METHOD FOR VISUALLY CUSTOMISING AN IDENTITY DOCUMENT
COMPRISING A LATENT IMAGE
The invention relates to a method for visually
customizing an identity document by customizing a latent
image.
An identity document should be understood here to
be any document produced by an issuer for a user in order
to enable him to justify his identity; it is in practice
a data medium, containing visual and/or electronic data,
such as a passport or an identity card, a care services
access card (such as a VitaleB card in France) or a
financial services access card (credit card) or a
communication card (telephone card, even SIM cards, even
mini-SIM cards or the like) or a card for accessing any
other type of services (various subscriptions, for
example sporting activities).
Such an identity document must be able to include
personal data, specific to its user, for example a visual
information item such as a photo representing this user
as faithfully as possible; it may also be desirable to
allow this user to choose a particular appearance even
when it is not of a visual nature unique to this card
(for example, by choice of an image out of a limited list
of possible images). Such a visual customization can be
done during the creation of the document itself, but the
benefit to be gained in being able to proceed with such a
customization in a step as late as possible, and
therefore as close as possible to the handover of this
document to its user, will be understood.
In this respect, a technique is known (see in
particular the documents WO-2011/124774 and
W0-2013/093230) whereby the fabrication of the documents
includes a step of formation of a latent image topped by
a mechanically protecting transparent layer, consisting
of a uniform array of elementary zones respectively
having different colors chosen from a small number of
possible colors (in practice three primary colors (they
can be blue, yellori and red, or the triplet known by the
acronym RGB (red, green and blue)), and white); in the
latent state, the uniform distribution of the zones of
each color is reflected by the fact that the latent image
has a neutral appearance, close to white and without any
detectable pattern; the mechanically protecting
transparent layer has the effect of preventing the
operations of handling of the document from being able to
alter the latent image, since the image obtained by
customization can then be modified easily. When a
customization of the document is desired, some of the
zones of the array are subjected to a more or less
significant darkening (even blackening) treatment, so as
to form a particular image comprising local variations of
intensity according to each of the initial colors; such a
darkening can be performed by local heat effect, or by
local photosensitive effect, which is compatible with the
existence of the protective transparent layer (the
material in which the various zones are formed is chosen
according to the technique used to darken them); in
practice, this darkening is obtained by total or partial
carbonization of each of the elementary zones concerned,
typically by application of a laser beam; the colors
chosen for the elementary zones are advantageously chosen
as being reflecting so as to subsequently promote a
contrast between the darkened zones and the intact zones.
In fact, the abovementioned documents mention that
the darkening can be done, depending on circumstances, at
the very point where the elementary zones are located, or
thereabove, in the protective transparent layer, even
thereunder.
The elementary zones are grouped together in lots
comprising at least one zone of each color (including
white) and a pixel of the customization image to be
formed is associated with such a lot; in the
abovementioned documents, each elementary zone is called
" sub-pixel".
It should be noted that this technique makes it
possible to form a latent image on a wide variety of
surfaces, planar, curved, even a surface locally
including reliefs.
It will be understood that the possible darkening
levels depend on the elementary surface that can be
chosen to be darkened, or not, within an elementary zone;
as an example, for a square elementary zone of 16 microns
a side a laser makes it possible, upon an impact, to
blacken, or not, elementary surfaces of the order of a
micron in diameter; it follows therefrom that it is
possible to define 256 darkening levels for this
elementary zone, which amounts to stating that the
corresponding pixel can be coded on a byte (the greater
the number of bits assigned to each pixel, the greater
the number of possible darkening shades for the
customization image).
Two major categories of arrays of elementary zones
can be envisaged, namely the arrays in which the subpixels
of a lot are in a block, grouped together in a
square (even in a rectangle, or in a hexagon, depending
on the number of elementary zones of each color), and the
arrays in which the pixels of a lot are grouped together
according to a segment (at right angles to the continuous
plotting lines; it will be understood that an array with
lots in segments is easier to form than an array with
lots blocked together (in squares or rectangles), since
it is sufficient to plot continuous lines parallel to the
direction of plotting of the elementary zones; in
particular, the offset printing technique makes it
possible to much more easily plot lines than isolated
zones.
