Registers – Records – Particular code pattern
Reexamination Certificate
1995-09-21
2001-02-06
Frech, Karl D. (Department: 2876)
Registers
Records
Particular code pattern
C235S487000
Reexamination Certificate
active
06182901
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to self-clocking glyph codes for recording digital information on graphic recording media, such as plain paper. Even more specifically, this invention pertains to techniques for increasing the tolerance of such glyph codes to geometric distortion and physical damage, while preserving their homogeneous visual appearance and enhancing their suitability for applications requiring random access to the information they encode.
CROSS REFERENCES TO RELATED APPLICATIONS
This application is related to commonly assigned, concurrently filed Hecht et al. United States patent applications on “Explicit Synchronization for Self-Clocking Glyph Codes” U.S. Pat. No. 5,449,895, issued Sep. 12, 1995, “Global Addressability for Self-Clocking Glyph Codes” U.S. Pat. No. 5,453,605, issued Sep. 26, 1995, “Framing Codes for Robust Synchronization and Addressing of Self-Clocking Glyph Codes” application U.S. Ser. No. 08/549,195 which is a continuation of application U.S. Ser. No. 08/172,443, and “Random Access Techniques for use with Self-Clocking Glyph Codes” U.S. Pat. No. 5,449,896, issued Sep. 12, 1995.
BACKGROUND OF THE INVENTION
In keeping with prior proposals, a basic self-clocking glyph code, such as shown in
FIG. 1
, typically is composed of an array
21
of elongated, slash-like symbols or “glyphs”
22
and
23
that are written with their longitudinal axes tilted at angles of approximately −45° and +45° with respect to the vertical axis
24
of a recording medium
25
to encode bit values of “1” and “0”, respectively, or vice-versa, in each of the glyphs. These codes are “self-clocking” because they include an optically detectable symbol (a “glyph”) for each of the values they encode. This means that the detection of the glyphs implicitly synchronizes the decoding process to the code once the decoding process has been properly spatially oriented with respect to the code. As will be evident, this implicit synchronization is valid so long as all of the glyphs are detected or otherwise accounted for in correct logical order. If, however, synchronization is lost, there is nothing to restore the implicit synchronization, so a loss of synchronization generally causes an implicitly synchronized decoding process to experience fatal error. For a more detailed discussion of these glyph codes and of techniques for decoding them, the following commonly assigned U.S. patent documents are hereby incorporated by reference: a copending application or Bloomberg et al. on “Self-Clocking Glyph Shape Codes,” which was filed Aug. 18, 1992 under U.S. Ser. No. 07/931,554; Bloomberg U.S. Pat. No. 5,168,147 which issued Dec. 1, 1992 on “Binary Image Processing for Decoding Self-Clocking Glyph Shape Codes;” Bloomberg et al. U.S. Pat. No. 5,091,966, which issued Feb. 25, 1992 on “Adaptive Scaling for Decoding Spatially Periodic Self-Clocking Glyph Shape Codes;” and Stearns et al. U.S. Pat. No. 5,128,525, which issued Jul. 7, 1992 on “Convolution Filtering for Decoding Self-Clocking Glyph Shape Codes.”
As will be seen, these prior proposals not only describe the use of two discriminable glyph shapes for the encoding of single bit binary values, but also teach that “glyph shape encoding” is extensible to the encoding of digital values of any given bit length, n, in each glyph by utilizing a code having 2
n
discriminable glyph shapes (where the discriminability between glyphs representing different values is based upon the distinctive rotational orientations and/or the distinctive geometric configurations of the different glyphs). Furthermore, another copending and commonly assigned U.S. patent application of David L. Hecht on “Self-Clocking Glyph Code Having Composite Glyphs for Distributively Encoding Multi-bit Digital Values,” which was filed Dec. 12, 1991 under U.S. Ser. No. 07/814,842 and which also is hereby incorporated by reference, provides a technique for encoding a plurality of bit values in each of the glyphs by constructing the glyphs so that they each have a plurality of independently modulatable and readily distinguishable (e.g., substantially orthogonal) characteristics. Thus, even though a straightforward self-clocking glyph code of the type shown in
FIG. 1
is featured in this disclosure to simplify the description, it will be evident that the broader aspects of this invention are applicable to other glyph codes, including more complex ones.
In practice, each of the glyphs
22
and
23
usually is defined by writing a recognizable pattern of “on” and “off” pixels into a two dimensional, array of pixel positions (i. e., a “symbol cell”). As a general rule, the pixels that form the body of the glyph (say, the “on” pixels) are written into contiguous pixel positions that are more or less centered within the symbol cell, and the other or “off” pixels are written into the remaining pixel positions of the symbol cell to provide a contrasting surround that demarks the edges of the glyph and separates it from its neighbors.
The symbol cells, in turn, ordinarily are tiled onto the recording medium in accordance with a preselected spatial formatting rule, so the logical order of the data values that the glyphs encode is preserved by the spatial order in which the glyphs are mapped onto the recording medium. For example, the symbol cells may be written on the recording medium in accordance with a regular and repeating spatial formatting rule that is selected to map the glyph encodings into a two dimensional, rectangular array of logical data blocks of predetermined size, such as data blocks having a 16 symbol cell×16 symbol cell format. These data blocks suitably are organized on the recording medium in left-to-right, top-to-bottom logical order.
The size of the symbol cells that are used for the glyphs depends on a variety of factors, including the spatial resolution of the printing process that is employed to write the glyphs, the type and extent of the degeneration that the printed glyph code is required to tolerate, and the spatial resolution of the lowest resolution scanning process that is expected to be able to recover the code. In view of these constraints, a 300 s.p.i. printer suitably centers the glyphs in 5 pixel×5 pixel or 7 pixel×7 pixel symbol cells. Even larger symbol cells can be employed for the glyphs if the increased granularity of the textured appearance of the printed glyph code is tolerable or unavoidable. As a general rule, of course, the smallest practical symbol cell size is esthetically most pleasing because the visual texturing appearance of the glyph code gradually blends as the symbol cell size is reduced. Indeed, codes composed of smaller symbol cells tend to have generally uniform gray scale appearances when they are viewed under ordinary lighting at normal viewing distances.
The existing techniques for decoding self clocking glyph codes are designed to be initialized at or near the center of a reference glyph that occupies a known spatial position relative to the remainder of the glyph code (for example, the glyph in the upper, lefthand corner of a rectangular array of glyphs). Thus, accurately locating this reference glyph clearly is a key to spatially synchronizing such a decoding process with the glyph code.
While synchronous initialization of the decoding process is a necessary condition for orderly decoding of a self-clocking glyph code, it may not be a sufficient condition to ensure accurate decoding of the code because the scanned-in image of the glyph code pattern often is distorted by skew and/or scaling errors. For this reason, prior decoding processes generally have attempted to determine the relative spatial positions of three or more reference glyphs in recognizeable positions that have a known nominal, non-colinear relationship with respect to each other (such as the corner glyphs of a rectangular array of glyphs) with sufficient precision to compute skew and scaling correction factors. These correction factors then are used to adjust the angle and magnitude of a vector that dictates the direc
Flores L. Noah
Hecht David L.
Frech Karl D.
Xerox Corporation
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