JPH0614682B2 - Image forming device - Google Patents

Description

TECHNICAL FIELD The present invention performs a conversion process on an image information signal obtained by photoelectrically scanning an original image by a novel gradation conversion method to form a recorded image having excellent gradation reproducibility. The present invention relates to an image forming apparatus that can be formed.

More specifically, the present invention includes images obtained from various original images (including continuous tone images of monochrome or color photographs, video images, and the like to be reproduced on a recording sheet; the same applies hereinafter). The present invention relates to a method and apparatus for performing conversion processing by a novel gradation conversion method and forming a recorded image having a pixel distribution corresponding to the color density of an original on a recording sheet based on the gradation-converted output signal. .

(Prior Art) When an image is formed 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, an analog processing (exposure) of an original is performed using photosensitive paper as the recording sheet. ), An image having continuous tone corresponding to the original is formed (silver salt photographic recording). On the other hand, with an electrophotographic copying machine 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 continuous gradation. Adjusting the balance is not easy.

Therefore, recently, much effort has been made to improve the reproducibility of gradation in the image forming apparatus.

Image formation in this type of image forming apparatus is performed by photoelectric scanning of an original image having continuous tones such as photographs as in the method of converting continuous tones to halftone dots in photoengraving in printing. The image information signal thus obtained is processed, and the signal is used to form an image on the recording sheet with a distribution of pixels having color density corresponding to the original image.

However, in such an image forming apparatus currently used, when the gradation characteristics of the original image are reflected in the recorded image based on the final pixel distribution, what kind of characteristics should the pixel distribution have? No particular consideration has been given to how to obtain such a pixel distribution, etc., and it is entirely dependent on the experience and intuition of the operator and the subjective judgment of the device designer. In particular, in order to faithfully reproduce the gradation, the device manufacturer decides the density characteristics of the pixel, which is extremely important, based on experience, intuition, and materials based on a limited number of fixed conditions, and stores it in the memory of the image forming apparatus. The data is used by the operator. Therefore, in the case of non-standard color originals that the device manufacturer did not expect, adjustment is not easy to form a desired 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-described problems in the conventional image forming apparatus is the first step in forming an image with a final pixel distribution from a document image such as a continuous tone image. In addition, the idea is for the process of gradation conversion of an image that plays an important role. 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 Problems) When the present invention is outlined, the present invention provides a recorded image based on a distribution of pixels corresponding to a document on a recording sheet based on an image information signal obtained from a document image by photoelectric scanning or the like. In the image forming apparatus for forming the image information signal, the basic density value of any sample point on the original image (x) (the density value at the sample point and the density value at the brightest part on the image and Difference) and the ratio (y) of the number of recorded unit pixels to the number of unit pixels forming the pixel block corresponding to the sample point in the formed recorded image are correlated, for example, the following relational expression The present invention relates to an image forming apparatus having a gradation adjusting mechanism that performs processing as defined in (1).

<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 same image from the density value at any sample point X on the original image.

y: The ratio of the number of pixels of the unit pixel to be recorded to the number of unit pixels forming the pixel block for the sample point X on the formed recorded image.

y _h : a ratio of the number of unit pixels to be recorded to the number of unit pixels forming the pixel block, which is set for the pixel block of the brightest portion H of the recorded image to be formed.

y _s : a ratio of the number of unit pixels to be recorded to the number of unit pixels forming the pixel block, which is set for the pixel block of the darkest portion S of the recorded image to be formed.

α: reflectance of the recording sheet.

β: Surface reflectance of recording material.

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

Respectively.

Hereinafter, the constitution of the present invention will be described in detail.

In photoengraving, the density of an image having continuous tone is expressed by the size of halftone dot processing, but in the electrophotographic image forming apparatus by digital image processing, it is necessary to form a latent image on the photoconductor. In addition, it is very difficult to change the diameter of the beam and express multi-step gradation by scanning with a laser beam or the like. Therefore, with the diameter of the beam kept constant, in a pixel block which is a matrix-shaped aggregate of pixels as a minimum unit formed by the beam, the number of unit pixels constituting the pixel block and the image are recorded (ie, The size of halftone dots is often adjusted by changing the ratio of the number of unit pixels (recorded with toner or the like). Of course, in the digital image processing technology, in addition to the gradation expression method (dot density modulation method) that changes the number and arrangement of dots (having a prescribed size) as described above, a method of changing the dot size ( There is also a dot size modulation method). Here, the former will be described as an example.

