JPH1188695A - Image-forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copy image improved in the reproducibility of gradation by adopting an image information value which is correlated with the quantity of light as the image information value of an original image to be adopted at the time of gradation conversion. SOLUTION: An image information detecting part 1 is constituted, so as to maintain the linearity of an input image information value and an output image information value. The image information detecting part 1 detects an image information value Dn , correlated with the density of an original information 5 recorded on a recording medium having a prescribed characteristic curve (characteristic curve specifying the correlation between the image information value Dn correlated to density and an image information value Xn correlated to a quantity of light). Then, this image information value Dn is converted into the image information value Xn correlated to the quantity of light, while utilizing the characteristic curve of the record medium. A gradation control part 3 of an image-forming device converts the image information value Xn correlated to the quantity of light inputted to the recording medium for recording the original image 5 through a prescribed gradation conversion expression to a gradation strength value for the gradation control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method capable of converting an image information signal obtained from a document image by a novel gradation conversion method to form a duplicate image having excellent gradation reproducibility. Related to the device.

More specifically, the present invention relates to various types of original images (in the present invention, the meaning of the original image should be interpreted in the broadest sense, and will be reproduced on various image expression media such as recording paper, CRT, and liquid crystal. Is the target.
Therefore, it should be noted that the concept of a document which is generally used in copying, copying, and the like is wider, and a subject such as a still life or a person, and an object to be photographed are also targets. ), A true image information value is obtained from the original image, and this is converted under a gradation adjustment mechanism using a specific gradation conversion formula. Image forming apparatus capable of forming a duplicated image having excellent reproducibility of gradation and color tone on an image expressing medium such as recording paper based on the output signal (in the present invention, the meaning of the image forming apparatus is broadly defined) Should be interpreted, copying equipment, printer equipment, prepress equipment, image transmission equipment, TV shooting equipment,
All devices having a function of producing a duplicate image, such as an electronic camera device, are applicable. ).

More specifically, the present invention relates to a method for producing a duplicate image from an original image, wherein an image information detecting section of an image forming apparatus (such as a photomultiplier, a CCD or a two-dimensional CCD, a photodiode, etc. The image information value for producing a duplicate image is obtained in (i) .Image information deterioration (based on the characteristics of the photoelectric conversion element of the image information detection unit). In order to eliminate (deterioration), linearity (linearization, liniarization) of the image information detection unit is ensured, and (ii) image information values (hereinafter described) correlated with density in the detection unit as in the related art. As such, this term should be interpreted in the broadest sense, and may simply be referred to as density information value.) Instead of obtaining the original image on the recording medium on which the original image is recorded, To obtain an image information value that is correlated to the amount of incident light, and then (iii).
The present invention relates to a completely new image forming apparatus having a mechanism of performing gradation conversion of an image information value correlated with the light amount according to a specific gradation conversion formula.

[0004]

2. Description of the Related Art Various types of printers and copying machines for digitally copying or copying an image based on a color original image do not use analog processing to form an image. The reproducibility is difficult, and especially in the case of copying a color original image, the reproducibility of the color tone (color balance) as well as the density gradation is not easy. For this reason, in various image forming apparatuses, efforts have been actively made to improve the reproducibility of gradation and color tone.

[0005] The formation of a duplicate image in the image forming apparatus includes:
In the same way as the method of converting the continuous tone of photoengraving into the halftone tone in the printing field in the printing field, a density information value obtained by photoelectrically scanning an original image having continuous tone such as a photograph is processed, and the signal thereof is used. It is intended to form an image composed of a distribution of pixels having gradations and color tones corresponding to a document on an image expression medium. However, in the current image forming apparatus, a method of converting the density information value obtained from the original image from a continuous tone to a halftone tone (halftone) in order to reproduce the density tone (gradation) is non-scientific. At present, satisfactory density gradation and reproducibility of a color tone closely related thereto have not been obtained.

As is well known, the density gradation of a duplicated image depends on the pixel density display method. As a method of displaying the density gradation of such a pixel, a method of changing the pixel coverage by the size of the dot (size modulation method, variable area dot. This method is a monochrome and color scanner for producing a printed image) , A piezoelectric type ink jet, etc.), a method of changing the pixel coverage by a specified (same size) dot arrangement number (density modulation method, constant dot. This method is found in hot melt transfer, etc.), And a method of changing the density of the specified (same size) dot itself (density modulation method, variable density dot. This method is found in thermal sublimation transfer. Also, a CRT, crystal, etc., which forms an image by adjusting the luminance of pixels) TV picture tubes and the like are also included in this category.)

