Self-clocking glyph shape codes

Abstract

This invention provides self-clocking glyph shape codes for encoding digital data in the shapes of glyphs that are suitable for printing on hardcopy recording media. Advantageously, the glyphs are selected so that they tend not to degrade into each other when they are degraded and/or distorted as a result, for example, of being photocopied, transmitted via facsimile, and/or scanned-in to an electronic document processing system. Moreover, for at least some applications, the glyphs desirably are composed of printed pixel patterns containing nearly the same number of ON pixels and nearly the same number of OFF pixels, such that the code that is rendered by printing such glyphs on substantially uniformly spaced centers appears to have a generally uniform texture. In the case of codes printed at higher spatial densities, this texture is likely to be perceived as a generally uniform gray tone. Binary image processing and convolution filtering techniques for decoding such codes also are disclosed, but this application focuses on the codes.

Description

[0001]ThisThis application is a reissue of U.S. Pat. No. 6,076,738 issued Jun. 20, 2000 from application Ser. No. 08 / 240,798 filed May 10, 1994, which is a continuation of application Ser. No. 07 / 931,554, filed Aug. 18, 1992 AB which, in turn, was a continuation of application Ser. No. 07 / 560,514, filed Jul. 31, 1990 AB.FIELD OF THE INVENTION[0002]This invention relates to self-clocking codes for recording digital data on hardcopy recording media and, more particularly, to codes composed of glyphs that have digital data values encoded in their shapes. Advantageously, the glyphs are selected so that they tend not to degrade into each other, but the broader aspects of this invention are directed toward codes composed of discriminable glyphs, without specific limitation to the amount of image degradation and / or distortion the codes can tolerate.[0003]Even more specifically, this invention relates to codes of the foregoing type that have a generally uniform textured appearance when they...

AI Technical Summary

Benefits of technology

[0009]In response to the foregoing and other needs, the present invention provides self-clocking glyph shape codes for encoding digital data in the shapes of glyphs that are suitable for printing on hardcopy recording media. Advantageously, the glyphs are selected so that they tend not to degrade into each other when they are degraded and / or distorted as a result, for example, of being photocopied, transmitted via facsimile, and / or scanned-in to an electronic document processing system. Moreover, for at least some applications, the glyphs desirably are composed of printed pixel patterns containing nearly the same number of ON pixels and nearly the same manner of OFF pixels, such that the code that is rendered by printing such glyphs on substantially uniformly spaced centers appears to have a generally uniform texture. In the case of codes printed at higher spatial densities, this texture is likely to be perceived as a generally uniform gray tone.

Problems solved by technology

This mottling is a readily discernible departure from the clean, crisp appearance of high quality printed documents, so it may be aesthetically objectionable to some observers.

Furthermore, another drawback of these bar-like codes is the overhead that they contemplate.

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