By the way, what is considered as a basic component for expressing an image is the distribution of this pixel (the ratio of the number of recorded pixels to the unit pixel that constitutes a predetermined pixel block and the color density in the distribution form). And the surface reflection density of the image recording material (toner, etc.), of which human vision is, for example, 1% of the size of the halftone dot area in the printed image.
As can be seen from the ability to easily discriminate differences in density as density differences, how to set the pixel density value represented by the distribution of pixels that has the same relationship as the size of the halftone dot area as an image forming means. It turns out that what to do is very important.

Further, in connection with the above, when a recorded image is to be formed by the image forming apparatus, the quality contents of the original image are varied, and the image forming process has various characteristics. In addition, there is a background such as uneven image quality evaluation, and these complicated and unstable factors must be overcome.

Therefore, when converting an original image such as a continuous tone image into a recorded image with a pixel distribution, the density ratio (y _h ) And the density ratio (y _s ) of the pixel block of the darkest part (S) can be arbitrarily selected, and the gradation of the image from the brightest part (H) to the darkest part (S) can be rationalized and It is absolutely necessary to provide a hand that can be easily adjusted and managed.

Based on such an idea, it was devised that the gradation adjusting method applied to the gradation adjusting mechanism of the image forming apparatus of the present invention is specifically 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 sheet and the surface reflectance of the image recording material (toner or the like), and the pixel blocks desired to be placed at H and S of the recorded image to be formed. Arbitrary sample points on the original image while arbitrarily selecting the ratio of the number of pixels to be recorded (y _h and y _s )
This is performed by obtaining the ratio (y) of the number of recorded pixels in the corresponding pixel block (Y) formed on the recorded image from the basic density value (x) of (X).

In the relational expression (1) of the present invention, the basic concentration value (x)
Numerical by the densitometer measurements (e.g., as a portrait of a positive color film, there. And those with a density value of 0.2 to 2.70) Set the, also in the pixel block of y _h [brightest part (H) If a percentage value (for example, a value of 5% or 95%) is used for y _s [the pixel density value set in the pixel block of the darkest part (S)] and y _s , y [on the original image The pixel density value recorded in the pixel block (Y) corresponding to an arbitrary sample point (X)] is calculated as a percentage value. The relational expression (1) may be modified and used as long as this point is taken into consideration. When measuring the above-mentioned basic density value (x), the density is generally measured by a color densitometer (transmissive type, reflective type, dedicated type, shared type, etc.).
Any concentration measuring means 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
The value may be any value as long as it correlates with the basic density value of the original image in some sense.

The relational expression (1) for obtaining the ratio (y) of the number of pixels described above is a generally accepted density formula (photographic density, optical density), that is, D = logI _o / I = log1 / T I _o ; Reflected light quantity or transmitted light quantity T = I / I _o ; derived from reflectance or transmittance. Applying this general formula for the density D in the case of image formation will be as follows.

Where A: unit area d _n ; sum of the area of recorded pixels to the number of unit pixels in the nth pixel block in the unit area α; reflectance of recording sheet β; pixel forming material (toner or the like) ) Is the surface reflectance.

The present invention relates to the density formula (D ') relating to the image formation, and the basic density value (x) at an arbitrary sampling point on the original image such as the continuous tone image described above and the image distribution corresponding to the basic density value (x) on the recorded image. The relational expression (1) is derived so that the logical value and the actual measurement value approximately match with each other by incorporating a request for associating with the ratio (y) of the number of recorded pixels in the pixel block.

Therefore, the gradation adjustment from the original image such as the continuous tone image of the present invention to the recorded image by the distribution of the pixels is performed by correlating the basic density value (x) with the ratio (y) of the number of recorded pixels. It covers everything that adjusts gradation.

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 a continuous gradation image has, for example, y _h and y _s are expressed by the relational expression (1), Or α and β
That is, it is possible to very easily know what kind of gradation characteristic the recorded image due to the distribution of pixels to be created should have, while arbitrarily selecting the values of and.

