JP2938498B2 - Inkjet printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention converts an image information signal obtained from a document image by a novel gradation adjustment method and has excellent gradation reproducibility. The present invention relates to an ink jet printer capable of forming a duplicate image.

More specifically, the present invention relates to various types of original images (in the present invention, all objects to be copied on recording paper are original images. It should be noted in the present invention that an original image is a normal image. When a duplicate image is to be produced from an original image in the sense, for example, a monochrome or color photographic image or a video signal (TV) image, the original image itself is not only an original image, but also a still life or a person that forms the original image. In some cases, a true image information value is obtained from a document image when a duplicate image is produced from the subject or the image-capturing object itself, that is, the image that is literally the original is sometimes referred to as a document image.) Conversion processing is performed under a gradation adjustment mechanism using a specific gradation conversion formula, and a reproduced image having excellent reproducibility of gradation and color tone is formed on recording paper based on the gradation-converted output signal. This It relates an inkjet printer that can.

More specifically, the inkjet printer of the present invention
When producing a duplicate image from a manuscript image, the image information value for duplication is input to various image information input media (for example, a photographic photosensitive material or a photoelectric conversion element such as a two-dimensional CCD, photomultiplier, photodiode, CCD, etc.). Are used.
In the present invention, these are collectively called a recording medium. )
(In the present invention, an image under the recording medium is referred to as a medium image recorded on the recording medium, or simply as a medium image in comparison with a document image in the present invention). However, instead of obtaining the image information value correlated with the density from the medium image as in the related art, an image correlated with the amount of light input to the recording medium for forming the medium image from the original image is obtained. This is a completely new ink jet printer having a tone adjustment mechanism for obtaining information values and converting such image information values under a specific tone conversion formula.

(Prior Art) When an image is copied from an original image having continuous tones such as a photograph, those using photosensitive paper as a recording sheet have continuous tones corresponding to the original by analog processing (exposure) of the original. An image is formed (silver salt photographic recording). on the other hand,
In an ink-jet printer device that records an image on plain paper instead of photosensitive paper, it is not possible to form an image by analog processing, and it is difficult to reproduce density gradation (gradation). It is not easy to adjust the color tone (color balance) together with the density gradation.

For this reason, efforts have been actively made to improve the reproducibility of gradation and color tone in printer devices. The formation of a duplicate image in an ink jet printer is similar to the method of converting continuous tone of photoengraving in printing to halftone tone,
Attempts to process density information values obtained by photoelectrically scanning an original image having continuous tones such as photographs, and to form an image on recording paper having a distribution of pixels having tones and color tones corresponding to the original image Is what you do.

However, the current printer apparatus is unscientific in the gradation adjustment method of processing the density information value obtained from the original image to reproduce the density gradation (gradation). At present, the reproducibility of the accompanying color tone has not been obtained.

As is well known, the density gradation of a duplicate image depends on the pixel density display method.

In the case of an ink-jet printer, as a method of displaying the density gradation of a pixel, a method of changing a pixel coverage by a dot size (size modulation method) and a method of displaying a pixel coverage by a prescribed (same size) dot arrangement number are used. There is a method of changing (density modulation method). However, when an original image is duplicated by an ink-jet printer, the density information value of a predetermined sample point (pixel pressing) on the original image is compared with the density or the density of the dot of the pixel on the duplicate image corresponding to the density information value. Should be set, that is, a value (hereinafter, referred to as a pixel gradation intensity value) that defines the density gradation of a pixel, and how to obtain such a pixel gradation intensity value At present, no scientific consideration has been made as to what should be done.

That is, for the density information value of a predetermined pixel on the original image, scientifically as to what gradation intensity value of the pixel should be correlated with the pixel on the duplicate image corresponding to the pixel. Correlation formulas have not been developed, and at present, these device manufacturers have to rely on experience, intuition, or those determined based on a limited number of fixed conditions.

For this reason, original images with image qualities that were not expected by equipment manufacturers, such as non-standard color films (excessive overexposed documents, underexposed documents too dark, high-key and low-key documents, color fogged or faded documents, etc.) In the case of a manuscript or the like, it is extremely difficult to obtain a desired duplicate image excellent in gradation and color tone. Therefore, a duplicate image of a desired image quality can be obtained from the above-mentioned non-standard document as well as a document having a standard image quality, and the image quality of the document can be arbitrarily changed or corrected (for example, gradation or color tone). (Changes and modifications) have not been possible to develop a flexible inkjet printer.

This is because a conventional inkjet printer converts a density information value of a predetermined pixel on a document image, which is an extremely important image information value for producing a duplicate image, into a tone intensity value of a corresponding pixel on the duplicate image. It means that they cannot be converted scientifically and rationally.

(Problems to be Solved by the Invention) The cause of the above-mentioned problem in the conventional printer device is that when a duplicate image based on pixel distribution is finally formed from an original image such as a continuous tone image, the And the concept of the conversion process of the density gradation of the image which plays an important role.

That is, when converting the density information value of a predetermined pixel on the original image into the gradation intensity value of the corresponding pixel on the duplicated image, the conventional image gradation conversion technology becomes a scientifically rational conversion technology. It is acknowledged that it was not based on experience, but depended exclusively on experience and intuition.

Under such circumstances, the present inventors have to establish rational image gradation conversion technology in order to ultimately rationalize the image forming process and produce a high-quality duplicate image. Based on the basic understanding that it must be done, we have conducted intensive research.

As a result, when a duplicate image is produced by an inkjet printer, the image information is detected or read on the image information detection (reading) mechanism of the printer, more specifically, on a recording medium such as a CCD, as an image information value essential for duplication of the image. Instead of the conventional method using the image information value obtained from the copied media image, the image information value of the object (original image) that is truly the target of the duplication is obtained, and the information is obtained in this manner. When the obtained image information values are processed by a specific gradation conversion formula to obtain a gradation intensity value, it has been found that a duplicate image having extremely excellent reproducibility of density gradation is produced.

As described above, in the present invention, what is used as an image information value that is indispensable for copying an image is emphasized, and an image information value different from the conventional one is adopted. ing. In order to clarify this from the viewpoint of a plurality of target images, in the present invention, before and after the duplication target is recorded or accumulated on the recording medium system constituting the image information obtaining mechanism of the inkjet printer, (I) An object that is truly a target of duplication is referred to as a document image or a substantial image that is the basis of a medium image (usually referred to as a document image, but also referred to as a substantial image to emphasize the features of the present invention). In addition, since the original image may be regarded as a subject or an object to be imaged, it is also referred to as a subject.) (Ii) An object recorded or accumulated on the recording medium is referred to as a medium image.

