# Source code for mmdet.core.bbox.assigners.center_region_assigner

```
import torch
from ..builder import BBOX_ASSIGNERS
from ..iou_calculators import build_iou_calculator
from .assign_result import AssignResult
from .base_assigner import BaseAssigner
def scale_boxes(bboxes, scale):
"""Expand an array of boxes by a given scale.
Args:
bboxes (Tensor): Shape (m, 4)
scale (float): The scale factor of bboxes
Returns:
(Tensor): Shape (m, 4). Scaled bboxes
"""
assert bboxes.size(1) == 4
w_half = (bboxes[:, 2] - bboxes[:, 0]) * .5
h_half = (bboxes[:, 3] - bboxes[:, 1]) * .5
x_c = (bboxes[:, 2] + bboxes[:, 0]) * .5
y_c = (bboxes[:, 3] + bboxes[:, 1]) * .5
w_half *= scale
h_half *= scale
boxes_scaled = torch.zeros_like(bboxes)
boxes_scaled[:, 0] = x_c - w_half
boxes_scaled[:, 2] = x_c + w_half
boxes_scaled[:, 1] = y_c - h_half
boxes_scaled[:, 3] = y_c + h_half
return boxes_scaled
def is_located_in(points, bboxes):
"""Are points located in bboxes.
Args:
points (Tensor): Points, shape: (m, 2).
bboxes (Tensor): Bounding boxes, shape: (n, 4).
Return:
Tensor: Flags indicating if points are located in bboxes, shape: (m, n).
"""
assert points.size(1) == 2
assert bboxes.size(1) == 4
return (points[:, 0].unsqueeze(1) > bboxes[:, 0].unsqueeze(0)) & \
(points[:, 0].unsqueeze(1) < bboxes[:, 2].unsqueeze(0)) & \
(points[:, 1].unsqueeze(1) > bboxes[:, 1].unsqueeze(0)) & \
(points[:, 1].unsqueeze(1) < bboxes[:, 3].unsqueeze(0))
def bboxes_area(bboxes):
"""Compute the area of an array of bboxes.
Args:
bboxes (Tensor): The coordinates ox bboxes. Shape: (m, 4)
Returns:
Tensor: Area of the bboxes. Shape: (m, )
"""
assert bboxes.size(1) == 4
w = (bboxes[:, 2] - bboxes[:, 0])
h = (bboxes[:, 3] - bboxes[:, 1])
areas = w * h
return areas
[docs]@BBOX_ASSIGNERS.register_module()
class CenterRegionAssigner(BaseAssigner):
"""Assign pixels at the center region of a bbox as positive.
Each proposals will be assigned with `-1`, `0`, or a positive integer
indicating the ground truth index.
- -1: negative samples
- semi-positive numbers: positive sample, index (0-based) of assigned gt
Args:
pos_scale (float): Threshold within which pixels are
labelled as positive.
neg_scale (float): Threshold above which pixels are
labelled as positive.
min_pos_iof (float): Minimum iof of a pixel with a gt to be
labelled as positive. Default: 1e-2
ignore_gt_scale (float): Threshold within which the pixels
are ignored when the gt is labelled as shadowed. Default: 0.5
foreground_dominate (bool): If True, the bbox will be assigned as
positive when a gt's kernel region overlaps with another's shadowed
(ignored) region, otherwise it is set as ignored. Default to False.
"""
def __init__(self,
pos_scale,
neg_scale,
min_pos_iof=1e-2,
ignore_gt_scale=0.5,
foreground_dominate=False,
iou_calculator=dict(type='BboxOverlaps2D')):
self.pos_scale = pos_scale
self.neg_scale = neg_scale
self.min_pos_iof = min_pos_iof
self.ignore_gt_scale = ignore_gt_scale
self.foreground_dominate = foreground_dominate
self.iou_calculator = build_iou_calculator(iou_calculator)
[docs] def get_gt_priorities(self, gt_bboxes):
"""Get gt priorities according to their areas.
Smaller gt has higher priority.
Args:
gt_bboxes (Tensor): Ground truth boxes, shape (k, 4).
Returns:
Tensor: The priority of gts so that gts with larger priority is \
more likely to be assigned. Shape (k, )
"""
gt_areas = bboxes_area(gt_bboxes)
# Rank all gt bbox areas. Smaller objects has larger priority
_, sort_idx = gt_areas.sort(descending=True)
sort_idx = sort_idx.argsort()
return sort_idx
[docs] def assign(self, bboxes, gt_bboxes, gt_bboxes_ignore=None, gt_labels=None):
"""Assign gt to bboxes.
This method assigns gts to every bbox (proposal/anchor), each bbox \
will be assigned with -1, or a semi-positive number. -1 means \
negative sample, semi-positive number is the index (0-based) of \
assigned gt.
Args:
bboxes (Tensor): Bounding boxes to be assigned, shape(n, 4).
gt_bboxes (Tensor): Groundtruth boxes, shape (k, 4).
gt_bboxes_ignore (tensor, optional): Ground truth bboxes that are
labelled as `ignored`, e.g., crowd boxes in COCO.
gt_labels (tensor, optional): Label of gt_bboxes, shape (num_gts,).
