import torch
import torch.nn as nn
import torch.nn.functional as F
from mmcv.cnn import normal_init
from mmdet.ops import batched_nms
from ..builder import HEADS
from .anchor_head import AnchorHead
from .rpn_test_mixin import RPNTestMixin
[docs]@HEADS.register_module()
class RPNHead(RPNTestMixin, AnchorHead):
"""RPN head.
Args:
in_channels (int): Number of channels in the input feature map.
""" # noqa: W605
def __init__(self, in_channels, **kwargs):
super(RPNHead, self).__init__(
1, in_channels, background_label=0, **kwargs)
def _init_layers(self):
"""Initialize layers of the head."""
self.rpn_conv = nn.Conv2d(
self.in_channels, self.feat_channels, 3, padding=1)
self.rpn_cls = nn.Conv2d(self.feat_channels,
self.num_anchors * self.cls_out_channels, 1)
self.rpn_reg = nn.Conv2d(self.feat_channels, self.num_anchors * 4, 1)
[docs] def init_weights(self):
"""Initialize weights of the head."""
normal_init(self.rpn_conv, std=0.01)
normal_init(self.rpn_cls, std=0.01)
normal_init(self.rpn_reg, std=0.01)
[docs] def forward_single(self, x):
"""Forward feature map of a single scale level."""
x = self.rpn_conv(x)
x = F.relu(x, inplace=True)
rpn_cls_score = self.rpn_cls(x)
rpn_bbox_pred = self.rpn_reg(x)
return rpn_cls_score, rpn_bbox_pred
[docs] def loss(self,
cls_scores,
bbox_preds,
gt_bboxes,
img_metas,
gt_bboxes_ignore=None):
"""Compute losses of the head.
Args:
cls_scores (list[Tensor]): Box scores for each scale level
Has shape (N, num_anchors * num_classes, H, W)
bbox_preds (list[Tensor]): Box energies / deltas for each scale
level with shape (N, num_anchors * 4, H, W)
gt_bboxes (list[Tensor]): Ground truth bboxes for each image with
shape (num_gts, 4) in [tl_x, tl_y, br_x, br_y] format.
img_metas (list[dict]): Meta information of each image, e.g.,
image size, scaling factor, etc.
gt_bboxes_ignore (None | list[Tensor]): specify which bounding
boxes can be ignored when computing the loss.
Returns:
dict[str, Tensor]: A dictionary of loss components.
"""
losses = super(RPNHead, self).loss(
cls_scores,
bbox_preds,
gt_bboxes,
None,
img_metas,
gt_bboxes_ignore=gt_bboxes_ignore)
return dict(
loss_rpn_cls=losses['loss_cls'], loss_rpn_bbox=losses['loss_bbox'])
def _get_bboxes_single(self,
cls_scores,
bbox_preds,
mlvl_anchors,
img_shape,
scale_factor,
cfg,
rescale=False):
"""Transform outputs for a single batch item into bbox predictions.
Args:
cls_scores (list[Tensor]): Box scores for each scale level
Has shape (num_anchors * num_classes, H, W).
bbox_preds (list[Tensor]): Box energies / deltas for each scale
level with shape (num_anchors * 4, H, W).
mlvl_anchors (list[Tensor]): Box reference for each scale level
with shape (num_total_anchors, 4).
img_shape (tuple[int]): Shape of the input image,
(height, width, 3).
scale_factor (ndarray): Scale factor of the image arange as
(w_scale, h_scale, w_scale, h_scale).
cfg (mmcv.Config): Test / postprocessing configuration,
if None, test_cfg would be used.
rescale (bool): If True, return boxes in original image space.
Returns:
Tensor: Labeled boxes in shape (n, 5), where the first 4 columns
are bounding box positions (tl_x, tl_y, br_x, br_y) and the
5-th column is a score between 0 and 1.
"""
cfg = self.test_cfg if cfg is None else cfg
# bboxes from different level should be independent during NMS,
# level_ids are used as labels for batched NMS to separate them
level_ids = []
mlvl_scores = []
mlvl_bbox_preds = []
mlvl_valid_anchors = []
for idx in range(len(cls_scores)):
rpn_cls_score = cls_scores[idx]
rpn_bbox_pred = bbox_preds[idx]
assert rpn_cls_score.size()[-2:] == rpn_bbox_pred.size()[-2:]
rpn_cls_score = rpn_cls_score.permute(1, 2, 0)
if self.use_sigmoid_cls:
rpn_cls_score = rpn_cls_score.reshape(-1)
scores = rpn_cls_score.sigmoid()
else:
rpn_cls_score = rpn_cls_score.reshape(-1, 2)
# we set FG labels to [0, num_class-1] and BG label to
# num_class in other heads since mmdet v2.0, However we
# keep BG label as 0 and FG label as 1 in rpn head
scores = rpn_cls_score.softmax(dim=1)[:, 1]
rpn_bbox_pred = rpn_bbox_pred.permute(1, 2, 0).reshape(-1, 4)
anchors = mlvl_anchors[idx]
if cfg.nms_pre > 0 and scores.shape[0] > cfg.nms_pre:
# sort is faster than topk
# _, topk_inds = scores.topk(cfg.nms_pre)
ranked_scores, rank_inds = scores.sort(descending=True)
topk_inds = rank_inds[:cfg.nms_pre]
scores = ranked_scores[:cfg.nms_pre]
rpn_bbox_pred = rpn_bbox_pred[topk_inds, :]
anchors = anchors[topk_inds, :]
mlvl_scores.append(scores)
mlvl_bbox_preds.append(rpn_bbox_pred)
mlvl_valid_anchors.append(anchors)
level_ids.append(
scores.new_full((scores.size(0), ), idx, dtype=torch.long))
scores = torch.cat(mlvl_scores)
anchors = torch.cat(mlvl_valid_anchors)
rpn_bbox_pred = torch.cat(mlvl_bbox_preds)
proposals = self.bbox_coder.decode(
anchors, rpn_bbox_pred, max_shape=img_shape)
ids = torch.cat(level_ids)
if cfg.min_bbox_size > 0:
w = proposals[:, 2] - proposals[:, 0]
h = proposals[:, 3] - proposals[:, 1]
valid_inds = torch.nonzero(
(w >= cfg.min_bbox_size)
& (h >= cfg.min_bbox_size),
as_tuple=False).squeeze()
if valid_inds.sum().item() != len(proposals):
proposals = proposals[valid_inds, :]
scores = scores[valid_inds]
ids = ids[valid_inds]
# TODO: remove the hard coded nms type
nms_cfg = dict(type='nms', iou_thr=cfg.nms_thr)
dets, keep = batched_nms(proposals, scores, ids, nms_cfg)
return dets[:cfg.nms_post]