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| # Copyright (c) Facebook, Inc. and its affiliates. | |
| import math | |
| from typing import List, Tuple | |
| import torch | |
| from fvcore.nn import giou_loss, smooth_l1_loss | |
| from detectron2.layers import cat | |
| from detectron2.structures import Boxes | |
| # Value for clamping large dw and dh predictions. The heuristic is that we clamp | |
| # such that dw and dh are no larger than what would transform a 16px box into a | |
| # 1000px box (based on a small anchor, 16px, and a typical image size, 1000px). | |
| _DEFAULT_SCALE_CLAMP = math.log(1000.0 / 16) | |
| __all__ = ["Box2BoxTransform", "Box2BoxTransformRotated"] | |
| class Box2BoxTransform(object): | |
| """ | |
| The box-to-box transform defined in R-CNN. The transformation is parameterized | |
| by 4 deltas: (dx, dy, dw, dh). The transformation scales the box's width and height | |
| by exp(dw), exp(dh) and shifts a box's center by the offset (dx * width, dy * height). | |
| """ | |
| def __init__( | |
| self, weights: Tuple[float, float, float, float], scale_clamp: float = _DEFAULT_SCALE_CLAMP | |
| ): | |
| """ | |
| Args: | |
| weights (4-element tuple): Scaling factors that are applied to the | |
| (dx, dy, dw, dh) deltas. In Fast R-CNN, these were originally set | |
| such that the deltas have unit variance; now they are treated as | |
| hyperparameters of the system. | |
| scale_clamp (float): When predicting deltas, the predicted box scaling | |
| factors (dw and dh) are clamped such that they are <= scale_clamp. | |
| """ | |
| self.weights = weights | |
| self.scale_clamp = scale_clamp | |
| def get_deltas(self, src_boxes, target_boxes): | |
| """ | |
| Get box regression transformation deltas (dx, dy, dw, dh) that can be used | |
| to transform the `src_boxes` into the `target_boxes`. That is, the relation | |
| ``target_boxes == self.apply_deltas(deltas, src_boxes)`` is true (unless | |
| any delta is too large and is clamped). | |
| Args: | |
| src_boxes (Tensor): source boxes, e.g., object proposals | |
| target_boxes (Tensor): target of the transformation, e.g., ground-truth | |
| boxes. | |
| """ | |
| assert isinstance(src_boxes, torch.Tensor), type(src_boxes) | |
| assert isinstance(target_boxes, torch.Tensor), type(target_boxes) | |
| src_widths = src_boxes[:, 2] - src_boxes[:, 0] | |
| src_heights = src_boxes[:, 3] - src_boxes[:, 1] | |
| src_ctr_x = src_boxes[:, 0] + 0.5 * src_widths | |
| src_ctr_y = src_boxes[:, 1] + 0.5 * src_heights | |
| target_widths = target_boxes[:, 2] - target_boxes[:, 0] | |
| target_heights = target_boxes[:, 3] - target_boxes[:, 1] | |
| target_ctr_x = target_boxes[:, 0] + 0.5 * target_widths | |
| target_ctr_y = target_boxes[:, 1] + 0.5 * target_heights | |
| wx, wy, ww, wh = self.weights | |
| dx = wx * (target_ctr_x - src_ctr_x) / src_widths | |
| dy = wy * (target_ctr_y - src_ctr_y) / src_heights | |
| dw = ww * torch.log(target_widths / src_widths) | |
| dh = wh * torch.log(target_heights / src_heights) | |
| deltas = torch.stack((dx, dy, dw, dh), dim=1) | |
| assert (src_widths > 0).all().item(), "Input boxes to Box2BoxTransform are not valid!" | |
| return deltas | |
| def apply_deltas(self, deltas, boxes): | |
| """ | |
| Apply transformation `deltas` (dx, dy, dw, dh) to `boxes`. | |
| Args: | |
| deltas (Tensor): transformation deltas of shape (N, k*4), where k >= 1. | |
| deltas[i] represents k potentially different class-specific | |
| box transformations for the single box boxes[i]. | |
