# US 10,766,288 B2 · Improving a depth image subject to a shadow effect

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- Number: US 10,766,288 B2
- Document ID: US10766288B2
- Status: Granted
- Kind: B2
- Application number: 16/319,442
- Filed: 2017-07-21
- Published: 2019-08-15
- Granted: 2020-09-08
- Earliest claimed: 2016-07-22
- Assignees: Idemia France
- Applicants: Idemia France
- Inventors: Coralie Vandroux; Benoît Berthe
- Web page: https://patentgrep.com/patent/US10766288B2

## CPC

- B41M 5/24: Ablative recording, e.g. by burning marks; Spark recording {(marking by high energetic means, e.g. by laser otherwise than burning or ablative removal B41M5/26; materials or methods for recording or reproduction by optical means G11B7/00)}
- B41M 3/14: Security printing {(securities B42D25/29)}
- B42D 25/00: 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)
- B42D 25/41: using electromagnetic radiation (B42D25/435 takes precedence)
- G06T 5/94: based on local image properties, e.g. for local contrast enhancement
- B41M: PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING, (correction of typographical errors B41J; processes for applying transfer pictures or the like B44C1/16; fluid media for correction of typographical errors by coating C09D10/00; printing textiles D06P)
- B42D: BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
- G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL

## Abstract

A method and device for producing a target image having pixels (2) juxtaposed in a substrate (1) presenting thickness and producing an image presenting thickness such that each pixel (2) produces a shadowing effect on its neighboring pixels. The method includes: determining a production setpoint from the target image; and producing an image made by the device using the production setpoint. The determining operation replaces the production setpoint with an improved production setpoint that is determined by modeling the image production device using a transfer function for transforming a production setpoint into a predicted image; and determining an improved production setpoint in which the image produced by the transfer function is as close as possible to the target image, so as to reduce the consequences of the shadowing effect in the resulting image. Also included is the image produced by such a method.

## Claims

### Claim 1

A processing method for producing a final image (IR) comprising pixels juxtaposed in a substrate presenting thickness and producing an image that possesses thickness so that each pixel produces a shadowing effect on its neighboring pixels, said method comprising:
determining, using a target image, a production setpoint suitable for being used by an image production device to produce said final image;
wherein the determining comprises:
modeling the image production device by means of a transfer function that transforms a production setpoint into a corresponding predicted image; and
by inverting at least a portion of the transfer function, determining an improved production setpoint suitable for being used as a production setpoint by the production device in order to produce said final image in such a manner as to correct, at least in part, the shadowing effect in the final image.

### Claim 2 (depends on 1)

A method according to claim 1, wherein, during the determining, the improved production setpoint is selected so that the corresponding predicted image is as close as possible to the target image in order to minimize the shadowing effect in the final image.

### Claim 3 (depends on 1)

A method according to claim 1, wherein the thickness of the substrate of the image is not less than n times the transverse dimension of a pixel, where n=1.5.

### Claim 4 (depends on 1)

A method according to claim 1, wherein the image production device is a laser etching device suitable for darkening a transparent substrate and wherein a production setpoint is a map of laser shots.

### Claim 5 (depends on 1)

A method according to claim 1, wherein the image production device is a microperforation device suitable for making microholes a transparent substrate and wherein a production setpoint is a map of perforations.

### Claim 6 (depends on 1)

A method according to claim 1, wherein the modeling of the image production device determines a transmittance for the production setpoint as an intermediate result.

### Claim 7 (depends on 1)

A method according to claim 1, wherein the transfer function F combines a transmittance first function F1 transforming a production setpoint S into a transmittance T, where T=F1(S), a reflectance second function F2 transforming a transmittance T into a reflectance R, where R=F2(T), and an image third function F3 transforming a reflectance R into a predicted image IP, where IP=F3(R), such that IP=F(S)=F3(F2(F1(S))).

### Claim 8 (depends on 7)

A method according to claim 7, wherein the first function F1 is defined in a parametric form, and the parameters are determined by calibration.

### Claim 9 (depends on 7)

A method according to claim 7, wherein the first function F1 is determined empirically and is tabulated.

### Claim 10 (depends on 7)

A method according to claim 7, wherein the second function F2 is given by the following formula:
R
=
F
⁢
⁢
2
⁢
(
T
)
=
b
·
k
1
·
T
2
1
-
k
2
·
T
2
+
(
1
-
b
)
·
k
1
·
(
T
*
M
)
·
T
1
-
k
2
·
(
T
2
*
M
)
where:
R is a reflectance matrix;
bϵ[0,1] is a scalar parameter;
k1, k2ϵ[0,1] are two optical constants;
T is the transmittance matrix;
* is the convolution operator; and
M is a convolution kernel.

