JPH03163958A - Gradation conversion method for picture - Google Patents

Abstract

PURPOSE:To adjust the gradation to a desired value depending on a gamma value by integrating individual dot characteristic curves so as to form a dot characteristic curve for gradation adjustment from H (brightest part) to S (darkest part) and converting a continuous gradation picture into a dot gradation picture. CONSTITUTION:Which range of gradation adjustment and how it is implemented is decided in advance by taking a basic dot characteristic curve as a reference. The luminous quantity on the X axis (0. 00-2.50 range) is divided into 3 ranges and individual dot characteristic curves are obtained. Thus, the gradation characteristic of the basic dot characteristic curve is optionally and rationally adjusted.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is directed to converting a continuous tone monochrome or multicolor original image into halftone gradation through processes such as color separation using electronic plate making or the like. This invention relates to an image gradation conversion method used when creating duplicate images such as monochrome or multicolor printed images. In particular, it relates to an image gradation conversion method that can arbitrarily and rationally adjust the image quality of halftone gradation images such as printed images through image gradation adjustment (including correction and change of gradation). It is.

(Prior Art and its Problems) As will be described later, the present invention is directed to the general techniques and basics of handling not only printed images but also digitally reproduced printer images, Coby ghost images, CRT mountain images, etc. It is used as a technology. Here, for convenience of explanation, conventional techniques and their problems will be explained using printing, which is the most representative industrial field, as an example in the production of reproduced images.

As is well known, the core technology in producing printed images from original images is color separation technology.

In the color separation technology, scanners (including monochrome and color) are currently manufactured using modern technology such as electronics and computers as working tools.

same as below. ), but in essence it is still an unscientific and irrational technology based on vague experience and intuition. The fact that even today in this industry there is a debate as to whether color separation work is an industry or a craft is a clear testament to this fact.

To explain this further, conventional color separation techniques were developed centering on color photograph processing techniques and photographic masking methods. In other words, the basic concept of the color separation technology for forming printed images is too biased toward photographic image processing technology, and there is a lack of understanding, consideration, and analysis of the essence of printed images and the production process of creating printed images. For this reason, with regard to conventional color separation technology, only color separation technology from the perspective of photographic processing technology has been studied and improved; it is located in the first process of printing image formation and has a decisive influence on the quality of printed images. Techniques such as conversion of the gradation of a printed image and subsequent adjustments, modifications, and alterations to the gradation, tone, and even color of a printed image have been left outside the scope of research, consideration, and improvement, and are therefore still subject to technology has made the fundamental mistake of remaining based on human experience and intuition.

At present, while using scanners, which are modern working devices, for color separation work, we are using halftone characteristic curves (for monochrome scanners, tone curves,
Color separation curve for color scanners,
It is also called a color separation characteristic curve. Same thing. ) setting technology is still used to select the necessary and optimal characteristic curve from among the several characteristic curves created based on the experience of scanner manufacturers and stored in the scanner's storage device (one day, this is the one that is fully satisfactory). (There is no guarantee that it will be the same), or each scanner user can create the same characteristic curve that is most suitable for their own work conditions based on their experience and intuition and store it in the scanner's memory. This is done by storing it in a device and calling it up when necessary to perform work.

This is a good example of how current color separation technology, while using scanners, is essentially based on human experience and intuition.

Although electronic prepress technology systems such as monochrome scanners and color scanners employ advanced mechanisms, the halftone characteristic curve itself, which is the core of scanner work, is not scientifically and rationally developed. The current situation is that the issue of making something is entirely a matter of personal interest. Scientifically and rationally creating the halftone characteristic curve, which is the core of the scanner's operation, is actually
This is an essential prerequisite for scientifically and rationally converting image gradations.

(Problems to be Solved by the Invention) The present invention aims to solve and overcome the drawbacks and limitations of the conventional color separation techniques described above, and to establish a scientific and rational color separation technique.

The present inventors first scientifically set the halftone characteristic curve that is the core of the work when forming a printed image with halftone gradation, and also Patent Application No. 148912-1982 (USP 3,811,
No. 108), and Japanese Patent Application No. 165231/1986 (USP 3, 8) as a plate-making technology applying the image gradation conversion technology.
No. 33,546), patent application No. 1988-1982 as a method for controlling the halftone dot area percentage by applying the gradation conversion technology of the image.
No. 302 was proposed.