Moreover, rather than having lasers that have a
resolution of the order of a micron (that is to say that
make it possible to blacken, or not, zones of the order ,
of a micron), it may be desirable to use lasers that have
wider beams, of which the impacts close to the arrays of
elementary zones are typically of the order of a few tens
of microns in diameter, but the power of which can be
modulated.
However, a difficulty stems from the fact that the
techniques that make it possible to plot lines for a cost
substantially lower than for the plotting of isolated
zones make it possible in practice to plot only lines of
a width very much greater than the dimensions of such
impacts; in particular, the technical limitations linked
to offset printing require the width of the lines that
can be plotted to be between approximately 50 and
130 microns, which represents at least twice the diameter
of the impacts that can be obtained with lasers of
average performance levels. If a choice is made to
increase accordingly the diameter of the laser impacts,
the printing resolution is consequently reduced parallel
to the lines; it thus seems preferable to accept
generating a number of impacts within the width of the
duly plotted lines and, since these impacts correspond to
a pixel of the image to be plotted, the impacts formed
through a line are identical. The resolution of the image
formed is then much better parallel to the lines than
transversely thereto.
Similarly, when the latent image is formed from
block zones (and not from lines or columns), the
dimensions of these zones may often be greater than those
of the impacts that can be obtained such that the
generation of a number of identical impacts in the two
dimensions of these block zones must be accepted.
The subject of the invention is a method for
customizing a latent image present in an identity
document, which alloris for a good resolution in at least
two directions, even when the elementary zones of each
color are formed in parallel lines.
To this end, the invention proposes a method for
visually customizing an identity document comprising a
latent image formed by an array of single-color portions
distributed in a succession of groups of identical
single-color portions, whereby, for each pixel of a
customization image to be formed on the latent image, a
segment is defined that extends over one of said groups
of single-color portions, each segment being formed by
elementary zones in which a darkening can be generated
with a level chosen from a plurality of possible
darkening levels so as to locally alter the appearance of
the array so as to reproduce, in this segment, said color
of the pixel of the customization image, characterized in
that, the portions having a dimension representing, at
most, a multiple of the average dimension of these
elementary zones, there are generated, in at least some
of the segments, successive darkening levels which are
respectively defined by a pixel of the image to be
reproduced and by at least one adjacent pixel in this
image to be reproduced in a given position.
Preferably, the array of portions corresponds to
columns.
Also preferably, the generation of a darkening
level is done by means of a laser. As a variant, the
generation of a darkening level in an elementary zone is
performed by darkening all of this zone with said
darkening level.
Advantageously, the generation of a darkening level
in an elementary zone is performed by darkening with a
predetermined level of a fraction of the surface of this
elementary zone corresponding to the ratio between the
desired darkening level and said predetermined level.
Preferably, each single-color portion has at least
a width and/or a length formed to receive a multiple of
elementary zones.
Advantageously, there are generated in each of the
segments, through the single-color portions, successive
darkening levels which are respectively defined by a
pixel of the image to be reproduced and by at least one
adjacent pixel in this image to be reproduced in a given
position.
Preferably, the latent image is formed under a
transparent outer layer.
Advantageously, the latent image is formed between
a transparent outer layer and a transparent underlying
layer, these two layers extending over a layer bearing a
visual element.
Preferably, each group of single-color portions
comprises three portions of which the respective colors
are chosen so as to make it possible, jointly, to
reproduce each possible color for the pixels of the
customization image, and a white portion.
The invention further proposes a document that can
be obtained by the method of the abovementioned type; in
particular, it proposes an identity document suitable for
being produced by the method, comprising an array of
single-color portions distributed in a succession of
groups of identical single-color portions, and
comprising, near this array, a plurality of segments
extending over one of said groups of single-color
portions by being formed by elementary zones in which
darkening levels are generated so as to locally alter the
appearance of the array so as to show a customization
image, each darkening level being chosen from a plurality
of possible darkening levels, the darkening levels of at
least some of the segments varying through some of the
single-color portions passed through by these segments.
