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space_time_conf - Increasing Space-Time Resolution in Video...

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Increasing Space-Time Resolution in Video Eli Shechtman, Yaron Caspi, and Michal Irani Dept. of Computer Science and Applied Math The Weizmann Institute of Science 76100 Rehovot, Israel { elishe,caspi,irani } @wisdom.weizmann.ac.il Abstract. We propose a method for constructing a video sequence of high space-time resolution by combining information from multiple low- resolution video sequences of the same dynamic scene. Super-resolution is performed simultaneously in time and in space. By “temporal super-resolution” we mean recovering rapid dynamic events that occur faster than regular frame-rate. Such dynamic events are not visible (or else observed incorrectly) in any of the input sequences, even if these are played in “slow-motion”. The spatial and temporal dimensions are very different in nature, yet are inter-related. This leads to interesting visual tradeoffs in time and space, and to new video applications. These include: (i) treatment of spatial artifacts (e.g., motion-blur) by increasing the temporal resolution, and (ii) combination of input sequences of different space-time resolutions (e.g., NTSC, PAL, and even high quality still images) to generate a high quality video sequence. Keywords. Super-resolution, space-time analysis. 1 Introduction A video camera has limited spatial and temporal resolution. The spatial reso- lution is determined by the spatial density of the detectors in the camera and by their induced blur. These factors limit the minimal size of spatial features or objects that can be visually detected in an image. The temporal resolution is de- termined by the frame-rate and by the exposure-time of the camera. These limit the maximal speed of dynamic events that can be observed in a video sequence. Methods have been proposed for increasing the spatial resolution of images by combining information from multiple low-resolution images obtained at sub-pixel displacements (e.g. [1,2,5,6,9,10,11,12,14]. See [3] for a comprehensive review). These, however, usually assume static scenes and do not address the limited tem- poral resolution observed in dynamic scenes. In this paper we extend the notion of super-resolution to the space-time domain. We propose a unified framework for increasing the resolution both in time and in space by combining information from multiple video sequences of dynamic scenes obtained at (sub-pixel) spatial and (sub-frame) temporal misalignments. As will be shown, this enables new visual capabilities of dynamic events, gives rise to visual tradeoffs between time A. Heyden et al. (Eds.): ECCV 2002, LNCS 2350, pp. 753–768, 2002. c Springer-Verlag Berlin Heidelberg 2002
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754 E. Shechtman, Y. Caspi, and M. Irani (a) (b) Fig. 1. Motion blur. Distorted shape due to motion blur of very fast moving objects (the tennis ball and the racket) in a real tennis video. The perceived distortion of the ball is marked by a white arrow. Note, the “V”-like shape of the ball in (a), and the elongated shape of the ball in (b). The racket has almost “disappeared”.
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