JPH0634500B2 - Management method of halftone dot area percentage when creating halftone image - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial field of application) The present invention relates to a novel method for controlling halftone dots, which is the most basic component of a printed image, and more specifically, photoengraving (photographing). A half-tone dot that is the most basic component of a halftone dot print image by using technology to form halftone dots using a contact screen) or electronic plate making (electronically forming halftone dots in a scanner, etc.). It is intended to provide a rational and scientific method of controlling the size of dot (dot area percentage) when forming dots.

(Prior art and its problems) In order to create a printed image (printed matter), a continuous tone original image must be changed to a halftone dot tone, and a platemaking process by halftone (screening) is essential. Is.

In this type of plate-making technology, continuous tone original images (one-color and multi-color photographic images, positive and negative photographic images,
Mainly photographic images such as reflection and transmission photographic images) are used for shading with a photomechanical camera, or electronic platemaking equipment such as a monochrome scanner, color scanner, total scanner, etc. Electronic color separation work and half-tone dot work are performed to create a printing original plate with halftone dots or a printing plate directly.

The so-called direct plate plate making method of directly making a printing plate is applied only to a very limited number of cases such as a newspaper in which the image quality of a printed image in a printed matter may be sacrificed.

Then, in these plate making techniques, the quality of the halftone dot print image formed in the printing original plate is inspected (plate inspection), in-school, re-school, etc. Then, it is a usual method to prepare a final printing plate.

That is, in the current ordinary method of photographic or electronic platemaking, halftone dot management, which is the most important in creating a print image with halftone dots, is irrationally and unscientifically performed.
Due to this, the work process of making and proofing the printing original plate is indispensable, and it is not possible to omit or greatly save labor.

The present inventors re-examined all processes, elemental works, elemental technologies, and technical systems from the production of original images to the production of printed images in order to establish a rational plate-making system, and included in that. We have made various proposals to rectify the errors and flaws. For example, a proposal for improving the image quality evaluation of a print image (a proposal for separately measuring and managing "the size of a halftone dot" and "the density of a printing ink" which are two basic elements of the print image configuration), color Tone adjustment in image adjustment to rationalize disassembly work Proposal of the first principle and 4-point management method (at the sample point for management, at least H (the brightest point in the highlight part), S (the darkest part in the shadow part) Points), M ₁ (intermediate density point of the image), and M ₂
(Proposal to include four positions of 50% halftone dot setting), and proposal for improvement of mechanism of advanced photomechanical machine applying these techniques (for these, see, for example, JP-A-54-9).
7101, 54-98801, 54-103101, 54-115901
No. 54-115902, Japanese Patent Publication No. 62-11337), and so on. Among the above proposals
No. 62-11337 relates to a gradation management method when a halftone dot print image is created from a continuous gradation original image, and the following management method is proposed there. There is.

That is, FIG. 1 shows a work reference characteristic curve (standard tone characteristic curve) that is a reference for work when converting a continuous tone image (original image) into a halftone image (print image). It has been proposed to set a curve passing through a specific range (hatched portion in FIG. 1) and manage the gradation. More specifically, in FIG. 1, the horizontal axis represents the optical density (OD) of the original image, the vertical axis represents the density (PD) of the halftone dot image, and the horizontal axis represents the original image density area (OD). HS, for example, the brightest point (H) density 0.02, the darkest point (S) density 3.02), the halftone dot density image on the vertical axis (hs, for example, set this mechanical range to 1.22) Yes) is set. Then, in such a coordinate system, the standard gradation characteristic curve is defined as: a halftone dot H ″ of the extreme point (the brightest point) of the highlight part of the document, and a halftone dot dot (the darkest point) of the shadow part of the document Point S ″, ● An intersection A ″ of a line XX ′ parallel to the horizontal axis on the 50% halftone dot and AA ′ which is a line parallel to the vertical axis of a = 1 / 4HS, and a line XX ′ and b = 1/3 HS, the intersection point B ″ with BB ′, which is a line parallel to the vertical axis, and MM ′, which is a line parallel to the vertical axis in the middle part of the density of the picture, and the horizontal axis of C = 1/4 hs. An intersection C ″ with a parallel line CC ′, a line DMM ′ with a line MM ′ and a line DD ′ parallel to the horizontal axis of d = 1 / 3hs, and the above H ″, A ″, The setting is made so as to pass through the shaded portion surrounded by B ″, C ″, D ″, and S ″, and the halftone dot gradation at the time of print image creation is managed based on this setting. This method of controlling the halftone dot gradation greatly advances from the method that depends on the experience and intuition of the operator, which is seen in the conventional plate making work, in the process of forming the most important halftone dot in the production of the printed image, and it is a constant method. It provides a reasonable work standard.

However, when creating a print image, it is of course necessary to simply create a print image in which continuous tone is faithfully converted to halftone dot tone, and to consciously modify the original image (for example, to emphasize a certain part). ), Or changing (for example, completely changing the image quality) a printed image, or in the halftone area (area that expresses gradation by halftone dots whose dot area is about 40-80%). It is also important to obtain a printed matter with excellent gradation, and from the viewpoint of appropriately dealing with these, there is a limit to the halftone gradation management method proposed above.

Those skilled in the art will carry out plate making work based on rational and scientific halftone dot management, eliminate proofreading work, or save labor as much as possible, and establish plate making technology that can obtain printed images with stable image quality. Is urgent.

(Problems to be Solved by the Invention) The present inventors eliminate the proofreading work or save labor as much as possible to rationally and scientifically create a print image of stable image quality and a print image corresponding to various requirements. For the purpose of establishing a plate-making technology that can be performed, we studied in more detail each process of photoengraving, each work, the elemental technology applied to them, and the overall technical system.

As a result, in the current photographic or electronic platemaking method, it is the first work in the work process in the process of creating a halftone dot print image from a continuous tone original image,
Moreover, the gradation conversion work (halftone dot management) of images by halftone dots, which is the most basic and basic work process, is unscientific and irrational, and if this is not solved, reliable platemaking technology will be established. Has come to the idea that is difficult.

