn.Conv2d(dim, dim, 3, 1, 1, bias=True, groups=dim)
def forward(self, hidden_states, height, width):
batch_size, seq_len, num_channels = hidden_states.shape
hidden_states = hidden_states.transpose(1, 2).view(batch_size, num_channels, height, width)
hidden_states = self.dwconv(hidden_states)
hidden_states = hidden_states.flatten(2).transpose(1, 2)
return hidden_states
class SegformerMixFFN(nn.Module):
def __init__(self, config, in_features, hidden_features=None, out_features=None):
super().__init__()
out_features = out_features or in_features
self.dense1 = nn.Linear(in_features, hidden_features)
self.dwconv = SegformerDWConv(hidden_features)
if isinstance(config.hidden_act, str):
self.intermediate_act_fn = ACT2FN[config.hidden_act]
else:
self.intermediate_act_fn = config.hidden_act
self.dense2 = nn.Linear(hidden_features, out_features)
self.dropout = nn.Dropout(config.hidden_dropout_prob)
def forward(self, hidden_states, height, width):
hidden_states = self.dense1(hidden_states)
hidden_states = self.dwconv(hidden_states, height, width)
hidden_states = self.intermediate_act_fn(hidden_states)
hidden_states = self.dropout(hidden_states)
hidden_states = self.dense2(hidden_states)
hidden_states = self.dropout(hidden_states)
return hidden_states
class SegformerLayer(nn.Module):
"""This corresponds to the Block class in the original implementation."""
def __init__(self, config, hidden_size, num_attention_heads, drop_path, sr_ratio, mlp_ratio):
super().__init__()
self.layer_norm_1 = nn.LayerNorm(hidden_size)
self.attention = SegformerAttention(
config, hidden_size=hidden_size, num_attention_heads=num_attention_heads, sr_ratio=sr_ratio
)
self.drop_path = DropPath(drop_path) if drop_path > 0.0 else nn.Identity()
self.layer_norm_2 = nn.LayerNorm(hidden_size)
mlp_hidden_size = int(hidden_size * mlp_ratio)
self.mlp = SegformerMixFFN(config, in_features=hidden_size, hidden_features=mlp_hidden_size)
def forward(self, hidden_states, height, width, output_attentions=False):
self_attention_outputs = self.attention(
self.layer_norm_1(hidden_states), # in Segformer, layernorm is applied before self-attention
height,
width,
output_attentions=output_attentions,
)
attention_output = self_attention_outputs[0]
outputs = self_attention_outputs[1:] # add self attentions if we output attention weights
# first residual connection (with stochastic depth)
attention_output = self.drop_path(attention_output)
hidden_states = attention_output + hidden_states
mlp_output = self.mlp(self.layer_norm_2(hidden_states), height, width)
# second residual connection (with stochastic depth)
mlp_output = self.drop_path(mlp_output)
layer_output = mlp_output + hidden_states
outputs = (layer_output,) + outputs
return outputs
class SegformerEncoder(nn.Module):
def __init__(self, config):
super().__init__()
self.config = config
# stochastic depth decay rule
dpr = [x.item() for x in torch.linspace(0, config.drop_path_rate, sum(config.depths))]
# patch embeddings
embeddings = []
for i in range(config.num_encoder_blocks):
embeddings.append(
SegformerOverlapPatchEmbeddings(
image_size=config.image_size // config.downsampling_rates[i],
patch_size=config.patch_sizes[i],
stride=config.strides[i],
num_channels=config.num_channels if i == 0 else config.hidden_sizes[i - 1],
hidden_size=config.hidden_sizes[i],
)
)
self.patch_embeddings = nn.ModuleList(embeddings)
# Transformer blocks
blocks = []
cur = 0
for i in range(config.num_encoder_blocks):
# each block consists of layers
layers = []
if i != 0:
cur += config.depths[i - 1]
for j in range(config.depths[i]):
layers.append(
SegformerLayer(
config,
hidden_size=config.hidden_sizes[i],
num_attention_heads=config.num_attention_heads[i],
drop_path=dpr[cur + j],
sr_ratio=config.sr_ratios[i],
mlp_ratio=config.mlp_ratios[i],
)
)
blocks.append(nn.ModuleList(layers))
self.block = nn.ModuleList(blocks)
# Layer norms
self.layer_norm = nn.ModuleList(
[nn.LayerNorm(config.hidden_sizes[i]) for i in range(config.num_encoder_blocks)]
)
def forward(
self,
pixel_values,
output_attentions=False,
output_hidden_states=False,
return_dict=True,
):