"This adjustment method" can be used by transforming this,
For example, the values of y _h and y _s , α and β are arbitrarily selected 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, in the present invention, when forming a recorded image with a pixel distribution based on an image information signal obtained by photoelectrically scanning an original image such as a continuous tone image, the above relational expression
The values of y _h , y _s , k defined in (1), By appropriately changing the value of, the gradation conversion and gradation correction (or change) of the image can be performed, which is extremely flexible.

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

<Part 1> Utilizing relational expression (1) for the purpose of forming an image faithful to the original image, that is, obtaining the same visual sensory image when observed by the human eye. Apply the relational expression (1) by thinking in a meaningful way. In the present invention, such a tone adjustment attitude is described by the term "(image) tone conversion".

<Part 2> From the technical need for image formation, the relational expression (1) is
Use it to change or modify the manuscript image due to artistic requirements or the needs of the ordering party. That is, the primary idea is to obtain a modified or altered visual sensory image itself when observed with the human eye.
Apply relation (1). Such a tone adjustment attitude is described in the present invention by the term “(image) tone correction (or change)”.

For the gradation adjustment work according to the present invention, specifically, the gradation conversion and gradation correction (or change) described above, the values of y _h , y _s , k, and E in the relational expression (1) are appropriately changed. Can be performed more easily.

At that time, it goes without saying that the relational expression (1) or the terms, numerical values, and coefficients included 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. None, the purpose, means of using the "this adjustment method",
The method is not subject to any restrictions.

When forming a multicolor image, for example, when copying a color original, color separation well known in the field of printing, that is, reflected light from the color original is blue (B) or green.
(G), obtain the image information signal by spectrally splitting into red (R), process the image information signal for each color by the gradation adjusting mechanism using the relational expression (1), and image based on this processing information. Should be formed. Alternatively, the y value of the reference color component (for example, yellow toner), that is, the reference gradation characteristic curve (y
Calculate the value and plot the y value against the x value,
A tone characteristic curve similar to the halftone characteristic curve in the printing technique is obtained. ), And the gradation characteristic curves of the other color components can be rationally determined by multiplying the y value of the reference color component by an appropriate adjustment value based on the gray balance ratio of each ink. Therefore, 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 not only a rational characteristic curve because it is defined by the relational expression (1), but also the mutual relationship between the characteristic curves regarding gradation and color tone is rational and It is appropriate.

In the image forming apparatus of the present invention, the gradation adjustment mechanism modulates the exposure scanning beam by the "main adjustment method", and performs arithmetic processing according to a predetermined pixel distribution pattern to sequentially form pixels. It is one that goes on.

In the case of the column (a) of FIG. 1, the distribution of the recorded pixels is in a positional relationship in which they are mutually dispersed within the pixel block as the number of recorded pixels increases. It may be possible to sequentially expand outward in a spiral shape, and in that case, it is similar to the halftone dot in photolithography. Further, in the column (b), one halftone dot having an area corresponding to the number of pixels in the column (a) is shown.

Although the pixel block has been described as a 4 × 4 matrix type here, 17 gradations are expressed by this. Generally, n ² + in an n × n matrix type pixel block
One level gradation (0 to 100%) is expressed.

Such a method of expressing the density of a document image such as a continuous tone image by the distribution of pixels formed in a matrix type pixel block is generally called a dither matrix method. Sho 58-85434, same
58-114569, 59-52969, 60-141585, 62-186
No. 663 etc.

In addition, a continuous tone image having a linear density tone characteristic curve is immediately output depending on whether conversion (or correction, change, etc.) is direct or indirect in the image tone adjustment method. A method of converting to a gradation image according to a pixel distribution, and a gradation conversion is first performed in a continuous gradation image, and a gradation image according to a pixel distribution is converted via the gradation-converted continuous gradation image ( Since the gradation conversion has already been performed, the term "conversion" is used here to distinguish). Further, in any of the above-described methods, the method of directly converting the density range of continuous gradation into the density range of the pixel distribution without compression depending on whether the density range is compressed, and the density range of the pixel distribution are supported. There is a method of performing it through a density range compressed original image.
In practice, the one suitable for the work environment is selected from the image gradation conversion methods obtained by the combination of these basic methods.

