mmdetection源码详细解读

简介

• GitHub地址：https://github.com/open-mmlab/mmdetection.
• 各模型的权重可以在model_zoo.md上下载。
• mmdetection官方使用教程https://mmdetection.readthedocs.io/en/latest/（强烈建议）

1. 测试代码

import mmcv
from mmdet.apis import init_detector, inference_detector, show_result_pyplot

config_file = 'configs/faster_rcnn/faster_rcnn_r50_fpn_1x_coco.py'
checkpoint_file = 'checkpoints/faster_rcnn_r50_fpn_1x_coco_20200130-047c8118.pth'

# build the model from a config file and a checkpoint file
model = init_detector(config_file, checkpoint_file, device='cuda:1')

# test a single image and show the results
img = 'demo.jpg'  # or img = mmcv.imread(img), which will only load it once
result = inference_detector(model, img)

# visualize the results in a new window
show_result_pyplot(model, img, result)

新建一个工程，其目录结构为：

实际上，我把mmdetection看成是第三方库（类比numpy、cv2等），所以我把下载下来的GitHub代码解压到了python的工程文件中，即

但我看有的人直接把mmdetection当做是工程文件也是没问题的，比如D2Det的官方代码就是如此：你可以发现其目录结构和mmdetection的源码结构是一样的。

2. mmdetection/mmdet/apis

该文件夹下有三个文件：

• inference.py：用于初始化模型、前向推理、读取图片、显示检测结果等。
• train：用于训练。
• test：用于测试。
  

2.1 mmdetection/mmdet/apis/inference.py

2.1.1 init_detector

def init_detector(config, checkpoint=None, device='cuda:0'):
    """Initialize a detector from config file.

    Args:
        config (str or :obj:`mmcv.Config`): Config file path or the config
            object.
        checkpoint (str, optional): Checkpoint path. If left as None, the model
            will not load any weights.

    Returns:
        nn.Module: The constructed detector.
    """
    if isinstance(config, str):
    	# 如果config是配置文件路径，则用mmcv.Config.fromfile()读取，
    	# 并返回类mmcv.Config()实例化后的object
    	# 如果config已经是类mmcv.Config()实例化后的object，则不需要其他操作。
        config = mmcv.Config.fromfile(config)
    elif not isinstance(config, mmcv.Config):
        raise TypeError('config must be a filename or Config object, '
                        f'but got {type(config)}')
    config.model.pretrained = None
    model = build_detector(config.model, test_cfg=config.test_cfg)
    if checkpoint is not None:
        map_loc = 'cpu' if device == 'cpu' else None
        checkpoint = load_checkpoint(model, checkpoint, map_location=map_loc)
        if 'CLASSES' in checkpoint['meta']:
            model.CLASSES = checkpoint['meta']['CLASSES']
        else:
            warnings.simplefilter('once')
            warnings.warn('Class names are not saved in the checkpoint\'s '
                          'meta data, use COCO classes by default.')
            model.CLASSES = get_classes('coco')
    model.cfg = config  # save the config in the model for convenience
    model.to(device)
    model.eval()
    return model

函数作用、输入参数、输出参数直接见注解。这里给出几个例子：

from mmdet.apis import init_detector, inference_detector, show_result_pyplot

config_file = 'configs/faster_rcnn/faster_rcnn_r50_fpn_1x_coco.py'
checkpoint_file = 'checkpoints/faster_rcnn_r50_fpn_1x_coco_20200130-047c8118.pth'

# build the model from a config file and a checkpoint file
model = init_detector(config_file, checkpoint_file, device='cuda:0')
# device 可以是'cpu'、'cuda:0'、'cuda:1'等。

2.1.2 inference_detector

def inference_detector(model, img):
    """Inference image(s) with the detector.

    Args:
        model (nn.Module): The loaded detector.
        imgs (str/ndarray or list[str/ndarray]): Either image files or loaded
            images.

    Returns:
        If imgs is a str, a generator will be returned, otherwise return the
        detection results directly.
    """
    cfg = model.cfg
    device = next(model.parameters()).device  # model device
    # build the data pipeline
    test_pipeline = [LoadImage()] + cfg.data.test.pipeline[1:]
    test_pipeline = Compose(test_pipeline)
    # prepare data
    data = dict(img=img)
    data = test_pipeline(data)
    data = collate([data], samples_per_gpu=1)
    if next(model.parameters()).is_cuda:
        # scatter to specified GPU
        data = scatter(data, [device])[0]
    else:
        # Use torchvision ops for CPU mode instead
        for m in model.modules():
            if isinstance(m, (RoIPool, RoIAlign)):
                if not m.aligned:
                    # aligned=False is not implemented on CPU
                    # set use_torchvision on-the-fly
                    m.use_torchvision = True
        warnings.warn('We set use_torchvision=True in CPU mode.')
        # just get the actual data from DataContainer
        data['img_metas'] = data['img_metas'][0].data

