Patent ID: 8545928

Claim:
A method of writing variable data to a fluorescence mark region of a digital image defining a document to be printed, said method comprising: defining first colorant mixture data for a first colorant combination; defining second colorant mixture data for a second colorant combination, the first and second colorant combinations being a metameric pair that define respective first and second colors that are at least substantially indistinguishable in visible light; defining a fluorescence mark region using said first colorant mixture data and said second colorant mixture data, said fluorescence mark region comprising colorant-free areas; defining third colorant mixture data for a third colorant combination that defines a third color that varies in average color from both said first and second colors in visible light; wherein said first, second and third colorant mixtures each comprise one or more colorants; modifying said fluorescence mark region to define a double layer fluorescence mark region including said fluorescence mark and also including at least one visible light object defined by the third colorant mixture data; wherein said modifying step comprises writing said third colorant mixture data into said fluorescence mark region to replace at least some of said first and second colorant mixture data with said third colorant mixture data while masking at least some of said colorant-free areas of said fluorescence mark region with a mask to prevent writing of said third colorant mixture data to said colorant-free areas of said fluorescence mark region such that said fluorescence mark region includes said first, second, and third colors and also includes said colorant-free areas that are protected by said mask; printing said digital image on paper including said double layer fluorescence mark region, wherein said first, second, and third colors defined respectively by said first, second, and third colorant mixture data are printed, with said third color and one of said first and second colors being darker or lighter than the other of said first and second colors when said printed document is viewed in UV light.