As a representative example, the basic density area of a continuous tone image (original image) having a linear density gradation characteristic curve in FIG. 2 (a) is proportionally compressed to obtain a density area compressed original image, which is then transmitted through this. In the example of converting to an image based on the pixel distribution, the continuous tone image (original image) having a linear density gradation characteristic curve is converted into gradation in the same figure (b), and at the same time the density range is compressed to adjust the gradation. An example is shown in which an already-compressed original image of the density range is obtained, and this image is converted proportionally to create an image based on the pixel distribution. Fig. 2
In (a) and (b), D _o is the density value of the original image which is a continuous tone image.

DR _o ... Basic density range of the original image which 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 within this DR _o becomes the basic density value (x).

D' _o ... Density value of a density range compressed original image obtained by proportionally compressing the density range from the value of k for a continuous tone original image.

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

D ″ _o ... Density value of continuous tone image obtained by subjecting a continuous-tone original image to tone conversion by the “main adjustment method” and compressing the density range.

DR ″ _o …… “Main adjustment method” for continuous-tone original images
The density range of a continuous-tone image in which the gradation is converted by and the density range is compressed.

D _p : Pixel area ratio of recorded image due to pixel distribution.

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

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.

H: Brightest point on document image (highest point of highlight part) S: Darkest part of original image (highest point of shadow part) M ₁ ... Point at intermediate density of the original image (intermediate density) Point) M ₂ ... In the recorded image by the distribution of the formed pixels, the positions of the pixel blocks each having a pixel area of 50% are shown, and the same applies to the following examples and description.

(Example) Hereinafter, the image forming apparatus of the present invention will be described in more detail based on examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

FIG. 3 is a block diagram of the image forming apparatus according to the first embodiment of the present invention.

As shown in FIG. 3, the image forming apparatus according to the present invention includes a detection unit 1 for spectrally reading transmitted light or reflected light of an original image into R (red), G (green), and B (blue).
A color separation unit 2 that converts the output signal of the detection unit 1 into Y (yellow), M (magenta), C (cyan), and K (black) color separation signals, and an appropriate pixel using the "main adjustment method". And an output unit 4 for exposing the electrophotographic photosensitive member with a laser beam based on the output signal of the gradation adjusting unit 3 to form an image gradation on the photosensitive member. The latent image thus formed is developed in the developing unit to form a toner image, which is transferred to the recording sheet and fixed in the fixing unit.

An independent photoconductor and a developing unit are provided for each component color for forming a color image, and the toner images formed are transferred sequentially to a recording sheet, or a latent image of the component color is formed on one photoconductor. Then, the toner image is developed and transferred to a recording sheet, and this process is repeated for each color component.

The detection unit 1 detects transmitted light or reflected light of each part of the document 5 by a photoelectric conversion element such as a photomultiplier or a solid-state image sensor (CCD) and outputs R, G, B, USM signals as currents, and outputs the signals. Is converted into a voltage signal in the A / V converter 6.

The color separation unit 2 includes the R, G, and
The voltage signals of B and USM are converted into density by logarithmic calculation, the black (K) component is separated from this density in the basic masking (Bm) 8, and Y, M and C are further separated.
Separate each component of. Next, color correction (CC) section 9
At Y for each color of R, G, B and Y, M, C
Components, M component and C component are controlled, and the black component of the original is controlled by UCR (under control remove) of UCR / UCA section 10.
el) or UCA (under control addition), the ratio expressed by the three components of Y, M, and C is determined. After these Y, M, C, and K components have been obtained, conventionally the gradation conversion unit (I
The area ratios ye ', me', ce ', ke' occupied by the pixels of each component in the gradation control unit in (MC) were obtained and inverse log transformed, but in this embodiment, the gradation control unit and the inverse log are transformed. The adjusting unit 11 is used in place of the converting unit, where Y, M, C, K to y
Converting to e ', me', ce ', ke'. Adjustment unit 1
1 has an algorithm for "this adjustment method" internally, Y,
Applying "this adjustment method" for each of M, C, K,
Find ye ′, me ′, ce ′, ke ′.

