JPH01254068A - Image forming device - Google Patents

Abstract

PURPOSE:To attain gradation conversion of a rational picture by applying processing so that a correlation is given between a reference density of an optional sample point on an original picture and a ratio of a number of unit picture elements to be recorded with respect to a number of a unit picture element constituting a picture element block corresponding to the sample point in a formed recording picture. CONSTITUTION:A gradation adjustment mechanism processing a picture information signal is provided to an image forming device in a way that a correlation exists between the reference density of an optional sample point on an original picture and a ratio of a number of unit picture elements to be recorded with respect to the number of unit picture elements constituting a picture element block corresponding to the sample point in the recording picture to be formed. Thus, the job such as color separation or gradation conversion is systemized theoretically and rationally to simplify the job thereby managing the gradation and color tone rationally.

Description

Detailed Description of the Invention (Technical Field) The present invention converts an image information signal obtained by photoelectrically scanning an original image using a new gradation conversion method, thereby producing a recorded image with excellent gradation reproducibility. It relates to image forming positions that can be formed.

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

(Prior art) When an image is formed on a recording sheet by an image forming device such as a copying machine from an original image having continuous gradation such as a photograph, analog processing (exposure) of the original is required when photosensitive paper is used as the recording sheet. ), an image having continuous gradations corresponding to the original is formed (silver halide photographic recording). On the other hand, with electrophotographic copying machines that record images on plain paper rather than photosensitive paper, it is not possible to form images using analog processing, and continuous tone reproduction is desired, and in the case of color image formation, Adjusting the color balance is also not easy.

For this reason, efforts have recently been made to improve the gradation reproducibility of image forming apparatuses.

Image formation in this type of image forming apparatus is similar to the method of converting continuous gradation to halftone gradation in the case of photolithography in printing, and photoelectric scanning of continuous gradation original images such as photographs. This method uses a method of processing an image information signal obtained by using the image information signal, and using the signal to form an image on a recording sheet with a distribution of pixels having a color density corresponding to the original image.

However, in currently used image forming apparatuses, when the gradation characteristics of the original image are reflected in the final recorded image based on the pixel distribution, it is difficult to determine what characteristics the pixel distribution should have. No particular study has been made as to how to obtain such a pixel distribution, and the method depends solely on the experience and intuition of the operator and the subjective judgment of the equipment designer. In particular, the density characteristics of pixels, which are extremely important in faithfully reproducing gradations, are determined in advance by equipment manufacturers based on experience, intuition, and data based on a limited number of fixed conditions, and are stored in the memory of the image forming device. Data is used by operators. For this reason, in the case of non-standard color originals that were not anticipated by the equipment manufacturer, it is difficult to make adjustments to form the desired recorded image.

It is difficult to maintain the image quality level and stabilize the image quality, and it lacks the flexibility to arbitrarily change or modify the image quality.

(Problems to be Solved by the Invention) The cause of the above-mentioned problems in conventional image forming apparatuses is the initial stage of forming an image with the final pixel distribution from a document image such as a continuous tone image. The idea lies in the process of image gradation conversion, which also plays an important role. In other words, the conventional approach to gradation conversion was not that ``it must be performed based on scientifically rational N-tone conversion means,'' but that it relied solely on experience and intuition. It is in.

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

(Means for Solving the Problems) To summarize the present invention, the present invention creates a recorded image on a recording sheet with a pixel distribution corresponding to the original based on an image information signal obtained from the original image by photoelectric scanning or the like. In the image forming apparatus for forming the image, the image information signal is converted into the basic density value (1) of an arbitrary sample point on the original image (the density value at the sample point and the density value at the brightest part on the same image). (difference between
For example, the present invention relates to an image forming apparatus having a gradation adjustment mechanism that performs processing as defined by the following relational expression (1).

(Relational expression) χ: Basic density value of an arbitrary sample point X on the original image.

That is, the density value is obtained by subtracting the density value at the brightest part H of the same image from the density value at an arbitrary sample point X of the same image.

y: Ratio of the number of recorded unit pixels to the number of unit pixels constituting the pixel block Y corresponding to the X on the recorded image to be formed.

yh: Ratio of the number of recorded unit pixels to the number of unit pixels constituting the pixel block, which is set for the pixel block of the brightest part H of the recorded image to be formed.

y8: Set for the pixel block of the darkest part S of the recorded image to be formed. The ratio of the number of recorded unit pixels to the number of unit pixels constituting the pixel block.

α: Reflectance of recording sheet.

β: Surface reflectance of recording material (toner, etc.).

k; Represents the ratio of (density range of the recorded image to be formed)/(density range of the original image).

Hereinafter, the configuration of the present invention will be explained in detail.

