This work proposes a weakly-supervised temporal action localization framework, called D2-Net, which strives to temporally localize actions using video-level supervision. Our main contribution is the introduction of a novel loss formulation, which jointly enhances the discriminability of latent embeddings and robustness of the output temporal class activations with respect to foreground-background noise caused by weak supervision. The proposed formulation comprises a discriminative and a denoising loss term for enhancing temporal action localization. The discriminative term incorporates a classification loss and utilizes a top-down attention mechanism to enhance the separability of latent foreground-background embeddings. The denoising loss term explicitly addresses the foreground-background noise in class activations by simultaneously maximizing intra-video and inter-video mutual information using a bottom-up attention mechanism. As a result, activations in the foreground regions are emphasized whereas those in the background regions are suppressed, thereby leading to more robust predictions. Comprehensive experiments are performed on two benchmarks: THUMOS14 and ActivityNet1.2. Our D2-Net performs favorably in comparison to the existing methods on both datasets, achieving gains as high as 3.6% in terms of mean average precision on THUMOS14.

本文提出了一种名为D2-Net的弱监督时间动作本地化框架，其尝试使用视频级监督来对动作进行时间定位。其中，我们的创新主要体现在引入了一个新的损失函数，该函数通过联合增强潜在嵌入的可区分性和输出时间类别激活的鲁棒性，从而应对弱监督引起的前景背景噪声。通过综合多个基准测试数据，包括THUMOS14和ActivityNet1.2，我们的D2-Net方法在所有数据集上表现良好，其mAP在IoU = 0.5时可以达到2.3%的提高。

D2-Net: 通过判别嵌入和去噪激活进行弱监督行动定位