That is, the image information value of the original image to be used in the conversion of the density gradation in the present invention is the density information value obtained from the medium image (this may be any physical quantity correlated with the density as described later). Rather, it should be interpreted in the broadest sense.) Instead, it defines the relationship between the density information value possessed by each recording medium and the image information value correlated to the amount of light from a document image incident on the recording medium. Characteristic curve (hereinafter, in any recording medium in the present invention,
The above-mentioned characteristic curves of the respective recording medium systems are collectively referred to as density characteristic curves. ) Is an image information value correlated to the light amount obtained through According to the present invention, when the image information value correlated with the light amount is processed by a specific <tone conversion formula> to obtain a tone intensity value for tone conversion, an image faithful to the original image (substantial image, subject) A duplicate image in which the image characteristics as well as the characteristics are arbitrarily changed can be obtained.

In the present invention, as described above, an original image (substantial image) refers to an image that is truly a target of duplication, and detects image information (e.g., image information in a printer device when obtaining image information for producing a duplicated image). It should be noted that this is distinguished from the medium image under the various recording media constituting the (reading) mechanism.

The present invention improves the technology of producing a duplicated image that emphasizes the density information value obtained from a medium image recorded on various recording media in the related art, and only an original image (substantial image) to be a true target of duplication. The image information value of the original, that is, the image information value correlated to the amount of light incident on the recording medium system from the original image is emphasized. It seeks to provide technology.

[Configuration of the invention]

(Means for Solving the Problems) To summarize the present invention, the present invention obtains the density information value of each pixel of a document image from a medium image in which the document image is recorded on a predetermined recording medium, and obtains the density information value. In the ink jet printer, the value is processed by a gradation adjusting mechanism, and based on the processing signal, a duplicate image having one or multiple halftones is formed on recording paper. The density information value (D _n value) of each pixel of the original image is converted into an image information value (X _n value) correlated with the amount of light incident on the recording medium from the original image via the density characteristic curve of the recording medium. (Ii) Further, an image information value (Xn value) correlated with the light amount is
The present invention relates to an ink-jet printer characterized in that the tone is converted into a tone intensity value (y value) for tone adjustment by the following <tone conversion formula (1)>.

<Tone conversion formula (1)> Hereinafter, the configuration of the present invention will be described in detail.

First, the theoretical background of the present invention will be mentioned, and the position of the present invention will be clarified.

Since the theory of gradation conversion according to the present invention was developed to address the problem of gradation conversion at the time of producing a printed image, which is a particularly typical field as a technique for producing a reproduced image, the production of a printed image Much is described in relation to technology. However, this is for the convenience of explanation, and since there is a similar problem in gradation conversion in an ink jet printer, the value of the theory of gradation conversion of the present invention described here may be of some value. It cannot be reduced.

The present inventors support rational theory in image tone conversion technology, and have reproducibility of tone (tone and tone) even from the various original images described above. In order to rationally produce a duplicated image having the following two factors, two of the core elemental technologies in the production of the duplicated image are a gradation control technology and a color correction technology. Prior to the improvement of color correction (correction) technology, conversion of density gradation of each pixel of an image (by changing the size of dots such as halftone dots (variable area dots) in plate making technology for printing, or as described above) It is well known that the density of pixels is reproduced on a duplicate image by changing the arrangement state of specified dots (constant dots) or by changing the density of the dots themselves (variable density dots). I believe that technology that can reasonably perform the above must be emphasized.

The above-mentioned point is a color correction (correction) in which scientific analysis (analysis by a masking equation or a Neugebauer equation) is relatively easy in the production of a duplicate image as typically seen in the production of a color print image. This is a great reflection on the prior art, which emphasizes the technology over the density gradation conversion technology of the image.

The present inventors have proposed a technique of converting the density gradation of the current image used when creating a duplicate image from the original image, using a color film original when creating a print image that is an original image, for example, a duplicate image. It is essential that the density characteristics of the (original image) from the brightest part to the darkest part are not reasonably grasped, and that the density characteristic of the original image is converted into a duplicate image with 1: 1 fidelity. He has a basic understanding that the determination of the correlation (gradation conversion formula) between the two images (the original image and the duplicated image) does not have a rational theory, and remains solely dependent on human experience and intuition.

Under such basic recognition, the present inventors have previously proposed a specific <gradation conversion formula> in order to make the gradation conversion technology of an image scientific and rational (Japanese Patent Application Laid-Open JP-A-64-7770, Japanese Patent Application No. 63-1111499, Japanese Patent Application No. 63-207326, U.S. Pat. No. 4,811,108).

However, in our subsequent work,
It has been found that there is a certain limit to the gradation conversion technique of an image performed under the above-mentioned specific gradation conversion formula.

This limitation means that the true target of the duplicated image should be the original image (substantial image), but in the conventional gradation conversion technology including the earlier proposal of the present inventors, the original image ( To obtain image information for duplication from a real image), an original image is recorded once on a recording medium system of a device for producing a duplicate image (that is, a medium image), and the density obtained therefrom is recorded. That is, gradation conversion of an image is performed using the information value as a clue. This depends on the photosensitive characteristics and photoelectric conversion characteristics of the recording medium system, and the image information value of the original image (substantial image) itself is not used.

This will be described by taking a case where a color print image is produced as a duplicate image as an example.

The color film original is a medium image according to the present invention in which an image of a still life, a person, or the like is captured on a recording medium called a photographic photosensitive material. Therefore, when the density information value is detected from a color film original (medium image) and is used for gradation conversion of an image, the density information value is not based on the image information value of the subject (substantial image). That is, in a conventional printing image production technique using a color film original (medium image), light incident on a photographic light-sensitive material (photographic light-sensitive emulsion layer) as a recording medium from a subject is exposed to a predetermined exposure condition ( As is well known, under the conditions of the incident light intensity I and the incident time t, the exposure amount E is represented by E = It.) Based on the density information value of the photographic image recorded by the color separation work (color separation) The work includes both the color correction and the gradation control described above.)

As is well known, photographic density is formed on a photographic light-sensitive material from which an object is photographed by development, and this is a medium image. A curve representing the correlation between the photographic density (degree of blackening) and the exposure amount E of the photographic light-sensitive material is a photographic density characteristic curve (photographic charact
eristic curve). This means that the vertical axis represents the photographic density (D) (D = log ^Io / I), and the horizontal axis represents the logarithmic value (log) of the exposure E.
E). In the case of a film or a dry plate (transmitted original), the intensity of transmitted light I and the intensity of incident light Io
And for photographic paper (reflective originals), the intensity of reflected light I
It goes without saying that the ratio of the intensity of the completely reflected light to the intensity Io is used.

