JPH02165977A - Laser beam printer - Google Patents

Abstract

PURPOSE:To form a recording picture excellent in the reproducibility of gradation by converting and processing the basic density value of an arbitrary sample point on an original picture based on a picture information signal into a picture-element density value at a position corresponding to the sample point of the recording picture formed by specific relational formula in a gradation adjusting mechanism. CONSTITUTION:In a laser beam printer, a picture information signal acquired from an original picture is processed by a gradation adjusting mechanism, and a recording picture corresponding to the original picture is formed onto recording paper on the basis of the signal. The gradation adjusting mechanism converts and processes a basic density value (x) (the difference of density difference at a sample point and a density value in a lightest section H on the original picture) at the arbitrary sample point on the original picture based on the picture information signal obtained from the original picture into a picture-element density value (y) at a position corresponding to the sample point of the recording picture shaped by formula (I). Where yH, yS in formula (I) are set to the pictures of the lightest section H and darkest section S of the recording picture formed. (y) represents the picture-element density value in desired size, alphathe reflectivity of recording paper, beta beta=10<-gamma>, (h) a numerical value acquired by gamma/(an original picture density region) and gamma an arbitrary coefficient respectively.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention converts image information signals obtained from original images using a new gradation adjustment method to form recorded images with excellent gradation reproducibility. Regarding laser beam printers that can be used.

More specifically, the present invention can reproduce various original images (continuous tone images such as monochrome or color photographs, video images obtained from television or computer video signals, etc.) to be reproduced on recording paper. The image information signal obtained from (all inclusive, the same shall apply hereinafter) is converted using a gradation adjustment mechanism using a new gradation conversion formula,
The present invention relates to a laser beam printer that can form a recorded image on recording paper based on this gradation-converted output signal.

(Prior art) When copying an image from a continuous tone original image such as a photograph onto a recording sheet using an image forming device such as a copying machine, analog processing of the original is required when photosensitive paper is used as the recording sheet. By (exposure), an image having continuous gradations corresponding to the original is formed (silver halide photographic recording). On the other hand, laser beam printers that record images on plain paper rather than photosensitive paper cannot form images using analog processing, and are difficult to reproduce density gradations, especially for color image reproduction. In this case, it is not easy to adjust the color tone (color balance) as well as the density gradation described above.

For this reason, many efforts are being made to improve the reproducibility of gradations and color tones in printer devices. Formation of recorded images in laser beam printers.

Similar to the method of converting continuous gradation to halftone gradation in photolithography in printing, the image information signal obtained by photoelectric scanning of a continuous gradation original image such as a photograph is processed, and the signal is used to convert the original The purpose is to form an image on recording paper consisting of a distribution of pixels with gradation and color tone corresponding to the image.

However, current printer devices use unscientific tone adjustment methods for processing image information signals obtained from original images to reproduce tone.

At present, satisfactory gradation reproducibility has not been achieved.

As is well known, the density gradation of a recorded image depends on the pixel density display method. In the case of laser beam printers, two methods are used to display pixel density gradation: one is to change the pixel coverage by changing the size of the dot (size modulation method), and the other is to change the pixel coverage by a specified number of dots (of the same size). There is a method of changing the density (density modulation method). However, when copying an original image using a laser beam printer, the coverage rate of pixels on the recorded image corresponding to the density value of a predetermined sample point on the original image, that is, the density gradation of the pixel. What the pixel density value (hereinafter simply referred to as the pixel density value) should be, and how to obtain such a pixel density value.

No scientific study has been conducted.

In other words, a scientific correlation formula is used to determine what pixel density value should be correlated to the density value of a predetermined sample point on the original image and the pixel on the recorded image corresponding to the sample point. has not been developed, and currently, these equipment manufacturers have no choice but to rely on what they have determined in advance based on experience, intuition, or a limited number of fixed conditions.

As a result, originals with image quality that equipment manufacturers did not expect,
For example, in the case of a color film original that is non-standard (an overexposed original that is too bright, an underexposed original that is too dark, etc.), it is difficult to obtain a desired recorded image with excellent gradation and color tone. Therefore, recorded images of the desired quality can be obtained not only from originals with standard image quality but also from non-standard originals mentioned above, and the image quality of the original can be arbitrarily changed or modified (changes in gradation or color tone, corrections etc.). ), it has not been possible to develop a flexible laser beam printer that can do this.

This means that conventional laser beam printers are unable to scientifically make pixel density values correspond to the density values of predetermined sample points on the original image.

(Problem to be Solved by the Invention) The cause of the above-mentioned problems in conventional printer devices is that when forming a recorded image based on the final pixel distribution from an original image such as a continuous tone image, the initial The concept lies in the process of image gradation conversion, which plays an important role at this stage.

That is, when converting the density value of a predetermined sample point on the original image into the pixel density value of the corresponding pixel on the recorded image.

The conventional way of thinking about gradation conversion was not that ``it must be done based on scientifically rational gradation conversion means,'' but that it relied solely on experience and intuition.

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 Problem m1) To summarize the present invention, the present invention processes an image information signal obtained from an original image using a gradation adjustment mechanism, and forms an original image on recording paper based on the processed signal. In a laser beam printer for forming a recorded image corresponding to
The difference between the density value at the sample point and the density value at the brightest part H on the same image) is expressed as follows: The present invention relates to a laser beam printer characterized in that conversion processing is carried out according to the following equation.