However, as described above, when an original image is to be copied by various conventional image forming apparatuses, the density information value of a predetermined sample point (pixel) on the original image is, for example, In the pixels on the duplicated image to be reproduced, the pixel coverage (the ratio of the number of unit pixels constituting the pixel block to be recorded) according to the size and density of the dots, that is, the density density of the pixels How is a value defining a tone (hereinafter, referred to as a pixel tone intensity value or simply a tone intensity value. This term is commonly used in the above-described methods of displaying the density tone of various pixels). At present, there is no scientific study on how to set and how to obtain such a gradation intensity value of a pixel.

That is, for a density information value of a predetermined pixel on a document image, a pixel on a duplicate image corresponding to the pixel is
No scientific correlation formula (gradation conversion formula) has been developed for what kind of pixel's gradation intensity value should be correlated. It depends on what is determined based on the prerequisites (correlation formula).

For this reason, a document image of a quality not expected by the device maker, such as a non-standard color film document (a document that is over-exposed too bright, a document that is under-exposed too dark, a high-key or low-key document, color fogging, It is extremely difficult to obtain a desired duplicate image having excellent density gradation and color tone.

Therefore, a copy image of a desired image quality can be obtained from the above-mentioned non-standard original image as well as the original image having the standard image quality, and the image quality of the original image is arbitrarily changed or corrected ( At present, it is impossible to develop a flexible image forming apparatus capable of performing density gradation and color tone change or correction).

This is because the conventional image forming apparatus converts the density information value of a predetermined pixel on a document image, which is an extremely important image information value for producing a duplicate image, into the corresponding pixel value on the duplicate image. It means that it cannot be scientifically and rationally converted to a tonal value.

[0012]

The above-mentioned problem in the conventional image forming apparatus is caused when a duplicate image based on a final pixel distribution is produced from an original image such as a continuous tone image. It is recognized that the conversion method of the density gradation of the adopted image is used.

That is, when converting the density information value of a predetermined pixel on a document image into the gradation intensity value of a pixel on a corresponding duplicated image, the conventional image gradation conversion technology is scientifically and rational. It is acknowledged that it is not something that depends solely on experience and intuition.

Under such circumstances, the present inventors have developed a rational image gradation conversion technique in order to ultimately rationalize the image forming process and produce a high-quality duplicate image. Based on the basic recognition that it must be established, he has been working diligently.

As a result, the present inventors detect (read) an image information value for producing a duplicate image from a document image as an image information value to be used in the conversion of the density gradation in the image forming apparatus. Linearization (linearization, liniariz)
image information value correlated with the density outputted under the image information detecting section in which the linearity is maintained (corrected so as to obtain the linearity) while the linearity is maintained (this will be described later). As described above, any physical quantity correlated with the concentration may be used, and should be interpreted in the broadest sense.)
Rather than using a characteristic curve of a predetermined recording medium on which a document image is recorded (a curve defining the correlation between the image information value correlated with the density and the image information value correlated with the light amount),
Obtain an image information value correlated to the light amount from the density information value,
Further, when the image information value correlated with the light amount is converted into a gradation intensity value for gradation conversion by a specific <gradation conversion formula>, not only an image characteristic faithful to the original image but also an arbitrary image It has been found that a duplicate image with modified or changed characteristics can be obtained.

According to the present invention, as described above, the technique of producing a duplicate image which emphasizes the density information value of the original image detected by the image information detecting section of the conventional image forming apparatus is improved, and a predetermined image to be duplicated is determined. A completely new duplicated image manufacturing technology that emphasizes the true image information value of the original image recorded on the recording medium, that is, the image information value correlated to the amount of light input to the recording medium for recording the original image. It is intended to provide an incorporated image forming apparatus.