In photolithography, the density of an image with continuous gradation is expressed by the size of the halftone dots through halftone processing, but in an electrophotographic image forming device using digital image processing, the density of an image with continuous gradation is expressed by the size of the halftone dot. The image is scanned by a laser beam or the like, and it is extremely difficult to express multiple gradations by changing the diameter of the beam. Therefore, the diameter of the beam is kept constant, and the number of unit pixels constituting the pixel block and the image are recorded in the pixel block, which is a matrix-like collection of pixels as the minimum unit formed by the beam (i.e. The size of halftone dots is often matched by changing the ratio to the number of unit pixels (recorded with toner, etc.).

Of course, in digital image processing technology, in addition to the gradation expression method (dot density modulation method) that changes the number and arrangement of dots (with a specified size) as described above, there are also methods that change the size of dots ( There is also a dot size modulation method).

Here, the former will be explained as an example.

By the way, what can be considered as a basic component for image expression is this pixel distribution (color density is determined by the ratio of the number of recorded pixels among the unit pixels constituting a given pixel block and its distribution form). ) and the surface reflection density of the image recording material (toner, etc.), of which human vision can detect, for example, 1% of the size of the halftone dot area in a printed image.
As can be seen from the fact that it has the ability to easily identify differences in density as differences in density, how can we calculate the pixel density value expressed by the pixel distribution, which has the same relationship as the size of the halftone dot area as an image forming means? It turns out that it is very important to decide whether to set it or not.

In addition, in connection with the above, when trying to form a recorded image with one image forming apparatus, the quality content of the original image varies widely, and the image forming process also has various characteristics. Furthermore, image quality evaluation standards are not uniform, and these complicated and unstable factors must be overcome.

For this reason, when converting a document image such as a continuous tone image into a recorded image based on the pixel distribution, the density ratio (yh) of the pixel block in the brightest part (H) in the recorded image based on the pixel distribution created in 2. and the density ratio (yQ) of the pixel block in 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 rationally and easily selected. It is absolutely necessary to have a means of coordinating and managing this.

Based on this idea, we devised the gradation adjustment method of the present invention described above, specifically, the gradation adjustment method defined by the relational expression (1) (hereinafter referred to as r water adjustment method). ”).

The gradation adjustment method of the present invention is based on the values of the reflectance of the recording sheet and the surface reflectance of the image recording material (toner, etc.), and determines which pixel blocks are desired to be placed at H and S of the recorded image to be formed. The ratio of the number of pixels recorded within (yh and ys
) while arbitrarily selecting an arbitrary sample point (X
) is used to calculate the ratio (y) of the number of recorded pixels in the corresponding pixel block (Y) on the recorded image formed from the basic density value (χ) of .

In addition, in the above-mentioned relational expression (■) of the present invention, the basal concentration value (1
) is measured using a densitometer (for example, some positive color film portraits have a density value of 0.2 to 2.70). ) and ys [pixel density value set for the pixel block of the darkest part (S)] using percentage values (for example, 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. When using the relational expression (■), as long as this point is taken into account, it may be modified and used in any way. When measuring the basic density value (x) mentioned above, the density measurement is generally performed using a color densitometer (transmission type, reflection type,
Any concentration measuring means may be used, such as a dedicated type, a shared type, etc.

In the gradation adjustment method of the present invention, the basic density value (1) is not limited to the value determined by the densitometer described above,
It goes without saying that the original image may be photoelectrically scanned to detect an electrical signal (current or voltage value) corresponding to the work value, and the y value may be determined based on this. That is, the process value may be any value as long as it correlates in some sense with the basic density value of the original image.

The above-mentioned relational expression for determining the ratio (y) of the number of pixels is the generally recognized density formula (photographic density, optical density), that is, D = logl, / I = log 1 /
T■. ; Incident light amount: reflected light amount or transmitted light amount T = I/I. ; derived from reflectance or transmittance. When this general formula regarding density is applied to image formation, it is as follows.

Density (D') in image formation = 1ogI/
I.

Here, A; unit area do; sum α of the area of recorded pixels relative to the number of unit pixels in the n-th pixel block within the unit area; reflectance β of the recording sheet; image forming material (toner, etc.) is the surface reflectance of

The present invention uses the basic density value (x) at an arbitrary sample point on an original image such as a continuous-tone image described above and the distribution of pixels corresponding to the basic density value (x) on a recorded image based on the density equation (D') related to image formation. Incorporating the request for association with the ratio (y) of the number of recorded pixels in the pixel block, the relational expression (2) is derived so that the theoretical value and the measured value approximately match.

