import mmcv
import numpy as np
import torch
from ..builder import BBOX_CODERS
from .base_bbox_coder import BaseBBoxCoder
[docs]@BBOX_CODERS.register_module()
class DeltaXYWHBBoxCoder(BaseBBoxCoder):
"""Delta XYWH BBox coder.
Following the practice in `R-CNN <https://arxiv.org/abs/1311.2524>`_,
this coder encodes bbox (x1, y1, x2, y2) into delta (dx, dy, dw, dh) and
decodes delta (dx, dy, dw, dh) back to original bbox (x1, y1, x2, y2).
Args:
target_means (Sequence[float]): Denormalizing means of target for
delta coordinates
target_stds (Sequence[float]): Denormalizing standard deviation of
target for delta coordinates
clip_border (bool, optional): Whether clip the objects outside the
border of the image. Defaults to True.
"""
def __init__(self,
target_means=(0., 0., 0., 0.),
target_stds=(1., 1., 1., 1.),
clip_border=True):
super(BaseBBoxCoder, self).__init__()
self.means = target_means
self.stds = target_stds
self.clip_border = clip_border
[docs] def encode(self, bboxes, gt_bboxes):
"""Get box regression transformation deltas that can be used to
transform the ``bboxes`` into the ``gt_bboxes``.
Args:
bboxes (torch.Tensor): Source boxes, e.g., object proposals.
gt_bboxes (torch.Tensor): Target of the transformation, e.g.,
ground-truth boxes.
Returns:
torch.Tensor: Box transformation deltas
"""
assert bboxes.size(0) == gt_bboxes.size(0)
assert bboxes.size(-1) == gt_bboxes.size(-1) == 4
encoded_bboxes = bbox2delta(bboxes, gt_bboxes, self.means, self.stds)
return encoded_bboxes
[docs] def decode(self,
bboxes,
pred_bboxes,
max_shape=None,
wh_ratio_clip=16 / 1000):
"""Apply transformation `pred_bboxes` to `boxes`.
Args:
bboxes (torch.Tensor): Basic boxes. Shape (B, N, 4) or (N, 4)
pred_bboxes (Tensor): Encoded offsets with respect to each roi.
Has shape (B, N, num_classes * 4) or (B, N, 4) or
(N, num_classes * 4) or (N, 4). Note N = num_anchors * W * H
when rois is a grid of anchors.Offset encoding follows [1]_.
max_shape (Sequence[int] or torch.Tensor or Sequence[
Sequence[int]],optional): Maximum bounds for boxes, specifies
(H, W, C) or (H, W). If bboxes shape is (B, N, 4), then
the max_shape should be a Sequence[Sequence[int]]
and the length of max_shape should also be B.
wh_ratio_clip (float, optional): The allowed ratio between
width and height.
Returns:
torch.Tensor: Decoded boxes.
"""
assert pred_bboxes.size(0) == bboxes.size(0)
if pred_bboxes.ndim == 3:
assert pred_bboxes.size(1) == bboxes.size(1)
decoded_bboxes = delta2bbox(bboxes, pred_bboxes, self.means, self.stds,
max_shape, wh_ratio_clip, self.clip_border)
return decoded_bboxes
@mmcv.jit(coderize=True)
def bbox2delta(proposals, gt, means=(0., 0., 0., 0.), stds=(1., 1., 1., 1.)):
"""Compute deltas of proposals w.r.t. gt.
We usually compute the deltas of x, y, w, h of proposals w.r.t ground
truth bboxes to get regression target.
This is the inverse function of :func:`delta2bbox`.
Args:
proposals (Tensor): Boxes to be transformed, shape (N, ..., 4)
gt (Tensor): Gt bboxes to be used as base, shape (N, ..., 4)
means (Sequence[float]): Denormalizing means for delta coordinates
stds (Sequence[float]): Denormalizing standard deviation for delta
coordinates
Returns:
Tensor: deltas with shape (N, 4), where columns represent dx, dy,
dw, dh.
"""
assert proposals.size() == gt.size()
proposals = proposals.float()
gt = gt.float()
px = (proposals[..., 0] + proposals[..., 2]) * 0.5
py = (proposals[..., 1] + proposals[..., 3]) * 0.5
pw = proposals[..., 2] - proposals[..., 0]
ph = proposals[..., 3] - proposals[..., 1]
gx = (gt[..., 0] + gt[..., 2]) * 0.5
gy = (gt[..., 1] + gt[..., 3]) * 0.5
gw = gt[..., 2] - gt[..., 0]
gh = gt[..., 3] - gt[..., 1]
dx = (gx - px) / pw
dy = (gy - py) / ph
dw = torch.log(gw / pw)
dh = torch.log(gh / ph)
deltas = torch.stack([dx, dy, dw, dh], dim=-1)
means = deltas.new_tensor(means).unsqueeze(0)
stds = deltas.new_tensor(stds).unsqueeze(0)
deltas = deltas.sub_(means).div_(stds)
return deltas
@mmcv.jit(coderize=True)
def delta2bbox(rois,
deltas,
means=(0., 0., 0., 0.),
stds=(1., 1., 1., 1.),
max_shape=None,
wh_ratio_clip=16 / 1000,
clip_border=True):
"""Apply deltas to shift/scale base boxes.
