JPH0684082B2 - Ink jet printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention converts an image information signal obtained from an original image by a novel gradation adjustment method to form a recorded image having excellent gradation reproducibility. The present invention relates to an ink jet printer.

More specifically, the present invention can be obtained from various original images (including continuous tone images such as monochrome or color photographs, video images, etc., which are all intended to be reproduced on recording paper. The same applies hereinafter). The image information signal is subjected to change processing under a new gradation adjustment mechanism, and an image composed of pixels having color density corresponding to the density of the original image is formed on the recording paper based on the output signal subjected to the gradation conversion. The present invention relates to an ink jet printer that can be used.

(Prior Art) When an image is reproduced on a recording sheet by an image forming apparatus such as a copying machine from an original image having a continuous tone like a photograph, a photosensitive paper is used as the recording sheet but an analog processing (exposure) of the original is performed. ), An image having continuous tone corresponding to the original is formed (silver salt 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, it is difficult to reproduce continuous gradation, and in the case of color image formation, color balance Adjustment is not easy either.

For this reason, efforts are being made to improve the reproducibility of gradation in printer devices. The image formation in the ink jet printer is obtained by photoelectric scanning or the like of an original image having continuous gradation such as a photograph as in the method of converting continuous gradation to halftone gradation in photoengraving in printing. The image information signal is processed, and an image having a distribution of pixels having a color density corresponding to the original image is formed on the recording paper by the signal.

However, in the currently used printer devices, the gradation adjustment method that processes the image information signal obtained from the original image for gradation reproduction is unscientific, so satisfactory gradation reproducibility is obtained. The current situation is that it has not been done.

As is well known, the gradation characteristics depend on the color density display performance of the pixel, and in the case of an ink jet printer, a method of changing the pixel coverage by the size of the dot as a method of displaying the color density of the pixel (size modulation method) And a method (density modulation method) in which the coverage of pixels is changed by the arrangement number of prescribed (same size) dots. However, when the original image is reproduced by an ink jet printer, the coverage of the pixel density of a predetermined sample point on the original image corresponding to the color density value of the original image, that is, the color density of the pixel. Value (hereinafter simply referred to as pixel (in) density value). What should be
Further, how to obtain such a pixel density value and the like have not been particularly examined, and it depends exclusively on the experience and intuition of the operator and the subjective judgment of the device designer. In particular, regarding the characteristics of the pixel density value, which is extremely important in reproducing the gradation, the device manufacturer has experienced in advance.
In consideration of this, the operator uses the data stored in the memory in the printer, which is determined by the material based on the limited number of fixed conditions. Therefore, in the case of non-standard color originals that the device manufacturer did not expect, adjustment is not easy to form a predetermined recorded image, and it is difficult to maintain the image quality level and stabilize the image quality. However, it lacks the flexibility to change or modify the image quality arbitrarily.

(Problems to be Solved by the Invention) The cause of the above-mentioned problems in the conventional printer apparatus is the first cause when an image with a final pixel distribution is formed from a document image such as a continuous tone image. The idea is for the process of gradation conversion of an image that plays an important role in stages. In other words, the conventional way of thinking about gradation conversion was not that "it must be performed based on a scientifically rational gradation conversion means", but that it depended solely on experience and intuition. .

The present inventor pays attention to such a situation, and in order to ultimately rationalize an image forming process and form a recorded image with excellent quality, a rational image gradation conversion technique must be established. Based on the basic recognition that

(Means for Solving the Problem) The present invention will be summarized. The present invention relates to an ink jet printer for forming a recorded image corresponding to a document image on a recording sheet based on an image information signal obtained from the document image. , The image information signal is formed as a basic density value (x) of an arbitrary sample point on 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). The present invention relates to an ink jet printer having a gradation adjusting mechanism that performs processing so as to correlate with a pixel density value (y) at a position corresponding to the sample point in a recorded image, for example, defined by the following relational expression (1). It is a thing.