Relational expression ...■ The configuration of the present invention will be explained in detail below.

In a recorded image formed by a laser beam printer, the basic component of the recorded image is the density value at one pixel (this is determined by the number and size of dots in the pixel on the recorded image formed as described above). These two factors are the surface reflection density of the image forming material (toner) and the surface reflection density of the image-forming material (toner). As can be seen from the fact that it has the ability to be easily identified as a density difference, the pixel density value, which has the same relationship as the size of the halftone dot area, plays an extremely important role as an image forming means. In other words, if we focus on a certain dot and examine the effects that changes in the amount of toner applied on that dot and changes in the size of the dot have on the gradation, we find that the latter is much larger, and the pixel How the concentration value should be set is an extremely important issue.

Further, in connection with the above, when a recorded image is to be formed using a laser beam printer, the quality of the original image varies widely; and 5. the image forming process also has various characteristics.

Furthermore, there is a background that 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 with halftones using a laser beam printer, the pixel density value (νH) of the pixel block in the brightest area (H) and the darkest area ( The pixel density value (νS) of the pixel block 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 adjusted and managed. It is absolutely necessary to provide a means to do so.

The gradation adjustment method of the present invention was devised based on this idea, specifically, the gradation adjustment method defined by the above-mentioned <Relational Expression 0>.

First, the process of deriving the above-mentioned relational expression (2) will be explained.

The present inventors believe that when creating a halftone print image etc. from a continuous tone color film original, 1) the tone is rationally converted (conversion from continuous tone to halftone tone). For this reason, we previously proposed a gradation conversion formula that is the predecessor of the above-mentioned relational formula (2). (Patent Application No. 148912/1983, Patent Application No. 1983-2)
(See No. 590).

The gradation conversion formula (hereinafter referred to as relational formula 〇〉) proposed earlier by the present inventors is useful not only for creating printed images, but also for various types of reproduced images, such as the creation of recorded images using the laser beam printer according to the present invention. Although it can also be used when creating a print image, the explanation will be limited to the creation of a print image as shown below.

Comparing the relational expression 〇〉 ...■ The relational expression ■〉 and the relational expression ■〉 show that the meanings of β values and 4 values are different, and the relational expression ■〉 does not specify the γ value. Although these differences will be described later, the process of deriving the relational expression 〇〉 will be explained to help understand the present invention.

The relational expression (2) for determining the numerical value (y) of the halftone dot area percentage used in creating the above-mentioned printed image is derived from the generally recognized density formula (photographic density, optical density).

When this general formula regarding density is applied to plate making and printing, it becomes as follows.

The relational formula ■〉 is the density formula (D') related to platemaking and printing.
In addition, it is possible to arbitrarily set halftone dots of a desired size in the H and 8 parts of the printed image, and the basic density value (1) at an arbitrary sample point on the continuous tone image and this Incorporating the requirement to reasonably relate the value (y) of the halftone area percentage of the halftone dot at the sample point on the halftone gradation image corresponding to the halftone image, and guide the theoretical value and the measured value to approximately match. This is what I did.

When applying the above relational expression 〇〉 to the image gradation conversion method when creating a printed image, the reflectance (α) of the printing paper,
Surface reflectance (β) of printing ink and printed image density range/
Based on the value of the original image density area ratio (A), determine the size of halftone dots (y
While arbitrarily selecting u * ys), calculate the value of the halftone dot area percentage of the halftone dot at the corresponding sample point (Y) on the printed image from the basic density value (1) of an arbitrary sample point (X) on the original image. It is operated to find (ν). As a result, the density gradation of the original image (continuous gradation image) can be faithfully reproduced on the printed image (halftone gradation image) in a 1:1 ratio.

In addition, multicolor plate making (generally cyan (C), magenta (M),
In the case of four plates (yellow (Y) and black (BL), which are considered to be one set), the standard plate (in the case of multicolor plate making, as is well known, the cyan plate (C) is the standard plate. ), i.e., the halftone gradation characteristic curve that is the standard for converting the density information value of the original image into the halftone area value of the printed image (obtained by graphing the above-mentioned work value and (This is a curve that serves as the basis for converting continuous tone to halftone.)
Once determined, the working standard characteristic curves for other color plates are determined.

It can always be determined rationally by multiplying the standard value of the plate by an appropriate adjustment value based on the gray balance ratio of each color of printing ink.

It goes without saying that the working standard characteristic curves for each color plate determined in this way are each reasonable characteristic curves, and furthermore, the interrelationships in terms of gradation and color tone between those characteristic curves are also rational. and appropriate.

In other words, when creating a halftone print image from a continuous tone original image, if the tone conversion is performed based on the above-mentioned relational expression (2), it is easier to create an image that relies on conventional experience and intuition. Breaking away from the gradation conversion method, it is possible to arbitrarily and rationally convert the gradation of an image, and it is also possible to rationally adjust the color tone, which is closely and inseparably related to the gradation.

As a result, it is possible to obtain a printed image having a density gradient and color tone that are natural to the human visual sense π. The above is the content previously proposed by the present inventors.

However, in subsequent research, the above-mentioned relational formula ■〉
It has been found that there are certain limitations in the operation of

Its limitations are: - It is extremely effective if the original image is of standard quality, but it is of non-standard quality.

In particular, it cannot adequately deal with extremely poor quality content (for example, over- or under-exposure during photographing).

