System and method for encoding and decoding an image or document and document encoded thereby

A secure document comprising:

• a substrate;
• a pattern formed integral with or carried by the substrate;
• said pattern formed from an array of cells having at least two substructure regions within each cell and displaying an unencoded component visible to the unaided eye of a viewer and an encoded covert image component not readily discernable to the unaided eye of a viewer from any viewing angle without a separate decoder;
• said substructure regions for image cells and for non-image cells having the same geometry but different contrast;
• the image cells having a contrast that is selected from the set:
• (i) diffractive regions, (ii) modulated-diffractive regions, and (iii) non-diffractive regions;
• the non-image cells having a contrast selected from the same set but different from the contrast of the image cells;
• said modulated-diffractive regions having at least one diffractive characteristic different than a diffractive characteristic of said diffractive regions;
• each cell and the at least two substructure regions within each cell being small enough to be not readily discernable to the unaided eye of a human viewer;
• each cell having at least one substructure that is a diffractive region and at least one substructure region that is a non-diffractive or modulated-diffractive region, the ratio of the area of the diffractive region to the area of the non-diffractive or modulated-diffractive region of the at least two substructure regions in each cell of the encoded or unencoded cells being substantially identical;
• the encoded component not visible to an unaided eye being encoded into said pattern by substantially reversing the contrast of each cell forming a portion of the encoded covert image component to change diffractive portions to non-diffractive or modulated-diffractive portions, and to change non-diffractive or modulated-diffractive portions to diffractive portions, the brightness within each cell remaining substantially unchanged as a result of the contrast reversal by maintaining a substantially constant ratio between the diffractive area to the non-diffractive or modulated-diffractive areas among the substructure regions within the cells so that the same amount of light is diffracted to the viewing location from the cells;
• and
• the encoded component not readily visible to an unaided eye of said viewer being rendered visible to the unaided eye of said viewer when viewed through an external decoding device.

A method for making a security device, said method comprising:

• generating a holographic image recording including a first non-covert holographic image having a plurality of diffractive grating elements and second covert image within said plurality of diffractive gratings having a pattern;
• forming said pattern as an array of cells having substructure regions within each cell that present an encoded component not readily discernable to the unaided eye of a viewer from any viewing angle without a separate decoder;
• said substructure regions supporting a contrast reversal upon being decoded and having characteristics selected from the set:
• (i) diffractive regions, (ii) modulated-diffractive regions, and (iii) non-diffractive regions;
• said modulated-diffractive regions having at least one diffractive characteristic different than a diffractive characteristic of said diffractive regions, at least two substructure regions in each cell having different characteristics from the set diffractive, modulated-diffractive, and non-diffractive characteristics;
• a ratio of the area of the different substructure regions within each cell being arbitrary but substantially identical.

A security device comprising:

• a pattern formed from an array of cells having substructure regions within each cell and displaying an unencoded component visible to the unaided eye of a viewer and an encoded covert image component not readily discernable to the unaided eye of a viewer from any viewing angle without a separate decoder;
• said substructure regions supporting a contrast reversal upon being decoded and having characteristics selected from the set:
• (i) diffractive regions, (ii) modulated-diffractive regions, and (iii) non-diffractive regions;
• said modulated-diffractive regions having at least one diffractive characteristic different than a diffractive characteristic of said diffractive regions, at least two substructure regions in each cell having different characteristics from the set diffractive, modulated-diffractive, and non-diffractive characteristics;
• a ratio of the area of the different substructure regions within each cell being arbitrary but substantially identical;
• and
• said pattern organized as an array of cells, each cell being small enough to be not readily discernable to the unaided eye of a human viewer.

A security device comprising:

• a plurality of cells including field cells and image cells encoding a covert image, said field cells and said image cells operating to diffract light in a direction relative to a viewing location;
• said plurality of both field cells and image cells having either substantially identical or similarly shaped substructures, and said substructures comprised of regions with characteristics selected from the set:
• (i) diffractive regions, (ii) modulated-diffractive regions, and (iii) non-diffractive regions;
• said modulated-diffractive regions having at least one diffractive characteristic different than a diffractive characteristic of said diffractive regions;
• at least two substructure regions in each cell having different characteristics from the set diffractive, modulated-diffractive, and non-diffractive characteristics;
• said image cells differing from said field cells by a contrast reversal, said contrast reversal achieved by filling spatially correspondent substructure regions of image cells and field cells with diffractive, modulated-diffractive, or non-diffractive characteristics which are different from each other, and
• a ratio of the area of the different substructure regions within a cell to each other being arbitrary but substantially identical for both said image cells and said field cells.

A secure document comprising:

• a substrate;
• a security pattern formed integral with or carried by said substrate;
• said security pattern formed from a plurality of cells including field cells and image cells encoding a covert image, said field cells and said image cells operating to diffract light in a direction relative to a viewing location;
• said plurality of both field cells and image cells having either substantially identical or similarly shaped substructures, and said substructures comprised of regions with characteristics selected from the set:
• (i) diffractive regions, (ii) modulated-diffractive regions, and (iii) non-diffractive regions;
• said modulated-diffractive regions having at least one diffractive characteristic different than a diffractive characteristic of said diffractive regions;
• at least two substructure regions in each cell having different characteristics from the set diffractive, modulated-diffractive, and non-diffractive characteristics;
• said image cells differing from said field cells by a contrast reversal, said contrast reversal achieved by filling spatially correspondent substructure regions of image cells and field cells with diffractive, modulated-diffractive, or non-diffractive characteristics which are different from each other;
• and
• a ratio of the area of the different substructure regions within a cell to each other being arbitrary but substantially identical for both said image cells and said field cells.

A method for making a security device, said method comprising:

• generating a holographic image recording as a pattern on a substrate, the holographic image including a covert holographic image contained substantially within an area containing a non-covert image;
• forming said pattern as a plurality of cells including field cells and image cells encoding a covert image, said field cells and said image cells operating to diffract light in a direction relative to a viewing location;
• said plurality of both field cells and image cells having either substantially identical or similarly shaped substructures, and said substructures comprised of regions with characteristics selected from the set:
• (i) diffractive regions, (ii) modulated-diffractive regions, and (iii) non-diffractive regions;
• said modulated-diffractive regions having at least one diffractive characteristic different than a diffractive characteristic of said diffractive regions;
• at least two substructure regions in each cell having different characteristics from the set diffractive, modulated-diffractive, and non-diffractive characteristics;
• said image cells differing from said field cells by a contrast reversal, said contrast reversal achieved by filling spatially correspondent substructure regions of image cells and field cells with diffractive, modulated-diffractive, or non-diffractive characteristics which are different from each other;
• and
• a ratio of the area of the different substructure regions within a cell to each other being arbitrary but substantially identical for both said image cells and said field cells.