JP2787216B2 - Ink jet printer - Google Patents

Description

DETAILED DESCRIPTION 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 to form a recorded image having excellent gradation reproducibility. Related to an ink jet printer.

More specifically, the present invention relates to various types of original images (continuous tone images such as monochrome or color photographs, video images obtained from television or computer video signals, and the like) which are to be reproduced on recording paper. The same applies to the following. The same applies to the following.) The image information signal obtained from the image conversion signal is converted under a gradation adjustment mechanism using a new gradation conversion formula, and on the recording paper based on the gradation-converted output signal. More particularly, the present invention relates to an ink jet printer capable of forming a recorded image having excellent tone and color tone reproducibility.

(Prior Art) When an image is duplicated on a recording sheet from a document image having a continuous tone like a photograph by using an image forming apparatus such as a copying machine, a method using photosensitive paper as a recording sheet is analog processing of the document. By (exposure), an image having a continuous tone corresponding to the document is formed (silver halide photographic recording). On the other hand, in an ink jet printer 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). In this case, 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. Forming a recorded image in an ink jet printer is similar to the method of converting continuous tone of photoengraving in printing to halftone tone in printing,
An image information signal obtained by photoelectrically scanning a document image having continuous gradation such as a photograph is processed, and an image composed of a distribution of pixels having gradations and color tones corresponding to the document image is processed on the recording paper by the signal. Is to be formed.

However, in the current printer device, satisfactory gradation reproducibility is obtained because the gradation adjustment method of processing an image information signal obtained from an original image for reproduction of gradation is unscientific. There is no present.

As is well known, the density gradation of a recorded image depends on the pixel density display method. In the case of an ink jet printer, there are two methods of displaying the density gradation of a pixel: a method of changing the pixel coverage by the size of a dot (size modulation method), and a method of displaying the pixel coverage by a specified (same size) dot arrangement number. (Density modulation method). However, when an original image is reproduced by an ink jet printer, the density of a predetermined sample point on the original image is compared with the coverage of the corresponding dot on the recorded image by a dot of the pixel, that is, the density gradation of the pixel. No scientific study has been made on what the values (hereinafter simply referred to as (at) pixel density values) should be, and how to obtain such pixel density values.

That is, for a density value of a predetermined sample point on a document image,
Regarding what pixel density value should be correlated to the pixel on the recorded image corresponding to the sample point, no scientific correlation formula has been developed. You have to rely on intuition or decisions based on a limited number of fixed conditions.

For this reason, originals with image quality that the equipment manufacturer did not expect, such as non-standard
In the case of, for example, a color film original with an underexposed underexposure), it is difficult to obtain a desired recorded image excellent in gradation and color tone. Therefore, a recorded image of a desired image quality can be obtained not only from a document having a standard image quality but also from the above-mentioned non-standard document, and the image quality of the document can be arbitrarily changed or corrected (change or correction of gradation or color tone). ) Has not been able to develop a flexible ink jet printer.

This means that the conventional ink jet printer cannot scientifically make the pixel density value correspond to the density value of the predetermined sample point on the original image.

(Problems to be Solved by the Invention) The cause of the above-mentioned problem in the conventional printer device is that when a recording image based on a final pixel distribution is formed from a manuscript image such as a continuous tone image, the first image is formed. And the concept of the image gradation conversion process which plays an important role at the stage. That is, when converting the density value of a predetermined sample point on a document image into the pixel density value of the corresponding pixel on the recorded image, the conventional concept of the tone conversion is changed to “a scientifically reasonable tone. It must be done based on the means of conversion, "he relied exclusively on experience and intuition.

The present inventor pays attention to such a situation, and in order to ultimately rationalize the image forming process and form a recorded image with excellent quality, a rational image gradation conversion technology must be established. We conducted intensive research based on the basic understanding that

(Means for Solving the Problems) In general, according to the present invention, an image information signal obtained from an original image is processed by a gradation adjusting mechanism, and the original image is formed on a recording sheet based on the processed signal. In the ink jet printer for forming a corresponding recorded image, the gradation adjusting mechanism may be configured such that a basic density value (x) of an arbitrary sample point on an original image based on an image information signal obtained from the original image
(Difference between the density value at the sample point and the density value at the brightest portion H on the same image) is added to the image density value (y) at the position corresponding to the sample point of the recorded image to be formed by the following <
The present invention relates to an ink jet printer characterized by performing conversion processing according to relational expression (1)>.

<Relational expression> Hereinafter, the configuration of the present invention will be described in detail.

