JP2754019B2 - Plate making method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention] (Industrial application field) The present invention relates to a novel plate making method for producing color plates (C, M, Y plates) of a color original image using a color scanner. . More specifically, the density of the original image is measured by each color filter (R, G, B filter) for color separation of the original scanning head of the scanner, and the measured density value is used to convert the continuous tone of the original to the halftone dot of each color plate. It relates to a plate making method whose main point is to use it for the operation of a new tone conversion formula for converting a tone.
According to the present invention, there is provided a plate making method in which color fogging, which requires a great deal of labor and experience when disassembling the scanner, sorting (coloring) of color documents before disassembling the scanner, and setting up the scanner are reduced or eliminated.

(Prior art) In the current plate making technology, it is necessary to separate a document using a scanner and a total scanner to produce each color plate such as a C / M / Y plate (hereinafter, referred to as a scanner separation). It has been recognized as a common law in the plate making and printing industries. However, the quality of the images of color originals to be submitted varies widely, and scanner disassembly technology that separates such originals with different image qualities still largely depends on human experience and intuition. The prepress work is quite confusing.

That is, about 90% of the manuscripts submitted to a plate making maker or the like are color manuscripts, and 30 to 70% of the color manuscript (the numerical value changes depending on a city, a peripheral city, a region, etc.) has a non-standard image quality. It is an image. The non-standard image quality refers to an image in which the tone of the color original image is dark or light overall and the image characteristics in the density region are inappropriate, and there is color fogging. However, in the art, even if such a non-standard color image of poor quality is received, the image quality of the color print image produced from the color image of the color original image produced from the color image of the standard image quality is reduced. It is usually required to be the same as

In particular, color fogging development occurs by combining the primary, secondary, and tertiary hues of cyan (C), magenta (M), and yellow (Y) with the two components of lightness. Therefore, solving the problem of color fogging is complicated and difficult. Moreover, in the actual image quality of a color original, the problem of complicated and difficult color fog and the problem of inadequate image characteristics in the density region often depend on each other while acting synergistically. At present, no rational platemaking technology has been established for obtaining excellent color print quality from such color originals.

This is a matter of course in view of the fact that the conventional scanner disassembly technique is essentially a technique dependent on human experience and intuition as described above. This point is symbolically indicated by a continuous tone image and a halftone image, which are the basis for converting a continuous tone image (color original image) into a halftone image (color print image). Determine the correlation of the tonal images,
That is, the setting of the so-called scanner disassembly curve depends on human experience and intuition. For example, in order for the scanner user to set the scanner separation curve, the color separation is actually performed using the color scanner, and the set scanner separation curve is good according to the image quality of the color print image obtained by calibration. You have determined whether or not. The operation of setting the scanner disassembly curve is an extremely cumbersome procedure, and it usually takes one to three months to set one scanner disassembly curve. In addition, scanner ・
A plurality of (usually 3 to 6) scanner disassembly curves preset in the memory of the scanner by the manufacturer are basically set in the same manner as the scanner user.

The scanner resolution curve, which is the core when converting the continuous tone into the halftone tone, includes the density of the brightest portion (H) and the darkest portion (S) of the color original image, and the density of the image from H to S. Although the density gradient must be set based on objective data, the conventional approach uses the H of the color original image.
It is almost indifferent to objectively obtain and use data on the concentration gradient from H to S simply by measuring the concentration values of S and S. That is, the acquisition of the image information of the density gradient from H to S is completely left to the judgment based on the visual sense of the operator.

Further, in the scanner disassembly, it is often necessary to modify or adjust the gradation (shade), color tone, color fog, color, and the like of a color original image closely related to the image quality of a color print image. However, there is no technology capable of performing the modification and adjustment rationally, and the color scanner also does not have a function capable of performing the modification and adjustment rationally. Therefore, for example, in order to remove color fog, scanner operators operate color scanners exclusively depending on their own experience and intuition.

These are the reasons why the present inventor argues that conventional scanner disassembly technology is essentially dependent on human experience and intuition.

Let's consider the problems of the current scanner disassembly technology in a little more practical way.

