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| # Copyright (c) OpenMMLab. All rights reserved. | |
| import torch | |
| import torch.nn as nn | |
| import torch.nn.functional as F | |
| from ..builder import LOSSES | |
| from .accuracy import accuracy | |
| from .cross_entropy_loss import cross_entropy | |
| from .utils import weight_reduce_loss | |
| def seesaw_ce_loss(cls_score, | |
| labels, | |
| label_weights, | |
| cum_samples, | |
| num_classes, | |
| p, | |
| q, | |
| eps, | |
| reduction='mean', | |
| avg_factor=None): | |
| """Calculate the Seesaw CrossEntropy loss. | |
| Args: | |
| cls_score (torch.Tensor): The prediction with shape (N, C), | |
| C is the number of classes. | |
| labels (torch.Tensor): The learning label of the prediction. | |
| label_weights (torch.Tensor): Sample-wise loss weight. | |
| cum_samples (torch.Tensor): Cumulative samples for each category. | |
| num_classes (int): The number of classes. | |
| p (float): The ``p`` in the mitigation factor. | |
| q (float): The ``q`` in the compenstation factor. | |
| eps (float): The minimal value of divisor to smooth | |
| the computation of compensation factor | |
| reduction (str, optional): The method used to reduce the loss. | |
| avg_factor (int, optional): Average factor that is used to average | |
| the loss. Defaults to None. | |
| Returns: | |
| torch.Tensor: The calculated loss | |
| """ | |
| assert cls_score.size(-1) == num_classes | |
| assert len(cum_samples) == num_classes | |
| onehot_labels = F.one_hot(labels, num_classes) | |
| seesaw_weights = cls_score.new_ones(onehot_labels.size()) | |
| # mitigation factor | |
| if p > 0: | |
| sample_ratio_matrix = cum_samples[None, :].clamp( | |
| min=1) / cum_samples[:, None].clamp(min=1) | |
| index = (sample_ratio_matrix < 1.0).float() | |
| sample_weights = sample_ratio_matrix.pow(p) * index + (1 - index) | |
| mitigation_factor = sample_weights[labels.long(), :] | |
| seesaw_weights = seesaw_weights * mitigation_factor | |
| # compensation factor | |
| if q > 0: | |
| scores = F.softmax(cls_score.detach(), dim=1) | |
| self_scores = scores[ | |
| torch.arange(0, len(scores)).to(scores.device).long(), | |
| labels.long()] | |
| score_matrix = scores / self_scores[:, None].clamp(min=eps) | |
| index = (score_matrix > 1.0).float() | |
| compensation_factor = score_matrix.pow(q) * index + (1 - index) | |
| seesaw_weights = seesaw_weights * compensation_factor | |
| cls_score = cls_score + (seesaw_weights.log() * (1 - onehot_labels)) | |
| loss = F.cross_entropy(cls_score, labels, weight=None, reduction='none') | |
| if label_weights is not None: | |
| label_weights = label_weights.float() | |
| loss = weight_reduce_loss( | |
| loss, weight=label_weights, reduction=reduction, avg_factor=avg_factor) | |
| return loss | |
| class SeesawLoss(nn.Module): | |
| """ | |
| Seesaw Loss for Long-Tailed Instance Segmentation (CVPR 2021) | |
| arXiv: https://arxiv.org/abs/2008.10032 | |
| Args: | |
| use_sigmoid (bool, optional): Whether the prediction uses sigmoid | |
| of softmax. Only False is supported. | |
| p (float, optional): The ``p`` in the mitigation factor. | |
| Defaults to 0.8. | |
| q (float, optional): The ``q`` in the compenstation factor. | |
| Defaults to 2.0. | |
| num_classes (int, optional): The number of classes. | |
| Default to 1203 for LVIS v1 dataset. | |
| eps (float, optional): The minimal value of divisor to smooth | |
| the computation of compensation factor | |
| reduction (str, optional): The method that reduces the loss to a | |
| scalar. Options are "none", "mean" and "sum". | |
| loss_weight (float, optional): The weight of the loss. Defaults to 1.0 | |
| return_dict (bool, optional): Whether return the losses as a dict. | |
| Default to True. | |
| """ | |
| def __init__(self, | |
| use_sigmoid=False, | |
| p=0.8, | |
| q=2.0, | |
| num_classes=1203, | |
| eps=1e-2, | |
| reduction='mean', | |
| loss_weight=1.0, | |
| return_dict=True): | |
| super(SeesawLoss, self).__init__() | |
| assert not use_sigmoid | |
| self.use_sigmoid = False | |
| self.p = p | |
| self.q = q | |
| self.num_classes = num_classes | |
| self.eps = eps | |
| self.reduction = reduction | |
| self.loss_weight = loss_weight | |
| self.return_dict = return_dict | |
| # 0 for pos, 1 for neg | |
| self.cls_criterion = seesaw_ce_loss | |
| # cumulative samples for each category | |
| self.register_buffer( | |
| 'cum_samples', | |
| torch.zeros(self.num_classes + 1, dtype=torch.float)) | |
| # custom output channels of the classifier | |
| self.custom_cls_channels = True | |
| # custom activation of cls_score | |
| self.custom_activation = True | |
