论文标题

通过重量平衡的长尾识别

Long-Tailed Recognition via Weight Balancing

论文作者

Alshammari, Shaden, Wang, Yu-Xiong, Ramanan, Deva, Kong, Shu

论文摘要

在真正的开放世界中,数据倾向于遵循长尾的班级分布,激发了经过深入研究的长尾识别(LTR)问题。天真的训练会产生模型,这些模型就更高的准确性而言是偏向普通类的模型。解决LTR的关键是平衡各个方面,包括数据分布,培训损失和学习梯度。我们探索了正交方向,重量平衡,这是由经验观察的激励,即经过训练的训练有素的分类器“人为地”在常规类别中“人为地”更大的重量(因为与稀有类别不同,有大量的数据可以训练它们。我们研究了三种技术,以平衡权重,L2差异化,重量衰减和最大值。我们首先指出,L2差异化“完美”平衡了每级重量为单位规范,但是这样的硬约束可能会阻止类学习更好的分类器。相比之下,重量衰减会更严重地惩罚更大的重量,因此学会了较小的平衡重量。 MaxNorm限制会鼓励在标准球内生长小重量,但将所有权重盖住半径。我们广泛的研究表明,既有助于学习平衡的权重,又可以极大地提高LTR的准确性。令人惊讶的是,尽管在LTR中毫无疑问,但重量衰减在先前的工作中显着改善。因此,我们采用了两个阶段的训练范式,并提出了一种简单的方法来实现LTR:(1)通过调谐体重衰减使用跨凝性损失的学习特征,以及(2)通过调谐重量衰减和MaxNorm使用类平衡损失的学习分类器。我们的方法在五个标准基准上实现了最先进的准确性,这是长尾识别的未来基线。

In the real open world, data tends to follow long-tailed class distributions, motivating the well-studied long-tailed recognition (LTR) problem. Naive training produces models that are biased toward common classes in terms of higher accuracy. The key to addressing LTR is to balance various aspects including data distribution, training losses, and gradients in learning. We explore an orthogonal direction, weight balancing, motivated by the empirical observation that the naively trained classifier has "artificially" larger weights in norm for common classes (because there exists abundant data to train them, unlike the rare classes). We investigate three techniques to balance weights, L2-normalization, weight decay, and MaxNorm. We first point out that L2-normalization "perfectly" balances per-class weights to be unit norm, but such a hard constraint might prevent classes from learning better classifiers. In contrast, weight decay penalizes larger weights more heavily and so learns small balanced weights; the MaxNorm constraint encourages growing small weights within a norm ball but caps all the weights by the radius. Our extensive study shows that both help learn balanced weights and greatly improve the LTR accuracy. Surprisingly, weight decay, although underexplored in LTR, significantly improves over prior work. Therefore, we adopt a two-stage training paradigm and propose a simple approach to LTR: (1) learning features using the cross-entropy loss by tuning weight decay, and (2) learning classifiers using class-balanced loss by tuning weight decay and MaxNorm. Our approach achieves the state-of-the-art accuracy on five standard benchmarks, serving as a future baseline for long-tailed recognition.

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