JPH0547156B2 - - Google Patents

Description

[Detailed description of the invention]

[Objective of the Invention] (Industrial Application Field) The present invention is a novel image gradation method used when creating a halftone image, which is a printed image, from a continuous tone image, which is an original image, in photolithography work, etc. This relates to a method of adjusting the key. (Prior art and its problems) When creating a halftone image from a photographic original using a photoengraving camera, or when creating a color photographic original using an electronic color separation device (monochrome scanner, color scanner) It is well known that the gradation of an original image must be converted from continuous gradation to halftone gradation, such as when performing color separation work. However, in the conventional photolithography technique, image gradation adjustment (in the present invention, this term refers to gradation conversion and gradation correction (or change) as described later)
shall mean. ), an unscientific approach is taken. In other words, what characteristics should a halftone gradation image (halftone film) for photolithography used when reflecting an original image into a printed image, and how to obtain such a halftone gradation image? Scientific analysis and study have been conducted on the question of how to define the halftone characteristic curve and what is a reasonable method to obtain such a halftone characteristic curve. Not added. The reality is that these problems have been dealt with solely by the experience and intuition of photolithographic engineers or by the subjective judgment of designers of electronic color separation devices (scanners). This is true even today, when total scanners, one of the most advanced photolithographic devices, are widespread in the photolithography and printing industry. Incidentally, when converting gradation by performing shading work or color separation/shading work using sophisticated photolithographic equipment such as monochrome scanners or color scanners, the standards for these work Work standard characteristic curve (characteristic curve of a halftone gradation image that serves as the standard for halftone work or color separation work, also known as color separation characteristic curve, halftone characteristic curve, etc.) The current situation is that these devices are pre-memorized in their storage devices and are determined by the device manufacturers based on their experience and intuition. Therefore, in photolithography technology, the gradation conversion work from a continuous tone image of an original to a halftone image of a printed image is not carried out in a rational and scientific manner, and this is a rational system for the entire photolithography technology. It is hindering the development of
An analysis of the operations for obtaining gradation images for printing plate making using many electronic color separation devices (scanners) currently on the market reveals that the following problems remain: (i) [Problems related to halftone gradation expression] (a) Despite the widespread use of advanced photolithography equipment, halftones (halftone area percentage on printed matter range from about 40% to approx. It is difficult to obtain the gray balance (density balance) of the 80% halftone gradation area. (b) Midtone colors are muddy and lack a clear tone. (c) It is difficult to create a sense of volume in midtones. (d) The delicate gradation of intermediate tones (of course, this is closely related to the gradation and color tone of the entire image) cannot be expressed well. (ii) [Problems related to creating work standard characteristic curves for non-standard color originals, etc.] When attempting to color separate objects (for which the phenomenon processing has not been properly performed), or similarly when performing color separation work using a color separation characteristic curve other than the color separation characteristic curve stored in advance in the device. In order to obtain a printed image with the desired quality and image quality, the characteristic curve of the halftone gradation image (i.e., the gradation conversion curve) must be determined based on the experience and intuition of the operator. In order to obtain such a characteristic curve, a great deal of time, money, effort, and experience must be spent on inputting the basic data of the color scanner. Further, when there is color fog in the highlight portion of a color original, color separation work is confused and the quality is unstable. Currently, the proportion of such manuscripts is 30~
It has reached 40%. (iii) [Problems with scanner operation] (a) It takes a very long time to acquire and train operating techniques and use them well. (b) When engineers and operators are replaced, variations in product quality occur, making it difficult to stabilize or maintain product quality.
It becomes difficult to achieve stability. (c) Even if the same scanner device is used, the quality of the product can vary greatly depending on the workplace and the worker. (d) There are many cases where the high performance of scanner equipment cannot be fully utilized. (e) When the quality of the manuscript changes, it becomes difficult to produce products of the same quality. (f) It is extremely difficult to produce a product with the quality desired by the client. (g) It is difficult to ensure uniform product quality when a large number of manuscripts are submitted at once and must be processed at multiple work sites. (H) Poor communication regarding equipment and product quality between scanner manufacturers and parties involved in plate making and printing. (iv) [Lack of scientific approach to producing tone images for photolithography] (1) Furthermore, there is a lack of true understanding of platemaking and printing technology possessed by design engineers of electronic color separation devices (scanners), etc. This results in a loss of flexibility in the work performed by the equipment, making it difficult to meet the diversifying needs of print customers, and creating new and creative color separation methods for photolithographic engineers. Problems such as making experiments and development difficult and causing a jump phenomenon in the gradation of halftone images while using the same device remain unsolved. (2) Moreover, more fundamentally, there is a lack of a universal and rational approach for tone conversion from a continuous image, which is essential for the formation of a printed image, to a halftone image, which is a printed image. This has caused unnecessary confusion not only in the photoengraving industry, but also in the printing industry and even those who order printed matter. (Problems to be Solved by the Invention) The present inventors believe that the true cause of the above-mentioned problems faced by this industry is that the original image (continuous tone image) is converted into a printed image (halftone image). The way we think about the image gradation conversion process, which is the first stage of work and plays the most important role when creating a toned image), is ``from a technical and practical perspective, Focusing on the fact that "it is sufficient to rely solely on human experience and intuition without possessing any means of converting gradations," we focused on the ultimate rationalization of photolithography technology and its operations. In order to achieve this goal, we conducted extensive research based on the basic understanding that we needed to establish a rational image gradation conversion technology. In particular, the present inventors have discovered that the quality of the gradation conversion of an image directly affects not only the quality of the gradation of the halftone image, but also the quality of its color tone. We believe that there are fundamental errors and flaws in the conventional approach to importation methods. In other words, conventional scanners primarily consider color analysis (color correction, color correction).