Returns:
:obj:`AssignResult`: The assigned result. Note that \
shadowed_labels of shape (N, 2) is also added as an \
`assign_result` attribute. `shadowed_labels` is a tensor \
composed of N pairs of anchor_ind, class_label], where N \
is the number of anchors that lie in the outer region of a \
gt, anchor_ind is the shadowed anchor index and class_label \
is the shadowed class label.
Example:
>>> self = CenterRegionAssigner(0.2, 0.2)
>>> bboxes = torch.Tensor([[0, 0, 10, 10], [10, 10, 20, 20]])
>>> gt_bboxes = torch.Tensor([[0, 0, 10, 10]])
>>> assign_result = self.assign(bboxes, gt_bboxes)
>>> expected_gt_inds = torch.LongTensor([1, 0])
>>> assert torch.all(assign_result.gt_inds == expected_gt_inds)
"""
# There are in total 5 steps in the pixel assignment
# 1. Find core (the center region, say inner 0.2)
# and shadow (the relatively ourter part, say inner 0.2-0.5)
# regions of every gt.
# 2. Find all prior bboxes that lie in gt_core and gt_shadow regions
# 3. Assign prior bboxes in gt_core with a one-hot id of the gt in
# the image.
# 3.1. For overlapping objects, the prior bboxes in gt_core is
# assigned with the object with smallest area
# 4. Assign prior bboxes with class label according to its gt id.
# 4.1. Assign -1 to prior bboxes lying in shadowed gts
# 4.2. Assign positive prior boxes with the corresponding label
# 5. Find pixels lying in the shadow of an object and assign them with
# background label, but set the loss weight of its corresponding
# gt to zero.
assert bboxes.size(1) == 4, 'bboxes must have size of 4'
# 1. Find core positive and shadow region of every gt
gt_core = scale_boxes(gt_bboxes, self.pos_scale)
gt_shadow = scale_boxes(gt_bboxes, self.neg_scale)
# 2. Find prior bboxes that lie in gt_core and gt_shadow regions
bbox_centers = (bboxes[:, 2:4] + bboxes[:, 0:2]) / 2
# The center points lie within the gt boxes
is_bbox_in_gt = is_located_in(bbox_centers, gt_bboxes)
# Only calculate bbox and gt_core IoF. This enables small prior bboxes
# to match large gts
bbox_and_gt_core_overlaps = self.iou_calculator(
bboxes, gt_core, mode='iof')
# The center point of effective priors should be within the gt box
is_bbox_in_gt_core = is_bbox_in_gt & (
bbox_and_gt_core_overlaps > self.min_pos_iof) # shape (n, k)
is_bbox_in_gt_shadow = (
self.iou_calculator(bboxes, gt_shadow, mode='iof') >
self.min_pos_iof)
# Rule out center effective positive pixels
is_bbox_in_gt_shadow &= (~is_bbox_in_gt_core)
num_gts, num_bboxes = gt_bboxes.size(0), bboxes.size(0)
if num_gts == 0 or num_bboxes == 0:
# If no gts exist, assign all pixels to negative
assigned_gt_ids = \
is_bbox_in_gt_core.new_zeros((num_bboxes,),
dtype=torch.long)
pixels_in_gt_shadow = assigned_gt_ids.new_empty((0, 2))
else:
# Step 3: assign a one-hot gt id to each pixel, and smaller objects
# have high priority to assign the pixel.
sort_idx = self.get_gt_priorities(gt_bboxes)
assigned_gt_ids, pixels_in_gt_shadow = \
self.assign_one_hot_gt_indices(is_bbox_in_gt_core,
is_bbox_in_gt_shadow,
gt_priority=sort_idx)
if gt_bboxes_ignore is not None and gt_bboxes_ignore.numel() > 0:
# No ground truth or boxes, return empty assignment
gt_bboxes_ignore = scale_boxes(
gt_bboxes_ignore, scale=self.ignore_gt_scale)
is_bbox_in_ignored_gts = is_located_in(bbox_centers,
gt_bboxes_ignore)
is_bbox_in_ignored_gts = is_bbox_in_ignored_gts.any(dim=1)
assigned_gt_ids[is_bbox_in_ignored_gts] = -1
# 4. Assign prior bboxes with class label according to its gt id.
assigned_labels = None
shadowed_pixel_labels = None
if gt_labels is not None:
# Default assigned label is the background (-1)
assigned_labels = assigned_gt_ids.new_full((num_bboxes, ), -1)
pos_inds = torch.nonzero(
assigned_gt_ids > 0, as_tuple=False).squeeze()
if pos_inds.numel() > 0:
assigned_labels[pos_inds] = gt_labels[assigned_gt_ids[pos_inds]
- 1]
# 5. Find pixels lying in the shadow of an object
shadowed_pixel_labels = pixels_in_gt_shadow.clone()
if pixels_in_gt_shadow.numel() > 0:
pixel_idx, gt_idx =\
pixels_in_gt_shadow[:, 0], pixels_in_gt_shadow[:, 1]
assert (assigned_gt_ids[pixel_idx] != gt_idx).all(), \
'Some pixels are dually assigned to ignore and gt!'