As described above, in the current state of scanner disassembly technology, it is difficult to set a scanner disassembly curve, so the number thereof is limited by itself, and an attempt is made to make the scanner disassembly work of color original images of various image qualities more efficient. If you do
It is necessary to classify (group) color documents in advance based on a preset scanner separation curve. Therefore, according to the prior art, before setting a color original on a scanner, the density values of H and S of the color original image are measured using a densitometer, and the image information of the density gradient from H to S is obtained. Judgment is made by visual observation of an operator, and the color original is classified based on those materials. In addition, since this sorting work is mainly performed based on the image characteristics in the density area, the problem of color fogging is left in the subsequent set-up work without taking any measures. .

For this reason, after the color original is mounted on the original drum of the scanner, the scanner is set up immediately before the start of the scanner disassembly operation, that is, specific color separation operation data is input to the scanner. In the work, it is customary for the worker to make judgments based on experience and intuition regarding many elements and requirements of the color separation work, and there is no rational judgment standard. Takes a long time, or the above-mentioned judgment becomes erroneous. A number of setup devices have been announced by scanner manufacturers, film manufacturers, etc. to solve the set-up problem several years ago, but they all show performance that matches the needs of the market. What you can't do is see how difficult it is to set up your scanner
This is clearly shown. Therefore, when disassembling the scanner according to the prior art, even if a color scanner equipped with electronics, a computer, and a mechatronics technology is used, 30 to 70 of a color original to be submitted is required.
It is a very difficult technique to disassemble a document image whose image quality occupying% is not a standard and to produce a color print image of a desired image quality with a regular work.

Also, due to the difficulty of the scanner disassembly operation, the effective operation rate of the color scanner is as low as 30 to 35% even today, and the practical productivity of the color scanner is extremely low. Even if a total scanner that requires a large investment is used, the rationalization of scanner disassembly, which is the fundamental elemental work, depends on technology based on irrational human experience and intuition. In addition, the plate making operation cannot be performed efficiently.

(Problems to be Solved by the Invention) The present inventors have made a plate-making method that has eliminated the irrationality and non-productivity of the above-mentioned scanner disassembling operation, in particular, it is possible to effectively remove color fogging, and before disassembling the scanner. Intensive study was conducted to develop a plate-making method that greatly reduces or eliminates color document sorting (grouping) and set-up operations. As a result, the present inventors have developed continuous tone, which has been developed based on the recognition that tone adjustment is more important than color correction (color correction) in the production of color print images. It has been found that it is extremely effective to use a new gradation conversion formula for converting to halftone gradation, and the present invention has been completed.

[Configuration of the invention]

(Means for Solving the Problems) To summarize the present invention, the present invention provides: 1. (i) arbitrarily specifying a brightest portion (H) and a darkest portion (S) on a color original image, Mounting the color original image on the original drum of the color scanner; (ii) setting the original scanning head of the color scanner on the H and S portions on the color original image, and setting a red (R) for color separation. , Green (G) and blue (B) color filters to measure the density values of the H and S parts, respectively. (Iii) H and S parts measured by the respective color filters (R, G, B) On the basis of the density value, on the given basic density characteristic curve of the color original film, while defining the individual density characteristic curve of the color original image, and defining the reference density characteristic curve of the standard color original image, (Iv) comparing the individual density characteristic curve with the reference density (V) adjusting the density value at the desired sample point of the color original image defined by the individual density characteristic curve to the density value specified by the reference density characteristic curve; C), magenta (M), yellow (Y)
A numerical value of a desired halftone dot area percentage to be set for each of the H portion and the S portion of each color plate, a numerical value of the specified halftone dot area percentage, and a density value adjusted in the step (iv), Using the following <gradation conversion formula (1)>, the numerical value of the halftone dot area percentage designated in the H and S portions of the C plate is combined with the density value measured through the R filter. The G filter, the Y plate, and the B filter are combined.) The density value at an arbitrary sample point on the color original image that is a continuous tone for each color plate is converted to a corresponding point on the dot image that is a dot tone. (Vi) converting the numerical value of the dot area percentage of each color plate (C, M, Y) obtained as described above into a dot image of each color plate; Each color plate is used to control the amount of exposure to produce A plate making method comprising the above steps.

