Color adaptive watermarking

• US 20040125983A1
• Filed: 07/03/2003
• Published: 07/01/2004
• Est. Priority Date: 02/14/2000
• Status: Active Grant

• Current Assignee: Digimarc Corporation
• Original Assignee: Digimarc Corporation
• Inventors: Reed, Alastair M., Rhoads, Geoffrey B.
• Granted Patent: US 7,391,880 B2
• Time in Patent Office: Days
• US Class Current: 382/100
• 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

A color mapping process enhances a watermark by computing a change in colors that is less visible for a given watermark strength. The mapping process provides smooth transitions from one color region to another, and may be implemented efficiently with a 3D look up table. A user interface scheme enables the user to control encoding of the watermark in desired color regions.

Claims

1. A method of color masking an image comprising:

reading color values of an image sample and a corresponding change of an attribute of the image sample; and

based on the color values of the image sample, mapping the change in the image sample attribute to a change in color components of the image sample that is equivalent to the change in the image sample attribute, yet reduces visibility of the change in the image sample attribute for the specific color values of the image sample.

2. The method of claim 1 wherein the image sample attribute is luminance.

3. The method of claim 1 wherein the image sample attribute is chrominance.

4. The method of claim 1 wherein the image sample attribute to be modified changes based on the color values of the image sample.

5. The method of claim 1 including:

repeating the method of claim 1 to effect changes to image sample attributes of image samples in an image as part of a process to encode a substantially imperceptible watermark in the image that carries auxiliary data.

6. In a watermark encoder, a user interface method comprising:

presenting a user interface to enable a user to control strength of a watermark to be encoded in a specified color or color region;

based on user input, controlling strength of a watermark encoded in the specified color or color region.

7. The method of claim 6 including:

providing visual feedback to the user to show how changes in the specified color or color region change an image encoded with the watermark.

8. The method of claim 6 including:

enabling the user to specify a color region by enabling the user to select a portion of an image to be watermarked and deriving a color or color region from image samples in the selected portion.

9. The method of claim 6 including:

altering the strength of the watermark in the specified color or color region so as to allow for a smooth transition in watermark strength between the selected color or color region and other colors or color regions.

10. A computer readable medium on which is stored software for performing the method of claim 6.

11. A method encoding an image with a digital watermark, wherein the image comprises a plurality of color channels, said method comprising:

determining a color characteristic for a group of image samples;

based at least in part on the characteristic, determining for the group of image samples which of the plurality of color channels should receiving encoding;

transforming from the group of image samples at least one determined color channel that should receive encoding into a transform domain; and

altering transform domain coefficients of the at least one determined color channel to encode the digital watermark.

12. The method of claim 11, further comprising transforming the altered color channel into a spatial domain.

13. The method of claim 11, where the characteristic identifies which of the color channels will best hide the digital watermark in terms of visibility.

14. A method of encoding a color image with an auxiliary signal, wherein the auxiliary signal comprises encoding values, and wherein the color image comprises an array of color values, said method comprising:

providing a set of encoding values for an image sample;

determining a color characteristic for the image sample based on its color values; and

selectively scaling color values in the image sample based on the color characteristic.

15. The method of claim 14, wherein scaling effects a change in luminance.

16. The method of claim 15, wherein the scaling comprises a scale to black.

17. The method of claim 15, wherein the scaling comprises a scale to white.

18. The method of claim 14, wherein the color characteristic comprises yellow content.