Preferably, the darkening levels of at least one
series of segments are such that the first elementary
zones through each single-color portion of a segment have
darkening levels equal to those of the second elementary
zones of each single-color portion of an adjacent
segment.
Objects, features and advantages of the invention
will become apparent from the following description,
given in a nonlimiting illustrative manner, in light of
the attached drawing in which:
- Figure 1 is a cross-sectional view of an
identity document according to the invention,
and
- Figure 2 is a plan view of a selection of
pixels produced on the document of figure 1, in
three regions of different resolutions.
Figure 1 represents, in partial cross section, an
identity document according to the invention; it can
notably be a document in the format of a credit card or
an identity card.
This document here comprises a core between two
protective layers. More specifically, this document
comprises a top outer layer 2 topping an underlying layer
3, a top core layer 4 and a bottom core layer 5, a bottom
outer layer 7 running along an underlying layer 6.
The core layers 4 and 5 (which could be replaced by
one core layer or, on the contrary, be replaced by a
greater number of layers) are here opaque, in practice of
white color, for example of polycarbonate; they here have
a thickness of between 100 and 300 microns; they
advantageously have the same thickness; the overall
thickness of these layers 4 and 5 is advantageously
between 300 and 500 microns. One of these layers (even
both) can bear a visual element on its face opposite the
other core layer, for example alphanumeric elements
identifying the holder, or issuer of the document.
The top outer layer 2 is transparent, that is to
say that its thickness and its constituent material allow
visual access to at least what is situated under it;
preferably, the upper underlying layer 3 is also
transparent (notably when visual elements are formed on
the core layer 4). Between these layers a latent image 1
is formed, in practice on only a part of the underlying
layer; as a variant, the latent image is formed on the
bottom face of the protective outer layer, or is formed
on a thin layer sandwiched between these layers 2 and 3.
The formation of such a latent image is known per se (see
the documents WO-2011/124774 and W0-2013/093230) and will
not be described here in more detail.
At least one of the layers 2 or 3 is formed by a
material that can be locally darkened, by heat or other
effect (photochromic or equivalent); it is advantageously
of a material that can be locally darkened by a laser
impact, which is expressed by stating that this material
can be lasered (see also the documents cited above). In a
simple embodiment, at least the layer 2 can be lasered
(that is to say that zones will be able to be darkened in
this zone, on (or above) the latent image 1. These layers
2 and 3 are advantageously leaves of transparent
polycarbonate with a thickness of between 20 and
150 microns (for an overall thickness advantageously of
between 100 and 200 microns); their respective
thicknesses can be equal, but it may be preferable for
them to be different, notably if the desire is to give
the impression that the latent image is at the same level
as the visual formed on the core layer, or, on the
contrary, that this latent image is situated clearly at a
level higher than that of this visual.
The lower layers 6 and 7 can be of any appropriate
materials, in any appropriate thicknesses, depending on
requirements. They can be transparent, for symmetry with
the upper layers; for simplicity, the materials and/or
the thicknesses of these layers are advantageously chosen
as being the same as for the layers 2 and 3.
It will be understood that there can be a number of
latent images on the document concerned, on the same
face, even on both faces of the document.
The latent image 1 has a thickness which is
determined by the technique used to form it; it is in
practice a thickness of between approximately 1 and
10 microns.
It is advantageously formed by an array of parallel
lines, preferably straight. In figure 2, these lines are
vertical and are denoted C1, C2, C3 or C4. This array of
lines is regular in that the lines follow one another in
the same order, in series C1-C2-C3-C4.
Here, these series are of four lines; in effect, in
practice, three colors are enough to generate, by
combination, any other color; the yellow-blue-red triplet
(more specifically, the yellow-cyan-magenta triplet) is
known in particular, as is the red-green-blue triplet);
however, it is often found useful to add the color white.
In other words, the number of lines per series is
advantageously three or four.