A typical photographic density characteristic curve (hereinafter, simply referred to as a density characteristic curve) includes a downwardly convex foot, a substantially linear straight part,
It is well known that this results in a fairly complex curve with an upwardly convex shoulder (see FIG. 1 below).

In other words, the conventional color separation technique for producing a color print image is a color separation technique that has been developed from the standpoint of the vertical axis (density value) of the density characteristic curve. Exposure amount incident on the material (hereinafter, in the present invention, since an absolute value of the exposure amount may be used or a relative value may be used as described later, the image information value is broadly referred to as an “image information value correlated to the light amount”). ), That is, a color separation technique assembled from the standpoint of the horizontal axis of the density characteristic curve (image information value correlated to the amount of light). The density information value of the color original image on which the prior art is based on the color separation work is different from the image information value correlated with the light amount of the subject (substantial image) as is apparent from the shape of the density characteristic curve. Due to changes in conditions such as development conditions, the aspect of the difference between the two varies widely.

That is, since the characteristics of the photographic photosensitive material as a recording medium are affected, the photographic density which is the density information value of the color film original which is the medium image and the image information value which is correlated with the light amount of the subject (real image, real scene). And a linear relationship (for example, 1: 1 4
(5 ゜ linear relationship).

On the other hand, in human vision, it is well known that the discrimination characteristic for light and darkness is logarithmic, and humans determine the amount of light incident on the visual system from a subject (substantial image) based on the discrimination characteristic. Has been evaluated. here,
I feel that the gradient of the density change is linear as a natural one.

Therefore, in the production of a color print image, when the work is performed with the density value (D = log ^Io / I) of the medium image recorded on the photographic photosensitive material as a clue, it is affected by the photosensitive characteristics of the photographic photosensitive material. This means that the density information value after use is used, and does not mean that the image information value correlated with the light amount of the subject (substantial image) that is the true target of the duplication is used.

The present inventors considered the photosensitive characteristics and photoelectric conversion of various image recording media (photosensitive milk material for photography or photoelectric conversion elements such as two-dimensional CCD, photomultiplier, photodiode, and CCD) based on the above situation. A primary (raw, primitive) image obtained from a document image (substantial image, subject) that is truly a target for duplication without using the density information value of the medium image already affected by the characteristics. The method of producing various kinds of duplicate images based on the image information value correlated with the light amount has been intensively studied.

As a result, in producing a printed image, (1) Although the density characteristic curve (photographic density characteristic curve) is used, the value of the horizontal axis (log E) is obtained from the value of the vertical axis (D = log ^Io / I) ( Hereinafter, the vertical axis is also referred to as a D axis, and the horizontal axis is also referred to as an X axis.)
In other words, the density information value on the D axis of the color film original (medium image) from the brightest portion to the darkest portion defined on the density characteristic curve is projected on the X axis, and (2) more specific The density information (D _n ) on the D axis of an arbitrary pixel on the medium image is projected on the X axis via the density characteristic curve, and the image information value (X _n ) of the corresponding pixel (X axis is In the photographic density characteristic curve, the logarithmic value of the exposure is shown, but in the present invention, it is equally effective to use the absolute value or the relative value read by the same scaling as the D axis, as described above. Then, this is referred to as “image information value correlated with the amount of light entering the recording medium from the subject” or simply “image information value correlated with the amount of light”).
Then, (3) the halftone dot area is calculated from the _Xn value based on the _Xn value obtained as described above and using the specific <gradation conversion formula> previously proposed by the present inventors. The tone intensity value indicating the% value is obtained,
As a result, it has been found that when the size of a halftone dot is controlled, an excellent printed image having image characteristics faithful to a subject (substantial image) can be obtained.

The gradation conversion theory employed in the ink jet printer of the present invention does not emphasize the density information value obtained from the conventional medium image as described above, but rather applies to a plurality of original target image (substantial image). It is a completely new type that emphasizes the amount of image information (image information value correlated with the amount of light incident on each recording medium from a subject).

Next, a method of deriving the <gradation conversion formula (1)> and characteristics of the present invention will be described.

In a duplicate image formed by an ink-jet printer, the basic components constituting the duplicate image are gradation intensity values at predetermined pixels (this is the number of dots or the number of dots in a pixel on the duplicate image formed as described above). And the surface reflection density of the image forming material (ink).
As can be seen from the fact that human vision has the ability to easily identify, for example, a 1% difference in the size of a dot area in a printed image as a density difference, the image forming means has the same size as the size of the dot area. The related tone intensity values play a very important role. That is, focusing on a given dot, and examining the effects of changes in the amount of ink applied on the dot and changes in the size of the dot on the density gradation, the latter is much larger, How to set the gradation intensity value is a very important issue. A replicated image having excellent reproducibility of density gradation is also excellent in reproducibility of color tone, which can be confirmed in many cases.

In connection with the above, when a duplicate image is to be produced by an ink-jet printer, the quality content of the original image is widely different, and the image forming process also has various characteristics. Furthermore, there is a background that the evaluation standard of the image quality is not uniform, and it is strongly desired that a mechanism for overcoming these complicated and unstable factors is built in the ink jet printer.

For this reason, when converting an original image such as a continuous tone image into a recording image having a halftone by an ink jet printer, the tone intensity value (y _h ) of the pixel block in the brightest portion (H) and the darkest portion The gradation intensity value (y _s ) of the pixel block of (S) can be arbitrarily selected, and the density gradation of the image from the brightest part (H) to the darkest part (S) can be rationally and simply. It is absolutely necessary to provide a means for coordination and management.

The tone adjustment method of the present invention devised based on such a concept, specifically, the tone adjustment method defined by the <tone exchange formula (1)>.

The present inventors rationally convert gradation (conversion of continuous gradation to halftone gradation) when producing a halftone gradation print image from a continuous gradation color film original. A gradation conversion formula similar to the <gradation conversion formula (1)> of the present invention used in the present invention was previously proposed (Japanese Patent Application Laid-Open No. Sho 64-7770, Japanese Patent Application No. 63-11 / 1988).
The operating conditions are completely different from those of the present invention.

