Note: Descriptions are shown in the official language in which they were submitted.
1066109
This invention relates to (1) a method of photo-
graphic reproduction of differences in the intensity
of light received from an object so as to create a line
deflection image, viz. an array of spaced lines in
which light intensity differences are recorded as
deviations of the lines from a predetermined array,
(2) the resultant line deflection image thus created,
and (3) a method of simulating a readily perceptible
image of the original object by means of superimposition
of the predetermined array on the resultant.
BACKGROUND OF THE INVENTION
It is known to use a half-tone screen for the
purpose of obtaining a photographic reproduction
of an original object suitable for printing. Such
half-tone reproductions may be obtained, for example,
by interposing a lined glass screen or vignetted contact
screen between the object photographed and the camera
lens. A high-contrast film may then be used to obtain
a negative in which bright areas are reproduced as
lines of relatively large width, and dark areas are
reproduced as lines having relatively small width.
The positive obtained from such negative will simulate,
by means of lines of varying width, the contrast of the
original object photographed.
It is also known to generate a relief or medallion
effect in the printing of an image by means of
variations in the direction of lines in a pattern of
lines constituting such image. Such effects have typically
been created by means of hand engraving by an artisan.
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It has also been previously proposed, as an anti-
counterfeiting measure in security printing, to create on a
printed article a pattern which does not readily convey
meaningful information to the unaided eye, but which conveys
meaningful information (e.g. readily recognizable image) when
a "finding screen" viz. a screen having a predetermined line
pattern or the like, is superimposed upon the printed article.
SUMMARY OF THE INVENTION
It is proposed, according to the present invention,
to utilize a novel variation of the aforementioned photographic
technique to devise a line deflection image. The line deflec-
tion image is obtained by combining the negative and offset
positive of a high-contrast half-tone image created in accordance
with the foregoing half-tone photographic technique. The
resultant is a photographically-derived image comprised of
lines of varying orientation, which can be used inter alia to
generate medallion effects and to generate "hidden" images
which become readily apparent to the eye when the images thus
created are overlaid by a finding screen having the same line
pattern as that through which the original object was photo-
graphed.
To this end, the object is first of all photographed
in conventional manner on high-contrast film through a line
screen to obtain a line negative in which bright areas are
reproduced as lines of uniform maximum width and dark areas
are reproduced as lines of uniform minimum width. The exposure
is arranged so that the lines of maximum width are separated
from one another by a distance equal to the width of any of
the lines of minimum width. Grey or transition areas are
reproduced as tapering lines of width varying from the maximum
to the minimum.
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A positive of the negative is then developed. The
positive is superimposed upon the negative almost exactly in
register but with the lines of the positive offset from the
lines of the negative through a distance equal to the said
minimum width. The result is a line deflection image, viz.
a set of spaced lines in which light intensity differences are
reproduced as deviations of the lines from the line pattern
of the line screen. If the lines of the line screen are of
uniform width and spacing, the lines of the line deflection
image will be of uniform width.
A line deflection image of a simple object obtained
in accordance with the foregoing procedure will frequently
create a medallion effect, particularly if the critical
dimensions of the object are of the same order of magnitude
as the line spacing in the line deflection image. More complex
objects having a high information content are reproduced in
line deflection image form as line patterns containing only
gross visual information. These images when viewed with the
unaided eye do not seem to contain more than a minimum of
information. However, if a lined transparency having the same
line pattern as that of the line screen pattern used to create
the negative from which the line deflection image was obtained
is superimposed upon the line deflection image, all of the
detail of the half-tone photographic reproduction is revealed
to the observer.
The invention is thus seen to afford a relatively
simple photographic technique for (a) simulating medallion
effects and (b) generating "hidden" images whose information
content is revealed when a finding screen is superimposed
thereon. Heretofore these effects had to be generated by
relatively laborious manual techniques.
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A special application of the invention lies in
the generation of coloured transitory image patterns of
the type described and claimed in Canadian Patent No.