Therefore, the tone adjustment of the present invention from an original image such as a continuous tone image to a recorded image based on the pixel distribution is performed by correlating the basic density value (1) described above with the ratio (y) of the number of recorded pixels. This applies to everything that adjusts the gradation.

It should be understood that the correlation between χ and y in the above relational expression 〇 is one example thereof, and the present invention is not limited to this. In other words, it is possible to make appropriate changes without departing from the scope of the present invention.6 The features of the gradation adjustment of the present invention are that it can be used regardless of the quality content of the original image such as a continuous tone image. , for example, as shown in the relational expression 〇, yh and y
By arbitrarily selecting the values of g or α and β, it is possible to very easily know what kind of gradation characteristics the recorded image should have based on the pixel distribution to be created. That's what it means.

This adjustment method can be modified and used.
For example, when the values of yh and y3, α and β are arbitrarily and appropriately selected, and in addition, when the density range of the original image such as a continuous tone color photographic image is different from the density range of the recorded image due to the pixel distribution, Adopts a well-known gradation compression method, that is, appropriately selects the value of the ratio of (recorded image density range)/(original image density range), and performs image adjustment by calculating it using "this adjustment method". Just go.

That is, in the present invention, when forming a recorded image based on 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 (
It has extremely high flexibility and can perform gradation conversion and gradation correction (or change) of '/h, '/s, and k images defined in 1).

To explain this in detail, it should be noted that the user (operator) has the following degrees of freedom when applying the "r book adjustment method".

Shit 1> Use the relational expression 〇 for the purpose of forming an image that is faithful to the original image. In other words, 1 with the human eye! The first thing to do is to get exactly the same visual and sensory image when you sense it.
Think logically and apply the relational expression 〇. In the present invention, such tone adjustment behavior is explained using the term "tone (of) conversion (of an image)."

<Part 2> Use the relational expression (■) to change or modify the original image based on the technical needs of image formation, artistic requests, or needs on the ordering side. That is, the relational expression (2) is applied with the primary consideration being to obtain an image in which the visual sensory image itself is modified or changed when observed with the human eye. In the present invention, such tone adjustment behavior is explained using the term "(image) tone (correction) (or change)."

The gradation adjustment work according to the present invention, specifically, the above-mentioned gradation conversion and gradation correction (or change),
/h, 'This can be easily done by changing the values of Is, k, and t as appropriate.

In that case, the above relational expression 〇 or the terms and values included therein,
It goes without saying that the coefficients may be processed, transformed, derived, omitted, etc. as appropriate as long as they do not impair the rationality of image gradation conversion, and the purpose, means, and method of using "this adjustment method" are It is not subject to any restrictions.

Note that when forming a multicolor image, for example, when duplicating a color original, color separation, which is well known in the field of printing, is used to separate light reflected from the color original into blue (B), green (G), and red (R). ) to obtain an image information signal, and process the image information signal for each color with a gradation adjustment mechanism using the above relational expression (1), that is, calculate the gradation characteristic curve (y value) that serves as a reference. , by plotting the y value against the y value, a gradation characteristic curve similar to the halftone gradation characteristic curve in printing technology can be obtained. This can be determined rationally by multiplying the y value of the color component by an appropriate adjustment value based on the gray balance ratio of each ink, so this image information can be used to form an image. Good.

y value for each color component determined as described above,
That is, the gradation characteristic curves for each color component are as follows.

Not only is the characteristic curve reasonable because it is defined by the relational expression (1), but also the interrelationship between these characteristic curves in terms of gradation and color tone is also reasonable and appropriate.

In the image forming apparatus of the present invention, the exposure scanning beam is modulated by the "r zero adjustment method" in its gradation adjustment mechanism, and pixels are sequentially formed by performing arithmetic processing according to a predetermined pixel distribution pattern. It is something that will continue.

In the case of the column (a) in Figure 1, the distribution of recorded pixels becomes more dispersed within the pixel block as the number of recorded pixels increases. It is also possible to make the dots spread outward in a spiral manner, in which case the dots will resemble halftone dots in photolithography.

Also, column (b) shows one halftone dot with an area corresponding to the number of pixels in column (a).

Although the pixel block has been described here as a 4×4 matrix type, 17 levels of gradation can be expressed by this.

In general, it is a matrix type pixel block of nXn with n2
+1 step of gradation (0 to 100%) is expressed.

This method of expressing the density of an original image such as a continuous tone image by the distribution of pixels formed in matrix-type pixel blocks is generally called the dither-matrix method, and is known as Showa 58-8543
No. 4, No. 58-114569, No. 59-52969, No. 60-141585, No. 62-186663, etc.