In a recorded image formed by an ink jet printer, a basic component constituting the recorded image is a density value in a pixel (this is determined by the number and size of dots in a pixel on the recorded image formed as described above). And the surface reflection density of the image forming material (ink). Of these, the human eye perceives, for example, a 1% difference in the size of the dot area in a printed image. As can be seen from the ability to easily discriminate as a density difference, a pixel density value having the same relationship as the size of a dot area plays an extremely important role as an image forming means. That is, focusing on a given dot and examining the effects of the change in the amount of ink applied on the dot and the change in the size of the dot on the gradation, the latter is much larger, How to set the density value is a very important issue.

Further, in connection with the above, when the recording image is to be formed by an ink jet printer, the quality content of the original image is various, the image forming process also has various characteristics, Furthermore, there is a background that the evaluation criteria of the image quality are not uniform, and it is necessary to overcome these complicated and unstable factors.

For this reason, when an original image such as a continuous tone image is converted into a recording image having a halftone by an ink jet printer, the pixel density value (y _H ) of the pixel block of the brightest portion ( _H ) and the darkest portion pixel density value of the pixel block of (S) (y _S) and optionally can be selected, moreover reasonably and easily adjust the tone of the image, from the brightest part (H) to the darkest portion (S) It is imperative that you have access to control.

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

First, the process of deriving <Relational expression (1)> will be described.

The present inventors rationally perform gradation conversion (conversion of continuous gradation to halftone gradation) when creating a halftone print image or the like from a continuous gradation color film original. To this end, a tone conversion equation, which is the predecessor of the above <Relationship equation (1)>, has been previously proposed. (See Japanese Patent Application Nos. 62-148912 and 63-2590).

The tone conversion equation proposed by the present inventors (hereinafter referred to as <relational expression (2)>) is not limited to the creation of a print image, but also includes various types of information such as creation of a recorded image by the ink jet printer according to the invention. Although it can also be used when creating a duplicate image, the description below is limited to creating a print image.

<Relational expression (2)> By comparing <Relational expression (1)> and <Relational expression (2)>,
The meanings of β value and κ value are different, and <Relational expression (2)>
Does not specify a γ value. These differences will be described later, and the derivation process of <Relational expression (2)> will be described to help the understanding of the present invention.

The <relational expression (2)> for calculating the numerical value (y) of the dot area percentage used when creating the print image is a generally accepted density formula (photo density, optical density), that is, Is derived from

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

<Relational expression (2)> makes it possible to arbitrarily set halftone dots of a desired size in the H portion and the S portion of the print image in the density expression (D ') relating to plate making and printing, and The basic density value (x) at an arbitrary sample point on the grayscale image and the numerical value (y) of the halftone dot notation percentage of the halftone dot at the sample point on the halftone grayscale image corresponding to the basic density value (x) It incorporates the requirement for association and guides the theoretical and measured values to approximately match.

When the above <Relational expression (2)> is applied to a gradation conversion method of an image when a print image is created, the reflectance (α) of the printing paper, the surface reflectance (β) of the printing ink, and the print image density Based on the numerical value of the area / original image density area ratio (k), while arbitrarily selecting the halftone dot size (y _H , y _S ) desired to be placed in the H and S parts of the print image, It is operated so as to obtain the numerical value (y) of the dot area percentage of the halftone dot at the corresponding sample point (Y) on the print image from the basic density value (x) of an arbitrary sample point (X) on the image. As a result, the density gradation of the original image (continuous gradation image) can be faithfully reproduced 1: 1 on the print image (halftone gradation image).

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 which is a reference for converting the density information value of the original image into the halftone dot area value of the print image (obtained by graphing the above-mentioned x value and y value). Once the curve has been determined, this is the basis for the work of converting continuous tone to halftone.) Once the working reference characteristic curves for the other color plates have been determined, By multiplying by an appropriate adjustment value based on the gray balance ratio of, it can always be determined rationally. The working reference characteristic curve of each color plate determined in this way is, of course, each a reasonable characteristic curve, and furthermore, the interrelationship between the characteristic curves regarding gradation and color tone is also reasonable. And appropriate.

In other words, when a halftone print image is created from a continuous tone original image, if the tone conversion is performed based on the <Relationship (2)>, an image based on conventional experience and intuition is used. Departing from the gradation conversion method, the gradation of the image can be arbitrarily and rationally converted, and accordingly, the color tone closely related to the gradation can be rationally adjusted. As a result, it is possible to obtain a printed image having a density gradient and a color tone that are natural for human visual perception. The above is the content proposed by the present inventors.

However, subsequent research has revealed that there is a certain limit in the operation of <Relational expression (2)>.

The limitations are as follows: very effective if the original image is of standard quality, but it is of non-standard quality, especially of extremely poor quality (for example, overexposure when taking a photo Or something that is under).