1,019,012 entitled COLOURED TRANSITORY IMAGES IN PRINTED
ARTICLES (R. Gordon Hutton and Trevor Merry) which issued
on 11 October 1977.
Reference has been made herein to "lines". sy a
"line" is meant a continuous narrow visual effect, whether
constituted by an absolutely continuous line or by series
of dots or spaced line segments. Conveniently, the line
screen used to generate the high-contrast negative from
which the line deflection image is obtained is a ruled
parallel straight line screen. However, it could conceivably
be comprised of a system of non-parallel straight or curved
lines. Indeed, for some anti-counterfeiting purposes it
may be useful to employ a more complex line screen pattern
than the convenient simple parallel line pattern.
The invention is a method of generating a line
deflection pattern, comprising
developing line-screen high-contrast negative and
positive photographic representations of an object in which
bright areas are represented in the negative by relatively
thick lines of generally uniform width and in the positive by
relatively thin lines of generally uniform width, dark areas
are represented in the negative by relatively thin lines of
generally uniform width and in the positive by relatively thick
lines of generally uniform width, and grey areas are represented
in both the negative and the positive by transitional line
areas in which the width of the line varies from the width of
the said thin lines to the width of the said thick lines, and
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wherein the thin lines of the negative are of substantially the
same width as the thin lines of the positive and the thick lines
of the negative are of substantially the same width as the thick
lines of the positive; and
offsetting the negative with respect to the positive
in a direction generally perpendicular to the direction of
extension of the lines through one thin line width while other-
wide maintaining alignment of the negative with the positive.
SUMMARY OF THE DRAWINGS
Figure 1 is a schematic greatly magnified partial
view of a high contrast negative of a parallel-line screened
object.
Figure 2 is a schematic magnified view of a corner
portion of a high-contrast negative of a parallel-line
screened object.
Figure 3 is a schematic magnified view of a corner
portion of a positive obtained from the negative of Figure 2.
Figure 4 illustrates the manner in which the
positive of Figure 3 is offset from and superimposed upon
the negative of Figure 2 to obtain a line deflection image
in accordance with the teachings of the present invention.
Figure 5 is an object composed of relatively
simple visual elements.
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Figure 6 is a line deflection image of the object
of Figure 5.
Figure 7 is a line deflection image obtained from
a relatively complex object, viz. the photographic portrait
of a woman.
Figure 8 is a regular arrangement of straight parallel
lines having the same frequency as the lines of the screen
used to generate the line deflection image of Figure 7.
Figure 9 illustrates the result of superimposing the
line arrangement of Figure 8 upon the line deflection image
of Figure 7.
Figure 10 is a schematic greatly magnified view of a
portion of a line screen comprised of non-parallel straight
lines.
Figure 11 is a schematic greatly magnified partial
view of a high-contrast negative obtained from an object
photographed through a line screen comprised of non-parallel
straight lines.
Figure 12 is a schematic magnified view of a portion
of a line screen comprised of wavy lines.
Figure 13 is a schematic greatly magnified partial
view of a high-contrast negative obtained from an object
photographed through a line screen comprised of wavy lines.
DETAILED DESCRIPTION WITH REFERENCE TO DRAWINGS
Figure 1 is a small portion of a line negative of
an object showing only a greatly enlarged detail of two adjacent
exposed areas 11, 13 on the negative. These lines each com-
prise, in that portion seen in Figure 1, a narrow portion (lla,
13a), a tapering portion (llb, 13b) and a wide portion (llc,
13c) respectively. Portions lla, 13a represent areas of low-
light intensity, areas llc and 13c represent relatively bright
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areas, and areas llb, 13b represent transition areas (grey
areas) between light areas and dark areas. These line-type
reproductions may be conventionally obtained on high-contrast
lithographic film (for example the film manufactured by the
Eastman-Kodak Company under the trade mark Kodalith), by means
of photographing the object through a lined glass screen,
vignetted contact screen or the like. The film and exposure
are selected so that the separation distance _ between adjace~t
dark areas llc, 13c is equal to the width _ of the narrow
exposed areas lla, 13a. It follows that the narrow areas lla,
13a are separated by a distance a equal to the width a of a
wide line area llc, 13c.
