Halftone watermarking and related applications

• US 7,286,685 B2
• Filed: 01/31/2006
• Issued: 10/23/2007
• Est. Priority Date: 10/11/2000
• Status: Expired due to Fees

• Current Assignee: Digimarc Corporation
• Original Assignee: Pitney Bowes Incorporated (Böwe Systec AG), Digimarc Corporation
• Inventors: Brunk, Hugh L., Zeller, Claude
• Primary Examiner(s): Ahmed; Samir
• Assistant Examiner(s): Tabatabai; Abolfazl
• Application Number:
  US11/345,648
• Publication Number:
  US 20060210108A1
• Time in Patent Office: 630 Days
• Field of Search: 382/100, 382/232, 382/240, 358/3.03, 358/3.06, 358/3.09, 358/3.1, 358/3.3, 358/534, 380/51, 380/54, 380/201, 380/210, 380/252, 380/287, 370522-529, 283/72, 283 74- 81, 283/85, 283/93, 283/901, 283/902
• US Class Current: 382/100
• CPC Class Codes: G06K 15/00 Arrangements for producing a permanent visual presentation of the output data , e.g. computer output printersprinting or plotting combined with another operation, e.g. with conveying, G06K17/00
• CPC Class Codes: G06K 15/1889 Merging with other data
• CPC Class Codes: G06T 1/0071 using multiple or alternating watermarks
• CPC Class Codes: G06T 1/0092 Payload characteristic determination in a watermarking scheme, e.g. number of bits to be embedded
• CPC Class Codes: G06T 2201/0051 Embedding of the watermark in the spatial domain
• CPC Class Codes: H04N 1/32144 embedded in the image data, i.e. enclosed or integrated in the image, e.g. watermark, super-imposed logo or stamp
• CPC Class Codes: H04N 1/32256 in halftone data
• CPC Class Codes: H04N 1/4052 by error diffusion, i.e. transferring the binarising error to neighbouring dot decisions
• CPC Class Codes: H04N 17/004 for digital television systems
• CPC Class Codes: H04N 21/4425 Monitoring of client processing errors or hardware failure
• CPC Class Codes: H04N 21/8358 involving watermark protecting executable software by watermarking G06F21/16; image watermarking in general G06T1/0021; watermarks inserted in still images for transmission purposes H04N1/32144; inserting watermarks during video coding H04N19/467
• CPC Class Codes: H04N 2201/3284 for error correction

Abstract

The present invention relates generally to digital watermarking. In one embodiment, a method of detecting copying of a printed object is provided. In another embodiment, a method is provided to measure digital watermark strength. In yet another embodiment, and for printing applications, an embedded digital watermark may be used to carry printer information that is later decoded by a watermark decoder and used to examine a digital scan of a printed object and determine whether the printed object is authentic. Other embodiments are provided as well.

Claims

1. A method of detecting copying of a printed object, the method comprising:

reading a digital watermark from an image scanned from the printed object, the digital watermark carrying a message with error correction coding;

using the error correction coding to determine errors in the message;

based on the errors, determining whether the printed object represents a copy.

2. The method of claim 1 including:

processing the image to extract estimates of error correction encoded bits carried in the digital watermark;

decoding the error correction encoded bits to compute a message payload;

re-encoding the message payload to compute error correction encoded bits;

computing a measure of watermark strength from the error correction encoded bits and the estimates of error correction encoded bits.

3. The method of claim 2 wherein the measure of watermark strength is compared with a strength threshold to detect degradation of the watermark signal.

4. The method of claim 1 wherein the message payload includes printer information about a printer used to print the image;

and the printer information is used to determine whether a printed object bearing the watermarked signal is an original or a copy.

5. A computer readable medium on which is stored instructions for executing the method of claim 1.

6. The method claimed in claim 1, wherein the using step includes using the error coding and the message to determine errors in the message and in the error coding.

7. The method claimed in claim 6, further including the step of:

determining the number of errors in the message and in the error coding to find the proportion of errors in the message and in the error coding.

8. The method claimed in claim 7, wherein if the proportion is greater than a threshold the printed image is a copy.

9. The method claimed in claim 7, wherein if the proportion is less than a threshold the printed image is a original.