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finetune/mmseg/models/losses/lovasz_loss.py
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finetune/mmseg/models/losses/lovasz_loss.py
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# Copyright (c) OpenMMLab. All rights reserved.
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"""Modified from https://github.com/bermanmaxim/LovaszSoftmax/blob/master/pytor
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ch/lovasz_losses.py Lovasz-Softmax and Jaccard hinge loss in PyTorch Maxim
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Berman 2018 ESAT-PSI KU Leuven (MIT License)"""
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import torch
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import torch.nn as nn
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import torch.nn.functional as F
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from mmengine.utils import is_list_of
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from mmseg.registry import MODELS
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from .utils import get_class_weight, weight_reduce_loss
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def lovasz_grad(gt_sorted):
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"""Computes gradient of the Lovasz extension w.r.t sorted errors.
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See Alg. 1 in paper.
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"""
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p = len(gt_sorted)
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gts = gt_sorted.sum()
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intersection = gts - gt_sorted.float().cumsum(0)
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union = gts + (1 - gt_sorted).float().cumsum(0)
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jaccard = 1. - intersection / union
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if p > 1: # cover 1-pixel case
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jaccard[1:p] = jaccard[1:p] - jaccard[0:-1]
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return jaccard
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def flatten_binary_logits(logits, labels, ignore_index=None):
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"""Flattens predictions in the batch (binary case) Remove labels equal to
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'ignore_index'."""
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logits = logits.view(-1)
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labels = labels.view(-1)
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if ignore_index is None:
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return logits, labels
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valid = (labels != ignore_index)
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vlogits = logits[valid]
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vlabels = labels[valid]
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return vlogits, vlabels
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def flatten_probs(probs, labels, ignore_index=None):
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"""Flattens predictions in the batch."""
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if probs.dim() == 3:
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# assumes output of a sigmoid layer
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B, H, W = probs.size()
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probs = probs.view(B, 1, H, W)
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B, C, H, W = probs.size()
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probs = probs.permute(0, 2, 3, 1).contiguous().view(-1, C) # B*H*W, C=P,C
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labels = labels.view(-1)
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if ignore_index is None:
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return probs, labels
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valid = (labels != ignore_index)
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vprobs = probs[valid.nonzero().squeeze()]
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vlabels = labels[valid]
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return vprobs, vlabels
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def lovasz_hinge_flat(logits, labels):
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"""Binary Lovasz hinge loss.
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Args:
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logits (torch.Tensor): [P], logits at each prediction
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(between -infty and +infty).
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labels (torch.Tensor): [P], binary ground truth labels (0 or 1).
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Returns:
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torch.Tensor: The calculated loss.
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"""
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if len(labels) == 0:
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# only void pixels, the gradients should be 0
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return logits.sum() * 0.
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signs = 2. * labels.float() - 1.
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errors = (1. - logits * signs)
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errors_sorted, perm = torch.sort(errors, dim=0, descending=True)
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perm = perm.data
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gt_sorted = labels[perm]
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grad = lovasz_grad(gt_sorted)
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loss = torch.dot(F.relu(errors_sorted), grad)
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return loss
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def lovasz_hinge(logits,
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labels,
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classes='present',
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per_image=False,
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class_weight=None,
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reduction='mean',
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avg_factor=None,
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ignore_index=255):
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"""Binary Lovasz hinge loss.
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Args:
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logits (torch.Tensor): [B, H, W], logits at each pixel
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(between -infty and +infty).
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labels (torch.Tensor): [B, H, W], binary ground truth masks (0 or 1).
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classes (str | list[int], optional): Placeholder, to be consistent with
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other loss. Default: None.
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per_image (bool, optional): If per_image is True, compute the loss per
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image instead of per batch. Default: False.
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class_weight (list[float], optional): Placeholder, to be consistent
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with other loss. Default: None.
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reduction (str, optional): The method used to reduce the loss. Options
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are "none", "mean" and "sum". This parameter only works when
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per_image is True. Default: 'mean'.
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avg_factor (int, optional): Average factor that is used to average
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the loss. This parameter only works when per_image is True.
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Default: None.
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ignore_index (int | None): The label index to be ignored. Default: 255.
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Returns:
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torch.Tensor: The calculated loss.
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"""
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if per_image:
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loss = [
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lovasz_hinge_flat(*flatten_binary_logits(
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logit.unsqueeze(0), label.unsqueeze(0), ignore_index))
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for logit, label in zip(logits, labels)
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]
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loss = weight_reduce_loss(
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torch.stack(loss), None, reduction, avg_factor)
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else:
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loss = lovasz_hinge_flat(
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*flatten_binary_logits(logits, labels, ignore_index))
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return loss
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def lovasz_softmax_flat(probs, labels, classes='present', class_weight=None):
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"""Multi-class Lovasz-Softmax loss.
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Args:
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probs (torch.Tensor): [P, C], class probabilities at each prediction
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(between 0 and 1).
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labels (torch.Tensor): [P], ground truth labels (between 0 and C - 1).
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classes (str | list[int], optional): Classes chosen to calculate loss.
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'all' for all classes, 'present' for classes present in labels, or
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a list of classes to average. Default: 'present'.
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class_weight (list[float], optional): The weight for each class.
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Default: None.
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Returns:
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torch.Tensor: The calculated loss.
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"""
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if probs.numel() == 0:
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# only void pixels, the gradients should be 0
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return probs * 0.