In addition, depending on the method of image gradation adjustment, whether the conversion (or correction, change, etc.) is direct or indirect, it is basically possible to immediately create a continuous tone image with a linear density gradation characteristic curve. There are two methods: converting into a tone image based on the pixel distribution, and converting the continuous tone image into a tone image using the pixel distribution. Since gradation conversion, etc. have already been performed, there is a method of converting (distinguished here by the term "conversion"). In addition, depending on whether or not to compress the density range, each of the above-mentioned methods includes a method that directly converts the continuous tone density range into a density range based on the pixel distribution without compressing it, and a method that supports the density range based on the pixel distribution. There is a method that uses a density range compressed original image. In reality, one should select one suitable for the working environment from among the image gradation conversion methods obtained by combining these basic methods.

As a typical example, the basic density range of a continuous tone image (original image) having a linear density gradation characteristic curve is proportionally compressed to obtain a density range compressed original image, as shown in FIG. Figure (b) shows an example of converting a continuous tone image (original image) with a linear density gradation characteristic curve into an image based on pixel distribution.
An example will be shown in which the tone is converted and the density range is compressed at the same time to obtain a tone-adjusted density range compressed original image, and then this image is proportionally converted to create an image based on pixel distribution. In FIGS. 2(a) and 2(b), Do: Density value of the original image, which is a continuous tone image.

DR, . . . 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 (extreme point of the highlight part; H) from the density value at the sample point (X) on the document in this DRo becomes the basic density value (1).

D, . . . Density value of an Ili degree range compressed original image obtained by compressing the density range of a continuous tone original image proportionally to the value of k.

DR,...density range of the density range compressed original image.

Do: Density value of a continuous tone image obtained by converting the tone of a continuous tone original image using the "main conversion method" and compressing the density range.

DR,...Continuous gradation original image is converted using the "main conversion method"
The density area of a continuous tone image that has been converted to a gradation and compressed the density area.

Dp: Pixel area ratio of a recorded image based on pixel distribution.

DRP: Density range of a recorded image based on 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 evaluate their consistency.

H...The brightest point on the original image (the extreme point of the highlight part) S...The darkest part (the extreme point of the shadow part) on the original image...The point at the middle of the density on the original image ( (middle density point) M2... In the recorded image based on the distribution of formed pixels, each indicates the position of a pixel block having a pixel area of 50%, and the same applies to the following examples and explanations.

(Examples) Hereinafter, an 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 unless the gist of the present invention is exceeded.

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

As shown in FIG. 3, the image forming apparatus of the present invention includes a detection unit 1 that spectrally reads transmitted light or reflected light of an original image into R (red), G (green), and B (blue);
Output signal of detection unit 1 is Y (yellow), M (magenta)
, C (cyan), and K (black) color separation unit 2, a gradation adjustment unit 3 that calculates image gradation according to an appropriate pixel distribution using “r adjustment method”; It has an output section 4 that exposes the electrophotographic photoreceptor to laser light based on the output signal of the gradation adjustment section 3, and the latent image formed on the photoreceptor is developed into a toner image in a development section.
The image is transferred to a recording sheet and fixed in a fixing section.

In order to form a color image, a separate photoreceptor and a developing section are provided for each component color, and the toner images formed in each are sequentially transferred to a recording sheet, or a latent image of each component color is transferred to a single photoreceptor. The procedure involves forming and developing a toner image, transferring it to a recording sheet, and repeating this process for each color component.

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

The color separation unit 2 uses the detection unit 1 in the log amplifier 7 to detect R, G,
The voltage signals of B and USM are logarithmically operated and converted into density, and the black (K) component is separated from this density in basic masking (BM) 8, and then the Y, M, and C components are separated.
Separate each component.

Next, in the color correction (CC) section 9, RlG,
Y component for each original color of B, Y, M, and C.

The M and C components are controlled, and the black component of the original is controlled by the UCR (unde
rcontrol removal), or U CA
(under control), the ratio expressed by the three components Y, M, and C is determined.

After obtaining these Y, M, and C components, conventionally, the gradation control section in the gradation conversion section (IMC) calculates the area ratios occupied by the pixels of each component, ye', l.
Find l1e', ce', ke' and reverse log
However, in this embodiment, the adjustment section 1 is used instead of the gradation control section and the inverse log conversion section.
1, where Y, M.

Conversion is performed from C, K to ye' t me' g Ce', ke'. The adjustment unit 11 has the algorithm of the "main adjustment method" internally, and applies the "r conversion method" to each of Y, M, and C, and calculates ye', me',
Find ce' and ke'.