<Relational expression (1)> However, x: basic density value of an arbitrary sample point X on the original image.

That is, a value obtained by subtracting the density value at the brightest portion H on the image from the density value at an arbitrary sample point X on the image.

y: the pixel density value of the pixel point Y corresponding to the sample point X on the formed recorded image.

y _h : Pixel density value set in the pixel of the brightest part H of the recorded image to be formed.

y _s : Pixel density value set in the pixel of the darkest part S of the recorded image to be formed.

α: reflectance of recording paper.

β: Surface reflectance of ink.

k: Ratio of (density threshold of recorded image to be formed) / (density threshold of original image).

Respectively.

The configuration of the present invention will be described in detail below.

In a recorded image formed by an ink jet printer, a basic constituent element of the recorded image is a density value in a pixel (this depends on the number and size of dots in the pixel on the formed recorded image as described above. The ratio of the coverage is shown) and the surface reflection density of the image forming material (ink). Of these, human vision can easily find a difference of 1% in the size of the dot area in the printed image as a density difference. As can be seen from the fact that it has the ability to discriminate, the image density value, which has the same relationship as the size of the halftone dot area, is extremely important as an image forming means. That is, how to set the pixel density value is very important.

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

Therefore, when converting an original image such as a continuous tone image into an image having a halftone by an ink jet printer, the density value (y _h ) of the pixel block of the brightest portion (H) and the darkest portion (S _h ) are converted. ), The density value (y _s ) of the pixel block can be arbitrarily selected, and the gradation of the image from the brightest part (H) to the darkest part (S) can be adjusted and managed rationally and easily. It is absolutely necessary to have a means to do so.

Based on such an idea, a method of adjusting a gradation applied to the gradation adjusting mechanism of the ink jet printer of the present invention described above is concretely defined by the relational expression (1). This is a gradation adjustment method (hereinafter, also referred to as “main adjustment method”).

The gradation adjusting method of the present invention is based on the numerical values of the reflectance of the recording paper and the surface reflectance of the image forming material (ink), and the pixel density value desired to be placed at H and S of the recorded image to be formed. While arbitrarily selecting, the pixel density value (y) of the pixel block (Y) corresponding to the position formed on the recorded image from the basic density value (x) of the arbitrary sample point (X) on the original image is determined. It is done as it is requested.

In the relational expression (1) of the present invention, there is a numerical value by a densitometer for measuring the basic density value (x) (for example, a person image of a positive color film has a density value of 0.2 to 2.70). ), And y _h [the pixel density value set in the pixel block of the brightest part (H)] and y _s [pixel density value set in the pixel block of the darkest part (S)] are numerical values (for example, If you use 5% or 95%.), Y
The [pixel density value recorded in the pixel block (Y) corresponding to an arbitrary sample point (X) on the original image] is calculated as a percentage value. In operating the relational expression (1), this point may be taken into consideration and modified and used. When measuring the above-mentioned basic density value (x), the density is measured by a color densitometer (transmissive type, reflective type, dedicated type,
Any concentration measuring means such as a common type) may be used.

In the gradation adjusting method of the present invention, the basic density value (x)
Is not limited to the numerical value obtained by the densitometer, and the original image may be photoelectrically scanned to detect an electric signal (current or voltage value) corresponding to the x value, and the y value may be calculated based on the electric signal. Needless to say, it's good. That is, x
Any value may be used as long as it is in some sense correlated with the basic density value of the original image.

The above-mentioned relational expression (1) for obtaining the pixel density value (y) is a generally accepted density formula (photographic density, optical density), that is, D = log I ₀ / I = log 1 / TI ₀ ; Reflected light quantity or transmitted light quantity T = I / I ₀ ; derived from reflection or transmittance.

Applying this general formula for the density D in the case of image formation will be as follows.