The customizing of the latent image consists in
locally darkening zones of these lines, segments
extending through a series of lines making it possible to
define a pixel of an image to be formed.
The darkening of a zone can be done by the
application of a laser impact with a power corresponding
to the desired degree of darkening; as a variant, the
laser has a very fine beam and makes it possible to
darken, to a given level, a greater or lesser fraction of
the elementary colored zone concerned.
A laser impact here denotes an elementary zone that
a laser can darken with a number of desired intermediate
levels between the absence of darkening and a total
darkening (corresponding to the fact that all of the zone
has been subjected to the maximum laser power). It will
be understood that a laser impact of 10% can correspond
equally to an impact affecting all of the surface of the
elementary zone with a power of 10% of the maximum, and
to an impact limited to 10% of the same elementary
surface with a 100% of the maximum power.
Hereinbelow, laser impacts covering all of a
colored elementary zone will be considered, with powers
chosen according to the desired degree of darkening, but
it will be understood that the comments that follow apply
equally to the case of a given darkening of a greater or
lesser fraction of a colored elementary zone.
It will further be considered that the colors
follow from left to right in the following order:
Cl = cyan, C2 = magenta, C3 = yellow and C4 = white.
Returning to figure 2, it can be seen that the
width of each vertical line corresponds to approximately
twice the diameter of a laser impact; to neutralize a
color in a given segment, two laser impacts are therefore
required. As an example, the segment corresponds to a
case where the color C2 has been neutralized; the
resulting color is a light green.
If the segment 52 is considered, it is the column
C3 which is neutralized by two laser impacts, which gives
red. The segment S3, in which the columns Cl and C2 are
neutralized, gives a yellow-brown and the segment 54, in
which the four columns are neutralized, corresponds to
black.
There can be a large number of possible levels
regarding the darkening of each laser impact; in the
example described hereinbelow, there are four levels
(which can be coded on two bits): a level without
darkening (the case of the column C4 in the segment S5),
a low level of darkening (the case of the column C3 in
this segment 55), a high level of darkening (the case of
the column C2 of segment 55) and a maximum level of
darkening (the case of the column Cl of segment 55).
It can be seen that the segments S5 to S7 are
defined by one or other of the darkening levels applied
to each of the colors. Since each segment corresponds to
a given pixel of the image to be formed in the latent
image, each color has an associated given darkening
level, and therefore two laser impacts generated with the
same power.
This can give full satisfaction for the formation
of block zones within the image to be formed; however,
that can lead to a lack of resolution in details,
transversely to the lines of color.
In such a case, the invention teaches abandoning
the association between the segments and the pixels, and
accepting, at least in the position of details meriting a
good resolution, defining each segment as a function of a
number of pixels of the image to be formed; that makes it
possible to bring the resolution of the image, in the
direction transverse to the lines of color, closer to the
resolution parallel to these lines of color.
More specifically, if the segment 58 is considered,
it is observed that it is formed by impacts that can be
different; in fact, this segment is formed by impacts
deducted from two adjacent pixels of the image to be
formed. It will thus be noted that the column C1 of S8
comprises an impact identical to the impacts of the
column C1 of S5 and an impact identical to those of the
column of S6, that the column C2 comprises an impact
identical to those of the column C2 of 55 and an impact
identical to those of the column C2 of S6, and so on.
Similarly, if the segment S9 is considered it is
observed that it is formed by impacts that can be
different; in fact, this segment is formed by impacts
deducted from two adjacent pixels of the image to be
formed. It will thus be noted that the column C1 of S9
comprises an impact identical to the impacts of the
column C1 of S6 and an impact identical to those of the
column of 57, that the column C2 comprises an impact
identical to those of the column C2 of S6 and an impact
identical to those of the column C2 of S7, and so on. The
segment situated to the right of the segment S9 would in
turn be formed, for each color, by a combination of
impacts identical to those of the segment S7 and of that
situated to its right.
If, to reproduce a series of pixels identical to
those reproduced by the segments S5, S6, S7, . the
segment S8 is generated (instead of the segment SS), the
segment S9 is generated (instead of the segment S6), and
so on, an image is obtained that is similar to that
formed by the segments S5, S6, etc., the resolution of
which is locally much better transversely to the color
columns.