color-correction-first-ism), and how changes in halftone dot area, which is extremely important knowledge regarding platemaking and printing, greatly affect changes in the gradation and color tone of printed images (gradation-first principle), tone
-rendering-fir-ism), many considerations have not been made. The basic components for expressing a printed image are the two elements "halftone dot area" and "ink reflection density", and the human visual sense recognizes a 1% difference in the "halftone dot area" percentage. Considering the objective fact that color correction, color correction, and color change are prioritized in conventional image adjustment, and the three-dimensional principle in image gradation adjustment management. Point management method (This is a comprehensive expression of the gradation management method used in the production of conventional halftone gradation images.In other words, regarding the quality content of the original image, H), the extreme point of the shadow area (darkest area S) and the intermediate area of density (intermediate density point M <sub>1</sub> ) are only managed, and the extremely important 50% of the plate-making printing technology is controlled.
It can be seen that there is a large limit to the problem of obtaining printed images with extremely high fidelity, especially for color photographic originals, in which the halftone dot placement position <sub>M2</sub> is not controlled. That is, in the conventional tone conversion method from a continuous tone image of an original to a halftone image of a printed image, the density value at an arbitrary control point on the continuous tone image and the corresponding halftone tone are There has been no means for rationally and universally relating the halftone dot area percentage of halftone dots at control points on a toned image. The inventors of the present invention have continued their intensive research to overcome the limitations of the conventional gradation conversion technology described above, and as a result, the density value at a predetermined position on the original image and the gray scale at the corresponding position on the printed image have been determined. This resulted in the invention of a new image gradation adjustment method that is associated with point area percentage. [Structure of the Invention] (Means and Effects for Solving the Problems) To summarize the present invention, the present invention is capable of producing continuous tone images (monochrome, color photographic images, negative photographic images, positive photographic images, transmission photographic images, reflection photographic images, etc.). In a method for adjusting gradation when creating a print image that is a halftone image based on an image information signal obtained by photoelectrically scanning a document image that is a continuous tone image (including all continuous tone images of the image), As an information signal, the basic density value x of an arbitrary sample point on the original image (the difference between the density value at the sample point and the density value at the brightest point on the same image) corresponds to the sample point on the print image. An original that is a continuous-tone image characterized by using an image processed so that the halftone dot area percentage y of the sample points to be processed is correlated, for example, as x and y are defined by the following relational expression (1). The present invention relates to a gradation adjustment method when creating a print image, which is a halftone gradation image, from an image. <Relational expression> y=yh+α(1-10- <sup>kx</sup> )/α-β(ys-yh)...(1) [However, x: Basic density value of an arbitrary sample point X on the original image.
That is, the difference between the density value at an arbitrary sample point X of the same image and the density value at the brightest part H of the same image. y: A numerical value of the halftone dot area percentage of the halftone dot of the sample point Y corresponding to the above-mentioned X on the printed image. yh: Set for the brightest part H of the printed image,
The numerical value of the dot area percentage for any desired size dot. ys: A numerical value of the halftone dot area percentage of a desired arbitrary size halftone dot, which is set for the darkest part S of the printed image. α: Reflectance of printing paper. β: Surface reflectance of printing ink. k: represents the ratio of (print image density range)/(original image density range). ] Hereinafter, the configuration of the present invention will be explained in detail. In a halftone gradation image that is a printed image, ●The basic structural elements for expressing a printed image are two elements: "area of halftone dots" and "reflection density of ink." ●Experience has shown that the above-mentioned Regarding the factor of "ink reflection density", the amount of ink that is adjusted on the printing press is about 20% (in some cases, it is adjusted by about 40% to improve image quality); Experience has shown that the human visual sense has the ability to easily identify a 1% difference in the percentage of "halftone dot area" as a difference in density, and that the amount of area variation for the same halftone dot can reach several tens of percent. , Considering the objective facts and empirical rules, it can be seen that halftone dot management is extremely important in creating halftone gradation images. In addition, in relation to the above, in photoengraving work, the quality content of the original image varies widely, and the printing image forming process that follows the photoengraving work is diverse, and each process has its own unique characteristics. In order to overcome these complex and unstable factors, it is necessary to use a continuous floor system. When converting a tone image to a halftone image, the minimum halftone dot at the brightest part of the halftone image to be created (printed image)
It is essential to provide a method that can arbitrarily select Yh and the maximum halftone point Ys of the darkest area, and also that can rationally and easily adjust and manage the gradation of the image from the brightest area to the darkest area. Both are necessary. Based on this idea, we devised the above-mentioned gradation adjustment method of the present invention, specifically the gradation adjustment method defined by the above-mentioned relational expression (1).