The adjustment unit 11 has the algorithm of "r main adjustment method" as software, and has I/D of A/D and D/A.
A general-purpose computer with F (interface), an electric circuit realized by a general-purpose IC with the algorithm as internal logic, and an RO that holds the calculation results of the algorithm.
It can take four different forms, such as an electric circuit including M, a PAL that embodies the algorithm as internal logic, a gate array, and a custom IC. In order to form an image with a laser beam corresponding to the density of the original image, the diameter and intensity of the laser beam are kept constant as described above, and the image is formed within an image block corresponding to the area of halftone dots in the case of photoengraving. The number of unit pixels and their distribution are calculated and the data is output.

The area ratio of the pixels obtained by the adjustment unit 11 is input to the color channel selector 12, and the color channel selector 12 selects ye', +ne', ce', ke.
' is output bi-selectively. This output is A/D converter 1
3, the signal is A/D converted and input to the output section 4.

In the output section 4, a dot control section 14 controls the laser beam based on the output of the gradation adjustment section 3.

FIG. 4 shows a second embodiment, in which the conventional inverse log conversion section 15 is used as is, and therefore the adjustment section 11 converts ye', me', Ce', ke' in logarithmic form.
is output. This allows the adjustment method to be applied by simply converting one component of conventional equipment.
An existing system can be modified to a system according to this method with fewer changes than those according to the first embodiment.

FIG. 5 shows a third embodiment, in which the conventional gradation control (IMC) section 16 is left as is,
The connection between the inverse log conversion section 15 and this gradation control section 16 is cut off. Then, the adjustment section is similar to that of the second embodiment, that is, ye', me', C in logarithmic form.
An adjustment section 11 that outputs 6' and ke' is employed.

The adjustment section 11 takes the Y, M, C, signals from the stage before the gradation control section 16, and converts them to an inverse log conversion section 15.
The value after conversion is output.

FIG. 6 shows a fourth embodiment, in which the inverse log conversion section 15 and color channel selector 12 are left as they are,
The connection between the two is cut off. That is, the adjustment section 11 adjusts Y, M, C,
The signals are taken from the input terminal and connected directly to the color channel selector 12, and the output signals are ye', me', and ce'.

ke' is not constrained by the conventional system, and ye is processed in the same optimal processing form as in the adjustment section of the first embodiment.
', me', ce', and ke' can be obtained.

As in the third embodiment, the system can be implemented by making slight modifications to the conventional system.

FIG. 7 shows a fifth embodiment, in which the entire conventional gradation conversion section is configured as a new adjustment section 11, so that "this adjustment method" can be applied to this adjustment section.

In the examples shown in Figures 3 to 7, the image forming section is of an electrophotographic type that forms an electrostatic latent image on a photoconductive photoreceptor by scanning a laser beam, but a recorded image is formed by the distribution of pixels. As a method, other methods such as electrostatic recording type, magnetic recording head, etc. can be adopted.

In electrostatic recording, as shown in Figure 8, each electrode of a recording head has a large number of electrodes arranged near or in contact with a recording body made of a moving sheet-like dielectric material in a direction perpendicular to its moving direction. A voltage is applied to form an electrostatic latent image. The steps after the step of adding toner to this latent image and developing it are the same as in the case of electrophotography. The dot control unit 14 of the output unit 4 for the recording head as a collection of electrodes.
A voltage is applied as an output signal corresponding to the image to be recorded. In addition, in the magnetic recording type, the recording medium is, for example, a drum whose surface is uniformly coated with a magnetic material, and a voltage as an image information signal is applied to the magnetic recording head in contact with the surface. A magnetic latent image is formed on the recording surface by relatively moving the recording surface and the recording surface.

In order to develop this latent image, a toner made of a magnetic material is used, but otherwise it is carried out in the same manner as in the case of electrophotography.

If you modify the gradation adjustment section of conventional equipment as described above,
It is also possible to combine the "r-book adjustment method" with other processing, and the system can be optimized to be faster and more compact, and the cost performance per system can be improved.

In the above embodiment, the color separation section has the same configuration as the conventional one, but by using "this adjustment method", the color correction (CC) section 9 and the USR/UCA section 10 can be omitted if they are not necessary. An omitted color separation section may be employed.

Furthermore, descriptions of commonly used effects, such as blur masks and sharpness effects that are not directly related to the present invention, have been omitted in the above embodiments.

Next, a supplementary explanation will be given regarding the usefulness of the "r book adjustment method" applied to the gradation adjustment mechanism of the image forming apparatus of the present invention.

This is a supplementary explanation to facilitate understanding of the present invention, and describes working examples (related to the present invention) regarding the main element of the image gradation adjustment mechanism of the present invention, the main adjustment method. This section will mainly explain in detail the operation of formula (g) and the significance of its results.