Here, A: unit area d _n : area covered by dots or the like at the nth pixel in the unit area α: reflectance of recording paper β: surface reflectance of image forming material (ink)

The present invention uses the density formula (D ') relating to the image formation in addition to the basic density value (x) at an arbitrary sample point on the original image such as the continuous tone image and the pixel block on the recorded image corresponding to the basic density value (x). The relational expression (1) is derived so that the theoretical value and the actually measured value approximately match with each other by incorporating a request for associating with the pixel density value (y).

Therefore, in the gradation adjustment from the original image such as the continuous gradation image to the recorded image by the pixel distribution of the present invention, the gradation adjustment is performed by correlating the basic density value (x) and the pixel density value (y). It covers all things.

It should be understood that the correlation between x and y in the relational expression (1) is an example, and the present invention is not limited to this. That is, appropriate changes can be made without departing from the scope of the present invention.

The feature of the gradation adjustment of the present invention is that, no matter what quality image the original image such as continuous gradation has, the y _h and y _s are expressed as shown in the relational expression (1) Alternatively, it is possible to extremely easily know what kind of gradation characteristic the recorded image due to the distribution of pixels to be created should have, by arbitrarily selecting the values of α and β. .

"This adjustment method" can be used by transforming this,
For example, the values of y _h and y _s , α and β are arbitrarily set appropriately,
In addition, if the original image density area such as a color photographic image having continuous gradation and the density area of the recorded image due to the pixel distribution are different, a well-known gradation compression method is adopted, that is, (recorded image density area) / The k value, which is the ratio value of the (original image density range), may be appropriately selected, and the image adjustment may be performed by the “main adjustment method”.

That is, according to the present invention, the relational expression (1) is used when a recorded image is formed with a pixel distribution based on an image information signal obtained by photoelectrically scanning an original image such as a continuous tone image.
The values of y _h , y _s , k defined by By appropriately changing the value of, the image gradation conversion and gradation correction (or change) can be performed, and the flexibility is extremely high.

To describe this in detail, it should be noted that the user (worker) has the following degrees of freedom when applying the “main adjustment method”.

<Part 1>: Use the relational expression (1) for the purpose of forming an image faithful to the original image, that is, to obtain the same visual sensory image when observed by the human eye. Apply the relational expression (1) with a primary consideration. In the present invention, such a tone adjustment attitude is described by the term "(image) tone conversion".

<Part 2>: Use the relational expression (1) to change or modify the manuscript image from the technical need of image formation, the artistic demand, or the needs of the ordering side. That is, the relational expression (1) is applied, primarily considering that a visually perceptual image itself observed or observed with the human eye is obtained as a corrected or changed image. In the present invention, such an attitude of gradation adjustment is described by the term "correction (or change) of gradation (of image)".

The gradation adjustment work according to the present invention, specifically, the gradation conversion and gradation correction (or change) described above is performed by the relational expression (1).
This can be easily done by appropriately changing the values of y _h , y _s , k, and E.

In that case, it goes without saying that the relational expression (1) or the terms, numerical values, and coefficients contained therein may be appropriately processed, deformed, guided, omitted, etc. as long as they do not impair the rationality in the gradation conversion of the image. Nor.

When forming a multicolor image, for example, when a color original is reproduced by an ink jet printer, color separation well known in the field of printing, that is, reflected light from the color original is blue (B) or clean (G). ), The image information signal is obtained by spectrally splitting into red (R), the image information signal for each color is processed by the gradation adjusting mechanism using the relational expression (1), and an image is formed based on this processing information. You can do it. Alternatively, if the y value of the reference color component (for example, yellow ink), that is, the reference gradation characteristic curve (the y value is calculated and the y value is plotted with respect to the x value, the halftone dot gradation in the printing technology is obtained. A gradation characteristic curve similar to the characteristic curve is obtained), and the gradation characteristic curves of the other color components are appropriately adjusted to the y value of the reference color component based on the gray balance ratio of each ink. Since it can be reasonably determined by multiplying it by a numerical value, it suffices to form an image using these image information.

