U.S. patent number 3,752,072 [Application Number 05/136,979] was granted by the patent office on 1973-08-14 for process for reproducing a full-color picture in one impression.
Invention is credited to Leslie H. Lorber.
United States Patent |
3,752,072 |
Lorber |
August 14, 1973 |
PROCESS FOR REPRODUCING A FULL-COLOR PICTURE IN ONE IMPRESSION
Abstract
Process for producing an apparent full color print of a
multicolored picture, comprising the steps of: a. with a composite
separation screen having interspersed first and second areas which
transmit substantially red and substantially green information,
respectively, of the multicolor picture, photomechanically forming
upon a printing surface a corresponding composite plate image, the
composite plate image being respective to a substantially neutral
tone dark ink; b. photomechanically forming upon the printing
plate, only in the plate portions corresponding to the first areas
of the composite separation screen, a substantially cyan plate
image of the multicolor picture, the cyan plate image being
receptive to a substantially red ink; c. inking the composite plate
image with the dark ink and the cyan plate image with the red ink;
and d. making a single impression of the printing surface upon a
receiving substrate having a selected pale color.
Inventors: |
Lorber; Leslie H. (Boston,
MA) |
Family
ID: |
22475296 |
Appl.
No.: |
05/136,979 |
Filed: |
April 23, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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754168 |
Aug 20, 1968 |
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Current U.S.
Class: |
101/211;
101/401.1; 101/450.1; 430/6; 430/301 |
Current CPC
Class: |
B41M
1/20 (20130101); G03F 3/04 (20130101); G03G
5/12 (20130101); G03G 13/01 (20130101) |
Current International
Class: |
B41M
1/20 (20060101); B41M 1/14 (20060101); G03G
13/01 (20060101); G03G 5/12 (20060101); G03F
3/04 (20060101); G03F 3/00 (20060101); B41m
001/20 (); B41m 003/00 () |
Field of
Search: |
;101/450-452,211,426,175,176,395,401.1 ;96/30-32 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
"Multicolor Effects on Two-Color Presses" Dupont Magazine,
Sept.-Oct., 1968, Vol. 62 No. 5, pages 2-5, E. I. du Pont de
Nemour, Wilmington, Del..
|
Primary Examiner: Fisher; J. Reed
Parent Case Text
This application is a continuation-in-part of my copending
application Ser. No. 754,168, now abandoned, filed Aug. 20, 1968
and titled PLATES FOR SINGLE-IMPRESSION MULTICOLOR PICTURE AND
TWO-COLOR PRINTING
Claims
What I claim is:
1. Process of producing an apparent full color print of a
multicolored picture, comprising the steps of:
a. with a composite separation screen having interspersed 1st and
2nd areas which transmit substantially red and substantially green
information, respectively, of said multicolor picture,
photomechanically forming upon a printing surface a corresponding
composite plate image, said composite plate image being receptive
to a substantially neutral tone dark ink;
b. photomechanically forming upon said printing plate, only in the
plate portions corresponding to said first areas of said composite
separation screen, a substantially cyan plate image of said
multicolor picture, said cyan plate image being receptive to a
substantially red ink;
c. inking said composite plate image with said dark ink and said
cyan plate image with said red ink; and
d. making a single impression of said printing surface upon a
receiving substrate having a selected pale color.
2. Process according to claim 1 wherein said composite plate image
and said cyan plate image are halftone images.
3. Process according to claim 1 wherein said dark and red inks are
mutually immiscible.
4. Process according to claim 1 wherein said tone of said
substantially neutral tone dark ink is bluish black.
5. Process according to claim 1 wherein said substantially red ink
is bright red.
6. Process according to claim 1 wherein said receiving substrate is
white.
7. Process according to claim 1 wherein said receiving substrate is
greenish white.
8. Process according to claim 1 wherein said substantially red
separation also records a minor amount of blues.
9. Process according to claim 1 wherein said substantially green
separation also records a minor amount of blues.
10. Process according to claim 1 wherein said substantially cyan
separation records blues more strongly than greens.
11. Process according to claim 1 wherein said printing surface has
text printing areas, and said text printing areas are inked with
said dark ink together with said composite plate image.
Description
This invention concerns a process of double-imaging latent 2-color
printing surfaces, and also concerns a method of using any printing
surface imaged as hereinafter described. Considered together, the
two aspects of this invention will advance the art of reproducing a
full-color picture from a single printing surface.
The following definitions will assist understanding:
"Printing Surface" refers generally to an imaged printing plate or
printing cylinder, and particularly to the face thereof;
A "2-Color Printing Surface" or "2-Color Surface" refers to a
printing surface having a 1st image intended to receive ink of a
1st color and a 2nd image intended to receive ink of a 2nd
color;
The term "1st-Image Elements" refers to all elements or portions of
a printing surface associated with a 1st image thereon, and the
term "2nd-Image Elements" refers to all elements or portions of a
printing surface associated with a 2nd image thereon;
A "latent" 2-color printing surface refers to a plate or cylinder,
considered as a whole, which plate or cylinder is structurally
suited to have 1st-image elements and 2nd-image elements formed on
its face;
"Full-Color Picture" refers to subject matter to be graphically
reproduced, normally having pictorial content in flat and/or
gradient tones which may be of any colors;
"Color" refers to a visual sensation commonly ascribed to surface,
e.g., red, green, blue, yellow, cyan, magenta, orange and brown,
also including the "achromatics" white, black and gray, and which
sensations may have any tint or shade or chromatic leaning;
An "effective" reproduction of a full-color picture is here
considered one which appears to contain all colors in the picture
even though the apparent colors are not precisely identical, and
which exhibits good general brightness, deep blacks and sharpness
of detail presuming such qualities were present in the said
picture.