In addition, the present inventors have sublimated the technique for setting the halftone characteristic curve described above so that it can be applied not only to standard originals with standard image quality, but also to non-standard originals such as overexposed and underexposed originals. Patent application 1986-
No. 114599, No. 63-207326, and furthermore, from a technical system that uses the density information of the original image when setting the halftone characteristic curve, the image information value regarding the amount of light (exposure 11) from the subject that makes up the original image is used. This was around the time that patent application No. 1-135825 was proposed as a technical system.

The present invention is related to these proposals, and relates to tone adjustment (including correction and change of tone) performed simultaneously with or subsequent to tone conversion of an original image. That is, the present invention aims to provide a technique for rationally converting the gradation of a printed image produced using an initially set halftone characteristic curve to a desired one. In other words, the present invention aims to replace conventional gradation conversion and adjustment techniques based on irrational experience and intuition with scientific and rational gradation conversion and adjustment techniques.

[Structure of the Invention] (Means for Solving the Problems) To summarize the present invention, the present invention provides a method for converting a continuous tone image into a halftone image to produce an arbitrarily desired halftone image. In the image gradation conversion method that converts the gradation to 12? i) Image information values and halftone dot area % from part I (brightest part) to part S (darkest part) of the original image for gradation conversion
A basic halftone characteristic curve that governs the correlation between the In order to convert the gradation to have a halftone gradation of
Set at least one in the image information values from H to S, (iii) For each area divided by the management points, use the following <gradation conversion formula> as follows for each area. Determining the individual halftone dot characteristic curve; (a) the desired halftone dot area % value for each control point, the yg value for determining the adjacent individual halftone dot characteristic curve, and the other individual halftone characteristic curve; (b) Adopting a desired value as the γ value for determining the adjacent individual halftone characteristic curve; (c) In a predetermined gradation adjustment area. , the numerical value of the desired halftone dot area % set for each control point, and at least one of the γ value for determining the individual halftone characteristic curve is the halftone dot area % at the corresponding control point on the basic halftone characteristic curve. (iv) gradation adjustment from H to S by integrating the individual halftone characteristic curves determined as above; The halftone characteristic curve for
The present invention relates to an image tone conversion method characterized in that the tone of a continuous tone image is converted into a halftone image under the tone adjustment halftone characteristic curve.

<Gradation Conversion Formula> l 5 Hereinafter, the configuration of the present invention will be explained in detail. The image gradation conversion method of the present invention will now be explained by taking the production of a printed image as an example.

The image gradation conversion method of the present invention is roughly divided into two types of setting of halftone characteristic curves.

The first halftone characteristic curve is set by the process of fi) described above in order to scientifically and rationally convert a continuous tone original image such as a color photograph into a printed image with halftone tone. The purpose is to set a halftone characteristic curve (hereinafter, this characteristic curve will be referred to as a basic halftone characteristic 1D line) which is the basis of tone adjustment. The basic halftone characteristic curve from the H part to the S part of the original image is determined by the gradation conversion formula of the present invention〉{l}16? , are set by operating under the initial setting conditions of each parameter (values set for y■.y5, γ).

The second halftone characteristic curve is based on the first basic halftone characteristic curve, and is based on the image information value related to the density information of the original image (this is the density measured by a densitometer as described later). The gradation may be adjusted (including corrections and changes) within the range of (Hereinafter, this characteristic curve will be referred to as the gradation adjustment halftone characteristic curve.) In other words, the second gradation adjustment halftone characteristic curve is set by determining whether to ) to (iii).

The younger brother of the present invention, the first 7j! The technique for setting the characteristic four-point line of X main dark blue was proposed by the present inventors in an earlier application (Japanese Patent Application No. 62-5).
No. 5831, No. 62-148912, etc.), so only the main points will be mentioned here.

The above-mentioned <gradation conversion formula> (1) used in setting the first basic halftone characteristic curve of the present invention is rationally derived as shown below. That is, in producing a halftone gradation printed image, the relational expression (
Equation) is the size of halftone dots desired to be placed in H (brightest part, highlight part) and S (darkest part, shadow part) of the printed image, based on the values of the reflection density of printing paper and printing ink. While arbitrarily selecting the density, from the basic density value (x) of an arbitrary control sample point (X) on the original image to the corresponding control sample point (Y) in the printed image, the halftone dot point +I1i at 43
It is desirable to formulate the equation so as to obtain the numerical value (y) of hJi Bersen 1.