That is, the image gradation conversion work for converting a continuous tone original image into a halftone dot print image by the current photoengraving method or electronic platemaking method is essentially a platemaking machine involved in these platemaking operations. It is unscientific and irrational in the present condition that it is done based on the experience and intuition of the designer of the site or the workers of the site, or based on one or more fixed data of the condition. Yes, and again lacks the flexibility of work.

For this reason, continuous gradation is converted to halftone gradation by performing half-tone dot work or color-resolving / half-tone dot work by using sophisticated electronic plate making equipment such as monochrome scanner or color scanner. At this time, a work reference characteristic curve which is a reference for those operations (a characteristic curve which should also be a reference for those operations when performing a halftone operation or a color separation operation, a halftone dot (halftone) characteristic curve, As the color separation (density) characteristic curve), it is determined in advance by the equipment manufacturer based on experience and intuition or a limited number of materials based on fixed conditions, and it is stored in the storage device of these equipment in an irrational manner. I have no choice but to use scientific and non-scientific ones.

Therefore, for the operator who uses the equipment, the quality and the number of technical work options in the plate making work are basically limited by the irrational and unscientific knowledge of the design engineer of the equipment. It's closed. In addition, the technical and technical needs for highly sophisticated and diverse needs for printed images and non-standard manuscript images (images of color manuscripts having qualities other than the color manuscript quality assumed by designers of plate making equipment) The quality and range of correspondence are limited, and in such a case, the gradation of the image is adjusted based on the experience and intuition of the operator.

In these devices, the operator arbitrarily sets a work reference characteristic curve (standard halftone dot gradation characteristic curve), stores it in the storage device of the same device, and stores it as necessary. There is also a system that can be used. However, even though the procedure involves complicated basic experiments and is a complicated work that requires a lot of time, labor, and cost, the newly set work standard characteristic curve has the above-mentioned limitations of the basic constraints. It cannot be set reasonably and scientifically beyond. In the current state of the industry, there are increasing cases in which work ratio characteristic curves must be newly set rationally and scientifically beyond the limits of the basic restrictions.

In addition, as described above, the present inventors
Sophisticated electronic platemaking equipment such as scanners and color scanners basically lack sufficient knowledge necessary for platemaking and printing, and their design technology is color separation based on the photographic masking method. Constructed with a primary focus on theory (dotted dots are essential components in printed images, but these are not treated primarily), and further improvements to the device I think that it was basically a corresponding therapeutic measure based on the color separation theory.

That is, in the conventional design technology of the scanner device, when the gradation is converted from the photographic original image to the halftone dot image in the color separation work, the color correction and the color correction are the primary meanings, and the adjustment of the gradation of the image is performed. Secondly, for that reason, it is extremely important for the adjustment and control of the gradation of the image to stabilize and enhance the quality of the printed image and to adjust and control the gray balance of the halftone.
% Position to set halftone dot (problem where 50% halftone dot is set in original image density area) and management of halftone dot area (how much halftone dot size should be set for each density point in original image density area) I was indifferent to the question of whether to set), and remained obsessed with the three-point control method, which suffices to control three points of H, S, and M ₁ . In addition, how a small change in halftone dot area at each halftone dot, which is an extremely important knowledge regarding plate making and printing, has a great influence on the change in gradation and color tone of a printed image, which is an aggregate of many halftone dots. The current situation is that sufficient consideration has not been given to this. Due to such reasons, in the conventional plate-making technology, the control of the position where 50% halftone dot is set and the halftone dot area are neglected. However, the print image with halftone dot gradation is expressed. There are two basic components for "area of dot" and "reflection density of ink".
Regarding the above-mentioned “ink reflection density” factor, the amount of ink that can be adjusted on the printing machine (in other words, the amount of ink that can be adjusted on halftone dots) is the Y plate (yellow plate), M plate (magenta plate). ), C version (cyan version) about 20% (black board about 40%)
In addition, considering the objective fact that the human visual sense has the ability to easily identify a 1% difference in “halftone dot area” percentage as a density difference, the halftone dot image is produced with halftone dots. It turns out that the management of the dot area is extremely important. A printed image is a world of halftone dots, and the primary consideration in creating a printed image is the adjustment of gradation by halftone dots and the management of halftone dots. In this respect, in the conventional gradation adjustment method from a continuous tone image to a halftone image, the density value at an arbitrary sample point on the continuous tone image and the corresponding halftone image on the halftone image There was no means (a method of controlling the dot area percentage) to reasonably and universally relate the dot area percentage of the dot at the sample point.

The inventors of the present invention have conducted earnest research to overcome the limitation of the conventional gradation adjustment technique from a continuous gradation image to a halftone dot image, which is irrational and unscientific. To devise a new gradation adjustment method that associates the basic density value of an arbitrary sampling point on a continuous gradation image with the numerical value of the dot area percentage at the sampling point corresponding to this Further, they have found that this new, rational, and scientific gradation adjustment method is extremely effective for halftone dot management at the time of plate making, and have completed the present invention.

[Structure of Invention]

(Means for Solving Problems) When the present invention is summarized, the present invention relates to a method for controlling a dot area percentage when a print image having a dot gradation is created from a document image having a continuous gradation. ● The brightest point (H
Point), the darkest point (S point), and the desired density point between the brightest point (H point) and the darkest point (S point), and the halftone dot area percentage of each control sample point. (Y) is calculated from the basic density value (x) at each control sample point (difference between the density value at each control sample point and the density value at the brightest point) using the following relational expression (1): A method of controlling the halftone dot area percentage when creating a halftone dot print image from a continuous tone original image, characterized in that the halftone dot area percentage of each control sample point is managed based on the value. It is about.