In Figure 2, a line negative 19 obtained in the above
manner has a plurality of adjacent dark lines 21, 23, 25, 27
and 29. Figure 3 shows a portion of the positive 32 of the
negative of Figure 2, and thus it shows the dark line (exposed)
areas 21 etc. of the negative 19 reproduced as white line or
empty space areas 31, 33, 35, 37, 39. If the positive of
Figure 3 is then superimposed upon the negative of Figure 2
with the upper left corner point 30 of the positive arranged
to lie below the upper left corner point 20 of the negative by
the distance s between adjacent lines of the positive (i.e.
the width s of a dark line of minimum thickness of the negative
corresponding to an unexposed area) then the resultant of the
Figure 4 is obtained. In this Figure, a plurality of lines 41,
43, 45, 47, 49, etc. of uniform width but of varying contour
are obtained. It will be observed that the change in contour
of the lines 41, 43, 45, 47, 49, etc. occurs at exactly the
areas of transition at which the wide portions of the lines on
the negative converge to narrow lines (i.e. at the grey areas
where bright area wide lines converge to dark area narrow lines).
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In other words, changes in density have been transformed via
the procedure just described to changes in line orientation
or contour. The resultant of Figure 4 may conveniently be
described as a line deflection image, which is the term used
herein.
Figures 5 and 6 illustrate the results of the
aforementioned technique. Figure 5 is a subject which contains
a relatively broad dark or black area 51, a broad bright or
white area 53, a broad grey area 55, and some finer detail,
namely the legend "$5000". Figure 6 is a line deflection image
of Figure 5. It can be observed that at the transition points
between those areas of Figure 5 of differing brightness, a
line deflection occurs in the line deflection image of Figure 6.
The effect for the broad areas is to generate, by means of
the visual continuity of the points of line deflection, a
visual outline of the broad shapes (triangular and square) of
Figure 5.
The effect for the finer detail is somewhat different
and surprising. If the spacing of the lines in the line
deflection image is chosen to be of the same order of magnitude
as the widths of areas constituting a visually significant
portion of a subject, the line deflection image generates a
relief or medallion effect in respect of such areas. This
effect is apparent in Figure 6 in respect of the line deflection
image reproduction of the "$5000" legend. The relief or medal-
lion effect of the Figure 6 reproduction of the legend will
be enhanced for at least some observers by viewing the Figure
at an angle or increasing the distance between the eye and
the Figure.
It is thus seen that the invention affords a simple
means of generating photographically medallion effects which
10661(~9
heretofore have been generated conventionally by hand engraving
or the like'.
Where the detail of the subject is appreciably finer
than the spacing of the lines in the line deflection image,
the visually apparent information content of the line deflection
image is relatively low, but can be made visually apparent
by the superimposition on the line deflection image of a finding
screen whose line pattern is the same as that of the vignetted
screen or the like which was used in the creation of the nega-
tive from which the line deflection image was obtained. Toillustrate the foregoing, Figure 7 is a line deflection image
of the portrait of a woman, which can be seen to have relative
low information content. The overall view can barely be
recognized as one resembling the portrait of a woman. The line
deflection image of Figure 7 was prepared using a straight
parallel line screen (Figure 8). When the parallel line screen
of Figure 8, whose line spacing is equal to the average line
spacing of Figure 7, is superimposed upon the line deflection
image of Figure 7, a startling result is achieved. Figure 9
illustrates the resulting superimposition of the parallel
line screen of Figure 8 on the contour line array of Figure 7.
It can be seen that the result of this superimposition is to
make apparent to the observer all of the latent information
content of Figure 7.