The relational expression for calculating the numerical value (y) of the halftone dot area percentage described above is based on the generally accepted density formula (photographic density, optical density), that is, D=logIo/I=I. It was derived from og1/T.

When this general formula regarding density D is applied to plate making and printing, it becomes as follows;

Then, in the density equation (D') related to plate making and printing, the minimum halftone area percentage (yH) at the brightest part and the maximum halftone dot area percentage (yH) at the darkest part of the halftone gradation image created as described above are added.
While setting the value of y8) to an arbitrary value of 19, print the basic density value (x) at an arbitrary control sample point (X) on the continuous tone original image and the corresponding halftone gradation. Incorporating the requirement to associate the value (y) of the halftone dot area percentage of the halftone dot at the control sample point (Y) on the image, a relational expression is derived so that the theoretical value and the measured value approximately match. As a result, the following relational expression for determining the numerical value (y) of the halftone dot area % is obtained.

In addition, in the above relational expression, among each parameter, β,
By using k with γ=an arbitrary value, it becomes extremely versatile. This point is disclosed in detail in the patent application previously proposed by the present inventors, which was explained in the section (Problems to be Solved by the Invention).

Therefore, in the relational expression that we want to derive as described above, when α = 1.0, the dot area % value (as determined in advance) is always set at the brightest and darkest areas as planned (as determined in advance). y
) can be set.

This is clear from the following points. That is, in the brightest part (H), by definition, X (basal concentration value) =
This is clear from the fact that in the darkest part, X=(image information value related to density information of the original image). Note that it is completely rational to use the <relational expression> as described above (to use α=1). This is because in this industry, when trying to obtain image density information using a densitometer, the zero point of the densitometer is always adjusted based on the whiteness of the printing paper. be.

The image gradation conversion method of the present invention is intended to be carried out rationally based on the above-mentioned gradation conversion formula (l) derived when a=1.

The gradation conversion formula (l) of the present invention has the above-mentioned relationship α=1 built-in, so when setting the halftone characteristic curve for tone adjustment, each adjacent individual halftone characteristic curve is Can be connected continuously without jumping.

Furthermore, it is clear from the characteristic τL of the related bars that the 1st line of gradation output set by the gradation conversion formula (1) of the present invention can be achieved by setting the γ value to a positive number. The shape of the curve can be changed to be convex upward, and by setting the γ value to a negative number, the shape of the curve can be changed to be convex downward. That is, the desired gradation can be adjusted by the γ value.

In the present invention, it is possible to produce a printed image having reasonably desired gradation characteristics while utilizing the characteristics of the above gradation conversion formula (1).

That is, following the setting process of the basic halftone characteristic curve in (i) above, it is determined which range of gradation is to be adjusted (including correction and change) based on the organic relationship with the basic halftone characteristic curve, and the above-mentioned iii) By the process of fiii), the individual halftone dot characteristic curve is determined, and the halftone dot characteristic curve for tone adjustment is set, and finally, by the process of (ivl), the continuous tone All that is required is to convert the tone image (original image) into a halftone tone image (print image).

The manner in which gradation is adjusted according to the present invention is not particularly limited. For example, in the process of fii), the control points for controlling the gradation adjustment area are set as follows; (l). Set to emphasize or suppress the highlight part of the original image.

(2). Set to emphasize or suppress the shadow part of the original image.

(3) Setting to emphasize or suppress only the brightest to middle density areas of the original image.

(4). Set to emphasize or suppress only the darkest density range from the middle part of the original image.

23 (5). Settings are made to emphasize the density range from the brightest part to the middle part of the original image, and also to emphasize the density range from the middle part to the darkest part.

(6). Settings are made to suppress the density range from the brightest part to the middle part of the document image, and also to suppress the density range from the middle part to the darkest part.

(7) Something that emphasizes or suppresses the highlight area, something that emphasizes or suppresses the shadow area, something that emphasizes or suppresses the intermediate density area from the brightest area, and an item that emphasizes or suppresses the density area from the intermediate area to the darkest area. , one that emphasizes the density range from the brightest to the middle part and also emphasizes the density range from the middle part to the darkest part, and one that suppresses the density range from the brightest part to the middle part and also suppresses the density range from the middle part to the darkest part. Set to combine multiple selections.

