File size: 10,216 Bytes
c9019cd |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 |
# Tutorial 4: Customize Models
We basically categorize model components into 5 types.
- backbone: usually an FCN network to extract feature maps, e.g., ResNet, MobileNet.
- neck: the component between backbones and heads, e.g., FPN, PAFPN.
- head: the component for specific tasks, e.g., bbox prediction and mask prediction.
- roi extractor: the part for extracting RoI features from feature maps, e.g., RoI Align.
- loss: the component in head for calculating losses, e.g., FocalLoss, L1Loss, and GHMLoss.
## Develop new components
### Add a new backbone
Here we show how to develop new components with an example of MobileNet.
#### 1. Define a new backbone (e.g. MobileNet)
Create a new file `mmdet/models/backbones/mobilenet.py`.
```python
import torch.nn as nn
from ..builder import BACKBONES
@BACKBONES.register_module()
class MobileNet(nn.Module):
def __init__(self, arg1, arg2):
pass
def forward(self, x): # should return a tuple
pass
```
#### 2. Import the module
You can either add the following line to `mmdet/models/backbones/__init__.py`
```python
from .mobilenet import MobileNet
```
or alternatively add
```python
custom_imports = dict(
imports=['mmdet.models.backbones.mobilenet'],
allow_failed_imports=False)
```
to the config file to avoid modifying the original code.
#### 3. Use the backbone in your config file
```python
model = dict(
...
backbone=dict(
type='MobileNet',
arg1=xxx,
arg2=xxx),
...
```
### Add new necks
#### 1. Define a neck (e.g. PAFPN)
Create a new file `mmdet/models/necks/pafpn.py`.
```python
from ..builder import NECKS
@NECKS.register_module()
class PAFPN(nn.Module):
def __init__(self,
in_channels,
out_channels,
num_outs,
start_level=0,
end_level=-1,
add_extra_convs=False):
pass
def forward(self, inputs):
# implementation is ignored
pass
```
#### 2. Import the module
You can either add the following line to `mmdet/models/necks/__init__.py`,
```python
from .pafpn import PAFPN
```
or alternatively add
```python
custom_imports = dict(
imports=['mmdet.models.necks.pafpn.py'],
allow_failed_imports=False)
```
to the config file and avoid modifying the original code.
#### 3. Modify the config file
```python
neck=dict(
type='PAFPN',
in_channels=[256, 512, 1024, 2048],
out_channels=256,
num_outs=5)
```
### Add new heads
Here we show how to develop a new head with the example of [Double Head R-CNN](https://arxiv.org/abs/1904.06493) as the following.
First, add a new bbox head in `mmdet/models/roi_heads/bbox_heads/double_bbox_head.py`.
Double Head R-CNN implements a new bbox head for object detection.
To implement a bbox head, basically we need to implement three functions of the new module as the following.
```python
from mmdet.models.builder import HEADS
from .bbox_head import BBoxHead
@HEADS.register_module()
class DoubleConvFCBBoxHead(BBoxHead):
r"""Bbox head used in Double-Head R-CNN
/-> cls
/-> shared convs ->
\-> reg
roi features
/-> cls
\-> shared fc ->
\-> reg
""" # noqa: W605
def __init__(self,
num_convs=0,
num_fcs=0,
conv_out_channels=1024,
fc_out_channels=1024,
conv_cfg=None,
norm_cfg=dict(type='BN'),
**kwargs):
kwargs.setdefault('with_avg_pool', True)
super(DoubleConvFCBBoxHead, self).__init__(**kwargs)
def forward(self, x_cls, x_reg):
```
Second, implement a new RoI Head if it is necessary. We plan to inherit the new `DoubleHeadRoIHead` from `StandardRoIHead`. We can find that a `StandardRoIHead` already implements the following functions.
```python
import torch
from mmdet.core import bbox2result, bbox2roi, build_assigner, build_sampler
from ..builder import HEADS, build_head, build_roi_extractor
from .base_roi_head import BaseRoIHead
from .test_mixins import BBoxTestMixin, MaskTestMixin
@HEADS.register_module()
class StandardRoIHead(BaseRoIHead, BBoxTestMixin, MaskTestMixin):
"""Simplest base roi head including one bbox head and one mask head.
"""
def init_assigner_sampler(self):
def init_bbox_head(self, bbox_roi_extractor, bbox_head):
def init_mask_head(self, mask_roi_extractor, mask_head):
def forward_dummy(self, x, proposals):
def forward_train(self,
x,
img_metas,
proposal_list,
gt_bboxes,
gt_labels,
gt_bboxes_ignore=None,
gt_masks=None):
def _bbox_forward(self, x, rois):
def _bbox_forward_train(self, x, sampling_results, gt_bboxes, gt_labels,
img_metas):
def _mask_forward_train(self, x, sampling_results, bbox_feats, gt_masks,
img_metas):
def _mask_forward(self, x, rois=None, pos_inds=None, bbox_feats=None):
def simple_test(self,
x,
proposal_list,
img_metas,
proposals=None,
rescale=False):
"""Test without augmentation."""