| boxes (Tensor): boxes to transform, of shape (N, 4) | |
| """ | |
| deltas = deltas.float() # ensure fp32 for decoding precision | |
| boxes = boxes.to(deltas.dtype) | |
| widths = boxes[:, 2] - boxes[:, 0] | |
| heights = boxes[:, 3] - boxes[:, 1] | |
| ctr_x = boxes[:, 0] + 0.5 * widths | |
| ctr_y = boxes[:, 1] + 0.5 * heights | |
| wx, wy, ww, wh = self.weights | |
| dx = deltas[:, 0::4] / wx | |
| dy = deltas[:, 1::4] / wy | |
| dw = deltas[:, 2::4] / ww | |
| dh = deltas[:, 3::4] / wh | |
| # Prevent sending too large values into torch.exp() | |
| dw = torch.clamp(dw, max=self.scale_clamp) | |
| dh = torch.clamp(dh, max=self.scale_clamp) | |
| pred_ctr_x = dx * widths[:, None] + ctr_x[:, None] | |
| pred_ctr_y = dy * heights[:, None] + ctr_y[:, None] | |
| pred_w = torch.exp(dw) * widths[:, None] | |
| pred_h = torch.exp(dh) * heights[:, None] | |
| x1 = pred_ctr_x - 0.5 * pred_w | |
| y1 = pred_ctr_y - 0.5 * pred_h | |
| x2 = pred_ctr_x + 0.5 * pred_w | |
| y2 = pred_ctr_y + 0.5 * pred_h | |
| pred_boxes = torch.stack((x1, y1, x2, y2), dim=-1) | |
| return pred_boxes.reshape(deltas.shape) | |
| class Box2BoxTransformRotated(object): | |
| """ | |
| The box-to-box transform defined in Rotated R-CNN. The transformation is parameterized | |
| by 5 deltas: (dx, dy, dw, dh, da). The transformation scales the box's width and height | |
| by exp(dw), exp(dh), shifts a box's center by the offset (dx * width, dy * height), | |
| and rotate a box's angle by da (radians). | |
| Note: angles of deltas are in radians while angles of boxes are in degrees. | |
| """ | |
| def __init__( | |
| self, | |
| weights: Tuple[float, float, float, float, float], | |
| scale_clamp: float = _DEFAULT_SCALE_CLAMP, | |
| ): | |
| """ | |
| Args: | |
| weights (5-element tuple): Scaling factors that are applied to the | |
| (dx, dy, dw, dh, da) deltas. These are treated as | |
| hyperparameters of the system. | |
| scale_clamp (float): When predicting deltas, the predicted box scaling | |
| factors (dw and dh) are clamped such that they are <= scale_clamp. | |
| """ | |
| self.weights = weights | |
| self.scale_clamp = scale_clamp | |
| def get_deltas(self, src_boxes, target_boxes): | |
| """ | |
| Get box regression transformation deltas (dx, dy, dw, dh, da) that can be used | |
| to transform the `src_boxes` into the `target_boxes`. That is, the relation | |
| ``target_boxes == self.apply_deltas(deltas, src_boxes)`` is true (unless | |
| any delta is too large and is clamped). | |
| Args: | |
| src_boxes (Tensor): Nx5 source boxes, e.g., object proposals | |
| target_boxes (Tensor): Nx5 target of the transformation, e.g., ground-truth | |
| boxes. | |
| """ | |
| assert isinstance(src_boxes, torch.Tensor), type(src_boxes) | |
| assert isinstance(target_boxes, torch.Tensor), type(target_boxes) | |
| src_ctr_x, src_ctr_y, src_widths, src_heights, src_angles = torch.unbind(src_boxes, dim=1) | |
| target_ctr_x, target_ctr_y, target_widths, target_heights, target_angles = torch.unbind( | |
| target_boxes, dim=1 | |
| ) | |
| wx, wy, ww, wh, wa = self.weights | |
| dx = wx * (target_ctr_x - src_ctr_x) / src_widths | |
| dy = wy * (target_ctr_y - src_ctr_y) / src_heights | |
| dw = ww * torch.log(target_widths / src_widths) | |
| dh = wh * torch.log(target_heights / src_heights) | |
| # Angles of deltas are in radians while angles of boxes are in degrees. | |
| # the conversion to radians serve as a way to normalize the values | |
| da = target_angles - src_angles | |
| da = (da + 180.0) % 360.0 - 180.0 # make it in [-180, 180) | |
