Computationally Efficient Histogram Extraction for Rectagular Image Regions

We present a novel method, which we refer as an integral histogram, to compute the histograms of all possible target regions in an image. Our method is computationally superior and makes it possible to employ even an exhaustive search process in real-time, which was impractical before. Furthermore, it enables the description of higher level histogram features. To accomplish fast extraction, we exploit the spatial arrangement of image points, and recursively propagate an aggregated histogram by starting from an origin and traversing through the remaining images along a given scan-line. At each step, we update a single histogram bin using the values of integral histogram at the previously visited neighboring points. After integral histogram is propagated, histogram of any target region can be computed easily by using simple arithmetic operations. Our numerical analysis proves that the integral histogram method drastically decreases the amount of the required computations. Proc. of Real-Time Image Processing This work may not be copied or reproduced in whole or in part for any commercial purpose. Permission to copy in whole or in part without payment of fee is granted for nonprofit educational and research purposes provided that all such whole or partial copies include the following: a notice that such copying is by permission of Mitsubishi Electric Research Laboratories, Inc.; an acknowledgment of the authors and individual contributions to the work; and all applicable portions of the copyright notice. Copying, reproduction, or republishing for any other purpose shall require a license with payment of fee to Mitsubishi Electric Research Laboratories, Inc. All rights reserved. Copyright c ©Mitsubishi Electric Research Laboratories, Inc., 2005 201 Broadway, Cambridge, Massachusetts 02139