# Copyright (c) OpenMMLab. All rights reserved. import torch import torch.nn as nn from mmcv.cnn import bias_init_with_prob, normal_init from mmcv.ops import batched_nms from mmcv.runner import force_fp32 from mmdet.core import multi_apply from mmdet.models import HEADS, build_loss from mmdet.models.utils import gaussian_radius, gen_gaussian_target from ..utils.gaussian_target import (get_local_maximum, get_topk_from_heatmap, transpose_and_gather_feat) from .base_dense_head import BaseDenseHead from .dense_test_mixins import BBoxTestMixin @HEADS.register_module() class CenterNetHead(BaseDenseHead, BBoxTestMixin): """Objects as Points Head. CenterHead use center_point to indicate object's position. Paper link Args: in_channel (int): Number of channel in the input feature map. feat_channel (int): Number of channel in the intermediate feature map. num_classes (int): Number of categories excluding the background category. loss_center_heatmap (dict | None): Config of center heatmap loss. Default: GaussianFocalLoss. loss_wh (dict | None): Config of wh loss. Default: L1Loss. loss_offset (dict | None): Config of offset loss. Default: L1Loss. train_cfg (dict | None): Training config. Useless in CenterNet, but we keep this variable for SingleStageDetector. Default: None. test_cfg (dict | None): Testing config of CenterNet. Default: None. init_cfg (dict or list[dict], optional): Initialization config dict. Default: None """ def __init__(self, in_channel, feat_channel, num_classes, loss_center_heatmap=dict( type='GaussianFocalLoss', loss_weight=1.0), loss_wh=dict(type='L1Loss', loss_weight=0.1), loss_offset=dict(type='L1Loss', loss_weight=1.0), train_cfg=None, test_cfg=None, init_cfg=None): super(CenterNetHead, self).__init__(init_cfg) self.num_classes = num_classes self.heatmap_head = self._build_head(in_channel, feat_channel, num_classes) self.wh_head = self._build_head(in_channel, feat_channel, 2) self.offset_head = self._build_head(in_channel, feat_channel, 2) self.loss_center_heatmap = build_loss(loss_center_heatmap) self.loss_wh = build_loss(loss_wh) self.loss_offset = build_loss(loss_offset) self.train_cfg = train_cfg self.test_cfg = test_cfg self.fp16_enabled = False def _build_head(self, in_channel, feat_channel, out_channel): """Build head for each branch.""" layer = nn.Sequential( nn.Conv2d(in_channel, feat_channel, kernel_size=3, padding=1), nn.ReLU(inplace=True), nn.Conv2d(feat_channel, out_channel, kernel_size=1)) return layer def init_weights(self): """Initialize weights of the head.""" bias_init = bias_init_with_prob(0.1) self.heatmap_head[-1].bias.data.fill_(bias_init) for head in [self.wh_head, self.offset_head]: for m in head.modules(): if isinstance(m, nn.Conv2d): normal_init(m, std=0.001) def forward(self, feats): """Forward features. Notice CenterNet head does not use FPN. Args: feats (tuple[Tensor]): Features from the upstream network, each is a 4D-tensor. Returns: center_heatmap_preds (List[Tensor]): center predict heatmaps for all levels, the channels number is num_classes. wh_preds (List[Tensor]): wh predicts for all levels, the channels number is 2. offset_preds (List[Tensor]): offset predicts for all levels, the channels number is 2. """ return multi_apply(self.forward_single, feats) def forward_single(self, feat): """Forward feature of a single level. Args: feat (Tensor): Feature of a single level. Returns: center_heatmap_pred (Tensor): center predict heatmaps, the channels number is num_classes. wh_pred (Tensor): wh predicts, the channels number is 2. offset_pred (Tensor): offset predicts, the channels number is 2. """ center_heatmap_pred = self.heatmap_head(feat).sigmoid() wh_pred = self.wh_head(feat) offset_pred = self.offset_head(feat) return center_heatmap_pred, wh_pred, offset_pred @force_fp32(apply_to=('center_heatmap_preds', 'wh_preds', 'offset_preds')) def loss(self, center_heatmap_preds, wh_preds, offset_preds, gt_bboxes, gt_labels, img_metas, gt_bboxes_ignore=None): """Compute losses of the head. Args: center_heatmap_preds (list[Tensor]): center predict heatmaps for all levels with shape (B, num_classes, H, W). wh_preds (list[Tensor]): wh predicts for all levels with shape (B, 2, H, W). offset_preds (list[Tensor]): offset predicts for all levels with shape (B, 2, 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. gt_labels (list[Tensor]): class indices corresponding to each box. 