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Title:  Fast algorithms for binary crosscorrelation 
Authors:  MUKHERJI, S 
Issue Date:  2005 
Publisher:  IEEE 
Citation:  IGARSS 2005: IEEE International Geoscience and Remote Sensing Symposium, Vols 18, Proceedings,340343 
Abstract:  Crosscorrelation is widely used to match images. Crosscorrelation of windows where pixels have binary values is necessary when thresholded signoflaplacian images are matched. Nishihara proposed that the sign of the laplacian of an image be used as a characteristic (that is robust to illumination changes and noise) to match images. We have reduced the number of multiplications required in the computation of the laplacian by half by making use of the symmetry of the convolution masks. Thresholding the sign of the laplacian of an image results in a binary image and image matching can then be done by matching corresponding windows of the binary images using crosscorrelation. Leberl proposed fast algorithms for computing binary crosscorrelation. We propose a fast implementation of his best algorithm. We also propose, in this paper, a bitbased algorithm which makes use of the fact that the binary data in the windows can be represented by bits. The algorithm packs the bits into integer variables and then uses the logical operations to identify matching bits in the windows. This very packing of bits into integer variables (that enables us to use the logical operations, hence speeding up the process) renders the step of counting the number of matching pixels difficult. This step, then, is the bottleneck in the algorithm. We solve this problem of counting the number of matching pixels by an algebraic property. The bitmethod is exceedingly simple and is most efficient when the number of bits is close to multiples of 32. Binary crosscorrelation can also be computed and, hence, speeded up by the FFT. We conclude the paper by comparing the bitbased method, Leberl's algorithm and the FFTbased method for computing binary crosscorrelation. 
URI:  http://dspace.library.iitb.ac.in/xmlui/handle/10054/16066 http://hdl.handle.net/100/2657 
ISBN:  0780390504 
Appears in Collections:  Proceedings papers

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