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Description  |
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FIELD OF THE INVENTION
This invention relates to a photomechanical apparatus, and more
specifically to a photomechanical apparatus equipped with a system for
converting pictorial information signals, which have been obtained by
photoelectrically scanning an original picture having a continuous tone,
in accordance with a novel tonal conversion method and then making a
machine plate for a printed picture of a halftone on the basis of signals
outputted subsequent to their tonal conversion.
BACKGROUND OF THE INVENTION
In the conventional photomechanical techniques, an original printing film
of a halftone picture is formed from an original picture of a continuous
tone (primarily, a photographic picture such as photographic monochrome or
multicolor picture, photographic positive or negative picture or
photographic reflection or transmission picture) by conducting halftone
scanning by means of a photomechanical camera or performing both color
separation and halftone scanning by means of an advanced photomechanical
apparatus such as monochrome scanner, color scanner or total scanner. In a
photomechanical process of the above sort, it is the routine practice to
inspect and confirm the quality of a picture, which has been formed in an
original printing film and is to be printed, by one to several proofs and
then to make a final machine plate for printing the picture.
On the other hand, the so-called direct-plate photomechanical process in
which the above-mentioned formation and proofs of an original printing
film is omitted has found actual utility only in extremely-limited cases,
for example, where an original does not contain any continuous-tone
picture (for instance, a photographic halftone reflection picture
contained in an original is considered to be a sort of line drawing in the
present field of art) or in the case of newspapers or the like in which
the quality of pictures in the prints may be sacrificed for shortening the
time required for the photomechanical plate-making work.
If the direct-plate photomechanical process practised only in
extremely-limited fields as described above is applied to an original
which contains one or more photographic continuous-tone pictures and is to
be printed (incidentally, such an original usually contains one or more
photographic continuous-tone pictures), it is extremely difficult to
stably produce generally-acceptable standard.
Except for the extremely-limited cases mentioned above, the direct-plate
photomechanical process has therefore not been recognized as one of
photomechanical processes.
Namely, the formation of an original printing film and the step of proof
are indispensable without exception for all photomechanical processes
known to date, so that they cannot not be omitted.
The present inventors have heretofore made various proposals with a view
toward improving the present direct-plate photomechanical process into a
rational technical system applicable to an original which contains one or
more usual photographic continuous-tone pictures. Namely, the present
inventors have reviewed all steps, basic work, fundamental techniques and
technical system involved in the overall process for forming from an
original picture a picture to be printed, and have made various proposals
in order to errors and defects included therein. For example, the present
inventors proposed to improve the quality evaluation of a printed picture
(i.e., to measure and control the two basic elements forming a printed
picture "the size of each dot " and "the density of each printing ink"
independently). Also proposed were the tone-rendering-first-ism and
4-point control method in the conversion of a picture, both, for the
rationalization of color separation work (i.e., the present inventors
proposed to include, as control points, at least four areas of H (the
brightest point in the high-light area), S (the darkest part in the shadow
area), M.sub.1 (intermediate density point of the picture) and M .sub.2
(the position where 50% dot area percentage is set). The present inventors
also proposed to improve the system of an advanced photomechanical
apparatus by using these techniques. Regarding these proposals, reference
may be had, for example, to Japanese Paten Laid-Open Nos. 97101/1979,
98801/1979, 103101/1979, 115901/1979 and 115902/1979 and Japanese Patent
Publication No. 11337/1987.
It was however unable to standardize, rationalize and systemtize the
photomechanical technology to such an extent that the formation of an
original printing film and proofing step mentioned above could be omitted
in the photomechanical work.
It is however of urgent necessity for the present field of art to establish
a direct-plate photomechanical technique which can substantially omit the
above-described formation of a original printing film and proofing step
and can also obtain printed pictures of stable quality.
The problem sought for solution in the present invention is concerned with
the non-rational and non-scientific means applied to date for the
conversion of the tone of a picture, namely, employed in the work for
converting a continuous-tone picture into a halftone picture.