The alignment of the line deflection image of Figure 7
with the screen of Figure 8 must be carefully selected to
obtain a positive. If the screen of Figure 8 were shifted
transversely through the distance between adjacent lines, then
a negative instead of a positive image would have appeared in
Figure 9.
lOS6109
Figure 8 may be considered a "finding screen" for
the line deflection image of Figure 7. If, for example,
the line deflection image of Figure 7 had been printed on a
security document such as a bank note or share certificate,
the superimposition by an observer of the finding screen of
Figure 8 (which may for example take the form of parallel dark
lines printed on a plastic transparency) on the document would
reveal the hidden image and thus tend to confirm that the
document was genuine. Departures from accuracy in the reproduc-
tion of the line deflection image (by counterfeiters, say)would tend to become accentuated in the visual effect obtained
by superimposition of the finding screen on the reproduction,
and thus detection of a counterfeit may be faciliatated through
the use of the invention. Furthermore, if the line deflection
image itself is not readily apparent on the document, as can
easily be devised through "camouflaging" of the image by other
art work on the document, a counterfeiter may not know that a
line deflection image is present, and may not recognize the
importance of accurate reproduction of the fine detail on the
document.
A special use of the present invention lies in the
generation of coloured transitory images of the type described
in copending Canadian Patent No. 1!019,012 - Hutton and Merry
entitled "Coloured Transitory Images in Printed Articles",
which issued on 11 October 1977. In that patent, disclosure is
made of printed articles bearing alternating coloured lines of
two different colours which are selectively occluded by embossed
lines in the articles so as to cause changes in visual effects as
the angle of view of the article is varied. A rècognition pattern
appears as a transitory image which can be generated by off-
setting or phase-shifting the alternating coloured line arrange-
ment in the recognition pattern area with respect to the
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alternating coloured line arrangement in the background.
Alternatively, the coloured line arrangement may be uniform
throughout and the recognition pattern generated by off-
setting the embossed lines in the recognition pattern area
with respect to the embossed lines in the background. In
either case, a line deflection image according to the
present invention can be prepared of the desired recognition
pattern, and the line deflection image then used to generate
either the coloured line arrangement or the embossed line
arrangement on the printed article. (The line deflection
image of Figure 6, for example, could be used to reconstruct
as a transitory image the recognition pattern of Figure 5.)
If the line deflection image is reproduced as the
coloured line pattern, then the embossed line image required
to complement the coloured line image on the printed article
should be generated as the equivalent of the "finding screen"
complementing the line deflection pattern in question.
Similarly, if the line deflection pattern is reproduced on
the printed article as a pattern of embossed lines, then the
coloured line pattern on the printed article should be
equivalent to the complementary finding screen for that
particular line deflection pattern. The lines of the line
deflection pattern in either case should extend in generally
the same direction as the lines of the complementary pattern,
but need not be exactly in register. The effects of generating
the two patterns on the documents slightly out of register
so as to create moiré effects and the like is discussed
in further detail in the aforementioned Canadian Patent
No. 1,019,012.
If the line deflection pattern is used to generate
the embossed line pattern on the printed article, then the
object photographed should include some low contrast areas
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~066109
so that there will be a phase shift of less than one
embossed line width in the resulting line deflection
pattern. As described in more detail in Canadian Patent
No. 1,019,012, a phase shift of less than one embossed
line width is required in order to produce the satisfactory
transitory image. On the other hand, if the line deflection
pattern is used to generate the coloured line pattern, then
object photographed to generate the line deflection pattern
should include some high contrast detail. This would give
the maximum line deflection and thus would be approximately
a deflection of about one coloured line width. This
condition is also required for the reproduction of good
transitory images as described in greater detail in
Canadian Patent No. 1,019,012. The difference in the two
approaches for the embossed line pattern on the one hand
and the coloured line pattern on the other is of course
explained by the fact that the embossed line frequency is
one-half the coloured line frequency (the embossed line
frequency is the same as the line frequency of either one
of the colours but since the two colours alternate, the
total line frequency is double that of the embossed lin~
frequency).