Y value for each color component determined as described above,
That is, the gradation characteristic curve for each color component is expressed by the relational expression (1).
Of course, it is a rational characteristic curve as defined by
The interrelationship between the characteristic curves relating to gradation and color tone is also rational and appropriate.

Basically, in the method of adjusting the gradation of an image in the gradation adjusting mechanism using the relational expression (1), whether the gradation conversion (or correction, change, etc.) is direct or indirect. According to the method, a continuous gradation image having a linear density gradation characteristic curve is immediately converted into a gradation image based on pixel distribution, and the gradation is first converted in the continuous gradation image, and this gradation conversion is performed. There is a method of converting into a recorded image by pixel distribution through a continuous tone image (here, since the tone conversion has already been performed, the term conversion is used for distinction).
Also, depending on whether or not the density range is compressed in any of the above methods, it corresponds to the method of directly converting the density range of continuous tone into the density range of pixel distribution without compression, and the density range of pixel distribution. There is a method of performing it via the density range compressed original image. In practice, a method suitable for the work environment is selected from the image gradation conversion methods obtained by the combination of these basic methods.

As a typical example, the basic density area of a continuous tone image (original image) having a linear density gradation characteristic curve in FIG. 1 (a) is proportionally compressed to obtain a density area compressed original image, which is then transmitted. FIG. 2B shows an example in which a recorded image is converted according to the pixel distribution.
A gradation image of a continuous gradation image (original image) having a linear density gradation characteristic curve is simultaneously converted, and at the same time, the density region is compressed to obtain a density region-compressed original image, and this image is proportionally An example of converting and creating an image based on the distribution of pixels will be described. In FIGS. 1A and 1B, D ₀ is the density value of the original image which is a continuous tone image.

DR ₀ ... Basic density range of the original image that is a continuous tone image. The density value obtained by subtracting the density value at the brightest point (the extreme point of the highlight portion; H) from the density value at the sample point (X) on the document in DR ₀ becomes the basic density value (x).

D' ₀ ... Density value of a density range compressed document image obtained by proportionally compressing the density range of a document image of continuous tone by the value of k.

DR ' ₀ ... Density range The density range of the compressed original image.

D ″ ₀ ... Density value of a continuous tone image obtained by converting the tone of a continuous tone original image by the “main adjustment method” and compressing the density range.

DR ″ ₀ ... The density range of a continuous tone image in which the original image of continuous tone is converted by the “main adjustment method” and the density range is compressed.

D _p ... Pixel density value of recorded image due to pixel distribution.

DR _p ... The density range of the recorded image due to the distribution of pixels.

P ... Gradation characteristic value based on the quality evaluation standard of the formed recorded image. The value of P is compared with the value of y to assess the consistency of the two.

The brightest point on the H ... original image (highlight portion of the pole) darkest point on the S ... original image points of the middle part of the concentration on the (shadow portion of the pole) M ₁ ... original image (middle density point) M ₂ shows density points at which a pixel density value of 50% is located in the formed recorded image, and the same applies to the following examples and description.

〔Example〕

Hereinafter, the ink jet printer of the present invention will be described in more detail based on examples, but it goes without saying that the present invention is not limited to the following examples unless it exceeds the gist of the present invention.

An embodiment of an ink jet printer of the present invention is shown in the drawings (second
This will be described with reference to FIGS.

FIG. 2 is a block diagram of the ink jet printer of the first embodiment of the present invention.

