Compression at the Source for Digital Camcorders
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Research Article Compression at the Source for Digital Camcorders Nir Maor,1 Arie Feuer,1 and Graham C. Goodwin2 1 Department 2 School
of Electrical Engineering (EE), Technion-Israel Institute of Technology, Haifa 32000, Israel of Electrical Engineering and Computer Science, University of Newcastle, Callaghan NSW 2308, Australia
Received 2 October 2006; Accepted 30 March 2007 Recommended by Russell C. Hardie Typical sensors (CCD or CMOS) used in home digital camcorders have the potential of generating high definition (HD) video sequences. However, the data read out rate is a bottleneck which, invariably, forces significant quality deterioration in recorded video clips. This paper describes a novel technology for achieving a better utilization of sensor capability, resulting in HD quality video clips with esentially the same hardware. The technology is based on the use of a particular type of nonuniform sampling strategy. This strategy combines infrequent high spatial resolution frames with more frequent low resolution frames. This combination allows the data rate constraint to be achieved while retaining an HD quality output. Post processing via filter banks is used to combine the high and low spatial resolution frames to produce the HD quality output. The paper provides full details of the reconstruction algorithm as well as proofs of all key supporting theories. Copyright © 2007 Nir Maor et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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INTRODUCTION: CURRENT TECHNOLOGY
In many digital systems, one faces the problem of having a source which generates data at a rate higher than that which can be transmitted over an associated communication channel. As a consequence, some means of compression are required at the source. A specific case of this problem arises in the current technology of digital home camcorders. Figure 1 shows a schematic diagram of a typical digital camcorder. Images are captured on a two-dimensional sensor array (either CCD or CMOS). Each sensor in the array gives a spatial sample of the continuous image, a pixel, and the whole array gives a temporal sample of the time-varying image, a frame. The result is a 3D sampling process of a signal having two spatial dimensions and one temporal dimension. A hard constraint on the spatial resolution in each frame is determined by the number of sensors in the sensor array, while a hard constraint on the frame rate is determined by the minimum exposure time required by the sensor technology. The result is a uniformly sampled digital video sequence which perfectly captures a time-varying image whose spectrum is bandlimited to a box as shown in Figure 2. We note that the cross-sectional area of the box depends on the spatial resolution constraint, while the other dimension of the box depends on the maximal frame rate. As it turns out, the spectrum of typical time-varying images can rea
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