In conventional "Process" printed reproduction of a full-color
picture, at least three inks are required by theory, of the colors
yellow, magenta and cyan, though practice usually demands use of a
fourth ink of black color. Component images in respective ink
colors are successively transferred into coincident register upon a
white substrate, from separate printing surfaces. Mostly by
subtractive interaction, the yellow, magenta and cyan inks,
variously distributed, optically produce close equivalents of all
the colors present in the original picture. The black ink improves
contrast and sharpness of detail, and can also print any
accompanying typographic matter. Process reproductions,
particularly those using black ink, can be very effective.
Various means have been proposed to as effectively reproduce a
full-color picture from a single printing surface.
To such end, dependence has of late been upon a printing surface
which can distinctly receive at least three inks, usually of the
colors yellow, magenta and cyan. The three inks may be generally
applied, as in C.S. Miller, U.S. Pat. No. 3,213,787, and separately
received by respective surface elements. A 3-color printing surface
can receive inks only in juxtaposed relation, and therefore
properly relies upon equal intermixing (on the substrate) of all
three inks to produce a black, upon equal mixing of a selected two
inks to produce primary red, green and blue, and upon proportionate
intermixing of all three inks to produce intermediate or tertiary
colors. The black so-produced is typically of poor depth and tone,
and cannot be produced in fine picture detail. For the latter
reason these surfaces are unable to print accompanying typographic
matter of small size (about 12-point or less), except in a
particular one of the three ink colors. Moreover, the colors
reproduced tend to appear paled, because of light reflected from
small unprinted, or weakly covered, portions of substrate between
adjacent deposits of ink. In many such processes, including that of
Miller, the chemical immiscibility of the inks interferes with
their admixture on the substrate, and makes the selection of
substrate a critical concern.
Miller's surface is believed outstanding of its kind, but
nevertheless cannot produce what is herein considered to be an
effective reproduction. Although the use of a fourth ink of black
color would sufficiently enhance such a reproduction, and is
proposed by Miller, he is unable to give any specific mechanism,
i.e., chemical treatment and ink formulation, which would allow it
to be distinctly received, nor is any apparent. Even with a fourth
ink of black color, his surface, and other surfaces having a fixed
array for ink-receiving elements, would still be unable to
reproduce fine black picture detail, because only every fourth
surface element would receive black ink. To compensate for the
aforementioned limitations, Miller's and other 3-color surfaces
are, in practice, best used as the first in series with a
conventional black-printing surface. The latter can overprint
amounts of black and also print any accompanying black typographic
matter. Accordingly, only by two impressions is an "effective"
reproduction produced.
Considering now 2-color printing surfaces, such as are known, none
are able to effectively reproduce a full-color picture in a single
impression. They have found use only (to knowledge) in reproducing
"duotone" pictures and other copy having just two color components
disposed either separately or in interspersion for limited additive
secondary color effects, and which components can be exactly
matched by the two ink colors, and also in reducing the number of
separate plates needed for "Process" and other reproductions by
three or more inks. The limitations experienced are to be expected
from classical color theory, which postulates the need for at least
three inks, usually of the colors yellow, magenta and cyan.
It has nevertheless been found that all colors, in certain
instances, and most colors, in most instances, can in fact be
perceived in a picture reproduced by only two colors or "stimuli".
This was strikingly demonstrated by Edwin H. Land with the aid of
paired photographic transparencies having the character of "red"
and "green" separation images, conjunctive with pairs of colored
illuminants (including white light as a "color"), as described in
Scientific American, May 1959, "Experiments in Color Vision", and
elsewhere. But attempts by Land, as in U.S. Pat. No. 3,034,890, and
by Lorber, of instance, in U.S. Pat. No. 3,429,702, to produce an
equivalently full range of colors on the printed page, by use of
only two inks, e.g., with red and black inks, have at best produced
only "multicolor" effects. These have been characteristically
deficient of blue, among particular shortcomings (poor contrast and
weak reddish blacks in the first instance, yellows poorly
distinguishable from white in the latter instance, to specify
some). For a variety of technical and practical reasons the use of
red and black inks is preferred to other combinations upon a white
or pale paper. But the deficiencies of known red-black
reproductions will persist if they are, by any apparent means,
produced from a 2-color printing surface instead of from separate
plates as was described in the art. Presumably, this accounts for
the before-mentioned commercial limitations of known 2-color
printing surfaces.