As shown in FIG. 2, the ink jet printer of the present invention converts transmitted light or reflected light of an image into R (red) and G
(Green), B (blue) spectrally read detector 1, and the output signal of the detector 1 is converted to Y (yellow), M (magenta), C (cyan), K (black) color separation signals. Color separation unit 2, a gradation adjustment unit 3 that processes the color separation signals so that an appropriate gradation image is formed by using the above-described “main adjustment method” of the present invention, and this gradation adjustment unit 3 And an output unit 4 for ejecting droplets of each color ink from the ink jet head based on the output signal of

Here, the detection unit 1 is a photomultiplier or a solid-state image sensor (CCD).
Such as detecting the transmitted light or reflected light of each part of the document 5,
The R, G, B, and USM signals as current values are output, and these signals are converted into voltage signals in the A / V converter 6.

The color separation unit 2 includes the R, G, and
B and USM voltage signals are logarithmically calculated and converted to concentration,
In the basic masking (BM) 8, the black (K) component is separated from this concentration, and further the Y, M and C components are separated. Next, in the color correction (CC) section 9, R,
Controls the Y, M, and C components for each original color of G, B, and Y, M, and C, and the UCR / UCA of the original black component.
UCR (under color removal) or UCA (under co
In lor addition), the ratio represented by three types of inks Y, M, and C and the ratio represented by K (black ink) are determined. After these Y, M, C, and K components are obtained, the tone adjustment unit 11
Pixel density values in the pixel block of each color component from Y, M, C, K, that is, ye ′, me ′, ce ′, k indicating the effective area ratio of each color component
Convert to e '. The gradation adjusting unit 11 has an algorithm of "main adjustment method" inside, applies the "main adjustment method" to each of Y, M, C and K, and obtains ye ', me', ce ', ke' .

The gradation adjustment unit 11 has a "main adjustment method" algorithm as software and a general-purpose computer that has an A / D, D / A I / F (interface), and an electric circuit that implements the algorithm as a logic with a general-purpose IC. Circuit, electric circuit including ROM holding the operation result of algorithm,
It can take various forms such as PAL that embodies the algorithm as an internal lodge, gate array, and custom IC.

The effective surface area ratio corresponding to the color density information 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 sets ye ′, me ′, c
Output e ', ke'. This output is A / D converted by the A / D converter 13.
Converted, dot control (D / C) section for each color 1
Entered in 4. Then, based on this input information, a drive voltage corresponding to the amount to be covered with dots in each pixel block, that is, a drive voltage corresponding to color density, is applied to the ink jet head 4 (4Y, 4M, 4C, 4K). . Then, the respective color inks are sequentially ejected onto the recording point 15 while being sequence-controlled to form a recorded image excellent in gradation.

FIG. 3 is a block diagram of an ink jet printer according to the second embodiment of the present invention. The one shown in FIG. 3 uses a TV signal as the image information signal of the original image, and this is the "main adjustment method"
Is input to the adjusting section having the above, is converted into a digital signal by the A / D converting section, and is input to the charging signal driving section 13. The ink droplet 6 is charged in the charging unit 7 based on this input signal. The charge amount corresponds to a pixel density value covered by dots in the pixel block, that is, a color density value. The ink droplets charged with the amount of electric charge corresponding to the color density are deflected by the deflecting unit 8 and reach the recording paper 10.

In forming an image by the ink jet printer of the present invention, the coverage of pixels (pixel density value) may be changed by the size of dots such as halftone dots in the printing technique (dot size modulation), or by dithering. It is also possible to devise the arrangement of prescribed dots (dots of a certain size) as seen in the matrix method (dot density modulation).

Next, the usefulness of the "main adjustment method" applied to the gradation adjustment mechanism of the ink jet printer of the present invention will be supplementarily described.

This is a supplementary explanation for facilitating the understanding of the present invention. Regarding the “main adjustment method”, which is a main element that establishes the image gradation adjustment mechanism according to the present invention, a working example (a relational expression of the present invention) The operation will be described in detail, focusing on (1) the operation and the significance of the result.

