In this paper we study the problem of estimating innercyclic time intervals within repetitive motion sequences of top-class swimmers in a swimming channel. Interval limits are given by temporal occurrences of key-poses, i.e. distinctive postures of the body. A key-pose is defined by means of only one or two specific features of the complete posture. It is often difficult to detect such subtle features directly. We therefore propose the following method: Given that we observe the swimmer from the side, we build a pictorial structure of poselets to robustly identify random support poses within the regular motion of a swimmer. We formulate a maximum likelihood model which predicts a key-pose given the occurrences of multiple support poses within one stroke. The maximum likelihood can be extended with prior knowledge about the temporal location of a key-pose in order to improve the prediction recall. We experimentally show that our models reliably and robustly detect key-poses with a high precision and that their performance can be improved by extending the framework with additional camera views.
In the context of key-frame selection in videos, poselets have been used for human activity recognition. @cite_20 proposed a framework based on poselet activations for selecting key-frames that represent key-states in an action sequence. An additional classifier trained on pairwise terms for all activations then decides if a specific action sequence occurred. @cite_7 select action specific postures by matching shape information from individual frames in order to recognize specific tennis strokes in game footage.
@cite_7 @cite_20
110427074 2025508903
Human action is, in general, characterized by a sequence of specific body postures. An action is often recognizable from a single view of an action specific posture. In this paper we demonstrate that specific actions can be recognized in long video sequence by matching shape information extracted from individual frames to stored prototypes representing key frames of the action. The matching algorithm is tolerant to substantial deformation between image and prototype and recognizes qualitatively similar image shapes produced by the body postures. The algorithm is applied to the recognition of specific tennis strokes in up to 2 min long video sequences. Using key-frames within the sequence all (1015) forehand strokes are found with no false positives. The backhand strokes are detected with somewhat lower performance. We conclude that this type of approach to action recognition has large potential for application to automatic video analysis and editing. Human activity can be described as a sequence of 3D body postures. The traditional approach to recognition and 3D reconstruction of human activity has been to track motion in 3D, mainly using advanced geometric and dynamic models. In this paper we reverse this process. View based activity recognition serves as an input to a human body location tracker with the ultimate goal of 3D reanimation in mind. We demonstrate that specific human actions can be detected from single frame postures in a video sequence. By recognizing the image of a person's posture as corresponding to a particular key frame from a set of stored key frames, it is possible to map body locations from the key frames to actual frames. This is achieved using a shape matching algorithm based on qualitative similarity that computes point to point correspondence between shapes, together with information about appearance. As the mapping is from fixed key frames, our tracking does not suffer from the problem of having to reinitialise when it gets lost. It is effectively a closed loop. We present experimental results both for recognition and tracking for a sequence of a tennis player. Human action recognition from videos is very important for visual analytics. Due to increasing abundance of diverse video content in the era of big data, research on human action recognition has recently shifted towards more challenging and realistic settings. Frame rate is one of key issues in diverse and realistic video settings. While there have been several evaluation studies investigating different aspects of action recognition such as different visual descriptors, the frame rate issue has been seldom addressed in the literature. Therefore, in this paper, we investigate the impact of frame rate on human action recognition with several state-of-the-art approaches and three benchmark datasets. Our experimental results indicate that those state-of-the-art approaches are not robust to the variations of frame rate. As a result, more robust visual features and advanced learning algorithms are required to further improve human action recognition performance towards its more practical deployments. In addition, we investigate key-frame selection techniques for choosing a set of suitable frames from an action sequence for action recognition. Promising results indicate that well designed key-frame selection methods can produce a set of representative frames and eventually reduce the impact of frame rate on the performance of human action recognition. HighlightsOne of the first studies on evaluating the impact of frame rate on video based human action recognition.Evaluation with four state-of-the-art methods and three widely used datasets.Investigation on novel key frame selection method for action recognition.A comprehensive study of exploring the impact of frame rate on action recognition performance. In this paper we propose a novel method for human action recognition based on boosted key-frame selection and correlated pyramidal motion feature representations. Instead of using an unsupervised method to detect interest points, a Pyramidal Motion Feature (PMF), which combines optical flow with a biologically inspired feature, is extracted from each frame of a video sequence. The AdaBoost learning algorithm is then applied to select the most discriminative frames from a large feature pool. In this way, we obtain the top-ranked boosted frames of each video sequence as the key frames which carry the most representative motion information. Furthermore, we utilise the correlogram which focuses not only on probabilistic distributions within one frame but also on the temporal relationships of the action sequence. In the classification phase, a Support-Vector Machine (SVM) is adopted as the final classifier for human action recognition. To demonstrate generalizability, our method has been systematically tested on a variety of datasets and shown to be more effective and accurate for action recognition compared to the previous work. We obtain overall accuracies of: 95.5 , 93.7 , and 36.5 with our proposed method on the KTH, the multiview IXMAS and the challenging HMDB51 datasets, respectively.