A variety of other means have been proposed to reproduce a
full-color picture from a single printing surface. None of these,
including "collecting" processes and surfaces, has been found
sufficiently effective and/or practical to complete commercially
with conventional "Process" reproductions. As the art now stands,
an "effective" reproduction of a full-color picture can neither be
accomplished in a single impression nor from a single printing
surface. In remedy of this situation, the principal objects of this
invention are:
To enable a 2-color printing surface to effectively reproduce a
full-color picture, conjunctive with appropriate inking;
To permit effective reproduction of a full-color picture by use of
only two inks not of complementary colors, thus avoiding
deficiencies typical of complementary-color prints;
To permit effective reproduction of a full-color picture by use of
only two inks, respectively of a black tone and a red color, yet by
means avoiding deficiencies herebefore experienced in the use of
red and black inks for such purpose;
To permit full-color pictorial reproduction of good quality from a
single printing surface doubly imaged and inked with two inks, one
of the inks having a black tone providing detail and contrast and
also being suited to reproduce any accompanying black typographic
matter or B&W pictures; and
To extend the commercial utility of 2-color printing surfaces.
Means to accomplish the above and other objects of this invention
will be understood from the following description, and by reference
to the accompanying Drawing, which is schematic and not to scale,
in which:
FIG. 1 shows a camera set-up for obtaining precursors to 1st and
2nd platemaking images;
FIG. 2 and FIG. 3 show different suggested patterns for a 2-color
screen used in direct composite color separation;
FIG. 4 repesents selected colors of a full-color picture;
FIG. 5 represents a section through a 2-color screen and general
filter combination;
FIG. 6 shows the encodement of selected picture colors in a
continuous-tone composite color separation;
FIG. 7 shows a positive halftone equivalent of the composite color
separation of FIG. 6;
FIG. 8 represents minus- "cyan" picture content as encoded in the
form of halftone densities in a 2nd platemaking image;
FIG. 9 depicts the printed representation of selected picture
colors (no color being observable here);
FIG. 10 shows photomechanical formation of 1st-image elements on an
exemplary latent 2-color printing surface; and FIG. 10-A shows the
suggested application of ultraviolet-opaque developing ink to said
surface subsequent to exposure and prior to development;
FIG. 11 and FIG. 11-A respectively depicts results of the procedure
of FIG. 10 and FIG. 10-A; FIG. 11-B show the optional application
of gum to hydrophilic portions of a singly imaged latent 2-color
surface obtained by above operations;
FIG. 12 shows photomechanical formation of 2nd-image elements on
the latent 2-color printing surface of FIG. 10, using the film
image shown in FIG. 8;
FIG. 13 shows an exemplary 2-color printing surface, absent of ink,
having special 1st and 2nd images as herein described;
FIG. 14 and FIG. 15 show procedures to convert the continuous-tone
composite color separation obtained in FIG. 1 into an equivalent
halftone negative of appropriate lateral sense for use in FIG.
10;
FIG. 16 and FIG. 18, in reverse order, show steps in converting the
"cyan" separation obtained in FIG. 1 into a laterally correct
intermittant halftone image of positive sense, having minus-"cyan"
information, such as shown in FIG. 8 and FIG. 10;
FIG. 17 shows means of using the 2-color surface doubly imaged as
described; and
FIG. 19 and FIG. 19-A depict a 2-color gravure surface which has
been double-imaged as herein described.
The instant process of double-imaging is applicable to more than
one species of latent 2-color surface, but is explained as it may
be practiced upon a latent 2-color surface described by R.S. Storms
in U.S. Pat. No. 3,368,483, intended for use in offset
lithography.
Referring to FIG. 1, a full-color picture 11 to be reproduced is,
for simplicity, assumed to only have the colors red (R), green (G),
blue (B), yellow (Y) and black (Bk) arranged as a cross upon a
white (W) background. The half-round protrusion in the red is
provided as a indication of lateral sense, for reference. The
selected colors shown, also assumed to be fully saturated and of a
uniform flat tone, are "key" colors, in that an understanding of
how they are reproduced on the printed page will assist in
understanding the reproduction of other colors. However, the visual
phenomena involved is not certainly understood even by the
inventor.
Through an optical system 12, preferably through a general color
filter 13, and through a 2-color screen 14, the picture 11 is
imaged upon the face of panchromatic film 17. The 2-color screen is
of a contact type, and has on its face an interspersed 2-part
pattern of transparent "red" elements 15 and "green" elements 16
which act as limited-area color filters. Acceptable results will
obtain if the "red" and "green" elements are substantially pure red
and green, or if only the "red" elements are substantially of pure
color. Preferably, and as a convenience in practice here assumed,
the "red" elements are a full magenta (transmitting equal red and
blue) and the "green" elements are a full cyan (transmitting equal
green and blue), while a general filter 13 is yellow of about 85
percent purity. Such combination of general filter and 2-color
screen effectively allows the "red" screen elements to transmit
full red plus about 15 percent blue, and the "green" screen
elements to transmit full green plus about 15 percent blue.
Hereinafter, references to "red" and "green" screen elements (or
components transmitted therethrough) will not imply that such
element (or components) need specifically be of the colors red and
green. If desired, the screen elements could be formulated so that
each transmits a minor amount of blue in addition to its primary
color, thus avoiding need for a separate yellow filter.
For a single and correct exposure to be made upon the film 17,
without need of balancing filters, a selected one set of screen
elements may have neutral density or a complementary color
component added, as required, to equalize the "filter factor" of
all screen elements. The single exposure may then be such as will
produce a substantially normal range of image densities.