(B) Operation experiment of "main adjustment method" The following two experiments were conducted as a basic experiment for incorporating the "main adjustment method" into the gradation adjustment mechanism.

a) First of all, an ordinary simple calculator, that is, a product name Sharp Pythagoras EL509A (manufactured by Sharp Corporation) is used to operate the simple calculator while applying a desired numerical value to the "main adjustment method". (1) (2) (3), Table 2 and Table 3 were prepared for the gradation adjustment table of the image.

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

b) The following experiment was also conducted.

Simple personal computer (NEC PC-9801-M2)
By inputting the desired software separately obtained as the function data, the basic density value (x) of the original image (continuous tone image) corresponds to the density value of the pixel on the recorded image (the y value of the relational expression (1)). ) Was adjusted.

As a result, naturally, the same numerical value as the result of the manual calculation using the above-mentioned simple calculator was obtained.

Moreover, in this experiment, the N88-BASIC attached to the personal computer was used to create the above software for adjusting the gradation of the image input to the personal computer, without using any special software. However, it only took an hour to complete.

In addition, conversion or correction of the gradation of the target image can be performed by software that can directly input the measured value by the densitometer from the highlight (H) to the shadow (S) of the original image instead of the basic density value of the original image. It was confirmed that can be done.

Using these software, on the original image, the desired density interval (for example, 0.00 to 1.00 in increments of 0.05, 1.00 to
It was possible to obtain the target pixel density value (y) by setting the value up to 3.00 in 0.10 steps and inputting the value to the personal computer.

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

The above-mentioned software pixel density value (y) can be output independently or simultaneously for both a positive image and a negative image.

Next, the usefulness of Tables (1), (2) and (3), Tables 2 and 3 will be described.

[Table 1 (1) (2) (3)] Table 1 shows the use of the density of the ink material (printed image density range) and the maximum pixel density value when a black and white image is created from the original image by the image forming apparatus. When the range changes, it is a list of how the pixel density value (y) at each sample point should be obtained in order to obtain an ideal gradation characteristic curve for gradation conversion. .

In addition, even if the ink density is the same from the list (that is, the recording image density range in the leftmost column of Table 1 is the same), it is ideal when the use range of the maximum pixel density value is changed. It is possible to know how the halftone dot gradation characteristic curve changes, and what must be changed. In Table 1, (1), (2), and (3), the pixel density value in the column of pixel density value (%) is a value when E = 1, (α = 1.0, β = 0), and the others are It is a value at the E value shown in the table.
In this case, the E value was determined using α = 1.0 and β was a value obtained from the ink density (recorded image density area), that is, β = 10 ⁻ (recorded image density area).

It should be noted that it is not possible to create a black-and-white image with a pixel distribution corresponding to 1: 1 from a document image such as a continuous-tone image, and to acquire techniques and methods that can arbitrarily adjust the gradation of the black-and-white image. It is also the basis of multicolor image formation.

[Table 2] Similar to Table 1, Table 2 shows the case where the density of the image forming material (ink) changes when forming a black-and-white image from the original image (that is, the case where the recorded image density range passes). , The pixel density value (y) is used from 0% to 100%, apart from the contrast of the whole pixel, in order to form an image having the same image tone and similar image quality to the human visual sense. It is a list of pixel density values (y) at required sample points.

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

[About Table 3] The basic conditions of Table 3 are the same as those of Table 2, but when the use range of pixel density values (5% to 95%) is used, 9 is a table showing what percentage of pixel density values should be set at sample points.

To date, color separation work such as creating print images is
Color correction by masking technology is of primary importance, and image gradation adjustment work basically depends on human experience and intuition, or a limited number of fixed subject materials. There is. Therefore, it is necessary to scientifically analyze the gradation adjustment of the image by standing on the side of the image to be reproduced such as the printed image or the image recorded by the printer.

The "main adjustment method" is capable of performing gradation adjustment work at the time of image formation by a rational method, and also shows the mutual relationship between the basic density value of the original image and the pixel density value of the formed image. The data shown in Tables 1 to 3 serve as useful basic data for scientifically examining various basic matters in the color separation work during image formation.

