Method for image encoding

• US 5,930,377 A
• Filed: 05/07/1998
• Issued: 07/27/1999
• Est. Priority Date: 07/31/1992
• Status: Expired due to Term

• Current Assignee: Digimarc Corporation
• Original Assignee: Digimarc Corporation
• Inventors: Powell, Robert D., Nitzberg, Mark J.
• Primary Examiner(s): Johns, Andrew W.
• Application Number:
  US09/074,632
• Time in Patent Office: 446 Days
• Field of Search: 382/100, 382/112, 382/232, 340/825.34, 356/71, 902/1, 902/4, 902/6, 283/17, 283/72, 283/73, 283/113, 283/901, 380/9, 380/23, 380/25, 380/54
• US Class Current: 382/100
• CPC Class Codes: G06Q 20/341 Active cards, i.e. cards including their own processing means, e.g. including an IC or chip
• 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 2201/0081 whereby both original and watermarked images are required at decoder, e.g. destination-based, non-blind, non-oblivious
• CPC Class Codes: G07D 7/0047 using checkcodes, e.g. coded numbers derived from serial number and denomination
• CPC Class Codes: G07D 7/0056 involving markings of altered colours
• CPC Class Codes: G07D 7/12 Visible light, infrared or ultraviolet radiation
• CPC Class Codes: G07D 7/2008 using pre-processing, e.g. de-blurring, averaging, normalisation or rotation
• CPC Class Codes: G07D 7/2033 Matching unique patterns, i.e. patterns that are unique to each individual paper
• CPC Class Codes: G07F 7/08 by coded identity card or credit card or other personal identification means without personal verification means G07F7/02
• CPC Class Codes: G07F 7/12 Card verification
• 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 1/32245 Random or pseudorandom selection of pixels
• 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 1/3232 Robust embedding or watermarking
• CPC Class Codes: H04N 2201/3233 of authentication information, e.g. digital signature, watermark
• CPC Class Codes: H04N 2201/3235 : Checking or certification of the authentication information, e.g. by comparison with data stored independently
• CPC Class Codes: H04N 2201/327 : which are undetectable to the naked eye, e.g. embedded codes

Abstract

A method and system for embedding signatures within visual images in both digital representation and print or film. A signature is inseparably embedded within the possible image, the signature persisting through image transforms that include resizing as well as conversion to print or film and back to digital form. Signature points are selected from among the pixels of an original image. The pixel values of the signature points and surrounding pixels are adjusted by an amount detectable by a digital scanner. The adjusted signature points form a digital signature which is stored for future identification of subject images derived from the image. In one embodiment, a signature is embedded within an image by locating relative extrema in the continuous space of pixel values and selecting the signature points from among the extrema. Preferably, the signature is redundantly embedded in the image such that any of the redundant representations can be used to identify the signature. Identification of a subject image includes ensuring that the subject image is normalized with respect to the original image or the signed image. Preferably, the normalized subject image is compared with the stored digital signature.

Claims

1. A method of processing an image encoded as points, each point having a parameter value, the method comprising:

identifying plural points within the image;

increasing the parameter value of each of a first group of said identified points, and also increasing the parameter values of a first patch of points surrounding each such point; and

decreasing the parameter value of each of a second group of said identified points and also decreasing the parameter values of a second patch of points surrounding each such point.

2. The method of claim 1 wherein each point corresponds to an electronically represented pixel.

3. The method of claim 1 wherein the parameter values of the points in each patch are changed by amounts having magnitudes that depend on their position within the patches.

4. The method of claim 1 wherein the parameter values of the points in each first patch are increased by a first amount, and the parameter values of the points in each second patch are decreased by a second amount, the first and second amounts depending on position within the patch.

5. The method of claim 1 further comprising associating each of said plural points with a plurality of adjacent points collectively forming a continuous patch, thereby defining several patches in the images.

6. The method of claim 5 wherein the patches are disjoint.

7. The method of claim 1 wherein the image is monochromatic.

8. The method of claim 1 wherein the image is color.

9. The method of claim 1 wherein the parameter is luminance.

10. The method of claim 1 wherein the parameter is chrominance.

11. The method of claim 1 wherein each patch is uniform in shape.

12. The method of claim 11 wherein each patch is rectangular in shape.

13. The method of claim 1 wherein each patch has a central point, and the identified point within each patch is said central point.

14. Apparatus for embedding data in an image, the apparatus comprising:

a computer memory for storing the image as an ordered set of pixels, each pixel having a pixel parameter value;

means for identifying plural points within the image; and

image altering means for increasing the parameter value of each of a first group of said identified points, and also for increasing the parameter values of a first patch of points surrounding each such point;

said image altering means further decreasing the parameter value of each of a second group of said identified points, and also for decreasing the parameter values of a second patch of points surrounding each such point.

15. The apparatus of claim 14 in which the image altering means increases the pixel parameter values of the pixels in the first patch by a first amount, and decreases the pixel parameter values of the pixels in each second patch by a second amount, the first and second amounts depending on position within the patch.

16. A method of processing an original source signal to yield an encoded source signal having N-bits of auxiliary data hidden therein, N being at least one, the original source signal having a representation including plural elements, each having a parameter value, the method including changing the parameter values of said elements to encode the auxiliary data therein, and scaling a magnitude of said changes in accordance with said parameter values, wherein elements of the source signal representation having larger parameter values are changed relatively more than elements of the source signal representation having smaller parameter values.

17. The method of claim 16 wherein the source signal is a pixel domain representation of an image, rather than a representation thereof in another domain, and said elements are pixels therein.