This will be explained from the point of view of the operation of the above-mentioned relational expression (■).

- In the case of a standard quality document (standard manuscript), the molecule that determines the four values is the solid print density value of yellow ink, which has a large stimulation value among printing inks (the typical density value is 0.9 to 1. 0
It is. ) when performing gradation conversion (when performing multicolor plate making).

The 0 version is produced using this value. ), although it is extremely effective, it is not fully satisfactory, especially for non-standard manuscripts with poor quality content as described above. - When dealing with non-standard manuscripts in terms of β value.

Printing ink (as mentioned above, yellow ink is the standard.

) and other numerical values may not be fully satisfactory.

In order to overcome the above-mentioned limitations, it is necessary to make the halftone gradation characteristic curve, which serves as the work standard for gradation conversion, applicable not only to standard manuscripts but also to non-standard manuscripts, and the shape of the curve can be rationally arbitrary. It must be possible to change the
As a result of studies, the present inventors have found that satisfactory results can be obtained when gradation conversion is performed under the following conditions.

- Completion value = γ/ ([density range value of striped image]) - γ value = any positive or negative value - β value: A value determined from the γ value that defines the above A value by β = 10.

By applying the above-mentioned relational formula (■) under the above conditions, it is possible to create printed images with excellent reproducibility of density gradation and inseparable color tones from standard and non-standard originals. can.

The above explanation has centered on the creation of printed images with halftone gradations, but it goes without saying that the theory that supports the gradation conversion work described above can also be applied to the creation of recorded images using laser beam printers. There is no such thing.

It goes without saying that the gradation conversion formula suitable for creating a recorded image using a laser beam printer becomes the relational formula 〇〉 by incorporating and rearranging the above-mentioned study results.

Next, the meaning of each term of the above-mentioned relational expression (2) of the present invention, the operational characteristics, etc. will be explained.

In the application of the above-mentioned relational expression (〇〉) of the present invention, the basic density value (1) must be found from the image information signal of the original image. The density information value may be any value as long as it reflects the physical quantity related to the density of each pixel of the original image, and should be interpreted in the broadest sense. Synonymous terms include reflection density, transmission density, brightness, light amount, current/voltage value, etc. These density information values may be extracted as density information signals by photoelectrically scanning the original image.

In addition, in the above <Relational Expression (2)> of the present invention, the basic density value (1) is measured using a value using a densitometer (for example, a portrait on a positive color film having a density value of 0°2 to 2.70). etc.), also? H [Brightest part (H)
The pixel density value set for the pixel block and ys [
Pixel density value set for the pixel block of the darkest part (S)]
A percentage value (for example, 5% or 95%).

), ? [The pixel density value recorded in the pixel block (Y) corresponding to an arbitrary sample point (X) on the original image is calculated as a percentage value.

In the operation of the above-mentioned relational expression (■) of the present invention, it is possible not only to modify and use it as follows, but also to use it by any processing, modification,
You are also free to use it as a guide.

"t = Vl(+E (1-bo'x)(ys=
yo) In the above modification, α=1. This is based on the surface reflectance of the recording paper (base material) being 100%. In practice, the value of α may be set to 1.0.

Further, according to the modification (α=1.0), Vl1 is applied to the brightest part H on the recorded image by the laser beam printer.
It is possible to set fs in the darkest part S as planned. This means that in the brightest part H on the recorded image,
In addition, in the darkest part S, the density area of the original image is satisfied.

It is clear from the fact that −(Equation = −γ).

In the operation of the above relational expression 〇〉 of the present invention, at tλ, α.

The numerical values of β and γ (the β value is defined by β=10 as described above) take various values. In the present invention, by appropriately selecting these values, it is possible to rationally perform image gradation conversion processing regardless of the quality characteristics of the original image.

That is, the image gradation conversion processing method based on the above-mentioned relational expression (■) of the present invention reproduces the gradation and color tone of a 1M original image, that is, reproduces the tone of the original image in a 1:1 ratio to the recorded image. However, its usefulness is not limited to this. In addition to faithfully reproducing the characteristics of the original image, the above-mentioned relational expression 〇〉 of the present invention can be applied to α, β, γ values, and even ? □.

This is extremely useful for rationally changing or modifying the characteristics of an original image by appropriately selecting the Vs value.

To explain this in detail, when applying the above relational expression ■〉,
It should be noted that users (workers) have the following degrees of freedom.

Bad point 1: Use the relational expression 〇〉 for the purpose of forming an image that is faithful to the original image, that is, to obtain an image that has exactly the same visual sensation when viewed with the human eye. In the present invention, this tone adjustment attitude is explained by the term "(>Wl tone (of) conversion of an image)" .

Shit 2: 〈Relational Expression 〇〉 is based on the technical necessity of image formation and artistic request.

Or, based on the needs of the ordering side, etc. To change or modify the striped image , i.e., with the human eye. The visual and sensory image when you sense Wt. has itself been modified or changed. The first priority is to obtain the desired results.

In the present invention, the use of the relational expression 〇〉 and the attitude of such gradation adjustment are explained using the term "(image) floor 11J () modification (or change)."

