Adaptive scaling for decoding spatially periodic self-clocking glyph shape codes

• US 5,091,966 A
• Filed: 07/31/1990
• Issued: 02/25/1992
• Est. Priority Date: 07/31/1990
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Tow, Robert F., Bloomberg, Dan S.
• Primary Examiner(s): Razavi, Michael
• Application Number:
  US07/560,658
• Time in Patent Office: 574 Days
• Field of Search: 382/21, 382/16, 382/23, 382/20, 382/56, 382/25, 382/26, 235/494, 235/470, 235/471, 235/456, 235/70, 235/454, 235/432, 235/494, 235/487, 356/71, 358/470, 358/452, 358/948
• US Class Current: 382/203
• CPC Class Codes: G06K 19/06037 multi-dimensional coding
• CPC Class Codes: G06K 7/143 Glyph-codes
• CPC Class Codes: G06V 30/224 of printed characters having additional code marks or containing code marks

Abstract

Weighted and unweighted convolution filtering processes are provided for decoding bitmap image space representations of self-clocking glyph shape codes and for tracking the number and locations of the ambiquities or "errors" that are encountered during the decoding. This error detection may be linked to or compared against the error statistics from an alternative decoding process, such as the binary image processing techniques that are described herein to increase the reliability of the decoding that is obtained.

Claims

1. A process for decoding a spatially periodic bitmap image space representation of a self-clocking glyph shape code of unknown spatial periodicity;

said code being composed of glyphs having shapes that encode digital data values, such that each distinct data value that is encoded by said code is represented by the shape of a respective glyph;

said glyphs being selected from a set of n permissible glyph shapes, with each said glyph shapes being preassigned to the encoding of a predetermined digital data value;

said glyphs being spatially distributed in said bitmap image space in substantial accordance with a spatial formatting rule;

said process comprising the steps of

analyzing said bitmap image space representation of said code for determining its spatial periodicity along an X axis and an Y axis;

scaling said spatial formatting rule to match the determined spatial periodicity of said glyph code;

filtering said bitmap image space representation of said code with at least n discrimination filters, each of said discrimination filters being selected to match a respective one of said permissible glyph shapes, thereby providing at least n filtered versions of said bitmap image space representation;

evaluating said filtered version, glyph-by-glyph in accordance with said scaled spatial formatting rule for determining a filtered value for each glyph as filtered by each filter;

comparing the filtered values for each of said glyphs for classifying said glyphs by their shapes; and

assigning decoded data values to said shape classified glyphs in accordance with the data values preassigned to said glyph shapes.

4. The process of any one of claim 1-3 wherein said discrimination filters are hit-miss filters.

5. The process of claim 4 wherein said hit-miss filters are weighted to more heavily value hits upon relatively distinctive features of the glyph shapes for which they are configured to preferentially respond than hits upon less distinctive features of said glyph shapes.

2. A process for decoding a self-clocking glyph shape code of unknown spatial periodicity based upon a spatially periodic bitmap image space representation of said code;

said code being composed of glyphs that are selected from a predefined set of n permissible and distinctive glyph shapes, with each of said glyph shapes being preassigned to the encoding of a unique predetermined data value;

said glyphs being spatially distributed in said bitmap image space in substantial conformity with a preselected spatial formatting rule;

said process comprising the steps of

analyzing the bitmap image space representation of said code to determine the spatial periodicity of said code along a pair of orthogonal axes;

scaling said spatial formatting rule in accordance with the determined spatial periodicity of said code for providing a scaled spatial formatting rule that conforms to the determined spatial periodicity of said code;

filtering said bitmap image space representation of said code with each of at least n different discrimination filters to provide at least n differently filtered version of said bitmap image space representation of said code, each of said discrimination filters being configured to preferentially respond to a respective one of said glyph shapes;

performing a glyph-by-glyph evaluation of each of the filtered version of the bitmap image space representation of said code in accordance with said scaled spatial formatting rule for determining a filtered value for each of said glyphs as filtered by each of said filters thereby providing at least n filtered values for each of said glyphs;

comparing said filtered values on a glyph-by-glyph basis for shape classifying said glyphs; and

assigning decoded data values to said shape classified glyphs in accordance with the data values encoded by said shapes.

3. The process of claim 2 wherein said analyzing step comprises a frequency domain analysis of said bitmap image space representation of said code.