import torch
import torch.nn as nn
from scipy.optimize import linear_sum_assignment
from easycv.models.detection.utils import (box_cxcywh_to_xyxy,
generalized_box_iou)
[docs]class HungarianMatcher(nn.Module):
"""This class computes an assignment between the targets and the predictions of the network
For efficiency reasons, the targets don't include the no_object. Because of this, in general,
there are more predictions than targets. In this case, we do a 1-to-1 matching of the best predictions,
while the others are un-matched (and thus treated as non-objects).
"""
[docs] def __init__(self, cost_dict, cost_class_type='ce_cost'):
"""Creates the matcher
Params:
cost_class: This is the relative weight of the classification error in the matching cost
cost_bbox: This is the relative weight of the L1 error of the bounding box coordinates in the matching cost
cost_giou: This is the relative weight of the giou loss of the bounding box in the matching cost
"""
super().__init__()
self.cost_class = cost_dict['cost_class']
self.cost_bbox = cost_dict['cost_bbox']
self.cost_giou = cost_dict['cost_giou']
self.cost_class_type = cost_class_type
assert self.cost_class != 0 or self.cost_bbox != 0 or self.cost_giou != 0, 'all costs cant be 0'
[docs] @torch.no_grad()
def forward(self, outputs, targets):
""" Performs the matching
Params:
outputs: This is a dict that contains at least these entries:
"pred_logits": Tensor of dim [batch_size, num_queries, num_classes] with the classification logits
"pred_boxes": Tensor of dim [batch_size, num_queries, 4] with the predicted box coordinates
targets: This is a list of targets (len(targets) = batch_size), where each target is a dict containing:
"labels": Tensor of dim [num_target_boxes] (where num_target_boxes is the number of ground-truth
objects in the target) containing the class labels
"boxes": Tensor of dim [num_target_boxes, 4] containing the target box coordinates
Returns:
A list of size batch_size, containing tuples of (index_i, index_j) where:
- index_i is the indices of the selected predictions (in order)
- index_j is the indices of the corresponding selected targets (in order)
For each batch element, it holds:
len(index_i) = len(index_j) = min(num_queries, num_target_boxes)
"""
bs, num_queries = outputs['pred_logits'].shape[:2]
# We flatten to compute the cost matrices in a batch
if self.cost_class_type == 'focal_loss_cost':
out_prob = outputs['pred_logits'].flatten(
0, 1).sigmoid() # [batch_size * num_queries, num_classes]
elif self.cost_class_type == 'ce_cost':
out_prob = outputs['pred_logits'].flatten(0, 1).softmax(
-1) # [batch_size * num_queries, num_classes]
out_bbox = outputs['pred_boxes'].flatten(
0, 1) # [batch_size * num_queries, 4]
# Also concat the target labels and boxes
tgt_ids = torch.cat([v['labels'] for v in targets])
tgt_bbox = torch.cat([v['boxes'] for v in targets])
# Compute the classification cost.
if self.cost_class_type == 'focal_loss_cost':
alpha = 0.25
gamma = 2.0
neg_cost_class = (1 - alpha) * (out_prob**gamma)
neg_cost_class = neg_cost_class * (-(1 - out_prob + 1e-8).log())
pos_cost_class = alpha * ((1 - out_prob)**gamma)
pos_cost_class = pos_cost_class * (-(out_prob + 1e-8).log())
cost_class = pos_cost_class[:, tgt_ids] - neg_cost_class[:,
tgt_ids]
elif self.cost_class_type == 'ce_cost':
# Compute the classification cost. Contrary to the loss, we don't use the NLL,
# but approximate it in 1 - proba[target class].
# The 1 is a constant that doesn't change the matching, it can be ommitted.
cost_class = -out_prob[:, tgt_ids]
# Compute the L1 cost between boxes
cost_bbox = torch.cdist(out_bbox, tgt_bbox, p=1)
# Compute the giou cost betwen boxes
cost_giou = -generalized_box_iou(
box_cxcywh_to_xyxy(out_bbox), box_cxcywh_to_xyxy(tgt_bbox))
# Final cost matrix
C = self.cost_bbox * cost_bbox + self.cost_class * cost_class + self.cost_giou * cost_giou
C = C.view(bs, num_queries, -1).cpu()
sizes = [len(v['boxes']) for v in targets]
indices = [
linear_sum_assignment(c[i])
for i, c in enumerate(C.split(sizes, -1))
]
return [(torch.as_tensor(i, dtype=torch.int64),
torch.as_tensor(j, dtype=torch.int64)) for i, j in indices]