This is called the "main conversion method." As mentioned above, the gradation adjustment method in "this conversion method" is based on the values of the reflectance of the printing paper and the surface reflectance of the printing ink, and adjusts the H and S of the printed image.
While arbitrarily selecting the size of the halftone dot that you want to place, calculate the value of the halftone dot area percentage of the halftone dot at the corresponding sample point Y on the printed image from the basic density value x of an arbitrary sample point X on the original image. This is done by finding y. The relational expression (1) for calculating the numerical value y of the dot area percentage mentioned above is the generally accepted density formula (photographic density, optical density), namely: D=log <sup>Io</sup> /I=log <sup>1</sup> /T Io=Incident light amount I=Reflected light amount Alternatively, the amount of transmitted light T=I/Io=reflectance is derived from the transmittance. When this general formula regarding density D is applied to plate making and printing, it becomes as follows. Density in plate making/printing (D') = logIo/I = = Unit area x Paper reflectance/(Unit area - Halftone area) x
Paper reflectance + halftone dot area × surface reflectance of ink = log αA / α {A - (d <sub>1</sub> + d <sub>2</sub> +...d <sub>o</sub> )} + β (d <sub>1</sub> + d <sub>2</sub>
+...d <sub>o</sub> ) Here, A: unit area do: area of halftone dots in unit area α: reflectance of <sub>printing</sub> paper β: surface reflectance of printing ink. The present invention uses the density formula (D′) related to platemaking and printing.
, there is a request for associating the basic density value x at an arbitrary sample point on the above-mentioned continuous tone image with the corresponding halftone area percentage y of the halftone dot at the sample point on the halftone image. The relational expression (1) is derived so that the theoretical value and the measured value approximately match. Therefore, the tone adjustment method of the present invention from a continuous tone image of an original to a halftone image of a printed image is one in which the tone is adjusted by correlating the basic density value x and the halftone area percentage y. It covers everything. It should be understood that the correlation between x and y in the above relational expression (1) is one example, and the present invention is not limited to this. That is, appropriate changes can be made without departing from the scope of the claims. The feature of the gradation adjustment method of the present invention is that no matter what kind of quality content a continuous gradation original image (photographic image) has, for example, yh and ys as shown in relational expression (1) Also, while arbitrarily selecting the α value and β value, you can determine what kind of halftone gradation characteristics, that is, the halftone gradation characteristic curve, the halftone gradation image you create should have. , which can be found very easily. As mentioned above, "this conversion method" can be used by modifying it, for example,
If yh and ys, α value and β value are arbitrarily and appropriately selected, and in addition, if the original image density range such as a continuous gradation color photographic image is different from the printed image density range of halftone gradation, the industry standard In other words, the k value, which is the ratio of (print image density range)/(original image density range), is appropriately selected, and the gradation is calculated using the "this conversion method". You just have to make adjustments. That is, when creating a print image that is a halftone image based on an image information signal obtained by photoelectrically scanning a continuous tone original image according to the present invention, the following relational expression (1) is defined. "This conversion method" is yh,
It has extremely high flexibility as it can perform gradation conversion or gradation change (or correction) of an image by appropriately changing ys, k value, α/α−β=ε value. To explain this in detail, when applying "this conversion method", users (workers) must keep in mind that they have the following degrees of freedom; (Part 1): Relational expression (1) is used for the purpose of obtaining a printed image that is faithful to the original image. That is,
Apply relational expression (1) with the primary consideration being to obtain exactly the same visual and sensory image when observed with the human eye. In the present invention, such tone adjustment behavior is explained using the term "tone (of) conversion (of an image)." (Part 2): Using relational expression (1) to change or modify the manuscript image due to photolithography/printing technical needs, artistic requests, or the needs of the person ordering the printed matter. That is, the relational expression (1) is applied with the primary consideration being to obtain a modified (or changed) visual sensory image itself when observed with the human eye. In the present invention, such gradation adjustment attitude is described as "(image)
It is explained by the term "modification (change) of gradation". Specifically, the gradation adjustment work according to the present invention includes the above-mentioned gradation conversion and gradation correction (change), and the relational expression (1).