The adjustment unit 11 has an algorithm of "this adjustment method" as software and has an I / F for A / D and D / A.
General-purpose computer having (interface), electric circuit embodying algorithm as general logic by general-purpose IC, electric circuit including ROM holding operation result of algorithm, PAL embodying algorithm as internal logic, gate array, custom IC It can take various forms such as. In order to form an image corresponding to the density of the original image by the laser beam, the diameter and intensity of the laser beam are made constant as described above, and it is formed in the image block as corresponding to the area of the halftone dot in photoengraving. The number of unit pixels and the distribution thereof are calculated and the data is output.

The pixel area ratio obtained by the adjusting unit 11 is input to the color channel selector 12, and the color channel selector 12 selectively outputs ye ', me', ce ', and ke' in the previous and next. This output is A / D converted by the A / D converter 13 and input to the output unit 4. In the output unit 4, the gradation adjustment unit 3
The dot control unit 14 controls the laser beam based on the output of the.

FIG. 4 shows the second embodiment, in which the conventional inverse log converter 15 is used as it is, and therefore the adjusting unit 11 outputs ye ', me', ce ', ke' in logarithmic form. It As a result, the "main adjustment method" can be applied only by converting one component in the conventional device, and the existing system can be remodeled into the system by the present method with fewer changes than those in the first embodiment.

FIG. 5 shows a third embodiment, in which the conventional gradation control (IMC) unit 16 is left as it is and
The connection between the log conversion unit 15 and this gradation control unit 16 is cut off. An adjusting unit similar to that of the second embodiment, that is, an adjusting unit 11 for outputting ye ', me', ce ', ke' in logarithmic form is adopted. The adjusting unit 11 takes Y, M, C, and K signals from the stage preceding the gradation control unit 16 and outputs the converted values to the inverse log converting unit 15.

FIG. 6 shows the fourth embodiment, and the inverse log converter 15
And the color channel selector 12 is left as it is, and the connection between them is cut off. That is, the adjusting unit 11 takes Y, M, C, K signals from the previous stage of the gradation control unit 16 and directly connects them to the color channel secreter 12.
ye ', me', ce ', ke' are not constrained by the conventional system, and ye ', me', ce ', ke' can be processed in an optimum processing mode similar to that in the adjusting unit of the first embodiment. Can be asked. As with the third embodiment, the system can be embodied by a slight modification of the conventional system.

FIG. 7 shows a fifth embodiment, in which the entire conventional gradation converting unit is configured as a new adjusting unit 11, and the “main adjusting method” can be applied to this adjusting unit.

In the example of FIGS. 3 to 7, the image forming section is an electrophotographic type in which an electrostatic latent image is formed on a photoconductive photoconductor by scanning a laser beam, but a recorded image is formed by the distribution of pixels. As the method, other methods such as an electrostatic recording type and a magnetic recording type can be adopted.

In the case of electrostatic recording, as shown in FIG. 8, each electrode of a recording head in which a large number of electrodes are arranged close to or connected to a recording body made of a moving sheet-shaped derivative and arranged in a direction perpendicular to the moving direction. A voltage is applied to form an electrostatic latent image. The process after the step of adding toner to this latent image and developing is the same as in the case of the electrophotographic system. A voltage as an output signal corresponding to an image to be recorded from the dot control section 14 of the output section 4 is applied to the recording head as an assembly of electrodes. In the magnetic recording type, for example, a drum body whose surface is uniformly covered with a magnetic body is used as a recording body, and the magnetic recording head is in contact with the surface while applying a voltage as an image information signal. And the surface of the recording medium are relatively moved to form a magnetic latent image on the surface of the recording medium. To develop this latent image, the use of a toner made of a magnetic material is carried out in the same manner as in the case of the electrophotographic system, except for that.

By modifying the tone adjustment section of conventional equipment as described above,
It is possible to combine the “main adjustment method” with other processing, and it is possible to realize high speed and compactness by optimizing the system and to improve cost performance per system.

In the above embodiment, the color separation unit has the same structure as the conventional one, but by using the “main adjustment method”, the color correction (CC) unit 9 and the USR / UCA unit 10 can be used if they are not necessary. The omitted color separation unit may be adopted.

In addition, the description of the portions relating to the effects that are generally used, such as the blur mask and the sharpness effect that are not directly related to the present invention, is omitted in the above embodiments.

