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# Modified from https://github.com/facebookresearch/detectron2/tree/master/projects/PointRend/point_head/point_head.py # noqa
import torch
import torch.nn as nn
from mmcv.cnn import ConvModule, normal_init
from mmcv.ops import point_sample, rel_roi_point_to_rel_img_point
from mmdet.models.builder import HEADS, build_loss
@HEADS.register_module()
class MaskPointHead(nn.Module):
"""A mask point head use in PointRend.
``MaskPointHead`` use shared multi-layer perceptron (equivalent to
nn.Conv1d) to predict the logit of input points. The fine-grained feature
and coarse feature will be concatenate together for predication.
Args:
num_fcs (int): Number of fc layers in the head. Default: 3.
in_channels (int): Number of input channels. Default: 256.
fc_channels (int): Number of fc channels. Default: 256.
num_classes (int): Number of classes for logits. Default: 80.
class_agnostic (bool): Whether use class agnostic classification.
If so, the output channels of logits will be 1. Default: False.
coarse_pred_each_layer (bool): Whether concatenate coarse feature with
the output of each fc layer. Default: True.
conv_cfg (dict | None): Dictionary to construct and config conv layer.
Default: dict(type='Conv1d'))
norm_cfg (dict | None): Dictionary to construct and config norm layer.
Default: None.
loss_point (dict): Dictionary to construct and config loss layer of
point head. Default: dict(type='CrossEntropyLoss', use_mask=True,
loss_weight=1.0).
"""
def __init__(self,
num_classes,
num_fcs=3,
in_channels=256,
fc_channels=256,
class_agnostic=False,
coarse_pred_each_layer=True,
conv_cfg=dict(type='Conv1d'),
norm_cfg=None,
act_cfg=dict(type='ReLU'),
loss_point=dict(
type='CrossEntropyLoss', use_mask=True, loss_weight=1.0)):
super().__init__()
self.num_fcs = num_fcs
self.in_channels = in_channels
self.fc_channels = fc_channels
self.num_classes = num_classes
self.class_agnostic = class_agnostic
self.coarse_pred_each_layer = coarse_pred_each_layer
self.conv_cfg = conv_cfg
self.norm_cfg = norm_cfg
self.loss_point = build_loss(loss_point)
fc_in_channels = in_channels + num_classes
self.fcs = nn.ModuleList()
for _ in range(num_fcs):
fc = ConvModule(
fc_in_channels,
fc_channels,
kernel_size=1,
stride=1,
padding=0,
conv_cfg=conv_cfg,
norm_cfg=norm_cfg,
act_cfg=act_cfg)
self.fcs.append(fc)
fc_in_channels = fc_channels
fc_in_channels += num_classes if self.coarse_pred_each_layer else 0
out_channels = 1 if self.class_agnostic else self.num_classes
self.fc_logits = nn.Conv1d(
fc_in_channels, out_channels, kernel_size=1, stride=1, padding=0)
def init_weights(self):
"""Initialize last classification layer of MaskPointHead, conv layers
are already initialized by ConvModule."""
normal_init(self.fc_logits, std=0.001)
def forward(self, fine_grained_feats, coarse_feats):
"""Classify each point base on fine grained and coarse feats.
Args:
fine_grained_feats (Tensor): Fine grained feature sampled from FPN,
shape (num_rois, in_channels, num_points).
coarse_feats (Tensor): Coarse feature sampled from CoarseMaskHead,
shape (num_rois, num_classes, num_points).
Returns:
Tensor: Point classification results,
shape (num_rois, num_class, num_points).
"""
x = torch.cat([fine_grained_feats, coarse_feats], dim=1)
for fc in self.fcs:
x = fc(x)
if self.coarse_pred_each_layer:
x = torch.cat((x, coarse_feats), dim=1)
return self.fc_logits(x)
def get_targets(self, rois, rel_roi_points, sampling_results, gt_masks,
cfg):
"""Get training targets of MaskPointHead for all images.
Args:
rois (Tensor): Region of Interest, shape (num_rois, 5).
rel_roi_points: Points coordinates relative to RoI, shape
(num_rois, num_points, 2).
sampling_results (:obj:`SamplingResult`): Sampling result after
sampling and assignment.
gt_masks (Tensor) : Ground truth segmentation masks of
corresponding boxes, shape (num_rois, height, width).
cfg (dict): Training cfg.
Returns:
Tensor: Point target, shape (num_rois, num_points).
"""
num_imgs = len(sampling_results)
rois_list = []
rel_roi_points_list = []
for batch_ind in range(num_imgs):
inds = (rois[:, 0] == batch_ind)
rois_list.append(rois[inds])
rel_roi_points_list.append(rel_roi_points[inds])
pos_assigned_gt_inds_list = [
res.pos_assigned_gt_inds for res in sampling_results
]
cfg_list = [cfg for _ in range(num_imgs)]
point_targets = map(self._get_target_single, rois_list,
rel_roi_points_list, pos_assigned_gt_inds_list,
gt_masks, cfg_list)
point_targets = list(point_targets)
if len(point_targets) > 0:
point_targets = torch.cat(point_targets)
return point_targets
def _get_target_single(self, rois, rel_roi_points, pos_assigned_gt_inds,
gt_masks, cfg):
"""Get training target of MaskPointHead for each image."""
num_pos = rois.size(0)
num_points = cfg.num_points
if num_pos > 0:
gt_masks_th = (
gt_masks.to_tensor(rois.dtype, rois.device).index_select(
0, pos_assigned_gt_inds))
gt_masks_th = gt_masks_th.unsqueeze(1)
rel_img_points = rel_roi_point_to_rel_img_point(
rois, rel_roi_points, gt_masks_th.shape[2:])
point_targets = point_sample(gt_masks_th,
rel_img_points).squeeze(1)
else:
point_targets = rois.new_zeros((0, num_points))
return point_targets
def loss(self, point_pred, point_targets, labels):
"""Calculate loss for MaskPointHead.