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. Default: None Returns: dict[str, Tensor]: which has components below: - loss_center_heatmap (Tensor): loss of center heatmap. - loss_wh (Tensor): loss of hw heatmap - loss_offset (Tensor): loss of offset heatmap. """ assert len(center_heatmap_preds) == len(wh_preds) == len( offset_preds) == 1 center_heatmap_pred = center_heatmap_preds[0] wh_pred = wh_preds[0] offset_pred = offset_preds[0] target_result, avg_factor = self.get_targets(gt_bboxes, gt_labels, center_heatmap_pred.shape, img_metas[0]['pad_shape']) center_heatmap_target = target_result['center_heatmap_target'] wh_target = target_result['wh_target'] offset_target = target_result['offset_target'] wh_offset_target_weight = target_result['wh_offset_target_weight'] # Since the channel of wh_target and offset_target is 2, the avg_factor # of loss_center_heatmap is always 1/2 of loss_wh and loss_offset. loss_center_heatmap = self.loss_center_heatmap( center_heatmap_pred, center_heatmap_target, avg_factor=avg_factor) loss_wh = self.loss_wh( wh_pred, wh_target, wh_offset_target_weight, avg_factor=avg_factor * 2) loss_offset = self.loss_offset( offset_pred, offset_target, wh_offset_target_weight, avg_factor=avg_factor * 2) return dict( loss_center_heatmap=loss_center_heatmap, loss_wh=loss_wh, loss_offset=loss_offset) def get_targets(self, gt_bboxes, gt_labels, feat_shape, img_shape): """Compute regression and classification targets in multiple images. Args: 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. gt_labels (list[Tensor]): class indices corresponding to each box. feat_shape (list[int]): feature map shape with value [B, _, H, W] img_shape (list[int]): image shape in [h, w] format. Returns: tuple[dict,float]: The float value is mean avg_factor, the dict has components below: - center_heatmap_target (Tensor): targets of center heatmap, \ shape (B, num_classes, H, W). - wh_target (Tensor): targets of wh predict, shape \ (B, 2, H, W). - offset_target (Tensor): targets of offset predict, shape \ (B, 2, H, W). - wh_offset_target_weight (Tensor): weights of wh and offset \ predict, shape (B, 2, H, W). """ img_h, img_w = img_shape[:2] bs, _, feat_h, feat_w = feat_shape width_ratio = float(feat_w / img_w) height_ratio = float(feat_h / img_h) center_heatmap_target = gt_bboxes[-1].new_zeros( [bs, self.num_classes, feat_h, feat_w]) wh_target = gt_bboxes[-1].new_zeros([bs, 2, feat_h, feat_w]) offset_target = gt_bboxes[-1].new_zeros([bs, 2, feat_h, feat_w]) wh_offset_target_weight = gt_bboxes[-1].new_zeros( [bs, 2, feat_h, feat_w]) for batch_id in range(bs): gt_bbox = gt_bboxes[batch_id] gt_label = gt_labels[batch_id] center_x = (gt_bbox[:, [0]] + gt_bbox[:, [2]]) * width_ratio / 2 center_y = (gt_bbox[:, [1]] + gt_bbox[:, [3]]) * height_ratio / 2 gt_centers = torch.cat((center_x, center_y), dim=1) for j, ct in enumerate(gt_centers): ctx_int, cty_int = ct.int() ctx, cty = ct scale_box_h = (gt_bbox[j][3] - gt_bbox[j][1]) * height_ratio scale_box_w = (gt_bbox[j][2] - gt_bbox[j][0]) * width_ratio radius = gaussian_radius([scale_box_h, scale_box_w], min_overlap=0.3) radius = max(0, int(radius)) ind = gt_label[j] gen_gaussian_target(center_heatmap_target[batch_id, ind], [ctx_int, cty_int], radius) wh_target[batch_id, 0, cty_int, ctx_int] = scale_box_w wh_target[batch_id, 1, cty_int, ctx_int] = scale_box_h offset_target[batch_id, 0, cty_int, ctx_int] = ctx - ctx_int offset_target[batch_id, 1, cty_int, ctx_int] = cty - cty_int wh_offset_target_weight[batch_id, :, cty_int, ctx_int] = 1 avg_factor = max(1, center_heatmap_target.eq(1).sum()) target_result = dict( center_heatmap_target=center_heatmap_target, wh_target=wh_target, offset_target=offset_target, wh_offset_target_weight=wh_offset_target_weight) return target_result, avg_factor @force_fp32(apply_to=('center_heatmap_preds', 'wh_preds', 'offset_preds')) def get_bboxes(self, center_heatmap_preds, wh_preds, offset_preds, img_metas, rescale=True, with_nms=False): """Transform network output for a batch into bbox predictions. Args: center_heatmap_preds (list[Tensor]): Center predict heatmaps for all levels with shape (B, num_classes, H, W). wh_preds (list[Tensor]): WH predicts for all levels with shape (B, 2, H, W). offset_preds (list[Tensor]): Offset predicts for all levels with shape (B, 2, H, W). img_metas (list[dict]): Meta information