Language-free layout analysis

A system for isolating blocks, lines, words, and symbols within images of machine-printed textual documents that is, to a large existent, independent of language and writing system is described. This is achieved by exploiting a small number of nearly universal typesetting and layout conventions. The system does not require prior knowledge of page orientation (module 90°), and copes well with nonzero skew and shear angles (within 10°). Also it locates blocks of text without reliance on detailed a priori layout models, and in spite of unknown or mixed horizontal and vertical text-line orientations. Within blocks, it infers text-line orientation and isolates lines, without knowledge of the language, symbol set, text sizes, or the number of text lines. Segmentation into words and symbols, and determination of reading order, normally require some knowledge of the language: this is held to minimum by relying on shape-driven algorithms. The underlying algorithms are based on Fourier theory, digital signal processing, computational geometry, and statistical decision theory. Most of the computation occurs within algorithms that possess unambiguous semantics (that is, heuristics are kept to a minimum). The effectiveness of the method on English, Japanese, Hebrew, Thai, and Korean documents is discussed