A computer-based method for producing a printed authenticable daylight luminescent color halftone image visible under daylight, comprising the steps of (a) selecting a luminescent set of inks comprising at least one daylight luminescent ink, selecting a non-luminescent set of inks comprising only non-luminescent inks, forming with said luminescent set of inks a luminescent gamut and forming with said non-luminescent set of inks a non-luminescent gamut; (b) selecting an output gamut from an intersection of said non-luminescent and luminescent gamuts; (c) mapping by computation the gamut of input image colors onto said output gamut by applying a gamut mapping step selected from the set of gamut expansion and gamut reduction; (d) under a reference illuminant, establishing by computation a color to surface coverage mapping between the gamut mapped input image colors and surface coverages of inks forming said luminescent set of inks; (e) relying on said color to surface coverage mapping, separating by computation the gamut mapped input image colors into ink layer color separations of said luminescent set of inks; (f) halftoning and printing said ink layer color separations, thereby obtaining said printed authenticable daylight luminescent color halftone image comprising a message which remains hidden under a reference illuminant and which is revealed under an illuminant different from the reference illuminant; where said reference illuminant is a white illuminant active in the visible wavelength range; where said daylight luminescent color halftone image is authenticated by examining its excitation trace image under an illuminant active within its excitation wavelength range and by comparing it with a previously registered excitation trace image; where the message is generated by printing with one of said selected non-luminescent and luminescent sets of inks within areas of said message and with the other of said selected non-luminescent and luminescent sets of inks outside areas of said message. (a) selecting a luminescent set of inks comprising at least one daylight luminescent ink, selecting a non-luminescent set of inks comprising only non-luminescent inks, forming with said luminescent set of inks a luminescent gamut and forming with said non-luminescent set of inks a non-luminescent gamut; (b) selecting an output gamut from an intersection of said non-luminescent and luminescent gamuts; (c) mapping by computation the gamut of input image colors onto said output gamut by applying a gamut mapping step selected from the set of gamut expansion and gamut reduction; (d) under a reference illuminant, establishing by computation a color to surface coverage mapping between the gamut mapped input image colors and surface coverages of inks forming said luminescent set of inks; (e) relying on said color to surface coverage mapping, separating by computation the gamut mapped input image colors into ink layer color separations of said luminescent set of inks; (f) halftoning and printing said ink layer color separations, thereby obtaining said printed authenticable daylight luminescent color halftone image comprising a message which remains hidden under a reference illuminant and which is revealed under an illuminant different from the reference illuminant;