[0017]

SUMMARY OF THE INVENTION In summary of the present invention,
The present invention relates to an image forming apparatus for forming a duplicate image from a document image having an image information detecting section and a gradation adjusting section, wherein (i) an image information detecting section of the image forming apparatus, (i) -1. The linearity between the input image information value (IP) and the output image information value (OP) is maintained. (I) -2. In the image information detecting section, a predetermined characteristic curve [image correlated with density] A curve defining the correlation between the information value (D _n ) and the image information value (X _n ) correlated with the light amount] is used to calculate the image information value (D _n ) correlated with the density of the original image recorded on the recording medium. Detect
And (i) -3. An image information value (D _n ) correlated with the density.
Is converted into an image information value (X _n ) correlated to the amount of light using the characteristic curve of the recording medium, and (ii) the gradation adjusting unit of the image forming apparatus is configured as described above. An image information value (X _n ) correlated with the amount of light input to the recording medium for recording the obtained document image is represented by the following <gradation conversion formula:
(1) to convert a document image to a tone intensity value (y value) for tone adjustment, thereby forming a duplicate image having excellent tone reproducibility from a document image. And an image forming apparatus. < ^Tone conversion formula (1)> y = y _H + [α (1-10− ^kx ) / (α−β)] · (y
_S− y _H ) However, in the above <gradation conversion formula (1)>, each symbol means the following. x: represents ( _{Xn- XHn} ). This is because the image information value (X _n ) correlated with the light quantity of the corresponding pixel obtained from the density information value (D _n value) of an arbitrary pixel (n point) on the original image using the characteristic curve of the recording medium. ), From the density information value (D _Hn ) of the brightest portion (H portion) on the original image, the image information value (D _Hn ) correlated with the light amount of the corresponding brightest portion (H portion) obtained by using the characteristic curve. X _Hn ). y: A gradation intensity value set for a pixel on the duplicate image corresponding to an arbitrary pixel on the original image. y _H: a preset tone intensity value that is in the brightest part of the duplicated image corresponding to the brightest portion of the document image (H section) (H unit). y _S : A gradation intensity value preset for the darkest part (S part) on the duplicate image corresponding to the darkest part (S part) on the original image. α: surface reflectance of an image expressing medium for forming a duplicate image. β: Numerical value determined by β = 10− ^γ . k: k = γ / (X _Sn −X _Hn ) where (X _Sn ) is a value obtained from the density information value (D _Sn ) of the darkest portion (S portion) on the original image using the characteristic curve. The image information value (X _Sn ) correlated with the light amount of the darkest part (S part) to be displayed. γ: arbitrary coefficient.

Hereinafter, the technical configuration and embodiments of the present invention will be described in detail. Although the present invention will be described with reference to the drawings, it is needless to say that the present invention is not limited to these drawings.

First, the theoretical background of the gradation conversion method of an image employed in the image forming apparatus of the present invention will be described, and the position of the present invention will be clarified.

The image tone conversion theory of the present invention has been developed to solve the problem of tone conversion at the time of producing a printed image, which is a particularly typical field as a technique for producing a duplicate image. As such, much is described in connection with the fabrication techniques of printed image scanners (monochrome and color scanners). However, this is for the convenience of the description, and there is a similar problem in gradation conversion in various image forming apparatuses such as printers, copiers, and DTP (desktop publishing) related devices. The value of the gradation conversion theory of the present invention, when built into these image forming apparatuses, does not reduce its value at all.

The present inventors support rational theory for the tone conversion technology of an image, and perform tone (this term is referred to as density gradation) even from an original image of various image qualities (standard or ratio standard) described above. In order to produce a duplicated image having a desired tone with a high reproducibility and a rational production of the duplicated image, two core technologies in producing the duplicated image, namely, Gradation conversion technology (gradation
control) and color correction (correction) technology (color correction)
Of these, prior to the improvement and improvement of the color correction (correction) technology, it is considered that a technology capable of rationally converting the density gradation of each pixel of the image must be primarily considered. I have.

The point described above is a color correction which is relatively easy to perform a scientific analysis (an analysis by a masking equation or a Neugebauer equation) in the production of a duplicate image as typically seen in the production of a color print image. This is a great reflection on the conventional R & D attitude of emphasizing (correcting) technology and color matching technology over image density gradation conversion technology.