This will be described in terms of the operation of <Relational expression (2)>. In the case of a standard quality (standard original), a yellow ink having a large stimulus value with printing ink is used as a numerator for determining the k value. (A typical density value is 0.9 to 1.0) when performing tone conversion (in the case of multi-color plate making, the C plate is manufactured using this value). Although it is extremely effective, in particular, the above-mentioned non-standard originals of poor quality are not sufficiently satisfied.- When the β value corresponds to a non-standard original, printing ink (as described above, The yellow ink is the standard), and it is not satisfactory even if the surface reflectivity and other values are arbitrarily selected and adopted.

In order to overcome the above-mentioned limitations, it is necessary to make the halftone gradation characteristic curve serving as a work reference for the gradation conversion correspond to not only the standard original but also the non-standard original, and the shape of the curve can be arbitrarily determined with a reasonable ratio. Must be able to be changed to As a result of the study, the present inventors have found that satisfactory results can be obtained when gradation conversion is performed under the following conditions.

K value = γ / (density range value of original image) γ value = any positive or negative numerical value β value: a numerical value obtained by β = 10− ^γ from the γ value defining the above k value.

By operating the above <Relational expression (2)> under the above conditions, a standard and non-standard original is formed into a print image having excellent reproducibility of density gradation and color tone inseparable from the density gradation. be able to.

Although the above description has focused on the creation of a halftone print image, it goes without saying that the theory supporting the tone conversion work described above can be diverted to the creation of a recorded image by an ink jet printer. That is not.

It goes without saying that the gradation conversion formula suitable for creating a recorded image by the ink jet printer is <Relational expression (1)> when the above-described examination results are incorporated and arranged.

Next, the meaning of each item of the <Relational expression (1)> of the present invention,
The characteristics of operation will be explained.

In the operation of <Relational expression (1)> of the present invention, the basic density value (x) must be obtained from the image information signal of the original image. 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, light intensity,
Voltage value, and the like. These density information values may be extracted as density information signals by photoelectrically scanning an original image. In the <relational expression (1)> of the present invention, the basic density value (x) is measured by a numerical value using a densitometer (for example, a person image of a positive color film having a density value of 0.2 to 2.70 is used). ) And y _H [the brightest part (H)
When a pixel value (eg, a numerical value such as 5% or 95%) is used for the pixel density value set for the pixel block of [1] and y _S [pixel density value set for the pixel block of the darkest part (S)], y is obtained. [Pixel density value recorded in pixel block (Y) corresponding to arbitrary sample point (X) on document image] is calculated as a percentage value.

In the operation of the above <Relational expression (1)> of the present invention, not only the following modified use, but also any processing, deformation, induction, etc. may be used freely.

_{y = y H + E (1-10} kx) (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.

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 clear from -k _x = −γ.

In the operation of <Relational expression (1)> of the present invention, α,
The values of 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 method of the image based on the <relational expression (1)> of the present invention reproduces the gradation and color tone of the original image, that is, the tone of the original image is 1: 1 to the recorded image. Although very useful in reproducing, its usefulness is not limited to this. The <relational expression (1)> of the present invention is represented by the following formula:
In addition to faithfully reproducing the characteristics of the original image, α, β, γ
Value, furthermore is extremely useful to modify or change the characteristics of the original image reasonably by selecting y _H, a y _S values as appropriate.

To be more specific, it should be noted that the user (operator) has the following degrees of freedom in the operation of the <Relational expression (1)>.

<Part 1>: <Relational expression (1)> is used for the purpose of forming an image faithful to a document image. That is, <Relational expression (1)> should be used with the primary consideration of obtaining exactly the same visual sensory image when observed with the human eye. In the present invention, such an attitude of the tone adjustment is described by the term “(tone) conversion of (image)”.

<Part 2>: Using <Relational expression (1)> so as to change or modify the original image according to the technical necessity of image formation, artistic request, or needs of the ordering side. That is, the <relational expression (1)> should be used with the primary consideration of obtaining a corrected or changed visual sensory image itself when observed with the human eye. In the present invention, such an attitude of the gradation adjustment is described by the term “(image) gradation (of) correction (or change)”.

When a multicolor image is formed using the above <Relational expression (1)>, for example, when a color original is reproduced by an ink jet printer, color separation known in the field of printing or the like, that is, reflected light from a color original And the like are separated into blue (B), green (G), and red (R) to obtain a density information signal for each color, and this is processed by a gradation adjustment mechanism using the <relational expression (1)>. An image may be formed based on this processing information. At this time, when the y value for 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, A tone characteristic curve similar to the halftone dot characteristic curve is obtained.), And the tone characteristic curves of the other color plates (M plate and Y plate) are expanded to the y value of the reference color plate. Since it can be determined rationally by multiplying an appropriate adjustment value based on the gray balance ratio of the diameter ink, an image may be formed using these gradation characteristic curves.