Though, for simplicity, a checkerboard pattern is shown, the
2-color screen may have any other interspersed 2-part pattern. In
practice the pattern of FIG. 2 is generally preferred, wherein the
"green" elements have about 5 percent smaller area than "red"
elements, as is also the case for the pattern of FIG. 3
(particularly recommended for use in preparing a 2-color gravure
surface). Diminished final results will be had if "red" and "green"
elements are of equal size or if "red" elements have smaller area
than "green" elements.
The screen elements must be very small relative to the size of the
reproduced picture, as they determine color resolution in the
print. A group of four coadjacent screen elements may be considered
the "normal" unit of color resolution, as shown for each "key"
color, except white, in FIG. 1. The white color images through many
"normal" units of color resolution, each comprising two "red"
screen elements and two "green" elements. In practice it will be
found that there is an "effective" unit of color resolution, of
indeterminate size, which is substantially smaller than the
"normal" unit, and which permits very small color detail to be
seen. This is in part due to a random factor, and in part due to
the synthesizing ability of the eye in reading pictures. Generally,
most colors will have a size enabling them to image through tens,
hundreds or thousands of coadjacent screen elements.
As with a halftone screen, the 2-color screen elements may be much
coarser for poster and like work than for a magazine, book or
newspaper picture. But in prints of the latter types it is neither
necessary nor desirable that the color screen pattern be so fine as
not be be resolvable when (the screen itself) viewed from a
comparable distance. For in the printed reproduction the screen
pattern will be effectively obscured by the co-presence of halftone
structure, and by the eye's concern for reading the subject content
of the reproduction, analogously to the non-perception of highlight
dots in a conventional halftone print.
Use of a (relatively) coarse 2-color screen is a practical and not
seriously compromising means to avoid resort to halftone screens of
excessive fineness. For example, "red" and "green" screen elements
could be nominally about one-sixtieth inch along a side (or across,
where round), when a halftone screen of 100, 133 or 150 lines is
subsequently to be employed. For news pictures, color screen
elements as coarse as about one-fortieth inch may be used, yet the
color screen pattern will be indistinct in the print. As a matter
of interest, color screen elements of about one-sixtieth inch will
prove more than sufficient to reproduce the color of such small
details as the iris of an eye in any common size picture wherein a
person is the principal subject.
The b 2-color screen 14 may be prepared by a variety of apparent
means, including the use of subtractive color film. So that the
very same screen may also be used in later procedures, it
preferably has a thin, e.g., 0.004 inch, base of dimensionally
stable material, e.g., "Estar", brand of polyethylene
terephthalate.
The developed image on film 17 is a continuous-tone composite color
separation, in effect, an interspersed 2-part encodement of "red"
and "green" picture content. This image is represented in FIG. 6.
To facilitate understanding, the colors represented by film density
are shown in FIG. 4, in positions above the corresponding film
densities. FIG. 5 depicts the 2-color screen 14 and yellow filter
13 combination through which the densities of FIG. 6 were obtained,
and the screen is shown to have "red" elements larger than "green"
elements, as recommended. The numbers shown below each "key" color
in FIG. 4 are in arbitrary units, merely intended to show an
assumed actinic potential of each color, and are not values which
might actually exist. Neither are the density values shown in FIG.
6 those which might actually result in practice. These values here
assume that about 15 percent blue was transmitted through both
"red" and "green" screen elements, but in practice a lesser amount
of blue can still produce effective final results.
Referring specifically to FIG. 6, it will be seen that blue is
differently represented than black, that black has the least value
and white the most, and that yellow has a density slightly less
than white. In each case the two pairs of densities that represent
each color are equal, but in practice some difference can exist in
the densities of conjunctive pairs. In the case of red and green,
one pair of densities is seen to have negligible value while the
conjunctive pair has a high, but not maximum, value. White is here
presumed to have been slightly overexposed. This is desired. The
correct exposure is best determined, in practice, if a yellow
sample photographed through the screen and filter combination
produces an average density of about 90 percent or slightly more,
when the resulting negative is routinely developed. This yellow
density is preferably higher, e.g., about 95 percent, if the yellow
filter 13 has a purity of 90-95 percent.
With reference now to FIG. 14, the developed image on film 17 is
printed onto the face of autoscreen film 18, or is otherwise
halftoned. The screen angle is best determined empirically, but may
be about 30.degree. different from the effective angle of the
2-color screen. The halftoned (and positive) form of the composite
color separation is shown in FIG. 7. Its correspondence to the
continuous-tone (negative) form may be seen by referring to FIG. 6,
above. Next, as shown in FIG. 16, the halftone image on film 18 is
printed onto copy film 19. The resulting halftone negative on film
19 has a desired lateral sense, and is the first platemaking
image.
Referring back to FIG. 1, the picture 11 is also imaged through the
optical system 12 onto the face of ortho film 21. The film 21 is
here assumed to also have an autoscreen feature and an effective
screen angle about 30.degree. different than that of film 18, but
in practice other halftoning means can be used. What is essentially
desired by this exposure is a "cyan" color separation, it merely
being a convenience to use ortho film and to directly halftone.