<Relational expression> However, x: basic density value of an arbitrary control sample point X on the original image. That is, the difference between the density value at the arbitrary control sample point X of the same image and the density value at the brightest point (point H) of the same image.

y: Numerical value of the halftone dot area percentage of the halftone dot of the control sample point Y corresponding to X on the printed image.

y _h: is set for the brightest point of the printed image (H point), any desired size of the dot area percent of the value of the halftone dots.

y _s : Numerical value of halftone dot area percentage of halftone dots of a desired arbitrary size set with respect to the darkest point (S point) of the printed image.

α: reflectance of printing paper.

β: Surface reflectance of printing ink.

k: Indicates the ratio of (print image density area) / (original image density area).

Hereinafter, the configuration of the present invention will be described in detail.

First, regarding the positioning of the relational expression (1) applied to the adjustment of the gradation that is the core of the method of controlling the halftone dot area percentage when creating a print image from a document image that is continuous gradation of the present invention explain.

In a halftone dot image which is a print image, the basic constituent elements for expressing the print image are two elements, "halftone dot area" and "reflection density of printing ink". Regarding the factor of "reflection density of printing ink", the amount of ink that is adjusted on the printing machine (in other words, the amount of ink that is adjusted on halftone dots) reaches about 20%. About 20 for Y, M and C editions
% (± about 10% based on the appropriate ink density), BL
The (black) plate is adjusted by about 40% (also ± 20%). Regarding the reflection density of printing inks of secondary colors or more, surface reflection, multiple internal reflection, opacity of ink, trapping, It is a generally accepted phenomenon that the principle of additive rule failure that the sum of individual ink densities does not result in the fact that the sum of individual ink densities does not occur due to factors such as light scattering into the paper. Considering the objective fact and the empirical rule that 1% difference in “dot area” percentage can be easily identified as the density difference, the halftone dot area (printed image) It turns out that management is extremely important, and that halftone dot management must be the primary important management point.

The size of halftone dots (percentage of halftone dots) is the variation of the exposure amount during plate making (variable factors such as exposure time and reduction of lamp irradiation ability), sagging of halftone dots during printing, printing pressure, etc. It is a well-known fact that the image quality varies greatly depending on the image quality. The change in diameter of halftone dots (circular or square dots) and the rate of change from the reference halftone dot area are summarized below, and even a slight change in halftone dot diameter causes a change in image quality (for human visual perception). The importance of its management is understood. Further, as shown in the table below, it can be easily understood that the variation amount of the size of the halftone dot is larger than the variation amount of the above-mentioned "reflection density of printing ink".

Further, in relation to the above, in the plate making work, the quality contents of the original image are varied, and the print image forming process following the plate making work is diverse, and each process has its own work characteristics. However, in order to overcome these complicated and unstable factors, the continuous tone of the original image When converting the image into a halftone dot image which is a print image, the respective halftone dot areas of the brightest minimum dot (y _h ) and the darkest maximum halftone dot (y _s ) in the halftone image to be created. While arbitrarily selecting the percentage, the gradation of the image from the brightest part to the darkest part of the two images (the original image and the printed image) is
It is absolutely necessary to provide a rational and simple gradation adjusting means that can correspond to 1: 1.

The tone adjustment method defined by the above relational expression (1) was devised based on such an idea, and in the present invention, this is also referred to as “main adjustment method”.

According to the present invention, the management of the halftone dot area percentage when a print image having halftone dot gradation is created from a document image having continuous gradation is to be rationally performed by the "main adjustment method" described above. .

The "main adjustment method" defined by the relational expression (1) is based on the numerical values of the reflection density of the printing paper and the printing ink, and the size of the halftone dot desired to be placed on H and S of the printed image is arbitrary. Select the value of the halftone dot area percentage (y) of the corresponding control sample point (Y) on the print image from the basic density value (x) of the arbitrary control sample point (X) on the original image. It is done as you ask. These densities are generally measured using a color densitometer (transmission type, reflection type, dedicated type, common type, etc.), but when using a scanner, the density measurement mechanism attached to the scanner is used. Just measure.

The above-mentioned relational expression (1) for obtaining the numerical value (y) of the dot area percentage is the generally accepted density formula (photographic density,
Optical density), that is, D = log I _o / I = log 1 / T I _o = incident light amount I = reflected light amount or transmitted light amount T = I _o / I = reflectance or transmittance.

Applying this general formula for density D to platemaking and printing, Here, A: unit area d _n : area of halftone dot in unit area α: reflectance of printing paper β: surface reflectance of printing ink

The present invention the concentration formulas for this plate-making and printing (D '), the brightest portion minimum halftone dot area percent of the halftone image created as described above (y _h) and darkest maximum dot area percent (y _s ) is set arbitrarily, and the basic density value (x) at any control sample point (X) on the continuous tone image
And the corresponding control sample point (Y) on the halftone image
The relational expression (1) is derived so that the theoretical value and the measured value approximately match with each other by incorporating a request to associate the numerical value (y) of the dot area percentage of the halftone dot.

Applied to the management of the dot area percentage of the present invention, the greatest feature of the "main adjustment method" defined by the relational expression (1) is that the brightest portion minimum dot in a printed image is a dot gradation. Of the halftone dot area percentage y _h and the maximum halftone dot halftone dot area percentage value y _s , and the α and β values are arbitrarily selected, and arbitrary control sample points on the continuous tone image are selected. The basic density value (x) in (X) can be converted into the numerical value (y) of the halftone dot area percentage of the halftone dot in the control sample point (Y) on the halftone dot image corresponding to that control sample point. That is, what characteristics the halftone dot gradation characteristic curve should have in the halftone dot gradation image (print image) that the operator is going to create is set at an arbitrary control sample point, for example, the H, M _2, M _1, at least 4 points S (4-point management method) By plotting the (x) value and the (y) value to obtain the characteristic curve, it is possible to know very easily, and based on the (x) and (y) values of these control sample points, or (x ) And the (y) value, the halftone dot characteristic curve is used to control the halftone dot forming operation during plate making to always and reliably guarantee the image quality of the printed image and print the image with the intended image quality in advance. This means that an image can be formed on a printing original plate or a printing plate.

