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| import torch.nn as nn | |
| from mmcv.cnn import ConvModule, bias_init_with_prob, normal_init | |
| from ..builder import HEADS | |
| from .anchor_head import AnchorHead | |
| class RetinaHead(AnchorHead): | |
| r"""An anchor-based head used in `RetinaNet | |
| <https://arxiv.org/pdf/1708.02002.pdf>`_. | |
| The head contains two subnetworks. The first classifies anchor boxes and | |
| the second regresses deltas for the anchors. | |
| Example: | |
| >>> import torch | |
| >>> self = RetinaHead(11, 7) | |
| >>> x = torch.rand(1, 7, 32, 32) | |
| >>> cls_score, bbox_pred = self.forward_single(x) | |
| >>> # Each anchor predicts a score for each class except background | |
| >>> cls_per_anchor = cls_score.shape[1] / self.num_anchors | |
| >>> box_per_anchor = bbox_pred.shape[1] / self.num_anchors | |
| >>> assert cls_per_anchor == (self.num_classes) | |
| >>> assert box_per_anchor == 4 | |
| """ | |
| def __init__(self, | |
| num_classes, | |
| in_channels, | |
| stacked_convs=4, | |
| conv_cfg=None, | |
| norm_cfg=None, | |
| anchor_generator=dict( | |
| type='AnchorGenerator', | |
| octave_base_scale=4, | |
| scales_per_octave=3, | |
| ratios=[0.5, 1.0, 2.0], | |
| strides=[8, 16, 32, 64, 128]), | |
| **kwargs): | |
| self.stacked_convs = stacked_convs | |
| self.conv_cfg = conv_cfg | |
| self.norm_cfg = norm_cfg | |
| super(RetinaHead, self).__init__( | |
| num_classes, | |
| in_channels, | |
| anchor_generator=anchor_generator, | |
| **kwargs) | |
| def _init_layers(self): | |
| """Initialize layers of the head.""" | |
| self.relu = nn.ReLU(inplace=True) | |
| self.cls_convs = nn.ModuleList() | |
| self.reg_convs = nn.ModuleList() | |
| for i in range(self.stacked_convs): | |
| chn = self.in_channels if i == 0 else self.feat_channels | |
| self.cls_convs.append( | |
| ConvModule( | |
| chn, | |
| self.feat_channels, | |
| 3, | |
| stride=1, | |
| padding=1, | |
| conv_cfg=self.conv_cfg, | |
| norm_cfg=self.norm_cfg)) | |
| self.reg_convs.append( | |
| ConvModule( | |
| chn, | |
| self.feat_channels, | |
| 3, | |
| stride=1, | |
| padding=1, | |
| conv_cfg=self.conv_cfg, | |
| norm_cfg=self.norm_cfg)) | |
| self.retina_cls = nn.Conv2d( | |
| self.feat_channels, | |
| self.num_anchors * self.cls_out_channels, | |
| 3, | |
| padding=1) | |
| self.retina_reg = nn.Conv2d( | |
| self.feat_channels, self.num_anchors * 4, 3, padding=1) | |
| def init_weights(self): | |
| """Initialize weights of the head.""" | |
| for m in self.cls_convs: | |
| normal_init(m.conv, std=0.01) | |
| for m in self.reg_convs: | |
| normal_init(m.conv, std=0.01) | |
| bias_cls = bias_init_with_prob(0.01) | |
| normal_init(self.retina_cls, std=0.01, bias=bias_cls) | |
| normal_init(self.retina_reg, std=0.01) | |
| def forward_single(self, x): | |
| """Forward feature of a single scale level. | |
| Args: | |
| x (Tensor): Features of a single scale level. | |
| Returns: | |
| tuple: | |
| cls_score (Tensor): Cls scores for a single scale level | |
| the channels number is num_anchors * num_classes. | |
| bbox_pred (Tensor): Box energies / deltas for a single scale | |
| level, the channels number is num_anchors * 4. | |
| """ | |
| cls_feat = x | |
| reg_feat = x | |
| for cls_conv in self.cls_convs: | |
| cls_feat = cls_conv(cls_feat) | |
| for reg_conv in self.reg_convs: | |
| reg_feat = reg_conv(reg_feat) | |
| cls_score = self.retina_cls(cls_feat) | |
| bbox_pred = self.retina_reg(reg_feat) | |
| return cls_score, bbox_pred | |