(The 2-color screen 14 is not employed). The exposure is preferably
just sufficient to leave about 8-10 percent "highlight windows" in
density representing picture white. Though the exact balance of
blue and green light recorded is not critical, superior final
results will obtain if one component is only about 85 percent the
strength of the other component. To this end a pale yellow filter
20 is inserted into the optical path, and will attenuate the blue
component. Instead, a pale magenta filter can be used to attenuate
the green component. Hereinafter, reference to a "cyan" separation
(or component) is not to imply that blue and green are equally
recorded (or present).
It is important to appreciate that densities in a "cyan" separation
are not reciprocal to densities in a (minus-red) print made from a
conventional red separation. In a "cyan" separation full green and
blue are each represented by densities of middle value, while in a
minus-red image green and blue are each represented by maximum
density. Similarly, the term "minus-cyan" does not mean "red", but
refers to densities which are reciprocal to those obtained in a
"cyan" separation, and to the complex component (including red) of
a picture directly represented by said reciprocal densities.
Next, as shown in FIG. 18, the developed halftone "cyan" separation
image on film 21 is printed onto the face of autopositive film 22.
This provides lateral reversal without change of negative-positive
sense. Subsequently, as shown in FIG. 16, the image on film 22 is
printed by red light, e.g., as passes through a red filter 23, onto
the face of panchromatic film 24 through the same 2-color screen 14
which was used in FIG. 1. As shown, the film 22 is face-down upon
the body of screen 14. By using the same 2-color screen, rather
than an identical twin, the possibility of misregister is greatly
minimized, as even symmetrical and regular patterns may have slight
irregularity. The screen 14 is suitably "keyed" to assure that the
same corner which was in the upper left part of the image in FIG.
1, is now in the corresponding corner of the image here passed
through it. By the procedure of FIG. 16 "green" screen elements
will block the passage of red light, so that the resulting
minus-"cyan" halftone image on film 24 is regularly interrupted or
blanked.
The developed minus-"cyan" image is represented in FIG. 8, and
would appear "positive" by visual examination. It will be noted
that, except where interruptions or blanks 25 occur, yellow and
green will be represented by about 41 percent halftone density, and
blue will be represented by about 48 percent halftone density
(assuming, for these values, that in the original "cyan" separation
the blue component had about 85 percent the strength of the green
component). Also to be noted are the small halftone dots 26, in
practice abut 10 percent size or less, which are a desired
consequence of the highlight windows formed in the original "cyan"
separation. This image is the second platemaking image, on film
24.
The first and second platemaking images obtained by the
aforementioned procedures may be used as follows:
Referring to FIG. 10, the 1st platemaking image on film 19 is
placed upon the sensitized coating 29 of Storms' latent 2-color
surface 30, having a Teflon body 28. (The coating sensitivity is
best largely or wholly in the visible range). Then an exposure is
made to light from a source 38, preferably having little or no
ultraviolet component. The exposure should be adequate to render
insoluble all portions of the coating 29 which were not shielded by
halftone density in the film image. (This operation corresponds to
that shown in FIG. 3 of Storms' patent.)
In departure from Storms' procedure, and with reference to FIG.
10-A, an ultraviolet-opaque developing ink 27 preferably is applied
to the exposed but undeveloped coating 29. Carbon-black inks are
suitably absorbent and may be used; flake aluminum ink can also be
used, among others which will be apparent. The ink-base is suitably
one which will quickly become surface-dry and which will be water
repellant.
FIG. 11 (corresponding to Storms' FIG. 4) shows the latent 2-color
surface 30' after development of the first image. The constituent
first-image elements 1 are, for schematic clarity, shown absent of
residual developing ink 27, but the presence of such ink, as shown
in FIG. 11-A, will be understood. The amount of relief of
first-image element is negligible, and is shown greatly
exaggerated. The first-image elements are oleophilic-hydrophobic,
whereas the plate surface 33 is hydrophilic (having been finely
etched in manufacture). It is important to understand that the
first image is an inverse representation of the composite color
separation on film 17 (also being halftoned), and therefore the
first-image elements represent "minus" amounts of "red" and "green"
in the picture 11. (The image on film 17 is properly a "positive"
record of "red" and "green", although appearing as a negative by
visual inspection.)
FIG. 11-B shows an ultraviolet-transparent gum coating 39 upon the
hydrophilic surface 33. This may be done as in conventional litho
platemaking, e.g., using gum arabic. This coating is optional, and
merely has as its function to level up the single-imaged surface
30' so that a second platemaking image can lay in flatter contact
on it.
With reference to FIG. 12 (corresponding to Storms FIG. 5, with
minor difference), the second platemaking image on film 24 is
optically printed onto the plate surface 33 by the action of
ultraviolet light from a source 32. Sufficiently intense U.V. light
has ability to smooth the etched surface 33, in which state it will
be repellant to both greasy ink and aqueous ink. In minor departure
from Storms' practice, it will be noted that the film 24 does not
have co-imaged thereon a "positive" equivalent of the first
platemaking image. The optical shielding which such a co-image
would provide above formed first-image elements 1 (FIG. 11) is
instead equivalently provided by a residual layer of developing ink
27 (FIG. 11-A).
