Importance

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Abstract

A technique for reducing images that provides useful information about the image and allows fast computation. Using threshold values near the extreme possible values for the convolution window size and using large subsampling tiles nevertheless allows extraction of the information about the typical textures that exist in the document image: text words, text lines, rules, and halftones. In a particular embodiment, 16.times.16 tiles are used for subsampling, 16.times.1 and 1.times.16 windows are used for the convolution, and threshold values of 1 and 16 are used. If the horizontal windows in tiles are aligned with 16-bit boundaries in the computer, the implementation is particularly efficient. For the 16.times.1 horizontal window, a threshold convolution with T=1 can be done on any of the sixteen 16-bit words in the tile by checking whether the word is zero or non-zero. For a 1.times.16 vertical window, a threshold convolution with T=1 can be done on any of the sixteen 16-bit columns in the tile by ORing the sixteen appropriately masked words.

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First Claim