Args:
point_pred (Tensor): Point predication result, shape
(num_rois, num_classes, num_points).
point_targets (Tensor): Point targets, shape (num_roi, num_points).
labels (Tensor): Class label of corresponding boxes,
shape (num_rois, )
Returns:
dict[str, Tensor]: a dictionary of point loss components
"""
loss = dict()
if self.class_agnostic:
loss_point = self.loss_point(point_pred, point_targets,
torch.zeros_like(labels))
else:
loss_point = self.loss_point(point_pred, point_targets, labels)
loss['loss_point'] = loss_point
return loss
def _get_uncertainty(self, mask_pred, labels):
"""Estimate uncertainty based on pred logits.
We estimate uncertainty as L1 distance between 0.0 and the logits
prediction in 'mask_pred' for the foreground class in `classes`.
Args:
mask_pred (Tensor): mask predication logits, shape (num_rois,
num_classes, mask_height, mask_width).
labels (list[Tensor]): Either predicted or ground truth label for
each predicted mask, of length num_rois.
Returns:
scores (Tensor): Uncertainty scores with the most uncertain
locations having the highest uncertainty score,
shape (num_rois, 1, mask_height, mask_width)
"""
if mask_pred.shape[1] == 1:
gt_class_logits = mask_pred.clone()
else:
inds = torch.arange(mask_pred.shape[0], device=mask_pred.device)
gt_class_logits = mask_pred[inds, labels].unsqueeze(1)
return -torch.abs(gt_class_logits)
def get_roi_rel_points_train(self, mask_pred, labels, cfg):
"""Get ``num_points`` most uncertain points with random points during
train.
Sample points in [0, 1] x [0, 1] coordinate space based on their
uncertainty. The uncertainties are calculated for each point using
'_get_uncertainty()' function that takes point's logit prediction as
input.
Args:
mask_pred (Tensor): A tensor of shape (num_rois, num_classes,
mask_height, mask_width) for class-specific or class-agnostic
prediction.
labels (list): The ground truth class for each instance.
cfg (dict): Training config of point head.
Returns:
point_coords (Tensor): A tensor of shape (num_rois, num_points, 2)
that contains the coordinates sampled points.
"""
num_points = cfg.num_points
oversample_ratio = cfg.oversample_ratio
importance_sample_ratio = cfg.importance_sample_ratio
assert oversample_ratio >= 1
assert 0 <= importance_sample_ratio <= 1
batch_size = mask_pred.shape[0]
num_sampled = int(num_points * oversample_ratio)
point_coords = torch.rand(
batch_size, num_sampled, 2, device=mask_pred.device)
point_logits = point_sample(mask_pred, point_coords)
# It is crucial to calculate uncertainty based on the sampled
# prediction value for the points. Calculating uncertainties of the
# coarse predictions first and sampling them for points leads to
# incorrect results. To illustrate this: assume uncertainty func(
# logits)=-abs(logits), a sampled point between two coarse
# predictions with -1 and 1 logits has 0 logits, and therefore 0
# uncertainty value. However, if we calculate uncertainties for the
# coarse predictions first, both will have -1 uncertainty,
# and sampled point will get -1 uncertainty.
point_uncertainties = self._get_uncertainty(point_logits, labels)
num_uncertain_points = int(importance_sample_ratio * num_points)
num_random_points = num_points - num_uncertain_points
idx = torch.topk(
point_uncertainties[:, 0, :], k=num_uncertain_points, dim=1)[1]
shift = num_sampled * torch.arange(
batch_size, dtype=torch.long, device=mask_pred.device)
idx += shift[:, None]
point_coords = point_coords.view(-1, 2)[idx.view(-1), :].view(
batch_size, num_uncertain_points, 2)
if num_random_points > 0:
rand_roi_coords = torch.rand(
batch_size, num_random_points, 2, device=mask_pred.device)
point_coords = torch.cat((point_coords, rand_roi_coords), dim=1)
return point_coords
def get_roi_rel_points_test(self, mask_pred, pred_label, cfg):
"""Get ``num_points`` most uncertain points during test.
Args:
mask_pred (Tensor): A tensor of shape (num_rois, num_classes,
mask_height, mask_width) for class-specific or class-agnostic
prediction.
pred_label (list): The predication class for each instance.
cfg (dict): Testing config of point head.
Returns:
point_indices (Tensor): A tensor of shape (num_rois, num_points)
that contains indices from [0, mask_height x mask_width) of the
most uncertain points.
point_coords (Tensor): A tensor of shape (num_rois, num_points, 2)
that contains [0, 1] x [0, 1] normalized coordinates of the
most uncertain points from the [mask_height, mask_width] grid .
"""
num_points = cfg.subdivision_num_points
uncertainty_map = self._get_uncertainty(mask_pred, pred_label)
num_rois, _, mask_height, mask_width = uncertainty_map.shape
h_step = 1.0 / mask_height
w_step = 1.0 / mask_width
uncertainty_map = uncertainty_map.view(num_rois,
mask_height * mask_width)
num_points = min(mask_height * mask_width, num_points)
point_indices = uncertainty_map.topk(num_points, dim=1)[1]
point_coords = uncertainty_map.new_zeros(num_rois, num_points, 2)
point_coords[:, :, 0] = w_step / 2.0 + (point_indices %
mask_width).float() * w_step
point_coords[:, :, 1] = h_step / 2.0 + (point_indices //
mask_width).float() * h_step
return point_indices, point_coords
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