In the “main adjustment method” defined by the relational expression (1) applied to the management of the dot area percentage of the present invention, y _h and y _s , α value and β value are arbitrarily selected as described above. In addition, if the original image density area of a continuous color tone such as a color photographic image and the print image density area of a halftone dot are different, a compression method known in the art is adopted, that is, (print image density area) /
The k value, which is the ratio value of the (original image density range), may be appropriately selected to adjust the gradation of the image.

Further, the “main adjustment method” defined by the relational expression (1) applied to the management of the halftone dot area percentage of the present invention is y _h , y
_s , k value, It is possible to rationally convert the gradation from continuous gradation to halftone dot gradation by changing appropriately, and it is possible to further correct or change the gradation, which is extremely flexible. That is a major feature. If this point is described in detail, it should be noted that the operator has the following degrees of freedom when operating the “main adjustment method” defined by the relational expression (1); ): Apply relational expression (1) to reproduce a printed image that is faithful to the original image. That is, the relational expression (1) should be used, primarily considering that the same visual sensory images as observed by the human eye are obtained. This attitude
In the present invention, the term "gradation conversion" is used.

(Part 2): Applying the relational expression (1) so as to correct or change the image quality of the original image according to platemaking / printing technical needs, artistic requirements, and needs of the print orderer. thing. That is, the relational expression is used to correct or change the visual sensory image itself observed by the human eye.
Use (1). This attitude is described in the present invention by the term "correction (or change) of gradation".

The above-mentioned gradation conversion and gradation correction (or change) are
This can be done by appropriately changing y _h , y _s , k value, and ε value of the relational expression (1).

Next, a method of managing the halftone dot area percentage when a print image having halftone dot gradation is created from a document image having continuous gradation according to the present invention will be described.

In the halftone dot area percentage management method of the present invention, first, it is necessary to determine what kind of image quality a print image is created from, that is, how to convert / correct / change the gradation. In the present invention, as described above, the conversion / correction / change of the gradation can be rationally performed by the “main adjustment method” defined by the relational expression (1).
Therefore, the constant values (y _h , y _s , α, β, of the relational expression (1) are adjusted so as to be suitable for the tone adjustment work (tone conversion / correction / change work) for obtaining a desired printed matter. k value). Then, the basic concentration value (x) of the desired control sample point (X)
Is substituted into the relational expression (1) to obtain the numerical value (y) of the dot area percentage. In addition, when the basic concentration value (x) is plotted on the horizontal axis of the plane coordinates and the halftone dot area percentage (y) is plotted on the vertical axis, and the numerical values of both are plotted based on the relational expression (1), the relational expression (1) is obtained. As a matter of course, a halftone dot gradation characteristic curve similar to the curve shown in FIG. 1 is obtained.

The halftone dot gradation characteristic curve defined by the relational expression (1) of the present invention is different from that of FIG. 1 in that the basic density value (x) and the halftone dot area percentage (y) at arbitrary control sample points. Is 1: 1
Corresponding to, and thus the percent dot area (dot size) at any number of the desired significant control sample points.
Since it can be calculated instantly, it is a very useful tool for controlling the dot area percentage (dot size).

In the control of halftone dot gradation, that is, in the control of halftone dot area percentage, an important control sample point to be particularly considered is the sample point between H and M ₁ . The reason is as follows.

As is well known in the plate making technology, as shown in FIG. 1, the H point (the brightest part) and the M point in the density range of the original image.
= 1 / 2HS (the intermediate density point of the pattern, which will be described as M ₁ in the present invention), in order to reproduce the original image (pattern) with halftone dots, a halftone dot area larger than 50% halftone dot is used. Must be used. In other words, it should be noted that the position where the 50% halftone dot is set does not correspond to the intermediate density point (M ₁ ) of the original image, but is much closer to the highlight portion. In the conventional halftone dot management, as mentioned above, we stick to the three-point management method, in which it is sufficient to manage the three points H, S, and M _{1. In} this management method, the printed matter is reproduced with halftone dots. It is extremely important to do this, and the control sample points that are convenient to set as a guideline for management, such as the above-mentioned 50% halftone dot management, are missing.

Due to the defect of the conventional halftone dot management described above, sophisticated scanners are now widespread, and electronic platemaking is actively performed by this, but halftone (on printed matter Halftone dots are about 40% to about 80% halftone dots)
It is difficult to obtain the gray balance (density balance) of
Adjusting the halftones, such as not being able to produce the volume feeling of the halftones (which naturally also has a close relationship with the tone and color tone of the entire pattern) and the difficulty of producing delicate tones of the halftones There are many problems in (gradation conversion / correction / change).

Therefore, in managing the halftone dot area percentage (size of halftone dot), for example, H, M ₂ (50% halftone dot original image is set as compared with the conventional three-point management method of H, M ₁ and S). It is extremely important to control four points (control sample points on the concentration range), M ₁ and S, and the method for controlling the dot area percentage of the present invention can reasonably perform this.

In the halftone dot area percentage control method of the present invention, an arbitrary number of control sample points can be concentrated in the vicinity of 50% halftone dots, which is extremely important in halftone reproduction as described above. It is possible to rationally solve various problems associated with the reproduction of halftones.

Further, in the present invention, in addition to the above-mentioned control points near 50% halftone dots, arbitrary control sample points between M ₁ and S can be set to control the halftone dot area percentage during plate making. The control point in this area is near the shadow area, and even if the size of each halftone dot becomes considerably large and the halftone dot area is slightly different from the optimum value, the color of the ink on the halftone dot The human eye irritation value does not affect the image quality of the printed matter as much as it does in the vicinity of 50% halftone dot. Therefore, the control points in this area are less important than the control sample points near the 50% halftone dot, which is important for the reproduction of halftones, etc., but the gradation of the shadow part is corrected. / Considering changes (such as emphasizing shadow areas) is still an important control point.