Next, the usefulness of the “main adjustment method” applied to the gradation adjustment mechanism of the image forming apparatus of the present invention will be supplementarily described.

This is a supplementary explanation for facilitating understanding of the present invention, and a working example (relationship of the present invention) regarding the "main adjustment method" which is a main element for establishing the image gradation adjustment mechanism according to the present invention. The operation will be described in detail mainly with respect to the operation of Expression (1) and the meaning of the result).

(A) 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 of an advanced image forming apparatus.

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 the required numerical values 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 (PC-9801 manufactured by NEC)
-M2) Input the required software separately as function data, and record the basic density value (x) of the original image (continuous tone image) in the pixel block on the recorded image according to the pixel distribution corresponding to it. The work of adjusting to the ratio of the number of pixels (hereinafter referred to as the area ratio of recorded pixels) (y) was performed.

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 created without using any special software to create the above software for adjusting the gradation of the image to be input to the personal computer. When I went, it only took an hour to complete.

Also, software that can directly input the measured values from the densitometer ranging from highlight (H) to shadow (S) of the original image instead of the basic density value of the original image can be used to convert or correct the gradation of the target 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 3.
The target pixel area ratio (y) could be obtained by providing the value up to 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 area ratio (y) of the recorded pixels corresponding to them.

The area ratio (y) of the pixels recorded by the software described above can be output independently or simultaneously for both positive and negative images.

Next, the usefulness of Tables (1), (2) and (3), Tables 2 and 3 will be described. (Note that in each table, the y value is the pixel density value.) [Table 1 (1) (2) (3)] Table 1 shows the case where a monochrome image is formed from an original image by an image forming apparatus. Density of image recording material such as toner (recorded image density range) and usage range of area ratio of recorded pixels (y
The value is set to _h and a y _s. In Table 1, 0-100
%, 0-98%, and 0-95%. Is a list of how the area ratio (y) of recorded pixels at each sample point should be obtained in order to obtain an ideal gradation characteristic curve.

Also, from this list, how should the ideal halftone dot gradation characteristic curve change when the usage range of the area ratio of recorded pixels is changed, even if the density of toner is the same, and it must be changed. You can know if you have to. Table 1
In (1), (2), and (3), the pixel density value (%) (in the table, the area ratio (y) of the pixels to be recorded is displayed as the pixel density value) is E = 1. , (Α = 1.0, β
= 0), and the others are values at the E value shown in the table. In this case, the E value is α = 1.0, β
Was determined using the value obtained from the toner density (recorded image density area), that is, β = 10 ⁻ (recorded image density area).

It should be noted that it is not possible to form a black and white image with a pixel distribution corresponding to 1: 1 from an original image such as a continuous tone image and to acquire a technique and a method capable of arbitrarily adjusting the tone of the black and white image. It is also the basis of multicolor image formation.

[Regarding Table 2] Similar to Table 1, Table 2 shows an image forming material (toner or the like) when a monochrome image is formed from an original image by an image forming apparatus.
If the density of the recorded image changes (that is, if the recorded image density range changes), the area ratio (y) of the recorded pixels is changed from 0% to 100%.
% Of the whole pixel, apart from the pixel-wide pixel contrast, of the recorded pixel at each sample point necessary to form an image with the same image tone, similar image quality to the human visual sense. It is a list of area ratios (y).

In other words, when the assumption is conservative, the area ratio of the recorded pixel of each sample point on the ideal gradation characteristic curve corresponding to the maximum density value of the image forming material (toner etc.) used ( This is a list of pixel density values (y).

[About Table 3] The basic conditions of Table 3 are the same as those of Table 2, but when the usage range (5% to 95%) of the area ratio of the pixels to be recorded is used, ideal gradation characteristics are obtained. 9 is a table showing what percentage of the area ratio (y) of recorded pixels should be set at each sample point on the curve.

To date, color separation work such as creating print images is
The color correction by the masking technology is the first priority, and the tone adjustment work of the image is basically a human experience.
Or it relies on a limited number of fixed materials. For this reason, it is necessary to stand on the side of an image to be reproduced, such as a printed image, and scientifically analyze the gradation adjustment of the image.