(a) Operational experiments of the "present adjustment method" As basic experiments for incorporating the "present adjustment method" into the gradation adjustment mechanism of an advanced image forming apparatus, the following two experiments were conducted.

a) First of all, using an ordinary simple calculator, namely the trade name Sharp Pythagoras EL509A (manufactured by Sharp Corporation),
The gradation adjustment tables for the image shown in Table 1 (3), Table 2, and Table 3 below were created by operating the simple calculator while applying the required values to "This Adjustment Method". .

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

b) The following experiment was also conducted.

Simple personal computer (NEC fRP C-
9801-M2), input the required software obtained separately as function data, and calculate the basic density value (1) of the original image (continuous tone image) in the pixel block on the recorded image according to the corresponding pixel distribution. Ratio of the number of recorded pixels (hereinafter referred to as the area ratio of recorded pixels)
(y) Adjustment work was carried out.

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

Moreover, in this experiment, the above software for adjusting the gradation of the image to be input to the personal computer was created without using any special software, but using the N88-BASIC that came with the personal computer. It took only one hour to complete.

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

Using these software, set the desired density interval (for example, 0.05 to 0.00 to 1.00) on the original image.
Increment, from 1°00 to 3.00 is 0. ] in o increments)
By setting the value and inputting the value to the personal computer, the target area ratio (y) of the pixel could be obtained.

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

Area ratio (y) of pixels recorded by the above software
It is possible to output either a positive image or a negative image individually or at the same time.

Next, the usefulness of Table 1 (3), Table 2, and Table 3 will be explained. (In each table, the y value is the pixel density value.) [About Table 1 ■■■ Table 1 shows the image recording materials such as toner used when forming a black and white image from an original image using an image forming device. When the usage range of density and area ratio of recorded pixels (values set for yi and ys) changes, in order to obtain an ideal gradation characteristic curve, the area of recorded pixels at each sample point changes. Ratio (y
) is a list of how things must be done.

Also, from this table, we can see how the ideal gradation characteristic curve changes when the usage range of the area ratio of recorded pixels is changed even if the density of toner etc. is the same, and how it must be changed. You can know what.

In addition, students will learn how to form a black-and-white image with a 1:1 pixel distribution from a manuscript image such as a continuous-tone image, and the techniques and methods that can arbitrarily adjust the gradation of a black-and-white image. It is also the basis of color image formation.

[About Table 2] Similar to Table 1, Table 2 shows image forming materials (toner, etc.) used when a black and white image is formed from a document image by an image forming device.
When the density changes (when the recorded image density range changes), the area ratio (y) of the recorded pixels is changed from 0% to 100.
% of the pixels recorded at each sample point necessary to form an image with the same image tone and similar quality to the human visual sense, apart from the codon last of the entire image. This is a list of area ratios (y).

In other words, when the conditions are ideal, list the area ratio of pixels recorded at 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 table.

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

Incidentally, there is no need to explain that this list is the prototype of ``this adjustment method.''

Until today, color separation work in the creation of printed images, etc.
Color correction using masking technology is primarily emphasized, and image gradation adjustment work is basically based solely on human experience and intuition.
Or they rely on a limited number of fixed and given materials. For this reason, it is necessary to scientifically analyze the gradation adjustment of an image based on the side of the image to be reproduced, such as a printed image.

"This adjustment method" can perform gradation adjustment work during image formation in a rational manner, and also allows the basic density value (1) of the original image described above and the area ratio of image pixels to be recorded (y
) The data in Tables 1 to 3, which show the interrelationship with be.

From each of these tables, what is the essence and principle that exists between the manuscript image and color separation work, and what should be paid attention to and considered in order to rationally match that essence and principle with practice. You can extract what you need to do.

In addition, in creating Tables 1 to 3, α = 100% in all cases.
, β=0%.

(b) Application of the r-adjustment method to correction (or change) of gradation Next, the r-adjustment method converts the gradation of an image (i.e., from a continuous-tone original image to a high-fidelity pixel distribution) This shows that the present invention is effective not only for converting to a gradation image) but also for modifying (or changing) the gradation of the original image itself. The correction (or change) of the gradation in the image to be formed is, for example, when the position (M2) where the recorded pixel area ratio is 50% is moved due to the size of the reduction/enlargement ratio, or when the area ratio of recorded pixels is moved, especially in highlight areas or shadows. This is a necessary means when you want to strongly express the gradation of the area.

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 one image forming material (toner, etc.) Due to changes in the reduction ratio or enlargement ratio of the recorded image formed from the original image, the area ratio (y) of recorded pixels, which is an extremely important control point on the recorded image due to pixel distribution, may become 50%. The set point (M
The problem is how to move 2) to correct or change the gradation of the image.

