Method of Printing Authentication Indicators with Amplitude Modulated Halftone Printing

A method of printing authentication indicators by applying an at least amplitude-modulated halftone print in a detection zone to an object, comprising:

• providing a halftone mountain having a plurality of halftone planes, wherein individual tone values of the halftone print are associated to the halftone planes for a halftone dot to be printed,
• providing adjoining halftone cells in the detection zone, wherein each halftone cell comprises a plurality of printable halftone elements, which halftone elements are arranged in a matrix,
• printing a halftone dot in each halftone cell from the matrix of printable halftone elements,
• wherein the associated halftone plane of the halftone mountain is modified in the detection zone in a predetermined manner for a plurality of tone values of halftone dots to be printed, and
• wherein a predetermined matrix image of the halftone elements to be printed is assigned to it while the tone value of the print remains constant.

A authenticating method of a printed object, wherein an at least amplitude-modulated halftone print in a detection zone is printed on this object, comprising:

• providing a portable image capture device having a microprocessor for executing an authentication program and having access to print data relating to the printed object,
• storing in the print data:
• data relating to a halftone mountain having a plurality of halftone planes, wherein individual tone values of the halftone print are associated to the halftone planes for a halftone dot to be printed,
• data relating to adjoining halftone cells in the detection zone, wherein each halftone cell comprises a plurality of printable halftone elements, which halftone elements are arranged in a matrix,
• data relating to the printed halftone dots in the halftone cells from the matrix of printable halftone elements,
• data relating to the predetermined modification, for a plurality of tone values of printed halftone dots, of the associated halftone plane of the halftone mountain in the detection zone, wherein a predetermined matrix image of the halftone elements to be printed is assigned to it while the tone value of the print remains constant,
• taking an image of a detection zone of the printed object,
• selecting a predetermined number of halftone dots in said detection zone from the image of the printed object,
• determining a print image of the detection zone predetermined from the halftone mountain data for a predetermined number of halftone dots of the printed object from said detection zone for a plurality of tone values,
• providing a computer program for identifying captured halftone dots from the image of the detection zone of the printed object,
• providing a computer program for comparing the captured halftone dots with the print image predetermined from the halftone mountain data for the plurality of predetermined tone values,
• comparing the taken print image of said halftone dots with the print images predetermined from the halftone mountain data for the same tone value, and
• deciding on the basis of the comparison whether or not there is an original print on the printed object.