The "main adjustment method" is capable of performing the gradation adjustment work at the time of image formation by a rational method, and the basic density value (x) of the original image described above and the area ratio (y The data in Tables 1 to 3 showing the interrelationship with), are useful basic data for adding a scientific study on various basic matters in color separation work during image formation. is there.

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) "Operation for correction (or change) of gradation of this adjustment method" Next, "adjustment method" is based on the conversion of image gradation (that is, by the distribution of high-fidelity pixels from the original image of continuous gradation). It is also effective not only in the conversion to gradation image) but also in the correction (or change) of the so-called gradation for correcting the original image itself. The correction (or change) of the gradation in the formed image is performed, for example, by appropriately moving the position (M ₂ ) where the area ratio of the recorded pixels is 50% depending on the size of the reduction / enlargement ratio. It is a necessary means when it is desired to express the gradation of a shadow portion or a shadow portion strongly.

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

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

It is possible to move the position (M ₂ ) at which the area ratio of pixels to be recorded reasonably is 50% by preparing a plurality of basic data according to the actual work needs. The gradation can be modified (or changed).

The density range of the recorded image formed in Table 4 (DR _{p in} FIG. 1)
Is determined by the solid density of the yellow toner such as the toner used (and the value of β is also determined based on this), and the number in () below is Is the value of.

The number in the upper left () in the corner space in the table is the basic density value (x) at that sample point, and the lower right number is the area ratio of the recorded pixels corresponding to each basic density value ( y) is shown.

However, the usage range of the area ratio of recorded pixels is 5% to 95
The calculated values shown in Table 4 using% are extremely important in controlling the position (M ₂ ) where the area ratio (y) of the recorded pixels is 50%.

For example, when creating an image with a reduction / enlargement ratio of 100% from a color original using film manufactured by E company, the recorded image density range is
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 original image basic density area (x) is plotted on the horizontal axis and the pixels printed on the vertical axis. The gradation characteristic curve is created by taking the area ratio (y). Next, when changing the reduction / enlargement ratio for the reference color component and reducing it, the area ratio of the recorded pixels is 50%.
The position is moved to the S side, and when enlarged, the position is moved to the H side to form an image.

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. When a test image with the same image quality as the image distribution due to the latter pixel distribution is selected and reduced to, for example, 1/2, when the density range of the formed image is 0.85 and the value of ε is expanded to 1.16449, 200%, It is assumed that the density range of the formed image is 1.10 and the value of ε is 1.05958. Then, these gradation characteristic curves are created, and the area ratio (y) of the recorded pixels on the curve is 5
Based on the intersection with the straight line that becomes 0%, the sample point of the density value of the original image (in practice, the sample point is found on the gray scale for the work standard that represents the original image)
It can be seen that the area ratio of the pixels to be recorded in 50% should be included. The density value at which the area ratio (y) of pixels recorded as sample points is 50% is selected because it is considered to check the recorded image by the pixel distribution after the color separation work. Therefore, as another method, sample points are selected as 2/8, 4/8 points in the density range of the original image, and what percentage of the area ratio of the recorded image corresponding to that is obtained from the gradation characteristic curve, Color separation work may be performed based on this. As described above, by using Table 4, it is possible to rationally correct (or change) the image at the same time as converting the gradation of the pixel.

It should be noted that the correction (or change) of the gradation of this image is not limited to the reduction and enlargement ratio of the image formed by one person,
Type of target image in color original, purpose of use of formed image, whiteness of recording paper, image recording material (toner, etc.)
In some cases, it may be necessary to carry out according to the density, etc., but in any case, it is possible to rationally deal with it by Table 4, and various color separation work can be standardized and standardized.

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

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

1) The density of a document image such as a continuous tone image, which is the most basic matter for image formation, and the area ratio of recorded pixels in a formed recorded image (image recorded according to pixel distribution) In determining the correlation of the above, conventionally, it was based on the irrational method of exclusively based on the experience and intuition of the operator, or based on a limited number of fixed-case data, but in the present invention, the You can replace this with a reasonable and simple decision method even under. When converting an original image such as a continuous tone image into a recorded image based on the distribution of pixels, the most important requirement is how to control the tone (conversion, correction or change of tone). Not only that, but the color tone of the image is directly deeply related, so that the present invention enables rational management of gradation and color tone. That is, an image forming apparatus that adopts the "main adjustment method" in the gradation adjustment mechanism can theoretically and rationally systematize the work such as color separation work and gradation conversion work to simplify the work. It is possible and the effect is extremely large.