With a view toward establishing a direct-plate photomechanical technique
also applicable to an original continuous-tone picture, the individual
steps and work of the photomechanical process, the fundamental techniques
applied to such steps and work, and the overall technical system of the
process were studied in detail. As a result, the lack of establishment of
the above-mentioned direct-plate photomechanical process by that time was
found to be attributable to the fact that the tonal conversion of a
picture, which is the first step of a process for forming a halftone
picture to be printed from an original continuous-tone picture and is also
the most important and basic step in color separation or the like, was
dependent on non-scientific and non-rational means.
The present inventors then reached a belief that the establishment of a
reliable direct-plate photomechanical technique would be difficult unless
the above problem was solved.
Incidentally, the present tonal conversion for converting an original
continuous-tone picture into a halftone picture to be printed is still
performed on the basis of the experiences of perception of men such as
designers of a photomechanical apparatus such as color scanner or its
users or depending on a plurality of fixed given data. The tonal
conversion is hence non-scientific and non-rational and lacks operational
flexibility.
Incidentally, a standard work characteristic curve is employed as a
standard or reference when a tonal conversion is effected by performing
halftone scanning or both color separation and halftone scanning with
advanced photomechanical equipment such as monochrome scanner or color
scanner. This standard work characteristic curve is a characteristic curve
of a halftone picture, which is to be used as a standard or reference upon
performing halftone scanning or color separation. It is also called "a
color-separation density characteristic curve", "a color-separation
characteristic curve", "a halftone characteristic curve" or the like. As
such a standard work characteristic curve, is used that determined by the
manufacturer on the basis of its experiences and perception or information
based on a limited number of fixed given conditions and stored in a memory
of such an apparatus.
For the operator of the apparatus, the details and number of technical and
operational choices in the photomechanical work have already been limited
due to the non-rational and non-scientific knowledge of the design
engineers of the apparatus. A limitation has also been imposed on the
details and range of technical and operational measures for advanced and
varied needs of the society for printed pictures and for nonstandard
original pictures (pictures of color originals having quality other than
the color original quality taken into consideration by the designers of
photomechanical apparatus). Otherwise, the conversion of the tone of a
picture is performed primarily on the basis of the experiences and
perception of an operator.
Such apparatus include those designed in such a way that an operator sets a
work standard characteristic curve as desired, scores it in a memory
thereof and then uses same as needed. This procedure however requires
complex basic experiments and is cumbersome work which requires a lot of
time, labor and cost. Nevertheless, the new work standard characteristic
curve cannot be set rationally and scientifically beyond the
aforementioned boundary of the fundamental limitation. In the present
state of the art, there are more and more cases in which a work standard
characteristic curve must be set newly in a rational and scientific manner
beyond the boundary of the fundamental limitation.
As has been described above, the present inventors have a view that the
present advanced photomechanical apparatus such as monochrome scanners and
color scanners basically do not make full use of the necessary and
sufficient finding and knowledge on plate-making and printing, their
design technology is composed of the theory of color separation based on
the non-rational and non-systematic, photographic masking method, and the
various improvements to the apparatus were basically only counter-measures
based on the theory of color separation.
The present inventors have hence carried out an extensive investigation
under the basic recognition that a technical means always capable of
assuring the quality of a picture to be printed, namely, a rational and
scientific technique for the tonal conversion of a picture has to be
established in place of the conventional photomechanical process in order
to establish a direct-plate photomechanical technique useful for the
eternal rationalization of the photomechanical technology and its
practice.