A gradation conversion formula for obtaining a numerical value (y) of the dot area percentage used when producing a print image of the above-mentioned halftone gradation (this is the <gradation conversion formula (1) of the present invention as described above). ), Except that the operating conditions are completely different.) Is a generally accepted density formula (photographic density, optical density), Can be derived by applying

Applying this general formula for density D to plate making and printing gives the following:

In the density formula (D ') relating to plate making and printing, it is possible to arbitrarily set halftone dots of a desired size in the H portion and the S portion of the print image, and to select any sample on the continuous tone image. It incorporates a request to rationally associate the basic density value (x) at a point with the numerical value (y) of the dot area percent of the dot at the sample point on the corresponding halftone image, corresponding to the theoretical value. The <gray scale exchange equation (2)> obtained by inducing the measured values to approximately match is represented by the following equation.

<Tone conversion formula (2)> When the <gradation conversion formula (2)> is applied to gradation conversion when producing a print image, the α, y _H , y _S , and γ values can be arbitrarily selected, and any pixel on the original image can be selected. Basal density value (x)
To calculate the numerical value (y) of the halftone dot area percentage of the halftone dot at the corresponding pixel on the print image. As a result, the density gradation of the original image (continuous tone image) can be faithfully reproduced 1: 1 on the print image (halftone image), and the desired image quality (desired density gradation) can be obtained. And images having a color tone) can be produced.

In the case of multicolor plate making (generally, four sets of cyan (C), magenta (M), yellow (Y), and black (BL) are considered to be one set), a reference plate (multicolor plate making) If
As is well known, the cyan plate (C) is the reference plate. ), I.e., a halftone gradation characteristic curve (obtained by graphing the above-mentioned x and y values) serving as a work reference for converting the density information value of the original image into the dot area value of the print image. Is determined, this is a reference for converting the continuous tone to the halftone tone).), The halftone characteristic curves of the other color planes are calculated based on the reference version. Is multiplied by an appropriate adjustment value based on the gray balance ratio of each color of the printing ink, it can always be determined rationally. The halftone gradation characteristic curve of each color plate determined in this way is, of course, each a reasonable characteristic curve, and furthermore, the mutual relationship between the characteristic curves regarding the gradation and color tone is also It is reasonable and appropriate.

That is, when a halftone print image is created from a continuous tone original image, if the tone conversion is performed based on the <tone conversion formula (2)>, conventional experience and intuition are used. It is possible to arbitrarily and rationally convert the gradation of an image, deviating from the gradation conversion method of an image, and to reasonably adjust the color tone which is inseparably related to the gradation. it can. This makes it possible to obtain a printed image having a natural density gradient and color tone according to the human visual interval.

The above description has focused on the production of a halftone printed image, but the theory behind the tone conversion operation using the <tone conversion formula (2)> is the production of a duplicate image by an ink jet printer. Needless to say, it can be diverted to:

However, when producing a duplicate image by using the <gradation conversion formula (2)>, the conversion of the density gradation uses the density information value.

On the other hand, in the gradation conversion suitable for producing a duplicate image by the ink jet printer of the present invention, in order to convert the density gradation more excellent as described above, the original image ( Instead of using the conventional density information value, an image information value correlated with the light amount is adopted as the image information value of the (substantial image). It is needless to say that if the operation conditions of the <gradation conversion formula (2)> are rearranged in order to perform the gradation conversion of the present invention, which is different from the conventional one, the gradation conversion formula (1) will be obtained. That is.

Next, the meaning of each item of the <gradation conversion formula (1)> of the present invention, characteristics of operation, and the like will be described.

In the operation of the <gradation conversion formula (1)> of the present invention,
A basic light amount value (x) must be obtained from a medium image in which a document image is recorded on a predetermined recording medium. As described above, the basic light amount value (x) is obtained through the density characteristic curve of the recording medium on which the document image is recorded, that is, using the density information value (Dn value) of a predetermined pixel of the document image as a clue. Things.

In the present invention, the density information value may be any value as long as it reflects a physical quantity related to the density of each pixel of the document image, and should be interpreted in the broadest sense. Synonyms include reflection density, transmission density, brightness, current / voltage value,
and so on. These density information values may be extracted as density information signals by photoelectrically scanning an original image. In addition,
In the <gradation conversion formula (1)> of the present invention, the basic light amount value (x) is obtained from the image information value correlated with the light amount on the horizontal axis graduated by the same scaling as the vertical axis of the density characteristic curve,
(E.g., as a portrait of a positive color film, in the longitudinal axis is such as having a density value of 0.2 to 2.70, but to adopt the values of the horizontal axis corresponding thereto.) In addition, y _H [brightest portion (Gray scale intensity value set for pixel block (H)] and y _S
A percentage value (for example, a pixel coverage of 5% or 95%) in [Grayscale intensity value set for pixel block of darkest part (S)]. Is used, the y value [the gradation intensity value set for the pixel block on the duplicate image corresponding to the arbitrary pixel block on the original image] is calculated as a percentage value.

In the operation of the <gradation conversion formula (1)> of the present invention,
In addition to being modified as described below, it can be freely used after being processed, deformed, or guided.

_{y = y H + E (1-10} -kH) (y S -y H) However, In the above modification, α = 1. this is,
The surface reflectance of the recording paper (base material) is 100%. The value of α may be practically 1.0 if the zero point adjustment of the density measuring mechanism is performed with reference to the printing paper.

Further, according to the modification (alpha = 1.0), a y _H in the brightest part H of the recording image by the ink jet printer can be set exactly as scheduled to y _S to darkest portion S. This means that x = 0 in the brightest portion H on the recorded image, and x = [document image density area] in the darkest portion S, that is, Therefore, it is apparent from -kX = -γ.

In the operation of the <gradation conversion formula (1)> of the present invention,
The values of α, β, and γ (which define the β value by β = 10− ^γ as described above) take various values. In the present invention, by appropriately selecting these numerical values, it is possible to rationally convert the gradation of an image regardless of the quality characteristics of the original image.

That is, the gradation conversion process of the image based on the <gradation conversion formula (1)> of the present invention is performed by reproducing the gradation and color tone of the original image, that is, by applying the tone of the original image to the recorded image on a 1: 1 basis. Although it is extremely useful for reproducing the above, its usefulness is not limited to this. The <gradation conversion formula (1)> according to the present invention, besides faithfully reproducing the characteristics of the original image, α, β, This is extremely useful for rationally changing or correcting the characteristics of the original image by appropriately selecting the γ value, and further, the y _H and y _S values. Among the parameters of the <gradation conversion formula (1)>, particularly, the γ value plays a large role in adjusting (including correction or change) the characteristics of the original image. It can be easily understood by using 1)>.