Y value for each color plate determined as described above,
That is, the gradation characteristic curve for each color plate is expressed by the following relational expression (1).
As a result, not only are the characteristic curves reasonable, but also the mutual relation between the characteristic curves relating to the gradation and the color tone is rational and appropriate.

As described above, when a print image is formed by an ink jet printer, hardware or software for performing tone conversion based on the <relational expression (1)> is incorporated in the tone adjustment mechanism of the inkjet printer. It is possible to obtain a recorded image that is excellent in tone reproduction as well as color tone reproduction, or a recorded image in which the image quality of a document image is arbitrarily modified or changed.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples as long as the gist of the present invention is not exceeded.

As described above, the greatest feature of the present invention is that the gradation adjustment mechanism of the ink-jet printer according to the present invention performs gradation conversion by <Relationship (1)>. Therefore, a mode in which the operation of <Relational expression (1)> is thorough,
In particular, the description will be made from the handling of the γ value.

(Example) (1) A method of determining a γ value adopted in <Relational expression (1)>.

The most significant feature of the present invention is that when a print image is formed by an ink jet printer, a core tone conversion operation in the process of creating the print image is performed under the above <Relationship (1)>. Having.

In this case, it is desirable that the same quality content as that of a recorded image formed from a standard standard document be formed even from a document image whose quality content varies widely, such as light and dark. It is not even.

For this purpose, it is necessary to obtain a gradation characteristic curve that defines the relationship between the x value and the y value that gives the same quality as the recorded image obtained from the standard document, without being affected by the quality of the document image. In the <relational expression (1)> of the present invention, the shape of the gradation characteristic curve can be largely changed because γ
Value.

Hereinafter, a method of determining a γ value that is extremely important in the operation of <Relational expression (1)> will be described. The ink jet printer of the present invention can form a recorded image with excellent tone and color tone reproducibility only by rationally determining the γ value.

Y values (ie, pixel density values) for various γ values
Table 1 shows how the values change. First
In the table, while changing the γ value (adopting γ value = 2.00 to −0.20 as shown in Table 1), the above <Relational expression (1)>
_{The, y H = 3%, y} S = 95%, α = 1.00, β = 10 -γ, k = γ
/ (Density area value of original image) = γ / (2.8-0.2)
The density range of the original image is divided into nine steps. 7) shows the y value.

According to Table 1, when the γ value is changed, individual gradation characteristic curves corresponding to the respective γ values are obtained. Therefore, gradation conversion may be performed by setting an optimum one based on the quality content of the given document image. The results in Table 1
Illustrated in the figure.

Therefore, when a document image having a predetermined quality content is given, the optimal γ to be adopted in <Relationship (1)>
The question is how to determine the value rationally.

To use a monochrome or color film, whose tone and color tone reproduction is considered faithful, as the original image, and establish a method for determining the γ value to be adopted in accordance with the image quality of the original I do. This is because if a method for determining an effective γ value under a monochrome or color film original with high tone reproducibility is established, it will be useful for other original images. .

A detailed analysis of the image quality of the color film used as the original shows that the image quality, such as high-key (photographed with over-exposure) and low-key (photographed with under-exposure), is standard color photographed with standard exposure. Compared to film manuscripts, there are many differences. However, differences in the image quality of the color film original, the exposure amount of the differences seen from the fact that a direct impact on the brightest portion density value H _n of the original,
By paying attention to this point, it can be objectively defined. As the present invention previously proposed, when the standard document (which exposure is performed properly.), The γ value is matched consider taking a value of 0.9 to 1.0, the H _n and γ What is necessary is to find the correlation. The reason why _Hn was selected is that the density region near the brightest part is important in reproducing the gradation. Theoretically, it is needless to say that may choose darkest density value S _n of the original.

Therefore using various color film original, to form an excellent recorded image quality, an experiment was performed to determine the relationship between H _n and γ values. The experimental data are shown in Table 2. In Table 2, Experiment No. 2 was for a standard manuscript, and 0.9 was adopted as the γ value.

From these experiments, the γ value can be rationally determined by the following equation.

(I) When the relationship between γ _n and H _{n in} Table 2 is graphed as shown in FIG. 2 (all logarithmic graph), γ _n is obtained by the following equation.

γ _n = γ _o ± | D _n | tanα (Ii) In addition, the standard manuscript (density range 0.20 to 2.80) is converted to γ _o =
An experiment was conducted in which a recorded image was formed under 1.00, and a recorded image of the same quality was obtained from various color film originals. As a result, the relationship between γ _n and H _n could be defined as follows.