It should be noted that multi-color plate making (generally considered to be one set of four plates of cyan, magenta, yellow, and black) and a reference plate (in the case of multi-color plate making, the cyan plate is the standard plate as well known). This is because the stimulus value of the cyan ink used for the cyan plate is smaller than that of the other inks, and in order to express an appropriate gray-black color, the maximum halftone dot of the cyan plate should be made larger than that of the other plates. The size of the halftone dots of other plates is determined based on the maximum halftone dot of this cyan plate.) Method, the work standard characteristic curves of other color plates are determined based on the results of the printing test, and the appropriate (y) value of the plate is based on the gray balance ratio of each printing ink. Always make a reasonable decision by multiplying the adjustment value Can. Moreover, the halftone dot gradation characteristic curves of each color plate determined in this way are not only rational characteristic curves, but also the mutual relations between the characteristic curves concerning gradation and color tone. Is also rational and appropriate. That is, the relational expression of the present invention
By controlling the halftone dot area percentage based on the halftone dot characteristic curve of each color plate defined in (1), the gradation conversion and correction (or change) of the print image in multicolor printing can be always and surely performed. , Can be done reasonably while guaranteeing the image quality of the printed image.

As described above, based on the “main adjustment method” defined by the relational expression (1) of the present invention, or the “main adjustment method”
By controlling the halftone dot area percentage based on the halftone dot gradation characteristic curve obtained by applying, a halftone dot management method that relies on conventional experience and intuition, or a fixed number of fixed conditions can be obtained. Eliminate the halftone dot management method based on materials, and perform rational and accurate conversion of gradations (and thus color tones) and corrections (or changes) of gradations, always and surely while guaranteeing the image. Will be able to.

The halftone dot area of the present invention is applied to the control method of percentage, and the "main adjustment method" itself defined in the relational expression (1) is directly applied to a printing image original plate (halftone film) or a printing plate. Needless to say, it can be used when making.

For example, a commercial scanner irradiates an original image that is a continuous tone image with a small spot light, separates this reflected light or transmitted light (image information signal) with a color filter, and receives it with a phototube unit (Photomul). Then, photoelectric conversion, A / V conversion, density conversion by a log amplifier, color conversion, gradation adjustment, etc. are performed by an analog type computer or an A / D converted and digital type computer, and finally a computer. A well-known existing plate-making system in which the current value output from the device is supplied to the exposure light source, and spotlight is applied to the photosensitive material (photosensitive film, photosensitive resin, organic semiconductor, and other photosensitive material) to perform platemaking. In the computer section,
All that is required is to incorporate the "main adjustment method" specified in (1). That is, the “main adjustment method” algorithm may be incorporated in the computer unit by software or the like, and the (y) value may be calculated from the (x) value as the image information signal.

If the spot light for photoelectric scanning is sequentially advanced while being divided into points, and the exposure unit is also synchronized with this, the relational expression
It is possible to prepare a printing image original plate or a printing plate having a halftone dot gradation having the halftone dot area percentage (y) defined in (1).

The halftone dot area percentage management method of the present invention makes it possible to rationalize the control of the plate making work by the existing system by utilizing the computer capability provided in the existing scanner or improving the management panel. Can be changed to

For example, an arbitrary number (however, 4 points of H, M ₂ , M ₁ and S are important control points) basic density values at control sample points are input to a computer of an existing scanner, and the control sample points are input to the control sample points. The halftone dot area percentage at the sample points on the corresponding printed image is calculated, and the calculation result is displayed numerically on the control panel of the existing scanner or on the TV screen to manage halftone dots during plate making. You can do it.

Needless to say, if the computer of the existing scanner does not have the surplus capacity, the result calculated by another microcomputer or the like may be displayed for the off type. An example of the display unit of the management panel is shown in FIG. 2, but it goes without saying that other display units may be used.

Next, before explaining the novel method of controlling the halftone dot area percentage of the present invention by way of examples, based on FIG.
An outline will be given of how the “main adjustment method” defined in (1) is used for image gradation adjustment (gradation conversion / correction / change).

For example, in the method of converting the gradation of an image, basically, a continuous gradation image having a linear density gradation characteristic curve is immediately converted into a halftone dot image depending on whether the conversion is direct or indirect. And a method of converting to a gradation in a continuous tone image first, and then converting to a halftone dot image through the gradation-converted continuous tone image (gradation conversion has already been performed. Therefore, the term conversion is used here). Further, in any of the above-mentioned methods, a method of directly converting a density range of a continuous tone image into a halftone dot density range without compression depending on whether or not the density range is compressed, and a halftone dot level of a print image There is a method of performing it through a density range compressed original image corresponding to a tonal density range. In the actual plate making practice, it is sufficient to combine the basic methods of the gradation conversion method of these images and select the one suitable for the work environment.

As a typical example, FIG. 3 (a) shows that the basic density area of a continuous tone image (original image) having a linear density gradation characteristic curve is proportionally compressed to obtain a density area-compressed original image. An example of converting to a halftone dot image via this is shown in Fig. 6 (b), where a continuous tone image (original image) having a linear density tone characteristic curve is tone converted and the density region is compressed at the same time. An example will be shown in which a gradation-adjusted density-area compressed original image is obtained, and then this image is proportionally converted to form a halftone dot image.

In FIGS. 3 (a) and 3 (b), D _o is the density value of the original image of continuous tone.

DR _o ... Basic density range of original image with continuous tone.

The difference between the density value at the sample point (X) on the original document within this DR _o and the density value at the brightest point (the extreme point of the highlight part) (point H) becomes the basic density value (x).

D _o ′ ... Density range compression obtained by proportionally compressing the density range from the k value of a continuous-tone original image The density value of the original image.

DR _o ′ ... Density area The density area of the compressed original image.

D _o ″ ... Density value of a continuous tone image obtained by converting the tone of a continuous tone original image by the “main adjustment method” and compressing the density range.