In the conventional design technology of scanners, color correction and
color modification were given the priority and the tonal conversion of a
picture was taken into secondary consideration, as described above, upon
performing tonal conversion of a photographic original picture into a
halftone picture in color separation work. In the tonal conversion of a
picture, the conventional design technology has hence stuck with the
3-point control method which regards sufficient the control of the three
points H, S and M.sub.1 without paying any attention to the control of the
position where 50% dot area percentage required for the stabilization and
improvement of the quality of a picture to be printed and for the
conversion and control of gray balance of an intermediate tone. It is also
the present state of the art that no sufficient consideration is give
regarding how big effects a slightest change in area of each dot gives to
the change in gradation and tone of a printed picture which is an assembly
of numerous dots, although the development of such effects is an extremely
important finding for plate-making and printing. The essential elements
for expressing or visualizing a printed halftone picture, in which the
control of the position for setting 50% dot area percentage and the
control of the dot area are also neglected for the above-mentioned reason,
are both "the area of each dot" and "the reflection density of an ink". As
to the factor of the above-described "reflection density of the ink", the
amount of an ink may be controlled within about .+-.20% in the case of Y,
M and C (about .+-.40% in the case of a black plate) on a printing
machine. Further, the visual sensation of a man has ability to easily
distinguish as a density difference the difference of 1% in terms of "dot
area" percentage. It is hence understood that the control of the area of
each dot is extremely important in the formation or conversion of a
halftone picture, when the above objective facts are taken into parallel
consideration. It is therefore understood that when a conventional color
separation technique is relied upon, a significant limitation lies as an
obstacle to the theme of obtaining a printed picture having extremely high
fidelity from an original picture such as photographic color picture.
In the conventional tonal conversion method of an original continuous-tone
picture into a halftone picture to be printed, there was no means for
correlating rationally and eternally the density at a desired control
point on the continuous-tone picture with the dot area percentage of the
dot at its corresponding control point on the halftone picture.
The present inventors have carried out an extensive investigation with a
view toward breaking up the above-mentioned limitation of the conventional
tonal conversion techniques which are non-rational and non-scientific. As
a result, the present inventors have found a novel tonal conversion method
for correlating the base density of a control point on the aforementioned
original continuous-tone picture with the dot area percentage at the
corresponding control point on the halftone picture. It has then been
found that the novel, rational and scientific, tonal conversion method can
be successfully applied to conventional photomechanical apparatus, can
break up the limitation of the conventional color separation technology
and can exhibit superb effects, leading to the completion of the present
invention.
SUMMARY OF HE INVENTION
In summary, the present invention relates to a photomechanical apparatus
suitable for use in the production of a printing plate, which is adapted
to print a halftone picture corresponding to an original continuous-tone
picture, on the basis of pictorial information signals obtained by
photo-electrically scanning the original continuous-tone picture. The
apparatus comprises a tonal conversion system for converting the pictorial
information signals in such a way that the base density (x) of a desired
control point on the original continuous-tone picture and the halftone
intensity (y) of a corresponding control point on the picture to be
reproduced are correlated in accordance with the following formula (1):
##EQU1##
where x: the base density of the desired control point on the original
continuous-tone picture, namely, a value obtained by subtracting the
density at the brightest area of the original continuous-tone picture from
the density at the desired control point of the original continuous-tone
picture;
y: the halftone intensity of the corresponding control point on the picture
to be reproduced;
y.sub.h : a desired halftone intensity set for the brightest area of the
picture to be reproduced;
y.sub.s : a desired halftone intensity set for the darkest area of the
picture to be reproduced;
.alpha.: the reflectivity of a base material on which the halftone picture
is to be reproduced;
.beta.: the surface reflectivity of a medium for visualizing the halftone
picture; and
k: the ratio of the density range of the halftone picture to be reproduced
to the density range of the original continuous-tone picture.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1(a) is a schematic illustration showing a tonal conversion method in
the present invention, which converts an original continuous-tone picture
into a halftone picture via an intermediate picture compressed in density;
FIG. 1(b) is a schematic illustration showing another tonal conversion in
this invention, which converts the original continuous-tone picture into a
halftone picture via an intermediate picture compressed in density range;
and
FIGS. 2-6 are block diagrams showing embodiments in each of which the tonal
conversion system of this invention has incorporated in a color scanner.
DETAILED DESCRIPTION OF THE INVENTION
First of all, a description will be made of a tonal conversion method which
constitutes a basis in the photomechanical apparatus of this invention and
is adapted to obtain from an original continuous-tone picture a halftone
picture to be printed.
