Source code for mmdet.models.roi_heads.roi_extractors.single_level
import torch
import torch.nn as nn
from mmdet import ops
from mmdet.core import force_fp32
from mmdet.models.builder import ROI_EXTRACTORS
[docs]@ROI_EXTRACTORS.register_module()
class SingleRoIExtractor(nn.Module):
"""Extract RoI features from a single level feature map.
If there are mulitple input feature levels, each RoI is mapped to a level
according to its scale.
Args:
roi_layer (dict): Specify RoI layer type and arguments.
out_channels (int): Output channels of RoI layers.
featmap_strides (int): Strides of input feature maps.
finest_scale (int): Scale threshold of mapping to level 0.
"""
def __init__(self,
roi_layer,
out_channels,
featmap_strides,
finest_scale=56):
super(SingleRoIExtractor, self).__init__()
self.roi_layers = self.build_roi_layers(roi_layer, featmap_strides)
self.out_channels = out_channels
self.featmap_strides = featmap_strides
self.finest_scale = finest_scale
self.fp16_enabled = False
@property
def num_inputs(self):
"""int: Input feature map levels."""
return len(self.featmap_strides)
def init_weights(self):
pass
def build_roi_layers(self, layer_cfg, featmap_strides):
cfg = layer_cfg.copy()
layer_type = cfg.pop('type')
assert hasattr(ops, layer_type)
layer_cls = getattr(ops, layer_type)
roi_layers = nn.ModuleList(
[layer_cls(spatial_scale=1 / s, **cfg) for s in featmap_strides])
return roi_layers
[docs] def map_roi_levels(self, rois, num_levels):
"""Map rois to corresponding feature levels by scales.
- scale < finest_scale * 2: level 0
- finest_scale * 2 <= scale < finest_scale * 4: level 1
- finest_scale * 4 <= scale < finest_scale * 8: level 2
- scale >= finest_scale * 8: level 3
Args:
rois (Tensor): Input RoIs, shape (k, 5).
num_levels (int): Total level number.
Returns:
Tensor: Level index (0-based) of each RoI, shape (k, )
"""
scale = torch.sqrt(
(rois[:, 3] - rois[:, 1]) * (rois[:, 4] - rois[:, 2]))
target_lvls = torch.floor(torch.log2(scale / self.finest_scale + 1e-6))
target_lvls = target_lvls.clamp(min=0, max=num_levels - 1).long()
return target_lvls
def roi_rescale(self, rois, scale_factor):
cx = (rois[:, 1] + rois[:, 3]) * 0.5
cy = (rois[:, 2] + rois[:, 4]) * 0.5
w = rois[:, 3] - rois[:, 1]
h = rois[:, 4] - rois[:, 2]
new_w = w * scale_factor
new_h = h * scale_factor
x1 = cx - new_w * 0.5
x2 = cx + new_w * 0.5
y1 = cy - new_h * 0.5
y2 = cy + new_h * 0.5
new_rois = torch.stack((rois[:, 0], x1, y1, x2, y2), dim=-1)
return new_rois
[docs] @force_fp32(apply_to=('feats', ), out_fp16=True)
def forward(self, feats, rois, roi_scale_factor=None):
out_size = self.roi_layers[0].out_size
num_levels = len(feats)
roi_feats = feats[0].new_zeros(
rois.size(0), self.out_channels, *out_size)
if num_levels == 1:
if len(rois) == 0:
return roi_feats
return self.roi_layers[0](feats[0], rois)
target_lvls = self.map_roi_levels(rois, num_levels)
if roi_scale_factor is not None:
rois = self.roi_rescale(rois, roi_scale_factor)
for i in range(num_levels):
inds = target_lvls == i
if inds.any():
rois_ = rois[inds, :]
roi_feats_t = self.roi_layers[i](feats[i], rois_)
roi_feats[inds] = roi_feats_t
else:
roi_feats += sum(x.view(-1)[0] for x in self.parameters()) * 0.
return roi_feats