As described above, the number of management points can be set as desired. In the present invention, the control points are arbitrarily set within the image information values H to S of the original image, and the 24 control points manage the gradation adjustment area. Once the gradation adjustment area is determined in this way, a desired halftone area % value is set for each control point, and the above ((
Individual halftone characteristic curves are determined by the ijil process. Then, this curve is integrated into a halftone characteristic curve for tone adjustment by process (iv).

Next, in the gradation conversion method for an image developed under the above-mentioned <gradation conversion formula> (l) of the present invention, the The specific contents of the image information value related to the density information that is used as the basis for calculating the value (basic density value) will be explained.

The present invention aims to convert density information of an original image into appropriate halftone information in the development of a scientific and rational gradation conversion technology that is the core of converting continuous gradation to halftone gradation. is of primary importance. Color correction is also important in the production of various types of reproductions of printed images, but the present invention is based on the idea that the primary emphasis is on tone adjustment (gradation control). There is. It goes without saying that this idea is reflected in the above-mentioned <gradation conversion formula> (l).

Therefore, in the present invention, the basic information to be obtained from the original image is density and image information values related thereto.

In the operation of the above-mentioned gradation conversion formula (1) of the present invention, the image information value related to the density information value of the original image used to calculate the X value (basic density value) should be interpreted in the broadest sense. It is. For example, there is a density value itself measured from a document image using a densitometer. It goes without saying that if the original image is a color or monochrome photograph, either transmission density or reflection density may be used. Furthermore, in addition to the density value from a densitometer, any physical quantity related to the density value of the original image, such as a current value or voltage value after photoelectric conversion, can be used.

In particular, in the present invention, the image information value related to the density information value of the original image is related to the amount of light incident on the recording medium from the original image forming the original image, that is, the subject (actual scene) described below. Physical quantities have extremely important meaning.

As is well known, original images are media images recorded on various recording media. For example, in the case of a photographic original, in a recording system using a photographic photosensitive agent, the photographic photosensitive agent is blackened by the amount of light from the subject (actual scene), that is, the amount of exposure, thereby forming the density of the image. In addition, recording media include photoconductors such as CCDs, photoconductors, optical disks, and magnetic disks, and the density of the image is formed depending on the photosensitive characteristics of each recording system. However, what must be noted about the medium images forming these original images is that the density information of the medium images depends on the photosensitive characteristics of the recording system.

The present inventors previously developed an image gradation conversion technique for media images recorded on various recording media by determining information values related to the amount of light that are not affected by the photosensitive characteristics of the recording system from the density information values of the original images. 27 We proposed a new image gradation conversion technique that applies to the above-mentioned gradation conversion formula (1) (Japanese Patent Application No. 1-13582).
No. 5, No. 1-212118). This new image gradation conversion technology is superior to the conventional image gradation conversion technology based on density information directly obtained from the original image in terms of reproducibility of original images.

The information value regarding the amount of light can be easily determined from the density information value of the medium image described above based on the characteristic curve regarding the amount of light and density of the recording system.

For example, in the case of a photographic original, the vertical axis (hereinafter referred to as the D axis) is the density value (D value = logI/I), and the horizontal axis (hereinafter referred to as the X axis) is the logarithm value of the exposure amount (E) (1ogE). A photographic characteristic curve (photography) expressed in a coordinate system
c characteristic curve)
By converting the value into a function, the physical quantity related to the exposure amount (hereinafter referred to as the X value) can be easily obtained from the D value.

For media images recorded on other recording media, physical quantities related to the amount of light can be obtained in the same manner. In the present invention, these physical quantities related to the amount of light are
It is positioned as an image information value related to density information value.

A specific example of determining the X value from the D value of the photographic image described above will be shown below. Note that the image gradation conversion technique based on this light amount value will be employed in the embodiments described later, so the following explanation will help in understanding it.

Ektachrome 64 manufactured by EK Co., Ltd. and Professional Film (Daylight) were used as the photographic characteristic curves described above, and the curves were expressed mathematically. Note that the method of formulating is not particularly limited, and it is sufficient to faithfully formulate the photographic characteristic curve. The results are shown in Table 1.

Further, Table 2 shows the results of formulating Fujichrome manufactured by Company F.

In addition, when formulating Ektachrome 64 manufactured by EK,
For each emulsion layer, ie R. Photographic characteristic curves were expressed mathematically for each of the G and B emulsion layers. In addition, each table also shows the D. A formula for determining xn for each division is shown.

