mirror of https://github.com/JDAI-CV/fast-reid.git
47 lines
1.7 KiB
Python
47 lines
1.7 KiB
Python
# encoding: utf-8
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"""
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@author: liaoxingyu
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@contact: sherlockliao01@gmail.com
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"""
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import torch
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from torch import nn
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class CenterLoss(nn.Module):
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"""Center loss.
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Reference:
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Wen et al. A Discriminative Feature Learning Approach for Deep Face Recognition. ECCV 2016.
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Args:
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num_classes (int): number of classes.
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feat_dim (int): feature dimension.
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"""
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def __init__(self, num_classes=751, feat_dim=2048, use_gpu=True):
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super(CenterLoss, self).__init__()
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self.num_classes,self.feat_dim = num_classes, feat_dim
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if use_gpu: self.centers = nn.Parameter(torch.randn(self.num_classes, self.feat_dim).cuda())
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else: self.centers = nn.Parameter(torch.randn(self.num_classes, self.feat_dim))
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def forward(self, x, labels):
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"""
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Args:
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x: feature matrix with shape (batch_size, feat_dim).
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labels: ground truth labels with shape (num_classes).
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"""
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assert x.size(0) == labels.size(0), "features.size(0) is not equal to labels.size(0)"
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batch_size = x.size(0)
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distmat = torch.pow(x, 2).sum(dim=1, keepdim=True).expand(batch_size, self.num_classes) + \
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torch.pow(self.centers, 2).sum(dim=1, keepdim=True).expand(self.num_classes, batch_size).t()
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distmat.addmm_(1, -2, x, self.centers.t())
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classes = torch.arange(self.num_classes).long()
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classes = classes.to(x.device)
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labels = labels.unsqueeze(1).expand(batch_size, self.num_classes)
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mask = labels.eq(classes.expand(batch_size, self.num_classes))
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dist = distmat * mask.float()
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loss = dist.clamp(min=1e-12, max=1e+12).sum() / batch_size
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return loss
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