### Claim 11 (depends on 10)

A method according to claim 10, wherein the second function F2 also includes noise K having the formula:
R
=
F
⁢
⁢
2
⁢
(
T
)
=
(
b
·
k
1
·
T
2
1
-
k
2
·
T
2
+
(
1
-
b
)
·
k
1
·
(
T
*
M
)
·
T
1
-
k
2
·
(
T
2
*
M
)
)
*
K
where:
* is the convolution operator; and
K is a convolution kernel.

### Claim 12 (depends on 11)

A method according to claim 11, wherein K is a two-dimensional Gaussian kernel of standard deviation σ.

### Claim 13 (depends on 10)

A method according to claim 10, wherein:
k1=(1−rs)·rg·(1−ri) and k2=rg·ri,
where rs is the specular reflection index of the air-image interface, ri is the internal Fresnel reflectance index of the air-image interface, and rg is the intrinsic reflectance index of a Lambertian reflector substrate.

### Claim 14 (depends on 10)

A method according to claim 10, wherein the convolution kernel M is a normalized unity square matrix of dimensions d×d, where M=[1/d2]d×d.

### Claim 15 (depends on 7)

A method according to claim 7, wherein the third function F3 is the identity function.

### Claim 16 (depends on 7)

A method according to claim 7, wherein the transfer function F is calibrated by identifying the parameters b, d and the standard deviation σ, by solving the following equation:
b
,
d
,
σ
=
arg
⁢
min
b
∈
[
0
,
1
]
⁢
⁢
d
>
0
⁢
⁢
σ
^
≥
0
⁢
∑
p
⁢
Δ
⁡
(
IR
p
,
IP
p
)
=
arg
⁢
min
b
∈
[
0
,
1
]
⁢
⁢
d
>
0
⁢
⁢
σ
^
≥
0
⁢
∑
p
⁢
Δ
⁡
(
IR
p
,
F
⁡
(
S
p
)
)
where:
S is a production setpoint;
IR is a final image obtained by means of the production device using the production setpoint S;
IP is a predicted image as predicted by the transfer function F from the production setpoint S, i.e. IP=F(S);
p is an index running through the pixels;
F is the transfer function; and
Δ is a colorimetric distance between two pixels.

### Claim 17 (depends on 16)

A method according to claim 16, wherein the solving operation is fed with calibration pairs comprising a production setpoint S and a final image (IR) by means of the production device using the production setpoint S.

### Claim 18 (depends on 1)

A method according to claim 1, wherein the step of determining an improved production setpoint SA comprises an automatic interactive calculation minimizing a distance between the target image and a predicted image as predicted by the transfer function F when applied to the improved production setpoint SA.

### Claim 19 (depends on 1)

A method according to claim 1, wherein the step of determining an improved production setpoint SA comprises solving the following equation:
SA
=
arg
⁢
min
S
^
⁢
∑
p
⁢
(
Δ
⁡
(
IO
p
,
IP
p
)
)
2
=
arg
⁢
min
S
^
⁢
∑
p
⁢
(
Δ
⁡
(
IO
p
,
F
⁡
(
S
p
)
)
)
2
where:
S is a production setpoint;
IO is a target image;
IP is an image as predicted by the transfer function from the production setpoint S, where IP=F(S);
p is an index running through the pixels;
F is the transfer function; and
Δ is a colorimetric distance between two pixels.

### Claim 20 (depends on 1)

A method according to claim 1, wherein, during the determining, the improved production setpoint is determined so that it also corrects at least in part a laser diffusion effect that can result from laser-material interaction in material of the substrate.

### Claim 21 (depends on 1)

A production setpoint determined by a method according to claim 1.

### Claim 22 (depends on 1)

A method of producing a final image, the method comprising:
using a processor device to determine an improved production setpoint by a method according to claim 1; and
using an image production device to produce said final image by using said improved production setpoint SA as its image production setpoint.

### Claim 23

A processor device configured to produce a final image that comprises pixels juxtaposed in a substrate presenting thickness and producing an image that possesses thickness so that each pixel produces a shadowing effect on its neighboring pixels, said processor device comprising:
an acquisition unit for acquiring a target image; and
a determination unit configured to use the target image to determine a production setpoint suitable for being used by an image production device to produce said final image;
wherein the determination unit is configured to perform operation comprising:
modeling the image production device by means of a transfer function transforming a production setpoint into a corresponding predicted image; and
by inverting at least a portion of the transfer function, determining an improved production setpoint suitable for use as a production setpoint by the production device in order to produce said final image in such a manner as to correct at least in part the shadowing effect in the final image.

### Claim 24 (depends on 23)

A processor device according to claim 23, further comprising:
a production device configured to produce said final image by using said improved production setpoint as its image production setpoint;
wherein the processor device and the production device form a system to produce the final image.