Typically the rois are anchor or proposed bounding boxes and the deltas are
network outputs used to shift/scale those boxes.
This is the inverse function of :func:`bbox2delta`.
Args:
rois (Tensor): Boxes to be transformed. Has shape (N, 4) or (B, N, 4)
deltas (Tensor): Encoded offsets with respect to each roi.
Has shape (B, N, num_classes * 4) or (B, N, 4) or
(N, num_classes * 4) or (N, 4). Note N = num_anchors * W * H
when rois is a grid of anchors.Offset encoding follows [1]_.
means (Sequence[float]): Denormalizing means for delta coordinates
stds (Sequence[float]): Denormalizing standard deviation for delta
coordinates
max_shape (Sequence[int] or torch.Tensor or Sequence[
Sequence[int]],optional): Maximum bounds for boxes, specifies
(H, W, C) or (H, W). If rois shape is (B, N, 4), then
the max_shape should be a Sequence[Sequence[int]]
and the length of max_shape should also be B.
wh_ratio_clip (float): Maximum aspect ratio for boxes.
clip_border (bool, optional): Whether clip the objects outside the
border of the image. Defaults to True.
Returns:
Tensor: Boxes with shape (B, N, num_classes * 4) or (B, N, 4) or
(N, num_classes * 4) or (N, 4), where 4 represent
tl_x, tl_y, br_x, br_y.
References:
.. [1] https://arxiv.org/abs/1311.2524
Example:
>>> rois = torch.Tensor([[ 0., 0., 1., 1.],
>>> [ 0., 0., 1., 1.],
>>> [ 0., 0., 1., 1.],
>>> [ 5., 5., 5., 5.]])
>>> deltas = torch.Tensor([[ 0., 0., 0., 0.],
>>> [ 1., 1., 1., 1.],
>>> [ 0., 0., 2., -1.],
>>> [ 0.7, -1.9, -0.5, 0.3]])
>>> delta2bbox(rois, deltas, max_shape=(32, 32, 3))
tensor([[0.0000, 0.0000, 1.0000, 1.0000],
[0.1409, 0.1409, 2.8591, 2.8591],
[0.0000, 0.3161, 4.1945, 0.6839],
[5.0000, 5.0000, 5.0000, 5.0000]])
"""
means = deltas.new_tensor(means).view(1,
-1).repeat(1,
deltas.size(-1) // 4)
stds = deltas.new_tensor(stds).view(1, -1).repeat(1, deltas.size(-1) // 4)
denorm_deltas = deltas * stds + means
dx = denorm_deltas[..., 0::4]
dy = denorm_deltas[..., 1::4]
dw = denorm_deltas[..., 2::4]
dh = denorm_deltas[..., 3::4]
max_ratio = np.abs(np.log(wh_ratio_clip))
dw = dw.clamp(min=-max_ratio, max=max_ratio)
dh = dh.clamp(min=-max_ratio, max=max_ratio)
x1, y1 = rois[..., 0], rois[..., 1]
x2, y2 = rois[..., 2], rois[..., 3]
# Compute center of each roi
px = ((x1 + x2) * 0.5).unsqueeze(-1).expand_as(dx)
py = ((y1 + y2) * 0.5).unsqueeze(-1).expand_as(dy)
# Compute width/height of each roi
pw = (x2 - x1).unsqueeze(-1).expand_as(dw)
ph = (y2 - y1).unsqueeze(-1).expand_as(dh)
# Use exp(network energy) to enlarge/shrink each roi
gw = pw * dw.exp()
gh = ph * dh.exp()
# Use network energy to shift the center of each roi
gx = px + pw * dx
gy = py + ph * dy
# Convert center-xy/width/height to top-left, bottom-right
x1 = gx - gw * 0.5
y1 = gy - gh * 0.5
x2 = gx + gw * 0.5
y2 = gy + gh * 0.5
bboxes = torch.stack([x1, y1, x2, y2], dim=-1).view(deltas.size())
if clip_border and max_shape is not None:
if not isinstance(max_shape, torch.Tensor):
max_shape = x1.new_tensor(max_shape)
max_shape = max_shape[..., :2].type_as(x1)
if max_shape.ndim == 2:
assert bboxes.ndim == 3
assert max_shape.size(0) == bboxes.size(0)
min_xy = x1.new_tensor(0)
max_xy = torch.cat(
[max_shape] * (deltas.size(-1) // 2),
dim=-1).flip(-1).unsqueeze(-2)
bboxes = torch.where(bboxes < min_xy, min_xy, bboxes)
bboxes = torch.where(bboxes > max_xy, max_xy, bboxes)
return bboxes