DR _o ″ ... The density range of a continuous tone image in which the original image of continuous tone is converted by the “main adjustment method” and the density range is compressed.

D _p ... halftone dot area percent area of a printed image having halftone gradation.

DR _p ... print image density range.

P: halftone dot gradation characteristic value based on the quality evaluation standard of the printed image. The P value is compared with the y value to assess the consistency of the two.

H ... the brightest point on the document (highlight portion of the pole) S ... darkest point on the original point of the middle part of the concentration on the (shadow portion of the pole) M ₁ ... document (middle density point) M ₂ ... Point for locating 50% halftone dot (area) in a halftone dot print image The meanings of these symbols are the same in the examples described later.

(Example) Hereinafter, based on the halftone dot area percentage management method of the present invention, that is, from the original image that is continuous tones to halftone dots based on the "main adjustment method" defined in the relational expression (1). A method of managing the halftone dot area percentage when creating a print image will be described in detail.

(i) Operation experiment of "this adjustment method" The following two experiments were conducted to create a halftone dot area percentage control table using this "adjustment method".

(a) First of all, an ordinary simple calculator, that is, a product name Sharp Pitachorus EL509A (manufactured by Sharp Corporation) is used to operate the simple calculator while applying a required numerical value to the "main adjustment method". Table 1 (1) (2) (3), 2nd
Tables and halftone dot area percentage control tables shown in Table 3 were prepared.

As a result, the time required for this was 3 hours, 2 hours, and 2 hours, including the inspection time of the calculation result.

If the operator is proficient in this work, the work time can be reduced to about 1/2.

(b) The following experiment was also conducted.

Simple personal computer (NEC PC-98
01-M2), the required software (relational expression (1)
The software for calculating the (y) value from the (x) value is input as function data based on the above, and from the density value of the original image (continuous tone image), the halftone dot of the halftone image corresponding to the density value is input. The work of calculating the numerical value of the dot area percentage was performed.

As a result, as a matter of course, the same numerical value as the result of the manual calculation using the above-mentioned simple calculator was obtained.

Moreover, in this experiment, the calculation software based on the relational expression (1) to be used for controlling the dot area percentage input to the personal computer was created without using special software. When the creation work was performed using the attached N88-BACIC, it took only 1 hour to complete the work.

Further, in an experiment for creating a halftone dot area percentage control table using the software created as described above, a densitometer for highlight (H) and shadow (S) of the original image is used instead of the basic density value of the original image. It was confirmed that even if the measured values were entered as they were, a similar control table of the dot area percentage could be created.

Further, based on the created software, a desired density interval (for example, 0.00 to 1.00 is incremented by 0.05 and 1.00 to 3.00 is incremented by 0.10) is provided in the density range of the original image, and the value (x) is set. By inputting an instruction to the same personal computer, it was possible to obtain the numerical value (y) of the halftone dot percentage corresponding thereto.

In addition, by inputting the density values of arbitrarily set control sample points from the highlight to the shadow on the original image, it is possible to obtain the numerical value of the halftone dot area percentage corresponding to it. It was

The numerical value of the halftone dot area percentage by the software described above can be output independently or at the same time for both a positive image and a negative image.

The usefulness of Tables 1 (1) (2) (3), 2nd Table and 3rd Table shown below will be described.

[Table 1 (1) (2) (3)] Table 1 shows the density of printing ink (print image density area) and the range of use of halftone dots (when printing black and white images from original images). In order to obtain an ideal halftone dot gradation characteristic curve when the use range of halftone dots is changed according to the standard method of black and white halftoning work, the numerical value of the halftone dot area percentage at each control sample point is obtained. It is a list of what must be done. In Table 1, the control sample points are 0/8 (point H), 1/8, and 2/8 of the original image density range.
(M ₂ points), 3/8, 4/8 (M ₁ point), 6/8, 8/8
It is set to (S point).

Further, from this list, even if the printing ink density (print image density area) is the same, how the ideal halftone dot gradation characteristic curve changes when the usage range of halftone dot area percentage is changed. Or you need to change it.

It should be noted that a technique and method capable of creating a black-and-white print image that is a halftone dot gradation image corresponding to 1: 1 from a document image that is a continuous-tone image and adjusting the gradation of the black-and-white print image arbitrarily Acquiring is also the basis of the multicolor plate making work.

[Table 2] Similar to Table 1, Table 2 shows that when a black-and-white print image is created from a document image, if the density of the printing ink (print image density range) changes, the halftone dot area percentage is 0%. (Part H) to 10
Each control sample required to produce a printed image with the same image tone and similar image quality to the human visual sense while using 0% (S part) This is a list of halftone dot area percentages for dots (halftone dot area percentage management table).

In other words, when the conditions are ideal, the halftone dot area percentage values of each control sample point on the ideal halftone dot gradation characteristic curve corresponding to the maximum density value of the printing ink used are listed. It was done.

[Table 3] Table 3 has the same basic conditions as Table 2, but the range of use of the halftone dot area (5% (H part) to
95% (S section)) is a halftone dot area percentage control table showing what percentage of halftone dots should be placed at each control sample point on the ideal halftone dot gradation characteristic curve. .

In the preparation of Tables 1 to 3, all α = 100,
β = 0%.

To date, color separation work has been primarily emphasized in photographic or electronic platemaking, and the work of adjusting the gradation of an image, which is the basis of print image formation, is basically considered as human experience. Or, because of the reliance on a limited number of fixed source materials, no attempt has been made to truly scientifically analyze the platemaking process from the side of the printed image.

However, the halftone dot area percentage management method based on the "present adjustment method" of the present invention can reasonably manage this important gradation adjustment operation. The data in Tables 1 to 3 above are related to various matters most basic for plate making work from the correlation between the basic density value of the original image of the "main adjustment method" and the dot area percentage of the printed image. It is a useful basic material for adding scientific examination.