_{(B) γ n = 1.70-2.2961 (logH n} +1) (γ n, H n together relationship obtained when displayed on a logarithmic scale) _{(ii) γ n = 1.70-2.3 (logH n} +1) (γ ₍ Relational expression obtained when _n is displayed on a normal scale and Hn is displayed on a logarithmic scale) From the above, recording with excellent tone reproducibility using an ink jet printer from an original image having various quality contents to duplicate an image, first from H _n values of the original image gamma _n
, And then adopt this as the γ value of <Relational expression (1)> to perform the gradation conversion process.

In the gradation adjustment mechanism of the ink jet printer, <
In order to operate the relational expression (1)> under the γ value determined as described above, a mechanism for measuring the H _{n of} various original images in the ink jet printer device, and calculating the γ value from H _n What is necessary is just to add the mechanism which performs. Alternatively, these measurements and calculations may be left to an operator.

(2) Method for fixing (constantizing) the γ value adopted in <Relational expression (1)> In applying the <Relational expression (1)> of the present invention,
The method of determining the γ value described above is complicated, and a recorded image created by this method is strictly different from a recorded image obtained from a standard original. Because, a matter of course from the fact that the brightest portion density values of the color film original (H _n) is different from that the brightest portion density values of the standard document (H _o).

As described above, in the relational expression (2) useful for gradation conversion of a standard document, a value of γ = 0.9 (or a value between 0.9 and 1.0) is excellent in tone reproducibility as well as gradation. A duplicate image can be formed. Therefore, the relational expression (1)
In the operation of <>, 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. Hereinafter, γ
A method for converting a value into a constant will be described.

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

As is well known, exposure amount of color film photosensitive material (X)
(Note that the sample point X is different from X described above.)
The relationship of the color film density (D) at that time is as shown by the basic density characteristic curve in FIG.

The standard document and the non-standard document depend on whether the exposure amount is appropriate or not. Each density characteristic curve is shown as having a specific range on the basic density characteristic curve. In FIG. 3, the former is shown as a reference density characteristic curve, and the latter is shown as an individual density characteristic curve (note that FIG. 3 shows an underexposed document as a non-standard original). Adjusting the density characteristics of a document to the density characteristics of a standard document can be performed very easily by making the basic density characteristic curve a function.

The basic density characteristic curve described above is defined by a function of D = f _D (X), as shown in Table 3 below (Table 3 also shows an inverse function). It should be noted that the method of functionalizing the basic density characteristic curve in Table 3 should be taken as an example.
A more simplified formula may be used.

In order to match the individual density characteristic curve of the color original with the reference density characteristic curve, the following procedure may be used (see FIG. 3).

(I) H and S density values of a color original image and a basic density characteristic curve (D = f) of a color film photosensitive material of the color original
_D (X)), the individual density characteristic curve of the color original image is defined, and (ii) the density values D _{Hn to} D _Sn of the color original are expressed as X
= F _X (D) to determine the value range of the color original image on the X axis, X _{Hn to} X _Sn , and (iii) the value range on the X axis of the density characteristic curve based on this, X _{Ho to} X _Align with _So.
(Iv) Next, the D axis value range of the reference density characteristic curve, D _{Ho to} D _So
Ask for.

As a matter of course, when the individual density characteristic curve of the color document coincides with the reference density characteristic curve, it is needless to say that the matching between the two is unnecessary. Further, an arbitrary allowable range is defined for the reference density characteristic curve, and when the value is within the allowable range, the image processing can be performed by regarding the same as the reference density characteristic curve.

In the matching procedure of the individual and the reference density characteristic curve described above, it is usual that XR _o (exposure range of the standard original) and XR _n (exposure range of the non-standard original for each color) do not match. , XR _n must be matched to XR _o (see steps (ii) and (iii) above). XR _n to XR _o
Simple matching (an attitude that matches the brightest part density value to the same value and makes the darkest part unmatched) and proportional matching (an attitude that matches both the brightest part density value and the darkest part density value) .)
There is. FIG. 3 shows a case where mathematically proportional matching is performed.

As shown in FIG. 3, the density information value (density information value between D _{Hn and} D _Sn , D _n ) of the individual density characteristic curve is substituted into the basic density characteristic curve D = f _D (X), and XR seek _n, which density information value of a color original with adjustments by X value was adjusted to XR _o (D _Ho ~D density information values between _So, D _o) but not to obtain, XR _n a relational expression for determining the X value was adjusted to XR _o becomes as follows by simple calculation.