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

By preparing multiple basic materials according to the actual work needs, it is possible to reasonably move the position (M2) where the area ratio of recorded pixels is 50%,
This allows the gradation of the image to be corrected (or changed).

The density range of the recorded image to be formed in Table 4 (DR in Figure 1)
(corresponding to p) is determined by the solid density of yellow toner such as the toner used (and the value of β is also determined based on this), and the number in parentheses below it is the value of ε=□.

α-β The number in parentheses at the top left in the corner space (frame) in the table is the basic density value (1) at that sample point, and the number at the bottom right is the number of recorded pixels corresponding to each basic density value. The area ratio (y) is shown.

However, the usage range of the area ratio of recorded pixels is 5% to 9
5% was used. The calculated values shown in Table 4 are extremely important when managing the position (M2) where the area ratio (y) of recorded pixels is 50%.

For example, when creating an image with a reduction/enlargement ratio of 100% from a color original using film made by Company E, the recorded image density area is 0.
．． 95. Assume that an image with desired image quality is formed when the E value is 1.12638. Next, based on the calculated values in Table 4, create a gradation characteristic curve to obtain a recorded image based on the pixel distribution (i.e., the horizontal axis represents the original image basic density area (
1), a gradation characteristic curve is created by taking the area ratio (y) of pixels recorded on the vertical axis).

Next, change the reduction/enlargement ratio for the reference color component, and when reducing, move the position where the recorded pixel area ratio is 50% to the S side, and when enlarging, move it to the H side. Perform formation.

The test image thus obtained is compared with the image quality of the image (reference component image) in which the desired image quality is obtained. When a test image with the same image quality as the image quality based on the latter pixel distribution is selected and reduced to, for example, 1/2, the density range of the image formed is 0.85 and the value of ε is 1.1644.
Assume that when the image is enlarged to 9.200%, the density range of the image formed is 1.10 and the value of E is 1.05958. Then, create those gradation characteristic curves, and based on the intersection point on the curve with a straight line where the area ratio (y) of recorded pixels is 50%, sample points of the density value of the original image ( Practically speaking, sample points are obtained on a work standard gray scale that represents the original image. The area ratio (y) of pixels recorded as sample points is 50
The reason why the density value of % was selected is to facilitate checking the recorded image based on the pixel distribution after the color separation process. Therefore, another method is to select a sample point at 278.4/8 of the density range of the original image, find out from the gradation characteristic curve what percentage of the area of the corresponding recorded image should be, and then It is also possible to perform color separation work based on this. By using Table 4 in this way, it is possible to rationally modify (or change) the image at the same time as converting the gradation of the image.

Note that the correction (or change) of the gradation of this image depends not only on the reduction/enlargement ratio of the image formed by one person, but also on the intention of the orderer,
Type of target image in color manuscript.

There may be cases where this is necessary depending on the purpose of use of the image to be formed, white discoloration of the recording paper, density of the image recording material (toner, etc.), etc., but in any case, it should be handled rationally according to Table 4. It is possible to standardize and standardize various color separation operations.

Furthermore, according to the present invention, it is possible to correct (or change) the gradation of images in highlight areas and shadow areas in the same way, and furthermore, special countermeasures can be taken to prevent color scattering in highlight areas of color originals. It can be automatically removed without having to do so.

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

1) The most basic matters for image formation are the density of the original image such as a continuous tone image and the area ratio of recorded pixels in the recorded image (image recorded by pixel distribution). In the past, determining the correlation between the Even if it is under , it can be replaced with a rational and simple decision method. In addition, when converting an original image such as a continuous tone image into a recorded image based on pixel distribution, the most important requirement is gradation management (
Conversion, modification, or change of gradation is not limited to just the gradation of an image, but also has a direct and deep relationship with the tone of the image, so the present invention allows for rational management of gradation and color tone. can do. In other words, an image forming apparatus that incorporates "this adjustment method" into a single gradation adjustment mechanism theoretically and rationally systematizes work such as color separation work and gradation conversion work.
The work can be simplified and the effect is extremely large.

2) By incorporating "this adjustment method" into the gradation adjustment mechanism of an image forming apparatus, equipment can be rationalized and simplified, manufacturing costs can be reduced, and the operation of these equipment can also be simplified. , the performance of the image forming apparatus can be greatly improved by greatly reducing the number of reworks and greatly reducing the consumption of consumables.

3) By using the gradation adjustment mechanism using the "present adjustment method," it is possible to rationally and easily define quality evaluation standards for recorded images based on pixel distribution, separated from the image information of the original image. In other words, "this adjustment method" can scientifically and objectively define the highlights, shadows, and density gradation characteristic curves from shadows to highlights of the original image, and also radically changes the configuration of current image forming equipment. can be rationalized.

