Abstract: Fast, low-overhead implementations of a powerful, reliable image matching engine based on the Hausdorff distance are disclosed. In one such implementation, a method is provided in which a processor receives two inputs. The first input is a pattern to be recognized in an image; the second, a digital image in which the pattern is to be recognized. The digital image is preprocessed with the processor using various morphological dilation operations so as to produce a set of preprocessed digital images. Thereafter, the processor performs a hierarchical search for the pattern in the digital image. The hierarchical search is performed over a search space, and includes a series of decisions, each decision indicating whether a portion of the search space can be eliminated from the search. Each decision is made by performing a plurality of comparisons between the pattern and the preprocessed digital images of the set and analyzing the results of these comparisons.

Abstract: A processor is provided with a first set of digital information that includes a first, resolution-independent structured representation of a document. This first representation is one from which various image collections (e.g., sets of page images) can be obtained, each such image in each such collection having a characteristic resolution. From the first set of digital information, the processor produces a second set of digital information that includes a second, resolution-dependent structured representation of the document. The second structured representation is a lossless representation of a particular one of the image collections obtainable from the first structured representation, and it includes a set of tokens and a set of positions. The second set of digital information is produced by extracting the tokens from the first structured representation, and by determining the positions from the first structured representation.