From these tables, when creating a halftone dot print image from a continuous tone original image, what is the essence or principle that exists in the image tone adjustment work, and what is the essence or principle? It is possible to extract what needs to be noted and taken into consideration in order to be reasonably aligned with the practice.

(ii) Comparison of halftone dot area percentage numerical table (halftone dot area percentage management table) with the “main adjustment method” and actual values The halftone dot area percentage control table (basic concentration) calculated using the “main adjustment method” "The adjustment method" by comparing the value (x) with the numerical value (y) of the halftone dot area percentage) and the actual value of the company that performs plate making using a color scanner
The effectiveness of halftone dot management based on is evaluated.

(1) Description of Table 4 In Table 4, the calculated values of "this adjustment method" and the color scanner CP-341ER manufactured by Hell in West Germany are used, and a standard gray scale (S.G.S. ) As a standard, a color film (E
(Company) and Fuji Film Co., Ltd. (manufactured by Company F) as originals are shown as a result of comparison with the work standard halftone dot area percent of Company A which is performing color separation work.

(2) Explanation of Table 5 In Table 5, the calculated values of "this adjustment method" and a color scanner SG-808 manufactured by Dainippon Screen Co., Ltd. are used, and a standard gray scale (S.G.S. ) As a standard, and contrasted with the work standard halftone dot area percentage of Company D, which is performing color separation using Eastman Kodak Company (manufactured by Company E) and Fuji Film Color Film (manufactured by Company F) as originals. The results are shown.

From the results of Tables 4 to 5 above, the standard halftone dot area percentages of the plate-making company A and the plate-making company are all based on the experience and intuition of the operator or a limited number of fixed materials. Considering the reality that they are set based on the above, and that those workers do not think that each standard halftone dot area percentage table is the best table and want further improvement, It can be judged that the standard halftone dot area percentage table and the halftone dot area percentage management table, which is the calculation result of this “adjustment method”, are practically consistent.

Since the "main adjustment method" of the present invention has a degree of freedom in operability as described above, it is possible to easily set the standard halftone dot area% control table to the best one, and It is extremely useful for management.

This is based on the reflection density of the printing ink (for example, DR _p
To affect the epsilon), by selecting DR _p (print image density region) values and epsilon values properly, it is possible to rationally manage halftone printed image.

The calculated values in Tables 4 to 5 are calculated once by a person with ordinary knowledge using a simple calculator under the trade name of Sharp Pythagoras (ET-509A) (manufactured by Sharp). By operation, predetermined y _h , y _s , ε value, and k value are set, and the y value can be easily obtained from the x value.

(iii) Management of halftone dot area percentage when correcting (or changing) the gradation Next, the "main adjustment method" is to convert the original image into halftone dot gradation (that is, continuous gradation with high fidelity). It is also effective not only in the conversion to point gradation) but also in the correction (or change) of the so-called gradation for correcting or changing the image quality of the original image. Therefore. During such gradation adjustment (correction / change), it is possible to rationally manage the dot area percentage based on the “main adjustment method”. The correction (or change) of the gradation of this image is performed, for example, when the reduction / enlargement ratio is large or small,
This is a necessary means especially when it is desired to express the gradation of the highlight part or the shadow part well (strongly). At that time, for example, the position of the 50% halftone dot position (M ₂ ) is set to which position in the original image density range. What to do becomes extremely important.

That is, the halftone dot area percentage of H and S of the printed image is 5
% And 95%, the change in the reflection density of the printing ink (based on the yellow ink) or the change in the reduction / enlargement ratio from the original image to the printed image will affect the halftone dot printed image. The problem is how to move the set point (M ₂ ) of the 50% halftone dot, which is an extremely important control point, to correct or change the gradation of the image.

Table 6 shows an example of basic materials useful for solving this type of problem.

As a basic material, it is possible to rationally move the position of 50% halftone dot (M ₂ ) by preparing a plurality of materials according to the actual work needs, thereby correcting the gradation of the image. (Or change) work can be reasonably managed.

Print image density range in Table 6 (corresponding to DR _p in Figure 3)
Is determined by the solid density of the yellow ink in the set ink used (and β value is also determined based on this), and the number in () below is The number in the upper left () in each space (frame) in the table is the basic density value (x) at the control sample point, and the number in the lower right is the halftone dot of each basic density value. The numerical value (y) of area percent is shown.

However, the usage range of the halftone dots was 5% to 95%, which is in accordance with the ordinary method in the art. The calculated values shown in Table 6 are 50
% It is extremely important for controlling the halftone dot position or controlling the halftone dot area percentage at the M ₂ point.

For example, when a print image with a reduction / enlargement ratio of 100% is formed from a color original using a film made by Company E, a print image with the desired image quality is obtained when the print image density range is 0.95 and the ε value is 1.12638. Suppose you got it. Next, a halftone dot gradation characteristic curve is created based on the calculated values in Table 6 (that is, the horizontal axis represents the original image basic density area and the vertical axis represents the halftone dot area%).
(Y) is taken to create a halftone dot characteristic curve. ). Next, change the reduction / enlargement ratio for the reference plate, move the 50% halftone dot position to the S side for reduction, move it to the H side for enlargement, and perform halftone dot gradation on the film. Create an image. The test image thus obtained is compared with the halftone dot image of the reference plate of the print image having the desired image quality. When a test image having the same image quality as the latter halftone dot image is selected and, for example, reduced to 1/2,
When the print image density range is 0.85 and the ε value is expanded to 1.16449, 200%, the print image density range is 1.10 and the ε value is 1.08629, 400%
When enlarged to, the print image density range is 1.25 and the ε value is 1.05.
It is 958. Then, these halftone dot gradation characteristic curves are created, and based on the intersection with the straight line showing the 50% halftone dot on the curve, the control sample point of the density value of which original image (in practice, the original image is representative. You will be able to find out if you should put 50% halftone dots on the work standard gray scale). The density value that includes 50% halftone dot as the control sample point is selected because it is convenient for checking the halftone dot image after the color separation work. Therefore, as another method, the control sample points are selected as points such as 2/8, 3/8, and 4/8 of the original image density area, and the percentage of the halftone dot area to be put therein is determined by It is also possible to obtain it from the point gradation characteristic curve and perform the gradation adjustment operation based on this. By using Table 6 in this way, it is possible to rationally correct (or change) the gradation of the image at the same time as converting the gradation of the image.