By formulating these photographic characteristic curves, it is possible to easily obtain the physical quantity (Xn value) related to the exposure amount closer to the subject from the density value (D value) which is influenced by the characteristics of the photographic emulsion. can.

(Hereinafter, blank space) Using the X, , value related to the exposure amount determined as described above, the y value (m-point area % value) can be determined by <gradation conversion formula> (l).

That is, a halftone characteristic curve and a color separation curve showing the correlation between the y value and the xn value (assumed to be the basic density value) are obtained. The present inventors calculated the image information obtained based on the density information value on the D axis into the D axis color separation cube, and the image information on the X axis regarding the exposure amount (light foot value), which is obtained by adding 17 to {1f(). The two are distinguished by using the X-axis color separation curve, and the latter is a color separation technique that has many advantages over the former.

When producing printed images, most of them are produced using four versions (generally considered to be one set of four versions: C version, M version, Y version, and K (black) version). To apply the above-mentioned <gradation conversion formula> (l) of the present invention, set each D-axis or X-axis color separation curve, and perform gradation conversion of an image, the following procedure may be performed. The above <gradation conversion formula> (l) is derived from the viewpoint of rationally determining the C plate, which is the most important plate among multicolor plate making. Therefore, what is derived by applying the above <gradation conversion formula> (l) is the D-axis or X-axis color separation curve for C plate, and the D axis color separation curve for other M plate and Y plate.
The axial or X-axis color separation curve may be determined by multiplying by appropriate adjustment values well known in the art to maintain gray balance and color balance. Further, the 1) axis or X-axis resolution curve of the K (black) printing plate may be determined according to a conventional method in the art from the viewpoint of reducing the consumption of C, M, and Y inks.

The image gradation conversion method of the present invention is not only applicable to the production of color printed images as described above, but has an extremely wide range of applications as will be described later. That is, the present invention can be applied to all fields in which output information of a reproduced image is obtained by processing image information values obtained by photographing or imaging conversion of image information of a real image using information transmission media such as light or electromagnetic waves.

Therefore, it goes without saying that the image gradation conversion method must be adapted to suit the system for producing each duplicate image.

Although the application aspects of the image gradation conversion method of the present invention have been described above specifically in relation to the production of printed images, its application is not limited to the production of printed images.

That is, as an application example of the image gradation conversion method of the present invention, (a) the above-described letterpress,
,1. '． j The size of the halftone dots (dots) found in printed images such as gravure, silk screen, etc., or thermal transfer images of the melt transfer type that can change the size of the dots (multi-level printing) It is useful not only when trying to express tone and color tone (this is also called the area gradation method), but also for sublimation transfer type thermal transfer images, heat development transfer images (using silver salt), conventional gravure images, etc. When attempting to express gradations and color tones by the shading of pigments, dyes, etc. such as printing ink 35 that are deposited per pixel (for example, per dot) of a certain area (this is also called the density gradation method). ), (c) Digital copying machine (color copy, etc.), printer (ink jet type, bubble jet type, etc.)
, or when trying to express gradation by changing the recording density per fixed area, such as in facsimiles, for example, the number of dots, the number and size of ink particles (this is the case described in (a) above). (2) A CRT image that expresses an image by adjusting the brightness intensity of a unit area using electrical signals related to image information such as video signals, television signals, and high-definition signals. If you are trying to obtain a printed matter or hard copy with gradation from this, (v) only in the case of image conversion processing between the original image and the reproduced image in the above-mentioned approximately equivalent density (brightness, illuminance) region. 36 Imaging in the spatially, luminance, wavelength, and temporally invisible range, for example, in the f-frequency nR degree region where the contrast of the original image is extremely low and the difference in the density range between the original image and the replicated image is small. In the case of manual conversion of image information (imaging with a high-sensitivity camera) (in such cases, emphasis is placed on image contrast enhancement conversion rather than image gradation conversion), fHel X-ray In precision medical images for examinations such as photographs, the subject (affected area, lesion, etc.)
If you want to perform 1 cooling more accurately by using 1. (h) In addition, use a densitometer with a density/gradation conversion mechanism that displays the density and fine point area %, for color separation inspection (for example, 4-cross color blue). It can be applied to printing-related equipment such as color separation education simulators and color separation education simulators.

