JPH02165964A - Ink jet printer - Google Patents

Abstract

PURPOSE:To form a recording image having excellent reproducibility of a gradation by converting an image information signal obtained from an original image by a specific gradation regulating system. CONSTITUTION:When an image information signal obtained from an original 5 is processed by a gradation regulating mechanism 11 and a recording image having monochromic or multicolor halftone is formed on a recording sheet on the basis of a process signal, the gradation regulating mechanism 11 converts a basic density value (X) of an arbitrary sampling point on the original image based on the image information signal (the difference between the density value of the sampling point and the density value on the brightest part on the same image) into a pixel density value (y) at a position corresponding to the sampling point of the formed recording image according to a formula (1), where, in the formula (1), YH and YS are pixel density values of a desired size, determined with respect to the pixels of the brightest part H and the darkest part S of formed recording images, alpha is reflectivity of recording sheet, beta is numeric value obtained by beta=10<-gamma>, h is numeric value obtained by gamma (density region of original image), and gamma is arbitrary coefficient.

Description

[Detailed description of the invention] (Industrial application field) The present invention uses image information signals obtained from original images.

The present invention relates to an inkjet printer that can perform conversion processing using a novel gradation adjustment method and form recorded images with excellent reproducibility of one gradation.

More specifically, the present invention is applicable to various original images (continuous tone images such as monochrome or color photographs, video images obtained from television or computer video signals, etc.) that are to be reproduced on recording paper. (hereinafter the same shall apply) is converted using a gradation adjustment mechanism using a new gradation conversion formula,
The present invention relates to an inkjet printer that can form a recorded image with excellent gradation and color tone reproducibility on recording paper based on the gradation-converted output signal.

(Prior art) When copying an image from a continuous tone original image such as a photograph onto a recording sheet using an image forming device such as a copying machine, analog processing of the original is required when photosensitive paper is used as the recording sheet. (exposure) to form an image with continuous gradations corresponding to the original (silver halide photographic recording).On the other hand, in inkjet printers that record images on plain paper rather than photosensitive paper, images are formed using analog processing. It is difficult to reproduce the density gradation (gradation), and especially in the case of duplicating a color image, it is not easy to adjust the tone (color balance) as well as the density gradation described above.

For this reason, many efforts are being made to improve the reproducibility of gradations and color tones in printer devices. Formation of recorded images in inkjet printers is similar to the method of converting from continuous gradation to halftone gradation in photolithography in printing, in which both images are obtained by photoelectric scanning of a continuous gradation document image such as a photograph. The purpose is to process information signals and use the signals to form on recording paper an image consisting of a pixel distribution with gradation and color tone corresponding to the original image.

However, current printer devices use unscientific tone adjustment methods for processing image information signals obtained from original images to reproduce tone.

At present, satisfactory gradation reproducibility has not been achieved.

As is well known, the density gradation of a recorded image depends on the pixel density display method. In the case of inkjet printers, two methods are used to display the density gradation of one pixel: one is to change the pixel coverage by changing the size of the dot (size modulation method), and the other is to change the pixel coverage by changing the number of dots (of the same size) arranged in a specified manner. There is a method of changing the density (density modulation method). However, when copying a document image using an inkjet printer, the coverage rate of pixels on the recorded image corresponding to the density values of predetermined sample points on the document image by dots, that is, the density gradation value of the pixels. (Hereinafter, simply referred to as the pixel density value), there has been no scientific study as to what the pixel density value should be or how to obtain such a pixel density value.

That is,! A scientific correlation formula has been developed to determine what kind of pixel density value should be correlated to the density value of a predetermined sample point on the original image and to the pixel on the recorded image that corresponds to that sample point. Currently, these equipment manufacturers have no choice but to rely on decisions made in advance based on experience, intuition, or a limited number of fixed conditions.

As a result, originals with image quality that one equipment manufacturer did not expect,
For example, in the case of non-standard color film originals (overexposed originals that are too bright, underexposed originals that are too dark, etc.), the task is to obtain a desired recorded image with excellent gradation and color tone. Therefore, recorded images of the desired quality can be obtained not only from originals with standard image quality but also from non-standard originals mentioned above, and the image quality of the original can be arbitrarily changed or modified (changes in gradation or color tone, corrections etc.). ), it has not been possible to develop an inkjet printer with the flexibility to do so.

This means that conventional inkjet printers are unable to scientifically make pixel density values correspond to the density values of predetermined sample points on the original image.

(Problem to be Solved by the Invention) The cause of the above-mentioned problems in conventional printer devices is that when forming a recorded image based on the final pixel distribution from an original image such as a continuous tone image, the initial The concept lies in the process of image gradation conversion, which plays an important role at this stage.

In other words, when converting the density value of a predetermined sample point on a document image into the pixel density value of a pixel on the corresponding recorded image, the conventional way of thinking about gradation conversion is ``scientifically rational gradation conversion. The reason is that it was not something that had to be done based on means, but something that relied exclusively on experience and intuition.

The present inventor has focused on this situation, and in order to ultimately streamline the image forming process and form recorded images of excellent quality, it is necessary to establish a rational image gradation conversion technology. Based on this basic understanding, we conducted extensive research.