The following objective facts and empirical rules have been known with
respect to a printed picture, namely, a halftone picture. Namely, there
are two basic elements for expressing or visualizing the printed picture,
i.e., "dot areas" and "the reflection density of an ink". Regarding the
factor of "the reflection density of the ink", the amount of the ink which
may be changed on a printing machine may be about 20%, more specifically,
about 20% (within about .+-.10% based on an appropriate ink amount) in the
case of Y, M and C plates of color printing plates, and about 40%
(similarly, about .+-.20%) in the case of a BL (black) plate. Empirically,
it has been known that the visual sensation of a man can easily
distinguish a difference as small as 1% between "dot area" percentages as
a density difference. It is hence appreciated that the control of each dot
area is extremely important and must be the most important matter in the
formation of a halftone picture. In relation to the matter mentioned
above, photomechanical plate-making work involves the following background
characteristics. Namely, original pictures have a wide variety of quality
and details. The step for the formation of a printed picture, which
follows the photomechanical plate-making work, is diversified and
moreover, each of such diversified kinds of printed-picture forming steps
has its own work characteristics. Furthermore, the quality evaluation
standard for printed pictures varies from one orderer for prints to
another. In order to overcome such complex and unstable factors, it is
therefore essential to provide a rational and simple, tonal conversion
means for allowing the tones, said tones ranging from the brightest area
to the darkest area, of the two pictures correspond to correspond at 1:1
to each other upon conversion of an original continuous-tone picture into
a halftone picture while allowing to freely choose the smallest dot
(Y.sub.h) at the brightest area and the largest dot (Y.sub.s) at the
darkest area in a halftone picture to be produced.
It is the tonal conversion method defined by the conversion formula (1)
that has been created and devised in light of such an approach and is
applied to the tonal conversion system of the photomechanical apparatus of
this invention. The method may hereinafter be-called "the present
conversion method".
The tonal conversion method defined by the conversion formula (1) is
practised to determine the value (y) of the dot area percentage of the dot
at a control point (Y) on a picture, which is to be printed, from the base
density (x) of a corresponding control point (X) on an original picture
while freely selecting the sizes of dots desired to be placed in the
highlight area H and shadow area S of the picture, which is to be printed,
on the basis of the reflection densities of printing paper and printing
ink. The measurement of these densities is generally performed by using a
color densitometer (transmission type, reflection type, dedicated type,
shared type, or the like). When a scanner is used, they may be measured by
a density measurement device which the scanner is equipped with.
The above-described conversion formula (1), which is useful in determining
dot area percentages (y), was derived from the density formula
(photographic density, optical density) accepted widely, namely,
D=log I.sub.o /I=log 1/T
where
I.sub.o : intensity of incident light,
I: intensity of light reflected or transmitted, and
T=I/I.sub.o = reflectivity or transmittance.
The above general formula for the density D may be applied to plate-making
and printing in the following manner.
##EQU2##
where A: the unit area,
d.sub.n : the area of each dot in the unit area,
.alpha.: the reflectivity of the printing paper, and
.beta.: the surface reflectivity of the printing ink.
In the present invention, the density formula (D') for plate-making and
printing was incorporated with the above-described requirement for the
maintenance of correlation between the base density (x) at a desired
control point on a continuous-tone picture and the dot area percentage (y)
of the dot at the corresponding control point on a resulting halftone
picture, whereby the conversion formula (1) has been derived so as to
bring a theoretical value into substantial conformity with its
corresponding value measure actually.
The greatest merits of the tonal conversion method defined by the
conversion formula (1), which is performed by a tonal conversion system
provided with the photomechanical apparatus of this invention and adapted
to process pictorial information signals, are that the base density (x) at
a desired control point (X) on a continuous-tone picture can be converted
into the value (y) of the dot area percentage of the dot at the
corresponding control point (Y) on the corresponding halftone picture
while selecting the value (y.sub.h) of the dot area percentage of the
smallest dot at the brightest area and the value (y.sub.s) of the dot area
percentage of the largest dot of the darkest area in the printed halftone
picture and the values .alpha. and .beta., it is hence possible to know
with extreme ease which characteristics the halftone characteristic curve
is supposed to have in a halftone picture that a worker wants to form, and
the quality of a picture to be printed is always assured and a picture of
quality intended beforehand, which is to be printed, can be formed
directly on a machine plate.