In order to apply the image gradation conversion method of the present invention to the various application fields described above, in each field, image information related to the density information value of the original image or the density information of the subject (substantive image) {1+ 't (e.g. light value, exposure value)
Image conversion processing unit (gradation conversion unit) of equipment in various application fields
Processing is performed using the above-mentioned <gradation conversion formula>, and the current value or voltage value of the recording unit (recording head) of the device or its printing is Halftone gradation in which the gradation is adjusted by controlling the time, etc., and changing the number of dots per fixed area (1 pixel), density per fixed area (for example, 1 dot), etc. What is necessary is to output a duplicate image such as a tone.

For example, in order to use the image gradation conversion method of the present invention to produce a printing image original that is a halftone gradation image, that is, a printing original, an existing system well known in the industry may be used. This is achieved by incorporating the image gradation conversion method of the present invention into a color separation/shading mechanism of a commercially available electronic color field device (color scanner, total scanner), etc.

(Example) The image gradation conversion method of the present invention will be explained in more detail below using an example in which a color print image is produced from a color original image, but the present invention is not limited to the example.

(Example 1) In Example 1, gradations that can produce a printed image with an arbitrary predetermined gradation based on the basic halftone characteristic curve (predetermined X-axis color separation curve) How to set the adjustment halftone characteristic curve will be explained.

(i) Setting of basic halftone characteristic curve (predetermined X-axis color separation curve) X value on the X-axis (hereinafter also referred to as light amount value) Range = 0.
00~2.50ro IDR-X=2. 5111yl4
= 5% y s ” 95% γ = 0.91) A basic halftone characteristic curve was set by operating <gradation conversion formula> 1l) with % 3 9 as a given condition (see Figures 1 to 4 below). This characteristic curve is illustrated in the figure). Setting data of the basic halftone characteristic curve (
y values) are shown in Table 4, which will be described later.

(ii) Setting the halftone characteristic curve for gradation adjustment Referring to the basic halftone characteristic curve obtained as described above, select the range (X
It was previously determined how to tone the on-axis light m {range of xn values with respect to ll'f). In addition, in this example, the light amount value range on the X axis is 0.00 to 2.50.
was divided into three ranges, and individual halftone characteristic curves were determined for each range.

Table 3 shows the conditions set for each gradation adjustment range.

As shown in Table 3, conditions are set for the basic halftone characteristic curve in consideration of various gradation adjustment cases. In other words, (ii) when trying to adjust the gradation especially in the highlight part with respect to the basic halftone characteristic curve; (2) when trying to adjust the gradation especially in the shadow part with respect to the basic halftone characteristic curve; Case, (3) Case in which the gradation of highlight and shadow areas is adjusted with respect to the basic halftone characteristic curve, (4)
) Related to (3) above, conditions are set for a case in which the gradation of both the highlight 1 and shadow areas is to be adjusted more strongly than in case {3).

In Table 3, each symbol means the following; Value OR-X... Light intensity value range value (range value) = XS-X ■
3'H... Halftone dot area % value set in the H part of each range 3's... Halftone area % value set in the S part of each range OR-y... ... Halftone dot area % range value (range value) in each range = 3's - 3'u γ... γ value for setting the individual halftone characteristic curve for each range.

Note that γ=0.50 is a positive number, γ= 0.5 means a negative value.

Based on the setting conditions in Table 3, the setting data of the halftone characteristic curve for tone adjustment calculated under the gradation conversion formula (ii) is
It is shown in Tables to Table 7.

When the halftone characteristic curves for tone adjustment are illustrated based on these fixed data, they are as shown in FIGS. 1 to 4. From these results, it is clear that the tone characteristics of the basic halftone characteristic curve can be adjusted arbitrarily and rationally, that is, it is possible to rationally obtain the tone characteristic curve for tone adjustment, which is essential for tone adjustment. .

(The following is a blank space) (Example 2) In this example, a typical basic halftone characteristic curve (X-axis color separation curve) in platemaking practice, and a typical tone adjustment A halftone characteristic curve (X-axis color separation curve for gradation adjustment) will be shown.

(Setting the basic halftone characteristic curve) The color film original used in this example was manufactured by EK (
Ektachrome64), X determined from the D value of 4″ x 5″
It was an indoor still life with a value range (light amount value range) of 0.00 to 2.50. Table 8 shows the setting data for the basic halftone characteristic curve.