< ^Tone conversion formula> y = y _h + [α · (1−10− ^kx ) / (α−β)] · (y _s −y _h ) (1) where x: each color filter (R, G, B filters) and a basic density value for each color filter at an arbitrary sample point X on a color document image. That is, the difference between the density value at an arbitrary sample point X on the same image and the density value at the brightest portion H on the same image.

y: Numerical value of the dot area percentage of the halftone dot for each color plate of the sample point Y corresponding to X on the halftone image of each color plate (C, M, Y plate).

y _h : Numerical value of the halftone dot area percentage of the halftone dot of the desired size set for the brightest portion H of the halftone dot image of each color plate (C, M, Y plate).

y _s : Numerical value of halftone dot area percentage of halftone dots of desired size set for the darkest part S of the halftone image of each color plane (C, M, Y plane).

α: surface reflectance of printing paper.

β: Numerical value obtained by β = 10− ^γ .

k: ratio of γ / (original image density range value).

γ: any coefficient.

Respectively.

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

The present inventors have studied a technology for converting continuous tone of a color original image into a halftone dot of a color print image, which is the basis of the color scanner disassembly technology. (Japanese Patent Application No. 63-
Nos. 2590, 63-207326 and 63-209431).

The present invention has been made to find that these previously proposed gradation conversion techniques can be used very effectively in the process of making a color original image having color fog.

In order to remove color fog rationally, it is important to clarify the factors that affect the image quality of a color print image and the magnitude of the influence. To solve the problem of shading, and then to solve the problem of color tone and color fogging, that is, convert the continuous tone density of a color original image into a numerical value of the dot area percentage of the halftone dots of a color print image with rationality and regularity. We believe that it is important to establish technologies that can be used first. The present inventors have called this a gradation-first principle. It should be noted that the tone-first principle described above is objectively realized by many examples when the tone conversion formula (1) is applied to a color image of a standard image quality (standard color document). Have been.

From these facts, the present inventors have found that the gradation conversion formula (1)
It is considered that conversion of the gradation of the image using is fundamental to rationally remove color fog.

The present inventors consider the following two factors as causes of color fogging in a color original image. The first is when the light quality of the photographing light at the time of photographing is different from the light quality of the photographing light designed at the time of manufacturing the color film. The density gradients of the Y, M, and C film layers 2 of the developed color film do not match as designed because the conditions for the development are not the same as the development conditions designed during the production of the color film. It is.

In the former case, the specific color is a color fog that appears uniformly throughout the image, and in the latter case, the color fog is not uniform throughout the image. Also, the two color fogs described above often appear at the same time.

Then, the present inventors use various color original images having color fog to obtain a color original image in H and S.
The density of each of the R, G, and B color separation filters is measured, the numerical value of the dot area percent of the halftone dots placed on H and S of the color print image is determined, and the tone conversion of the image is performed using the tone conversion formula (1). As a result, it was found that the above-mentioned color fog can be rationally and regularly removed.

After examining the conditions for removing color fog, when performing gradation conversion of an image using the above-mentioned gradation conversion formula (1), the conditions for removing color fog are α, β (= 10− ^γ ), γ, y
_h , y _s must be constant, and the density characteristic curve of the color original (shows the correlation between the amount of light incident on the photographic material and the density formed on the photographic material. Are different from each other (hereinafter, attributes of the shape of the density characteristic curve are the same).

Among the above-mentioned causes of color fogging, the first one is considered to have a relationship in which the density characteristic curve of the color original has shifted in parallel with each other depending on the degree of color fogging, and the second one is the degree of color fogging. Therefore, it is considered that the gradients of the density characteristic curves are different from each other (in other words, the areas defined on the density characteristic curve of the color original are different). However, when the above condition is satisfied and the gradation conversion of the image is performed by the gradation conversion formula (1), no matter how the density characteristic curve of the color original is translated due to color fog, No matter how the gradient changes, color fog is eliminated. When the obtained halftone image was analyzed, it was found that the arrangement state of the halftone dots was always the same.

FIG. 1 schematically illustrates the principle of removing color fog when the density characteristic curve is straightforward.

