ENCODING MESSAGE DATA IN A COVER CONTONE IMAGE VIA HALFTONE DOT ORIENTATION

• US 20100060942A1
• Filed: 09/10/2008
• Published: 03/11/2010
• Est. Priority Date: 09/10/2008
• Status: Active Grant

• Current Assignee: University of Rochester, Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: SHARMA, Gaurav, BULAN, Orhan, MONGA, Vishal
• Granted Patent: US 8,023,160 B2
• Time in Patent Office: Days
• US Class Current: 358/3.280
• CPC Class Codes: G06K 1/121 by printing code marks applying code marks to labels B65C9/46; marking or coding completed packages B65B61/26
• CPC Class Codes: G06K 2019/06234 miniature-code
• CPC Class Codes: G06T 1/005 Robust watermarking, e.g. average attack or collusion attack resistant
• 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: H04N 1/32203 Spatial or amplitude domain methods H04N1/32309 takes 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 1/32256 in halftone 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

Abstract

What is disclosed is a novel system and method for encoding/decoding data in a cover contone image via halftone dot orientation modulation. Arrays of halftone threshold values are used to determine a desired orientation, e.g. 0/90°±45° for a given single data value of the original message to be embedded. Message data is embedded as a function of halftone dot orientation. Detection modeling of the print-scan process enables the determination of dot orientation from the image scan via statistically motivated image moments. A probabilistic model of the print-scan channel conditions received moments on input orientation. Density values of the received moments are used to determine dot orientation for each halftone cell. The embedded data is retrieved based on the determined orientations. The present method is applicable to areas of data embedding, document security, and the like.

Claims

1. A method for embedding data in an image via halftone dot orientation, the method comprising:

receiving a cover contone image having an intensity value associated with each pixel location of said image, a data message is to be embedded in said received image, said message comprising a plurality of data values, each single data value taking only one unique state from a set of possible values;

defining a uniform periodic tiling for said image, each of said uniform tiles having identical dimensions and encompassing an array of pixel intensity values;

for each unique state, defining an array of threshold values, each array of threshold values having a one-to-one correspondence with each array of pixel intensity values, and wherein each of said threshold values in said threshold array is defined for a given screen frequency and a given dot shape;

for each single data value of said message, identifying a unique uniform periodic tile wherein a single data value is to be embedded;

for each identified unique periodic tile wherein a current single data value is to be embedded, comparing each intensity value in said current periodic tile with a corresponding value of said threshold array defined for the unique state of said current single data value, said comparison producing a binary output value for each pixel location in said current tile, all of said comparisons collectively producing a binary mask for said current tile; and

rendering said image, each unique periodic tile wherein a single data value is to be embedded is rendered according to said binary mask produced for that tile.

2. The method of claim 1, wherein said produced a binary output value comprises one of a binary value of 1 for a pixel being turned “

ON”

at said pixel location, and a binary value of 0 for a pixel being turned “

OFF”

at said pixel location.

3. The method of claim 1, further comprising associating a unique orientation direction with each of said unique states, each of said unique orientation directions being oriented with respect to a horizontal and a vertical axis of the rendered image.

4. The method in claim 1, wherein said array of threshold values is determined using a spot function comprising:

T(x,y)=sgn(cos(2π

f_xx)cos(2π

f_yy))|cos(2π

f_xx)|^2x|cos(2π

f_yy)|<sup>γ

y</sup>,

wherein γ

_x, γ

_y are selected such that each possible state of said data values yields a preferential orientation in a specific direction representative of said state.

5. The method in claim 4, wherein two sets of values for γ

_x, γ

_y are chosen and two rotations of the coordinate axes are utilized so that said data values take on one of four possible states corresponding respectively to 0, 90, ±

45, and −

45 degree orientations.

6. The method of claim 1, further comprising defining at least one region within said image wherein said data message is to be embedded and only embedding single data values of said data message in said defined region.

7. The method of claim 1, further comprising performing error control coding on said message prior to embedding said message in said image.