(Means for Solving the Problems) To summarize the present invention, the present invention processes an image information signal obtained from an original image using a gradation adjustment mechanism, and creates an original image on recording paper based on the processed signal. In an inkjet printer for forming a corresponding recorded image, the gradation adjustment mechanism calculates the basic density value (1) of an arbitrary sample point on the original image based on the image information signal obtained from the 1M original image.
The difference between the density value at the sample point and the density value at the brightest part H on the same image) is set as the pixel density value (ν) at the position corresponding to the sample point of the recorded image to be formed.

The present invention relates to an inkjet printer characterized in that conversion processing is performed using the following relational expression (2).

Relational expression ...■ The configuration of the present invention will be explained in detail below.

In a recorded image formed by an inkjet printer, the basic constituent elements constituting the recorded image are density values in pixels (this is the density value covered by the number and size of dots in the pixels on the recorded image formed as described above). These two factors are the surface reflection density of the image forming material (ink) and the surface reflection density of the image-forming material (ink). As can be seen, the pixel density value, which has the same relationship as the size of the halftone dot area, plays an extremely important role as a means of forming one image, since it has the ability to be easily identified as a difference in density. In other words, when we focus on a certain dot and examine the effects of changes in the amount of ink applied on that dot and changes in the size of the dot on the gradation, we find that the latter is much larger, How the concentration value should be set is an extremely important issue.

Also, in connection with the above, when attempting to form a recorded image using an inkjet printer.

The quality content of original images varies widely, the image forming process has various characteristics, and the evaluation standards for image quality are not uniform. , instability factors must be overcome.

For this reason, when converting a document image such as a continuous tone double image into a recorded image with halftones using an inkjet printer, it is necessary to determine the pixel density value (?H) of the pixel block in the brightest area (H) and the darkest area. The pixel density value (?S) of the pixel block (S) can be arbitrarily selected, and the gradation of the image from the brightest part (H) to the darkest part (S) can be rationally and easily adjusted. It is absolutely necessary to have a means to manage it.

Based on this idea, the gradation adjustment method of the present invention was devised, specifically, the gradation adjustment method defined by the above-mentioned relational expression (2).

First, the process of deriving the above relational expression 〇〉 will be explained.

The present inventors have proposed that when creating a halftone print image etc. from a continuous tone color film original, 1.
In order to perform the conversion (conversion of continuous gradation to halftone gradation), we previously proposed a gradation conversion formula that is the predecessor of the above-mentioned relational expression 〇〉. (Patent Application No. 148912/1983, Patent Application No. 1983
-2590).

The gradation conversion formula (hereinafter referred to as relational formula 〇〉) proposed by the present inventors is useful not only for creating printed images, but also for creating various types of reproduced images, such as creating recorded images using the inkjet printer according to the present invention. Although it can also be used when creating a print image, the explanation will be limited to creating a print image as shown below.

Assuming that the relational expression 〉...■ is given, the process of deriving the relational expression 〇〉 will be explained in order to help the understanding of the present invention.

The relational expression (■) used to calculate the numerical value (ν) of the dot area percentage used when creating the printed image described above is based on the generally recognized density formula (photographic density, optical density), that is, D = +log / I = log7 T It was induced.

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

Comparing the relational expression 〇〉 and the relational expression ■〉, the meanings of the β value and the i value are different, and the relational expression 〇〉 does not specify the γ value. These differences will be explained later in <Relational Expression 0>, which allows halftone dots of a desired size to be arbitrarily set in the H and 8 parts of the printed image in the density equation (D') related to plate making and printing. And then.

The basic density value (1
) and the numerical value (ν) of the halftone area percentage of the halftone dot at the corresponding sample point on the halftone gradation image, and the theoretical value and the measured value approximately match. I was induced to do so.

When applying the above <Relational Expression ■> to the image gradation conversion method when creating a printed image, the reflectance (α) of the printing paper,
Surface reflectance (β) of printing ink and printed image density range/
Based on the value of the ratio (d) of the original image density area, determine the size of halftone dots (ν
H1? S), the value of the halftone dot area percentage (ν ). Thereby, the density gradation of the original image (continuous tone image) can be faithfully reproduced on the printed image (pi-tone halftone image) with 1=1.

In addition, multicolor plate making (generally cyan (C), magenta (M),
In the case of four plates (yellow (Y) and black (BL), which are considered to be one set), the standard plate (in the case of multicolor plate making, as is well known, the cyan plate (C) is the standard plate. ), that is, the halftone gradation characteristic curve that is the standard for converting the density information value of the original image into the halftone fineness value of the printed image (obtained by graphing the work value and ν value described above). This curve is the standard for converting continuous gradation to halftone gradation.)
Once determined, the working standard characteristic curves for other color plates can always be determined by multiplying the value of ν of the standard plate by an appropriate adjustment value based on the gray balance ratio of each printing ink color.
It can be decided rationally.

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 interrelationships in terms of gradation and color tone between those characteristic curves are also rational. and appropriate.

In other words, when creating a halftone print image from a continuous tone original image, if the tone conversion is performed based on the above relational expression (■), then the tone of the image can be calculated by relying on conventional experience and intuition. Breaking away from the conversion method, it is possible to arbitrarily and rationally convert the gradation of an image, and it is also possible to rationally adjust the color tone, which is closely and inseparably related to the gradation. As a result, it is possible to obtain a printed image having a density gradient and color tone that are natural to the human visual sense. The above is the content previously proposed by the present inventors.