In FIG. 1, the density characteristic curve of the C plate having the standard image quality is _denoted by C0. Also the characteristic curves obtained by the translated C ₀ and _{C 1, C 2, C 3} , which shows a state of a first color fog described above. Further, in order to indicate the state of the second color fog described above, density characteristic curves having different gradient rates from C ₀ are represented by C ₁ ′, C ₂ ′, and C ₃ ′.
And α, β, γ, y _h , and y _s become constants when a given color document is scanned by the scanner.

As an example, let y _h be 5% and y _s be 95%. The halftone dot area percentage of dot placed at any M-th image density area fraction step of C ₀ and m%. Points with m% (= m _0%) and the value of the same dot area percent from the arrangement of the halftone dots on the halftone image obtained by concentration characteristic curve by changing the translation or gradient index, m _1, m ₂ , m ₃ , m ₁ ′, m ₂ ′, m ₃ ′
_0-h −m ₀ / m ₀ −C _0-s = C _1-h −m ₁ / m ₁ −C _1-s = C _2-h −m ₂ / m ₂ −
_{C 2-s = C 3-} h -m 3 / m 3 -C 3-s = C 1 '-h -m 1' / m 1 '-C 1' -s
_{= C 2 '-h -m 2'} / m 2 '-C' 2-s = C 3 '-h -m 3' / m 3 '-C
₃ ′ _-s .

Next, a line parallel to the x-axis is drawn at each point to obtain a point on each density characteristic curve at which an m% halftone dot can be obtained on each halftone gradation surface. Intersection was found. Next, it was found that connecting the intersections results in a straight line M "MM 'as shown in FIG.

Therefore, when the density characteristic curve is a straight line, regardless of whether the density characteristic curve moves in parallel or the gradient rate changes, as long as the above-mentioned calculation conditions are satisfied using the above-mentioned gradation conversion formula (1), the C-tone image is displayed. dot arrangement state obtained above is always equal to the dot arrangement of C _0. This is the return route for removing color fog.

As described above, the principle of removing color fog has been described using the density characteristic curve that is a straight line.
See table. ), Even in the case of the curve of the normal scanner decomposition curve, in the same image density area dividing step, even if the density values of H and S change, the same halftone dot area percentage is obtained. A numerical value is obtained.

Therefore, for example, H and S are determined in the color film original without changing the attribute of the shape of the density characteristic curve for the C plate, and the halftone dots placed on H and S on the color print image corresponding to the H and S are set. Is determined so that the desired image quality can be obtained in a color print image, and α, β, γ are kept constant, and the gradation conversion of the image is performed using the gradation conversion formula (1). By doing so, it is possible to obtain a C-tone halftone image without color fogging from any color original image with C color fogging.

As described above, the principle of removing color fogging described in the C version can be similarly applied to the M and Y versions.

In connection with the operation of the gradation conversion formula (1), specific values of α, β, γ, and α (1−β) / (α−
The values of β) are shown in Table 1 below. By calculating the y value based on such numerical values, various scanner resolution curves can be obtained. The shape of the scanner decomposition curve is largely controlled by the value of γ. And
By associating an optimum scanner resolution curve with the image quality of a color original image, a color print image with correct gradation can be obtained.

Next, when the halftone images of the three color planes of C, M and Y are superimposed and printed, the gray balance and the color balance are adjusted over the entire gradation range of the image from H to S. The color fog of the color must be removed.

In order to achieve the above-mentioned point, each color plate (C, M, Y
The density attribute curve of the color plate has the same attribute, and then the halftone dots from H to S of the halftone image of each color plate so that the gray balance of each color of C, M and Y of the printing ink is adjusted. Properly determining the correlation between the numerical values of the point area percentage.

A means for making the attribute of the shape of the density characteristic curve of each color plate the same will be described with reference to FIG.

