Applying digital watermarks using dot gain correction

• US 6,700,995 B2
• Filed: 07/30/2002
• Issued: 03/02/2004
• Est. Priority Date: 04/19/2000
• Status: Expired due to Term

• Current Assignee: Digimarc Corporation
• Original Assignee: Digimarc Corporation
• Inventors: Reed, Alastair M.
• Primary Examiner(s): Patel, Jayanti K.
• Application Number:
  US10/209,053
• Publication Number:
  US 20030079130A1
• Time in Patent Office: 581 Days
• Field of Search: 382/100, 382/232, 382/162, 382/233, 382/239, 382/112, 382/135, 382/166, 382/167, 382/270, 382/242-250, 235/468, 383/72, 358/3.28, 380/200, 380/201, 380/204, 380/51, 700/37, 700/38, 713/176
• US Class Current: 382/100
• CPC Class Codes: G06F 18/00 Pattern recognition
• CPC Class Codes: G06T 1/0021 Image watermarking
• CPC Class Codes: G06T 1/0028 Adaptive watermarking, e.g. Human Visual System [HVS]-based watermarking
• CPC Class Codes: G06T 1/0064 Geometric transfor invariant watermarking, e.g. affine transform invariant
• CPC Class Codes: G06T 2201/0051 Embedding of the watermark in the spatial domain
• CPC Class Codes: G06T 2201/0052 Embedding of the watermark in the frequency domain
• CPC Class Codes: H04H 20/31 using in-band signals, e.g. subsonic or cue signal
• CPC Class Codes: H04N 1/32154 Transform domain methods H04N1/32309 takes precedence
• CPC Class Codes: H04N 1/32203 Spatial or amplitude domain methods H04N1/32309 takes precedence
• CPC Class Codes: H04N 1/32208 involving changing the magnitude of selected pixels, e.g. overlay of information or super-imposition H04N1/32219, H04N1/32224 take precedence
• CPC Class Codes: H04N 1/32229 with selective or adaptive application of the additional information, e.g. in selected regions of the image H04N1/32213 takes precedence
• CPC Class Codes: H04N 1/32251 in multilevel data, e.g. greyscale or continuous tone data
• CPC Class Codes: H04N 1/32288 Multiple embedding, e.g. cocktail embedding, or redundant embedding, e.g. repeating the additional information at a plurality of locations in the image
• CPC Class Codes: H04N 1/32293 Repeating the additional information in a regular pattern
• CPC Class Codes: H04N 1/32309 in colour image data
• CPC Class Codes: H04N 1/32352 Controlling detectability or arrangements to facilitate detection or retrieval of the embedded information, e.g. using markers for decoding, detection or retrieval operations H04N1/32149 and subgroups take precedence
• CPC Class Codes: H04N 19/467 characterised by the embedded information being invisible, e.g. watermarking
• CPC Class Codes: H04N 19/645 by grouping of coefficients into blocks after the transform
• CPC Class Codes: H04N 21/23892 involving embedding information at multiplex stream level, e.g. embedding a watermark at packet level
• CPC Class Codes: H04N 21/44008 involving operations for analysing video streams, e.g. detecting features or characteristics in the video stream arrangements characterised by components specially adapted for monitoring, identification or recognition of video in broadcast systems H04H60/59
• CPC Class Codes: H04N 21/4627 : Rights management associated to the content security in data switching network management H04L41/28; security management or policies for network security H04L63/20; access security in wireless networks H04W12/08
• 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 2201/3233 : of authentication information, e.g. digital signature, watermark
• CPC Class Codes: H04N 2201/327 : which are undetectable to the naked eye, e.g. embedded codes
• CPC Class Codes: H04N 2201/3284 : for error correction
• CPC Class Codes: H04N 7/163 : by receiver means only

Abstract

The color values in an image data are first modified in accordance with the forward dot gain curve of an offset printing press, next the watermark “tweak” values (i.e. the watermark signal values) are calculated for this modified image data. The calculated “tweak” values are then modified in accordance with the backward dot gain values of the printing press. The modified tweak values are then added to the original image data values. The image is then printed on the offset printing press. The result is that the “effective” watermark tweak on the printed paper is not materially affected by the dot gain curve of the printing press.

Claims

1. A method of watermarking an image comprising the steps of

modifying said image in accordance with the values in a forward dot gain curve,

calculating change values necessary to watermark said modified image,

modifying said change values in accordance with a backward dot gain curve, and

combining said modified dot gain values and said image to produce a watermarked image.

2. The method recited in claim 1 wherein said dot gain curve is the dot gain curve associated with an offset printing press.

3. The method recited in claim 1 wherein said backward dot gain curve is the inverse of said forward dot gain curve.

4. The method recited in claim 1 wherein said image includes CYMK (cyan yellow, magenta, and black) colors.

5. The method of claim 1 wherein said image is watermarked using the scale to black technique.

6. The method recited in claim 1 wherein said image is watermarked using the scale to white technique.

7. A system for watermarking an image comprising,

means for modifying said image in accordance with a forward dot gain curve,

means for generating change values needed to watermark said modified image with a particular watermark,

means for calculating change values necessary to watermark said modified image,

means for modifying said change values in accordance with a backward dot gain curve, and

means for combining said modified dot gain values and said image to produce a watermarked image.

8. The system recited in claim 7 wherein said dot gain curve is the dot gain curve associated with an offset printing press.

9. The system recited in claim 7 wherein said backward dot gain curve is the inverse of said forward dot gain curve.

10. The system recited in claim 7 wherein said image includes CYMK (cyan yellow, magenta, and black) colors.

11. A method of watermarking an image which will be printed on an offset printing press comprising the steps of

modifying said image in accordance with the values a forward dot gain curve applicable to said offset printing press,

calculating change the values necessary to watermark said modified image with a particular watermark,

modifying said change values in accordance with the backward dot gain curve of said offset printing press,

combining said modified dot gain values and said image to produce a watermarked image, and

printing said watermarked image on said offset press.

12. A method of processing an image comprising the steps of

modifying said image in accordance with the values in a forward dot gain curve,

calculating change values necessary to watermark said modified image with a particular watermark,

modifying said change values in accordance with a backward dot gain curve,

combining said modified dot gain values and said image to produce a watermarked image,

printing said watermarked image, and

reading the watermark in said printed image.

13. The method recited in claim 12 wherein said image is printed on an offset press.

14. The method recited in claim 13 wherein said dot gain curves are the dot gain curves of said offset press.

15. A method of watermarking an image with a particular watermark prior to printing by an offset press comprising the steps of,

calculating changes values needed to embed said particular watermark in said image,

changing the color values of said image by an amount which results in changes in ink value equal to said changes values, said amount including compensation for a variation in a relationship of an input color value and ink provided by said offset press to represent said in put color values,

whereby said image is watermarked with said particular watermark when printed on said offset press.