Patent ID: 8659799

Claim:
A method of printing an image encoded with an IR watermark on a substrate associated with a printing device including a plurality of colorants, the method comprising: a) generating a first device dependent multidimensional color space representation of the printing device using a first constant value of one or more of the plurality of colorants as an input to a calibration process, the first device dependent multidimensional color space representation defining a first gamut associated with the printing device; b) generating a second device dependent multidimensional color space representation of the printing device using a second constant value of the one or more of the plurality of colorants as an input to the calibration process, the second constant value of the one or more of the plurality of colorants offset from the first constant value of the one or more of the plurality of colorants, the second device dependent multidimensional color space representation defining a second gamut associated with the printing device; c) defining an effective gamut associated with the printing device formed by the intersection of the first gamut and second gamut; d) defining a third device dependent multidimensional color space representation of the printing device including only the first device dependent multidimensional color space representation of the printing device using the first constant value of one or more of the plurality of colorants within the effective gamut; e) defining a fourth device dependent multidimensional color space representation of the printing device including only the second device dependent multidimensional color space representation of the printing device using the second constant value of one or more of the plurality of colorants within the effective gamut; f) generating a device dependent multidimensional color space representation of the image encoded with the watermark by encoding the watermark using a metameric pair of device dependent multidimensional color space representations of the image color associated with the watermark location, the metameric pair including a first metamer of the image color derived from the third device dependent multidimensional color space representation of the printing device to generate a first fixed infrared response and a second metamer of the image color derived from the fourth device dependent multidimensional color space representation of the printing device to generate a second fixed infrared response, whereby the differential infrared response of the metameric pair is substantially constant; and g) printing the device dependent multidimensional color space representation of the image encoded with the watermark on the substrate using the associated printing device.