FIG. 2 shows the principle for matching the individual density characteristic curve of a color original with the reference density characteristic curve of a color original (standard original) of a standard image. Both curves are on the basic density characteristic curve showing the correlation between the exposure amount and the color original density,
The only difference is the bricks occupying the curve. In FIG. 2, the exposure amount is shown on the horizontal axis (X axis), and the density of the color original is shown on the vertical axis (D axis). Although only one individual density characteristic curve is shown in FIG. 2, a number of individual density characteristic curves can be drawn according to various image qualities (overexposure, underexposure). Also, it is clear that the range of the reference density characteristic curve of a color original (standard original) of standard image quality is one. This is, needless to say, that the reference density characteristic curve is one color document recognized as having a standard image quality among many color documents.

The above-mentioned basic density characteristic curve can be easily defined by a function of D = _D (X) as shown in Table 2 below. The function definition of the basic density characteristic curve in Table 2 should be understood as an example, and it goes without saying that it can be arbitrarily defined.

As shown in FIG. 2, an individual density characteristic curve of the color original image is defined from the density values of H and S of the color original image and the basic density characteristic curve of the color film photosensitive material of the color original. Density values D _{Hn to} D of the color original
_By projecting _Sn on the X axis, the value range of the color original image on the X axis is matched with the value range on the X axis of the density characteristic curve based on X _{Hn to} X _Sn . For example, (which is what the reference quality is set arbitrarily so as to obtain.) Reference density characteristic curve set in the reference density characteristic curve or another for C version X on axis value range, X _H0 to X _S0 To match. Then the range of the D-axis of the reference characteristic curves, by obtaining the D _H0 to D _S0, C, M,
The attribute of the shape of the density characteristic curve of each color plate can be made the same. As a matter of course, when the individual density characteristic curve of the color document coincides with the reference density characteristic curve, it is needless to say that the matching between the two is unnecessary. Further, an arbitrary allowable range is defined in the reference density characteristic curve, and when the value is within the allowable range, image processing can be performed by regarding the same as the reference density characteristic curve.

As a means for matching individual and reference density characteristic curves, it is normal that XR ₀ (exposure range of standard original) and XR _n (exposure range of non-standard color original) do not match. It is necessary to match the characteristic curves. The matching includes simple matching (an attitude in which the brightest part density value is matched to the same value and matching of the darkest part is not considered) and comparative matching (an attitude in which both the brightest part density value and the darkest part density value are matched). ). FIG. 2 shows a case in which mathematically proportional matching is performed.

Here, the matching between the individual density characteristic curve and the reference density characteristic curve will be described in detail with reference to FIG.

As shown in FIG. 2, from the relational expression used for the matching operation, that is, the density information value (D _n ) of the individual density characteristic curve,
The relational expression for obtaining the X value for obtaining the image information of the color original adjusted by substituting into the basic density characteristic curve D = f _D (X) is as follows.

(I) simple case of matching _{X = f x (D) ±} | m | (ii) if the proportional matching However, m: Required translation amount (| m | = | X _Hn −X _H0 |) XR ₀ : Exposure range of reference density characteristic curve of standard original on X axis XR _n : Non-standard on X axis Exposure range of individual density characteristic of individual document In order to match the image information of the individual density characteristic curve with the reference density characteristic curve, any means other than the above-described method may be employed.

A color film is originally intended to balance the gray balance and gradation from H to S when designing an emulsion. Therefore, in order to adjust the gray balance and the gradation balance of a color original image having color fogging by the above-described method, when producing each color plate of C, M, and Y, the respective density characteristic curves are changed to the reference density characteristic curve. Is a rational method.

Next, in order to appropriately maintain the correlation between the C, M, and Y color plates, that is, the correlation between the halftone dot area percentage values of the halftone dots from the H portion to the S portion of the halftone image of each color plate. May be determined so that the gray balance is adjusted in the entire gradation range from the H portion to the S portion of the color print image according to an ordinary method. According to an example of a common method used in the art, the correlation between the dot area% values of each color plate is as shown in Table 3 below. From Table 3, it is possible to easily determine the numerical values of the halftone dot area percentages to be set in the H and S portions of each color plate (C, M, Y plates).

The plate making method of the present invention, which is particularly excellent in removing color fog,
As described above, the improvement of the mechanism and functions of the color scanner for embodying the present invention will now be described.