| # custom accuracy of the classsifier | |
| self.custom_accuracy = True | |
| def _split_cls_score(self, cls_score): | |
| # split cls_score to cls_score_classes and cls_score_objectness | |
| assert cls_score.size(-1) == self.num_classes + 2 | |
| cls_score_classes = cls_score[..., :-2] | |
| cls_score_objectness = cls_score[..., -2:] | |
| return cls_score_classes, cls_score_objectness | |
| def get_cls_channels(self, num_classes): | |
| """Get custom classification channels. | |
| Args: | |
| num_classes (int): The number of classes. | |
| Returns: | |
| int: The custom classification channels. | |
| """ | |
| assert num_classes == self.num_classes | |
| return num_classes + 2 | |
| def get_activation(self, cls_score): | |
| """Get custom activation of cls_score. | |
| Args: | |
| cls_score (torch.Tensor): The prediction with shape (N, C + 2). | |
| Returns: | |
| torch.Tensor: The custom activation of cls_score with shape | |
| (N, C + 1). | |
| """ | |
| cls_score_classes, cls_score_objectness = self._split_cls_score( | |
| cls_score) | |
| score_classes = F.softmax(cls_score_classes, dim=-1) | |
| score_objectness = F.softmax(cls_score_objectness, dim=-1) | |
| score_pos = score_objectness[..., [0]] | |
| score_neg = score_objectness[..., [1]] | |
| score_classes = score_classes * score_pos | |
| scores = torch.cat([score_classes, score_neg], dim=-1) | |
| return scores | |
| def get_accuracy(self, cls_score, labels): | |
| """Get custom accuracy w.r.t. cls_score and labels. | |
| Args: | |
| cls_score (torch.Tensor): The prediction with shape (N, C + 2). | |
| labels (torch.Tensor): The learning label of the prediction. | |
| Returns: | |
| Dict [str, torch.Tensor]: The accuracy for objectness and classes, | |
| respectively. | |
| """ | |
| pos_inds = labels < self.num_classes | |
| obj_labels = (labels == self.num_classes).long() | |
| cls_score_classes, cls_score_objectness = self._split_cls_score( | |
| cls_score) | |
| acc_objectness = accuracy(cls_score_objectness, obj_labels) | |
| acc_classes = accuracy(cls_score_classes[pos_inds], labels[pos_inds]) | |
| acc = dict() | |
| acc['acc_objectness'] = acc_objectness | |
| acc['acc_classes'] = acc_classes | |
| return acc | |
| def forward(self, | |
| cls_score, | |
| labels, | |
| label_weights=None, | |
| avg_factor=None, | |
| reduction_override=None): | |
| """Forward function. | |
| Args: | |
| cls_score (torch.Tensor): The prediction with shape (N, C + 2). | |
| labels (torch.Tensor): The learning label of the prediction. | |
| label_weights (torch.Tensor, optional): Sample-wise loss weight. | |
| avg_factor (int, optional): Average factor that is used to average | |
| the loss. Defaults to None. | |
| reduction (str, optional): The method used to reduce the loss. | |
| Options are "none", "mean" and "sum". | |
| Returns: | |
| torch.Tensor | Dict [str, torch.Tensor]: | |
| if return_dict == False: The calculated loss | | |
| if return_dict == True: The dict of calculated losses | |
| for objectness and classes, respectively. | |
| """ | |
| assert reduction_override in (None, 'none', 'mean', 'sum') | |
| reduction = ( | |
| reduction_override if reduction_override else self.reduction) | |
| assert cls_score.size(-1) == self.num_classes + 2 | |
| pos_inds = labels < self.num_classes | |
| # 0 for pos, 1 for neg | |
| obj_labels = (labels == self.num_classes).long() | |
| # accumulate the samples for each category | |
| unique_labels = labels.unique() | |
| for u_l in unique_labels: | |
| inds_ = labels == u_l.item() | |
| self.cum_samples[u_l] += inds_.sum() | |
| if label_weights is not None: | |
| label_weights = label_weights.float() | |
| else: | |
| label_weights = labels.new_ones(labels.size(), dtype=torch.float) | |
| cls_score_classes, cls_score_objectness = self._split_cls_score( | |
| cls_score) | |
| # calculate loss_cls_classes (only need pos samples) | |
| if pos_inds.sum() > 0: | |
| loss_cls_classes = self.loss_weight * self.cls_criterion( | |
| cls_score_classes[pos_inds], labels[pos_inds], | |
| label_weights[pos_inds], self.cum_samples[:self.num_classes], | |
| self.num_classes, self.p, self.q, self.eps, reduction, | |
| avg_factor) | |
| else: | |
| loss_cls_classes = cls_score_classes[pos_inds].sum() | |
| # calculate loss_cls_objectness | |
| loss_cls_objectness = self.loss_weight * cross_entropy( | |
| cls_score_objectness, obj_labels, label_weights, reduction, | |
| avg_factor) | |
| if self.return_dict: | |
| loss_cls = dict() | |
| loss_cls['loss_cls_objectness'] = loss_cls_objectness | |
| loss_cls['loss_cls_classes'] = loss_cls_classes | |
| else: | |
| loss_cls = loss_cls_classes + loss_cls_objectness | |
| return loss_cls | |