A tracklet is a short sequence of detections of an entity of interest, such as a person's face, in contiguous frames of a video. In this paper we consider clustering tracklets in long videos, an important problem of current interest in Computer Vision. It involves identifying tracklets in short segments of the video and finding associations between tracklets over the entire video. These tasks require careful modelling of spatio-temporal cues. State of the art [27] proposes a probabilistic model which incorporates the spatio-temporal cues by parametrizing them through clique potentials in HMRF. The attendant learning and inference problems make the model un-wieldy resulting in failure to handle long videos with many cluster labels. In this paper we circumvent the problem of explicitly encoding spatio-temporal cues by exploiting Temporal Coherence (TC). The major contribution of the paper is to develop Temporally Coherent Chinese Restaurant Process (TC-CRP), a novel Bayesian Non-parametric (BNP) prior which models Temporal Coherence. To the best of our knowledge this is the first work which models TC in a BNP framework and thus makes a significant addition to BNP priors suited for video analytics. On an interesting problem of discovering persons and their tracklets from user-uploaded videos of long TV series episodes from Youtube we show that TC-CRP is very effective. It can also filter out tracklets resulting from false detections. We explore alternative approaches based on low-rank matrix recovery and constrained subspace clustering, but find these to be very slow and less accurate than our method. Finally, we show that TC-CRP can be useful in Low-rank Matrix Recovery when the desired matrix has sets of identical columns.
Finally, has been studied for a few years in the Computer Vision community. The aim is to provide a short but comprehensive summary of videos. This summary is usually in the form of a few , and sometimes as a short segment of the video around these keyframes. A recent example is @cite_2 which models a video as a matrix, each frame as a column, and each keyframe as a , in terms of which the other columns are expressed. A more recent work @cite_34 considers a kernel matrix to encode similarities between pairs of frames, uses it for of the video, assigns an importance label to each of these segments using an SVM (trained from segmented and labelled videos), and creates the summary with the important segments. However, such summaries are in terms of low-level visual features, rather than high-level semantic features which humans use. An attempt to bridge this gap was made in @cite_35 , which defined movie scenes and summaries in terms of characters. This work used face detections along with for semantic segmentation into shots and scenes, which were used for summarization.
@cite_35 @cite_34 @cite_2
2012754317 2094325573 2144139464 2079169833
In video summarization, a short video clip is made from lengthy video without losing its semantic content using significant scenes containing important frames, called keyframes. This process finds importance in video content management systems. The proposed method involves automatic summarization of motion picture based on human face. In this method, those frames within which the appearances of an actor or actress, selected by the user, occurs are treated as keyframes. In the first step, the video is segmented into shots by Mutual Information. Then it detects the available faces in the frames of each shot using the local Successive Mean Quantization Transform (SMQT) features and Sparse Network of Winnows (SNoW) classifier. Then the face of an actor of interest is selected to match with different available faces, already extracted, using Eigenfaces method. A shot is taken into consideration, if the method succeeds in finding at least one matched face in the shot. The selected shots are finally combined to create summarized video. Video summarization helps users obtain quick comprehension of video content. Recently, some studies have utilized local features to represent each video frame and formulate video summarization as a coverage problem of local features. However, the importance of individual local features has not been exploited. In this paper, we propose a novel Bag-of-Importance (BoI) model for static video summarization by identifying the frames with important local features as keyframes, which is one of the first studies formulating video summarization at local feature level, instead of at global feature level. That is, by representing each frame with local features, a video is characterized with a bag of local features weighted with individual importance scores and the frames with more important local features are more representative, where the representativeness of each frame is the aggregation of the weighted importance of the local features contained in the frame. In addition, we propose to learn a transformation from a raw local feature to a more powerful sparse nonlinear representation for deriving the importance score of each local feature, rather than directly utilize the hand-crafted visual features like most of the existing approaches. Specifically, we first employ locality-constrained linear coding (LCC) to project each local feature into a sparse transformed space. LCC is able to take advantage of the manifold geometric structure of the high dimensional feature space and form the manifold of the low dimensional transformed space with the coordinates of a set of anchor points. Then we calculate the l2 norm of each anchor point as the importance score of each local feature which is projected to the anchor point. Finally, the distribution of the importance scores of all the local features in a video is obtained as the BoI representation of the video. We further differentiate the importance of local features with a spatial weighting template by taking the perceptual difference among spatial regions of a frame into account. As a result, our proposed video summarization approach is able to exploit both the inter-frame and intra-frame properties of feature representations and identify keyframes capturing both the dominant content and discriminative details within a video. Experimental results on three video datasets across various genres demonstrate that the proposed approach clearly outperforms several state-of-the-art methods. The authors propose a novel technique for video summarization based on singular value decomposition (SVD). For the input video sequence, we create a feature-frame matrix A, and perform the SVD on it. From this SVD, we are able, to not only derive the refined feature space to better cluster visually similar frames, but also define a metric to measure the amount of visual content contained in each frame cluster using its degree of visual changes. Then, in the refined feature space, we find the most static frame cluster, define it as the content unit, and use the context value computed from it as the threshold to cluster the rest of the frames. Based on this clustering result, either the optimal set of keyframes, or a summarized motion video with the user specified time length can be generated to support different user requirements for video browsing and content overview. Our approach ensures that the summarized video representation contains little redundancy, and gives equal attention to the same amount of contents. This paper presents an approach for human action recognition by finding the discriminative key frames from a video sequence and representing them with the distribution of local motion features and their spatiotemporal arrangements. In this approach, the key frames of the video sequence are selected by their discriminative power and represented by the local motion features detected in them and integrated from their temporal neighbors. In the key frame’s representation, the spatial arrangements of the motion features are captured in a hierarchical spatial pyramid structure. By using frame by frame voting for the recognition, experiments have demonstrated improved performances over most of the other known methods on the popular benchmark data sets. Recognizinghumanactionfromimagesequencesis an appealingyet challengingproblem in computer vision with many applications including motion capture, human-computer interaction, environment control, and security surveillance. In this paper, we focus on recognizing the activities of a person in an image sequence from local motion features and their spatiotemporal arrangements. Our approach is motivated by the recent success of “bag-of-words” model for general object recognition in computer vision[21, 14]. This representation, which is adapted from the text retrieval literature, models the object by the distribution of words from a fixed visual code book, which is usually obtained by vector quantization of local image visual features. However, this method discards the spatial and the temporal relations among these visual features, which could be helpful in object recognition. Addressing this problem, our approach uses a hierarchical representation for the key frames of a given video sequence to integrate information from both the spatial and the temporal domains. We first apply a spatiotemporal feature detector to the video sequence and obtain the local motion features. Then we generate a visual word code book by quantization of the local motion features and assign a word label to each of them. Next we select key frames of the video sequence by their discriminative power. Then, for each key frame, we integrate the visual words from its nearby frames, divide the key frame spatially into finer subdivisions and compute in each cell the histograms of the visual words detected in this key frame and its temporal neighbors. Finally, we concatenate the histograms from all cells and use