import mmcv
import numpy as np
import torch
from .builder import ANCHOR_GENERATORS
[docs]@ANCHOR_GENERATORS.register_module()
class AnchorGenerator(object):
"""Standard anchor generator for 2D anchor-based detectors
Args:
strides (list[int]): Strides of anchors in multiple feture levels.
ratios (list[float]): The list of ratios between the height and width
of anchors in a single level.
scales (list[int] | None): Anchor scales for anchors in a single level.
It cannot be set at the same time if `octave_base_scale` and
`scales_per_octave` are set.
base_sizes (list[int] | None): The basic sizes of anchors in multiple
levels. If None is given, strides will be used as base_sizes.
scale_major (bool): Whether to multiply scales first when generating
base anchors. If true, the anchors in the same row will have the
same scales. By default it is True in V2.0
octave_base_scale (int): The base scale of octave.
scales_per_octave (int): Number of scales for each octave.
`octave_base_scale` and `scales_per_octave` are usually used in
retinanet and the `scales` should be None when they are set.
centers (list[tuple[float, float]] | None): The centers of the anchor
relative to the feature grid center in multiple feature levels.
By default it is set to be None and not used. If a list of tuple of
float is given, they will be used to shift the centers of anchors.
center_offset (float): The offset of center in propotion to anchors'
width and height. By default it is 0 in V2.0.
Examples:
>>> from mmdet.core import AnchorGenerator
>>> self = AnchorGenerator([16], [1.], [1.], [9])
>>> all_anchors = self.grid_anchors([(2, 2)], device='cpu')
>>> print(all_anchors)
[tensor([[-4.5000, -4.5000, 4.5000, 4.5000],
[11.5000, -4.5000, 20.5000, 4.5000],
[-4.5000, 11.5000, 4.5000, 20.5000],
[11.5000, 11.5000, 20.5000, 20.5000]])]
>>> self = AnchorGenerator([16, 32], [1.], [1.], [9, 18])
>>> all_anchors = self.grid_anchors([(2, 2), (1, 1)], device='cpu')
>>> print(all_anchors)
[tensor([[-4.5000, -4.5000, 4.5000, 4.5000],
[11.5000, -4.5000, 20.5000, 4.5000],
[-4.5000, 11.5000, 4.5000, 20.5000],
[11.5000, 11.5000, 20.5000, 20.5000]]), \
tensor([[-9., -9., 9., 9.]])]
"""
def __init__(self,
strides,
ratios,
scales=None,
base_sizes=None,
scale_major=True,
octave_base_scale=None,
scales_per_octave=None,
centers=None,
center_offset=0.):
# check center and center_offset
if center_offset != 0:
assert centers is None, 'center cannot be set when center_offset' \
f'!=0, {centers} is given.'
if not (0 <= center_offset <= 1):
raise ValueError('center_offset should be in range [0, 1], '
f'{center_offset} is given.')
if centers is not None:
assert len(centers) == len(strides), \
'The number of strides should be the same as centers, got ' \
f'{strides} and {centers}'
# calculate base sizes of anchors
self.strides = strides
self.base_sizes = list(strides) if base_sizes is None else base_sizes
assert len(self.base_sizes) == len(self.strides), \
'The number of strides should be the same as base sizes, got ' \
f'{self.strides} and {self.base_sizes}'
# calculate scales of anchors
assert ((octave_base_scale is not None
and scales_per_octave is not None) ^ (scales is not None)), \
'scales and octave_base_scale with scales_per_octave cannot' \
' be set at the same time'
if scales is not None:
self.scales = torch.Tensor(scales)
elif octave_base_scale is not None and scales_per_octave is not None:
octave_scales = np.array(
[2**(i / scales_per_octave) for i in range(scales_per_octave)])
scales = octave_scales * octave_base_scale
self.scales = torch.Tensor(scales)
else:
raise ValueError('Either scales or octave_base_scale with '
'scales_per_octave should be set')
self.octave_base_scale = octave_base_scale
self.scales_per_octave = scales_per_octave
self.ratios = torch.Tensor(ratios)
self.scale_major = scale_major
self.centers = centers
self.center_offset = center_offset
self.base_anchors = self.gen_base_anchors()
@property
def num_base_anchors(self):
return [base_anchors.size(0) for base_anchors in self.base_anchors]
@property
def num_levels(self):
return len(self.strides)
def gen_base_anchors(self):
multi_level_base_anchors = []
for i, base_size in enumerate(self.base_sizes):
center = None
if self.centers is not None:
center = self.centers[i]
multi_level_base_anchors.append(
self.gen_single_level_base_anchors(
base_size,
scales=self.scales,
ratios=self.ratios,
center=center))
return multi_level_base_anchors
def gen_single_level_base_anchors(self,
base_size,
scales,
ratios,
center=None):
w = base_size
h = base_size
if center is None:
x_center = self.center_offset * w
y_center = self.center_offset * h
else:
x_center, y_center = center
h_ratios = torch.sqrt(ratios)
w_ratios = 1 / h_ratios
if self.scale_major:
ws = (w * w_ratios[:, None] * scales[None, :]).view(-1)
hs = (h * h_ratios[:, None] * scales[None, :]).view(-1)
else:
ws = (w * scales[:, None] * w_ratios[None, :]).view(-1)
hs = (h * scales[:, None] * h_ratios[None, :]).view(-1)
# use float anchor and the anchor's center is aligned with the
# pixel center
base_anchors = [
x_center - 0.5 * ws, y_center - 0.5 * hs, x_center + 0.5 * ws,
y_center + 0.5 * hs
]
base_anchors = torch.stack(base_anchors, dim=-1)
return base_anchors
def _meshgrid(self, x, y, row_major=True):
xx = x.repeat(len(y))
yy = y.view(-1, 1).repeat(1, len(x)).view(-1)
if row_major:
return xx, yy
else:
return yy, xx
[docs] def grid_anchors(self, featmap_sizes, device='cuda'):
"""Generate grid anchors in multiple feature levels
Args:
featmap_sizes (list[tuple]): List of feature map sizes in
multiple feature levels.