An example of a high contrast detail is represented
in Figure 5 by the black and white triangular areas, which
give rise to maximum line deflection as appears from
Figure 6. An example of low contrast detail is exemplified
in Figure 5 by the transition between the white triangle
and the grey background or between the black triangle and
the grey background. It can be seen by referring to Figure 6
that the line deflection going from the background area to
either the black triangle or the white triangle is less than
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the line deflection going from the white triangle to the
black triangle.
The pattern of lines used for generating the
negative (or as a complementary screen) need not be a
pattern of parallel straight lines. Figures 10 and 12
show respectively a pattern of converging straight lines
and a pattern of regular wavy lines, each of which could be
used to achieve essentially the same kind of resulting line
deflection image.
Figure 10 shows as a pattern for the line screen
tor complementary finding screen), a pattern of converging
lines (shown in greatly magnified portional view in Figure
10). A portion of the further magnified converging line
pattern of a representative negative obtained from such line
screen is illustrated in Figure 11. The extent of convergence
is, within limits, arbitrary, but over a six-inch length of
printed document, a variation from 60 lines per inch to 100
lines per inch is representative. The angle of convergence
in Figures 10 and 11 is exaggerated for purposes of illustra-
tion. The opaque and transparent areas of the screen of
Figure 10 would be of equal (but different) widths at each
end of the screen and would taper uniformly from one end
to the other. Again, in Figure 11, the bright areas of
the object photographed appear as thick opaque lines 111 and
the darker areas of the object photographed generate only
relatively narrow opaque lines 113. The production of a
positive from the negative is obtained in the manner previously
described, and the composite line deflection image is again
obtained by shifting the positive through a distance _,
variable over the length of the pattern, equal to the width
o a narrow line 113 at every point along the length of the
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converging line system. This means that, for example, if
at one end of the document the lines occupy 1/60 of an
inch and at the other end, the lines occupy 1/100 of an
inch, then at the first end of the document, the positive
would be displaced with respect to the negative by 1/60
of an inch, and at the other end of the document would be
displaced by 1/100 of an inch with respect to the negative.
The above result can be obtained in a different
way without using the line screen of Figure 10 and the
negative of Figure 11. Instead, the parallel line screen,
negative and positive described with reference to Figures 1
to 4 and 8 can be used to generate a line deflection pattern
as previously described. Then the line deflection pattern
and line screen can be subjected to optical distortion (as
by inclining the object with respect to the camera) to
generate a converging line deflection pattern and finding
screen.
Referring to Figure 12, the wavy line pattern to
be used to generate the negative comprises alternate opaque
and transparent wavy lines of uniform thickness. Again, the
pattern is presented in greatly magnified portional view.
A portion of a representative resulting negative is illustrated
in Figure 13 in further magnified view. The bright areas
of the object photographed generate relatively wide opaque
areas 91 on the high contrast film, whereas the darker areas
of the object photographed generate only relatively narrow
opaque lines 93. A positive can be made, in the same manner
described previously, from the negative of Figure 13. The
positive and negative are then combined with the positive
offset from the negative through a distance _ representing
the thickness of one of the narrow lines 93 of Figure 13,
so as to generate a resultant line deflection image in which
~;066109
the variations resulting from changes in contrast appear
as deflections from the basic wavy line pattern.
The resultant line deflection image derived from
any of the aforementioned line screen patterns can be
characterized as comprising latent visual information super-
imposed upon a basic pattern of lines. The latent informa-
tion can be considered to comprise differential dark areas
which when "added" to a superimposed complementary finding
screen yield a resultant total visual effect conveying
relatively high information content to the eye. The informa-
tion content is disguised by the fact that the differentials
or variations are present in a line pattern that, in the
absence of the dark areas contributed by the finding screen,
does not appear to the eye to have the same degree of
information content. The reason for this apparently is
that it is very difficult, sometimes virtually impossible,
for the mind or the eye to perform the addition without the
actual presence of the finding screen.
Variations in the techniques described above may
occur to those skilled in the art. The scope of the invention
is not to be considered limited by specific examples dis-
cussed above but is as set forth in the appended claims.
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