However, in subsequent research, the relational expression 〇〉
It has been found that there are certain limitations in the operation of

What are its limits?

・It is extremely effective if the original image is of standard quality, but it is extremely effective for documents with non-standard quality, especially those with extremely poor quality content (for example, those with over- or under-exposure when taking photographs) ).

This will be explained from the point of view of the operation of the above-mentioned <Relational Expression (■)>.

・In the case of standard quality (W semi-manuscript), the molecule that determines the A value is the solid printing density value of yellow ink, which has a large stimulation value (its typical density value is 0.9 to 1). .0
It is. ) to perform gradation conversion (in the case of multi-color plate making, the 6th edition is produced using this value), it is extremely effective, but it is especially useful for non-standard manuscripts with poor quality content as mentioned above. not being fully satisfied.

- Regarding the β value, when dealing with non-standard originals, it is sufficient to use the surface reflectance of the printing ink (as mentioned above, yellow ink is the standard) and other values arbitrarily selected. What you can't do.

etc.

In order to overcome the above-mentioned limitations, it is necessary to adapt the halftone gradation characteristic curve, which serves as the work standard for gradation conversion, to not only standard originals but also non-standard originals.

The shape of the curve must be able to be changed arbitrarily and rationally. As a result of studies, the present inventors have found that satisfactory results can be obtained when gradation conversion is performed under the following conditions.

・i value = γ/(, [density range value of both original images) ・γ value = any positive or negative value ・β value: A value determined from the γ value that defines the above O value by β = 10.

By applying the above-mentioned relational formula (■) under the above conditions, it is possible to create printed images with excellent reproducibility of density gradation and inseparable color tones from standard and non-standard originals. can.

The above explanation has centered on the creation of printed images with halftone gradations, but it goes without saying that the theory that supports the gradation conversion work described above can also be applied to the creation of recorded images using inkjet printers. That's true.

It goes without saying that the gradation conversion formula suitable for creating a recorded image using an inkjet printer can be summarized by incorporating the above-mentioned study results into <Relational Formula 0>.

Next, the meaning of each term in the above relational expression 〇〉 of the present invention.

Explain the operational characteristics.

In the operation of the above-mentioned relational expression (2) of the present invention, the basic density value (1) must be found from the image information signal of the original image. The density information value may be any value as long as it reflects the physical quantity related to the density of each pixel of the original image, and should be interpreted in the broadest sense. Synonyms include 1 reflection density, transmission density, m degree, light amount, current/voltage value, etc. These density information values may be extracted as density information signals by photoelectrically scanning the original image.

In addition, in the above <Relational Expression 0> of the present invention, the basic density value (1) is measured using a densitometer (for example, a portrait of a positive color film with a density value of 0.2 to 2.70). ), and ν.

[Pixel density value set in the pixel block of the brightest part (H) and ts [Pixel density value set in the pixel block of the darkest part (S)] with a percentage value (for example, 5% or 95
A numerical value of %. ), the pixel density value recorded in the pixel block (Y) corresponding to an arbitrary sample point (X) on the original image is calculated as a percentage value.

In the operation of the above-mentioned relational expression (■) of the present invention, it is possible not only to modify and use it as follows, but also to use it by any processing, modification,
You are also free to use it as a guide.

shi=shiH+E (110-' ”)(shig-?)l)
In the above modification, α=1. This is based on the surface reflectance of the recording paper (base material) being 100%. In practice, the value of α may be set to 1.0.

Moreover, according to the modification (α=1.0), the brightest part H on the image recorded by the inkjet printer? ■() can be set as planned in the darkest part S. This means that in the brightest part H on the recorded image, the value is 0, and in the darkest part S, the value is 0. This is clear from the fact that -(D=-γ).

In the operation of the above relational expression 〇〉 of the present invention, α.

The numerical values of β and γ (the β value is defined by β=io−' as described above) take various values6. In the present invention, by appropriately selecting these numerical values, the original image can be adjusted. Image gradation conversion processing can be performed rationally regardless of the quality characteristics.

That is, 1. The image gradation conversion processing method based on the above-mentioned relational expression (0) of the present invention reproduces the gradation and color tone of the original image, that is, reproduces the tone of the original image in a recorded image in a 1:1 ratio. However, its usefulness is not limited to this.2 The above relational expression of the present invention is useful not only for faithfully reproducing the characteristics of the original image, but also for α, β, γ. value, and even ν□.

? By appropriately selecting eight values, it is extremely useful for rationally changing or correcting the characteristics of a document image.

To explain this in detail, when applying the above relational expression ■〉,
It should be noted that users (workers) have the following degrees of freedom.

Bad point 1: Use the relational expression 〉 for the purpose of forming an image that is faithful to the original image, that is, to obtain an image that visually and perceptually looks exactly the same when observed with the human eye. Think first and use the relational expression. In the present invention, such tone adjustment behavior is explained using the term "tone conversion (of an image)."

Shit 2: Use the <relational expression ■> to change or modify the original image due to the technical needs of image formation, artistic requirements, or the needs of the ordering party. In other words, the primary consideration is to obtain an image in which the visual sensory image itself when observed with the human eye is corrected or changed, and the relational expression 〇 is used. In the present invention, such tone adjustment behavior is explained using the term "(image) tone (correction) (or change)."

