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# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
import math
import numpy as np
import torch
from torch import nn
from maskrcnn_benchmark.structures.bounding_box import BoxList
class BufferList(nn.Module):
"""
Similar to nn.ParameterList, but for buffers
"""
def __init__(self, buffers=None):
super(BufferList, self).__init__()
if buffers is not None:
self.extend(buffers)
def extend(self, buffers):
offset = len(self)
for i, buffer in enumerate(buffers):
self.register_buffer(str(offset + i), buffer)
return self
def __len__(self):
return len(self._buffers)
def __iter__(self):
return iter(self._buffers.values())
class AnchorGenerator(nn.Module):
"""
For a set of image sizes and feature maps, computes a set
of anchors
"""
def __init__(
self,
sizes=(128, 256, 512), # 32, 64, 128, 256, 512
aspect_ratios=(0.5, 1.0, 2.0), # 0.25, 0.5, 1.0, 2.0, 4.0
anchor_strides=(8, 16, 32), # 4, 8, 16, 32, 64
straddle_thresh=0, # 0
):
super(AnchorGenerator, self).__init__()
if len(anchor_strides) == 1:
anchor_stride = anchor_strides[0]
cell_anchors = [
generate_anchors(anchor_stride, sizes, aspect_ratios).float()
]
else:
# This step is done
if len(anchor_strides) != len(sizes):
raise RuntimeError("FPN should have #anchor_strides == #sizes")
cell_anchors = [
generate_anchors(
anchor_stride,
size if isinstance(size, (tuple, list)) else (size,),
aspect_ratios
).float()
for anchor_stride, size in zip(anchor_strides, sizes)
]
self.strides = anchor_strides
self.cell_anchors = BufferList(cell_anchors)
self.straddle_thresh = straddle_thresh
def num_anchors_per_location(self):
return [len(cell_anchors) for cell_anchors in self.cell_anchors]
def grid_anchors(self, grid_sizes):
anchors = []
for size, stride, base_anchors in zip(
grid_sizes, self.strides, self.cell_anchors
):
grid_height, grid_width = size
device = base_anchors.device
shifts_x = torch.arange(
0, grid_width * stride, step=stride, dtype=torch.float32, device=device
)
shifts_y = torch.arange(
0, grid_height * stride, step=stride, dtype=torch.float32, device=device
)
shift_y, shift_x = torch.meshgrid(shifts_y, shifts_x)
shift_x = shift_x.reshape(-1)
shift_y = shift_y.reshape(-1)
shifts = torch.stack((shift_x, shift_y, shift_x, shift_y), dim=1)
anchors.append(
(shifts.view(-1, 1, 4) + base_anchors.view(1, -1, 4)).reshape(-1, 4)
)
return anchors
def add_visibility_to(self, boxlist):
image_width, image_height = boxlist.size
anchors = boxlist.bbox
if self.straddle_thresh >= 0:
inds_inside = (
(anchors[..., 0] >= -self.straddle_thresh)
& (anchors[..., 1] >= -self.straddle_thresh)
& (anchors[..., 2] < image_width + self.straddle_thresh)
& (anchors[..., 3] < image_height + self.straddle_thresh)
)
else:
device = anchors.device
inds_inside = torch.ones(anchors.shape[0], dtype=torch.uint8, device=device)
boxlist.add_field("visibility", inds_inside)
def forward(self, image_list, feature_maps):
grid_sizes = [feature_map.shape[-2:] for feature_map in feature_maps] # size of features
anchors_over_all_feature_maps = self.grid_anchors(grid_sizes)
anchors = []
for i, (image_height, image_width) in enumerate(image_list.image_sizes):
anchors_in_image = []
for anchors_per_feature_map in anchors_over_all_feature_maps:
boxlist = BoxList(
anchors_per_feature_map, (image_width, image_height), mode="xyxy"
)
self.add_visibility_to(boxlist)
anchors_in_image.append(boxlist)
anchors.append(anchors_in_image)
return anchors # [image,number,[n,4]]
def make_anchor_generator(config):
anchor_sizes = config.MODEL.RPN.ANCHOR_SIZES # 32, 64, 128, 256, 512
aspect_ratios = config.MODEL.RPN.ASPECT_RATIOS # 0.25, 0.5, 1.0, 2.0, 4.0
anchor_stride = config.MODEL.RPN.ANCHOR_STRIDE # 4, 8, 16, 32, 64
straddle_thresh = config.MODEL.RPN.STRADDLE_THRESH #0
if config.MODEL.RPN.USE_FPN: # This step is done
assert len(anchor_stride) == len(
anchor_sizes
), "FPN should have len(ANCHOR_STRIDE) == len(ANCHOR_SIZES)"
else:
assert len(anchor_stride) == 1, "Non-FPN should have a single ANCHOR_STRIDE"
anchor_generator = AnchorGenerator(
anchor_sizes, aspect_ratios, anchor_stride, straddle_thresh
)
return anchor_generator
def make_anchor_generator_retinanet(config):
anchor_sizes = config.MODEL.RETINANET.ANCHOR_SIZES
aspect_ratios = config.MODEL.RETINANET.ASPECT_RATIOS
anchor_strides = config.MODEL.RETINANET.ANCHOR_STRIDES
straddle_thresh = config.MODEL.RETINANET.STRADDLE_THRESH
octave = config.MODEL.RETINANET.OCTAVE
scales_per_octave = config.MODEL.RETINANET.SCALES_PER_OCTAVE
assert len(anchor_strides) == len(anchor_sizes), "Only support FPN now"
new_anchor_sizes = []
for size in anchor_sizes:
per_layer_anchor_sizes = []
for scale_per_octave in range(scales_per_octave):
octave_scale = octave ** (scale_per_octave / float(scales_per_octave))
per_layer_anchor_sizes.append(octave_scale * size)
new_anchor_sizes.append(tuple(per_layer_anchor_sizes))
anchor_generator = AnchorGenerator(
tuple(new_anchor_sizes), aspect_ratios, anchor_strides, straddle_thresh
)
