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Source code for mmcls.models.losses.label_smooth_loss

# Copyright (c) OpenMMLab. All rights reserved.
import torch
import torch.nn as nn

from ..builder import LOSSES
from .cross_entropy_loss import CrossEntropyLoss
from .utils import convert_to_one_hot


[docs]@LOSSES.register_module() class LabelSmoothLoss(nn.Module): r"""Initializer for the label smoothed cross entropy loss. Refers to `Rethinking the Inception Architecture for Computer Vision <https://arxiv.org/abs/1512.00567>`_ This decreases gap between output scores and encourages generalization. Labels provided to forward can be one-hot like vectors (NxC) or class indices (Nx1). And this accepts linear combination of one-hot like labels from mixup or cutmix except multi-label task. Args: label_smooth_val (float): The degree of label smoothing. num_classes (int, optional): Number of classes. Defaults to None. mode (str): Refers to notes, Options are 'original', 'classy_vision', 'multi_label'. Defaults to 'original' reduction (str): The method used to reduce the loss. Options are "none", "mean" and "sum". Defaults to 'mean'. loss_weight (float): Weight of the loss. Defaults to 1.0. Notes: if the mode is "original", this will use the same label smooth method as the original paper as: .. math:: (1-\epsilon)\delta_{k, y} + \frac{\epsilon}{K} where epsilon is the `label_smooth_val`, K is the num_classes and delta(k,y) is Dirac delta, which equals 1 for k=y and 0 otherwise. if the mode is "classy_vision", this will use the same label smooth method as the facebookresearch/ClassyVision repo as: .. math:: \frac{\delta_{k, y} + \epsilon/K}{1+\epsilon} if the mode is "multi_label", this will accept labels from multi-label task and smoothing them as: .. math:: (1-2\epsilon)\delta_{k, y} + \epsilon """ def __init__(self, label_smooth_val, num_classes=None, mode='original', reduction='mean', loss_weight=1.0): super().__init__() self.num_classes = num_classes self.loss_weight = loss_weight assert (isinstance(label_smooth_val, float) and 0 <= label_smooth_val < 1), \ f'LabelSmoothLoss accepts a float label_smooth_val ' \ f'over [0, 1), but gets {label_smooth_val}' self.label_smooth_val = label_smooth_val accept_reduction = {'none', 'mean', 'sum'} assert reduction in accept_reduction, \ f'LabelSmoothLoss supports reduction {accept_reduction}, ' \ f'but gets {mode}.' self.reduction = reduction accept_mode = {'original', 'classy_vision', 'multi_label'} assert mode in accept_mode, \ f'LabelSmoothLoss supports mode {accept_mode}, but gets {mode}.' self.mode = mode self._eps = label_smooth_val if mode == 'classy_vision': self._eps = label_smooth_val / (1 + label_smooth_val) if mode == 'multi_label': self.ce = CrossEntropyLoss(use_sigmoid=True) self.smooth_label = self.multilabel_smooth_label else: self.ce = CrossEntropyLoss(use_soft=True) self.smooth_label = self.original_smooth_label
[docs] def generate_one_hot_like_label(self, label): """This function takes one-hot or index label vectors and computes one- hot like label vectors (float)""" # check if targets are inputted as class integers if label.dim() == 1 or (label.dim() == 2 and label.shape[1] == 1): label = convert_to_one_hot(label.view(-1, 1), self.num_classes) return label.float()
def original_smooth_label(self, one_hot_like_label): assert self.num_classes > 0 smooth_label = one_hot_like_label * (1 - self._eps) smooth_label += self._eps / self.num_classes return smooth_label def multilabel_smooth_label(self, one_hot_like_label): assert self.num_classes > 0 smooth_label = torch.full_like(one_hot_like_label, self._eps) smooth_label.masked_fill_(one_hot_like_label > 0, 1 - self._eps) return smooth_label
[docs] def forward(self, cls_score, label, weight=None, avg_factor=None, reduction_override=None, **kwargs): r"""Label smooth loss. Args: pred (torch.Tensor): The prediction with shape (N, \*). label (torch.Tensor): The ground truth label of the prediction with shape (N, \*). weight (torch.Tensor, optional): Sample-wise loss weight with shape (N, \*). Defaults to None. avg_factor (int, optional): Average factor that is used to average the loss. Defaults to None. reduction_override (str, optional): The method used to reduce the loss into a scalar. Options are "none", "mean" and "sum". Defaults to None. Returns: torch.Tensor: Loss. """ if self.num_classes is not None: assert self.num_classes == cls_score.shape[1], \ f'num_classes should equal to cls_score.shape[1], ' \ f'but got num_classes: {self.num_classes} and ' \ f'cls_score.shape[1]: {cls_score.shape[1]}' else: self.num_classes = cls_score.shape[1] one_hot_like_label = self.generate_one_hot_like_label(label=label) assert one_hot_like_label.shape == cls_score.shape, \ f'LabelSmoothLoss requires output and target ' \ f'to be same shape, but got output.shape: {cls_score.shape} ' \ f'and target.shape: {one_hot_like_label.shape}' smoothed_label = self.smooth_label(one_hot_like_label) return self.ce.forward( cls_score, smoothed_label, weight=weight, avg_factor=avg_factor, reduction_override=reduction_override, **kwargs)
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