Granted Patent B2

US 8,098,880 · App. 11/897,826 · Granted Jan 17, 2012

Abstract

Claims (35)

1. A method for digital watermarking of a multi-color image, comprising:

receiving the image to be watermarked;

determining the watermarks to be embedded in the image;

embedding a plurality of invisible digital watermarks into the image, wherein a first watermark is embedded into a first color layer and a second watermark is embedded into a second color layer; wherein embedding a plurality of invisible digital watermarks, further comprises

for each color layer in which watermarks are embedded, generating a multi-dimensional threshold array, and

using the multi-dimensional threshold array, pixel-wise halftoning the image to embed the watermarks therein, and

outputting the watermarked image containing the embedded invisible digital watermarks, wherein at least two of the color layers in the image include invisible digital watermarks therein.

2. The method according to claim 1 , wherein pixel-wise halftoning further comprises applying a phase-shift transition.

3. The method according to claim 2 , wherein applying a phase-shift transition further comprises, for a given location with coordinates x and y, choosing an input value from the image and a threshold value determined by the coordinates x and y, for a phase shift s, and where the resultant gray level g is read from the processed watermark image.

4. The method according to claim 1 , further comprising applying a low-pass filter to the image before embedding the watermark.

5. The method according to claim 4 , wherein halftones for each of said first and second watermarks are distinguished from one another by a shift in an angle between the respective color channels.

6. The method according to claim 5 , wherein the shift in the angle is between about 5 degrees and about 45 degrees.

7. The method according to claim 5 , wherein the shift in the angle is 30 degrees.

8. The method according to claim 4 , wherein halftones for each of said first and second watermarks are distinguished from one another by a shift in frequency between the respective color channels.

9. The method according to claim 1 , wherein generating a multi-dimensional threshold array includes storing the resultant array data in a memory.

10. A method for digital watermarking of a multi-color image, comprising:

receiving the image to be watermarked;

determining a first watermark, a second watermark and a third watermark to be embedded in the image;

embedding the first, second and third watermarks into the image, wherein the first watermark is embedded into a first color layer, the second watermark is embedded into a second color layer and the third watermark is embedded into a third color layer; and

outputting the watermarked image containing the embedded invisible digital watermarks, wherein the image includes invisible digital watermarks in at least three of the color layers therein and where embedding a plurality of invisible digital watermarks, further comprises

for each color layer, in which watermarks are embedded, generating a multi-dimensional threshold array, and

using the multi-dimensional threshold array, pixel-wise halftoning the image to embed each of the watermarks therein.

11. The method according to claim 10 , wherein pixel-wise halftoning further comprises applying a phase-shift transition.

12. The method according to claim 11 , wherein applying a phase-shift transition further comprises, for a given location with coordinates x and y, choosing an input value from the image and a threshold value determined by the coordinates x and y, for a phase shift s, and where the resultant gray level g is read from the processed watermark image.

13. The method according to claim 10 , further comprising applying a low-pass filter to the image before embedding the watermark.

14. The method according to claim 10 , wherein halftones for each of said first, second and third watermarks are distinguished from one another by a shift in an angle between the respective color channels.

15. A system for digital watermarking of a multi-color image, comprising:

an input image source;

image memory for storing the input image to be watermarked;

watermark memory for storing the watermarks to be embedded in the image;

an image processor for embedding a plurality of invisible digital watermarks into the image, wherein a first watermark is embedded into a first color layer and a second watermark is embedded into a second color layer;

a low-pass filter, operating in conjunction with said image processor, to smooth edges of the input image prior to embedding of a watermark; and

a multi-dimensional threshold array operatively associated with said image processor to provide varying and independent thresholds for each of a plurality of color layers based upon a variable.

16. The system of claim 15 , wherein said variable is a shift in the angle between respective color layers.

17. The system of claim 15 , wherein said variable is a change in the frequency of a screen applied between respective color layers.

Assignments (9)