The present inventors have proposed that the current image density gradation conversion technique used when creating a duplicate image from a document image uses a technique for creating a document image, for example, a print image that is a duplicate image. For a color film original (original image) recorded on a predetermined photosensitive material (recording medium), the density characteristics from the brightest part to the darkest part are not reasonably grasped, and the density characteristic of the original image is There is no reasonable theory to determine the correlation (gradation conversion formula) between the two images (original image and duplicate image), which is indispensable for converting the image into a duplicate image with 1: 1 fidelity. He has a basic understanding that he remains dependent on experience and intuition.

Under such basic recognition, the present inventors have previously proposed a specific <tone conversion formula> in order to make the image tone conversion technology scientific and rational. (JP 6
4-7770, Japanese Patent Application No. 63-114599, Japanese Patent Application No. 63-207326, U.S. Pat. No. 4,811,1
08 specification). However, in the subsequent research and development of the present inventors, the present inventors have found that there is a certain limit to the tone conversion technology of an image performed under the above-mentioned specific <tone conversion formula>. Was.

As described above, the limit item is that the true object of the duplicated image is the original image itself (in the case of photographic exposure, the subject itself). Although the true image information value that should be used should be used, in the conventional image tone conversion technology including the previous proposal of the present inventors, the image information is detected under the image information detecting unit of the image forming apparatus. That is, the tone conversion of the image is performed by using the obtained image information value, in particular, the density information value relating to the density and luminance of the original image. This depends on the photoelectric conversion characteristics of the image information detector of the image forming apparatus, and does not use the image information of the original image itself.

This will be described by taking as an example a case where a color print image is produced as the above-mentioned duplicate image. As is well known, when producing a color print image, a color film original (in the present invention, in which a subject (original image) such as a still life or a person is photographed on a recording medium called a photographic photosensitive material,
This is also called a medium image in order to distinguish it from the subject described above. ) Is the starting point of the work. Then, the color film original (medium image) is color-separated (color separation) for each color by an image information detection unit of the scanner using a color scanner (color separation device), and an image information value is detected. Utilizes color print images.

Here, the characteristics of the color film original (medium image) will be described. (i) When viewed from the side of the image information detecting section of the color scanner, a color film original can be called an original image. If (ii) a subject such as a still life or a person is regarded as an original image, a color film original can be regarded as a medium image for detecting image information of the original image. In the present invention, the character (ii) of the color film original (medium image) must be strongly recognized from the viewpoint of correctly reproducing the gradation of the original image (the object such as the still life or the person described above). It is.

As described above, in producing a color print image, conventionally, light incident from a subject (original image) to a photographic light-sensitive material (photographic light-sensitive emulsion layer) as a recording medium is exposed to light under predetermined exposure conditions ( As is well known, under the condition of the incident light intensity I and the incident time t, the exposure amount E is represented by E = I × t.) (The color separation work includes both the color correction and the gradation control described above.)

The photographic light-sensitive material on which the subject (original image) has been photographed has a photographic density by development.
density) is formed, which becomes a color film original (medium image). A curve representing the correlation between the photographic density (degree of blackening) and the exposure E of the photographic light-sensitive material is a photographic density characteristic curve (photographic density characteristic).
eristic curve). The photographic density characteristic curve is displayed by taking the photographic density (D) (D = log Io / I) on the vertical axis and the logarithmic value (log E) of the exposure amount E on the horizontal axis. In the case of a film or a dry plate (transmitted original), the ratio between the intensity I of transmitted light and the intensity Io of incident light is equal. In the case of photographic paper (reflective original), the intensity I of reflected light is equal to the intensity Io of completely reflected light. It goes without saying that the ratio is used. A typical photographic density characteristic curve is a fairly complicated curve having a downwardly convex foot, a substantially linear straight line, and an upwardly convex shoulder (see FIG. 1 described later). )) Is well known.

In other words, the conventional color separation technique for producing a color print image is a color separation technique assembled from the standpoint of the vertical axis (density value) of the photographic density characteristic curve, and From the original image of the original) to the photographic light-sensitive material (hereinafter, in the present invention, the absolute value of the exposure amount may be used or a relative value may be used as described later. It is not a color separation technique that is generally assembled from the standpoint of the horizontal axis of the photographic density characteristic curve (the image information value correlated to the light amount).