4) By adopting "this adjustment method," it is possible to effectively educate and train technicians, which is required as image forming equipment becomes more sophisticated, and eliminate unnecessary labor in daily work. It is possible to secure time for new creative research and development.

[Brief explanation of the drawing]

FIG. 1(a) shows an example of a case where a continuous tone original image is expressed by the distribution of unit pixels within a pixel block, and FIG. 1(b) shows a photolithographic process corresponding to the case of (a). FIG. 3 is a diagram showing a case in which the size of halftone dots is expressed in FIG. FIG. 2(a) shows an example of converting a density-compressed original image into a recorded image based on pixel distribution, and FIG. 2(b)
2 is a diagram showing an example of converting a gradation-converted density range compressed original image of an original image into a recorded image based on pixel distribution; FIG. FIG. 3 is a block diagram of an image forming apparatus according to the first embodiment of the present invention, FIG. 4 is a block diagram of an image forming apparatus according to the second embodiment,
FIG. 5 is a block diagram of the image forming apparatus of the third embodiment, and FIG.
The figure is a block diagram of an image forming apparatus according to a fourth embodiment, and FIG. 7 is a block diagram of an image forming apparatus according to a fifth embodiment. FIG. 8 is a diagram showing an image forming section in an electrostatic recording type. Patent applicant Yamatoya Shokai Co., Ltd. Agent Patent attorney Yoshio Mizuno'B n-no-no Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Scope of Claims] 1. An image forming apparatus for forming a recorded image with a distribution of corresponding pixels on a recording sheet based on an image information signal obtained by photoelectric scanning or the like of a document image, comprising: The signal is calculated by combining the basic density value (x) of an arbitrary sample point on the original image (the difference between the density value at the sample point and the density value at the brightest part on the same image) and the above in the recorded image to be formed. The ratio (y
). 1. An image forming apparatus comprising: a gradation adjustment mechanism that performs processing so that the values of 2. The image information signal gradation adjustment mechanism adjusts the image information signal to the basic density value (x) of an arbitrary sample point on the original image and the sample point on the recorded image according to the distribution of pixels to be formed. 2. The image forming apparatus according to claim 1, wherein processing is performed such that a ratio (y) of the number of unit pixels recorded in a corresponding pixel block is defined by the following relational expression (1). (Relational expression) y=y_h+{α(1-10^-^h^x)/(α-β
)}(y_s-y_h)...(1) However, x: Basic density value of an arbitrary sample point X on the original image. That is, the density value is obtained by subtracting the density value at the brightest part H of the same image from the density value at an arbitrary sample point X of the same image. y: Ratio of the number of recorded unit pixels to the number of unit pixels constituting the pixel block Y corresponding to the X on the recorded image to be formed. y_h; Ratio of the number of recorded unit pixels to the number of unit pixels constituting the pixel block, set for the pixel block of the brightest portion H of the recorded image to be formed. y_s; Ratio of the number of recorded unit pixels to the number of unit pixels constituting the pixel block, set for the pixel block of the darkest part S of the recorded image to be formed. α: Reflectance of recording sheet. β: Surface reflectance of recording material (toner, etc.). k; Represents the ratio of (density range of the recorded image to be formed)/(density range of the original image). 3. For recording pixels on a recording sheet, a latent image representing the distribution of the pixels is formed by scanning a laser beam on an image forming member having a uniformly charged photoconductive layer, and the latent image is 3. The image forming apparatus according to claim 1, wherein the image is developed with toner, transferred onto a recording sheet, and further fixed. 4. A series of operations or a part thereof of forming a latent image on the image forming body, developing it with toner, and transferring it to a recording sheet is performed using toner of a specific color, and the same operation is performed using toner of a different color. 3. A color image is formed by repeating the same operation for the required number of colors, aligning and transferring onto the same recording sheet, and then fixing.
The image forming apparatus described in . 5. To record pixels on a recording sheet, a voltage is applied to a large number of recording electrodes arranged in a direction perpendicular to the moving direction of an electrostatic recording body to create an electrostatic latent on the electrostatic recording body. 3. The image forming apparatus according to claim 1, wherein an image is formed, the latent image is developed with toner, and then transferred onto a recording sheet and further fixed. 6. Forming a latent image on the electrostatic recording material, developing with toner,
Perform a series of operations or part of the operation of transferring to a recording sheet using toner of a specific color, then perform the same operation using toner of a different color, and then repeat the same operation for the required number of colors to transfer to the same recording sheet. 6. The image forming apparatus according to claim 5, wherein a color image is formed by aligning the image, transferring the image, and then fixing the image.