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Tutorial 3: Adding New Modules

In self-supervised learning domain, each model can be divided into following four parts:

  • backbone: used to extract image’s feature

  • projection head: projects feature extracted by backbone to another space

  • loss: loss function the model will optimize

  • memory bank(optional): some methods, e.g. odc, need extract memory bank to store image’s feature.

Add new backbone

Assuming we are going to create a customized backbone CustomizedBackbone

1.Create a new file mmselfsup/models/backbones/customized_backbone.py and implement CustomizedBackbone in it.

import torch.nn as nn
from ..builder import BACKBONES

@BACKBONES.register_module()
class CustomizedBackbone(nn.Module):

    def __init__(self, **kwargs):

        ## TODO

    def forward(self, x):

        ## TODO

    def init_weights(self, pretrained=None):

        ## TODO

    def train(self, mode=True):

        ## TODO

2.Import the customized backbone in mmselfsup/models/backbones/__init__.py.

from .customized_backbone import CustomizedBackbone

__all__ = [
    ..., 'CustomizedBackbone'
]

3.Use it in your config file.

model = dict(
    ...
    backbone=dict(
        type='CustomizedBackbone',
        ...),
    ...
)

Add new necks

we include all projection heads in mmselfsup/models/necks. Assuming we are going to create a CustomizedProjHead.

1.Create a new file mmselfsup/models/necks/customized_proj_head.py and implement CustomizedProjHead in it.

import torch.nn as nn
from mmcv.runner import BaseModule

from ..builder import NECKS


@NECKS.register_module()
class CustomizedProjHead(BaseModule):

    def __init__(self, *args, **kwargs):
        super(CustomizedProjHead, self).__init__(init_cfg)
        ## TODO
    def forward(self, x):
        ## TODO

You need to implement the forward function, which takes the feature from the backbone and outputs the projected feature.

2.Import the CustomizedProjHead in mmselfsup/models/necks/__init__.

from .customized_proj_head import CustomizedProjHead

__all__ = [
    ...,
    CustomizedProjHead,
    ...
]

3.Use it in your config file.

model = dict(
    ...,
    neck=dict(
        type='CustomizedProjHead',
        ...),
   ...)

Add new loss

To add a new loss function, we mainly implement the forward function in the loss module.

1.Create a new file mmselfsup/models/heads/customized_head.py and implement your customized CustomizedHead in it.

import torch
import torch.nn as nn
from mmcv.runner import BaseModule

from ..builder import HEADS


@HEADS.register_module()
class CustomizedHead(BaseModule):

    def __init__(self, *args, **kwargs):
        super(CustomizedHead, self).__init__()

        ## TODO

    def forward(self, *args, **kwargs):

        ## TODO

2.Import the module in mmselfsup/models/heads/__init__.py

from .customized_head import CustomizedHead

__all__ = [..., CustomizedHead, ...]

3.Use it in your config file.

model = dict(
    ...,
    head=dict(type='CustomizedHead')
    )

Combine all

After creating each component, mentioned above, we need to create a CustomizedAlgorithm to organize them logically. And the CustomizedAlgorithm takes raw images as inputs and outputs the loss to the optimizer.

1.Create a new file mmselfsup/models/algorithms/customized_algorithm.py and implement CustomizedAlgorithm in it.

# Copyright (c) OpenMMLab. All rights reserved.
import torch

from ..builder import ALGORITHMS, build_backbone, build_head, build_neck
from ..utils import GatherLayer
from .base import BaseModel


@ALGORITHMS.register_module()
class CustomizedAlgorithm(BaseModel):

    def __init__(self, backbone, neck=None, head=None, init_cfg=None):
        super(SimCLR, self).__init__(init_cfg)

        ## TODO

    def forward_train(self, img, **kwargs):

        ## TODO

2.Import the module in mmselfsup/models/algorithms/__init__.py

from .customized_algorithm import CustomizedAlgorithm

__all__ = [..., CustomizedAlgorithm, ...]

3.Use it in your config file.

model = dict(
    type='CustomizedAlgorightm',
    backbone=...,
    neck=...,
    head=...)
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