8. A system for embedding data in an image via halftone dot orientation, the system comprising:

a storage medium capable of storing data; and

a processor in communication with said storage medium, said processor capable of executing a machine readable instruction for performing the method of;

receiving a cover contone image having an intensity value associated with each pixel location of said image, a data message is to be embedded in said received image, said message comprising a plurality of data values, each single data value taking only one unique state from a set of possible values;

for each unique state, defining an array of threshold values, each array of threshold values having a one-to-one correspondence with each array of pixel intensity values, and wherein each of said threshold values in said threshold array is defined for a given screen frequency and a given dot shape;

for each single data value of said message, identifying a unique uniform periodic tile wherein a single data value is to be embedded;

for each identified unique periodic tile wherein a current single data value is to be embedded, comparing each intensity value in said current periodic tile with a corresponding value of said threshold array defined for the unique state of said current single data value, said comparison producing a binary output value for each pixel location in said current tile, all of said comparisons collectively producing a binary mask for said current tile; and

rendering said image, each unique periodic tile wherein a single data value is to be embedded is rendered according to said binary mask produced for that tile.

9. The system of claim 8, wherein said produced a binary output value comprises one of a binary value of 1 for a pixel being turned “

ON”

at said pixel location, and a binary value of 0 for a pixel being turned “

OFF”

at said pixel location.

10. The system of claim 8, further comprising associating a unique orientation direction with each of said unique states, each of said unique orientation directions being oriented with respect to a horizontal and a vertical axis of the rendered image.

11. The system in claim 8, wherein said array of threshold values is determined using a spot function comprising:

T(x,y)=sgn(cos(2π

f_xx)cos(2π

f_yy))|cos(2π

f_xx)|^2x|cos(2π

f_yy)|<sup>γ

y</sup>,

wherein γ

_x, γ

_y are selected such that each possible state of said data values yields a preferential orientation in a specific direction representative of said state.

12. The system in claim 11, wherein two sets of values for γ

_x, γ

_y are chosen and two rotations of the coordinate axes are utilized so that said data values take on one of four possible states corresponding respectively to 0, 90, +45, and −

45 degree orientations.

13. The system of claim 8, further comprising defining at least one region within said image wherein said data message is to be embedded and only embedding single data values of said data message in said defined region.

14. The system of claim 8, further comprising performing error control coding on said message prior to embedding said message in said image.

15. A computer program product for embedding data in an image via halftone dot orientation, the computer program product comprising:

a computer-usable data carrier storing instructions that, when executed on a computer, cause the computer to perform a method comprising;

receiving a cover contone image having an intensity value associated with each pixel location of said image, a data message is to be embedded in said received image, said message comprising a plurality of data values, each single data value taking only one unique state from a set of possible values;

defining a uniform periodic tiling for said image, each of said uniform tiles having identical dimensions and encompassing an array of pixel intensity values;

for each unique state, defining an array of threshold values, each array of threshold values having a one-to-one correspondence with each array of pixel intensity values, and wherein each of said threshold values in said threshold array is defined for a given screen frequency and a given dot shape;

for each single data value of said message, identifying a unique uniform periodic tile wherein a single data value is to be embedded;

for each identified unique periodic tile wherein a current single data value is to be embedded, comparing each intensity value in said current periodic tile with a corresponding value of said threshold array defined for the unique state of said current single data value, said comparison producing a binary output value for each pixel location in said current tile, all of said comparisons collectively producing a binary mask for said current tile; and

rendering said image, each unique periodic tile wherein a single data value is to be embedded is rendered according to said binary mask produced for that tile.

16. The computer program product of claim 15, wherein said produced a binary output value comprises one of a binary value of 1 for a pixel being turned “

ON”

at said pixel location, and a binary value of 0 for a pixel being turned “

OFF”

at said pixel location.

17. The computer program product of claim 15, further comprising associating a unique orientation direction with each of said unique states, each of said unique orientation directions being oriented with respect to a horizontal and a vertical axis of the rendered image.

18. The computer program product in claim 15, wherein said array of threshold values is determined using a spot function comprising:

T(x,y)=sgn(cos(2π

f_xx)cos(2π

f_yy))|cos(2π

f_xx)|^2x|cos(2π

f_yy)|<sup>γ

y</sup>,

wherein γ

_x, γ

_y are selected such that each possible state of said data values yields a preferential orientation in a specific direction representative of said state.

19. The system in claim 18, wherein two sets of values for γ

_x, γ

_y are chosen and two rotations of the coordinate axes are utilized so that said data values take on one of four possible states corresponding respectively to 0, 90, +45, and −

45 degree orientations.

20. The computer program product of claim 15, further comprising performing error control coding on said message prior to embedding said message in said image.