The possibility of sharing one's point of view makes the use of wearable cameras compelling. These videos are often long, boring, and coupled with extreme shaking, as the camera is worn on a moving person. Fast-forwarding (i.e., frame sampling) is a natural choice for quick video browsing. However, this accentuates the shake caused by natural head motion in an egocentric video, making the fast-forwarded video useless. We propose EgoSampling, an adaptive frame sampling that gives stable, fast-forwarded, hyperlapse videos. Adaptive frame sampling is formulated as an energy minimization problem, whose optimal solution can be found in polynomial time. We further turn the camera shake from a drawback into a feature, enabling the increase in field of view of the output video. This is obtained when each output frame is mosaiced from several input frames. The proposed technique also enables the generation of a single hyperlapse video from multiple egocentric videos, allowing even faster video consumption.

While egocentric video is becoming increasingly popular, browsing it is very difficult. In this paper we present a compact 3D Convolutional Neural Network (CNN) architecture for long-term activity recognition in egocentric videos. Recognizing long-term activities enables us to temporally segment (index) long and unstructured egocentric videos. Existing methods for this task are based on hand tuned features derived from visible objects, location of hands, as well as optical flow. Given a sparse optical flow volume as input, our CNN classifies the camera wearer's activity. We obtain classification accuracy of 89%, which outperforms the current state-of-the-art by 19%. Additional evaluation is performed on an extended egocentric video dataset, classifying twice the amount of categories than current state-of-the-art. Furthermore, our CNN is able to recognize whether a video is egocentric or not with 99.2% accuracy, up by 24% from current state-of-the-art. To better understand what the network actually learns, we propose a novel visualization of CNN kernels as flow fields.

While egocentric cameras like GoPro are gaining popularity, the videos they capture are long, boring, and difficult to watch from start to end. Fast forwarding (i.e. frame sampling) is a natural choice for faster video browsing. However, this accentuates the shake caused by natural head motion, making the fast forwarded video useless. We propose EgoSampling, an adaptive frame sampling that gives more stable fast forwarded videos. Adaptive frame sampling is formulated as energy minimization, whose optimal solution can be found in polynomial time. In addition, egocentric video taken while walking suffers from the left-right movement of the head as the body weight shifts from one leg to another. We turn this drawback into a feature: Stereo video can be created by sampling the frames from the left most and right most head positions of each step, forming approximate stereo-pairs.

The use of wearable cameras makes it possible to record life logging egocentric videos. Browsing such long unstructured videos is time consuming and tedious. Segmentation into meaningful chapters is an important first step towards adding structure to egocentric videos, enabling efficient browsing, indexing and summarization of the long videos. Two sources of information for video segmentation are (i) the motion of the camera wearer, and (ii) the objects and activities recorded in the video. In this paper we address the motion cues for video segmentation. Motion based segmentation is especially difficult in egocentric videos when the camera is constantly moving due to natural head movement of the wearer. We propose a robust temporal segmentation of egocentric videos into a hierarchy of motion classes using a new Cumulative Displacement Curves. Unlike instantaneous motion vectors, segmentation using integrated motion vectors performs well even in dynamic and crowded scenes. No assumptions are made on the underlying scene structure and the method works in indoor as well as outdoor situations. We demonstrate the effectiveness of our approach using publicly available videos as well as choreographed videos. We also suggest an approach to detect the fixation of wearer's gaze in the walking portion of the egocentric videos.

Multi dimensional probability distributions are used in many surveillance tasks such as modeling color distribution of background pixels for Background Subtraction. Accurate representation of such distributions, e.g. in a histogram, requires much memory that may not be available when a histogram is computed for each pixel. Parametric representations such as Gaussian Mixture Models (GMM) are very efficient in memory but may not be accurate enough when the distribution is not from the assumed model. We propose a memory efficient representation for distributions. Histograms cells usually have equal width, and count the hits in each cell (Equi-width histograms). In most cases a 1D distribution can be represented more efficiently when cell sizes change so that each cell will have same number of hits (Equi-depth histograms). We propose to describe compactly multi-dimensional distributions (e.g. color) using an equi-depth histograms. Online computation of such histograms is described, and examples are given for background subtraction.

Image alignment and mosaicing are usually performed on a set of overlapping images, using features in the area of overlap for alignment and for seamless stitching. Without image overlap current methods are helpless, and this is the case we address in this paper. So if a traveler wants to create a panoramic mosaic of a scene from pictures he has taken, but realizes back home that his pictures do not overlap, there is still hope. The proposed process has three stages: (i) Images are extrapolated beyond their original boundaries, hoping that the extrapolated areas will cover the gaps between them. This extrapolation becomes more blurred as we move away from the original image. (ii) The extrapolated images are aligned and their relative positions recovered. (iii) The gaps between the images are inpainted to create a seamless mosaic image.