When forming a multicolor image using the above relational expression ■〉,
For example, when copying a color original using an inkjet printer, color separation, which is well known in the printing field, is used to separate the reflected light from the color original into blue (B), green (G), and red (R). It is sufficient to obtain the density information signal for each image, process it with a gradation adjustment mechanism using the above-mentioned relational expression (2), and form an image based on this processed information. At that time, the γ value for the reference color plate (for example, 0 plate), that is, the gradation characteristic curve of the reference color plate (
By calculating the V value and plotting the γ value against the χ value, a gradation characteristic curve similar to the halftone gradation characteristic curve in printing technology is obtained. ), and the N timing curve for other color versions (M version, Y version) is determined by multiplying the γ value of the reference color version by an appropriate adjustment value based on the gray balance ratio of each ink. Since these gradation characteristic curves can be determined more rationally, images can be formed using these gradation characteristic curves.

What about each color version determined as described above? The value, that is, the gradation characteristic curve for each color plate, is defined by <Relational Expression 〇>, so it is not only a reasonable characteristic curve, but also the mutual relationship regarding gradation and color tone between those characteristic curves is also rational. be objective and appropriate;

As described above, when a recorded image is formed by an inkjet printer, hardware or software that performs gradation conversion based on the above-mentioned <Relational Expression (2)> is incorporated into the gradation adjustment mechanism section.

It is possible to obtain a recorded image that is excellent in reproducing not only the Pl tone but also the color tone, or a recorded image in which the image quality of the original image is arbitrarily corrected or changed.

The present invention will be explained in more detail below based on Examples, but the present invention is not limited to these Examples unless it goes beyond the gist of the present invention.

As described above, the present invention has the greatest feature in that the gradation is converted in the gradation adjustment mechanism section of the inkjet printer using the relational expression (2). Therefore, we will explain how to use the relational expression 〇〉 with ease, especially the handling of the γ value.

(Example) (1) Regarding the method for determining the γ value adopted in <the relational expression>.

The main feature of the present invention is that when forming a recorded image using an inkjet printer, the core gradation conversion work in the process of creating the recorded image can be performed based on the above-mentioned relational expression 〇〉. .

In this case, it is desirable to create an image of the same quality as a recorded image formed from a standard original whose quality content is standard, even from original images that vary in quality such as brightness or darkness. Of course.

To achieve this, it is necessary to find a process value that can produce images of the same quality as recorded images obtained from standard originals, without being influenced by the quality of the original images.
It is necessary to obtain a tone characteristic curve that defines the value relationship. In the relational expression (2) of the present invention, it is the γ value that can greatly change the shape of this gradation characteristic curve.

Below, we will explain how to determine the γ value, which has extremely important significance in the operation of the relational expression 〇〉.The inkjet printer of the present invention can
For the first time, recorded images with excellent gradation and color tone reproducibility can be formed.

For various γ values? Table 1 shows how the values (that is, pixel density values) change. Table 1 shows that while changing the γ value (γ
Value = 2.00 to -0.20).

The above 〈Relational Expression ■〉, 〉 = 3%, 〉 8 = 95%, α =
1.00. β=IO, i=γ/ (1)! Each density step (Table 1 shows the density range of the original image in 9 steps) calculated under the condition of density γ/(2,8-0,2) (density range of striped image) )? It indicates the value.

(The following is a blank space) From Table 1, when the γ value is changed, individual wI timing characteristic curves corresponding to each change can be obtained.

Therefore, it is only necessary to set the optimum quality from the quality contents of a given original image and perform gradation conversion. The results in Table 1 are illustrated in FIG.

Therefore, when a document image with predetermined quality content is given, the optimal γ value to be adopted in the relational expression 〇〉 is determined as follows:
rjJM is how to decide rationally.

To establish a method for determining the γ value to be adopted in accordance with the image quality of the original by using monochrome or color film, which is said to be particularly faithful in reproducing gradation and color tone, as an i-striped image. Make it. This is because if a method for determining the γ value that is effective for monochrome and color film originals with high gradation reproducibility is established, it will be useful for other original images as well. .

A detailed analysis of the image quality of the original color film revealed that
The image quality, such as high-key (photographed with overexposure) and low-key (photographed with underexposure2), is vastly different compared to a standard color film original photographed with standard exposure. be. However, the difference in image quality of color film originals is because the difference in exposure directly affects the brightest density value Hn of the original.
By focusing on this point, it is possible to define it objectively.

Then, as the inventors proposed earlier, the standard manuscript (
Proper exposure. ), the γ value is 0.9~
Considering that it takes a value of 1.0, it is sufficient to find the correlation between Ho and γ. Note that Hn was selected because the density region near the brightest part is important in gradation reproduction. Theoretically, 1 of m drafts! It goes without saying that the t# portion density value Sn may be selected.

Therefore, we conducted an experiment to form recorded images of excellent image quality using various color film originals and to determine the relationship between Hn and γ value. Experimental data are shown in Table 2.

In Table 2, Experiment Ha 2 was based on the standard manuscript, and 0.9 was adopted as the γ value.

Table 2 (Note) Hn and Sn indicate the brightest and darkest density values of a given individual color film original.

From these experiments, the γ value can be reasonably determined by the following formula.

(i) When the relationship between γ7 and Hn in Table 2 is graphed as shown in FIG. 2 (total logarithm graph), γ1 is obtained by the following formula.