When forming a multicolor image using the <gradation conversion formula (1)>, for example, when producing a duplicate image using a color film original, color separation well known in the field of printing and the like, that is, a color original The reflected light from the light is separated into blue (B), green (G), and red (R) to obtain a density information value (D value) for each color, and this is correlated with the light amount to obtain an image information value (X value). ), And further processed by a gradation adjusting mechanism using the <gradation conversion formula (1)>. Based on the processed information value (y value), the recording unit of the inkjet printer is adjusted to form an image. I hope you go. At this time, when the y value relating to the reference color plate (for example, C plate), that is, the gradation characteristic curve of the reference color plate (the y value is calculated and the y value is plotted against the x value, the above-described printing is performed. A tone characteristic curve similar to the halftone dot characteristic curve in the technology is obtained.), And the tone characteristic curves of the other color plates (M plate and Y plate) are set to the y value of the reference color plate. It can be rationally determined by multiplying by an appropriate adjustment value based on the gray balance ratio of each ink, and an image may be formed using these gradation characteristic curves.

Y value for each color plate determined as described above,
That is, since the gradation characteristic curve for each color plate is defined by the <gradation conversion formula (1)>, it is of course a reasonable characteristic curve, and of course, the interrelationship between the characteristic curves relating to gradation and color tone. Is also reasonable and appropriate.

Next, using the density characteristic curve of each recording medium, the density information value (D value) of an arbitrary pixel on the original image is converted to the image information value correlated with the light amount of the corresponding pixel incident on each recording medium. A method for obtaining (X value) will be described.

In the present invention, in order to obtain image information values for gradation conversion, particularly density information values, from an original image, the original image is recorded on various recording media, for example, a photographic photosensitive material, or a two-dimensional image.
The image is recorded on the recording medium according to the present invention, such as a photoelectric conversion element such as a CCD, a photomultiplier, or a photodiode, and becomes a medium image. The density information value (D value) at each pixel of the original image obtained from the medium image is determined by a unique density characteristic curve (density information value read by the recording medium system of the original image and each density information curve) of each recording medium. It is necessary to obtain an image information value (X value) correlated with the light amount of the corresponding pixel via a characteristic curve that defines a relationship with the image information value correlated with the light amount from the document image incident on the medium. For that purpose, the density characteristic curve of each recording medium must be accurately (approximately) approximated (formulated).

Here, a method of formulating a photographic density characteristic curve (hereinafter simply referred to as a density characteristic curve) will be described, taking as an example a case where a color film original (medium image) which is a photographic photosensitive material is used as a recording medium. The mathematical expression of the density characteristic curve of another recording medium may be performed in the same manner. When a color film original (medium image) is used, the object (original image) that is truly the target of duplication may not be a still object or a person (substantial image) such as a still life or a person photographed in the color film original. As described above.

As the photographic density characteristic curve, a color film (Fujichrome, manufactured by Fuji Photo Film Co., Ltd.) shown in FIG. 1 was used. In the following mathematical expression, it is assumed that the gradation characteristic curve for the C-plate, which is a reference among the multicolor plate-making, is set.
The photosensitive characteristic curve (photographic density characteristic curve) of the emulsion layer is shown. Therefore, G, B for other color plates (M plate, Y plate)
It goes without saying that the photosensitive characteristic curve (photographic density characteristic curve) of the emulsion layer can also be used.

The mathematical expression of the photographic density characteristic curve may be obtained by an appropriate method and is not subject to any restrictions.

For example, the vertical axis = D = log ^Io / I, the horizontal axis = X (however, the scale scale of the X axis is made to coincide with the D axis), and a, b, c, d, and f are constants. (A) Toe portion of the density characteristic curve (region where the D value is small at the downward convex shape) D = abc ^{(X + d) + e} + f (b) Substantially linear portion (substantially linear shape) D = a · X + b or D = a · X ² + bX + c (c) Shoulder (region where D value is large at the upward convex shape) D = a · log ｛ The expression may be expressed as b + (X + c)｝ + d.

Table 1 shows the content of the density characteristic curve shown in FIG. Table 1 shows a plurality of formula divisions in order to formulate the density characteristic curve as accurately as possible.

In the present invention, as shown in FIG. 1, a D-axis scale indicating a density value of a color film original (medium image);
The functions of D and X were performed assuming that the scale of the X axis indicating the image information value indicated by logE of the subject (real image) was the same.

This is a kind of relativization (imitation) from the following viewpoints
It is considered by the present inventors to be reasonable.

That is, in the photographic density characteristic curve, the logarithmic value of the exposure amount E (log E = log I × t) is originally positioned on the X axis. In view of the above, the relative ratio (simulation) of making the scaling of the D-axis and the X-axis the same in view of the above points is reasonable. Think. As will be shown in the embodiments described later, excellent results can be obtained in the gradation conversion of an image even under this relative ratio (imitation). In the present invention, it is needless to say that the above-mentioned scale is a kind of simple method and is not limited to this.

The present invention is not to the density information values represented by D axis (D _n value) basis included in each pixel of the subject (actual image) As described above, the image information values correlated to the amount of light represented by X-axis (X _n value). Then, as shown in Table 1, the D _n value and the X _n value are represented by X =
Since f (D) is correlated by the mathematical formula, D _n can be easily obtained.
The _Xn value can be determined from the value.

As described above, the image information value (X _n value) correlated with the amount of light incident on the photosensitive photosensitive material layer from the subject (substantial image)
Can be easily obtained.

Then, the X _n value of each pixel of the thus reasonably obtained document image (medium image) using said <tonal conversion formula (1)>, to obtain the y values corresponding to each pixel Can be.

In the present invention, the X axis (horizontal axis) indicating the _Xn value, y
As described above, when the y value corresponding to the X _n value is plotted on the orthogonal coordinate system on the vertical axis for displaying the value, a gradation characteristic curve is obtained as described above. In order to distinguish the present invention from the prior art, the gradation characteristic curve is referred to as an X-axis color separation curve, and the conventional one that emphasizes the density information value on the D-axis is referred to as a D-axis color separation curve.

The features of the X-axis separation curve obtained by the present invention and the conventional D-axis color separation curve will be described.

The <gradation conversion formula (1)> of the present invention is operated under constant conditions, that is, the α, y _H , y _S , and γ values are each kept constant, and the image quality is different as the original image (that is, each original has a different image quality). When obtaining each X-axis color separation curve (tone characteristic curve) using a duplicate original image having different density ranges and density information values, the obtained respective X-axis color separation curves (tone characteristics) Curve) has a characteristic that all the arrangement states of the y values from the H portion to the S portion of the duplicate image, which is the final product, have relatively the same relationship. This is a very important feature of the present invention.
In other words, as shown in an embodiment described later, even if the range of the image information value (X value) correlated with the light amount on the X axis of each document image is different (this is because the density of the document image is different). If the range is different, it is natural that the X-axis color separation curve (gradation characteristic curve) obtained by the present invention fits into one (only one) when adjusted to the same predetermined X-axis range. That's what it means. Therefore, based on the respective X-axis color separation curves (gradation characteristic curves), for example, from the arrangement state of the halftone dots (when the y values correspond to the halftone area% values), Can be obtained or evaluated correctly in advance without proofing.

