3D human pose estimation is a major focus area in the field of computer vision, which plays an important role in practical applications. This article summarizes the framework and research progress related to the estimation of monocular RGB images and videos. An overall perspective of methods integrated with deep learning is introduced. Novel image-based and video-based inputs are proposed as the analysis framework. From this viewpoint, common problems are discussed. The diversity of human postures usually leads to problems such as occlusion and ambiguity, and the lack of training datasets often results in poor generalization ability of the model. Regression methods are crucial for solving such problems. Considering image-based input, the multi-view method is commonly used to solve occlusion problems. Here, the multi-view method is analyzed comprehensively. By referring to video-based input, the human prior knowledge of restricted motion is used to predict human postures. In addition, structural constraints are widely used as prior knowledge. Furthermore, weakly supervised learning methods are studied and discussed for these two types of inputs to improve the model generalization ability. The problem of insufficient training datasets must also be considered, especially because 3D datasets are usually biased and limited. Finally, emerging and popular datasets and evaluation indicators are discussed. The characteristics of the datasets and the relationships of the indicators are explained and highlighted. Thus, this article can be useful and instructive for researchers who are lacking in experience and find this field confusing. In addition, by providing an overview of 3D human pose estimation, this article sorts and refines recent studies on 3D human pose estimation. It describes kernel problems and common useful methods, and discusses the scope for further research.

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IntroductionBoxing as a sport is growing on Chinese campuses, resulting in a coaching shortage. The human pose estimation technology can be employed to estimate boxing poses and teach interns to relieve the shortage. Currently, 3D cameras can provide more depth information than 2D cameras. It can potentially improve the estimation. However, the input channels are inconsistent between 2D and 3D images, and there is a lack of detailed analysis about the key point location, which indicates the network design for improving the human pose estimation technology.MethodTherefore, a model transfer with channel patching was implemented to solve the problems of channel inconsistency. The differences between the key points were analyzed. Three popular and highly structured 2D models of OpenPose (OP), stacked Hourglass (HG), and High Resolution (HR) networks were employed. Ways of reusing RGB channels were investigated to fill up the depth channel. Then, their performances were investigated to find out the limitations of each network structure.Results and discussionThe results show that model transfer learning by the mean way of RGB channels patching the lacking channel can improve the average accuracies of pose key points from 1 to 20% than without transfer. 3D accuracies are 0.3 to 0.5% higher than 2D baselines. The stacked structure of the network shows better on hip and knee points than the parallel structure, although the parallel design shows much better on the residue points. As a result, the model transfer can practically fulfill boxing pose estimation from 2D to 3D.

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