γn=γof D, l tanα (n)::(1), etc., #R quasi-original (density range o, 20
~2.80) as γ. :1.00 to form a recorded image, and experiments were conducted to obtain recorded images of the same quality from various color film originals. As a result, γ. The relationship between and Hn could be defined as linear.

(a) Yn=1.70-2.2961(1ogHn
+1) (Relational expression obtained when both γ. and Ho are displayed on a logarithmic scale) % formula %) (Relational expression obtained when γ. is expressed on a normal scale l Hn on a logarithmic scale) From the above In order to reproduce a recorded image with excellent gradation reproducibility using an inkjet printer from an original image with a wide variety of quality contents, first, γ is calculated from the H0 value of the original WI image. It is only necessary to determine this, then use it as the γ value of <Relational Expression 0>, and perform the gradation conversion process.

In the gradation adjustment mechanism of an inkjet printer, in order to operate the relational expression , Hn, a mechanism for calculating the γ value may be added. Alternatively, these measurements and calculations may be left to the operator.

■ Fixation (constantization) of the γ value adopted in <Relational expression■>
Regarding the method for determining the above-mentioned relational expression of the present invention, the method for determining the γ value described above is complicated, and the recorded image created by this method is, strictly speaking, the recorded image obtained from the standard manuscript. There is a difference between This is natural since the brightest density value CHn> of the color film original is different from the brightest density value (Ho) of the standard original.

As explained earlier, in the relational formula (■) useful for gradation conversion of standard originals, when γ=0.9 (or a value between 0.9 and 1.0), not only gradation but also color tones can be reproduced. It is possible to create duplicate images with excellent quality. Therefore, <of the relational expression>
In order to make the value of γ a constant such as γ = 0.9, the density gradation of the original image must be adjusted (corrected) to the density gradation of the standard image. , γ
We will explain how to convert a value into a constant.

In the case of a color film original, the density gradation adjustment described above can be performed very rationally. This will be explained with reference to FIG.

As is well known, the relationship between the exposure amount (X) of the color film sensitive material (note that it is different from X of the sample point X mentioned above) and the color film density (D) at that time is shown in Figure 3. This is as shown in the basic concentration characteristic curve.

The standard original and non-standard original depend on whether the exposure amount is appropriate or not, and each density characteristic curve is shown as having a specific range on the basic density characteristic curve.6 In Fig. 3, The former is shown as a standard concentration characteristic curve, and the latter is shown as an individual concentration characteristic curve (in addition,
FIG. 3 shows an underexposed original as a non-standard original. ) Therefore, the density characteristics of the non-standard original are changed to the density characteristics of the standard original i! li! ! ! This can be done extremely easily by converting the basic concentration characteristic curve into a function.

The basic concentration characteristic curve described above is defined by the function D=fo(X), as shown in Table 3 below (Table 3 also shows the inverse function).

Note that the method of converting the basic concentration characteristic curve into a function in Table 3 should be understood as an example, and a more simplified formula may be used.

(Leaving space below) Table 3 (Example of function representation of basic concentration characteristic curve) (Note) On the basic concentration characteristic front shown in Figure 3, the function f o (X) for determining X)D is its inverse function. A function f x (D) for determining D−+X is shown.

(Note) In order to faithfully define the basic concentration characteristic curve, it is expressed mathematically for each domain of X or D.

The following procedure can be used to match the individual density characteristic curve of a color original to the standard density characteristic curve (see Figure 3).
.

(i) Density values of H and S of a color original image and the basic density characteristic curve of the color film sensitive material of the color original (D=fo
(X)), define the individual density characteristic curve of the color original image, and (...) the density value of the color original I)HnxI
)sn to X=fX(D) to find the value range of the color original image on the X-axis, xHn-xsn, and (■) the value range on the X-axis of the density characteristic curve based on this, Xoo~
Align to x8°. (N) Next, the value range of the D-axis of the reference concentration characteristic curve, D) lo to OSO, is determined.

It goes without saying that if the individual density characteristic curve of a color document matches the reference density characteristic curve, matching of the two is unnecessary.

It is also possible to set an arbitrary tolerance range for the reference density characteristic curve, and perform image processing by assuming that the curve is the same as the reference density characteristic curve when it is within the tolerance range.

In the matching procedure of the individual and group $ concentration characteristic curves described above,
XRo (exposure range for standard originals) and XR.

(exposure range for non-standard color-based originals), it is necessary to align XRn with XRo (see steps (ii) and (m) above). ,). To match XRn to XRo, there are two methods: simple matching (matching the brightest density value to the same value and not caring about the matching of the darkest part) and proportional matching (matching both the brightest density value and the darkest density value). Figure 3 shows the case of mathematically proportional matching.

As shown in FIG. 3, the density information value of the individual density characteristic curve (density information value ton between DHn-Dsn) is substituted into the basic density characteristic curve D=fo(X), and XRn is obtained.
The density information value of the color original (density information value between DHO and OSO,
Do), but change XR, to XR6 ws
! ! The relational expression for determining the X value after the change is calculated as follows by simple calculation.

■ In the case of simple alignment Exposure range of the individual density characteristics of the above non-standard individual originals As color film originals, standard image quality CD No.
0.20. Dso=2JO), high key (overexposure) (Don=0.10. Dsn=2.70)
, and the low-key (underexposed) one (1), n
==0.60゜Dsn=3゜20) and match the individual concentration characteristic curve to the standard concentration characteristic curve under the basic concentration characteristic curve shown in Table 3. It is shown in Table 4.

