Digital watermarking using stochastic screen patterns

Claim 1

A process for generating a document to be authenticated, wherein an authentication image inserted therein is not readily visually perceptible, including the steps of: generating a first stochastic halftone pattern, and generating a first user image using said first stochastic halftone pattern; generating a second stochastic halftone pattern, related and distinct from the first; generating a second user image using the first stochastic halftone pattern, and replacing portions of said second user image using the second stochastic pattern to form the authentication image therein; whereby upon placing the first and second user images in superposition relationship to allow viewing of both user images together, correlation between the first stochastic halftone pattern in the first and second user images occurs everywhere within the first and second user images where the first stochastic halftone pattern is used, and visible non-correlation occurs where the area where the second stochastic pattern occurs and the authentication image placed therein using the second stochastic screen becomes visible to authenticate the document to be authenticated.

Claim 6

A method of providing a document to be authenticated including the steps of: generating a first user image from a first stochastic halftone pattern; generating a second user image, using the first stochastic halftone pattern and a second, different stochastic halftone pattern, said second stochastic pattern used to form an authentication image in the second user image; for a document to be authenticated and distributed, including therein one of said first and second user images; providing the other of said first and second images to a user for authentication purposes; providing a viewing arrangement to view said first and second user images in registered superposition, whereby correlation areas and non-correlation areas render said authentication image visible therein.

Claim 7

A method of providing a document to be authenticated including the steps of: generating a first user image from a first stochastic halftone pattern; generating a second user image, using the first stochastic halftone pattern and a second, different stochastic halftone pattern, said second stochastic pattern used to form an authentication image in the second user image; for a document to be authenticated and distributed, including therein one of said first and second user images; providing the other of said first and second images to a user for authentication purposes; providing a viewing arrangement to view said first and second user images in registered superposition, whereby correlation areas and non-correlation areas render said authentication image visible therein.

Claim 9

A method of providing a document to be authenticated including a continuous tone image, said continuous tone image defined pixels each having an intensity defined by an N-bit pixels, including: generating a first user image from a first stochastic halftone pattern comprising binary values representing said first user image; generating a second user image, using the first stochastic halftone pattern and a second, different stochastic halftone pattern, comprising binary values representing said second user image, said second stochastic pattern used to form an authentication image in the second user image; receiving said document containing said continuous tone image defined by pixels, the intensity of which are defined by N-bit values; for an area of the document containing said continuous tone image, replacing a first less significant bit value, with binary values from said first user image.

Claim 10

A method of providing a document to be authenticated including a continuous tone image, said continuous tone image defined pixels each having an intensity defined by an N-bit pixels, including: generating a first user image from a first stochastic halftone pattern comprising binary values representing said first user image; generating a second user image, using the first stochastic halftone pattern and a second, different stochastic halftone pattern, comprising binary values representing said second user image, said second stochastic pattern used to form an authentication image in the second user image; receiving said document containing said continuous tone image defined by pixels, the intensity of which are defined by N-bit values; for an area of the document containing said continuous tone image, replacing a first less significant bit value, with binary values from said first user image.

Claim 13

A method of providing a document to be authenticated including a continuous tone image, said continuous tone image defined pixels each having an intensity defined by an N-bit pixels, including: receiving said document containing said continuous tone image defined by pixels, the intensity of which are defined by N-bit values, as a first user image; generating a second continuous tone user image defined by pixels, the intensity of which are defined by N bit values, including a set of binary values at a less significant bit thereof, which are derived from a less significant bit of the first user image; inserting into the second user image, an image pattern varying from said second user image, to form an authentication image in the second user image.

Claim 14

A method of providing a document to be authenticated including a continuous tone image, said continuous tone image defined pixels each having an intensity defined by an N-bit pixels, including: receiving said document containing said continuous tone image defined by pixels, the intensity of which are defined by N-bit values, as a first user image; generating a second continuous tone user image defined by pixels, the intensity of which are defined by N bit values, including a set of binary values at a less significant bit thereof, which are derived from a less significant bit of the first user image; inserting into the second user image, an image pattern varying from said second user image, to form an authentication image in the second user image.

Claim 18

A method for generating watermarks in a digitally reproducible document which are substantially invisible when viewed including the steps of: (1) producing a first stochastic screen pattern suitable for reproducing a gray image on a document; (2) deriving at least one stochastic screen description that is related to said first pattern; (3) producing a document containing the first stochastic screen; (4) producing a second document containing one or more of the stochastic screens in combination, whereby correlation between the first stochastic pattern on each document occurs everywhere within the documents where the first screen is used, and correlation does not occur where the area where the derived stochastic screens occur and the image placed therein using the derived stochastic screens becomes detectable.

Claim 19

A method for generating watermarks in a digitally reproducible document which are substantially invisible when viewed including the steps of: (1) producing a first stochastic screen pattern suitable for reproducing a gray image on a document; (2) deriving at least one stochastic screen description that is related to said first pattern; (3) producing a document containing the first stochastic screen; (4) producing a second document containing one or more of the stochastic screens in combination, whereby correlation between the first stochastic pattern on each document occurs everywhere within the documents where the first screen is used, and correlation does not occur where the area where the derived stochastic screens occur and the image placed therein using the derived stochastic screens becomes detectable.

Claim 20

A method of providing a document to be authenticated including a continuous tone image described by at least one separations, each separation of said continuous tone image defined by pixels each having an intensity defined by N-bits, including: generating an authentication image from a first pattern comprising binary values in a less significant bit in one of said separations; generating an authentication key image, using the first pattern and a second, different pattern, in a different less significant bit in one of said separations; whereby upon placing the authentication image and key in superposition relationship to allow viewing of both user images together, correlation between the first stochastic halftone pattern in the first and second user images occurs everywhere within the first and second user images where the first stochastic halftone pattern is used, and visible non-correlation occurs where the area where the second stochastic screen occurs and the authentication image placed therein using the second stochastic pattern becomes visible to authenticate the document to be authenticated.

Claim 21

A method of providing a document to be authenticated including a continuous tone image described by at least one separations, each separation of said continuous tone image defined by pixels each having an intensity defined by N-bits, including: generating an authentication image from a first pattern comprising binary values in a less significant bit in one of said separations; generating an authentication key image, using the first pattern and a second, different pattern, in a different less significant bit in one of said separations; whereby upon placing the authentication image and key in superposition relationship to allow viewing of both user images together, correlation between the first stochastic halftone pattern in the first and second user images occurs everywhere within the first and second user images where the first stochastic halftone pattern is used, and visible non-correlation occurs where the area where the second stochastic screen occurs and the authentication image placed therein using the second stochastic pattern becomes visible to authenticate the document to be authenticated.