(1) Simple For matching _{X = f x (D n)} ± | m | (2) when the proportional matching Where: m: Required translation amount XR _o : Exposure range of reference density characteristic curve of standard original on X axis XR _n : Exposure range of individual density characteristic of non-standard individual original on X axis Color film original As standard quality (D _Ho =
0.20, D _So = 2.80), high key (over exposure) (D _Hn = 0.10, D _Sn = 2.70) and low key (under exposure) (D _Hn = 0.60, D _Sn = 3.20) Table 4 below shows matching data when the individual density characteristic curves are matched with the reference density characteristic curves under the basic density characteristic curves shown in Table 3.

In the above-mentioned matching experiment, the density regions (DR) of the three color film originals used were all 2.60, so that one was based on simple matching and the other was based on proportional matching.

In the density value of D _n and D _o of the Table 4 were determined based on the D _o <relation (1)> by y values (pixel density value,%). The results are shown in Table 5. Also shows the correlation between the y values and D _n value of Table 5 in Figure 4. The curve shown in FIG.
A recorded image with excellent gradation reproducibility can be created from a document image in a non-standard room. 7 is a gradation characteristic curve that defines a correlation between an x value and a y value.

In the gradation adjustment mechanism of the ink jet printer,
In order to fix (use a constant) the γ value of <Relational expression (1)>, an ink jet printer device measures the density of the original image (H and S, and the density of H to S). Measurement), software and hardware must be incorporated to match the original density characteristic curve of the original image with the reference density characteristic curve. This makes it possible to create a recorded image with excellent gradation and color tone from any quality original. Can be.

(3) Ink jet printer apparatus The ink jet printer of the present invention will be described with reference to FIGS.

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

As shown in FIG. 5, the ink jet printer of the present invention converts transmitted light or reflected light of an image into R (red), G
(Green), B (blue), and the detection unit 1 for reading and converting the output signal of the detection unit 1 into Y (yellow), M (magenta), C (cyan), and K (black) color separation signals A color separation unit 2 for performing color separation signals so as to form a proper gradation image using the above-described <Relational expression (1)> of the present invention; It is composed of four blocks, namely, an output unit 4 for ejecting droplets of each color ink from an ink jet head based on an output signal of the unit 3.

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 5 is detected, and R, G, B, and USM signals as current values are output.
The A / V converter 6 converts this signal into a voltage signal.

The color separation unit 2 uses the log amplifier 7 to detect R,
Each of the voltage signals of G, B, and USM is logarithmically calculated and converted into a density. In a basic masking (BM) 8, a black (K) component is separated from the density, and each of Y, M, and C components is further separated. Next, a color correction (CC) unit 9 controls the Y, M, and C components for each of the R, G, B, and Y, M, and C document colors, and furthermore, converts the black component of the document to UCR /
UCA (under color removal) or UCA (un
In der color addition), the ratio expressed by three types of inks of Y, M, and C and the ratio expressed by K (black ink) are determined. After these Y, M, C, and K components are obtained, the tone adjusting unit 11 uses the Y, M, C, and K to obtain a pixel density value in a pixel block of each color component, that is, ye ′ indicating an effective area ratio of each color component. , m
Conversion to e ', ce', ke 'is performed. The tone adjusting unit 11 has the algorithm of <Relationship (1)> inside, applies <Relationship (1)> for each of Y, M, C, and K, and
Find e ', ce', ke '.

The tone adjusting unit 11 has an algorithm of <Relationship (1)> as software and has an A / D, D / A I / F
A general-purpose computer with an (interface), an electric circuit embodied by a general-purpose IC using the algorithm as logic, an electric circuit including a ROM holding the operation results of the algorithm, and the algorithm implemented as internal logic.
It can take various forms such as PAL, gate array, custom IC, and the like.

The effective interview rate corresponding to the pixel density value of each color component obtained by the gradation adjusting unit 11 is input to the color 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. Based on this input information, a drive voltage corresponding to the amount of each pixel block to be covered with dots, that is, a color density, is applied to the ink jet 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. 6 is a block diagram of an ink jet printer according to a second embodiment of the present invention. 6 uses a TV signal as an image information signal of a document image, inputs the signal to an adjustment unit having an algorithm of <Relational expression (1)> therein, and converts the signal into a digital signal by an A / D conversion unit. The signal is converted and input to the charging signal drive unit 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 forming an image using the ink jet 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 by dithering. The arrangement of prescribed dots (dots of a fixed size) as seen in the matrix method may be devised (dot density modulation).

(4) Usefulness of <Relational expression (1)> Next, supplementary explanation will be given on the usefulness of <Relational expression (1)> applied to the gradation adjusting mechanism of the ink jet printer of the present invention.