```
Double Head's modification is mainly in the bbox_forward logic, and it inherits other logics from the `StandardRoIHead`.
In the `mmdet/models/roi_heads/double_roi_head.py`, we implement the new RoI Head as the following:
```python
from ..builder import HEADS
from .standard_roi_head import StandardRoIHead
@HEADS.register_module()
class DoubleHeadRoIHead(StandardRoIHead):
"""RoI head for Double Head RCNN
https://arxiv.org/abs/1904.06493
"""
def __init__(self, reg_roi_scale_factor, **kwargs):
super(DoubleHeadRoIHead, self).__init__(**kwargs)
self.reg_roi_scale_factor = reg_roi_scale_factor
def _bbox_forward(self, x, rois):
bbox_cls_feats = self.bbox_roi_extractor(
x[:self.bbox_roi_extractor.num_inputs], rois)
bbox_reg_feats = self.bbox_roi_extractor(
x[:self.bbox_roi_extractor.num_inputs],
rois,
roi_scale_factor=self.reg_roi_scale_factor)
if self.with_shared_head:
bbox_cls_feats = self.shared_head(bbox_cls_feats)
bbox_reg_feats = self.shared_head(bbox_reg_feats)
cls_score, bbox_pred = self.bbox_head(bbox_cls_feats, bbox_reg_feats)
bbox_results = dict(
cls_score=cls_score,
bbox_pred=bbox_pred,
bbox_feats=bbox_cls_feats)
return bbox_results
```
Last, the users need to add the module in
`mmdet/models/bbox_heads/__init__.py` and `mmdet/models/roi_heads/__init__.py` thus the corresponding registry could find and load them.
Alternatively, the users can add
```python
custom_imports=dict(
imports=['mmdet.models.roi_heads.double_roi_head', 'mmdet.models.bbox_heads.double_bbox_head'])
```
to the config file and achieve the same goal.
The config file of Double Head R-CNN is as the following
```python
_base_ = '../faster_rcnn/faster_rcnn_r50_fpn_1x_coco.py'
model = dict(
roi_head=dict(
type='DoubleHeadRoIHead',
reg_roi_scale_factor=1.3,
bbox_head=dict(
_delete_=True,
type='DoubleConvFCBBoxHead',
num_convs=4,
num_fcs=2,
in_channels=256,
conv_out_channels=1024,
fc_out_channels=1024,
roi_feat_size=7,
num_classes=80,
bbox_coder=dict(
type='DeltaXYWHBBoxCoder',
target_means=[0., 0., 0., 0.],
target_stds=[0.1, 0.1, 0.2, 0.2]),
reg_class_agnostic=False,
loss_cls=dict(
type='CrossEntropyLoss', use_sigmoid=False, loss_weight=2.0),
loss_bbox=dict(type='SmoothL1Loss', beta=1.0, loss_weight=2.0))))
```
Since MMDetection 2.0, the config system supports to inherit configs such that the users can focus on the modification.
The Double Head R-CNN mainly uses a new DoubleHeadRoIHead and a new
`DoubleConvFCBBoxHead`, the arguments are set according to the `__init__` function of each module.
### Add new loss
Assume you want to add a new loss as `MyLoss`, for bounding box regression.
To add a new loss function, the users need implement it in `mmdet/models/losses/my_loss.py`.
The decorator `weighted_loss` enable the loss to be weighted for each element.
```python
import torch
import torch.nn as nn
from ..builder import LOSSES
from .utils import weighted_loss
@weighted_loss
def my_loss(pred, target):
assert pred.size() == target.size() and target.numel() > 0
loss = torch.abs(pred - target)
return loss
@LOSSES.register_module()
class MyLoss(nn.Module):
def __init__(self, reduction='mean', loss_weight=1.0):
super(MyLoss, self).__init__()
self.reduction = reduction
self.loss_weight = loss_weight
def forward(self,
pred,
target,
weight=None,
avg_factor=None,
reduction_override=None):
assert reduction_override in (None, 'none', 'mean', 'sum')
reduction = (
reduction_override if reduction_override else self.reduction)
loss_bbox = self.loss_weight * my_loss(
pred, target, weight, reduction=reduction, avg_factor=avg_factor)
return loss_bbox
```
Then the users need to add it in the `mmdet/models/losses/__init__.py`.
```python
from .my_loss import MyLoss, my_loss
```
Alternatively, you can add
```python
custom_imports=dict(
imports=['mmdet.models.losses.my_loss'])
```
to the config file and achieve the same goal.
To use it, modify the `loss_xxx` field.
Since MyLoss is for regression, you need to modify the `loss_bbox` field in the head.
```python
loss_bbox=dict(type='MyLoss', loss_weight=1.0))
```
|