Next, the H and S parts are set in advance on the original drum of the color scanner.
A color original image with a designated copy
The document scanning head is set in the section and the S section, and the density of the H section and the S section are respectively passed through the R, G, and B color separation filters.
And the concentration ranging from the H part to the S part is measured. The density information value thus obtained is used as input image information of a mechanism that performs tone conversion of an image using the tone conversion formula (1) and performs exposure control at the time of halftone dot formation based thereon. .

At this time, it is also possible to display the density values on the color scanner operation panel in order to confirm the result of the measurement of the density values through the R, G, and B filters in the H portion and the S portion of the color document image. . From the input image information and the image information of the basic density characteristic curve of the color film photosensitive material of the color original, an individual density characteristic curve of the image of the color original is defined, and the image information adjusted via the reference density characteristic curve is further obtained. And a method for obtaining the density value information, which is the adjusted continuous tone image information, using the tone conversion formula (1) to calculate the halftone dot area percentage of the halftone dots, which are the halftone dot image information. The mechanism for converting into numerical information is not particularly limited, and may be performed by, for example, ordinary computer processing.

As described above, the H of the color original image obtained from each color separation filter (R, G, B) of the original scanning head mechanism.
The densities of the parts and the S part, and the density information values over the H and S parts can be used as input image information of a mechanism for performing gradation conversion of an image using the gradation conversion formula (1). Then, it is possible to significantly reduce or eliminate the work of separating and grouping the color originals (grouping) and scanner at-up work, which were essential before the scanner was disassembled.
Further, as described above, it is possible to produce a color print image having a desired image quality without color fogging and having a well-balanced gray balance and color balance.

In the case of multi-color plate making, usually, a BK (black) plate is used in addition to the C, M, and Y plates described above, and this BK plate may be prepared according to a common method in the art. That is, the signal amount for the BK plate is appropriately extracted from the signal amounts for the C, M, and Y plates, and the BK plate may be created based on the extracted signal amount.

Further, C, M, Y can be obtained by the above (i) to (v) of the present invention.
The image processing mechanism for obtaining the signal amount for the plate is not limited to the application only to the color plate making method. Examples of this type of application are: (a) Duplicate images with the size of halftone dots (dots) seen in printed images already described in detail, or in melt-transfer type thermal transfer images where the size of dots can be changed (B) Sublimation transfer type thermal transfer image, (using silver salt) heat development transfer image, conventional gravure image, etc. When trying to express gradation or color tone by the density of pigments such as printing ink and dyes (dyes) attached per pixel (for example, per dot) of a certain area (this is also called a density gradation method) ), (C) Constant values found in digital copiers (such as color copiers), printers (such as ink jet type and bubble jet type), and facsimile machines When the gradation is to be expressed by changing the recording density per product, for example, the number of dots, the number or size of ink particles, and the like (this is similar to the area gradation in (i) above). ), (D) Obtain a CRT image that expresses an image by adjusting the intensity of brightness per unit area from an electrical signal related to image information such as a video signal, a television signal, a high-definition signal, etc. (E) Not only in the case of the above-described image conversion processing between the original image and the duplicate image in the approximately equivalent density (brightness, illuminance) area, but also in the spatial, luminance, wavelength, and Image conversion in a temporally invisible area, for example, input conversion of image information in a low illuminance area where the difference in density area between the original image and the duplicate image is small because the contrast of the original image is extremely low (In such a case, the emphasis is on the conversion of the contrast of the image rather than the conversion of the gradation of the image.) (F) In addition, the dot area% and the like are displayed together with the density display. Density meter with density / gradation conversion mechanism
It can be applied to printing related equipment such as color separation preliminary inspection (for example, color proof for proofing) and simulator for color separation education.

(Example) Next, the present invention will be further described with reference to examples.

Embodiment 1. As described in the section (Means for Solving the Problems), in the operation of the gradation conversion formula (1) of the present invention, even if various color originals having various image quality When the attributes of the characteristic curves are the same and α, β, γ, y _h , and y _s are constant, on a halftone image (printed image) produced from these various color originals, He explained that the arrangement of the halftone dots was the same, and that this was extremely important in removing color fog. Therefore, in the first embodiment, first, the above will be demonstrated.

