With the prevalence of RGB-D cameras, multi-modal video data have become more available for human action recognition. One main challenge for this task lies in how to effectively leverage their complementary information. In this work, we propose a Modality Compensation Network (MCN) to explore the relationships of different modalities, and boost the representations for human action recognition. We regard RGB/optical flow videos as source modalities, skeletons as auxiliary modality. Our goal is to extract more discriminative features from source modalities, with the help of auxiliary modality. Built on deep Convolutional Neural Networks (CNN) and Long Short Term Memory (LSTM) networks, our model bridges data from source and auxiliary modalities by a modality adaptation block to achieve adaptive representation learning, that the network learns to compensate for the loss of skeletons at test time and even at training time. We explore multiple adaptation schemes to narrow the distance between source and auxiliary modal distributions from different levels, according to the alignment of source and auxiliary data in training. In addition, skeletons are only required in the training phase. Our model is able to improve the recognition performance with source data when testing. Experimental results reveal that MCN outperforms state-of-the-art approaches on four widely-used action recognition benchmarks.

本文提出一种Modality Compensation Network（MCN）用于RGB-D摄像机采集的视频中的人类动作识别。该网络通过深度CNN和LSTM网络构建，使用骨骼作为辅助模态来提取源模态的更具有区分性的特征，并通过调整适应性表示学习，以弥补测试时甚至是训练时骨架的信息损失。实验结果表明，在四个广泛使用的动作识别基准测试上，MCN优于现有的最佳方法。

模态补偿网络：用于动作识别的跨模态自适应