The density information value of the color film original on which the prior art is based on the color separation operation is determined by the complex shape of the photographic density characteristic curve (see FIG. 1), as is clear from the subject (true original image). It differs from the image information value correlated with the light amount (in other words, the image information of the subject is not given linearly), and the difference between the two depends on the change of the conditions such as the exposure condition and the development condition. It will be different. That is, since the sensitivity of the photographic emulsion as a recording medium is affected, the image information value correlated with the photographic density, which is the density information value of the color film original (medium image), and the light amount of the subject (true original image). Cannot be correlated in a linear relationship (1: 1 45 ° linear relationship).

On the other hand, it is well known that, in human vision, the discrimination characteristic for light and darkness is logarithmic, and humans determine the amount of light incident on the visual system from a subject (true original image) by the discrimination characteristic described above. Is evaluated based on the gradation. Here, it is felt that the gradient of the density change is linear as a natural one. Therefore, in the production of a color print image,
When working on the density value (D = log Io / I) of a color film original (medium image) recorded on a photographic light-sensitive material, the density information after being affected by the light-sensitive properties of the photographic light-sensitive emulsion is obtained. This means that the image information value correlated with the light amount of the subject (true original image) that is the true target of the duplication is not used.

The present inventors have taken the above situation into consideration,
In the production of a duplicate image, the photosensitive characteristics of a recording medium (such as a photosensitive emulsion for photography) as described above, or a photoelectric conversion element such as a photomultiplier, a photodiode, a CCD or a two-dimensional CCD which constitutes an image information detector of an image forming apparatus. Without using the density information value of the original image after being affected by the photoelectric conversion characteristic of the first (raw, primitive) image from the original image (subject, real image) that is truly the target of the duplication. 3) The method of producing various duplicate images based on the image information value correlated with the light amount has been eagerly studied.

As a result, the present inventors, in the production of a color print image, (1). The image information detection unit of the image forming apparatus, the input image information value (IP) and the output image information value (OP)
The linearity (linearization) is maintained, and an image information value (D _n ) correlated with the density of the original image is detected by an image information detecting unit in which the linearity (linearization) is maintained. Reading (detecting), and then (2) using the photographic density characteristic curve of the photographic light-sensitive material capturing the original image, the value of the vertical axis (D = log Io / I) to the horizontal axis (log E )
(Hereinafter, the vertical axis is also referred to as the D axis and the horizontal axis is also referred to as the X axis). In other words, a color film original (medium image) from the brightest portion to the darkest portion defined on the photographic density characteristic curve )
The density information value (D value) on the D axis of
(3). More specifically, the density value (D _n value) on the D axis of an arbitrary pixel (n point) on a color film original (medium image) is obtained. ) Is projected onto the X-axis via the photographic density characteristic curve, and the image information value (X _n value) of the corresponding pixel (X value indicates the logarithmic value of the exposure amount in the photographic density characteristic curve, but the present invention It is equally effective to use the absolute value or the relative value read by scaling the same as the D axis, as described above. Therefore, as described above, this is correlated with the amount of light incident on the recording medium from the subject. (Referred to as “image information value” or simply “image information value correlated to light quantity”), and then (4). The image information value (X _n value) correlated to light quantity obtained as described above is used as a basis. And using the specific <gradation conversion formula> previously proposed by the present inventors, _n value) determined tone intensity value that indicates the dot area percent value from which the time of controlling the size of the halftone dots, better halftone having faithful image characteristics to the subject (the true original image) It was found that a printed image of

As described above, according to the present invention, first, while maintaining the linearity (linearization) of the image information detecting section, a predetermined recording is performed under the image information detecting section in which the linearity is guaranteed. A density information value (D _n ) is detected from a document image recorded on the medium, and then the amount of light incident on the recording medium using a characteristic curve of a recording medium such as a photographic photosensitive material recording the document image. Image information (X _n ) that is correlated with is obtained, and this is referred to as the <gradation conversion formula (1)>
To obtain the gradation intensity value by performing gradation conversion under
It has a large feature point.

In an image forming apparatus for forming a duplicate image having an image information detecting section and a gradation adjusting section according to the present invention,
First, the configuration of the image information detection unit will be described.

As is apparent from the above description, in the image forming apparatus of the present invention, the image information detecting section constitutes a detecting system from a document image recorded on a predetermined recording medium such as a photographic material. It is configured such that true image information that is not deteriorated (degraded) due to the characteristics (photoelectric conversion characteristics) of a photoelectric conversion element such as a CCD is received. In the following description, a color film original (medium image) is used and a subject photographed on a color film (recording medium) is faithful to an original image that is truly a target of duplication. A case of producing a color print image will be described.