This can be easily done by appropriately changing yh, ys, k value, and ε value. The "present conversion method" can be applied regardless of the image gradation conversion method, and there are no restrictions on how the "present conversion method" can be used. That is, when processing image information signals obtained by photoelectric scanning of original images using the "present conversion method," the above-mentioned relational expression (1) or the terms, numerical values, and coefficients contained therein are used for image gradation conversion and adjustment ( As long as it does not impair the rationality of the gradation adjustment of the gradation-converted printed image, it may be processed, transformed, guided, omitted, etc. as appropriate, and the purpose, means, and method of using "this conversion method" are arbitrary. It is not subject to any restrictions. For example, "this conversion method" is not limited to halftone photography performed using a photoengraving camera, etc., and image gradation conversion and correction (or change) work performed using an advanced photoengraving machine (scanner). It can also be used for rational management of image adjustment work, and can also be used to adjust the gradation of halftone dot generators used in photolithography and analog images (continuous tone images).
It can also be used to control the amount of ink ejected in an ink jet printing method and the heating temperature in a thermal transfer printing method when converting an image into a digital image (black and white binary image). In addition, in the case of multicolor plate making (generally considered to be one set of four plates: cyan, magenta, yellow, and ink), the standard plate (in the case of multicolor plate making, as is well known, the cyan plate is the standard plate) Once the working standard characteristic curve (that is, the standard halftone gradation characteristic curve) for It can always be determined rationally by multiplying by an appropriate adjustment value based on the ratio. Moreover, it goes without saying that the working standard characteristic curves for each color plate determined in this way are each reasonable characteristic curves, and furthermore, the alternating relationships in terms of gradation and color tone between those characteristic curves are also rational. be objective and appropriate; In other words, the gradation conversion of the image is called "this conversion method".
Based on this, it is possible to rationally adjust and manage the gradations of printed images in multicolor printing. As described below, by using "this conversion method," we can move away from the conventional gradation management method that relies on experience and intuition, and adjust the gradation (and color tone) of images arbitrarily and rationally. You will be able to do this. In addition, in order to make the adjustment and management of the work standard characteristic curve more rational based on the strong demands of photolithography technology, we have changed the position and number of control sample points to arbitrary locations, such as near the 50% halftone dot. , it is also possible to easily concentrate an arbitrary number. (Examples) Hereinafter, the gradation adjustment method of the present invention will be explained in more detail based on Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. (i) (Outline of gradation adjustment method using ``this conversion method'') First, an overview of a typical image gradation adjustment method using ``this conversion method'' will be explained based on FIG. 1. The method of image tone adjustment basically depends on whether the conversion (or correction, change, etc.) is direct or indirect, and it immediately transforms a continuous tone image with a linear density tone characteristic curve. The method of converting to a halftone image is that the continuous tone image is first converted into a tone, and then the continuous tone image that has undergone this tone conversion is converted to a halftone image (the tone has already been converted). In this article, we use the term "conversion" to distinguish between conversion methods. In addition, in any of the above methods, there is a method in which the density region of a continuous tone image is directly converted into a halftone density region without compressing it depending on whether or not the density region is compressed, and a method in which the density region of a continuous tone image is directly converted into a halftone density region without compressing the density region, and a method in which the density region of a continuous tone image is directly converted into a halftone density region, and another method is a method in which the density region of a continuous tone image is directly converted into a halftone density region without compressing the density region. There is a method that uses a density range compressed original image corresponding to the tone density range. In actual platemaking practice, the method suitable for the work environment is selected from among the image gradation conversion methods obtained by combining these basic methods. As a typical example, Fig. 1a shows a continuous tone image (original image) with a linear density gradation characteristic curve.
Figure b shows an example of proportionally compressing the density of a document to obtain a density range compressed original image, and then converting it to a halftone image. An example of converting the tone of an image (original image) and compressing the density range at the same time to obtain a tone-converted density range compressed original image, and then proportionally converting this image to create a halftone image. shows. Regarding FIGS. 1a and b, Do...Density value of continuous tone original image. DRo: Basic density range of continuous tone original image. The density value at the sample point X on the document in this DRo and the brightest point (extreme point of the highlight part) H
The difference between the density values at is the basic density value x. D'o...Density value of a density range compressed original image obtained by proportionally compressing the density range of a continuous tone original image using the k value. DR′o...Density value of the density range compressed original image. D″o...Density value of a continuous tone image obtained by converting the tone of a continuous tone original image using the "this conversion method" and compressing the density range. DR″o...The density range of a continuous-tone image obtained by converting the gradation of a continuous-tone original image using "this conversion method" and compressing the density range. Dp...The halftone area percentage of the printed image, which is the halftone gradation. DRp...Print image density range. P: Halftone characteristic value based on quality evaluation standards for printed images. The P value is compared with the y value to assess consistency between the two. H...The brightest point on the document (the extreme point of the highlight area) S...The darkest point on the document (the extreme point of the shadow area) M <sub>1</sub> ...The point in the middle of the density on the document (the intermediate density point) M <sub>2</sub> ...In a printed image with halftone gradation, 50
Points for positioning % halftone dots (area) Existing systems well known in the industry are used to produce, for example, the original plate of a printed image, which is a halftone gradation image, that is, a halftone film for photolithography, using "this conversion method". commercially available electronic color separation equipment (color scanner, total color separation device).