shadowed_pixel_labels[:, 1] = gt_labels[gt_idx - 1]
override = (
assigned_labels[pixel_idx] == shadowed_pixel_labels[:, 1])
if self.foreground_dominate:
# When a pixel is both positive and shadowed, set it as pos
shadowed_pixel_labels = shadowed_pixel_labels[~override]
else:
# When a pixel is both pos and shadowed, set it as shadowed
assigned_labels[pixel_idx[override]] = -1
assigned_gt_ids[pixel_idx[override]] = 0
assign_result = AssignResult(
num_gts, assigned_gt_ids, None, labels=assigned_labels)
# Add shadowed_labels as assign_result property. Shape: (num_shadow, 2)
assign_result.set_extra_property('shadowed_labels',
shadowed_pixel_labels)
return assign_result
[docs] def assign_one_hot_gt_indices(self,
is_bbox_in_gt_core,
is_bbox_in_gt_shadow,
gt_priority=None):
"""Assign only one gt index to each prior box.
Gts with large gt_priority are more likely to be assigned.
Args:
is_bbox_in_gt_core (Tensor): Bool tensor indicating the bbox center
is in the core area of a gt (e.g. 0-0.2).
Shape: (num_prior, num_gt).
is_bbox_in_gt_shadow (Tensor): Bool tensor indicating the bbox
center is in the shadowed area of a gt (e.g. 0.2-0.5).
Shape: (num_prior, num_gt).
gt_priority (Tensor): Priorities of gts. The gt with a higher
priority is more likely to be assigned to the bbox when the bbox
match with multiple gts. Shape: (num_gt, ).
Returns:
tuple: Returns (assigned_gt_inds, shadowed_gt_inds).
- assigned_gt_inds: The assigned gt index of each prior bbox \
(i.e. index from 1 to num_gts). Shape: (num_prior, ).
- shadowed_gt_inds: shadowed gt indices. It is a tensor of \
shape (num_ignore, 2) with first column being the \
shadowed prior bbox indices and the second column the \
shadowed gt indices (1-based).
"""
num_bboxes, num_gts = is_bbox_in_gt_core.shape
if gt_priority is None:
gt_priority = torch.arange(
num_gts, device=is_bbox_in_gt_core.device)
assert gt_priority.size(0) == num_gts
# The bigger gt_priority, the more preferable to be assigned
# The assigned inds are by default 0 (background)
assigned_gt_inds = is_bbox_in_gt_core.new_zeros((num_bboxes, ),
dtype=torch.long)
# Shadowed bboxes are assigned to be background. But the corresponding
# label is ignored during loss calculation, which is done through
# shadowed_gt_inds
shadowed_gt_inds = torch.nonzero(is_bbox_in_gt_shadow, as_tuple=False)
if is_bbox_in_gt_core.sum() == 0: # No gt match
shadowed_gt_inds[:, 1] += 1 # 1-based. For consistency issue
return assigned_gt_inds, shadowed_gt_inds
# The priority of each prior box and gt pair. If one prior box is
# matched bo multiple gts. Only the pair with the highest priority
# is saved
pair_priority = is_bbox_in_gt_core.new_full((num_bboxes, num_gts),
-1,
dtype=torch.long)
# Each bbox could match with multiple gts.
# The following codes deal with this situation
# Matched bboxes (to any gt). Shape: (num_pos_anchor, )
inds_of_match = torch.any(is_bbox_in_gt_core, dim=1)
# The matched gt index of each positive bbox. Length >= num_pos_anchor
# , since one bbox could match multiple gts
matched_bbox_gt_inds = torch.nonzero(
is_bbox_in_gt_core, as_tuple=False)[:, 1]
# Assign priority to each bbox-gt pair.
pair_priority[is_bbox_in_gt_core] = gt_priority[matched_bbox_gt_inds]
_, argmax_priority = pair_priority[inds_of_match].max(dim=1)
assigned_gt_inds[inds_of_match] = argmax_priority + 1 # 1-based
# Zero-out the assigned anchor box to filter the shadowed gt indices
is_bbox_in_gt_core[inds_of_match, argmax_priority] = 0
# Concat the shadowed indices due to overlapping with that out side of
# effective scale. shape: (total_num_ignore, 2)
shadowed_gt_inds = torch.cat(
(shadowed_gt_inds, torch.nonzero(
is_bbox_in_gt_core, as_tuple=False)),
dim=0)
# `is_bbox_in_gt_core` should be changed back to keep arguments intact.
is_bbox_in_gt_core[inds_of_match, argmax_priority] = 1
# 1-based shadowed gt indices, to be consistent with `assigned_gt_inds`
if shadowed_gt_inds.numel() > 0:
shadowed_gt_inds[:, 1] += 1
return assigned_gt_inds, shadowed_gt_inds
```