(Hereinafter, blank space) In the alignment experiment described above, since the density range (DR) of the three color film originals used was all 2.60, it was decided that one was based on simple alignment and the others were based on proportional alignment.

For the density values of Dn and Do in Table 4 above, the ν value (pixel density value 2%) was determined using the following relational expression (2) with Do as a reference. The results are shown in Table 5. Also, the V value and D in Table 5
FIG. 4 shows the correlation of n values.

The curve shown in FIG. 4 makes it possible to create a recorded image with excellent gradation reproducibility from a non-standard quality original image.

This is a gradation characteristic curve that defines the correlation between the engineering value and the ν value.

(Left below) Table 5 (Tone characteristic curve setting data) In the gradation adjustment mechanism of an inkjet printer,
In order to fix (make constant) the γ value of the relational expression, it is necessary to have an inkjet printer with a mechanism for measuring the density of the original image (measuring density across H and S, and H-S), and an original. Although it is necessary to incorporate software and hardware to match the individual density characteristic curve of the image with the standard density characteristic curve, it is possible to create a recorded image with excellent gradation and color tone from an original of any quality content.

(2) Regarding the inkjet printer device The inkjet printer of the present invention will be explained based on FIGS. 5 and 6.

FIG. 5 is a block diagram of an inkjet printer according to a first embodiment of the present invention.

As shown in FIG. 5, the inkjet printer of the present invention converts the transmitted light or reflected light of the image into
Detection unit 1 that separates and reads the spectroscopy into green) and B (blue)
The output signals of the detection unit 1 are Y (yellow), 1M (magenta), and C (cyan).

a color separation unit 2 that converts into a K (black) color separation signal;
A gradation adjustment section 3 that processes color separation signals using the above-mentioned relational expression (2) of the present invention so that an appropriate Wi-tone image is formed; It is composed of four blocks including an output section 4 that makes droplets of ink of each color fly from the head.

Here, the detection unit 1 includes a photomultiplier or a solid-state image sensor (CCD).
), etc., detects transmitted light or reflected light from each part of the original 5, and outputs R, G, B, and USM signals as current values,
This signal is converted into a voltage signal in the A/V converter 6.

In the log amplifier 7, the color separation unit 2 has R,
The voltage signals of G, B, and USM are converted into density by logarithmic operation, and the black (K) component is separated from this density in basic masking (BM) 8, and then the Y, M,
Primary color correction (CC) that separates each component of C
) unit 9 controls the Y component, 2 open components, and C component for each original color of R, G, B, Y, M, and C, and further controls the black component of the original by TJ of the UCR/UCA unit 10.
CR (11d6rcolor removal) or UCA (under color additio)
In n), the ratio expressed by three types of ink, Y, M, and C, and the ratio expressed by K (black ink) are determined.

These Y, M.

After the C and C components are obtained, the gradation adjustment section 11 obtains the Y and M components.

ye'rme' which indicates the pixel density value in the pixel block of each color component from C and K, that is, the effective area ratio of each color component.
, ce', ke'. Gradation adjustment section 1
1 has the algorithm of 〈Relational Expression〉 inside, and Y.

Apply the relational expression to M, C, and obtain the above-mentioned ye', me', co', and ke'.

The gradation adjustment unit 11 has the algorithm of <Relational formula (■)> as software, and has I/O of A/D and D/A.
a general-purpose computer with F (interface),
An electric circuit that uses an algorithm as logic and is realized using a general-purpose IC, and a ROM that stores the calculation results of the algorithm.
It can take four different forms, such as an electric circuit containing the algorithm, a PAL that embodies the algorithm as internal logic, a gate array, and a custom IC.

The effective area ratio corresponding to the pixel density value of each color component obtained by the gradation adjustment section 11 is determined by the color channel selector 12.
and the color channel selector 12 inputs ya'
, me, ce', ke' are output. This output is A/D converted by an A/D conversion section 13 and input to a dot control (D/C) section 14 for each color. Based on this input information, the inkjet head 4 (4Y, 4M, 4G, 4K) corresponds to the amount that each pixel block should be covered with dots. That is, a driving voltage corresponding to the color density is applied. Then, each color ink is sequentially ejected onto the recording paper 15 under sequence control.

Form a recorded image with excellent gradation.

FIG. 6 is a block diagram of an inkjet printer according to a second embodiment of the present invention. The one in Figure 6 uses a TV signal as the image information signal of the original image, and the relational expression ■〉
The algorithm is inputted to the adjustment section which has an internal
The converter converts the signal into a digital signal and inputs it to the charging signal driver 13. The ink droplet 6 is charged to the charging unit 7 based on this input signal.
is charged with electricity. The amount of charge corresponds to the pixel density value covered by dots in the pixel block, that is, the color density value.The ink droplet charged to the amount of charge corresponding to the six color densities is deflected by the deflection unit 8 and recorded. Paper 10 is reached.

In forming an image using the inkjet printer of the present invention, pixel coverage (pixel density value) ti' may be changed by changing the size of dots such as halftone dots in printing technology (dot size modulation).

Alternatively, the arrangement of prescribed dots (dots of a constant size) as seen in the dither matrix method may be devised (dot density change II).