In this figure 2, there are therefore zones in
which there is, or not, darkening of a color column
(segments S1 to S4), zones where there is darkening of a
color column by a doublet of impacts generated with a
same power (segments 55 to S7), and zones where the
darkening of a color column can vary in its width, by
generation of impacts of different powers, where it is
desired to increase the resolution transversely to the
color columns.
Thus, according to the invention, the starting
point is an identity document initially comprising a
latent image formed from a regular array of single-color
columns C1-C4 extending in a given direction (here
vertically) and distributed in a succession of groups of
identical single-color columns (Cl-C4, C1-C4, C1-C4 ... ) ;
for each pixel of a customization image to be formed on
the latent image, transversely to the direction of the
columns, a segment is formed that extends transversely
over one of said groups of single-color columns, each
segment being formed by elementary zones in which a
darkening can be generated with a level chosen from a
plurality of possible darkening levels so as to locally
alter the appearance of the array so as to reproduce, in
this segment, said color of the pixel of the
customization image, in accordance with a preestablished
mapping table between each color and the darkening levels
to be generated on each single-color column; the columns
have a width representing a multiple of the average
dimension of these elementary zones (they are in practice
block zones having a form factor of the order of 1); in
at least some of the segments, through the single-color
columns, successive darkening levels are generated which
are respectively defined by a pixel of the image to be
reproduced and by at least one adjacent pixel in this
image to be reproduced in a given position. Thus, the
darkening levels through a single-color column are not
systematically identical, even though that is possible
when the mapping table assigns identical darkening levels
for adjacent pixels to a given color.
Advantageously, each segment of the image is formed
by combination of the impacts corresponding to two
adjacent pixels.
Assuming the width of the color columns to be a
larger multiple of the diameter of the laser impacts (in
which elementary zones for which it is possible to vary
the darkening), each segment will be formed by a
combination of an equal number of adjacent pixels in the
image to be reproduced.
When the width of a column corresponds to a small
number of times (for example two or three times) the
diameter of a laser impact, the adjacent pixels to be
taken into consideration in the image to be reproduced
can be situated at right angles to the direction of the
columns; when the number is greater than two, the pixels
to be taken into consideration can be situated on either
side of the pixel to be reproduced (thus, if the width of
the columns was three times the diameter of the laser
impacts, a segment similar to S9 could comprise, through
each color column, an impact identical to those of the
same color in 55, an impact identical to those of the
same color in S6 and an impact identical to those of the
same color in S7).
In practice, the laser operator has the scope to
adjust the diameter of the impacts to a sub-multiple of
the width of each color column.
What has been described with regard to figure 2
applies equally to any number of possible darkening
levels for each color of each series. However, other
modalities for constructing the plotted pixels are
possible.
Colorimetric base computation work is
advantageously set up upstream, before proceeding with
the least customization. The analysis of each shade to be
obtained can be done by decomposition over three colors
(for example red, green and blue, hence an RGB
combination, in short), and the colorimetric base is used
to make a combination of the colors of which the columns
of the latent image are made up correspond to it.
If each basic color can be coded on a byte, there
are 255*255*255 possible RGB combinations as input
(16 581 375 possible colors), and as many possible
combinations of firings on the CMYW color lines to obtain
a color.
Take for example the following desired values (with
a maximum of 255). and their corresponding degrees of
darkening to be performed to obtain these values:
The sequence sent to the laser, in accordance with
the known solution, can therefore be represented by the
following doublets, by using C1 (PI) to denote the value
of the pixel P1 of the original image for the color C1,
and so on, and Cl(p1) to denote the value of the pixel pl
of the image to be plotted for one of the impacts of the
color C1, and so on:
Pixel 1
Pixel 2
However, in accordance with the invention, each
series of eight pulses is not formed by doublets
corresponding to the color targeted for a given pixel; it
has been proposed, with respect to figure 2, that each
series of eight pulses be formed by an alternation of
impacts corresponding to the targeted pixel and of
impacts corresponding to the adjacent pixel. As a
variant, each series is formed by a succession of impacts
corresponding to a pair of successive pixels different
from those used to form the preceding pixel; thus,
according to this other exemplary implementation of the
invention, the sequence sent to the laser will be:
R
100
0
G
150
100
B
170
240
C1
13
89
C2
128
217
C 3
217
255
C4
6 4
191
in which the question marks are to be replaced by the
values corresponding respectively to the third pixel and
to the fourth pixel to be reproduced in the image
concerned.