When forming a multicolor image using the above <Relational Expression ■> 1
For example, when copying a color original using a laser beam printer, color separation, which is well known in the printing field, is used to separate the reflected light from the color original into blue (B), green CG), and red (R). It is sufficient to obtain the density information signal for each image, process it with a gradation adjustment mechanism using the above-mentioned relational expression (2), and form an image based on this processed information. In that case, the standard color plate (e.g. 6th plate)
Regarding? value, that is, the gradation characteristic curve (γ
By calculating the value and plotting the γ value against the work value,
A tone characteristic curve similar to the halftone tone characteristic curve in printing technology is obtained. ) and other color versions (M version, Y version)
These gradation characteristic curves can be reasonably determined by multiplying the γ value of the reference color plate by an appropriate adjustment value based on the gray balance ratio of each ink. All you have to do is form an image using .

What about each color version determined as described above? The values, ie, the tone characteristic curves for each color plate, are:

Since it is defined by the relational expression (2), it is a reasonable characteristic curve, and the interrelationships between these characteristic curves in terms of gradation and color tone are also reasonable and appropriate.

As explained above, when a recorded image is formed using a laser beam printer, the gradation can be adjusted by incorporating hardware or software that performs gradation conversion based on the above-mentioned <Relational Expression ■> into the gradation adjustment mechanism section. In addition, it is possible to obtain a recorded image with excellent color tone reproduction, or a recorded image in which the image quality of the original image is arbitrarily corrected or changed.

Hereinafter, the present invention will be explained in more detail based on Examples, but the present invention is not limited to these Examples unless the gist of the present invention is exceeded.

As described above, the present invention has the greatest feature in that the gradation is converted in accordance with <Relational Expression (1)> in the gradation adjustment mechanism section of the laser beam printer. Therefore,
I will explain how to use the relational expression 〇〉 in detail, starting with the handling of the γ value.

(Example) ■ Regarding the method for determining the γ value adopted in the relational expression (υ).

The main feature of the present invention is that when a recorded image is formed by a laser beam printer, the core gradation conversion work in the process of creating the recorded image is performed based on the above-mentioned relational expression (■). .

In this case, it is desirable to create an image of the same quality as a recorded image formed from a standard original whose quality content is standard, even from original images that vary in quality such as brightness or darkness. Of course.

To achieve this, we must be independent of the quality of the original image.

It is necessary to obtain a gradation characteristic curve that defines the relationship between the process value and the γ value that provides a recorded image of the same quality as that obtained from a standard original. In the relational expression of the present invention, the shape of the gradation characteristic curve can be changed greatly because γ
It is a value.

Below, a method for determining the γ value, which has extremely important significance in the operation of <Relational Expression 0>, will be explained. By rationally determining this γ value, the laser beam printer of the present invention can
For the first time, recorded images with excellent gradation and color tone reproducibility can be formed.

Table 1 shows how the γ value (that is, pixel density value) changes with respect to various γ values. Table 1 shows that while changing the γ value (γ
Value = 2.00 to -0.20), the above relational expression ■
〉, ν□=3%y? 5=95%, α=i, oo, β
=io, <=γ/(density range value of original image)=γ/ (2
, 8-0, 2) at each density step (Table 1 divides the density range of the original image into 9 steps). According to Table 1, when the γ value is changed, individual gradation characteristic curves corresponding to each change can be obtained.

Therefore, it is sufficient to perform gradation conversion by setting the optimum quality based on the quality content of a given original image. The results in Table 1 are illustrated in FIG.

Therefore, when a document image with predetermined quality content is given, the optimal γ value to be adopted can be calculated using the following relational expression
The problem is how to make a rational decision.

We used monochrome and color films, which are said to have particularly faithful reproduction of gradations and tones, as original images, and established a method for determining the γ value to be adopted according to the image quality of the original. do. This is because if a method for determining the γ value that is very effective for monochrome and color film originals with high gradation reproducibility is established, it will be useful for other original images as well. .

A detailed analysis of the image quality of the original color film revealed that
The image quality, such as high-key (photographed with overexposure) and low-key (photographed with underexposure), is vastly different compared to a standard color film original photographed with standard exposure. be. However, the difference in image quality of color film originals is because the difference in exposure directly affects the brightest density value Hn of the original.
By focusing on this point, it is possible to define it objectively.

Then, as the inventors proposed earlier, the standard manuscript (
In case of proper exposure,), the γ value is 0.9~
Considering that it takes a value of 1.0, it is sufficient to find the correlation between Hn and γ.6 The reason for choosing Hn is that the density region near the brightest part is important in tone reproduction. This is because. It goes without saying that theoretically, the darkest part density value Sn of the document may be selected.

Therefore, we conducted an experiment to form recorded images of excellent image quality using various color film originals and to determine the relationship between Hn and γ value. Experimental data are shown in Table 2.

In addition, in Table 2, experiment Nα2 is from the standard manuscript,
0.9 was adopted as the γ value.

Table 2 (Note) Hn and Sn indicate the brightest and darkest density values of a given individual color film original.

From these experiments, the γ value can be reasonably determined by the following formula.

(i) γ in Table 2. When the relationship between and Hn is graphed as shown in Figure 2 (total logarithmic graph).

γ. is determined by the formula below.

γn=γ0±l I)1 l tana(ii)
In addition, standard manuscripts (density range 0.20 to 2.80) are γ.

= 1.00, and an experiment was conducted to obtain recorded images of the same quality from various color film originals. As a result, γ. The relationship between and Hn could be defined as follows.