For this reason, in the present invention, the image information detecting section is configured so that the input image information value (IP) and the output image information value (DP) maintain linearity (linearization). As means for maintaining the linearity (linearization) of the image information detection unit, for example, an LUT (lookup table) that can perform high-speed processing with a simple memory configuration may be used. As we all know,
The LUT (Look Up Table) is a term representing a circuit capable of outputting any value when an input value stored in a predetermined memory is input. Further, in the present invention, in order to maintain the linearity (linearization) of the image information detection unit, gray-step data (gray-step tuplet) of linear density, in other words, linearity
It is important to sufficiently maintain the linearity (linearization) of the image information detection unit.

In the image forming apparatus according to the present invention, the image information detecting section, in which the linearity is maintained at a high level, scans the original image and detects the image information value (D _n ) correlated with the density. Take in.

Next, from the density information value (D _n value) of an arbitrary pixel (n point) on the original image, a desired recording medium (for example,
A method for obtaining an image information value ( _Xn value) correlated with the light amount of a corresponding pixel incident on a photographic material or the like,
This will be described in more detail.

In the following description, a color print original (medium image) is used, and a color print image faithful to a subject (true original image) photographed on a color film (recording medium) is to be produced. The case will be described. In order to determine the image information image information values correlated to the concentration (D _n value) is correlated to the amount (X _n value), photographic characteristic curves of photosensitive material is a recording medium of the original image (subject) Needs to be properly formulated. Hereinafter, the method of formulating the photographic density characteristic curve will be described in more detail.

As a photographic density characteristic curve, a color film (Fujichrome, manufactured by Fuji Photo Film Co., Ltd.) shown in FIG. 1 was used. In the following mathematical formula, it is assumed that the gradation characteristic curve for the C plate, which is a reference among the multicolor plate making, is set. Therefore, FIG. 1 shows the photosensitive characteristic curve (R) of the R emulsion layer of the color film. (Photo density characteristic curve)
It is shown. Therefore, it goes without saying that the photosensitive characteristic curves (photographic density characteristic curves) of the G and B emulsion layers can be used for other color plates (M plate and Y plate).

The mathematical expression of the photographic density characteristic curve may be obtained by an appropriate method, and is not subject to any restrictions. For example, the vertical axis = D = log Io / I, the horizontal axis = X (however, the scale of the X axis is made to match the D axis), and a, b, c, d, e, and f are constants. Then, (a). The foot portion of the photographic density characteristic curve (a region where the D value is small at the downward convex shape) D = abc ^{(X + d) + e} + f (b). Part (region where D value is an intermediate value at a substantially linear shape) D = a · X + b or D = a · X ² + bX +
c (c). Shoulder portion (region where the D value is large at the upward convex shape) D = a · log {b + (X + c)} + d

Table 1 shows the contents of the photographic density characteristic curve shown in FIG. Table 1 shows a plurality of formula divisions in order to formulate the photographic density characteristic curve as accurately as possible.

[0045]

[Table 1]

In the present invention, as shown in FIG. 1, a D-axis scale indicating a density value of a color film original (medium image) and a log E which is incident on the color film (recording medium) from the original image (subject). The correlation between D and X was expressed as a function, assuming that the scales of the X axis indicating the image information values indicated by are the same. This is a kind of relativization (imitation) performed from the following viewpoint, and is considered to be reasonable by the present inventors. That is, originally, in the photographic density characteristic curve,
The logarithmic value of the exposure amount E (log E = log I × t) is positioned on the X axis, which is a linear (linear) or linear evaluation by exponentially evaluating the illusion characteristics of light and darkness of vision. In view of the above, it is considered that the relativization (imulation) of making the scaling of the D axis and the X axis the same in view of the above points is rational. As will be shown in the embodiments described later, excellent results can be obtained in gradation conversion of an image under this relativization (simulation). In the present invention, the above grading is a kind of simple method, and it is needless to say that the grading is not limited to this.