This is a supplementary explanation for facilitating the understanding of the present invention, and the operation of <Relational expression (1)> applied to the gradation adjusting mechanism of the ink jet printer and the significance of the result will be mainly described in detail.

(A) Operational Experiment of <Relational Expression (1)> As a basic experiment for incorporating <Relational Expression (1)> into the gradation adjustment mechanism, the following two experiments were performed.

a) First of all, the following simple computer is operated by using an ordinary simple computer, that is, Sharp Pythagoras EL509A (manufactured by Sharp Corporation) and applying the desired numerical value to <Relationship (1)> while applying the desired numerical value. 6 tables (1) (2)
(3) The gradation adjustment tables of the images shown in Tables 7 and 8 were prepared.

As a result, the time required for these operations was 3 hours, 2 hours, and 2 hours, respectively, including the inspection time of the calculation results.

b) The following experiment was also performed.

Simple personal computer (PC-9801-M manufactured by NEC)
2) Input desired software separately obtained as function data in step 2), and adjust the basic density value (x) of the original image (continuous tone image) to the corresponding density value (y) of the pixel on the recorded image. Was done.

As a matter of course, the same numerical value as the result of manual calculation using the simple calculator was obtained.

Moreover, in this experiment, there was no need to use special software to create the above software to use the gradation adjustment of the image input to the personal computer, and the creation work was performed using the N88-BASIC attached to the personal computer. It took only one hour to complete.

Further, conversion or correction of the gradation of the target image can also be performed by software capable of directly inputting the measurement values from the highlight (H) to the shadow (S) of the document image by the densitometer instead of the basic density value of the document image. It was confirmed that it could be performed.

Using these software, a desired density interval (for example, 0.00 to 1.00 in 0.05 steps, 1.00
To 0.10 in increments of 0.10), and input that value to the personal computer to obtain the desired pixel density value (y).

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

The pixel density value (y) by the above software is a positive image,
Any of the negative images can be output alone or simultaneously.

(B) Calculation results obtained from <Relational expression (1)> and their usefulness Next, Table 6 (1) (2) (3), Table 7,
The usefulness of Table 8 will be described.

[Table 6 (1), (2), and (3)] Table 6 shows the density of the ink material (the density of the recorded image in the table) when a black and white image is formed from an original image by an image forming apparatus such as an ink jet printer. Area, which corresponds to the γ value of <Relationship (1)>) and when the range of use of the maximum pixel density value changes (0 to 0 in the table).
Three cases are shown: 100%, 0-98%, 0-95%. The table shows how the pixel density value (y) at each sample point must be set in order to obtain an ideal gradation characteristic curve.

Further, from this list, even if the density of the ink material is the same (that is, even if the recording image density area in the leftmost column of Table 1 is the same as the γ value), the use range of the maximum pixel density value is changed. If you change it, how the ideal gradation characteristic curve changes,
You can also see if you need to change it.

In Table 6, the β value that determines the ε value is β = 10 ^−1γ
Is determined. Incidentally, the recorded image density range = γ value = 1.0
In this case, ε = 1 / (1−β) = 1.11111. The values in the same row as the pixel density value (%) are theoretical values when β = 0 (ε = 1.0).

Forming a black-and-white image based on a distribution of pixels corresponding to 1: 1 from an original image such as a continuous-tone image, and acquiring techniques and techniques that can arbitrarily adjust the gradation characteristics of the black-and-white image. Is also the basis of multicolor image formation.

[Table 7] Table 7 shows a case where the density of the ink material changes when a black-and-white image is formed from a document image, similarly to Table 6.
(When the recorded image density range = γ value changes), while using the maximum pixel density value in a range of 0% to 100%, except for the contrast of the entire image, the same image tone and the same image quality as the human visual sense. This is a table listing pixel density values (y) at each sample point necessary to form an image having such image quality.

In other words, the table lists the pixel density values (y) of each sample point on the ideal gradation characteristic curve corresponding to the density value of the ink material to be used when the precondition is ideal.

[Table 8] Table 8 has the same basic conditions as Table 7, but when the use range of the maximum pixel density value (5% to 95%) is used, the ideal gradation characteristic curve Indicates what percentage of the pixel density value (y) should be set at each sample point.

To date, color separation work, such as the creation of print images, has been performed using masking techniques for color correction.
The tone adjustment of the image basically depends solely on human experience and intuition, or on a limited number of fixed preliminary documents. For this reason, it is necessary to make the gradation conversion technology for creating a duplicate image scientific based on the side of the image to be duplicated, such as a print image or a recorded image by a printer.

<Relational expression (1)> of the present invention is to perform gradation conversion at the time of creating a duplicate image by a rational method. Tables 6 to 6 showing the interrelationship between the basic density value of the original image obtained by <Relational expression (1)> and the pixel density value of the formed image.
The data in Table 8 serves as useful basic data for scientifically examining various basic matters in color separation work at the time of image formation.