(I) As color original images, originals of various density ranges as shown in Table 4 below (including fogged color originals).

(Ii) The operating conditions of the gradation conversion formula (1) are as follows.

α = 1.00 β = 10− ^γ γ = 0.90 y _h = 5.0% y _s = 95.0% (iii) The calculation results are shown in Table 4 below.

As shown in Table 4, even when the density range of the color original is different, the same halftone dot area% can be set for the same density division step by using the gradation conversion formula (1).

Example 2 Next, an experiment for removing color fogging was performed using a standard original and originals of high key (overexposed) and low key (underexposed) with color fog.

The color film originals used were of standard image quality without color fog (D _H0 = 0.20, DS ₀ = 2.80), high key with color fog (D _Hn = 0.10, D _Sn = 2.70) and color fog. A low key one (D _Hn = 0.60, D _Sn = 3.2
0), a proof print image having the same image quality as a proof print image obtained by color separation of a standard quality color original without color fog from the latter two originals with color fog using the three originals with color fog. An experiment was performed to determine whether or not が was obtained.

In the experiment, a cross-field M-460 was used as a color scanner, and DUPONT's Chromalin method was used to produce a proof print image.

First, in order to define an individual density characteristic curve of each color film original and adjust the image information of each color film original, that is, the density value from H to S, in accordance with the reference density characteristic curve, the technical data of Company F is used. , A density characteristic curve diagram of a color film photosensitive material used for a color film original was selected, and the curve was sectioned into a plurality of sections to formulate.
The result is a function display of the basic density characteristic curve in Table 2.

Next, by using this function, the individual density characteristic curve of the color film original is matched with the reference density characteristic curve, and the density value of the color film original is modified through the reference density characteristic curve, whereby a color with color fog is obtained. Even from a film original, a scanner separation curve for obtaining a halftone printed image having the same quality as a halftone printed image obtained by performing color separation from a standard quality color film original was set. (See FIG. 2.) The results are shown in Table 5. In this embodiment, the above 3
The density range and DR of two color film originals are both 2.60
In order to match the individual density characteristic curve with the reference density characteristic curve, one was determined by simple matching and one was determined by proportional matching.

In the density value of D _n and D ₀ of the Table 5 it was determined y value (halftone dot area%) by the gradation conversion formula (1) with respect to the D _0. The results are shown in Table 6. Also shows the correlation between the y values and D _n value of Table 6 in Figure 3. The curve shown in FIG. 3 is obtained by modifying the continuous tone density value of the color film original through the reference density characteristic curve, and by the halftone dot of the halftone print having the desired image without color fog. This is a so-called scanner decomposition curve, which is converted into a numerical value of the area percentage.

Note that when setting the scanner decomposition curve, the α value in the tonal conversion formula (1) 1.00, gamma value 0.9, the y _H 5
%, And 95% a y _S. The correlation between the dot area percentages of the C, M, and Y color plates is shown in Table 3 in accordance with a conventional method in the art.

In order to evaluate the image quality of the halftone print image obtained as a result of the scanner disassembly, the image quality of the proof print image was examined by the Chromain proofreading method. The three proof prints I made are
Both have almost the same tone, that is, the same gradation and the same color tone, all of which have a well-balanced gray balance and color balance, and color fogging that was present on high-key and low-key color film originals has been completely removed. Was. As to the details of the image quality, it is a matter of course that, in the proof print image produced by the technique of the present invention, the gradation of the highlight part is obtained in the high key color film original, and the dark part is obtained in the low key color film original. The gradation was made richer and more natural.

In the case of a high-key color film original, slight unevenness was observed around the highest highlight part of the proof print image. The reason for this was that the scanner disassembly curve was set using an existing scanner. It turned out that the computational power of the formulating computer for setting the curve was based on lack. On the other hand, when the continuous tone density value of the color film original is directly converted into a numerical value of the dot area percentage of the halftone dot printed image via the reference characteristic curve using the tone conversion formula (1), It has been confirmed that this problem does not occur. However, this problem is not related to the removal of color fog.