A person skilled in the art will be able to modify
accordingly the pixel decomposition of the image to be
reproduced and therefore the data file to be used to
control the impacts.
What has just been described with regard to the
combination of two pixels of the image to be reproduced
to plot the pixels of the image plotted, whether in a
sliding manner (each pixel of the image to be reproduced
being taken into consideration to plot two pixels of the
image plotted) or not (each pixel of the image to be
reproduced being taken into consideration, with another
pixel, only to plot a single pixel of the image plotted),
applies equally to other numbers of pixels taken in
combination.
Thus, according to another embodiment of the
invention, each series of eight pulses is not formed by
doublets corresponding to the color targeted for a given
pixel but is formed by a series of impacts corresponding
to the targeted pixel and of impacts corresponding to the
adjacent pixels; in a first implementation, each pixel of
the plotted image is plotted from eight pixels of the
image to be reproduced ( P I to P8) while the next pixel in
the direction concerned being plotted from a series of
eight pixels repeating some of the pixels used for the
first pixel (that is to say, the pixels P2 to P9);
however, according to another implementation, the
sequence sent to the laser will be:
As previously, a person skilled in the art brill be
able to modify accordingly the pixel decomposition of the
image to be reproduced and therefore the data file to be
used for the plotting of the image desired on the latent
image.
It will be understood that, thus, the resolution is
enhanced without affecting the colorimetric rendering of
the image.
. As .indicated above, the identity document concerned
can be a credit card, a pass for entering into premises,
a national identity card issued by the state of
residence, a driving license, a personalized treatment or
services access card, a pass for entering into premises
or into transport means, etc.
According to the technique used to plot the singlecolor
columns of the latent image, and according to the
requirements, it may be useful to generate 2, 3, even 4
laser impacts (beyond that number, although the invention
can still be put into practice, it seems preferable to
increase the size of the impacts); also, the adjacent
pixels taken into consideration can be, in addition to
the pixel corresponding to the pixel of the image to be
reproduced, the preceding pixel, or the next pixel (even
both) .
The number and the constituent material of the
various layers can be modified. Thus, there may be no
layers behind the document, or only a single layer;
similarly, there may be only a single core layer, even a
single top layer (if the latent image is formed
substantially at the level of the surface of the core
layer. Instead of being opaque, the core layers can also
be transparent. With regard to the materials used, they
can be polycarbonate, but also PETF, PEC, PVC, etc.
The number of single-color lines in each series of
the array can be iimited to tr.10, even be four (even
more), with or without r~ihite (that is to say, with or
without non-printed columns), subject to having
established colorimetric tables for mapping with the
colors to be reproduced. Among the colors used, there are
often blue and red, but the third color can be, depending
on the case, yellow or green, but other combinations may
be preferred depending on the requirements.
The above description has been given in the case of
a laser customization of a latent image situated at a
certain distance under the free face of an identity
document; as a variant, the invention applies also to
cases where the array of single-color columns is not
covered by a protective transparent layer; in such a
case, the darkening of such or such a zone of the array
can be done by a printing technique such as the
deposition of a drop of ink (inkjet) or by deposition of
an opaque resin (for example by heat transfer); the size
of the elementary darkening zone then being defined by
the size of the ink drops or of the resin drops.
It should be noted that an identity document which
has been customized by the method of the invention is
recognized (a simple microscope may suffice) by the fact
that single-color columns of the initial latent image
comprise, through their width, darkening differences.