The tonal conversion method which is practised by the photomechanical
apparatus of this invention and is defined by the conversion formula (1)
permits the selection of suitable y.sub.h, y.sub.s, .alpha. and .beta. as
desired. In addition, where the density range of an original
continuous-tone picture such a photographic color picture is different
from the density range of a printed halftone picture, it is only necessary
to conduct the tonal conversion of the picture by using a compression
method known very well in the present field of art, namely, by suitably
choosing the k value which is the ratio of the concentration range of the
picture to be printed to the density range of the original picture.
The photomechanical apparatus of this invention is equipped with a system
which performs the tonal conversion of pictorial information signals. "The
present conversion method", which is practised in the tonal conversion
system of the photomechanical apparatus of this invention, can conduct the
tonal conversion, modification or change of a picture by changing y.sub.h,
y.sub.s, k value, .alpha./(.alpha.-.beta.)=value .epsilon. suitably and
therefore has an extremely high degree of flexibility. In this regard, a
user (worker) should keep in mind that "the present conversion method"
defined by the conversion formula (1) has the following freedom upon its
application.
Freedom 1
The conversion formula (1) can be used to obtain a printed picture
conforming its corresponding original picture very well. Namely, the
conversion formula (1) can be applied while giving the priority to the
provision of a printed picture which looks exactly the same as the
original picture to the eyes of a man. Such a manner is described by the
term "tonal conversion" in this invention.
Freedom 2
The conversion formula (1) can be used to change or modify an original
picture in light of needs from the viewpoint of photomechanical
plate-making and printing techniques, artistic demands, orderers' needs,
etc. Namely, the conversion formula (1) can be applied in such a way that
a picture as observed through the eyes of a man itself is modified or
changed. Such a manner is described by terms "tonal modification (or
change)" in this invention.
The above-mentioned tonal conversion or tonal modification (or change) can
be carried out by changing the y.sub.h, y.sub.s, k value and .epsilon.
value suitably in the conversion formula (1).
"The present modification method" defined by the conversion formula (1) can
be practised by various apparatus capable of performing a photomechanical
process while processing pictorial information signals of an original and
conducting the tonal conversion and/or tonal modification (change) of the
picture, for example, photomechanical apparatus such as monochrome
scanners and color scanners and pictorial information processing apparatus
having analogous purpose, function and construction.
By allowing the tonal conversion system for pictorial information signals
to perform "the conversion method" of this invention in the above
described manner, it is possible to get rid of the conventional tonal
control method which relies upon experiences and perception, and hence to
perform the conversion of gradation (hence, tonal conversion) of a picture
rationally and suitably as desired while always assuring the quality of
the picture.
In the case of multi-color plate-making (the four plates, namely, cyan
plate, magenta plate, yellow plate and black plate are generally
considered to make up a unit), once the standard work characteristic
curve, namely, the standard halftone characteristic curve of a base plate
[in the case of multi-color plate-making, the cyan plate serves as a base
plate as known very well in the art] is determined, the standard work
characteristic curves of the other color plates can always be determined
rationally by multiplying the value y of the base plate with appropriate
conversion values which are based respectively on the gray balance ratios
of the corresponding individual printing inks on the basis of results of a
printing test. Moreover, all of the work characteristic standard curves
thus determined for the individual color plates are of course rational
characteristic curves and moreover, the mutual relationship in gradation
and tone among these characteristic curves is also rational and
appropriate. So long as the tonal conversion of a picture is conducted in
accordance with "the present conversion method", the conversion and
modification (change) of the gradation of a picture to be printed in
accordance with a multi-color printing technique can be effected
rationally while assuring the quality of the picture to be printed.