This is achieved by incorporating ``this conversion method'' into the color separation/shading mechanism of scanners, etc. In other words, a small spot light is irradiated onto an original image, which is a continuous tone image, and this reflected light or transmitted light (image information signal) is received by a phototube, and the strength of the light is converted into the strength of an electric current, which is then sent to a computer. In the well-known system, a current value (retouched image information signal) outputted from a computer is supplied to an exposure light source, where a spot light is applied to the raw film. Conversion method”
All you have to do is install software that can do the calculations. If the spot light for photoelectric scanning is sequentially divided into points and propagated, and the exposure section is also synchronized with this, a halftone dot floor having a halftone dot area percentage y defined by the above relational expression (1) can be obtained. It is possible to easily obtain halftone film for photolithography. In addition, the control panel _of commercially available scanners displays _the basic concentration value
It goes without saying that the dot area % value y or the dot gradation characteristic curve may be displayed for convenience of management. (ii) (Consistency between calculated values of "this conversion method" and practice) Using the calculated values of "this conversion method" (relationship between basic density value x and halftone area percentage y) and a color scanner. We evaluated the effectiveness of ``this conversion method'' by comparing the actual values of companies that perform color separation work. The results are shown in Tables 1 and 2. (1) Comments on Table 1 Table 1 shows the calculated values of "this conversion method" and Standard Gray Scale (SGS) manufactured by Eastman Kodak Co., Ltd. using color scanner CP-341ER manufactured by West Germany Hell Co., Ltd. is the standard, and the working standard halftone area percentage of Company A, which performs color separation work using Eastman Kodatsu's color film (manufactured by Company E) and Fuji Film Company's color film (manufactured by Company F) as manuscripts. The results of comparison are shown. (2) Comments on Table 2 Table 2 shows the calculated values of "this conversion method" and the color scanner SG- manufactured by Dainippon Screen Co., Ltd.
808, with Fujifilm Standard Gray Scale (SGS) as the standard, and Eastman Kodatsuk Co. (manufactured by E Company) and Fujifilm Company Color Film (manufactured by F Company) as manuscripts for color separation work. The results are shown in comparison with the standard halftone dot area percentage of company D's work. From the results in Tables 1 and 2 above, we can see that the standard halftone area percentages for platemaking company A and platemaking company D are both set based on the experience and intuition of the operators, and that these operators Considering that each standard halftone dot area percentage table (table) is not considered to be the best and that further improvements are desired, we have compared these standard halftone dot area percentage tables with "this conversion method". The calculation results can be judged to be consistent with practice. It should be noted that since the "present conversion method" of the present invention has a degree of freedom in operability as described above, it is possible to easily set the standard halftone dot area % table to the best one. In addition, when using "this conversion method",
Based on the reflective density of the printing ink (this is
By appropriately selecting the DRp (print image density range) value and the ε value, it is possible to rationally manage the halftone gradation of the printed image. The calculated values in Tables 1 to 2 (and the settlement values in each table described later) can be calculated using a simple calculator with the trade name Sharp Pythagoras (ET-509A) (manufactured by Sharp Corporation) by someone with ordinary knowledge. By one continuous calculation operation, given yh, ys, ε
By setting the k value and the k value, the y value can be easily determined from the x value. (iii) Application of "this conversion method" to correction (or change) of gradation Next, "this conversion method" only converts the gradation of an image (i.e., converting from continuous gradation to halftone gradation). This is so-called gradation correction, in which the original image is modified (or changed) in such a way that the visual sensory image itself as observed by the human eye of the printed image after image gradation conversion is corrected (or changed). (or change)
This shows that it is also effective. This modification (or change) of the gradation of the printed image can be done, for example, by moving the 50% halftone dot position _M2 depending on the reduction/enlargement ratio, or by improving (strongly) the gradation of the highlight or shadow areas. When you want to express,
This is a necessary measure. For example, when the H and S halftone dot areas of a printed image are fixed at specific values of 5% and 95%, changes in the reflection density of the printing ink (based on yellow ink) or from the original image How can the 50% halftone setting point _M2 , which is an extremely important control point on the halftone print image, be moved to correct the gradation of the image and change the scaling ratio of the printed image? The question is whether changes should be made. Table 3 shows an example of basic materials useful in solving this type of problem. By preparing multiple materials as basic materials, you can reasonably move the 50% halftone dot position _M2 according to the actual work needs.