FIG. 13 (corresponding to Storms' FIG. 6) shows the double-imaged
2-color printing surface 30" (absent of any ink), which is obtained
by the preceding operations. Instead of having had two arbitrary
images formed thereon, first-image elements 1 and second-image
elements 2 have particular dispositions and information content
which will cooperatively allow the surface 30", when appropriately
inked, to effectively reproduce a full-color picture. It is
important to note that only certain of the halftone densities on
film 24 have formed as corresponding hydrophilic second-image
elements 2. The prior presence of first-image elements 1 has
effectively limited the extent to which the second image formed. To
be especially noted, are the very few second-image elements within
the plate portion representing blue. This limited presence is
deliberate, instead of total absence. Also to be noted is the
complete absence of second-image elements in plate portions
representing green and black, and the interrupted distribution of
second-image elements 26 of about 10 percent halftone value in the
plate portion representing white. Except as noted, the interference
of first-image elements with the formation of second-image
elements, will allow the latter to form generally proportionate to
the degree in which a red-light component is present in a picture
color, though not to an extent greater than corresponding density
on film 24. By such mechanism (and with the understanding that red
ink will be received by second-image elements) the red quantity in
such colors as red, orange, yellow, yellow-green and purple is
provided. The intermediate halftone density for yellow, relative to
the full halftone density for red, in the image on film 24 (FIG. 12
and FIG. 8), acts to limit the maximum formation of second-image
elements in the yellow-representing plate portion. Similar biasing
occurs in systematic manner for other colors containing red, as a
consequence of the "cyan" separation, and is deliberate and
desired. The exact parts of any given halftone densities on film
24, which are able to form as second-image elements, will depend on
the random "lay" of halftone structure in the first and second
platemaking images as results from the prescribed differential
angling. For example, the few second-image elements in the
blue-representing plate portion may not have the particular
positions shown, or even be completely circular, though they will
form generally in the same quarters of said portion. It should be
appreciated that second-image elements actually represent amounts
of minus-"cyan", although they will receive red ink.
Referring to FIG. 17, the 2-color printing surface 30",
double-imaged as described, may be used on substantially
conventional offset lithographic equipment, e.g., including a plate
cylinder 3, an offset cylinder 4, and impression cylinder 5 and two
fountains 6 and 7 having distribution and form rollers. Normally
the fountain first in line according to the direction of cylinder
rotation, e.g., fountain 6, would be used to apply a colorless,
aqueous, wetting solution to hydrophilic plate areas, while the
fountain next in line, fountain 7, would apply greasy lithographic
ink of any desired color. As here adapted, the greasy lithographic
ink 1 is specifically of a black tone and the aqueous solution 2 is
of red color, and may include binder and other components of an
ink. The 2-color printing surface 30" is mounted to cylinder 3, and
will be given successive general applications of the inks 1 and 2
(in reverse order) as the cylinder rotates. But ink 1, of black
tone, being greasy will be received only by first-image elements of
the surface 30", and ink 2, of red color, being aqueous will be
received by 2nd-image elements of the surface 30". If desired, the
two inks could be components of an emulsion applied from a single
fountain, the component inks being selectively received by
first-image elements and second-image elements. Such emulsion
systems are known for lithography, though usually the aqueous
component is colorless. Hereinafter, reference to "1st" and "2nd"
inks will not imply sequence or even separate application, nor (as
will be understood from further example), necessary difference in
composition or base.
Regarding ink colors, the black tone is preferably blue-black (such
as will also be suited to reproduce typographic matter), and the
red color is preferably a bright red. Departure from these
recommended colors, e.g., a neutral black or green-black, or a very
deep or medium red, is permissible but will be less effective.
Conjunctive with the recommended use of blue-black ink and bright
red ink, most effective results will be obtained when the printed
substrate 8, e.g., paper, is of a selected pale color other than
neutral white. The preferred substrate color is a pale green, e.g.,
about a 5-8 percent green tint. Such a substrate color would be
analogous to the color of "Eye-Ease" writing paper, but lacking a
bluish quality. The use of such off-white paper will negligibly
affect the subjective general brightness or "crispness" of the
reproduction, because of the excellent contrast and detail provided
by the black-tone ink and because of other factors, e.g., a large
proportion of substrate show-through for green and colors having a
green-light component. A substrate of exceptionally high
reflectance is not essential for effectiveness.
The printed representation of selected "key" colors is shown in
FIG. 9, relative to FIG. 4, above. A substrate 8 of pale green tint
has had simultaneously printed upon it, e.g., by the 2-color
surface 30", deposits 1' of a "first" ink having blue-black tone
and deposits 2' of a "second" ink having bright red color. The ink
deposits are in the form of halftone densities, and areas uniformly
shaded in the drawing represent full halftone density. By reference
to FIG.4 it will be self-evident how the red and blue-black ink
deposits "represent" respective "key" colors, but it will not be
evident how such representation gives rise to the perception of
correct color in each instance. The following paragraphs will
attempt to clarify this.