(iii Setting the halftone characteristic curve for gradation adjustment In this example, the gradation is set in the light amount value range 0.00 to 0.30, 0.30
Adjustments were made in three areas: ~1.80 and 1.80~2.5. The gradation adjustment in this embodiment was aimed at emphasizing the contrast between highlight and shadow areas. Table 8 also shows the setting data for the halftone characteristic curve for tone adjustment.

4 6 If the X-axis color separation curve for basic and gradation adjustment is illustrated based on Table 8, it will be as shown in FIG.

(iii) Magnuscan M-6 is used as a color scanner for image quality evaluation and color separation.
Color separation was performed using 45 (manufactured by Crossfield). For color proofing, a color proof printed image was produced using a Cromarin proofing machine (manufactured by DuPont), and the image quality was evaluated. The results were in accordance with the content of the gradation adjustment determined in advance and were fully satisfactory.

(Embodiment 3) In this embodiment, a method of adjusting gradation using a high-key color original will be described. The high-key manuscript used in this embodiment is typically a wedding commemorative photograph. In other words, when the manuscript is a color photograph in which black and white coexist, such as the bride's wedding dress and the bride's wedding dress, this is especially true when the delicate gradation of white (highlight area) 47 (woven pattern, lace pattern) is used. It is extremely difficult to reproduce the pattern (such as the pattern of a shishu).

(i) Setting the basic halftone characteristic curve A wedding commemorative photograph, which is a high-key color original, was prepared by EK (Ektachrome 64), 4" x 5"(7").
) The range of the X value (light amount value range) determined from the D value is 0.
25 to 2.80 was used. Table 9 shows the setting conditions for the basic halftone characteristic curve.

Setting of halftone characteristic curve for gradation adjustment In this embodiment, consideration was given to faithfully reproducing the delicate gradations of the bride's wedding dress. Taking into consideration the preferable results of Example 2, the gradation was set to a light amount value range of 0. 2500~0.556
0,0. 556-2. 086ro, 2.0860～
2. I decided to make adjustments in three areas of 800. Table 9 also shows the setting data for the halftone characteristic curve for tone adjustment.

Table 9 shows the light amount value range 0.25 to 2.80 from 000 to
The halftone area % value (y value) for the light amount value after adjusting to 2.55 is shown.

Furthermore, when the basic and gradation adjustment X-axis color separation curves are illustrated based on Table 9, they become as shown in FIG.

Color separation and color calibration were performed in the same manner as in Example 2 for image quality evaluation, and the results were fully satisfactory, with no deterioration in the subtle gradation of the wedding dress area or the gradation of the monitoring area. I was able to create something that fully reproduced the no-key gradation.

(See 1. Margin) [Effects of the Invention] The image gradation conversion method of the present invention was originally designed to rationally change the gradation of reproduced images such as printed images produced based on the set Koshimoto halftone characteristic curve. It is possible to make adjustments (including corrections and changes).

That is, once it is determined in which range of the basic halftone characteristic curve the tone adjustment should be performed, it is possible to rationally set the halftone characteristic curve for tone adjustment corresponding to the degree of demand.

This means that, at present, we have not yet developed a rational tone conversion technology that is the core of producing reproduced images such as halftone print images from continuous tone original images. In view of the current situation in which duplicate images are produced and the gradations thereof are adjusted, relying largely on the experience and intuition of the operator, the present invention makes an extremely significant contribution.

[Brief explanation of the drawing]

FIG. 1 illustrates a halftone characteristic curve for adjusting the gradation of a highlight part by 5 2 set by the image gradation conversion method of the first embodiment of the present invention. FIG. 2 is a diagram illustrating a halftone characteristic curve for adjusting the gradation of a shadow portion set by the image level a conversion method according to a single embodiment of the present invention. FIG. 3 is a diagram illustrating halftone characteristic curves for adjusting the gradations of highlight and shadow areas set by the image gradation conversion method of the first embodiment of the present invention. FIG. 4 shows a halftone characteristic curve for adjusting the gradations of highlight and shadow areas in a different manner from that shown in FIG. 3, which is set by the image gradation conversion method of the first embodiment of the present invention. This is an illustration. FIG. 5 is a diagram illustrating halftone characteristic curves for basic and gradation adjustment set according to the second embodiment of the present invention. FIG. 6 is a diagram illustrating halftone characteristic curves for basic and gradation adjustment set according to the third embodiment of the present invention. 5 3