When the tonal conversion of a picture is performed by "the present
conversion method" at the tonal conversion system of the photomechanical
apparatus of this invention, no jumping (the gradation or tone becomes
discontinuous in a halftone picture) occurs in gradation on a printed
picture to be obtained. In order to rationalize the conversion and control
of a work standard characteristic curve further in response to a technical
demand in the photomechanical process, the position and number of control
points may be concentrated easily, for example, around 50% dot area
percentage as desired. This indicates the usefulness of this invention for
the solution of various problems pertaining the tonal conversion and
modification (change) of an intermediate tone, such that it is difficult
to achieve the gray balance (density balance) of an intermediate tone
(which means a halftone area, whose dot area percentage ranges from about
40% to about 80% on a print) in spite of today's wide-spread adoption of
advance photomechanical apparatus, the color of the intermediate tone is
dull and does not have any vivid tone, it is difficult to emphasize or
stress the intermediate tone (which is of course related closely to the
gradation and tone of the entire pattern), and the delicate gradation of
the intermediate tone cannot be reproduced well.
Although the photomechanical apparatus of the present invention is intended
to form a machine plate directly as described above, it is not excluded to
form an original printing film or to proof in order to control the quality
of a picture to be printed.
Furthermore, no limitation is imposed on the kind or type of the plate
material and the plate-making method, so long as a machine plate can be
formed. No limitation is imposed either on the means or method for
utilizing output signals obtained from a photo-mechanical apparatus such
as scanner.
In order to produce an original halftone film (halftone film) for a printed
picture from an original printing film in accordance with "the present
conversion method" defined by the conversion formula (1), a conventional
system known well in the present field of art can be used. The production
of such an original film can be achieved, for example, by designing the
color separation and halftone scanning system of a commercial electronic
color separation apparatus (color scanner or total scanner) or the like to
perform "the present conversion method".
In a commercial scanner for example, a small spot light is irradiated to
the original picture which is a continuous-tone picture. Reflected or
transmitted light (pictorial information signals) is separated through a
color filter, received at a phototube (photomultiplier), followed by
photoelectric conversion, A/V conversion, density conversion by a
logarithmic amplifier, and color modification and picture conversion by an
analog-type computer or after A/D conversion, by a digital-type computer.
Each current outputted finally from the computer is fed to an exposing
light source. A raw stock is then exposed to a spot light to form machine
plate adapted to make a printing plate. In such a well-known conventional
system, it is only necessary to design the conversion unit of the computer
in such a way that the tonal conversion method defined by the conversion
formula (1) is performed.
By causing a photoelectrically-scanning spot light to advance successively
in spots and synchronizing the exposure unit with the scanning, a machine
plate for a halftone picture which has the dot area percentage (y) defined
in the above conversion formula (1) and is to be printed can be formed.
Depending whether conversion is direct of indirect, tonal conversion
methods for pictures may be classified basically into methods for
immediately converting a continuous-tone picture having a linear density
gradation characteristic curve into a halftone picture and methods for
firstly performing the tonal conversion of a continuous-tone picture into
another continuous-tone picture and then transforming the thus-converted
continuous-tone picture into a halftone picture (since the tonal
conversion has been performed, the term "transform" is used here to
distinguish it from the conversion).
Each of the above-mentioned methods includes two approaches depending
whether a density range is compressed or not, namely, one for converting
the density range of a continuous-tone picture directly into a halftone
density range without compressing the former density range and the other
for converting the density range of a continuous-tone picture into a
halftone density range by way of an intermediate picture having a density
range corresponding to the halftone density range of a picture to be
printed. In the actual practice of plate-making, it is only necessary to
combine these fundamental methods of tonal conversion of a picture and to
choose one suited to the environment of the work.
As a representative example, FIG. 1(a) shows one embodiment in which the
base density range of a continuous-tone picture (original picture) having
a linear density gradation characteristic curve is proportionally
compressed to obtain an intermediate picture of a compressed density
range. Another example of converting the original picture into a halftone
picture by way of the intermediate picture of the compressed density range
is shown in FIG. 1(b). Namely, the continuous-tone picture (original
picture) having the linear density gradation characteristic curve is
tonally converted and at the same time, its density range is compressed,
thereby obtaining an intermediate picture whose tone has been converted
and whose density range has been compressed. This picture is then
converted proportionally to form a halftone picture.