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C = probs.size(1)
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losses = []
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class_to_sum = list(range(C)) if classes in ['all', 'present'] else classes
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for c in class_to_sum:
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fg = (labels == c).float() # foreground for class c
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if (classes == 'present' and fg.sum() == 0):
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continue
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if C == 1:
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if len(classes) > 1:
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raise ValueError('Sigmoid output possible only with 1 class')
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class_pred = probs[:, 0]
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else:
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class_pred = probs[:, c]
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errors = (fg - class_pred).abs()
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errors_sorted, perm = torch.sort(errors, 0, descending=True)
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perm = perm.data
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fg_sorted = fg[perm]
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loss = torch.dot(errors_sorted, lovasz_grad(fg_sorted))
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if class_weight is not None:
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loss *= class_weight[c]
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losses.append(loss)
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return torch.stack(losses).mean()
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def lovasz_softmax(probs,
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labels,
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classes='present',
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per_image=False,
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class_weight=None,
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reduction='mean',
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avg_factor=None,
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ignore_index=255):
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"""Multi-class Lovasz-Softmax loss.
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Args:
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probs (torch.Tensor): [B, C, H, W], class probabilities at each
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prediction (between 0 and 1).
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labels (torch.Tensor): [B, H, W], ground truth labels (between 0 and
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C - 1).
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classes (str | list[int], optional): Classes chosen to calculate loss.
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'all' for all classes, 'present' for classes present in labels, or
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a list of classes to average. Default: 'present'.
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per_image (bool, optional): If per_image is True, compute the loss per
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image instead of per batch. Default: False.
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class_weight (list[float], optional): The weight for each class.
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Default: None.
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reduction (str, optional): The method used to reduce the loss. Options
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are "none", "mean" and "sum". This parameter only works when
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per_image is True. Default: 'mean'.
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avg_factor (int, optional): Average factor that is used to average
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the loss. This parameter only works when per_image is True.
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Default: None.
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ignore_index (int | None): The label index to be ignored. Default: 255.
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Returns:
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torch.Tensor: The calculated loss.
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"""
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if per_image:
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loss = [
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lovasz_softmax_flat(
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*flatten_probs(
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prob.unsqueeze(0), label.unsqueeze(0), ignore_index),
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classes=classes,
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class_weight=class_weight)
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for prob, label in zip(probs, labels)
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]
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loss = weight_reduce_loss(
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torch.stack(loss), None, reduction, avg_factor)
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else:
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loss = lovasz_softmax_flat(
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*flatten_probs(probs, labels, ignore_index),
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classes=classes,
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class_weight=class_weight)
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return loss
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@MODELS.register_module()
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class LovaszLoss(nn.Module):
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"""LovaszLoss.
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This loss is proposed in `The Lovasz-Softmax loss: A tractable surrogate
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for the optimization of the intersection-over-union measure in neural
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networks <https://arxiv.org/abs/1705.08790>`_.
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Args:
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loss_type (str, optional): Binary or multi-class loss.
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Default: 'multi_class'. Options are "binary" and "multi_class".
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classes (str | list[int], optional): Classes chosen to calculate loss.
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'all' for all classes, 'present' for classes present in labels, or
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a list of classes to average. Default: 'present'.
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per_image (bool, optional): If per_image is True, compute the loss per
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image instead of per batch. Default: False.
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reduction (str, optional): The method used to reduce the loss. Options
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are "none", "mean" and "sum". This parameter only works when
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per_image is True. Default: 'mean'.
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class_weight (list[float] | str, optional): Weight of each class. If in
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str format, read them from a file. Defaults to None.
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loss_weight (float, optional): Weight of the loss. Defaults to 1.0.
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loss_name (str, optional): Name of the loss item. If you want this loss
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item to be included into the backward graph, `loss_` must be the
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prefix of the name. Defaults to 'loss_lovasz'.
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"""
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def __init__(self,
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loss_type='multi_class',
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classes='present',
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per_image=False,
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reduction='mean',
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class_weight=None,
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loss_weight=1.0,
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loss_name='loss_lovasz'):
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super().__init__()
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assert loss_type in ('binary', 'multi_class'), "loss_type should be \
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'binary' or 'multi_class'."
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if loss_type == 'binary':
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self.cls_criterion = lovasz_hinge
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else:
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self.cls_criterion = lovasz_softmax
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assert classes in ('all', 'present') or is_list_of(classes, int)
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if not per_image:
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assert reduction == 'none', "reduction should be 'none' when \
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per_image is False."
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self.classes = classes
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self.per_image = per_image
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self.reduction = reduction
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self.loss_weight = loss_weight
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self.class_weight = get_class_weight(class_weight)
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self._loss_name = loss_name
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def forward(self,
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cls_score,
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label,
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weight=None,
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avg_factor=None,
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reduction_override=None,
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**kwargs):
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"""Forward function."""
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assert reduction_override in (None, 'none', 'mean', 'sum')
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reduction = (
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reduction_override if reduction_override else self.reduction)
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if self.class_weight is not None:
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class_weight = cls_score.new_tensor(self.class_weight)
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else:
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class_weight = None
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# if multi-class loss, transform logits to probs
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if self.cls_criterion == lovasz_softmax:
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cls_score = F.softmax(cls_score, dim=1)
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loss_cls = self.loss_weight * self.cls_criterion(
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cls_score,
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label,
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self.classes,
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self.per_image,
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class_weight=class_weight,
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reduction=reduction,
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avg_factor=avg_factor,
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**kwargs)
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return loss_cls
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@property
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def loss_name(self):
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"""Loss Name.
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This function must be implemented and will return the name of this
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loss function. This name will be used to combine different loss items
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by simple sum operation. In addition, if you want this loss item to be
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included into the backward graph, `loss_` must be the prefix of the
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name.
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Returns:
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str: The name of this loss item.
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"""
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return self._loss_name
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