From each of these tables, pay attention to what essence and principles exist between the original image and the color separation work, and what should be considered in order to rationally match the essence and principles with practice. You can extract what you have to go.

(C) Application of <Relational expression (1)> to correction (or change) of gradation <Relational expression (1)> is used to convert the gradation of an image (that is, from the increase of the continuous gradation original to the fidelity). This is effective not only for conversion (to conversion to a gradation image by a distribution of high pixels) but also for correction (or change) of so-called gradation, which corrects the original image itself. The correction (or change) of the gradation of the image is performed by changing the reduction / enlargement ratio of the recorded image to be formed, the intention of the orderer, the type of the target image in the color original, the purpose of the image to be formed, and the whiteness of the recording paper. In some cases, this must be performed depending on the degree and the density of the image recording material (ink), but in any case, the operation of <Relational expression (1)> can be rationally dealt with, and various colors can be handled. Standardize disassembly work,
Can be standardized.

Further, according to the present invention, correction (or change) of the gradation of an image in a highlight portion or a shadow portion can be similarly performed. As shown in FIG. 1, this is a gradation characteristic curve (curve defining the correlation between the x value and the y value) depending on the γ value employed.
It is clear from the fact that the shape of can be changed arbitrarily. Further, it was confirmed that the color conversion in the highlight portion of the color original was automatically removed without taking a special countermeasure by the gradation conversion according to the <relational expression (1)> of the present invention.

[Effects of the Invention] The present invention has the following excellent effects.

1) Correlation between the density value of a document image such as a continuous tone image and the pixel density value of a recorded image (image recorded by pixel distribution), which is the most basic matter for image formation In the past, the decision was made in an irrational way, based solely on the experience and intuition of the worker or on a limited number of fixed preliminary documents. On the other hand, according to the present invention, even under any precondition, this can be rationally determined under <Relational expression (1)>. When converting a document image such as a continuous tone image into a recorded image based on pixel distribution, the most important requirement of tone management (conversion, correction or change of tone) is simply that of the image. In addition to this, the present invention has a direct and deep relationship with the color tone of an image, so that the present invention makes it possible to rationally manage gradation and color tone. That is, the ink jet printer adopting the algorithm of <Relational expression (1)> of the present invention in the gradation adjustment mechanism systematically and rationally organizes the gradation conversion work (color separation work), and Can be simplified. The effect is extremely large.

2) By adopting the algorithm of <Relational expression (1)> in the gradation adjusting mechanism of the ink jet printer, the printer device can be rationalized and simplified, and the manufacturing cost can be reduced. Also, the operation is simplified and clarified, the number of reworking operations is extremely reduced, the consumption of consumables is greatly reduced, and the performance of the ink jet printer can be greatly improved. In particular, in the performance of an ink jet printer, there is a great merit that a recorded image excellent in gradation and color tone can be formed regardless of the quality of a document image.

3) A gradation adjustment mechanism that adopts the algorithm of <Relational expression (1)> stipulates, rationally and simply, the evaluation criteria for the quality of a recorded image based on pixel distribution separately from image information of a document image. Can be. Therefore, it is possible to rationally respond to the diversified needs of customers.

4) By adopting <Relational expression (1)>, the education of engineers required as the
The training can be effectively performed through the operation of <Relationship (1)>, and unnecessary labor in daily work can be omitted, and time can be secured for new creative development.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a γ value and a change in the shape of a gradation characteristic curve. FIG. 2 is a correlation diagram between γ _n and H _n . FIG. 3 is a diagram for explaining the principle of matching between an individual density characteristic curve of a color film original image and a 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 the ink jet printer according to the first embodiment of the present invention. FIG. 6 is a block diagram of an ink jet printer according to a second embodiment of the present invention.

Claims (3)

(57) [Claims] An ink jet for processing an image information signal obtained from a document image by a gradation adjusting mechanism and forming a recording image having one or multiple halftones on recording paper based on the processing signal. In the printer, the gradation adjusting mechanism may be configured to determine 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 value at the brightest portion on the image). Difference)
Is converted into a pixel density value (y) at a position corresponding to the sample point of a recorded image to be formed by the following <Relational expression (1)>. <Relational expression> 2. The image according to claim 1, wherein the recorded image having a halftone is a dot size modulated image formed by changing the recording dot diameter by controlling the amount of liquid ejected from the ink jet head. Ink jet printer. 3. The ink jet printer according to claim 1, wherein the recorded image having a halftone is a modulated image of a dot density formed by a dither matrix.