Method of generating a secure image
AssigneeAssa Abloy AB
InventorsHermann Hecker, Frantz Mercier
Life of this patent
Estimating the term…
Abstract
A secure image for a security document is generated by performing a rasterization process for each of a plurality of mono-color base images using a plurality of different threshold functions. For each base image, the plurality of threshold functions cover different intensity regions and result in a complex rasterization pattern depending on the intensity of the input image. The resulting binary images obtained by the rasterization process are combined using offset printing with fluorescent inks of different colors, to result in a multi-color fluorescent output image including a plurality of different complex rasterization patterns.
Claims20
A non-transitory computer readable medium comprising executable code, that when executed by one or more processors, causes the one or more processors to:
- separate a multi-color input image comprising a plurality of pixels into a plurality of mono-color base images, each pixel in each base image having an intensity value I(x, y) between a minimum intensity value Imin and a maximum intensity value Imax;
- for each base image:
- divide the base image into a plurality of cells;
- provide at least two two-dimensional threshold functions T1(x, y), T2(x, y), . . . , Tn(x, y) for each cell, wherein the threshold functions do not intersect each other and define a plurality of intervals between Imax and Imin, and
- generate a binary image by, for each cell:
- comparing the intensity value I(x, y) of each pixel to the at least two threshold functions to determine an interval including the intensity value of the pixel;
- and
- setting the intensity value of each pixel to one of a first value or a second value associated with the interval, the first value and the second value being alternatingly associated with adjacent intervals;
- and
- generate the secure image by combining all the binary images generated for all the base images.
A method of generating a secure image for a security document, the method comprising:
- separating a multi-color input image comprising a plurality of pixels into a plurality of mono-color base images, each pixel in each base image having an intensity value I(x, y) between a minimum intensity value Imin and a maximum intensity value Imax;
- for each base image:
- dividing the base image into a plurality of cells;
- providing at least two two-dimensional threshold functions T1(x, y), T2(x, y), . . . , Tn(x, y) for each cell, wherein the threshold functions do not intersect each other and define a plurality of intervals between Imax and Imin;
- and
- generating a binary image by, for each cell:
- comparing the intensity value I(x, y) of each pixel to the at least two threshold functions to determine an interval including the intensity value of the pixel;
- and
- setting the intensity value of each pixel to one of a first value or a second value associated with the interval, the first value and the second value being alternatingly associated with adjacent intervals;
- and
- generating the secure image by combining all the binary images generated for all the base images.
A security document comprising a security image generated by a method comprising:
- separating a multi-color input image comprising a plurality of pixels into a plurality of mono-color base images, each pixel in each base image having an intensity value I(x, y) between a minimum intensity value Imin and a maximum intensity value Imax;
- for each base image:
- dividing the base image into a plurality of cells;
- providing at least two two-dimensional threshold functions T1(x, y), T2(x, y), . . . , Tn(x, y) for each cell, wherein the threshold functions do not intersect each other and define a plurality of intervals between Imax and Imin;
- and
- generating a binary image by, for each cell:
- comparing the intensity value I(x, y) of each pixel to the at least two threshold functions to determine an interval including the intensity value of the pixel;
- and
- setting the intensity value of each pixel to one of a first value or a second value associated with the interval, the first value and the second value being alternatingly associated with adjacent intervals;
- and
- generating the secure image by combining all the binary images generated for all the base images.
Dependencies are inferred from the claim text.