Synthesis of authenticable halftone images with non-luminescent halftones illuminated by an adjustable luminescent emissive layer

Patent metadata

Field	Value
Publication number	US-9085190-B2
Application number	US-201213716226-A
Country	US
Kind code	B2
Filing date	Dec 17, 2012
Priority date	Dec 17, 2012
Publication date	Jul 21, 2015
Grant date	Jul 21, 2015

Abstract

A method and computing system are proposed for producing an authenticable security device with two sides. The verso side is covered with an adjustable luminescent emissive layer formed by invisible luminescent ink halftones and possibly a UV absorbing printed layer. The recto side is covered with transmissive non-luminescent ink halftones. The backlit colors resulting from the emissions of the luminescent layer or resulting from illumination by normal white light through the transmissive non-luminescent ink halftones are predicted by a backlighting model. This model enables computing the surface coverages of the luminescent and/or non-luminescent ink halftones in order to obtain a desired color either under excitation light (UV light) or under normal white light. This enable creating authenticable backlit images substantially similar to pre-stored reference images, either under normal white light, under excitation light, or under both the normal white light and the excitation light.

First claim

The invention claimed is:

1. A computer-based method for producing an authenticable security device as part of a valuable item, said security device comprising at least one luminescent emissive layer composed of luminescent emissive material and one non-luminescent layer composed of non-luminescent light absorbing ink halftones, authenticable by observing a backlit color image under normal white light and under excitation light, the method comprising the steps of
(a) selecting an authentication intent from the set of (i) accurate luminescent backlit color image under excitation light, (ii) accurate non-luminescent backlit color image under normal white light, (iii) jointly accurate non-luminescent backlit color image under normal white light and accurate backlit luminescent color image under excitation light;
(b) performing a gamut mapping between an input color space and a color space deduced from the selected authentication intent;
(c) establishing according to the selected authentication intent a non-luminescent ink surface coverage separation table associating to colors mapped according to said gamut mapping corresponding surface coverages of the non-luminescent inks;
(d) by relying on said non-luminescent ink surface coverage separation table, separating by computation an input image with colors mapped according to said gamut mapping into surface coverages of non-luminescent inks;
e) halftoning and printing said surface coverages of non-luminescent inks, thereby forming said non-luminescent layer;
where said luminescent emissive layer is superposed with said non-luminescent layer, with a separating transmissive layer between them.

2. The method of claim 1 , where said separating transmissive layer is a layer made of a material selected from the set of paper and plastic.

3. The method of claim 1 , where an additional UV absorbing non-luminescent ink halftone layer is placed on top of said luminescent emissive layer, thereby locally adjusting its emission intensity and where said non-luminescent ink surface coverage separation table also comprises surface coverages of the UV absorbing non-luminescent ink halftones.

4. The method of claim 1 , where said luminescent emissive material emits light at variable intensity and is formed by an element selected from the set of variable luminescent emissive ink halftones, variable luminescent emissive ink pixel dot sizes, variable emissive material concentration, and variable emissive material thickness.

5. The method of claim 4 , where in case that said authentication intent is an accurate luminescent backlit color image under excitation light, a backlighting model for predicting the luminescent backlit colors is used for establishing said non-luminescent ink surface coverage separation table;
where in case that said authentication intent is an accurate non-luminescent backlit color image under normal light, a transmittance prediction model for predicting the transmitted colors of the non-luminescent transmissive image is used for establishing said non-luminescent ink surface coverage separation table;
and where in case that said authentication intent is a jointly accurate non-luminescent backlit color image under normal white light and accurate backlit luminescent color image under excitation light, a joint emissive-transmissive prediction model predicting the color stimuli resulting from the luminescent emissive ink halftones transmitted through the non-luminescent transmissive image is used for calculating the surface coverages of the luminescent emissive ink halftones.

6. The method of claim 5 , where the backlighting model for predicting the backlit color stimuli resulting from emission spectra transmitted through the non-luminescent transmissive image relies on luminescent backlit spectra predicted by multiplying the spectra emitted by surface coverages of the luminescent ink halftones with the surface coverage dependent transmittances of the light absorbing non-luminescent ink halftones.

7. The method of claim 6 , where the equation yielding the luminescent backlit spectra E T as a function of surface coverages u I of the luminescent emissive ink halftones and of the surface coverages u J of the non-luminescent ink halftones is

E
T

⁡

(

a
i

,

a
j

,

E
i

,

T
j

)

=

(

∑
i

⁢

⁢

D
i

⁡

(

u
I

)

·

E
i

⁡

(
λ
)

1
n

)

n

·

(

∑
j

⁢

⁢

D
j

⁡

(

u
J

)

·

T
j

⁡

(

Assignees

• Andres Julien
• Hersch Roger D
• Ecole Polytech

Inventors

• Andres Julien
• Hersch Roger D

Classifications

• G07D7/122

  Physics · mapped topic

• B41M3/144 Primary

  using fluorescent, luminescent or iridescent effects · CPC title

• B42D25/00

  Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof (printing processes to produce identification or security features B41M3/14) · CPC title

• B42D2033/06

  Operations & Transport · mapped topic

• B41M3/14

  Security printing {(securities B42D25/29)} · CPC title