On the other hand, in the D-axis color separation curve, curves corresponding to the respective image qualities are obtained. Therefore, it is not possible to accurately determine whether or not the predetermined gradation conversion has been performed unless the respective proofs are printed. In a relationship.

In connection with the above point, due to the nature of the present invention <gradation conversion formula (1)>, by arbitrarily changing the α, y _H , y _S , and γ values (particularly by changing the γ value), That the shape of the gradation characteristic curve can be changed, that is, the operator who manages the gradation conversion operation can adjust (correct, change) the gradation of the duplicated image to any desired one; This is a very important characteristic, and the conversion work of the gradation can be rationally managed based on the X-axis color separation curve.

As described above, the features and characteristics of the image tone adjustment mechanism, which is the central mechanism in the inkjet printer of the present invention, have been described mainly by taking the production of a printed image as an example. There is no substantial difference between the production method and the method of producing a duplicate image using an inkjet printer.

However, in the case of an ink jet printer, the original image is rarely recorded on a photographic photosensitive material (especially a negative type), and a printed original or a photograph (positive) is truly a target of duplication. (Substantial images), and these are recorded or accumulated in a density information reading mechanism (a recording medium system such as a CCD) of a printer system to form a medium image (of course, it may be a transient image). Needless to say, a duplicate image is produced based on the density information value obtained from this.

As this type of recording medium, various types of devices, for example, a two-dimensional CCD, a photomultiplier, a photodiode, a photoelectric conversion element such as a CCD are used, and these recording media are the same as the photographic photosensitive material described above. Similarly, an image is formed (imaged) from a document image using image information values correlated with the amount of light incident on these recording medium systems. Since these recording media have a unique density characteristic curve (photoelectric conversion characteristic curve) as referred to in the present invention, when producing a duplicate image from a medium image recorded on these recording media, As in the case of the film original, the basic light amount value (X) is obtained by using the density characteristic curve (photoelectric conversion characteristic curve), and then the gradation conversion may be performed by <gradation conversion formula (1)>.

On the other hand, in the ink jet printer of the present invention, a color film original (negative type) recorded on a photographic photosensitive material (recording medium according to the present invention) can be used as an object to be copied (copied). In such a case,
When converting the density information value obtained from the density measurement mechanism (for example, a CCD configuration) of the ink jet printer into the image information value correlated to the light amount, whether to use the photoelectric conversion characteristic curve of the CCD or the photographic density characteristic curve Although this poses a problem, an image information value correlated with the light amount may be obtained by any of the methods. However, in the case of monochrome or color film manuscripts,
That is, if an object closer to the subject (substantial image) that is the basis of the medium image recorded on the recording medium, which is a photographic photosensitive material, is used, it is better to use the photographic density characteristic curve. The same applies to the case where a video (TV) image, that is, a paper image, for example, which is displayed on a CRT, is to be copied, is a medium image (in this case, a predetermined image sensor serves as a recording medium). However, this is also the case when trying to produce a copy close to the object to be imaged (substance image) from the medium image.

In the case of producing a duplicate image according to the present invention, if a specific density characteristic curve (photoelectric conversion characteristic curve) possessed by these recording media can be defined as a recording medium such as a photodiode or a CCD constituting the recording medium system described above. An existing recording medium is sufficient, so that a duplicate image having excellent gradation (density gradation and color tone) is produced. That is, efforts have been made to improve the characteristics (photosensitive characteristics and photoelectric conversion characteristics) of various recording media in an attempt to produce high-quality duplicate images. However, when producing duplicate images according to the present invention, it is not always the case. Higher grades and higher performance of various recording media are not required, and existing performance (characteristics) are sufficient. This is based on the gradation conversion method incorporated in the ink jet printer of the present invention, and forms another feature of the present invention.

As described above, when a duplicate image is formed by the inkjet printer of the present invention, hardware or software that performs gradation conversion based on the <gradation conversion formula (1)> is provided in the gradation adjustment mechanism unit. By incorporating the image, it is possible to obtain a recorded image having excellent tone reproduction as well as gradation, or a recorded image in which the image quality of a document image is arbitrarily corrected or changed. At this time, the tone intensity value (y value) obtained by the arithmetic processing of <tone conversion formula (1)> is made to correspond to the density display method (size modulation method, density modulation method) suitable for the output form of the ink jet printer. Needless to say, it is only necessary.

(Examples) Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

The most important feature of the present invention is that the core image gradation conversion is performed under the <gradation conversion formula (1)> in the production of a duplicate image by the ink jet printer. Therefore, first, a setting example of a color separation curve (gradation characteristic curve) that determines the quality of a duplicate image as a final product will be described. Here, the setting example of the X-axis color separation curve of the present invention and the conventional D-axis color separation curve and their differences will be clarified. Next, a description will be given of an ink jet printer having a gradation adjustment mechanism incorporating hardware or software for performing gradation conversion based on the <gradation conversion formula (1)> of the present invention.

Example 1 (Setting of X-axis color separation curve) 1. Density characteristic curve used for experiment The density characteristic curve shown in FIG. 1 (DX Cartesian coordinate system) (Fujichrome, manufactured by Company F) was used. . First
In the figure, the D axis (vertical axis) indicates the density value of the color original image. On the other hand, the X-axis shows the exposure amount (logE = logI × t) in a general density characteristic curve, but here, the numerical value is expressed by the same scaling as the D-axis. The function formula of the special curve for the concentration used was that described in Table 1 (1).

2. Original manuscript images The image quality of color film manuscripts (medium images) is generally standard (appropriate exposure) or non-standard (over / under exposure) depending on the exposure conditions during photography. Different. In order to verify whether the present invention can reasonably respond to these various color film originals, the density range of the color film original (Density
An experiment was performed on a sample having a different range (range = DR) (a sample having a different concentration range on the D axis).

3. Calculation of data for setting the X-axis color separation curve On the D-axis of various color film originals (medium images), using the density characteristic curve of FIG. 1 and the function equation of the density characteristic curve of Table 1 (1). of D _n values were converted to X _n value on the X axis. Next, the _Xn value was converted into a gradation intensity value (y value) by <gradation conversion formula (1)>.