(B) γr+”1,70 2.2961 (12ogH
n+ 1 ) (Relational expression obtained when γ. and Hn are both displayed on a logarithmic scale) % formula %) (Relational expression obtained when γ. is expressed on a normal scale and Hn is expressed on a logarithmic scale) The above Therefore, in order to reproduce a recorded image with excellent gradation reproducibility using a laser beam printer from an original image with a wide variety of quality contents, first, the γ value is calculated from the Hn value of the original image.
. It is only necessary to determine this, then use it as the γ value of the relational expression (2), and perform the gradation conversion process.

In the gradation adjustment mechanism of the laser beam printer, in order to operate the relational expression 〇〉 based on the γ value determined as described above, it is necessary to measure Ho of various original images in the laser beam printer device. A mechanism for calculating the γ value from Hn may be added. Alternatively, these measurements and calculations may be left to the operator.

■ Fixation (constantization) of the γ value adopted in <Relational expression 〇>
Regarding the method for determining the above-mentioned relational expression (■) of the present invention, the method for determining the γ value described above is complicated, and the recorded image created by this method is, strictly speaking, the recorded image obtained from a standard manuscript. There is a difference between This is natural because the brightest density value (Hn) of the color film original is different from the brightest density value (Ho) of the standard document.

As explained earlier, in the relational formula (■) useful for gradation conversion of standard originals, when γ=0.9 (or a value between 0.9 and 1.0), not only gradation but also color tones can be reproduced. It is possible to create duplicate images with excellent quality. Therefore, the relational expression 〉
In this operation, in order to set the value of γ to a constant such as γ=0.9, the density gradation of the original image must be adjusted (corrected) to the density gradation of the standard image. Below, γ
We will explain how to convert a value into a constant.

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

As is well known, the relationship between the exposure amount (X) of the color film sensitive material (note that it is different from X of the sample point X mentioned above) and the color film density (D) at that time is shown in Figure 3. This is as shown in the basic concentration characteristic curve.

The standard document and the non-standard document depend on whether the exposure amount is appropriate or not, and each density characteristic curve is shown as having a specific range on the basic density characteristic curve. In fig.

The former is shown as a standard density characteristic curve, and the latter is shown as an individual density characteristic curve (note that an underexposed one is shown as a non-standard original in Fig. 3). Adjustment to the density characteristics of a standard original can be made extremely easily by converting the basic density characteristics curve into a function.

The basic concentration characteristic curve described above is defined by the function D=fo(X), as shown in Table 3 below (Table 3 also shows the inverse function).

Note that the method of converting the basic concentration characteristic curve into a function in Table 3 should be understood as an example, and a more simplified formula may be used.

(Leaving space below) Table 3 (Example of function representation of basic concentration characteristic curve) (Note) In the basic concentration characteristic curve shown in Figure 3, the function f o (X) for determining X→D is its inverse function. A function f x (D) for determining D−+X is shown.

(Note) In order to faithfully define the basic concentration characteristic curve, it is expressed mathematically for each domain of X or D.

The following procedure can be used to match the individual density characteristic curve of a color original to the standard density characteristic curve (see Figure 3).
.

(i) Density values of H and S of a color original image and the basic density characteristic curve of the color film sensitive material of the color original (D = f
o(X)), define the individual density characteristic curve of the color original image, and (ii) define the density value DH of the color original.
Substituting n ”” D sn into X='fx(D),
The value range of the color original image on the X-axis, xHn"xsn, is determined, and (iii) this is matched with the value range on the X-axis, XH0 to X5o, of the density characteristic curve based on the reference. (iv) Next, the reference density characteristic curve is determined. Find the value range of the D axis, DHo~OSO.

It goes without saying that if the individual density characteristic curve of a color document matches the reference density characteristic curve, matching of the two is unnecessary.

It is also possible to set an arbitrary tolerance range for the reference density characteristic curve, and perform image processing by assuming that the curve is the same as the reference density characteristic curve when it is within the tolerance range.

In the matching procedure of the individual and reference concentration characteristic curves described above,
Since it is normal that XR, (exposure range for standard originals) and XRn (exposure range for non-standard color-based originals) do not match, it is necessary to match XRnt & XRO゛ (as described above). (See steps (ii) and (fit).) To match XR to There is proportional matching (an attitude of matching both the brightest density value and the darkest density value). In FIG. 3, the case of mathematical proportional matching is shown.

As shown in FIG. 3, the density information value of one individual density characteristic curve (density information value between Din"Dsn, Dn) is substituted into the basic density characteristic curve D=fo(X), and XRn is obtained.
The density information value of the color original (density information value between Doo and DSo, Do) is obtained by adjusting the X value adjusted to XRo, but the X value after adjusting XRn to XR, The relational expression for determining the value can be obtained by simple calculation as follows.

■ For simple alignment: X = fx (Dn) ± 1ml ■ For proportional alignment, m: Required parallel movement amount XR,: Exposure amount range of the standard density characteristic curve of the standard original on the X-axis Exposure range of individual density characteristics of non-standard individual originals Color film originals with standard image quality (DH0=
0.20. Ds0=2.80), high key (overexposed) CDon=0-10+ Dsn=2.70)
, and a low-key (underexposed) one (D on =
0.60 tDs, = 3°20), the matching data when matching the individual concentration characteristic curve to the standard concentration characteristic curve based on the basic concentration characteristic curve shown in Table 3 is shown in Table 4 below. Shown below.

