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Zero
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# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved
from typing import Any, List
import torch
from torch.nn import functional as F
from detectron2.config import CfgNode
from detectron2.structures import Instances
from .utils import resample_data
class SegmentationLoss:
"""
Segmentation loss as cross-entropy for raw unnormalized scores given ground truth
labels. Segmentation ground truth labels are defined for the bounding box of
interest at some fixed resolution [S, S], where
S = MODEL.ROI_DENSEPOSE_HEAD.HEATMAP_SIZE.
"""
def __init__(self, cfg: CfgNode):
"""
Initialize segmentation loss from configuration options
Args:
cfg (CfgNode): configuration options
"""
self.heatmap_size = cfg.MODEL.ROI_DENSEPOSE_HEAD.HEATMAP_SIZE
self.n_segm_chan = cfg.MODEL.ROI_DENSEPOSE_HEAD.NUM_COARSE_SEGM_CHANNELS
def __call__(
self,
proposals_with_gt: List[Instances],
densepose_predictor_outputs: Any,
packed_annotations: Any,
) -> torch.Tensor:
"""
Compute segmentation loss as cross-entropy on aligned segmentation
ground truth and estimated scores.
Args:
proposals_with_gt (list of Instances): detections with associated ground truth data
densepose_predictor_outputs: an object of a dataclass that contains predictor outputs
with estimated values; assumed to have the following attributes:
* coarse_segm - coarse segmentation estimates, tensor of shape [N, D, S, S]
packed_annotations: packed annotations for efficient loss computation;
the following attributes are used:
- coarse_segm_gt
- bbox_xywh_gt
- bbox_xywh_est
"""
if packed_annotations.coarse_segm_gt is None:
return self.fake_value(densepose_predictor_outputs)
coarse_segm_est = densepose_predictor_outputs.coarse_segm[packed_annotations.bbox_indices]
with torch.no_grad():
coarse_segm_gt = resample_data(
packed_annotations.coarse_segm_gt.unsqueeze(1),
packed_annotations.bbox_xywh_gt,
packed_annotations.bbox_xywh_est,
self.heatmap_size,
self.heatmap_size,
mode="nearest",
padding_mode="zeros",
).squeeze(1)
if self.n_segm_chan == 2:
coarse_segm_gt = coarse_segm_gt > 0
return F.cross_entropy(coarse_segm_est, coarse_segm_gt.long())
def fake_value(self, densepose_predictor_outputs: Any) -> torch.Tensor:
"""
Fake segmentation loss used when no suitable ground truth data
was found in a batch. The loss has a value 0 and is primarily used to
construct the computation graph, so that `DistributedDataParallel`
has similar graphs on all GPUs and can perform reduction properly.
Args:
densepose_predictor_outputs: DensePose predictor outputs, an object
of a dataclass that is assumed to have `coarse_segm`
attribute
Return:
Zero value loss with proper computation graph
"""
return densepose_predictor_outputs.coarse_segm.sum() * 0
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