Assuming a whole reproduction and not just selected individual
colors thereof, all picture detail and tonal values would be
represented by the halftone deposits of the blue-black ink. In the
absence of red ink the reproduction would seem to be an ordinary
"black-and-white" halftone print. But the particular distribution
and amounts of red ink cause the observer to perceive a full-color
reproduction. This phenomena (not observable from the Drawing) is
related to the previously cited discoveries of Edwin H. Land, but
as here applied to the printed page incorporates certain
refinements. In common with Land's projected images and illuminated
transparencies, the perceived colors here elicited are
indistinguishable from "real" colors and have excellent constancy.
Their physical absence would not be suspected, neither does
knowledge of their physical absence diminish their apparent
reality.
By physical measure (if possible) or by direct comparison, colors
perceived in this reproduction will not be as bright as those in a
conventional "Process" print. (The relative lack of brightness
should not be confused for paleness.) Subjectively, however, the
reproduction will appear more natural and correct than does a
"Process" print. This is because a reduction of a life scene to
page size normally has the psychological effect of making the
reader unnaturally aware of the colors, per se. Reproductions of
the instant type, in distinction, may be generally described as
having a character akin to that of a skillfully hand-dyed photo
print having both tints and tones of color, with comparable
sharpness of detail and contrast (allowing for normal losses due to
halftoning). The color quality of hand-dyed photoprints is unique
and pleasing, although such prints are largely obscure because of
more rapid means of reproducing color.
White is perceived even though there is a presence of about 10
percent red dots, whether on a pale green substrate or a white
substrate, presumably by reference to the reproduction as a whole.
The red dots provide density to give other apparent colors correct
value relative to perceived white. (By a variety of mechanical
means the red dots can be prevented from forming in accent areas of
a picture.) The absence of highlight black dots in areas
representing white is instrumental in permitting the perception of
yellow distinctly from white.
The sensation of yellow is experienced presumably because, in the
immediate presence of red ink, exposed portions of substrate assume
the additive role of a bright green, and also because the presence
of slight black density provide a correct relative value compared
with areas representing white. A full amount of red ink in yellow
areas would render the yellow as orange, and such full presence of
red has therefore been prevented.
Luminosity (by reflectance) from exposed portions of the substrate
in areas representing green, gives rise to a strong sensation of
green although there may be no red deposits immediate thereto to
account for such effect by simultaneous contrast. A red referent
elswhere in the reproduction is presumably responsible. This effect
is not dependent upon the use of a green-tinted paper.
The sensation of full red is seen in areas representing red,
presumably by the substantial absence of any other luminosity from
such area. Slight desaturation is caused by the minor blue
component in blue-black ink, and this is largely compensated by the
larger relative size of red deposits than blue-black ink deposits
in the red-representing areas. The apparent brightness of reds is
increased by the phenomena of simultaneous contrast, when, as
recommended, the 2-color screen pattern is slightly coarser than
could not be resolved by the eye. Accordingly, a physical measure
of red intensity would be misleading. (Similar reinforcement of
apparent intensity is present in areas representing green.)
The apparent presence of blue is believed to result from the fact
that areas representing blue have slightly less halftone density
than areas representing black, together with the small, permissibly
almost insignificant, amounts of red therein. The red component is
believed to additively combine with the minor blue component of the
blue-black ink to form a dark purple, either confused with blue or
which gives rise to a sensation of blue. (It is known that strong
blue light will cause a sensation of weak purple.) By another
explanation, the small amount of luminance from portions of
substrate in such area tends to accentuate the blue component of
the blue-black ink.
In any area representing black the blue quality of the blue-black
ink is unnoticed, presumably because these areas are the darkest in
a picture and automatically are considered black in the picture
context. The absence of small "shadow dots" is deliberate, and
intended to prevent accentuation of the blue quality of the
blue-black ink, such as occurs (presumably) for blue.
The production of other apparent colors results from minor
differences in amounts of red and black such as occur for the "key"
colors, flesh tones, metallic tones, oranges, browns and purples
being among those perceivable.
The recommended inclusion of a blue quantity in the black ink is in
recognition of the fact that the first-image elements do not merely
represent amounts of minus-"red" and minus-"green", but also
represent positive (indeterminate) amounts of blue, at least for
all colors not purely red and/or green, or the color black. By some
visual mechanism not well-understood, the bluish quality of the
blue-black ink becomes pronounced generally to a degree which is
locally appropriate. Because the substrate acts largely as if it
were green (while at the same time its paleness enhances the
picture brightness), the "green" together with the red ink and the
blue of the blue-black ink, may in part operate in accordance with
classical 3-color additive theory to produce an effective color
reproduction.
Although a picture is the only matter which has been shown
double-imaged upon the 2-color surface 30", it will be understood
that the "first" image on the surface 30" could include incidental
matter which is to reproduce in black (or blue-black) ink, while
incidental matter which is to reproduce in red ink could comprise
part of the "second" image on the surface 30". It will therefore be
appreciated that this invention is concerned only with forming a
quantity (all or less than all) of first-image elements and
second-image elements which cooperate to reproduce a full-color
picture, when suitably inked.
The aforementioned procedures may be modified to form such
cooperating first-image elements and second-image elements upon
other latent 2-color printing surfaces. The necessary modifications
will be dictated by the structure of the particular other latent
2-color surface.