(Left below) In the alignment experiment described above, the density range (D R) of the three color film originals used was all 2.60, so it was decided to use simple alignment for one and proportional alignment for the others. .

In the density values of Dn and Do in Table 4 above, the ν value (pixel density value) is determined by the relational expression based on Do.

%) was calculated. The results are shown in Table 5. Also, V in Table 5
FIG. 4 shows the correlation between the Dn value and the Dn value. The curve shown in FIG. 4 is a gradation characteristic curve that defines the correlation between the X value and the ν value, which makes it possible to create a recorded image with excellent gradation reproducibility from a non-standard quality original image.

(Left below) Table 5 (Tone characteristic curve setting data) In the tone adjustment mechanism of a laser beam printer,
In order to fix (make constant) the γ value in relational expression (1) and operate it, a mechanism for measuring the density of the original image (measuring density across H, S, and H-3) must be installed in the laser beam printer device. ), it is necessary to incorporate software and hardware that matches the individual density characteristic curve of the original image with the standard density characteristic curve, but this makes it possible to create recorded images with excellent gradation and color tones from originals of any quality content. can.

(1) Regarding the laser beam printer device The laser beam printer device of the present invention will be explained below based on the drawings.

FIG. 5(a) is a block diagram showing a schematic configuration of a laser beam printer of the present invention.

In the figure, the image processing unit (20) has the relational expression 〇〉 of the present invention.
A gradation adjustment mechanism with an algorithm is built in, and the rest is based on existing ones such as a shading correction circuit, γ
Correction circuit, masking processing circuit.

It is composed of a UCR processing circuit, a dither processing circuit, a multi-value processing circuit, etc.

When the original image is in color, the relational expressions 〉 for Y, M, and C are applied to correspond to each halftone based on the well-known dither matrix method. A dot pattern as shown in FIG. 2(b) is output.

Image information signals such as TV images are gradation-converted according to the relational expression (1) of the image processing section (20), and then sent to the laser tube (L
), and a recorded image with good gradation reproducibility is developed on recording paper through a photosensitive drum and a transfer drum using well-known electrophotographic techniques.

FIG. 6 is a block diagram of a laser beam printer according to a first embodiment of the present invention. as an image signal.

The image obtained by photoelectric scanning is used.

As shown in FIG. 5, the laser beam printer of the present invention converts the transmitted light or reflected light of the original image into R (red),
A detection unit 1 separates the spectroscopy into G (green) and B (blue) and reads it, and the output signal of the detection unit 1 is divided into Y (yellow) and 2M (
magenta), C (cyan).

a color separation unit 2 that converts into a K (black) color separation signal;
A gradation adjustment unit 3 that processes the color separation signal using the above-mentioned relational expression of the present invention so that an appropriate gradation image is formed.
and (2) an output section 4 which exposes the photosensitive drum with a laser modulated based on the output signal of the gradation adjustment section 3 to form a latent image.

Here, the detection unit 1 includes a photomultiplier or a solid-state image sensor (CCD).
), etc., detects transmitted light or reflected light from each part of the original 5, outputs R, G, and B-USM signals as fl flow values, and converts these signals into voltage signals in the A/V converter 6. do.

In the log amplifier 7, the color separation unit 2 has R,
The voltage signals of G, B, and USM are converted into density by logarithmic operation, and the black (K) component is separated from this density in basic masking (BM) 8, and then the Y, M,
Separate each component of C. Next, color correction (CC)
) unit 9 controls the Y component 2 open component and C component for each original color of R, G, B, Y, M, C, and further controls the black component of the original to the UCR/UCA unit 10.
R (under color removal) or UCA (under color addition)
In n), the ratio expressed by three types of ink, Y, M, and C, and the ratio expressed by K (black ink) are determined.

These Y, M.

After the C and C components are obtained, the gradation adjustment section 11 obtains the Y and M components.

ye'*me' indicating the pixel density value in the pixel block of each color component from C and K, that is, the effective area ratio of each color component
, ce', ke'. Gradation adjustment section 1
1 has the algorithm of <Relational Expression ■> inside, and Y.

Applying the relational expression 〇〉 for each of M, C, and calculating the above-mentioned ye', ms', ce', and ke' - The gradation adjustment unit 11 has the algorithm of the relational expression 〇〉 as software. In addition, a general-purpose computer has an A/D and D/A I/F (interface), an electric circuit that uses the algorithm as logic and is realized by a general-purpose IC, and an R that holds the calculation results of the algorithm.
Electric circuits including OM, PAL that embodies algorithms as internal logic, gate arrays, custom ICs, etc. 4
It can take various forms.

The effective area ratio corresponding to the color density information of each color component obtained by the gradation adjustment section 11 is determined by the color channel selector 12.
and the color channel selector 12 selects ye'
, me', ce', and ke' are output. This output is A/D converted by the A/D converter 13 and input to the dot control section 14. Thereafter, modulated laser light is emitted by the laser light source 15 according to the output of the dot control section, and an electrostatic latent image is formed on the photosensitive drum. Thereafter, the images formed by the developing machines 16a" and 16d for each color are developed on a recording paper 17 and then fixed by a fixing machine 18. Note that 19 is a charging machine for uniformly charging the photosensitive drum.