| da *= wa * math.pi / 180.0 | |
| deltas = torch.stack((dx, dy, dw, dh, da), dim=1) | |
| assert ( | |
| (src_widths > 0).all().item() | |
| ), "Input boxes to Box2BoxTransformRotated are not valid!" | |
| return deltas | |
| def apply_deltas(self, deltas, boxes): | |
| """ | |
| Apply transformation `deltas` (dx, dy, dw, dh, da) to `boxes`. | |
| Args: | |
| deltas (Tensor): transformation deltas of shape (N, k*5). | |
| deltas[i] represents box transformation for the single box boxes[i]. | |
| boxes (Tensor): boxes to transform, of shape (N, 5) | |
| """ | |
| assert deltas.shape[1] % 5 == 0 and boxes.shape[1] == 5 | |
| boxes = boxes.to(deltas.dtype).unsqueeze(2) | |
| ctr_x = boxes[:, 0] | |
| ctr_y = boxes[:, 1] | |
| widths = boxes[:, 2] | |
| heights = boxes[:, 3] | |
| angles = boxes[:, 4] | |
| wx, wy, ww, wh, wa = self.weights | |
| dx = deltas[:, 0::5] / wx | |
| dy = deltas[:, 1::5] / wy | |
| dw = deltas[:, 2::5] / ww | |
| dh = deltas[:, 3::5] / wh | |
| da = deltas[:, 4::5] / wa | |
| # Prevent sending too large values into torch.exp() | |
| dw = torch.clamp(dw, max=self.scale_clamp) | |
| dh = torch.clamp(dh, max=self.scale_clamp) | |
| pred_boxes = torch.zeros_like(deltas) | |
| pred_boxes[:, 0::5] = dx * widths + ctr_x # x_ctr | |
| pred_boxes[:, 1::5] = dy * heights + ctr_y # y_ctr | |
| pred_boxes[:, 2::5] = torch.exp(dw) * widths # width | |
| pred_boxes[:, 3::5] = torch.exp(dh) * heights # height | |
| # Following original RRPN implementation, | |
| # angles of deltas are in radians while angles of boxes are in degrees. | |
| pred_angle = da * 180.0 / math.pi + angles | |
| pred_angle = (pred_angle + 180.0) % 360.0 - 180.0 # make it in [-180, 180) | |
| pred_boxes[:, 4::5] = pred_angle | |
| return pred_boxes | |
| def _dense_box_regression_loss( | |
| anchors: List[Boxes], | |
| box2box_transform: Box2BoxTransform, | |
| pred_anchor_deltas: List[torch.Tensor], | |
| gt_boxes: List[torch.Tensor], | |
| fg_mask: torch.Tensor, | |
| box_reg_loss_type="smooth_l1", | |
| smooth_l1_beta=0.0, | |
| ): | |
| """ | |
| Compute loss for dense multi-level box regression. | |
| Loss is accumulated over ``fg_mask``. | |
| Args: | |
| anchors: #lvl anchor boxes, each is (HixWixA, 4) | |
| pred_anchor_deltas: #lvl predictions, each is (N, HixWixA, 4) | |
| gt_boxes: N ground truth boxes, each has shape (R, 4) (R = sum(Hi * Wi * A)) | |
| fg_mask: the foreground boolean mask of shape (N, R) to compute loss on | |
| box_reg_loss_type (str): Loss type to use. Supported losses: "smooth_l1", "giou". | |
| smooth_l1_beta (float): beta parameter for the smooth L1 regression loss. Default to | |
| use L1 loss. Only used when `box_reg_loss_type` is "smooth_l1" | |
| """ | |
| anchors = type(anchors[0]).cat(anchors).tensor # (R, 4) | |
| if box_reg_loss_type == "smooth_l1": | |
| gt_anchor_deltas = [box2box_transform.get_deltas(anchors, k) for k in gt_boxes] | |
| gt_anchor_deltas = torch.stack(gt_anchor_deltas) # (N, R, 4) | |
| loss_box_reg = smooth_l1_loss( | |
| cat(pred_anchor_deltas, dim=1)[fg_mask], | |
| gt_anchor_deltas[fg_mask], | |
| beta=smooth_l1_beta, | |
| reduction="sum", | |
| ) | |
| elif box_reg_loss_type == "giou": | |
| pred_boxes = [ | |
| box2box_transform.apply_deltas(k, anchors) for k in cat(pred_anchor_deltas, dim=1) | |
| ] | |
| loss_box_reg = giou_loss( | |
| torch.stack(pred_boxes)[fg_mask], torch.stack(gt_boxes)[fg_mask], reduction="sum" | |
| ) | |
| else: | |
| raise ValueError(f"Invalid dense box regression loss type '{box_reg_loss_type}'") | |
| return loss_box_reg | |