Methods and means for embedding machine readable digital data in halftone images

• US 5,315,098 A
• Filed: 12/27/1990
• Issued: 05/24/1994
• Est. Priority Date: 12/27/1990
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Tow, Robert F.
• Primary Examiner(s): PITTS, HAROLD I
• Application Number:
  US07/634,990
• Time in Patent Office: 1,244 Days
• Field of Search: 235/469, 235/470, 382/21
• US Class Current: 235/494
• CPC Class Codes: G06K 1/121 by printing code marks applying code marks to labels B65C9/46; marking or coding completed packages B65B61/26
• CPC Class Codes: G06K 19/06037 multi-dimensional coding
• CPC Class Codes: G06T 1/0028 Adaptive watermarking, e.g. Human Visual System [HVS]-based watermarking
• CPC Class Codes: G06T 2201/0051 Embedding of the watermark in the spatial domain
• CPC Class Codes: H04N 1/32203 Spatial or amplitude domain methods H04N1/32309 takes precedence
• CPC Class Codes: H04N 1/32256 in halftone data
• CPC Class Codes: H04N 2201/327 which are undetectable to the naked eye, e.g. embedded codes

Abstract

The present invention provides methods and means for encoding digital data in the angular orientation of circularly asymmetric halftone dot patterns that are written into the halftone cells of digital halftone images. In keeping with standard practices, the sizes of these halftone dot patterns are modulated in accordance with the grayscale data sample values that are provided to define the image, so the average reflectance or transmittance of each of the halftone cells is modulated to provide a more or less standard halftone rendering of the image. In accordance with this invention, however, provision is made for modulating the angular orientation of the halftone dot patterns in accordance with digital data values, thereby embedding the digital data in the halftone image.

Claims

1. A system for encoding digital data in halftone images, said system comprising

a halftone generator for supplying circularly asymmetric halftone dot patterns that are size modulated in accordance with grayscale input image sample values;

pattern rotating means for angularly orienting said halftone dot patterns in accordance with respective digital data values; and

output means for writing said angularly oriented dot patterns into tiled halftone cells of predetermined size on a recording medium for producing a halftone rendering of said image with said digital data encoded in the angular orientation of the halftone dot patterns.

2. The system of claim 1 further including

means coupled to said pattern rotating means for pseudo randomly modulating the angular orientation of said halftone dot patterns.

3. The system of claim 1 further including

pseudo random encoding means for pseudo randomly encoding said digital data values, thereby superimposing a pseudo random modulation on the angular orientation of said halftone dot patterns.

4. The system of any one of claims 1-3 further including

pseudo random encoding means for pseudo randomly encoding said grayscale values, thereby superimposing a pseudo random modulation on said halftone rendering of said image.

5. A method for encoding digital data in a hardcopy rendering of a halftone image that is defined by circularly asymmetric halftone dot patterns of varying size;

said method comprising the steps of

rotationally modulating said halftone dot patterns in accordance with said digital data; and

writing said rotationally modulated dot patterns into tiled halftone cells of predetermined size on a recording medium, thereby producing said hardcopy rendering with said digital data encoded therein.

6. The method of claim 5 further including the step of

pseudo randomly modulating the rotation of said halftone dot patterns.

7. The method of claim 6 wherein

said digital data values are pseudo randomly modulated to pseudo randomly modulate the rotation of said halftone dot patterns.

8. The system of any one of claims 5-7 further including the steps of

generating said half tone dot patterns in response to respective grayscale values, and

pseudo randomly encoding said grayscale values, thereby superimposing a pseudo random modulation on said hardcopy rendering of said image.