From each of these tables, what is the essence or principle that exists between the manuscript image and the color separation work, and what is important in order to reasonably match the essence or principle and practice? You can extract what you have to do.

(B) Application of “main adjustment method” to gradation correction (or change) Next, “main adjustment method” is to convert image gradation (that is, distribution of high-fidelity pixels from a continuous-tone original image). It is also effective not only in the conversion into a gradation image by the above) but also in the correction (or change) of the gradation, that is, the correction of the original image itself. The correction (or change) of the gradation in such an image is performed, for example, when the position (M ₂ ) where the pixel density value is 50% is appropriately moved depending on the size of the reduction / enlargement ratio, especially in the highlight portion or the shadow portion. It is a necessary means for strongly expressing gradation.

For example, when the H and S pixel density values of the formed image are fixed to specific values of 5% and 95%, the change in the reflection density of the image forming material (ink) (based on the yellow ink) or the original The pixel density value (y), which is an extremely important control point in image formation due to the distribution of pixels, is 50% due to changes in the reduction ratio and enlargement ratio of the recorded image formed from the image.
The problem is how to move the set point (M ₂ ) to be corrected and change or change the gradation of the image.

Table 4 shows an example of basic materials useful for solving this type of problem.

It is possible to rationally move the position (M ₂ ) where the pixel density value is 50% by preparing multiple basic data according to the actual work needs. (Or change).

The density range of the recorded image in Table 4 (corresponding to DR _p in FIG. 1) is determined by the solid density of the yellow ink used (and the value of β is also determined based on this), and )
The number inside is The number in the upper left () in each space (frame) in the table is the basic density value (x) at the sample point, and the number in the lower right is the pixel density value (y) corresponding to each basic density value. Show.

However, the usable range of the pixel density value was 5% to 95%.
The calculated values shown in Table 4 are extremely important when managing the position of the pixel density value (y) of 50%.

For example, when creating an image with a reduction / enlargement ratio of 100% from a color original using film made by E company, the recorded image density range is 0.9%.
5. When the ε value is 1.12638, it is assumed that an image having a desired image quality is formed. Next, a gradation characteristic curve for obtaining a recorded image based on the distribution of pixels is created based on the calculated values in Table 4 (that is, the basic density value (x) of the original image is plotted on the horizontal axis and the pixel density is plotted on the vertical axis. A gradation characteristic curve is created by taking the value (y). Next, change the reduction / enlargement ratio for the reference color component, and move the position of the pixel area ratio of 50% to the S side for reduction, and move it to the H side for enlargement to form an image. To do.

The image quality of the test image thus obtained is compared with the image quality of the image (the image of the reference component) in which the desired image quality is obtained. Select a test image that has the same image quality as the image quality of the latter pixel distribution and, for example, reduce it to 1/2. If the density range of the image to be formed is 0.85 and the ε value is enlarged to 1.16449,200%, it is formed. The density range of the image is 1.10 and the ε value is 1.
It is assumed that it is 05958. Then, these gradation characteristic curves are created, and based on the intersection with the straight line where the pixel density value (y) on the curve becomes 50%, sample points of the density value of the original image (in practice, the original image Pixel density value (y) to sample points on the gray scale for work standards
You can know that you can enter 50%. The reason why the pixel density value (y) of 50% is selected as the sample point is that it is convenient for checking the recorded image by the pixel distribution after the color separation work. Therefore, as another method, sample points are selected as points 2/8 and 4/8 of the density range of the original image, and the percentage of the image density value corresponding to them is calculated from the gradation characteristic curve, and based on this, Color separation work may be performed.
By using Table 4 in this way, it is possible to rationally correct (or change) the image at the same time as converting the gradation of the image.