Note that the gradation (or change) of the gradation of this image is not only applied when reducing or enlarging a single manuscript image to create a print image, but also the intention of the printed matter orderer and the target image taken on the color manuscript. Must be done depending on the type of paper, the purpose of using the printed image, the whiteness of the printing paper, the difference in the reflection density of the printing ink, etc., but in any case, it is possible to rationally respond according to Table 6. .

Further, based on the “main adjustment method” of the present invention, the gradation of the image of the highlight portion or the shadow portion can be corrected (or changed) in a similar manner, and the gradation adjustment of the image described above can be performed. That is, by performing gradation conversion and / or gradation correction (or change) of an image, color fog in the highlight portion of a color original is automatically removed without taking any special measures. You can

As described above, in the present invention, the conversion of the gradation of the image and the conversion of the gradation of the image, which have been carried out based on the experience and intuition and skill of human beings or the limited number of fixed materials so far. Modification (or change) work can be managed scientifically and reasonably under any conditions.

[Advantages of the Invention] The present invention has the following excellent effects: When producing a halftone dot image (print image) from a continuous tone image (original image), halftone dot tone The most basic and important management of halftone dots in the conversion, correction, or change of is directly related not only to the gradation of the image but also to the tone of the image. Conventionally, the management of this important halftone dot is performed by an irrational method of being exclusively based on the experience and intuition of the operator or based on a limited number of fixed data, but in the present invention, Even under such conditions, this can be reasonably done based on the "this adjustment method".

The halftone dot management method of the present invention is a “main adjustment” in which the density value of the control sample point on the original image and the halftone dot area percentage of the sample point on the print image corresponding to this control sample point are rationally correlated. Method is used, when making a printing original plate or printing plate with halftone dots by photographic or electronic plate making,
The halftone dot forming work can be systematically and theoretically systematically and managed.

When the tone adjustment work (tone conversion / correction / change) is performed under the halftone dot management method of the present invention, that is, the halftone dot area percentage management method, the image quality of the printed image is always and surely Since it is guaranteed, the plate making work can be made efficient. For example, the proofreading work can be eliminated, the labor can be greatly saved, and the consumption of consumable materials can be significantly reduced, thereby greatly improving the productivity of the plate making equipment.

The halftone dot area percentage management method based on the "main adjustment method" of the present invention can reasonably and easily define the quality evaluation standard of the printed image independently of the quality content of the original image.

That is, it becomes possible to have a common rational image evaluation means between the printed matter orderer and the photomechanical engineer. Therefore, communication between the two parties becomes extremely easy and reliable, and it is possible to appropriately answer the needs of the person ordering the printed matter, or to make a proposal from the plate-making engineer side.

; By adopting the halftone dot area percentage control method based on the "main adjustment method" of the present invention, the importance of scientificity and rationality in halftone dot forming work during plate making is made aware of the parties concerned and daily work It saves us time and frees up new creative research and development.

[Brief description of drawings]

FIG. 1 shows a group of halftone dot gradation characteristic curves used for gradation management when creating a conventional print image according to the previous proposal of the present inventors. FIG. 2 is a plan view of a management panel for displaying management items determined by the halftone dot area percentage management method of the present invention. FIGS. 3 (a) and 3 (b) show the relationship between the "main adjustment method" applied to the management of the halftone dot area percentage of the present invention and a typical image gradation adjustment method. Figure
(a) is an example of converting an original image into a halftone dot gradation image via a density compressed original image, and FIG. 3 (b) is an example of converting an original image into a halftone dot image via a gradation converted density area compressed original image. An example of converting to a toned image will be shown.

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Claims (3)

[Claims] 1. A method of controlling a halftone dot area percentage when a print image having a halftone dot gradation is created from an original image having a continuous gradation, wherein the brightest point ( H
Point), the darkest point (S point), and a desired density point between the H point and the S point, and the halftone dot area percentage (y) of each of the control sample points at each control sample point. Calculated from the basic density value (x) (the difference between the density value at each control sample point and the density value at the brightest point) using the following relational expression (1): ● The network of each control sample point based on the calculated value A method of controlling a dot area percentage when creating a print image having a dot tone from a continuous tone original image, which is characterized by managing a dot area percentage. <Relational expression> However, x: basic density value of an arbitrary control sample point X on the original image. That is, the difference between the density value at the arbitrary control sample point X of the same image and the density value at the brightest point (point H) of the same image. y: Numerical value of the halftone dot area percentage of the halftone dot of the control sample point Y corresponding to X on the printed image. y _h: is set for the brightest point of the printed image (H point), any desired size of the dot area percent of the value of the halftone dots. y _s : Numerical value of halftone dot area percentage of halftone dots of a desired arbitrary size set with respect to the darkest point (S point) of the printed image. α: reflectance of printing paper. β: Surface reflectance of printing ink. k: Indicates the ratio of (print image density area) / (original image density area). 2. In addition to the brightest point (H point) and the darkest point (S point) as control sample points in the original image density area, an intermediate density point (M ₁
Claim ₁ ), which includes or does not include any one or both of an intermediate density point (M ₂ point) of the H point and the M ₁ point, and sets an arbitrary number of desired density points. Control method of dot area percentage described in. 3. Halftone dot area percentage (y) of each control sample point
From the basic concentration value (x) at each control sample point
In the calculation using (1), the numerical value of the halftone dot area percentage desired for the brightest point (point H) and the darkest point (point S) (y _h ,
The control method of the halftone dot area percentage according to claim 1, wherein y _s ) is determined and one or more numerical values of α / α-β, β, and k are arbitrarily selected and determined.