[0047] The present invention is not to the density information values represented by D axis (D _n value) basis included in each pixel of the original image as described above, the image information values correlated to the amount of light represented by X-axis (X _n value). And
As shown in Table 1, the photographic density characteristic curve is (D _n
Value) and (X _n value) are correlated by the function formula of X = f (D), so that (X _n value) can be easily converted from (D _n value) to (X _n value).
_n value). As described above, it is possible to easily obtain an image information value ( _Xn value) correlated with the amount of light incident on the photographic emulsion layer from the original image (subject).

Next, the (X _n value) at each pixel of the original image (subject) rationally obtained as described above is used for each pixel by using the <gradation conversion formula (1)>. The y value (gradation intensity value) can be obtained. In the present invention, the X-axis to display the (X _n value) (horizontal axis), the orthogonal coordinate system Y axis displaying the y value (vertical axis), to (X _n value) and the (X _n value) As described above, when a corresponding (y value) is plotted, a gradation characteristic curve is obtained. In order to distinguish the present invention from the prior art, the gradation characteristic curve is represented by X
The axis color separation curve is referred to as the axis color separation curve, and the conventional one that emphasizes the density information value on the D axis is called the D axis color separation curve.

Next, the configuration of the gradation adjusting section of the image forming apparatus of the present invention will be described. First, a method of deriving the <gradation conversion formula (1)> applied to the gradation adjusting unit and characteristics thereof will be described.

In a duplicate image formed by the image forming apparatus, the basic components constituting the duplicate image are a gradation intensity value at a predetermined pixel and a surface reflection density (ink or toner) of an image forming material (ink or toner). (Luminance value for TV images, etc.)
Of these, as can be seen from the fact that human vision has the ability to easily identify, for example, a 1% difference in dot area size in a printed image as a density difference, The gradation intensity value of a pixel having the same relationship as the size of the halftone dot area plays a very important role. For example, paying attention to the dots set in a certain pixel, and examining the effects of the change in the amount of ink applied on the dots and the change in the size of the dots on the density gradation, the latter Is much larger, and how to set the tone intensity value in the production of a duplicate image with excellent tone reproducibility,
This is a very important issue. A replicated image with excellent reproducibility of density gradation is also excellent in reproducibility of color tone, which can be confirmed in many cases.

In connection with the above, when a duplicate image is to be produced by an image forming apparatus, the quality of the original image varies widely and the image forming process has various characteristics. In addition, there is a background that image quality evaluation criteria are not uniform, and it is strongly desired that a mechanism for overcoming these complex and unstable factors be built in the image forming apparatus. ing.

For this reason, when producing a duplicate image having a halftone by an image forming apparatus from an original image such as a continuous tone image, the tone intensity value of the pixel of the brightest part (H) on the duplicate image (y _n) and tone intensity value of a pixel of the darkest (S) (y _S) and a can be arbitrarily selected, moreover density floor of images ranging from the lightest part (H) to the darkest portion (S) It is absolutely necessary to establish a means by which the key can be reasonably and easily adjusted and managed.

Based on such a concept, a method for adjusting a gradation according to the present invention has been devised.
(1) This is a method of adjusting the gradation using <>. We have:
When producing a halftone print image from a continuous tone color film original, the present invention requires a <gradation> in order to rationally perform the tone conversion (conversion to the continuous tone halftone tone). <Tone conversion formula> similar to <Conversion formula (1)> was previously proposed (see Japanese Patent Application Nos. 64-7770 and 63-114599), but its operating conditions are completely different from those of the present invention. Things.

A tone conversion formula for obtaining a numerical value (y) of a dot area percentage used when producing a print image of the dot tone proposed above (this is a basic skeleton as described above) Is similar to the <gradation conversion formula (1)> of the present invention, but the operation conditions are completely different.)
Can be derived from the following generally accepted density formula (photographic density, optical density). D = log ( ^Io / I) = log ( ¹ / T) However, in the above formula, each symbol means the following. Io = incident light quantity, I = reflected light quantity or transmitted light quantity, T = I / Io = reflectance or transmittance.

When the above-mentioned general formula regarding the density D is applied to plate making and printing, the following equation can be obtained. Density in plate making and printing (D ') = log (Io / I) =
(Unit area × paper reflectance) / [(unit area−dot area)
X paper reflectance + halftone dot area x ink surface reflectance] = log
(ΑA) / [α {A− (d ₁ + d ₂ +... D _n )} + β
(D ₁ + d ₂ +... D _n )] However, in the above formula, each symbol means the following. A: unit area, d _n: the area of the halftone dots of respective within a unit area, alpha: reflectance of the printing paper, beta: the surface reflectance of the printing ink.