return anchor_generator
# Copyright (c) 2017-present, Facebook, Inc.
#
# 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.
##############################################################################
#
# Based on:
# --------------------------------------------------------
# Faster R-CNN
# Copyright (c) 2015 Microsoft
# Licensed under The MIT License [see LICENSE for details]
# Written by Ross Girshick and Sean Bell
# --------------------------------------------------------
# Verify that we compute the same anchors as Shaoqing's matlab implementation:
#
# >> load output/rpn_cachedir/faster_rcnn_VOC2007_ZF_stage1_rpn/anchors.mat
# >> anchors
#
# anchors =
#
# -83 -39 100 56
# -175 -87 192 104
# -359 -183 376 200
# -55 -55 72 72
# -119 -119 136 136
# -247 -247 264 264
# -35 -79 52 96
# -79 -167 96 184
# -167 -343 184 360
# array([[ -83., -39., 100., 56.],
# [-175., -87., 192., 104.],
# [-359., -183., 376., 200.],
# [ -55., -55., 72., 72.],
# [-119., -119., 136., 136.],
# [-247., -247., 264., 264.],
# [ -35., -79., 52., 96.],
# [ -79., -167., 96., 184.],
# [-167., -343., 184., 360.]])
def generate_anchors(
stride=16, sizes=(32, 64, 128, 256, 512), aspect_ratios=(0.5, 1, 2)
):
"""Generates a matrix of anchor boxes in (x1, y1, x2, y2) format. Anchors
are centered on stride / 2, have (approximate) sqrt areas of the specified
sizes, and aspect ratios as given.
"""
return _generate_anchors(
stride,
np.array(sizes, dtype=np.float) / stride,
np.array(aspect_ratios, dtype=np.float),
)
def _generate_anchors(base_size, scales, aspect_ratios):
"""Generate anchor (reference) windows by enumerating aspect ratios X
scales wrt a reference (0, 0, base_size - 1, base_size - 1) window.
"""
anchor = np.array([1, 1, base_size, base_size], dtype=np.float) - 1
anchors = _ratio_enum(anchor, aspect_ratios)
anchors = np.vstack(
[_scale_enum(anchors[i, :], scales) for i in range(anchors.shape[0])]
)
return torch.from_numpy(anchors)
def _whctrs(anchor):
"""Return width, height, x center, and y center for an anchor (window)."""
w = anchor[2] - anchor[0] + 1
h = anchor[3] - anchor[1] + 1
x_ctr = anchor[0] + 0.5 * (w - 1)
y_ctr = anchor[1] + 0.5 * (h - 1)
return w, h, x_ctr, y_ctr
def _mkanchors(ws, hs, x_ctr, y_ctr):
"""Given a vector of widths (ws) and heights (hs) around a center
(x_ctr, y_ctr), output a set of anchors (windows).
"""
ws = ws[:, np.newaxis]
hs = hs[:, np.newaxis]
anchors = np.hstack(
(
x_ctr - 0.5 * (ws - 1),
y_ctr - 0.5 * (hs - 1),
x_ctr + 0.5 * (ws - 1),
y_ctr + 0.5 * (hs - 1),
)
)
return anchors
def _ratio_enum(anchor, ratios):
"""Enumerate a set of anchors for each aspect ratio wrt an anchor."""
w, h, x_ctr, y_ctr = _whctrs(anchor)
size = w * h
size_ratios = size / ratios
ws = np.round(np.sqrt(size_ratios))
hs = np.round(ws * ratios)
anchors = _mkanchors(ws, hs, x_ctr, y_ctr)
return anchors
def _scale_enum(anchor, scales):
"""Enumerate a set of anchors for each scale wrt an anchor."""
w, h, x_ctr, y_ctr = _whctrs(anchor)
ws = w * scales
hs = h * scales
anchors = _mkanchors(ws, hs, x_ctr, y_ctr)
return anchors
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