all_hidden_states = () if output_hidden_states else None
all_self_attentions = () if output_attentions else None
batch_size = pixel_values.shape[0]
hidden_states = pixel_values
for idx, x in enumerate(zip(self.patch_embeddings, self.block, self.layer_norm)):
embedding_layer, block_layer, norm_layer = x
# first, obtain patch embeddings
hidden_states, height, width = embedding_layer(hidden_states)
# second, send embeddings through blocks
for i, blk in enumerate(block_layer):
layer_outputs = blk(hidden_states, height, width, output_attentions)
hidden_states = layer_outputs[0]
if output_attentions:
all_self_attentions = all_self_attentions + (layer_outputs[1],)
# third, apply layer norm
hidden_states = norm_layer(hidden_states)
# fourth, optionally reshape back to (batch_size, num_channels, height, width)
if idx != len(self.patch_embeddings) - 1 or (
idx == len(self.patch_embeddings) - 1 and self.config.reshape_last_stage
):
hidden_states = hidden_states.reshape(batch_size, height, width, -1).permute(0, 3, 1, 2).contiguous()
if output_hidden_states:
all_hidden_states = all_hidden_states + (hidden_states,)
if not return_dict:
return tuple(v for v in [hidden_states, all_hidden_states, all_self_attentions] if v is not None)
return BaseModelOutput(
last_hidden_state=hidden_states,
hidden_states=all_hidden_states,
attentions=all_self_attentions,
)
class SegformerPreTrainedModel(PreTrainedModel):
"""
An abstract class to handle weights initialization and a simple interface for downloading and loading pretrained
models.
"""
config_class = SegformerConfig
base_model_prefix = "segformer"
def _init_weights(self, module):
"""Initialize the weights"""
if isinstance(module, (nn.Linear, nn.Conv2d)):
# Slightly different from the TF version which uses truncated_normal for initialization
# cf https://github.com/pytorch/pytorch/pull/5617
module.weight.data.normal_(mean=0.0, std=self.config.initializer_range)
if module.bias is not None:
module.bias.data.zero_()
elif isinstance(module, nn.Embedding):
module.weight.data.normal_(mean=0.0, std=self.config.initializer_range)
if module.padding_idx is not None:
module.weight.data[module.padding_idx].zero_()
elif isinstance(module, nn.LayerNorm):
module.bias.data.zero_()
module.weight.data.fill_(1.0)
SEGFORMER_START_DOCSTRING = r"""
This model is a PyTorch `torch.nn.Module <https://pytorch.org/docs/stable/nn.html#torch.nn.Module>`_ sub-class. Use
it as a regular PyTorch Module and refer to the PyTorch documentation for all matter related to general usage and
behavior.
Parameters:
config (:class:`~transformers.SegformerConfig`): Model configuration class with all the parameters of the model.
Initializing with a config file does not load the weights associated with the model, only the
configuration. Check out the :meth:`~transformers.PreTrainedModel.from_pretrained` method to load the model
weights.
"""
SEGFORMER_INPUTS_DOCSTRING = r"""
Args:
pixel_values (:obj:`torch.FloatTensor` of shape :obj:`(batch_size, num_channels, height, width)`):
Pixel values. Padding will be ignored by default should you provide it. Pixel values can be obtained using
:class:`~transformers.SegformerFeatureExtractor`. See
:meth:`transformers.SegformerFeatureExtractor.__call__` for details.
output_attentions (:obj:`bool`, `optional`):
Whether or not to return the attentions tensors of all attention layers. See ``attentions`` under returned
tensors for more detail.
output_hidden_states (:obj:`bool`, `optional`):
Whether or not to return the hidden states of all layers. See ``hidden_states`` under returned tensors for
more detail.
return_dict (:obj:`bool`, `optional`):
Whether or not to return a :class:`~transformers.file_utils.ModelOutput` instead of a plain tuple.
"""
class SegformerMLP(nn.Module):
"""
Linear Embedding.
"""
def __init__(self, config: SegformerConfig, input_dim):
super().__init__()
self.proj = nn.Linear(input_dim, config.decoder_hidden_size)
def forward(self, hidden_states: torch.Tensor):
hidden_states = hidden_states.flatten(2).transpose(1, 2)
hidden_states = self.proj(hidden_states)
return hidden_states