Methods for digital watermarking of images and images produced thereby

• US 20040013284A1
• Filed: 07/16/2002
• Published: 01/22/2004
• Est. Priority Date: 07/16/2002
• Status: Active Grant

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Yu, Hong Heather
• Granted Patent: US 7,046,820 B2
• Time in Patent Office: Days
• US Class Current: 382/100
• 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: G06T 2201/0061 Embedding of the watermark in each block of the image, e.g. segmented watermarking
• CPC Class Codes: G06T 2201/0083 whereby only watermarked image required at decoder, e.g. source-based, blind, oblivious

Abstract

The present invention, in one configuration, is a method for watermarking an image utilizing a computer in which the computer is utilized to: step through multipixel blocks of a digitized image having regions of a plurality of different densities; analyze the multipixel blocks of the digitized image to determine whether the multipixel blocks of the digitized image are replaceable with coded blocks indicative of a watermark code, wherein the replaceable multipixel blocks are thus codable blocks; and substitute coded blocks indicative of a watermark for codable blocks of the digitized image.

Claims

1. A method for watermarking an image utilizing a computer, said method comprising utilizing the computer to:

step through multipixel blocks of a digitized image having regions of a plurality of different densities;

analyze the multipixel blocks of the digitized image to determine whether the multipixel blocks of the digitized image are replaceable with coded blocks indicative of a watermark code, said replaceable multipixel blocks thereby being codable blocks; and

substitute coded blocks indicative of a watermark for codable blocks of the digitized image.

2. A method in accordance with claim 1 wherein said analyzing comprises determining whether any pixel in a multipixel block has either a maximum or minimum density, wherein said multipixel block is thereby noncodable.

3. A method in accordance with claim 1 wherein said image includes a plurality of densities representable by consecutive integers from 0 to D, and said analyzing comprises analyzing multipixel blocks of the digitized image containing more pixels than the integer D.

4. A method in accordance with claim 1 wherein said analyzing comprises determining whether the pixels in a multipixel block are of nonuniform density, wherein said multipixel block is thereby noncodable.

5. A method in accordance with claim 1 wherein said substituting is restricted to substituting coded blocks for multipixel blocks of the digitized image in which each pixel is the same density and the density is neither a minimum density nor a maximum density.

6. A method in accordance with claim 1 wherein coded blocks are mapped to code symbols of a watermark.

7. A method in accordance with claim 6 wherein said substituting coded blocks indicative of a watermark for codable blocks of the digitized image comprises, for each code symbol comprising the watermark, substituting a coded block mapped to said code symbol.

8. A method in accordance with claim 7 wherein said substituted coded block comprises substituting a coded block having an average density equal to that of the pixels in the codable block of the digitized image.

9. A method in accordance with claim 1 wherein said coded blocks represent halftone patterns, and wherein said substituting of coded blocks indicate of a watermark for codable blocks of the digitized image comprises substituting coded blocks having the same average density as the codable blocks, wherein the halftone patterns of the coded blocks are selected in accordance with the watermark code.

10. A method in accordance with claim 9 wherein, for at least one density, only selected pattern variations are coded and other pattern variations are not coded and are thereby null variations, and further comprising utilizing null variations to substitute for blocks at selected locations of the image.

11. A method in accordance with claim 1 wherein the image is a color image, the digitized image represents a plurality of colors, and said method is performed utilizing at one of said colors.

12. A method in accordance with claim 11 wherein said method is performed separately for more than one said color.

13. A method in accordance with claim 1 further comprising conditioning at least said substituting of coded blocks upon a state of a pseudorandom generator.

14. A printed watermarked imaged produced in accordance with the method of claim 1.

15. A method for watermarking an image utilizing a computer, said method comprising utilizing the computer to replace pixels of the image with a code representing a symbol having an apparent printed density corresponding to the density of the replaced pixel, and to select said symbol from a plurality of symbols having equivalent printed densities depending upon a watermark symbol being encoded at a location of a replaced pixel.

16. A method in accordance with claim 15, further comprising printing the picture utilizing the selected symbols at the locations of the replaced pixels.

17. A watermarked image produced in accordance with the method of claim 16.

30. A method in accordance with claim 15 wherein said applying a border point modulation comprises embedding a repetition coded watermark.

18. A method for watermarking an image utilizing a computer, said method comprising utilizing the computer to:

analyze a representation of a digitized image to determine contiguous edges of the image;

select edges for modulation in accordance with a data hiding criterion; and

apply a watermark-dependent edge point modulation to pixels on the selected edges.

19. A method in accordance with claim 18 wherein said analyzing to determine contiguous edges produces lists of pixel pointers, each list containing pointers to pixel locations of a contiguous edge.

20. A method in accordance with claim 19 wherein said criterion selects lists corresponding to low contrast, low smoothness edges.

21. A method in accordance with claim 20 wherein said applying a watermark-dependent edge point modulation comprises replacing a pixel e of an edge with a new pixel e′

having a value δ

*W(G)*(b−

a)+a, where δ

is a modulation level, W(G) is the Gth bit in a binary watermark stream W, a is a value corresponding to a metric used to describe color in a color space of the digitized image for the edge pixel e, and b is a value of an adjacent pixel in an approximately normal direction.

22. A method in accordance with claim 21 further comprising pseudorandomly shuffling said pixel pointers.

23. A printed watermarked image produced in accordance with the method of claim 18.

24. A method in accordance with claim 18 wherein said applying an edge point modulation comprises embedding a repetition coded watermark.

25. A method for watermarking an image utilizing a computer, said method comprising utilizing the computer to:

analyze a representation of a digitized image to determine border lines within an image;

select border lines for modulation in accordance with a data hiding criterion; and

apply a watermark-dependent border point modulation to pixels in the selected border lines.

26. A method in accordance with claim 25 wherein said analyzing to determine border lines produces lists of pixel pointers, each list containing pointers to pixel locations of a border line.

27. A method in accordance with claim 26 wherein said criterion selects lists corresponding to low smoothness borders.

28. A method in accordance with claim 27 wherein said applying a watermark-dependent edge point modulation comprises replacing a pixel e of an edge with a new pixel e′

having a value e′

=e·

K′

[J]+(K[J]+e·

K[J])·

W[G], where K[J] is the Jth value in a key array K, K′

[J] is the complement of K[J], and W(G) is the Gth watermark symbol from watermark stream W.

29. A method in accordance with claim 28 further comprising pseudorandomly shuffling said pixel pointers.

31. A printed watermarked image produced in accordance with the method of claim 25.

32. A method for watermarking a color image utilizing a computer, said method comprising utilizing the computer to:

step through multipixel blocks of a digitized color image having regions of a plurality of different colors;

analyze the multipixel blocks of the digitized image to determine whether the multipixel blocks of the digitized image are replaceable with coded blocks indicative of a watermark code, said replaceable multipixel blocks thereby being codable blocks; and

substitute coded blocks indicative of a watermark for codable blocks of the digitized image.

33. A method in accordance with claim 32 wherein said substituting comprising substituting blocks having coded patterns of colored pixels.