2) By adopting the "main adjustment method" into the gradation adjustment mechanism of the image forming apparatus, the equipment can be rationalized and simplified, the manufacturing cost can be reduced, and the operation of the equipment can be simplified. As a result, it is possible to significantly improve the performance of the image forming apparatus by clarifying and re-doing the work extremely, and saving the consumption of consumables.

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 at the same time drastically improves the configuration of the current image forming apparatus. Can be rationalized.

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

[Brief description of drawings]

FIG. 1 (a) shows an example in which an original image having continuous tone is represented by the distribution of unit pixels in a pixel block, and FIG. 1 (b) shows a photoengraving corresponding to the case of (a). FIG. 6 is a diagram showing a case of representing the size of halftone dots in FIG. FIG. 2 (a) is an example of converting a density image of a document image into a recorded image based on the distribution of pixels through the document image, and FIG. 2 (b) is a document image of which gradation conversion has been performed on the document image. FIG. 7 is a diagram showing an example of converting a recorded image according to a pixel distribution. 3 is a block diagram of the image forming apparatus of the first embodiment of the present invention, FIG. 4 is a block diagram of the image forming apparatus of the second embodiment,
FIG. 5 is a block diagram of an image forming apparatus according to the third embodiment, and FIG.
FIG. 7 is a block diagram of the image forming apparatus of the fourth embodiment, and FIG. 7 is a block diagram of the image forming apparatus of the fifth embodiment. FIG. 8 is a diagram showing an electrostatic recording type image forming unit.

Claims (5)

[Claims] 1. An image forming apparatus for forming a recorded image by a distribution of pixels on a recording sheet based on image information of an original image, wherein the image forming apparatus performs gradation conversion of image information of the original image of the original image. As a gradation adjusting mechanism, a mechanism for converting the basic density value (x) of an arbitrary sample point on the original image into (y) on the recorded image by the following <relational expression (1)> should be provided. An image forming apparatus characterized by. <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 same image from the density value at any sample point X on the original image. y: The ratio of the number of pixels of the unit pixel to be recorded to the number of unit pixels forming the pixel block for the sample point X on the formed recorded image. y _h : a ratio of the number of unit pixels to be recorded to the number of unit pixels forming the pixel block, which is set for the pixel block of the brightest portion H of the recorded image to be formed. y _s : a ratio of the number of unit pixels to be recorded to the number of unit pixels forming the pixel block, which is set for the pixel block of the darkest portion S of the recorded image to be formed. α: reflectance of the recording sheet. β: Surface reflectance of recording material. k: ratio of (density threshold of recorded image to be formed) / (density threshold of original image). Respectively. 2. A distribution of the pixels is represented by scanning with a laser beam on an image forming body having a uniformly charged photoconductive layer to form a recorded image with the distribution of the pixels on a recording sheet. The image forming apparatus according to claim 1, wherein a latent image is formed, the latent image is developed with toner, then transferred to a recording sheet, and further fixed. 3. A series of operations of forming a latent image on the image forming body, developing with toner, transferring to a recording sheet or a part thereof is performed using toner of a specific color, and the same operation is performed with different colors. 3. A color image is formed by performing the same operation as described above, repeating the same operation for the required number of colors, aligning and transferring the same onto the same recording sheet, and further fixing. Image forming apparatus. 4. A voltage is applied to a moving electrostatic recording medium to a large number of recording electrodes arranged in a direction perpendicular to the moving direction in order to form a recorded image with a pixel distribution on the recording sheet. The image forming apparatus according to claim 1, wherein an electrostatic latent image is formed on the electrostatic recording body by the toner, the latent image is developed with toner, then transferred to a recording sheet, and further fixed. 5. A series of operations including formation of a latent image on the electrostatic recording medium, development with toner, transfer to a recording sheet or a part thereof is performed using toner of a specific color, and the same operation is different. 5. A color image is formed by performing color toner formation, and then repeating the same operation for a required number of colors, aligning and transferring the same onto a recording sheet, and further fixing. Image forming device.