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# Copyright 2020 Google Research. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""Base box coder.
Box coders convert between coordinate frames, namely image-centric
(with (0,0) on the top left of image) and anchor-centric (with (0,0) being
defined by a specific anchor).
Users of a BoxCoder can call two methods:
encode: which encodes a box with respect to a given anchor
(or rather, a tensor of boxes wrt a corresponding tensor of anchors) and
decode: which inverts this encoding with a decode operation.
In both cases, the arguments are assumed to be in 1-1 correspondence already;
it is not the job of a BoxCoder to perform matching.
"""
import torch
from typing import List, Optional
from .box_list import BoxList
# Box coder types.
FASTER_RCNN = 'faster_rcnn'
KEYPOINT = 'keypoint'
MEAN_STDDEV = 'mean_stddev'
SQUARE = 'square'
"""Faster RCNN box coder.
Faster RCNN box coder follows the coding schema described below:
ty = (y - ya) / ha
tx = (x - xa) / wa
th = log(h / ha)
tw = log(w / wa)
where x, y, w, h denote the box's center coordinates, width and height
respectively. Similarly, xa, ya, wa, ha denote the anchor's center
coordinates, width and height. tx, ty, tw and th denote the anchor-encoded
center, width and height respectively.
See http://arxiv.org/abs/1506.01497 for details.
"""
EPS = 1e-8
#@torch.jit.script
class FasterRcnnBoxCoder(object):
"""Faster RCNN box coder."""
def __init__(self, scale_factors: Optional[List[float]] = None, eps: float = EPS):
"""Constructor for FasterRcnnBoxCoder.
Args:
scale_factors: List of 4 positive scalars to scale ty, tx, th and tw.
If set to None, does not perform scaling. For Faster RCNN,
the open-source implementation recommends using [10.0, 10.0, 5.0, 5.0].
"""
self._scale_factors = scale_factors
if scale_factors is not None:
assert len(scale_factors) == 4
for scalar in scale_factors:
assert scalar > 0
self.eps = eps
#@property
def code_size(self):
return 4
def encode(self, boxes: BoxList, anchors: BoxList):
"""Encode a box collection with respect to anchor collection.
Args:
boxes: BoxList holding N boxes to be encoded.
anchors: BoxList of anchors.
Returns:
a tensor representing N anchor-encoded boxes of the format [ty, tx, th, tw].
"""
# Convert anchors to the center coordinate representation.
ycenter_a, xcenter_a, ha, wa = anchors.get_center_coordinates_and_sizes()
ycenter, xcenter, h, w = boxes.get_center_coordinates_and_sizes()
# Avoid NaN in division and log below.
ha += self.eps
wa += self.eps
h += self.eps
w += self.eps
tx = (xcenter - xcenter_a) / wa
ty = (ycenter - ycenter_a) / ha
tw = torch.log(w / wa)
th = torch.log(h / ha)
# Scales location targets as used in paper for joint training.
if self._scale_factors is not None:
ty *= self._scale_factors[0]
tx *= self._scale_factors[1]
th *= self._scale_factors[2]
tw *= self._scale_factors[3]
return torch.stack([ty, tx, th, tw]).t()
def decode(self, rel_codes, anchors: BoxList):
"""Decode relative codes to boxes.
Args:
rel_codes: a tensor representing N anchor-encoded boxes.
anchors: BoxList of anchors.
Returns:
boxes: BoxList holding N bounding boxes.
"""
ycenter_a, xcenter_a, ha, wa = anchors.get_center_coordinates_and_sizes()
ty, tx, th, tw = rel_codes.t().unbind()
if self._scale_factors is not None:
ty /= self._scale_factors[0]
tx /= self._scale_factors[1]
th /= self._scale_factors[2]
tw /= self._scale_factors[3]
w = torch.exp(tw) * wa
h = torch.exp(th) * ha
ycenter = ty * ha + ycenter_a
xcenter = tx * wa + xcenter_a
ymin = ycenter - h / 2.
xmin = xcenter - w / 2.
ymax = ycenter + h / 2.
xmax = xcenter + w / 2.
return BoxList(torch.stack([ymin, xmin, ymax, xmax]).t())
def batch_decode(encoded_boxes, box_coder: FasterRcnnBoxCoder, anchors: BoxList):
"""Decode a batch of encoded boxes.
This op takes a batch of encoded bounding boxes and transforms
them to a batch of bounding boxes specified by their corners in
the order of [y_min, x_min, y_max, x_max].
Args:
encoded_boxes: a float32 tensor of shape [batch_size, num_anchors,
code_size] representing the location of the objects.
box_coder: a BoxCoder object.
anchors: a BoxList of anchors used to encode `encoded_boxes`.
Returns:
decoded_boxes: a float32 tensor of shape [batch_size, num_anchors, coder_size]
representing the corners of the objects in the order of [y_min, x_min, y_max, x_max].
Raises:
ValueError: if batch sizes of the inputs are inconsistent, or if
the number of anchors inferred from encoded_boxes and anchors are inconsistent.
"""
assert len(encoded_boxes.shape) == 3
if encoded_boxes.shape[1] != anchors.num_boxes():
raise ValueError('The number of anchors inferred from encoded_boxes'
' and anchors are inconsistent: shape[1] of encoded_boxes'
' %s should be equal to the number of anchors: %s.' %
(encoded_boxes.shape[1], anchors.num_boxes()))
decoded_boxes = torch.stack([
box_coder.decode(boxes, anchors).boxes for boxes in encoded_boxes.unbind()
])
return decoded_boxes
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