device (str): Device where the anchors will be put on.
Return:
list[torch.Tensor]: Anchors in multiple feature levels.
The sizes of each tensor should be [N, 4], where
N = width * height * num_base_anchors, width and height
are the sizes of the corresponding feature lavel,
num_base_anchors is the number of anchors for that level.
"""
assert self.num_levels == len(featmap_sizes)
multi_level_anchors = []
for i in range(self.num_levels):
anchors = self.single_level_grid_anchors(
self.base_anchors[i].to(device),
featmap_sizes[i],
self.strides[i],
device=device)
multi_level_anchors.append(anchors)
return multi_level_anchors
def single_level_grid_anchors(self,
base_anchors,
featmap_size,
stride=16,
device='cuda'):
feat_h, feat_w = featmap_size
shift_x = torch.arange(0, feat_w, device=device) * stride
shift_y = torch.arange(0, feat_h, device=device) * stride
shift_xx, shift_yy = self._meshgrid(shift_x, shift_y)
shifts = torch.stack([shift_xx, shift_yy, shift_xx, shift_yy], dim=-1)
shifts = shifts.type_as(base_anchors)
# first feat_w elements correspond to the first row of shifts
# add A anchors (1, A, 4) to K shifts (K, 1, 4) to get
# shifted anchors (K, A, 4), reshape to (K*A, 4)
all_anchors = base_anchors[None, :, :] + shifts[:, None, :]
all_anchors = all_anchors.view(-1, 4)
# first A rows correspond to A anchors of (0, 0) in feature map,
# then (0, 1), (0, 2), ...
return all_anchors
[docs] def valid_flags(self, featmap_sizes, pad_shape, device='cuda'):
"""Generate valid flags of anchors in multiple feature levels
Args:
featmap_sizes (list(tuple)): List of feature map sizes in
multiple feature levels.
pad_shape (tuple): The padded shape of the image.
device (str): Device where the anchors will be put on.
Return:
list(torch.Tensor): Valid flags of anchors in multiple levels.
"""
assert self.num_levels == len(featmap_sizes)
multi_level_flags = []
for i in range(self.num_levels):
anchor_stride = self.strides[i]
feat_h, feat_w = featmap_sizes[i]
h, w = pad_shape[:2]
valid_feat_h = min(int(np.ceil(h / anchor_stride)), feat_h)
valid_feat_w = min(int(np.ceil(w / anchor_stride)), feat_w)
flags = self.single_level_valid_flags((feat_h, feat_w),
(valid_feat_h, valid_feat_w),
self.num_base_anchors[i],
device=device)
multi_level_flags.append(flags)
return multi_level_flags
def single_level_valid_flags(self,
featmap_size,
valid_size,
num_base_anchors,
device='cuda'):
feat_h, feat_w = featmap_size
valid_h, valid_w = valid_size
assert valid_h <= feat_h and valid_w <= feat_w
valid_x = torch.zeros(feat_w, dtype=torch.bool, device=device)
valid_y = torch.zeros(feat_h, dtype=torch.bool, device=device)
valid_x[:valid_w] = 1
valid_y[:valid_h] = 1
valid_xx, valid_yy = self._meshgrid(valid_x, valid_y)
valid = valid_xx & valid_yy
valid = valid[:, None].expand(valid.size(0),
num_base_anchors).contiguous().view(-1)
return valid
def __repr__(self):
indent_str = ' '
repr_str = self.__class__.__name__ + '(\n'
repr_str += f'{indent_str}strides={self.strides},\n'
repr_str += f'{indent_str}ratios={self.ratios},\n'
repr_str += f'{indent_str}scales={self.scales},\n'
repr_str += f'{indent_str}base_sizes={self.base_sizes},\n'
repr_str += f'{indent_str}scale_major={self.scale_major},\n'
repr_str += f'{indent_str}octave_base_scale='
repr_str += f'{self.octave_base_scale},\n'
repr_str += f'{indent_str}scales_per_octave='
repr_str += f'{self.scales_per_octave},\n'
repr_str += f'{indent_str}num_levels={self.num_levels}\n'
repr_str += f'{indent_str}centers={self.centers},\n'
repr_str += f'{indent_str}center_offset={self.center_offset})'
return repr_str
@ANCHOR_GENERATORS.register_module()
class SSDAnchorGenerator(AnchorGenerator):
"""Anchor generator for SSD
Args:
strides (list[int]): Strides of anchors in multiple feture levels.