18. The method of claim 16 wherein said changing includes increasing some parameter values, and decreasing other parameter values.

19. The method of claim 16 wherein the source signal represents an image, and said parameter values are luminance values within said image.

20. The method of claim 16 wherein said scaling is linear, so that elements having parameter values differing by a factor of two have corresponding changes whose magnitudes differ by a factor of two.

21. The method of claim 16 wherein the source signal represents image data, and said changes are slight enough as to be inconspicuous to a human viewer of the image.

22. The method of claim 16 wherein the source signal represents still image data.

23. The method of claim 16 in which N is at least two.

24. The method of claim 16 which includes changing parameter values at other elements adjoining said plural elements.

25. The method of claim 24 in which said other elements adjoin said plural elements in the pixel domain.

26. The method of claim 24 which includes increasing parameter values at elements adjoining plural elements whose parameter values are increased, and decreasing parameter values at elements adjoining plural elements whose parameter values are decreased.

27. The method of claim 24 in which the values of said other elements are changed in value less than the values of said plural elements adjacent thereto.

28. The method of claim 16 including selecting said plural elements so as to reduce human-perceptible corruption of the source signal.

29. The method of claim 28 in which the source signal represents pixels of an image, and said selecting includes identifying pixels of relative extrema therein.

30. A method of encoding N bits of first data, N being at least one, within a work of authorship represented by plural elements of second data, each element having a value, the method including, for each bit of the first data:

mapping said bit to at least one element of the second data by a process that includes a random function; and

changing the value of said at least one element of the second data;

wherein changes to the work of authorship are essentially human imperceptible.

31. The method of claim 30 wherein N is at least two.

32. The method of claim 30 wherein the work of authorship is an image, and the plural elements of second data comprise pixels.

33. The method of claim 30 in which the change in value to said at least one element of the second data is dependent, at least in part, on the value of said bit of the first data.

34. The method of claim 30 in which the mapping includes identifying elements of the second data having an advantageous data hiding property, and selecting from said identified elements.

35. The method of claim 34 in which the advantageous data hiding property is a relative extrema among said plural elements.

36. The method of claim 30 wherein the mapping comprises mapping said bit to plural elements of the second data.

37. The method of claim 30 which further includes changing other elements of the second data that adjoin said at least one element.

38. The method of claim 30 which further includes changing the value of said at least one element of the second data in accordance with another factor not related to the bit of the first data.

39. A method of encoding N-bits of auxiliary data within a source signal, N being at least one, the method including:

evaluating data hiding characteristics of plural locations in the source signal; and

encoding the auxiliary data in the source signal, avoiding the locations that have poor data hiding characteristics;

wherein the auxiliary data is encoded where it is relatively less perceptible, said encoding resulting in changes to the source signal that are so slight as to be essentially imperceptible to humans.

40. The method of claim 39 in which the source signal is comprised of samples, each having a binary value, and the encoding includes:

increasing the values of certain source signal samples;

decreasing the values of other source signal samples;

the foregoing steps changing the values of more than N samples, wherein redundant encoding of at least part of said auxiliary data is effected.

41. The method of claim 39 wherein the source signal represents image data.

42. The method of claim 39 wherein the source signal represents still image data.

43. The method of claim 39 in which N is at least two.

44. The method of claim 39 which includes increasing values of source signal samples adjoining the certain source signal samples whose values are increased, and decreasing values of source signal samples adjoining the certain source signal samples whose values are decreased.

45. The method of claim 44 in which the values of the adjoining source signal samples are changed in value less than the certain source signal samples adjacent thereto.

46. A method of encoding N-bits of auxiliary data within an image represented by a set of data, N being at least one, the method including:

evaluating data hiding characteristics of different portions of said set of data; and

encoding the auxiliary data in the set of data, avoiding the portions that have poor data hiding characteristics;

wherein the auxiliary data is encoded where it is relatively less perceptible, said encoding resulting in changes to the image that are so slight as to be essentially imperceptible to humans.

47. The method of claim 46 in which N is at least two.

48. A method of encoding N-bits of auxiliary data within an image represented by a set of data, N being at least one, the method including:

identifying portions of the set of data having a predetermined data hiding attribute; and

changing the set of data in at least certain of said portions to effect encoding of the auxiliary data therein;

wherein the auxiliary data is encoded where it is relatively less perceptible, said encoding resulting in changes to the image that are so slight as to be essentially imperceptible to humans.

49. A method of encoding N-bits of auxiliary data within a source signal, N being at least one, the method including:

identifying portions of the source signal having a predetermined data hiding attribute; and

changing the source signal in at least certain of said portions to effect encoding of the auxiliary data therein;

wherein the auxiliary data is encoded where it is relatively less perceptible, said encoding resulting in changes to the source signal that are so slight as to be essentially imperceptible to humans.

50. The method of claim 49 in which the source signal is comprised of samples, each having a binary value, and the encoding includes:

increasing the values of certain source signal samples;

decreasing the values of other source signal samples;

the foregoing steps changing the values of more than N samples, wherein redundant encoding of at least part of said auxiliary data is effected.

51. The method of claim 49 wherein the source signal represents image data.

52. The method of claim 49 wherein the source signal represents still image data.

53. The method of claim 49 in which N is at least two.

54. The method of claim 49 which includes increasing values of source signal samples adjoining the certain source signal samples whose values are increased, and decreasing values of source signal samples adjoining the certain source signal samples whose values are decreased.

55. The method of claim 54 in which the values of the adjoining source signal samples are changed in value less than the certain source signal samples adjacent thereto.