FIG. 7 is a block diagram of a laser beam printer according to a second embodiment of the present invention. Image information signal 1 such as TV signal
The signal is inputted to an adjustment unit 11' having a relational expression (2) where 0' is subtracted, subjected to one-level conversion processing, and inputted to each color layer optical system 1a to 1b through a color channel selector 12'. The laser beam modulated based on the signal outputted from the laser beam forms an electrostatic latent image having a halftone corresponding to the image information signal on each photosensitive drum 2a' to 2d', and the latent image is an electrophotographic image. The image is transferred as a color image onto the recording paper on the conveyor belt 7' by the press.

(b) Regarding the usefulness of <relational expression>.

Next, the usefulness of the relational expression (g)> applied to the gradation adjustment mechanism of the laser beam printer of the present invention will be supplementarily explained.

This is a supplementary explanation for the purpose of facilitating understanding of the present invention, and will mainly describe in detail the operation of the relational expression applied to the gradation adjustment mechanism of a laser beam printer and the significance of its results.

(a) Operational experiment of the relational expression (2) As a basic experiment for incorporating the relational expression (■) into the gradation adjustment mechanism, the following two experiments were conducted.

a) First of all, use a normal simple calculator, namely Sharp Vitagoras EL509A (manufactured by Sharp Corporation), and apply the desired numerical value to the relational expression 〇〉 while operating the simple calculator to calculate the following 6. Tone adjustment sections for images shown in Tables (2) (2), (7), and (8) were created.

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 (PC-9 manufactured by NEC Corporation)
801-M2), input the desired software obtained separately as function data, and convert the basic density value (1) of the M-stripe image (continuous tone image) to the corresponding density value (y) of the pixel on the recorded image. I worked on making adjustments.

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, there was no need to use any special software to create the above software used for adjusting the gradation of images input to the personal computer, and the work was created using the N88-BASIC that came with the personal computer. As it turned out, it only took an 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, on the manuscript image.

Set a desired density interval (for example, from 0.00 to 1.00 in 0.05 increments, and from 1.00 to 3.00 in 0.10 increments), and input the values into the personal computer. By doing so, the target pixel density value (y)
I was able to get

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

The pixel density value (y) generated by the software described above is designed to be able to output either a positive image or a negative image, either individually or simultaneously.

(b) Calculation results obtained from the relational expression 〇〉 and their usefulness Next, the usefulness of Tables 6, 7, and 8 will be explained.

[About Table 6 ■Circulation■] Table 6 shows that when a black and white image is formed from an original image using an image forming device such as a laser beam printer, the density of the toner material (in the table, it is indicated as the density range of the recorded image, This corresponds to the γ value in relational expression 〇〉) and when the usage range of the maximum pixel density value changes (0 to 100
%, 0-98%.

Three cases from 0 to 95% are shown. ) is a list of how the pixel density value (ν) at each sample point must be set in order to obtain an ideal gradation characteristic curve.

Also, from this table, even if the density of the toner material is the same (that is, even if the recorded image density range = γ value in the leftmost column of Table 1 is the same), the usage range of the maximum pixel density value You can see how the ideal gradation characteristic curve changes when you change it, and whether you need to change it.

In Table 6, the β value that determines the ε value is determined by β=10. By the way, recorded image density range = γ value = 1.0
When, i=1/(1-β)=1.1111.

Also, the value associated with one pixel density value (%) is β = 0 (ε =
1.0) is the theoretical value.

In addition, students will be able to form a black and white image using a pixel distribution corresponding to 1:1 from a manuscript image such as a continuous tone image, and to acquire Technique 1 method that can arbitrarily adjust the tone characteristics of a black and white image. is also the basis of multicolor image formation.

[About Table 7] Similar to Table 6, Table 7 shows the case where the density of the image forming material (toner) changes when forming a black and white image from a 1M draft image (i.e., recorded image density range = γ value). changes),
While the range of maximum pixel density value used is 0% to 100%, the values necessary to form an image with the same image tone and similar image quality to the human visual sense, apart from the contrast of the entire image. This is a list of pixel density values (S) at each sample point.

In other words, in the ideal case, the pixel density value (-t) of each sample point on the ideal gradation characteristic curve corresponding to the density value of the image forming material (toner) used can be viewed. This is a table.

[About Table 8] The basic conditions in Table 8 are the same as those in Table 7, but when using the maximum pixel density value range (5% to 95%), the ideal gradation characteristic curve This shows what percentage of the pixel density value (-t) should be set at each sample point.

Until today, color separation work in the creation of printed images, etc.
Color correction using masking technology
The image gradation adjustment work basically remains dependent solely on human experience and intuition, or on a limited number of fixed, given data. For this reason, it is necessary to develop a scientific gradation conversion technique when creating a duplicate image, based on the side of the image to be duplicated, such as a printed image or an image recorded by a printer.

The relational expression 〇〉 of the present invention performs gradation conversion in a rational method when creating a duplicate image.

In addition, the data in Tables 6 to 8 showing the correlation between the basic density value of the original image obtained by <Relational Expression (1)> and the pixel density value of the image to be formed is based on the color separation during image formation. It serves as a useful basic material for scientific consideration of various basic matters in work.

From each of these parts, we will discuss what the essence and principles that exist between manuscript images and color separation work are, and what attention and consideration should be given to rationally align that essence and principle with practice. It is possible to extract what must be done.