This allows the gradation of the image to be adjusted. Print image density range in Table 3 (DRp in Figure 1)
) is determined depending on the solid density of yellow ink in the set ink used (and
The β value is also determined based on this), and the number in parentheses below it is the value of ε=α/α−β. The number in parentheses at the top of each space (frame) in the table is the basic density value x at that sample point, and the number at the bottom is the halftone area percentage y of the halftone dot corresponding to each basic density value. Indicates the numerical value of However, the range of halftone dots used was 5% to 95% of the halftone dot area, following the usual method in the industry. The calculated values shown in Table 3 are based on the control of 50% halftone dot position, or
M This is extremely important for managing the halftone area pattern at _two points. For example, when creating a print image with a reduction/enlargement ratio of 100% from a color original using film manufactured by Company E, the print image density area is set to 0.95, and the ε value is set to 0.95.
1.12638, a printed image with the desired image quality is obtained. Next, create a halftone gradation characteristic curve based on the settlement values in Table 3 (that is, create a characteristic curve by taking the original image basic density area x on the horizontal axis and the halftone area %y on the vertical axis). create.). Next, change the reduction/enlargement ratio for the standard plate, move the 50% halftone dot position to the S side when reducing, and move it to the H side when enlarging, and apply the halftone dot to the film. Create a tone image. The test image thus obtained is compared with the halftone gradation image of the reference version of the printed image in which the desired image quality was obtained. Select a test image with the same image quality as the latter halftone image, for example, 1/
When it is reduced to 2, the print image density area is 0.85 and the ε value is 1.16449, when it is expanded to 200%, the print image density area is 1.10 and the ε value is 1.08629, and when it is expanded to 400%, the print image density area is 1.25 and the ε value is 1.05958. Suppose it's hot. Then, create a halftone characteristic curve for these dots, and based on the intersection of the curve with the straight line indicating the 50% halftone dot, select the sample point at which density value of the original image (in practice, the sample point represents the original image). (The sample points will be found on the gray scale for work standards.)
You can know whether it is appropriate to set the halftone dot to 50%. The density value at which the 50% halftone dot is included as the sample point was chosen for convenience in checking the halftone gradation image after formula decomposition work. Therefore, another method is to select sample points at 2/8 or 4/8 of the density range of the original image, and determine what percentage of the halftone area should be placed there using the halftone gradation characteristic curve. It is also a good idea to perform color separation work based on this. By using Table 3 in this way, it is possible to rationally convert the image gradation and correct (or change) the image gradation. In addition, correction (or change) of the gradation of this image
is not only the reduction/enlargement rate of the single print image, but also
This must be done depending on the intentions of the person ordering the printed matter, the type of target image captured on the color manuscript, the purpose of use of the printed image, the whiteness of the printing paper, the density of the printing ink, etc., but in any case. Based on Table 3, it is possible to respond rationally and standardize various color separation operations. In addition, correction (or change) of the gradation of the image in the hydrite area and shadow area can be performed in the same manner, and furthermore, the gradation adjustment of the image described above, that is, the gradation change and/or correction of the gradation of the image. (or change), it is possible to automatically remove color fog in highlighted areas of a blank original without taking any special countermeasures. As described below, in the present invention, conversion of image gradation and correction (or change) of image gradation in color separation work, which has been performed based on human experience, intuition, and skill, can be scientifically performed. It can be rationalized to (iv) Other tables calculated using "this conversion method" and their usefulness Until now, photolithography, especially color separation work, is the first work step, and is also the basis for printing image formation. Conversion work (in the present invention, this is done based on gradation-first principle, tone-
The term "rendering-first-ism" (the importance of rendering-first-ism) has relied exclusively on human experience and intuition, and there have been no attempts to truly theoretically analyze color separation work from the printed image side. It has never been done. However, the "present conversion method" of the present invention is
This can be modified into a rational method. Next, based on the correlation between the basic density value of the original image and the halftone dot area % of the printed image using this conversion method, we will theoretically consider various matters that are most basic for color separation work. Useful basic data are shown in Tables 4 to 8. From each of these tables, we focus on what is the essence and principle of dependence between the original image and color separation work, and what can be done to rationally align the essence and principle with practice. It is possible to identify what needs to be considered. In the preparation of Tables 4 to 7, α=100% and β=0% were used. [About Table 4] Table 4 shows the human impact when the reflective density of the printing ink changes based on the print image density range (or image contrast) when α = 100% and β = 0%. The effect on the visual density is shown in terms of halftone area %. However, since α=100% and β=0% are the standards, the numerical value of the halftone area % is the same as the density value recognized by the visual sense when observing the printed image. [About Table 5] Table 5 shows that under the same conditions, when the density of printing ink changes, the halftone area % is changed from 0% to
The halftone area at each sample point required to produce a printed image with the same image tone and similar image quality to the human visual sense, while using up to 100%, apart from the overall image contrast. This is a list of percentage values. In other words, when the given conditions are ideal,
This is a list of values for the halftone area % of each sample point on the ideal halftone gradation characteristic curve corresponding to the maximum density value of the printing ink used. [About Table 6] Similar to Table 5, Table 6 shows each sample on the ideal halftone gradation characteristic curve when the usage range of halftone area % is from 0% to 95%. Dot halftone area%
This is a list of numerical values. [About Table 7] Table 7 has the same basic conditions as Table 5, but when using the range of halftone dot area commonly used in the industry (5% to 95%), This is a table showing what percentage of halftone dots should be placed at each sample point on the ideal halftone tone characteristic curve. Incidentally, it is unnecessary to explain that this list is the prototype of "this conversion method." [About Table 8] Table 8 shows the density of printing ink (printed image density range) when creating a black and white printed image from an original image.