In FIGS. 1(a) and 1(b),
D.sub.o : The density of an original picture whose gradation is continuous.
DR.sub.o : The base density range of the original picture whose gradation
is continuous. A value obtained by subtracting the density at the
brightest area (H; the smallest dot at the high-light area) from the
density at a control point (X) on the original, said density falling
within the range DR.sub.o, is the base density (x).
D'.sub.o : The density of an intermediate picture having a density range
obtained by compressing the density range of the original continuous-tone
picture by the k value.
DR'.sub.o : The density range of the intermediate picture having the
compressed density range.
D".sub.o : The density of a continuous-tone picture obtained by converting
the tone of the original continuous-tone picture in accordance with "the
present conversion method" and also by compressing the density range of
the original continuous-tone picture.
D.sub.p : The dot area percentage of a halftone picture to be printed.
DR.sub.p : The density range of the picture to be printed.
P: Halftone characteristic value based on a quality evaluation standard for
a picture to be printed. P value is compared with y value to evaluate
their matching.
H: The brightest area on the original (the smallest dot in the high-light
area).
S: The darkest area on the original (the largest dot in the shadow area).
M.sub.1 : An area on the original, which has an intermediate density
(intermediate density area).
M.sub.2 : A density area on the original, which determines the position of
the 50% dot (area) on a halftone picture to be printed.
These symbols will have the same meaning in Examples which will be given
subsequently herein.
ADVANTAGES OF THE INVENTION
The present invention exhibits the following superb effects.
(1) It is the most fundamental problem for the formation of a picture,
which is to be printed, how to determine the relationship between the
densities of an original picture (continuous-tone picture) and the values
of their corresponding dot area percentages of a picture (halftone
picture) to be printed. The determination has heretofore been conducted
primarily by a non-rational method, namely, depending on the experiences
and perception of a worker or based on information of a limited number of
fixed given conditions. By "the conversion method", the conventional
method can be replaced by a rational and simple method under any given
conditions. In view of the fact that the quality of tonal condition (tonal
conversion, modification or change), which is the most important
requirement for converting a continuous-tone picture into a halftone
picture, has a close and direct relation not only to the gradation of the
picture but also to the tone of the picture. The photomechanical apparatus
in which its important system for the conversion of a tone has been
designed to perform "the present conversion method" can systematize
theoretically, operatively and rationally the halftone scanning, color
separation work or electronic color separation work, so that the work can
be simplified. Its effect is hence extremely significant.
This contributes considerably not only to the photomechanical step but also
to the rationalization, systematization and simplification of the overall
process for the formation of printed pictures, including the
photomechanical step.
(2) By having the tonal conversion system of the photomechanical apparatus
perform "the present conversion method", the tonal conversion system of
pictures which is a source for confusion in the use of present electronic
color separation apparatus becomes no longer needed, so that the apparatus
can be rationalized and simplified and the production cost can hence be
cut down. The operation of such apparatus is also simplified and rendered
straight forward, whereby the redoing of the work can be reduced to an
extreme extent (original halftone films and proofs can be omitted), the
consumption of expendable supplies can be reduced significantly, and the
productivity of photomechanical apparatus can be improved substantially.
(3) Owing to the system which processes pictorial information signals and
performs "the present conversion method", a standard can be set up
rationally and easily for the quality evaluation of printed pictures
independently of the quality and details of original pictures.
In other words, a rational technical medium can be provided commonly to an
orderer of prints and a photomechanical engineer. It is hence ensured to
achieve mutual understanding with extreme ease between the orderer and
photomechanical engineer. It is hence possible to suitably meet needs of
an orderer or to make proposals from the side of plate-making engineers.