It should be noted that the correction (or change) of the gradation of the image is not limited to the reduction / enlargement ratio of the image formed by one person, the intention of the orderer, the type of the target image in the color original, the purpose of use of the formed image, and the recording. In some cases, the whiteness of the paper and the density of the image recording material (ink) may have to be used. In any case, Table 4 can be used to reasonably support the various color separation work. Standard, can be standardized.

Further, according to the present invention, the gradation of the image of the highlight portion and the shadow portion can be corrected (or changed) in the same manner, and a special measure is taken for the color fog in the highlight portion of the color original. It can be removed automatically without any action.

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

1) Correlation between the density of a document image such as a continuous tone image and the pixel density value of a recorded image (image recorded by pixel distribution) to be formed, which is the most basic item for image formation. Conventionally, the decision was made by the irrational method of exclusively based on the experience and intuition of the operator, or a limited number of fixed-case data. However, this can be replaced by a rational and simple determination method. When converting an original image such as a continuous tone image to a recorded image based on the pixel distribution,
The most important requirement, gradation management (gradation conversion, correction or change), is not limited to image gradation,
Since the color tone of the image is directly deeply related, the gradation and the color tone can be rationally managed by the present invention. In other words, an ink jet printer that adopts the "main adjustment method" in the gradation adjustment mechanism can systematically and reasonably systematize color separation work and gradation conversion work, and simplify the work. The effect is extremely large.

2) By adopting the "main adjustment method" in the gradation adjustment mechanism of the ink jet printer, the printer device can be rationalized and simplified, the manufacturing cost can be reduced, and the operation can be simplified and clarified. , It is possible to significantly reduce the number of rework operations and to greatly reduce the consumption of consumables, and to greatly improve the performance of the ink jet printer.

3) By the gradation adjusting mechanism using the "main adjustment method", the quality evaluation standard of the recorded image based on the pixel distribution can be rationally and simply separated from the image information of the original image. In other words, the "main adjustment method" is capable of scientifically and objectively defining the highlight and shadow of the original image and the density gradation characteristic curve from the shadow to the highlight, and radically streamlining the current printer mechanism. can do.

4) By adopting the "main adjustment method", it is possible to effectively carry out the education and training of technicians that are required with the sophistication of printer equipment, and save unnecessary labor in daily work. It is possible to secure time for creative research and development.

[Brief description of drawings]

FIG. 1 (a) shows an example in which a density image of a document image is converted into a recorded image with a pixel distribution through a document image, and FIG.
FIG. 6 is a diagram showing an example of converting a document image into a recorded image having a pixel distribution via a gradation-converted density region compressed document image. FIG. 2 is a block diagram showing a first embodiment of the ink jet printer of the present invention. FIG. 3 is a block diagram showing the second embodiment.

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Claims (3)

[Claims] 1. An ink jet printer for forming a recording image having a halftone of one color or multiple colors on a recording sheet based on image information of the original image, wherein the ink jet printer converts the image information of the original image to the halftone. As a gradation adjusting mechanism for gradation conversion, the basic density value (x) of an arbitrary sample point on the original image is converted into the pixel density value (y) of the corresponding point on the recorded image by the following <relational expression (1)>. An ink jet printer having a mechanism for gradation conversion. <Relational expression (1)> However, x: basic density value of an arbitrary sample point X on the original image. That is, a value obtained by subtracting the density value at the brightest portion H on the image from the density value at an arbitrary sample point X on the image. y: the pixel density value of the pixel point Y corresponding to the sample point X on the formed recorded image. y _h : Pixel density value set in the pixel of the brightest part H of the recorded image to be formed. y _s : Pixel density value set in the pixel of the darkest part S of the recorded image to be formed. α: reflectance of recording paper. β: Surface reflectance of ink. k: Ratio of (density threshold of recorded image to be formed) / (density threshold of original image). Respectively. 2. The ink 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. Jet printer. 3. The ink jet printer according to claim 1, wherein the recorded image having a halftone is a dot density modulated image formed by a dither matrix.