of each image, e.g., image size, scaling factor, etc. rescale (bool): If True, return boxes in original image space. Default: True. with_nms (bool): If True, do nms before return boxes. Default: False. Returns: list[tuple[Tensor, Tensor]]: Each item in result_list is 2-tuple. The first item is an (n, 5) tensor, where 5 represent (tl_x, tl_y, br_x, br_y, score) and the score between 0 and 1. The shape of the second tensor in the tuple is (n,), and each element represents the class label of the corresponding box. """ assert len(center_heatmap_preds) == len(wh_preds) == len( offset_preds) == 1 result_list = [] for img_id in range(len(img_metas)): result_list.append( self._get_bboxes_single( center_heatmap_preds[0][img_id:img_id + 1, ...], wh_preds[0][img_id:img_id + 1, ...], offset_preds[0][img_id:img_id + 1, ...], img_metas[img_id], rescale=rescale, with_nms=with_nms)) return result_list def _get_bboxes_single(self, center_heatmap_pred, wh_pred, offset_pred, img_meta, rescale=False, with_nms=True): """Transform outputs of a single image into bbox results. Args: center_heatmap_pred (Tensor): Center heatmap for current level with shape (1, num_classes, H, W). wh_pred (Tensor): WH heatmap for current level with shape (1, num_classes, H, W). offset_pred (Tensor): Offset for current level with shape (1, corner_offset_channels, H, W). img_meta (dict): Meta information of current image, e.g., image size, scaling factor, etc. rescale (bool): If True, return boxes in original image space. Default: False. with_nms (bool): If True, do nms before return boxes. Default: True. Returns: tuple[Tensor, Tensor]: The first item is an (n, 5) tensor, where 5 represent (tl_x, tl_y, br_x, br_y, score) and the score between 0 and 1. The shape of the second tensor in the tuple is (n,), and each element represents the class label of the corresponding box. """ batch_det_bboxes, batch_labels = self.decode_heatmap( center_heatmap_pred, wh_pred, offset_pred, img_meta['batch_input_shape'], k=self.test_cfg.topk, kernel=self.test_cfg.local_maximum_kernel) det_bboxes = batch_det_bboxes.view([-1, 5]) det_labels = batch_labels.view(-1) batch_border = det_bboxes.new_tensor(img_meta['border'])[..., [2, 0, 2, 0]] det_bboxes[..., :4] -= batch_border if rescale: det_bboxes[..., :4] /= det_bboxes.new_tensor( img_meta['scale_factor']) if with_nms: det_bboxes, det_labels = self._bboxes_nms(det_bboxes, det_labels, self.test_cfg) return det_bboxes, det_labels def decode_heatmap(self, center_heatmap_pred, wh_pred, offset_pred, img_shape, k=100, kernel=3): """Transform outputs into detections raw bbox prediction. Args: center_heatmap_pred (Tensor): center predict heatmap, shape (B, num_classes, H, W). wh_pred (Tensor): wh predict, shape (B, 2, H, W). offset_pred (Tensor): offset predict, shape (B, 2, H, W). img_shape (list[int]): image shape in [h, w] format. k (int): Get top k center keypoints from heatmap. Default 100. kernel (int): Max pooling kernel for extract local maximum pixels. Default 3. Returns: tuple[torch.Tensor]: Decoded output of CenterNetHead, containing the following Tensors: - batch_bboxes (Tensor): Coords of each box with shape (B, k, 5) - batch_topk_labels (Tensor): Categories of each box with \ shape (B, k) """ height, width = center_heatmap_pred.shape[2:] inp_h, inp_w = img_shape center_heatmap_pred = get_local_maximum( center_heatmap_pred, kernel=kernel) *batch_dets, topk_ys, topk_xs = get_topk_from_heatmap( center_heatmap_pred, k=k) batch_scores, batch_index, batch_topk_labels = batch_dets wh = transpose_and_gather_feat(wh_pred, batch_index) offset = transpose_and_gather_feat(offset_pred, batch_index) topk_xs = topk_xs + offset[..., 0] topk_ys = topk_ys + offset[..., 1] tl_x = (topk_xs - wh[..., 0] / 2) * (inp_w / width) tl_y = (topk_ys - wh[..., 1] / 2) * (inp_h / height) br_x = (topk_xs + wh[..., 0] / 2) * (inp_w / width) br_y = (topk_ys + wh[..., 1] / 2) * (inp_h / height) batch_bboxes = torch.stack([tl_x, tl_y, br_x, br_y], dim=2) batch_bboxes = torch.cat((batch_bboxes, batch_scores[..., None]), dim=-1) return batch_bboxes, batch_topk_labels def _bboxes_nms(self, bboxes, labels, cfg): if labels.numel() > 0: max_num = cfg.max_per_img bboxes, keep = batched_nms(bboxes[:, :4], bboxes[:, -1].contiguous(), labels, cfg.nms) if max_num > 0: bboxes = bboxes[:max_num] labels = labels[keep][:max_num] return bboxes, labels