(4) The present invention can eliminate conventional operational
limitations caused by the poor photomechanical knowledge of design
engineers of color scanners, such that the selectable range of halftone
characteristic curves and color separation characteristic curves in the
present scanners is limited and the number of selectable curves in the
limited selectable range is very small (usually, only 3 curves).
Owing to the adoption of "the present conversion method", the work required
for a worker to input his desired halftone characteristic curves has been
rationalized and simplified, so that the time for the work can be
shortened to 1/5-1/10 compared with commercial scanners. When a scanner
equipped with a tonal picture conversion system capable of performing "the
present conversion method" is used, the input work itself is of course
rendered unnecessary.
(5) In the conversion of a continuous-tone picture for the formation of a
halftone picture from the continuous-tone picture, the relationship
between the conversion of the graduation of the picture add the conversion
of the tone of the picture as well as the relationship between the
conversion of the tone and color correction, color modification, color
change and retouching can be clarified by the adoption of "the present
conversion method". It hence becomes feasible to rationally meet each of
such operations.
The color modification work required as everyday work in the present color
separation work, namely, the correction of the so-called color fogging in
color pictures can hence be omitted automatically, provided that the color
separation work is conducted basically by using "the present conversion
method", the tone0rendering-first-ism in the tonal conversion of the
picture and the 4-point control method for the tonal conversion and by
maintaining good gray balance over the entire gradation of the picture to
be printed.
Owing to these features, the photomechanical apparatus of this invention
has provided an extremely effective means for the rationalization of the
process of photomechanical work.
(6) The use of "the present conversion method" has made it possible to
rationally and easily set up a standard for the quality evaluation of a
halftone picture (printed picture) independently of signals corresponding
to the pictorial information of an original picture. Coupled with the
possibility of provision of density gradation characteristic curves for
the high-light area, shadow area and high-light to shadow area of the
original picture, it is possible to substantially rationalize the system
of the present advanced photomechanical apparatus.
(7) The adoption of "the present conversion method" for the processing of
pictorial information signals has made it possible to effectively conduct
the education and training of engineers, which are considered to be
indispensable in view of the advancement of photomechanical apparatus. It
is hence possible to avoid unnecessary labor in the daily work and to
secure sufficient time for new and creative R & D activities.
EMBODIMENTS OF THE INVENTION
The photomechanical apparatus of this invention will hereinafter be
described in detail on the basis of certain embodiments. It should however
be borne in mind that the present invention is not limited to or by the
following embodiments so long as the essential features thereof are not
departed. (i) Application of a tonal conversion system, which can perform
"the present conversion method", to conventional scanners:
Embodiments of the photomechanical apparatus according to this invention
will next be described with reference to FIG. 2--FIG. 6. These embodiments
will demonstrate that the application of a tonal conversion system
pertaining to this invention to a present color scanner can simplify or
significantly modify its construction to improve its function.
In FIG. 2, a color scanner is constructed of four blocks, namely, a
detection unit 1 for reading an original, a color separation unit 2 for
converting output signals Y,M,C,K of the detection unit 1 into their
corresponding color-separated signals, a tonal conversion unit 3 for
obtaining an appropriate halftone gradation by using "the conversion
method" described above, and an output unit 4 for performing the exposure
of a film by a laser beam on the basis of signals outputted from the tonal
conversion unit 3. The blocks of the detection unit 1, color separation
unit 2 and output unit 4 have constructions similar to their corresponding
units in conventional scanners.
The detection unit 1 detects light transmitted through or reflected by each
area of an original 5 by means of a photomultiplier (not illustrated) or
the like and outputs individual signals R,G,B,USM as current values. The
signals are then converted into their corresponding voltage signals at an
A/V converter 6.
The color separation unit 2 subjects the individual voltage signals
R,G,B,USM, which have been fed from the detection unit 1, to a logarithmic
operation at a logarithmic amplifier 7 so as to convert them into their
corresponding densities. At a basic masking 8, the gray (K) component is
separated from these densities, followed by separation of the individual
components Y,M,C. Y-plate component, M-plate component and C-plate
component are then controlled relative to the individual original color
components R,G,B and Y,M,C at a color collection u | | |