The operation conditions of the <gradation conversion formula (1)> are as follows.

x = X _n −X _Hn y _H = 5%, y _S = 95%, γ = 1.00, β = 10 ^−γ = 0.1, α = 1.00 k = γ / X _Sn −X _Hn , (Table 2 below ( In the case of 1), X _Hn = 0.4781 X _Sn = 2.2300
Becomes Otherwise, see Table 2. The results are shown in Table 2.

In Table 2, 〜 in Table 2 indicates an overexposed (light original), 〜 in Table 2 indicates an exposure close to proper exposure, and 〜 in Table 2 indicates an underexposed (dark original), respectively. .

4. X-axis color separation curve The data in Table 2 are shown in FIGS. 2 and 3. The second
In FIG. 3 to FIG. 3, it should be noted that the vertical axis indicates the y value, but the characteristics of the horizontal axis are different. The horizontal axis in FIG. 2 shows the image information value correlated to the light amount, and the horizontal axis in FIG. 3 shows the color film original. In making the graph, numerical values adjusted as ranges for the same light amount and density (25,000 in the case of this example) were used for the sake of comparison. The value after this adjustment is shown in Table 2 as (D _n →)
D _n ′, (X _n →) X ′. The adjustment from D _n → D _n ′ is performed in the case of Table 2 (1). It may be calculated by: Similarly, X _n → X _n ′ is It may be calculated by:

Figure 2 is a gradation characteristic curve according to the present invention, i.e. X-axis color separation curve indicates (Xn 'and the relationship y as described above), as FIG. 3 was D axis color separation curve (the D _n 'And y, which can be regarded as a conventional example of setting a color separation curve.)

As is apparent from FIGS. 2 and 3, a very surprising fact can be found. In other words, no matter what color film original is used, when the four values of α, y _H , y _S , and γ in the <gradation conversion formula (1)> are the same, FIG. As shown, it is a surprising fact that each X-axis color separation curve is aggregated into one and the same curve, and that the tone of the color reproduction image obtained after the color separation is uniformly displayed. is there. That is, according to the gradation characteristic curve (X-axis color separation curve) setting technique of the present invention, regardless of the quality of a color film original, a duplicate image of the same quality having the same arrangement of y values is obtained. A tone characteristic polarity that can be manufactured is obtained. In addition, an operator who produces a duplicate image by using an inkjet printer can change the X-axis color separation curve obtained as described above by changing the parameters in the <gradation conversion formula (1)>, particularly the γ value. It can be changed to a desired shape. That is, the gradation can be rationally managed so that a desired image quality and tone can be obtained based on the X-axis color separation curve.

On the other hand, in the setting example of the conventional color separation curve shown in FIG. 3, a D-axis color separation curve corresponding to the image quality of each color film original is obtained, and a color print image obtained after the color separation is obtained. It is not possible to know in advance exactly what the tone is. That is, there is a disadvantage that it is impossible to determine whether the image quality and tone of the final product are appropriate unless the proof is actually printed and evaluated under the conventional D-axis color separation curve.

This requires a setup operation in which an appropriate color separation curve must be selected from a large number of color separation curves in a color separation operation by an ink jet printer, and a grouping operation of color documents in a pre-process of the setup operation. Means that.
That is, with the conventional D-axis color separation curve setting technique, it is not possible to efficiently execute and manage the tone conversion work.

Embodiment 2 (Inkjet Printer) FIGS. 4 to 5 show an inkjet printer of the present invention.
Description will be made based on the drawings.

FIG. 4 is a block diagram of the ink jet printer according to the first embodiment of the present invention. As shown in FIG. 4, the ink jet printer of the present invention transmits transmitted light or reflected light of an image by R (red), A detection unit 1 for reading by splitting into G (green) and B (blue), and outputting signals from the detection unit 1 to Y (yellow), M
(Magenta), C (cyan), K (black) color separation unit 2 which converts the color separation signals into color separation signals, and converts the color separation signals into an appropriate A tone conversion unit 3 for processing so that a toned image is produced, and an output unit 4 for ejecting droplets of each color ink from an ink jet head based on an output signal of the tone conversion unit 3. Is done.

Here, the detection unit 1 is a photomultiplier or a solid-state image sensor (CC
D), etc., the transmitted light or reflected light of each part of the original image 5 is detected, and R, G, B, and USM signals as current values are output, and these signals are converted into voltage signals by the A / V conversion unit 6. Convert.

The color separation unit 2 uses the log amplifier 7 to detect R,
G, B, and USM are converted to densities by logarithmically calculating the respective voltage signals, and a basic masking (BM) 8 separates blacking (K) components from the densities, and further separates Y, M, and C components. I do. That is, in the ink jet printer of the present invention, the original image 5 which is the object to be copied (printed matter or the like) is first recorded or accumulated in the image information reading mechanism composed of a photomultiplier or a solid-state imaging device (CCD) in the detection unit 1. Then, the color separation unit 2 obtains a density information value (D _n ) as image information of the copy target. This is determined for each color (Y, M, C) component as described above. Then
The density information value (D _n ) is converted into an image information value (X _n ) correlated with the light amount and further to a basic light amount value (X) by using, for example, a photoelectric conversion characteristic curve of a CCD as a recording medium. . These may be performed under software or hardware (not shown).
A function of obtaining an image information value (X _n ) correlated with the light amount from the density information value (D _n ) is provided by a gradation adjusting unit 11 described below.
It may be incorporated in

FIG. 4 shows a color correction (CC) unit 9 as a configuration of the color separation unit 2. Where R, G,
The Y, M, and C components are controlled for the B, Y, M, and C original colors, and the black component of the original is also converted to the UCR / UCA unit 1.
0 UCR (under color removal) or UCA (under co
lor addition), a ratio expressed by three types of inks of Y, M, and C and a ratio expressed by K (black ink) are determined.

In this way, the Y, M, C, and K components converted into image information values correlated with the light amount are converted into pixel density values (Y, M, C, and K) of each color component in the pixel block ( Gradation intensity value),
That is, ye ', me', ce ', ke' indicating the effective area ratio of each color component
Convert to The tone adjusting unit 11 is <tone conversion formula (1)>
And the <tone conversion equation (1)> is applied to each of Y, M, C, and K, and the aforementioned ye ′, me ′, c
Find e ′, ke ′.

The gradation adjusting unit 11 has an algorithm of <gradation conversion formula (1)> as software, and performs A / V and D / A I / O.
General-purpose computer with F (interface), electric circuit embodied by general-purpose IC with algorithm as logic, electric circuit including ROM holding algorithm operation results, PAL, gate array, custom IC embodied with algorithm as internal logic It can take various forms.