Claims (1)

[Claims] 1. In an image tone conversion method for converting the tone of a continuous tone image into a halftone image to produce a desired halftone image, (i) tone A basic halftone characteristic curve that governs the correlation between the image information value from the H part (the brightest part) to the S part (the darkest part) of the original image for conversion and the halftone dot area % is created based on the initial setting conditions. Operating and setting the following <gradation conversion formula>, (ii) In order to perform tone conversion to have the desired halftone tone instead of tone conversion using the basic halftone characteristic curve,
setting at least one management point within the image information values from H to S for setting the area where the gradation is to be adjusted; (iii) for each area divided by the management point, the following Determine the individual halftone characteristic curve for each area by operating the gradation conversion formula as follows; (a) Set the desired halftone area % value to each control point to one adjacent individual halftone point. The y_S value for determining the characteristic curve, and the y_H value for determining the other individual halftone characteristic curve; (b) A desired value as the γ value for determining the adjacent individual halftone characteristic curve. (c) In a predetermined gradation adjustment area, at least one of the desired halftone area % value set for each control point and the γ value for determining the individual halftone characteristic curve is , the numerical value of the halftone area % at the relevant control point on the basic halftone characteristic curve and the γ value used to determine the basic halftone characteristic curve, (iv) determined as described above. The individual halftone dot characteristic curves are integrated to form a halftone dot characteristic curve for tone adjustment ranging from H to S,
An image tone conversion method comprising: converting a continuous tone image into a halftone image under the tone adjustment halftone characteristic curve. <Gradation conversion formula> y=y_H+(1-10^-^k^x)(y_S-y_
H)/1-β...(1) [\However,\x: Subtract the image information value of the H section on the original image from the image information value related to the density information value of any pixel on the original image. Indicates the required basal concentration value. y: Halftone area % value of the halftone gradation image corresponding to an arbitrary pixel on the original image. y_H: Desired halftone area % value set in the H section on the original image when setting the basic halftone characteristic curve, or as the brightest part at each control point when setting the individual halftone characteristic curve. Desired halftone area % value to be set. y_S: Desired halftone area % value set in the S section on the original image when setting the basic halftone characteristic curve, or set as the darkest part in each management when setting the individual halftone characteristic curve Desired halftone area % value. β: A value determined by 10^-^γ. k: Numerical value determined by γ/△I. ΔI: When setting the basic halftone characteristic curve, indicates the difference in image information values related to density information in the S portion and H portion of the original image. Furthermore, when setting the individual halftone characteristic curve, the difference between the image information values related to the density information in the darkest part and the brightest part in the gradation adjustment area is indicated. γ: Any number. 2. The image gradation conversion method according to claim 1, wherein the image information value related to the density information is a density information value of a document. 3. The image gradation conversion method according to claim 1, wherein the image information value related to the density information is a photographic density of a color or monochrome photographic original. 4. The image gradation conversion method according to claim 1, wherein the image information value related to the density information is related to an exposure value determined from a photographic density characteristic curve of a color or monochrome photographic original. 5. The image information value related to the density information is related to the light amount value of the object determined from the density characteristic curve that governs the correlation between the image density of the medium on which the original image is recorded and the light amount value from the object. The image gradation conversion method according to item 1. 6. The image gradation conversion method according to claim 1, wherein the management points for managing the gradation adjustment area are set to emphasize or suppress highlight areas of the original image. . 7. The image gradation conversion method according to claim 1, wherein the management points for managing the gradation adjustment area are set to emphasize or suppress shadow areas in the density area of the original image. . 8. The image processing system according to claim 1, wherein the management points for managing the gradation adjustment area are set so as to emphasize or suppress only the brightest to intermediate density area of the original image density area. Gradation conversion method. 9. The image gradation according to claim 1, wherein the management points for managing the gradation adjustment area are set to emphasize or suppress only the middle to darkest density area of the original image density area. Tonal conversion method. 10. A claim in which the control points for managing the gradation adjustment area are set so as to emphasize the density area from the brightest to the middle part of the original image density area, and also emphasize the density area from the middle part to the darkest part. The image gradation conversion method according to item 1. 11. A claim in which the control points for managing the gradation adjustment area are set so as to suppress the density area from the brightest to the middle part of the original image density area, and also to suppress the density area from the middle part to the darkest part. The image gradation conversion method according to item 1.