(c) Application of relational expression 〇〉 to correction (or change) of gradation Relational expression 〇〉 is used to transform the gradation of an image (i.e., the distribution of high-fidelity pixels from a continuous-tone original image). It is effective not only for converting the original image into a gradation image (by converting it into a gradation image), but also for correcting (or changing) the gradation of the original image itself. The correction (or change) of the gradation of this image is based on the intention of the orderer, the type of target image in the color document, the purpose of use of the image to be formed, the white charcoal of the recording paper, etc. However, in any case, it can be handled rationally by applying the relational formula (■), and various color separation operations can be performed. It can be standardized and standardized.

Furthermore, according to the present invention, it is possible to modify (or change) the gradation of an image in a highlight portion or a shadow portion in the same manner. This is clear from the fact that, as shown in FIG. 1, the shape of the gradation characteristic curve (the curve that defines the correlation between the engineering value and the V value) can be arbitrarily changed depending on the γ value employed. Furthermore, it has been confirmed that the gradation conversion according to the relational expression (2) of the present invention can automatically remove color fog in highlighted areas of a color original without taking any special countermeasures.

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

1) The most basic matters for image formation, the density value of the original image such as a continuous tone image and the recorded image to be formed (
In the past, determining the correlation between the pixel density value of an image (recorded by pixel distribution) was based solely on the experience and intuition of the operator, or on an irrational method based on a limited number of fixed data. It was something. On the contrary,
In the present invention, no matter how many conditions exist, this can be determined rationally based on the relational expression 〇〉. Furthermore, when converting an original image such as a continuous tone image into a recorded image based on pixel distribution, the most important requirement, gradation management (gradation conversion, correction, or change), is simply a matter of the image gradation. The present invention allows for rational management of gradation and color tone, since it has a direct and deep relationship not only with the color tone of one image but also with the color tone of one image.

In other words, the laser beam printer that incorporates the algorithm of the present invention's relational formula (■) into the gradation adjustment mechanism theoretically and rationally systematizes the one-gradation conversion work (color separation work) and simplifies the work. can be done, and the effect is extremely large.

2) By incorporating the algorithm of <Relational Expression (2)> into the gradation adjustment mechanism of a laser beam printer, the printer device can be rationalized and simplified, and manufacturing costs can be reduced. In addition, the operation is simplified and clear, the number of reworks is extremely reduced, the consumption of consumables is greatly reduced, and the performance of the laser beam printer is greatly improved. In particular, laser beam printers have the great advantage of being able to form recorded images with excellent gradation and color tone, regardless of the quality of the original image.

3) With the gradation adjustment mechanism that incorporates the algorithm of <Relational Expression ■>, it is possible to rationally and easily define the evaluation criteria for the quality of recorded images based on pixel distribution, separate from the image information of the original image. . Therefore, it is possible to rationally respond to the diversified needs of customers.

4) By adopting <Relational Expression ■>, the education and training of engineers required as printer equipment becomes more sophisticated can be effectively carried out through the operation of Relational Expression This saves unnecessary effort and frees up time for new creative development.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the γ value and the shape change of the gradation characteristic curve. Figure 2 shows γ. Figure 6, which is a correlation diagram between Hn and Hn, is
FIG. 3 is a diagram illustrating the principle of matching between an individual density characteristic curve of a color film original image and a reference density characteristic curve. FIG. 4 is a diagram showing a gradation characteristic curve set for a non-standard original. FIG. 5(a) is a block diagram showing a schematic configuration of a laser beam printer of the present invention. FIG. 5(b) is an explanatory diagram of the dither matrix. FIG. 6 is a block diagram of a laser beam printer according to a first embodiment of the present invention. FIG. 7 is a block diagram of a laser beam printer according to a second embodiment of the present invention. Patent Applicant Yamatoya Shokai Co., Ltd. Representative Patent Attorney Yoshio Mizuno Figure 1 Relationship between γ value and shape change of gradation characteristic curve (7': -
0.20~2.00) Figure (gradation characteristic curve) Continuous tone density step (a) (b) Figure

Claims (1)

[Claims] 1. An image information signal obtained from an original image is processed by a gradation adjustment mechanism, and a recorded image having halftones of one color or multiple colors is formed on recording paper based on the processed signal. In a laser beam printer that uses density value) to a pixel density value (y) at a position corresponding to the sample point of the recorded image to be formed, according to the following <Relational Expression (1)>. laser beam printer. <Relational expressions> ▲There are mathematical formulas, chemical formulas, tables, etc.▼ [However, x: the basic concentration value of any sample point X on the original image, that is,
Density value y 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: pixel density value of the position Y corresponding to the above-mentioned X on the recorded image to be formed. y_H: A pixel density value of a desired size that is set for a pixel in the brightest part H of the recorded image to be formed. y_S: A pixel density value of a desired size, which is set for the pixel in the darkest part S of the recorded image to be formed. α: Reflectance of recording paper. β: Numerical value determined by β=10^-^γ. k: Numerical value determined by γ/(density range of original image). γ: arbitrary coefficient. respectively. ] 2. 2. The laser beam printer according to claim 1, wherein the image information signal is obtained by photoelectric scanning or a solid-state image sensor. 3. The laser beam printer according to claim 1, wherein the image information signal is a video signal. 4. The laser beam printer according to any one of claims 1 to 3, wherein the recorded image having multicolor halftones is obtained by a plurality of developing sections provided on a single recording drum. . 5. The laser beam printer according to claim 1, wherein the recorded image having multicolor halftones is obtained by each developing section provided on a plurality of recording drums.