The effective area ratio corresponding to the pixel density value of each color component obtained by the gradation adjusting unit 11 is input to an alert channel selector 12, and the color channel selector 12 outputs ye ', me', c
Outputs e ', ke'. This output is A / D converted by the A / D converter 13.
Converted, dot control (D / C) unit 1 for each color
Entered in 4. Then, based on this input information, a drive voltage corresponding to the amount of each pixel block to be covered with dots, that is, a drive voltage corresponding to the color density, is applied to the inkjet head 4 (4Y, 4M, 4C, 4K). Then, while the respective color inks are sequentially controlled on the recording paper 15, they are sequentially discharged to form a recorded image having excellent gradation.

FIG. 5 is a block diagram of an ink jet printer according to a second embodiment of the present invention. FIG. 5 uses a TV signal as an image information signal of a document image. The TV signal is correlated with the image information value of the object to be copied, and this is already correlated with the light amount as in the first embodiment using the photoelectric conversion characteristic curve of an image sensor such as a CCD for imaging the subject. It is needless to say that the image information value is converted into the image information value.

The Y, M, C, and K component signals of the TV signal are input to an adjustment unit having an algorithm of <gradation conversion formula (1)> therein, and are converted into digital signals by an A / D conversion unit, and a charging signal drive is performed. Input to section 13. The ink droplet 6 is charged by the charging unit 7 based on the input signal. The charge amount corresponds to a pixel density value covered with dots in the pixel block, that is, a color density value. The ink droplet charged to a charge amount corresponding to the color density is deflected by the deflecting unit 8 and reaches the recording paper 10.

In the production of a duplicate image by the inkjet printer of the present invention, the pixel coverage (pixel density value) may be changed by changing the size of a dot such as a halftone dot in a printing technique (dot size modulation), or The arrangement of prescribed dots (dots of a fixed size) as seen in the dither matrix method may be devised (dot density modulation).

〔The invention's effect〕

The present invention has the following excellent effects.

1) Density values of predetermined pixels on an original image such as a continuous tone image and a duplicate image (an image recorded by pixel distribution) which are the most basic items in producing a duplicate image. In determining the correlation with the gradation intensity value of the corresponding pixel in the past, it was based on the experience and intuition of the worker exclusively, or based on a limited number of fixed preliminary materials, an irrational method . On the other hand, in the present invention, even under any precondition, this can be rationally determined based on the <gradation conversion formula (1)>. When converting a document image such as a continuous tone image into a duplicate image based on pixel distribution, the most important elemental technology, gradation management (conversion, correction or change of gradation), is simply determined by the image gradation. Since the present invention is directly related not only to the tone but also to the tone of the image, the present invention makes it possible to rationally manage the tone and the tone. That is, the ink jet printer device adopting the algorithm of the <gradation conversion formula (1)> of the present invention in the gradation adjustment mechanism theoretically and rationally systematizes the gradation conversion work (color separation work). The operation can be simplified, and the effect is extremely large.

2) By adopting the algorithm of <gradation conversion formula (1)> in the gradation adjustment mechanism of the inkjet printer, the printer device can be rationalized and simplified, and the manufacturing cost can be reduced. In addition, operation is simplified,
The clarity makes it possible to significantly reduce the number of reworkings, greatly reduce the consumption of consumable materials, and greatly improve the performance of the ink jet printer. In particular, in the performance of an ink jet printer, there is a great merit that, regardless of the quality of a document image, a recorded image excellent in gradation and color tone can be formed.

3) A gradation adjustment mechanism that adopts the algorithm of <gradation conversion formula (1)> rationally and easily defines the evaluation criteria of the quality of the recorded image by the pixel distribution separately from the image information of the original image. can do. Therefore, it is possible to rationally respond to the diversified needs of customers.

4) By adopting the <gradation conversion formula (1)>, it is possible to effectively provide education and training of technicians required with the advancement of printer equipment through the use of the <gradation conversion formula (1)>. And eliminate unnecessary work in daily work, and secure time for new creative development.

[Brief description of the drawings]

FIG. 1 shows a density characteristic curve of a color film. FIG. 2 shows an X-axis color separation curve (the present invention) set based on the density characteristic curve of FIG. FIG. 3 shows a D-axis color separation curve (conventional example) set based on the density characteristic curve of FIG. FIG. 4 is a block diagram of the ink jet printer according to the first embodiment of the present invention. FIG. 5 is a block diagram of an ink jet printer according to a second embodiment of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 2/205 B41J 2/21 H04N 1/40

Claims (7)

(57) [Claims] 1. A density information value of each pixel of an original image is obtained from a medium image in which the original image is recorded on a predetermined recording medium, the density information value is processed by a gradation adjusting mechanism, and based on the processing signal. In an ink jet printer for forming a duplicate image having one color or multi-color halftone on a recording sheet, the gradation adjusting mechanism includes: (i) a density information value (D _n value) of each pixel of a document image; Converting the original image into an image information value ( _Xn value) correlated with the amount of light incident on the recording medium via the density characteristic curve of the recording medium; and (ii) further converting the image information value correlated with the amount of light ( _Xn value). Xn value),
An ink-jet printer characterized by converting into a tone intensity value (y value) for tone adjustment by the following <tone conversion formula (1)>. <Tone conversion formula (1)> 2. The ink jet printer according to claim 1, wherein the medium image is recorded on a photoelectric conversion element as a recording medium. 3. A method according to claim 1, wherein the characteristic curve of the recording medium is a density information value (D
3. The ink jet printer according to claim 2, which is a photoelectric conversion characteristic curve that defines a relationship between the image information value (X value) and the image information value (X value) correlated to the amount of light incident on the recording medium from the document image. 4. The ink jet printer according to claim 1, wherein the medium image is recorded on a photographic material as a recording medium. 5. A method according to claim 1, wherein the characteristic curve of the recording medium is a density information value (D
5. The ink jet printer according to claim 4, which is a photographic density characteristic curve that defines the relationship between the image information value (X value) and the image information value (X value) correlated to the amount of light incident on the recording medium from the original image. 6. A duplicated image, which is a modulated image of dot size, is formed by changing the recording dot diameter by controlling the amount of liquid ejected from the ink jet head with the gradation intensity value (y value). The inkjet printer according to claim 1, wherein 7. A reproduction image in which a tone density value (y value) is a dot density modulated image by changing a dot density by controlling a dot density formed by a dither matrix. The inkjet printer according to claim 1, wherein