For example, FIG. 19 shows a gravure equivalent of the 2-color
printing surface 30'. In the gravure surface 40, first-image
elements 1 and second-image elements 2 are recessed. The
first-image elements (shown with cross-shading) and the
second-image elements (shown with linear shading) may be assumed to
have relative dispositions and information content equivalent to
their counterparts on the 2-color surface 30", except that a
2-color screen as in FIG. 3 was used for compositing the "red" and
"green" separations. The portion of gravure surface represented is
schematic, and of an arbitrary section of a whole reproduction, and
elements therein are not intended to be a representation of any
particular color. Use of the 2-color screen of FIG. 3 has given
second-image elements of relatively full halftone density a
generally circular, rather than rectangular, shape, the circular
shape being believed more suited for smooth traverse of a doctor
blade.
Subsequent to their formation, first-image elements have been
chemically treated to be exclusively receptive to a first ink, of
black tone, and subsequent to their formation second-image elements
have been given a chemical treatment so they will be exclusively
receptive to a second ink, of a red color. The first and second
inks may, aside from color, be of respective greasy and aqueous
composition, or of any other compositions which are mutually
immiscible, and they should have a consistency suited for gravure
as well as different physical density. Such differential treatment
of gravure cavities, together with suitably different ink
compositions and means of generally applying such inks, is known in
the art, e.g., as described by C.S. Miller in U.S. Pat. No.
3213787, previously cited. FIG. 19-A shows 1st and second inks as
selectively received.
It is essential that the first-image elements and second-image
elements be of a halftone structure such as will result from a
so-called "halftone gravure" process employing a halftone screen,
and providing variable dot sizes (and optionally, variable depths).
As in the preparation of Storms' surface, the first-image elements
must be formed first, so their presence can govern the extent to
which second-image elements will form. It will also be apparent
that both platemaking images must normally be "positive", as
etching of the surface 40 will be through a photo-resist. As a
peculiar requirement of a 2-color gravure surface is that
individual pockets be formed for respective inks, precautions must
be taken to form a thin wall 41 around all first-image elements
wherever they may be intimately juxtaposed to subsequently formed
second-image elements. Optical formation of a thin ring of resist
around all first-image elements will assure that a wall 41 will
remain thereunder. Various particulars of these procedures will be
apparent to those familiar with the preparation of gravure
surfaces.
It must be understood that film intermediates of any kind,
including first and second platemaking images, will not always be
essential to actually forming the prescribed two images upon a
latent 2-color printing surface, neither need there be material
difference between first-image elements and second-image elements
for them to be selectively receptive of generally applied inks. The
following paragraphs will illustrate both these points by a single
example.
Any photoconductive (PC) surface, e.g., a xerographic surface, is
latently a 2-color printing surface, because techniques are known
to form two (or more) images in common register thereon, and to
give each image a distinctive color of ink. But it has been
unobvious to form two images having disposition and information as
hereinbefore described. Provided only that the PC surface is of a
kind having sensitivity also to red light, the novel images may be
formed as follows:
a. The PC surface is electrostatically charged.
b. A full-color picture to be reproduced is projected onto the PC
surface, through a 2-color screen and separate yellow filter
combination substantially as hereinbefore described.
By choice of illuminant, or by balancing filters or adjustment of
screen colors, the PC surface is given an effective panchromatic
sensitivity, if it was but poorly sensitive to red. The 2-color
screen is preferably microfine and in the form of a reticle in the
optical system, and has a pattern suited to allow "stepping" of the
screen by an increment which will transpose spatial positions of
red (sic) and "green" screen elements. If the PC surface does not
have sufficient resolution to reproduce continuous-tones, a
shiftable-angle halftone screen, e.g., of cross-line type,
micro-ruled, may be placed just in front of the 2-color screen, or
an equivalent halftone screen, macro-ruled, may be positioned close
above the PC surface. (Red screen elements should here not transmit
blue.)
c. Toner of blue-black color is conventionally applied, and is
received by the first-image elements optically formed in (b).
d. The PC surface is recharged. Properly done, e.g., as with a
charge of slightly lesser intensity, this need not cause separation
of blue-black toner from the singly imaged PC surface.
e. The yellow filter is removed from the optical path and a "cyan"
filter is substituted; also, the 2-color screen is "stepped", and
the halftone screen (if one is used) is suitably reangled from the
angle previously employed.
f. A second exposure is made, the remaining charge areas being the
second-image elements.
When no halftoning was used, the charges forming second-image
elements will vary in strength, and may be co-incident with toner
deposits on 1st-image elements. When halftoning was employed, these
charges will be of uniform strength and in discrete areas
co-disposed among the inked first-image elements. The presence of
inked first-image elements will in either case limit the extent of
formation of the charges constituting second-image elements.
g. Toner of bright red color is conventionally applied, and is
received substantially only by second-image elements optically
formed as in (f).
h. The two applied and received toners are conventionally
transferred to a substrate of pale color, e.g., white or pale
green, and conventionally fixed upon the substrate.
The above procedures, which are subject to refinement and
modification as may be obvious, will produce a good representation
of the original full-color picture, though involving slight
compromise in general quality.
Any quantitative values which were hereinbefore given were solely
to assist in understanding, and are not to be considered as
limiting.
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