When the range of halftone dots used (the range of halftone dots used was selected according to the usual method for black-and-white halftone photography work in the industry) changes, in order to obtain the ideal halftone gradation characteristic curve, it is necessary to This is a list of how the values for the halftone dot area % at sample points should be determined. Also, from this table, we can see how the ideal halftone gradation characteristic curve changes when the usage range of the halftone dot area is changed, even if the density of the printing ink is the same. You can know what you need. In Table 8 (1), (2), and (3), the halftone percentage values in the theoretical halftone percentage column are E=1,
(a=1.0, β=0), and other values are the E values shown in the table. In this case, the E value was determined using α=1.0 and β a value determined from the printing ink density (printed image density range), that is, β=10 ⁻ (printed image density range). In addition, students will learn techniques and techniques for creating black-and-white printed images, which are halftone images corresponding to 1:1, from originals, which are continuous-tone images, and to arbitrarily adjust the gradation of black-and-white printed images. This is also the basis of color separation work in multicolor plate making. By repeatedly conducting theoretical studies from various angles on the continuous tone basic density and the halftone dot area percentage shown in the above example, we were able to determine the conversion and Establishment of a rational method for converting image gradation and correcting (or changing) gradation, distinguishing between correction (or change), and converting gradation and correcting (or changing) gradation at the same time. Scope, content, and limits can be determined theoretically and scientifically. (v) Experimental example The measured density values of H and S of the image are 0.2~
The original image is a positive color film with a still life of 2.80 and a portrait of 0.2 to 2.70, the solid printing density of the yellow plate is 0.9 (the β value is calculated from this value), and the paper reflectance α is 100. %, 3% halftone dot on H and 95 on S of the indigo printing image which is the color separation standard and plate.
% halftone dots, the image information obtained by the relational expression (1) was used as the color separation characteristic curve (halftone gradation characteristic curve) of the indigo plate C. Furthermore, based on the color separation characteristic curve of the indigo plate C, H is 2%
A characteristic curve that yields halftone dots, 90% halftone dots for S, and halftone dots with a halftone area percentage 8 to 10% smaller than that of the indigo plate for midtones, is determined using a computer using relational formula (1). These were used as color separation characteristic curves for yellow version Y and red version M. For the black version BL, we decided to use the previous color separation characteristic curve as is, and the color correction and color correction remained the same. Under the above conditions, CP-
When I performed color separation using a 341ER scanner and performed color proofing with Cromarin (trade name, manufactured by Dupont), I was able to obtain extremely satisfactory results, as I had predicted. In other words, the overall tone of the printed image depends on the color
The quality and image quality of the film original image were not inferior to that of the original image, and the sharpness of the color gradation of the image was also satisfactory. In particular, it is now possible to simultaneously express (reproduce) the image quality of both soft subjects such as blankets and hard subjects such as metal products, which have been said to be difficult to reproduce in printed images. What was achieved was an effect of the present invention that was not initially anticipated.