ratios (list[float]): The list of ratios between the height and width
of anchors in a single level.
basesize_ratio_range (tuple(float)): Ratio range of anchors.
input_size (int): Size of feature map, 300 for SSD300, 512 for SSD512.
scale_major (bool): Whether to multiply scales first when generating
base anchors. If true, the anchors in the same row will have the
same scales. It is always set to be False in SSD.
"""
def __init__(self,
strides,
ratios,
basesize_ratio_range,
input_size=300,
scale_major=True):
assert len(strides) == len(ratios)
assert mmcv.is_tuple_of(basesize_ratio_range, float)
self.strides = strides
self.input_size = input_size
self.centers = [(stride / 2., stride / 2.) for stride in strides]
self.basesize_ratio_range = basesize_ratio_range
# calculate anchor ratios and sizes
min_ratio, max_ratio = basesize_ratio_range
min_ratio = int(min_ratio * 100)
max_ratio = int(max_ratio * 100)
step = int(np.floor(max_ratio - min_ratio) / (self.num_levels - 2))
min_sizes = []
max_sizes = []
for ratio in range(int(min_ratio), int(max_ratio) + 1, step):
min_sizes.append(int(input_size * ratio / 100))
max_sizes.append(int(input_size * (ratio + step) / 100))
if input_size == 300:
if basesize_ratio_range[0] == 0.15: # SSD300 COCO
min_sizes.insert(0, int(input_size * 7 / 100))
max_sizes.insert(0, int(input_size * 15 / 100))
elif basesize_ratio_range[0] == 0.2: # SSD300 VOC
min_sizes.insert(0, int(input_size * 10 / 100))
max_sizes.insert(0, int(input_size * 20 / 100))
else:
raise ValueError(
'basesize_ratio_range[0] should be either 0.15'
'or 0.2 when input_size is 300, got '
f'{basesize_ratio_range[0]}.')
elif input_size == 512:
if basesize_ratio_range[0] == 0.1: # SSD512 COCO
min_sizes.insert(0, int(input_size * 4 / 100))
max_sizes.insert(0, int(input_size * 10 / 100))
elif basesize_ratio_range[0] == 0.15: # SSD512 VOC
min_sizes.insert(0, int(input_size * 7 / 100))
max_sizes.insert(0, int(input_size * 15 / 100))
else:
raise ValueError('basesize_ratio_range[0] should be either 0.1'
'or 0.15 when input_size is 512, got'
' {basesize_ratio_range[0]}.')
else:
raise ValueError('Only support 300 or 512 in SSDAnchorGenerator'
f', got {input_size}.')
anchor_ratios = []
anchor_scales = []
for k in range(len(self.strides)):
scales = [1., np.sqrt(max_sizes[k] / min_sizes[k])]
anchor_ratio = [1.]