Regarding the usefulness of <Relational formula (■)>, next is the gradation W141 of the inkjet printer of the present invention.
We will provide a supplementary explanation of the usefulness of the relational formula (■) applied to one mechanism.

This is a supplementary explanation for the purpose of facilitating understanding of the present invention, and will mainly describe in detail the operation of the relational expression (2) applied to the gradation adjustment mechanism of an inkjet printer and the significance of its results.

(a) Operational experiment of the relational expression (■) The following two experiments were conducted as basic experiments for incorporating the relational expression (■) into the gradation adjustment mechanism.

a) First of all, use a normal simple calculator, that is, Sharp Pythagoras EL509A (trade name) (Sharp Corporation i), and apply the desired value to the relational expression 〇〉 while operating the simple calculator to calculate the table 6 below. ■■■, image gradation adjustment sections shown in Tables 7 and 8 were created.

As a result, the times required for these tasks, including the time required to check the calculated results, were 3 hours, 2 hours, and 2 hours, respectively.

b) The following experiment was also conducted.

Simple personal computer (PC manufactured by NEC, -
9801-M2), input the desired software obtained separately as function data.

Work was performed to adjust the basic density value (1) of both images of the original (continuous tone image) to the corresponding density value (ν) of the pixel on the recorded image.

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

Moreover, in this experiment, there was no need to use any special software to create the above software used for adjusting the gradation of images input to the personal computer, and the work was created using the N88-BASIC that came with the personal computer. As it turned out, it only took an hour to complete.

In addition, software that allows you to directly input the measured values from a densitometer ranging from highlights (H) to shadows CS') of the original image instead of the basic density value of the original image can also be used to convert or correct the gradation of the target image. It was confirmed that this can be done.

Using these software, I created both images.

Set a desired density interval (for example, from 0.00 to 1.00 in 0.05 increments, and from 1.00 to 3.00 in 0.10 increments), and input the values into the personal computer. By doing so, the desired pixel density value (?)
was able to obtain.

Furthermore, by inputting density values at a plurality of locations from highlights to shadows on both the JM manuscript images, it was possible to obtain desired pixel density values (y-) corresponding thereto.

The pixel density values (?) generated by the software described above are designed to be output either as a positive image or as a negative image, either singly or at the same time.

(b) Calculation results obtained from the relational expression (■) and their usefulness Next, the usefulness of Tables 6, 7, and 8 will be explained.

[About Table 6 ■■■] Table 6 shows that when forming both black and white images from an original image using an image forming device such as an inkjet printer, the density of the ink material (in the table, it is indicated as the density range of the recorded image, and this ) and when the usage range of the maximum pixel density value changes (0 to 100 in the table).
%, 0-98%.

Three cases from 0 to 95% are shown. ) is a list of how pixel density values (?) at each sample point should be set in order to obtain an ideal gradation characteristic curve.

Also, from this table, even if the density of the ink material is the same (that is, even if the recorded image density range = γ value in the leftmost column of Table 1 is the same), the usage range of the maximum pixel density value You can see how the ideal gradation characteristic curve changes when you change it, and whether you need to change it.

In Table 6, the β value that determines the ε value is determined by β=10. By the way, recorded image density range = γ value = 1.0
When ε=1/(1-β)=1.1111. Also, the pixel density value (%) and the same value are β = 0 (ε = 1
．． 0) is the theoretical value.

In addition, students will be able to form a black and white image using a pixel distribution corresponding to 1=1 from a manuscript image such as a continuous tone image, and to acquire Technique 1 method that can arbitrarily adjust the tone characteristics of a black and white image. is also the basis of multicolor image formation.

[About Table 7] Table 7, like Table 6, shows cases where the density of the ink material changes when forming a black and white image from a document image (i.e., when the recorded image density range = γ value changes) , in order to form an image with the same image tone and similar image quality for human visual sense, apart from the contrast of the entire image, while setting the range of maximum pixel density value to be used from 0% to 100%. This is a list of pixel density values (y) at each necessary sample point.

In other words, it is a list of the pixel density values (ν) of each sample point on the ideal gradation characteristic curve corresponding to the density value of the ink material used when the conditions are ideal. .

[About Table 8] The basic conditions in Table 8 are the same as those in Table 7, but when using the maximum pixel density value range (5% to 95%), the ideal gradation characteristic curve This indicates what percentage of the pixel density value (ν) should be set at each sample point.

Until today, color separation work in the creation of printed images, etc.
Color correction using masking technology
tion) is primarily emphasized, and the work of adjusting the gradation of images is basically solely based on human experience and intuition.

Or they remain dependent on a limited number of fixed and given materials. For this reason, it is necessary to develop a scientific gradation conversion technique when creating a duplicate image, based on the side of the image to be duplicated, such as a printed image or an image recorded by a printer.

The relational expression (2) of the present invention performs gradation conversion in a rational manner when creating a duplicate image.

In addition, a sixth equation showing the correlation between the basic density value of the original image obtained by <Relational Expression 〇> and the pixel density value of the image to be formed.
The data in Tables 8 to 8 serve as useful basic data for scientific examination of various basic matters in color separation work during image formation.

From each of these parts, we will discuss what the essence and principles that exist between manuscript images and color separation work are, and what attention and consideration should be given to rationally align that essence and principle with practice. It is possible to extract what must be done.