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〔Effect of the invention〕

The image gradation adjustment method of the present invention has the following excellent effects: The relationship between document image density and halftone dot area percentage, which was conventionally left to the operator's judgment based on experience and intuition, has been improved. , more specifically, the relationship between the basic density value of a certain basic point on the original image (continuous tone image) and the corresponding halftone area percentage on the printed image (halftone image), that is, the relationship that the printed image should have. Regarding reasonable halftone image characteristics and an image tone adjustment method for obtaining a halftone image having such characteristics, rational and simple solution means (gradation changing means and tone changing method) means) are provided. Therefore, the present invention can rationally systemize the theory and technology of the work process for obtaining halftone images, and this can streamline not only the photolithography process but also the entire process of printing image formation. , which forms the basis for systematization. This conversion method, which can scientifically and rationally define the H, S, and gradation (density) characteristic curves from H to S of a manuscript image, is applied to image gradation conversion mechanisms such as photolithography equipment. For example, by incorporating the image adjustment mechanism, which is a source of confusion in current electronic color separation devices, it is possible to eliminate the need for image adjustment mechanisms, streamline and simplify the equipment, and
It is possible to reduce manufacturing costs. "This conversion method" clarifies the work procedure for gradation conversion or gradation correction (or change), so the number of reworks is extremely reduced compared to conventional methods, achieving a significant improvement in work efficiency and production. performance can be improved, and at the same time, the consumption of consumable materials can be significantly saved. The "present conversion method" makes it possible to rationally and simply define the quality evaluation criteria for printed images, independent of the quality content of the original image. In other words, since it becomes possible to have a common rational technical medium between the print orderer and the photolithographic engineer, communication between the two becomes extremely easy and reliable. In the work of creating print images using the "main conversion method," it becomes possible to have technical flexibility that can meet the needs of those who order printed matter. With this conversion method, the work of inputting the work standard characteristic curves (color separation characteristic curves, shading characteristic curves) desired by the operator into a color scanner etc. becomes rational and easy, and the work time is reduced to 1/5th. It can be shortened to ~1/10. Therefore, the limitations in workability of conventional color scanners can be removed, and the flexibility of the work of the device can be greatly increased. This conversion method solves the problem of halftone gradation expression, which is an important practical problem in this industry, the problem of color cast in the highlight part of color film originals, and the problem of gradation jump-up (printed image This effectively solves problems such as tone jumps (discontinuous tone jumps). ``This conversion method'' can rationally determine whether the image gradation adjustment function (gradation conversion, gradation correction) used in current photolithography equipment is good or bad. In addition, in image gradation adjustment during color separation work in photolithography, we streamlined the process of color tone adjustment (maintaining good gray balance across the entire gradation range of the printed image), color correction, color correction, color change, and retouching. It is possible to distinguish between
It becomes possible to add scientific considerations to solving various problems in color separation work. These things provide extremely effective means for streamlining the photomechanical process. This conversion method will enable the training and training of engineers needed as photolithographic machinery becomes more sophisticated.
Training can be carried out effectively, unnecessary effort in daily tasks can be saved, and time can be given for new creative research and development.

[Brief explanation of the drawing]

Figure 1 shows typical examples of image gradation conversion. Figure 1a shows an example of converting an original image into a halftone gradation image via a density-compressed original image, and Figure 1b shows an example of converting an original image into a halftone gradation image. An example will be shown in which an image is converted to a halftone image via a tone-converted density range compressed original image. Do...Density value of continuous tone original image.
DRo: Basic density range of continuous tone original image.
The difference between the density value at the sample point X on the document in this DRo and the density value at the brightest point (extreme point of the highlight portion) H becomes the basic density value x. Do: Density value of a density range compressed original image obtained by proportionally compressing the density range of a continuous tone original image using the k value. DRo...
Density range compression The density range of the original image. Do...Density value of a continuous tone image obtained by converting the tone of a continuous tone original image using "this conversion method" and compressing the density range. DRo...Density area of a continuous tone image obtained by converting the tone of a continuous tone original image using the "this conversion method" and compressing the density area. Dp...The halftone area percentage of the printed image, which is the halftone gradation. DRp...Print image density range. P: Halftone characteristic value based on quality evaluation standards for printed images. The P value is compared to the y value,
Consistency between the two is evaluated. H...The brightest point on the original (the extreme point of the highlight area), S...The darkest point on the original (the extreme point of the shadow area), _M1 ...The point at the middle of the density on the original (the intermediate density) point), M ₂ ...The point at which the 50% halftone dot (area) is located in the printed image, which is the halftone gradation.

Claims (1)

[Scope of Claims] 1. In a gradation adjustment method when creating a print image that is a halftone image from an original image that is a continuous tone image, the basic density value ( A continuous tone image characterized in that the difference (difference between the density value at the sample point and the density value at the brightest part on the same image) x is converted into a halftone dot area percentage value y using the following relational expression (1). A gradation adjustment method when creating a print image that is a halftone gradation image from an original image. <Relational expression (1)> y = y _h + α (1-10 - ^kx ) / α - β (y _s - y _h )... (1) where, x: the basis of any sample point X on the original image Concentration value.
That is, the value obtained by subtracting the density value at the brightest part H on the original image from the density value at an arbitrary sample point X on the original image. y: A numerical value of the halftone dot area percentage of the halftone dot of the sample point Y corresponding to the sample point X on the printed image. y _h : A numerical value of the halftone dot area percentage of a desired arbitrary size halftone dot, which is set for the brightest part H of the printed image. y _s : Floor set for the darkest part S of the printed image,
The numerical value of the dot area percentage for any desired size dot. α: Reflectance of printing paper. β: Surface reflectance of printing ink. k: Ratio of (print image density range)/(original image density range). respectively.