As shown by the above experimental examples, whatever the image quality and color fog of a color film original according to the present invention,
Halftone print image with desired image quality without color fog,
It can be made with work regularity.

〔The invention's effect〕

The present invention has the following excellent effects.

While adjusting the individual density characteristic curve that defines the characteristics of the color original to a reference density characteristic line with standard image quality,
By using a new tone conversion formula that converts continuous tone to halftone tone, color with standard image quality can be set according to any image quality, especially from color original images with color fog. A color print image of the same quality or a desired image quality as a color print image produced from a document image can be produced with a regular work.

In other words, the color scanner color separation technology has been reasonably automated.

Eliminating the complicated tasks such as color document image sorting (grading), which had to be performed before scanner color separation, and scanner setup after setting the color document image on the scanner. Therefore, the effective operation rate and the substantial productivity of the color scanner can be increased at least twice or more.

The consumption of consumables can be reduced by at least 30%.

In addition, the efficient use and productivity of the total scanner can be at least doubled.

It is possible to reduce the scanner color separation cost by about half.

It is possible to almost eliminate the overtime and late night work which are constant in the industry.

Unskilled workers can operate the color scanner.

[Brief description of the drawings]

FIG. 1 schematically illustrates the principle of color fog removal, and FIG. 2 schematically illustrates the principle of matching between an individual density characteristic curve of a color original image and a reference density characteristic curve. is there. FIG. 3 shows a scanner disassembly curve employed in the embodiment.

Claims (2)

(57) [Claims] (I) arbitrarily specifying a brightest portion (H) and a darkest portion (S) on a color document image, and mounting the color document image on a document drum of a color scanner; A document scanning head of a color scanner is set on the H portion and the S portion on the color document image, and the color scanning is performed through red (R), green (G), and blue (B) color filters. Measuring the density value of the color original film based on the density values of the H and S portions measured by the color filters (R, G, B). Defining an individual density characteristic curve of the color original image on the curve, and defining a reference density characteristic curve of a standard color original image; and (iv) adjusting the individual density characteristic curve to a reference density characteristic curve. , The individual density characteristic curve The density value of a desired sample point of the color original image defined, adjusted to the density value defined by the reference density characteristic curve that by, (v) cyan (C), magenta (M), yellow (Y)
A numerical value of a desired halftone dot area percentage to be set for each of the H portion and the S portion of each color plate, a numerical value of the specified halftone dot area percentage, and a density value adjusted in the step (iv), Using the following <gradation conversion formula (1)>, the numerical value of the halftone dot area percentage designated in the H and S portions of the C plate is combined with the density value measured through the R filter. The G filter, the Y plate, and the B filter are combined.) The density value at an arbitrary sample point on the color original image that is a continuous tone for each color plate is converted to a corresponding point on the dot image that is a dot tone. (Vi) converting the numerical value of the dot area percentage of each color plate (C, M, Y) obtained as described above into a dot image of each color plate; Each color plate is used to control the amount of exposure to produce A plate making method comprising the above steps. < ^Tone conversion formula> y = y _h + [α · (1−10− ^kx ) / (α−β)] · (y _s −y _h ) (1) where x: each color filter (R, G, B filters) and a basic density value for each color filter at an arbitrary sample point X on a color document image. That is, the difference between the density value at an arbitrary sample point X on the same image and the density value at the brightest portion H on the same image. y: Numerical value of the dot area percentage of the halftone dot for each color plate of the sample point Y corresponding to X on the halftone image of each color plate (C, M, Y plate). y _h : Numerical value of the halftone dot area percentage of the halftone dot of the desired size set for the brightest portion H of the halftone dot image of each color plate (C, M, Y plate). y _s : Numerical value of halftone dot area percentage of halftone dots of desired size set for the darkest part S of the halftone image of each color plane (C, M, Y plane). α: surface reflectance of printing paper. β: Numerical value obtained by β = 10− ^γ . k: ratio of γ / (original image density range value). γ: any coefficient. Respectively. 2. A basic density characteristic curve is defined by an X-D orthogonal coordinate system between an exposure amount (X) incident on a photographic material and a density value (D) formed on the photographic material. The plate making method according to claim 1, which is a density characteristic curve.