    # forward the model
    with torch.no_grad():
        result = model(return_loss=False, rescale=True, **data)
    return result

3. build_detector()

model = build_detector(cfg.model, train_cfg=cfg.train_cfg, test_cfg=cfg.test_cfg)

• 根据配置文件构建神经网络

以configs/fcos/fcos_r50_caffe_fpn_4x4_1x_coco.py配置文件为例，cfg.model，cfg.train_cfg，cfg.test_cfg均为字典类型，分别与配置文件中的内容相对应。

DETECTORS = Registry('detector')
def build_detector(cfg, train_cfg=None, test_cfg=None):
    """Build detector."""
    return build(cfg, DETECTORS, dict(train_cfg=train_cfg, test_cfg=test_cfg))

• Registry是一个大工厂，工厂中包含了很多小仓库，共有7个小仓库，这些仓库在train.py开始import 模块时就自动创建，并且每个仓库中都放了各种样的小商品，比如在detectors/__init__.py中可以看到，仓库DETECTORS的小商品有：。

BACKBONES = Registry('backbone')
NECKS = Registry('neck')
ROI_EXTRACTORS = Registry('roi_extractor')
SHARED_HEADS = Registry('shared_head')
HEADS = Registry('head')
LOSSES = Registry('loss')
DETECTORS = Registry('detector')

# detectors/__init__.py
from .atss import ATSS
from .base import BaseDetector
from .cascade_rcnn import CascadeRCNN
from .fast_rcnn import FastRCNN
from .faster_rcnn import FasterRCNN
from .fcos import FCOS
from .fovea import FOVEA
from .fsaf import FSAF
from .gfl import GFL
from .grid_rcnn import GridRCNN
from .htc import HybridTaskCascade
from .mask_rcnn import MaskRCNN
from .mask_scoring_rcnn import MaskScoringRCNN
from .nasfcos import NASFCOS
from .point_rend import PointRend
from .reppoints_detector import RepPointsDetector
from .retinanet import RetinaNet
from .rpn import RPN
from .single_stage import SingleStageDetector
from .two_stage import TwoStageDetector

• 此时参数cfg是字典类型，执行build_from_cfg()

def build(cfg, registry, default_args=None):
    if isinstance(cfg, list):
        modules = [build_from_cfg(cfg_, registry, default_args) for cfg_ in cfg]
        return nn.Sequential(*modules)
    else:
        return build_from_cfg(cfg, registry, default_args)

• 比如在fcos.py文件中，修饰器@DETECTORS.register_module()的作用就是将创建好的小商品FCOS放入仓库DETECTORS中。

@DETECTORS.register_module()
class FCOS(SingleStageDetector):
    """Implementation of `FCOS `_"""

    def __init__(self,
                 backbone,
                 neck,
                 bbox_head,
                 train_cfg=None,
                 test_cfg=None,
                 pretrained=None):
        super(FCOS, self).__init__(backbone, neck, bbox_head, train_cfg,
                                   test_cfg, pretrained)

• 在register_module()函数中，你可以看到它的用法，小商品的名字就是在注册时指定的，而注册时的名字就是类名FCOS或ResNet等。所以你要创建自己的检测器，你需要构建一个类，把这个类当做小商品，然后将其放在相应的仓库中（注册）。

    def register_module(self, name=None, force=False, module=None):
        """Register a module.

        A record will be added to `self._module_dict`, whose key is the class
        name or the specified name, and value is the class itself.
        It can be used as a decorator or a normal function.

        Example:
            >>> backbones = Registry('backbone')
            >>> @backbones.register_module()
            >>> class ResNet:
            >>>     pass

            >>> backbones = Registry('backbone')
            >>> @backbones.register_module(name='mnet')
            >>> class MobileNet:
            >>>     pass

            >>> backbones = Registry('backbone')
            >>> class ResNet:
            >>>     pass
            >>> backbones.register_module(ResNet)

• obj_type='FCOS'，在

def build_from_cfg(cfg, registry, default_args=None):
    """Build a module from config dict."""
    args = cfg.copy()
    obj_type = args.pop('type') # 'FCOS'
    if is_str(obj_type):
        obj_cls = registry.get(obj_type)
        if obj_cls is None:
            raise KeyError(
                f'{obj_type} is not in the {registry.name} registry')
    elif inspect.isclass(obj_type):
        obj_cls = obj_type
    else:
        raise TypeError(
            f'type must be a str or valid type, but got {type(obj_type)}')

    if default_args is not None:
        for name, value in default_args.items():
            args.setdefault(name, value)
    return obj_cls(**args)