(c) Relational expression 〇〉 regarding the application of <relational expression ω> to correction (or change) of gradation is the conversion of the gradation of one image (i.e., the distribution of high-fidelity pixels from a continuous-tone original image) (conversion into a gradation image) as well as modifying the original image itself. It is also effective for so-called gradation correction (or change). The correction (or change) of the gradation of this image is based on the intention of the orderer, the type of target image in the color document, the purpose of use of the image to be formed, the whiteness of the recording paper, etc. However, there may be cases where it is necessary to do so due to changes in color, the density of the image recording material (ink), etc.

In any case, it is possible to deal with it rationally by applying the relational expression 〉, and various color separation operations can be standardized.

Furthermore, according to the present invention, it is possible to modify (or change) the gradation of an image in a highlight portion or a shadow portion in a similar manner. This is clear from the fact that, as shown in FIG. 1, the shape of the gradation characteristic curve (the curve that defines the correlation between the engineering value and the ν value) can be arbitrarily changed depending on the γ value employed. Furthermore, WIWi according to the relational expression (■) of the present invention
By conversion.

It has been confirmed that color fog in highlighted areas of color originals can be automatically removed without any special measures being taken.

(Margin below) 〔Effect of the invention〕 The present invention has the following excellent effects.

1) The most basic matters for image formation, the density value of the original image such as a continuous tone image and the recorded image to be formed (
Conventionally, determining the correlation between the pixel density value of an image recorded by the pixel distribution has been based solely on the experience and intuition of the operator, or on irrational methods based on a limited number of stator data. It was something. On the contrary,
In the present invention, this can be rationally determined based on the relational expression 〇〉, no matter what the preconditions are. Furthermore, when converting an original image such as a continuous tone image into a recorded image based on pixel distribution, the most important requirement, gradation management (gradation conversion, correction, or change), is simply a matter of the image gradation. Not only this, but also directly and closely related to the tone of the image, the present invention allows for rational management of gradation and tone.

In other words, an inkjet printer that incorporates the algorithm of the present invention's relational expression (1) into the gradation adjustment mechanism logically systematizes the 5-gradation conversion work (color separation work) and simplifies the work. can be done, and the effect is extremely large.

2) By incorporating the algorithm of <Relational Expression 〇> into the gradation adjustment mechanism of an inkjet printer, the printer device can be rationalized and simplified, and manufacturing costs can be reduced. In addition, the operation is simplified and clear, the number of reworks is extremely reduced, the consumption of consumables is greatly reduced, and the performance of the inkjet printer is greatly improved. In particular, in terms of performance, inkjet printers have the great advantage of being able to form recorded images with excellent gradation and color tone, regardless of the quality of the original image.

3) By using the gradation adjustment mechanism that incorporates the algorithm of <Relational Expression 0>, it is possible to rationally and easily specify evaluation criteria for the quality of both recorded images based on the pixel distribution separately from the image information of the original image. can. Therefore, it is possible to rationally respond to the diversified needs of customers.

4) By adopting <Relational Expression 〇>, the education and training of engineers required as printer equipment becomes more sophisticated can be effectively carried out through the operation of Relational Expression ■〉, and can be carried out on a daily basis. This saves unnecessary effort and frees up time for new creative development.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the γ value and the shape change of the gradation characteristic curve. Figure 2 shows γ. It is a correlation diagram of Hn and Hn. FIG. 3 is a diagram illustrating the principle of matching between the individual density characteristic curve of a color film original image and the reference density characteristic curve. FIG. 4 is a diagram showing a gradation characteristic curve set for a non-standard original. FIG. 5 is a block diagram of an inkjet printer according to a first embodiment of the present invention. FIG. 6 is a block diagram of an inkjet printer according to a second embodiment of the present invention.

Claims (1)

[Claims] 1. An image information signal obtained from an original image is processed by a gradation adjustment mechanism, and a recorded image having halftones of one color or multiple colors is formed on recording paper based on the processed signal. In the inkjet printer, the gradation adjustment mechanism has a basic density value (x) of an arbitrary sample point on the original image based on the image information signal (the density value at the sample point and the density at the brightest part on the same image). The method is characterized in that the pixel density value (y) at a position corresponding to the sample point of the recorded image to be formed is converted into a pixel density value (y) according to the following <relational expression (1)>. inkjet printer. <Relational expressions> ▲There are mathematical formulas, chemical formulas, tables, etc.▼ However, x: the basic density value of an arbitrary sample point X on the original image, that is, the density value at an arbitrary sample point Density value y obtained by subtracting the density value at the brightest portion H: pixel density value at position Y corresponding to the above-mentioned X on the recorded image to be formed. y_H: A pixel density value of a desired size, which is set for the pixel in the brightest part H of the recorded image to be formed. y_S: A pixel density value of a desired size, which is set for the pixel in the darkest part s of the recorded image to be formed. α: Reflectance of recording paper. β: Numerical value determined by β=10^-^γ. k: A value determined by γ/(density range of original image). γ: arbitrary coefficient. respectively. 2. The inkjet printer according to claim 1, wherein the recorded image having halftones is a dot size modulation image formed by changing the recording dot diameter by controlling the amount of liquid ejected from the inkjet head. 3. The inkjet printer according to claim 1, wherein the recorded image having halftones is a dot density modulation image formed by a dither matrix.