for r in ratios[k]:
anchor_ratio += [1 / r, r] # 4 or 6 ratio
anchor_ratios.append(torch.Tensor(anchor_ratio))
anchor_scales.append(torch.Tensor(scales))
self.base_sizes = min_sizes
self.scales = anchor_scales
self.ratios = anchor_ratios
self.scale_major = scale_major
self.center_offset = 0
self.base_anchors = self.gen_base_anchors()
def gen_base_anchors(self):
multi_level_base_anchors = []
for i, base_size in enumerate(self.base_sizes):
base_anchors = self.gen_single_level_base_anchors(
base_size,
scales=self.scales[i],
ratios=self.ratios[i],
center=self.centers[i])
indices = list(range(len(self.ratios[i])))
indices.insert(1, len(indices))
base_anchors = torch.index_select(base_anchors, 0,
torch.LongTensor(indices))
multi_level_base_anchors.append(base_anchors)
return multi_level_base_anchors
def __repr__(self):
indent_str = ' '
repr_str = self.__class__.__name__ + '(\n'
repr_str += f'{indent_str}strides={self.strides},\n'
repr_str += f'{indent_str}scales={self.scales},\n'
repr_str += f'{indent_str}scale_major={self.scale_major},\n'
repr_str += f'{indent_str}input_size={self.input_size},\n'
repr_str += f'{indent_str}scales={self.scales},\n'
repr_str += f'{indent_str}ratios={self.ratios},\n'
repr_str += f'{indent_str}num_levels={self.num_levels},\n'
repr_str += f'{indent_str}base_sizes={self.base_sizes},\n'
repr_str += f'{indent_str}basesize_ratio_range='
repr_str += f'{self.basesize_ratio_range})'
return repr_str
[docs]@ANCHOR_GENERATORS.register_module()
class LegacyAnchorGenerator(AnchorGenerator):
"""Legacy anchor generator used in MMDetection V1.x
Difference to the V2.0 anchor generator:
1. The center offset of V1.x anchors are set to be 0.5 rather than 0.
2. The width/height are minused by 1 when calculating the anchors' centers
and corners to meet the V1.x coordinate system.
3. The anchors' corners are quantized.
Args:
strides (list[int]): Strides of anchors in multiple feture levels.
ratios (list[float]): The list of ratios between the height and width
of anchors in a single level.
scales (list[int] | None): Anchor scales for anchors in a single level.
It cannot be set at the same time if `octave_base_scale` and
`scales_per_octave` are set.
base_sizes (list[int]): The basic sizes of anchors in multiple levels.
If None is given, strides will be used to generate base_sizes.
scale_major (bool): Whether to multiply scales first when generating
base anchors. If true, the anchors in the same row will have the
same scales. By default it is True in V2.0
octave_base_scale (int): The base scale of octave.
scales_per_octave (int): Number of scales for each octave.
`octave_base_scale` and `scales_per_octave` are usually used in
retinanet and the `scales` should be None when they are set.
centers (list[tuple[float, float]] | None): The centers of the anchor
relative to the feature grid center in multiple feature levels.
By default it is set to be None and not used. It a list of float
is given, this list will be used to shift the centers of anchors.
center_offset (float): The offset of center in propotion to anchors'
width and height. By default it is 0.5 in V2.0 but it should be 0.5
in v1.x models.
Examples:
>>> from mmdet.core import LegacyAnchorGenerator
>>> self = LegacyAnchorGenerator(
>>> [16], [1.], [1.], [9], center_offset=0.5)
>>> all_anchors = self.grid_anchors(((2, 2),), device='cpu')
>>> print(all_anchors)
[tensor([[ 0., 0., 8., 8.],
[16., 0., 24., 8.],
[ 0., 16., 8., 24.],
[16., 16., 24., 24.]])]
"""
def gen_single_level_base_anchors(self,
base_size,
scales,
ratios,
center=None):
w = base_size
h = base_size
if center is None:
x_center = self.center_offset * (w - 1)
y_center = self.center_offset * (h - 1)
else:
x_center, y_center = center
h_ratios = torch.sqrt(ratios)
w_ratios = 1 / h_ratios
if self.scale_major:
ws = (w * w_ratios[:, None] * scales[None, :]).view(-1)
hs = (h * h_ratios[:, None] * scales[None, :]).view(-1)
else:
ws = (w * scales[:, None] * w_ratios[None, :]).view(-1)
hs = (h * scales[:, None] * h_ratios[None, :]).view(-1)
# use float anchor and the anchor's center is aligned with the
# pixel center
base_anchors = [
x_center - 0.5 * (ws - 1), y_center - 0.5 * (hs - 1),
x_center + 0.5 * (ws - 1), y_center + 0.5 * (hs - 1)
]
base_anchors = torch.stack(base_anchors, dim=-1).round()
return base_anchors
@ANCHOR_GENERATORS.register_module()
class LegacySSDAnchorGenerator(SSDAnchorGenerator, LegacyAnchorGenerator):
"""Legacy anchor generator used in MMDetection V1.x
The difference between `LegacySSDAnchorGenerator` and `SSDAnchorGenerator`
can be found in `LegacyAnchorGenerator`.
"""
def __init__(self,
strides,
ratios,
basesize_ratio_range,
input_size=300,
scale_major=True):
super(LegacySSDAnchorGenerator,
self).__init__(strides, ratios, basesize_ratio_range, input_size,
scale_major)
self.centers = [((stride - 1) / 2., (stride - 1) / 2.)
for stride in strides]
self.base_anchors = self.gen_base_anchors()