Furthermore, when the number of segments where the
invention is applied is sufficient, it may be noted on
such an identity document that the darkening levels of at
least one series of segments are such that the first
elementary zones through each single-color column of a
segment have darkening levels equal to those of the
second elementary zones of each single-color column of an
adjacent segment (see the particular sequence described
above) .
It should be noted that the regularity of the singlecolor
zones or portions is not a necessity, given that
the images to be reproduced may involve the available
colors very differently (as an example, blue is of little
use in reproducing faces). Similarly, the fact that the
dimensions of the columns or of the block zones (in which
case there are two right-angled dimensions) are multiples
of the dimensions of the elementary zones is no longer a
necessity in as much as it can be easily taken into
consideration, in the definition of the plotting data,
that certain impacts can simultaneously affect adjacent
zones. An overlapping of the elementary zones can be
envisaged.
CLAIMS
1. A method for visually customizing an identity
document comprising a latent image formed by an array of
single-color portions distributed in a succession of
groups of identical single-color portions, whereby, for
each pixel of a customization image to be formed on the
latent image, a segment is defined that extends over one
of said groups of single-color portions, each segment
being formed by elementary zones in which a darkening can
be generated with a level chosen from a plurality of
possible darkening levels so as to locally alter the
appearance of the array so as to reproduce, in this
segment, said color of the pixel of the customization
image, characterized in that, the portions having a
dimension representing, at most, a multiple of the
average dimension of these elementary zones, there are
generated, in at least some of the segments, successive
darkening levels which are respectively defined by a
pixel of the image to be reproduced and by at least one
adjacent pixel in this image to be reproduced in a given
position.
2. The method as claimed in claim 1, wherein the
array of portions corresponds to columns.
3. The method as claimed in claim 1 or claim 2,
wherein the generation of a darkening level is done by
means of a laser.
4. The method as claimed in any one of claims 1 to
3, wherein the generation of a darkening level in an
elementary zone is performed by darkening all of this
zone with said darkening level.
5. The method as claimed in any one of claims 1 to
3, wherein the generation of a darkening level in an
elementary zone is performed by darkening with a
predetermined level of a fraction of the surface of this
elementary zone corresponding to the ratio between the
desired darkening level and said predetermined level.
6. The method as claimed in any one of claims 1 to
5, wherein each single-color portion has at least a width
and/or a length formed to receive a multiple of
elementary zones.
7. The method as claimed in any one of claims 1 to
6, wherein there are generated in each of the segments,
through the single-color portions, successive darkening
levels which are respectively defined by a pixel of the
image to be reproduced and by at least one adjacent pixel
in this image to be reproduced in a given position.
8. The method as claimed in any one of claims 1 to
7, wherein the latent image is formed under a transparent
outer layer.
9. The method as claimed in any one of claims 1 to
7, wherein the latent image is formed between a
transparent outer layer and a transparent underlying
layer, these two layers extending over a layer bearing a
visual element.
10. The method as claimed in any one of claims 1
to 9, wherein each group of single-color portions
comprises three portions of which the respective colors
are chosen so as to make it possible, jointly, to
reproduce each possible color for the pixels of the
customization image, and a white portion.
11. An identity document obtained by the method as
claimed in any one of claims 1 to 10.
12. An identity document suitable for being
produced by the method as claimed in any one of claims 1
to 10, comprising an array of single-color portions
distributed in a succession of groups of identical
single-color portions, and comprising, near this array, a
plurality of segments extending over one of said groups
of single-color portions by being formed by elementary
zones in which darkening levels are generated so as to
1ocal.ly alter the appearance of the array so as to show a
customization image, each darkening level being chosen
from a plural.ity of possible darkening levels, the :
darkening levels of at least some of the segments varying
through some of the single-color portions passed through '
by this segments.
13. The identity document as claimed in claim 11
or claim 12, in which the darkening levels of at least
one series of segments are such that the first elementary
zones through each single-color portion of a segment have
darkening levels equal to those of the second elementary
zones of each sing1.e-color portion of an adjacent
segme.nt .