The density equation (D
'), It is possible to arbitrarily set halftone dots of a desired size in the H and S portions of the print image, and to obtain the basic density value at any sample point on the continuous tone image (original image). (X) and a request to rationally associate the numerical value (y) of the halftone dot area percentage of the halftone dot at the sample point on the halftone dot image (printed image) corresponding thereto with the theoretical value and the actual measurement The result obtained by inducing the values to approximately match is <gradation conversion formula (2)> represented by the following expression.

< ^Tone conversion equation (2)> y = y _H + [α (1-10− ^kx ) / (α−β)] · (y
_S− y _H ) However, in the above, each symbol means the following. x: Basic density value of an arbitrary pixel on the original image. That is, the density value at an arbitrary pixel of the same image and the brightest portion H of the same image
Difference in density value at. y: Numerical value of the dot area percentage of the dot of the pixel corresponding to the pixel on the printed image. y _H : Numerical value of halftone dot area percentage of halftone dots of any desired size set for the brightest portion H on the print image. y _S : Numerical value of the dot area percent of a desired arbitrary size dot set for the darkest portion S on the print image. α: reflectance of printing paper. β: Numerical value obtained by β = 10− ^γ . k: Numerical value obtained by γ / (density area of original image). γ: arbitrary coefficient.

When applying the <tone conversion formula (2)> to tone conversion of an image when producing a print image, α, y _H ,
While arbitrarily selecting y _s and γ values, a numerical value (y) of a halftone dot area percentage of a halftone dot at a corresponding pixel on a print image is obtained from a basic density value (x) of an arbitrary pixel on a document image. It is operated. Thereby, the density gradation of the original image (continuous gradation image) is 1: 1 on the printed image (halftone gradation image).
Not only can be reproduced faithfully, but also a printed image having desired image quality (having desired density gradation and color tone) can be produced.

The multi-color plate making (generally, four plates of cyan (C), magenta (M), yellow (Y), and black (BL)
It is considered a pair. ), The working reference characteristic curve of the reference plate (in the case of multi-color plate making, the cyan plate (C) is the reference plate as is well known), that is, the density information value of the original image is represented by the halftone dot of the printed image. A halftone characteristic curve (a curve obtained by graphing the above-mentioned x value and y value, which serves as a working reference for converting into an area value, which is a reference for converting continuous tone into halftone tone) Is determined, the dot gradation characteristic curves of the other color plates are obtained by multiplying the y value of the reference plate by an appropriate adjustment value based on the gray balance ratio of each printing ink color. Can always be reasonably determined. The halftone gradation characteristic curves of the respective color plates determined as described above are, of course, each a reasonable characteristic curve, and furthermore, the mutual relation concerning the density gradation and color tone between these characteristic curves. Relationships are also rational and appropriate.

As is apparent from the above description, when a halftone dot print image is created from a continuous tone original image,
If the gradation conversion of the image is performed based on the <gradation conversion formula (2)>, it is possible to arbitrarily and rationally deviate from the conventional gradation conversion method of the image relying on experience and intuition. The conversion can be performed, and the color tone which is inextricably inextricably related to the density gradation can be rationally adjusted. This makes it possible to produce a printed image having a density gradient and a color tone that are natural for human visual perception.

The above description has been made mainly on the case where a halftone print image is produced as a duplicated image, but supports the tone conversion operation using the above <tone conversion formula (2)>. Needless to say, the theory can be applied to the production of a duplicate image by an image forming apparatus such as various printers and copying machines. However, as described above <
When producing a duplicate image using the gradation conversion formula (2)>,
The conversion of the density gradation uses the density information value.

On the other hand, in the gradation conversion of an image applied to the image forming apparatus of the present invention, an original to be adopted at the time of gradation conversion in order to achieve better density gradation conversion as described above. As the image information value of the image, an image information value correlated with the light amount is adopted instead of using the conventional density information value. In order to perform a tone conversion completely different from the conventional one, the operation conditions of the <tone conversion formula (2)> are summarized. Needless to say, this is obtained.

Next, the meaning of each item of the <gradation conversion formula (1)> of the present invention and the characteristics of the operation will be described.

In the present invention, the density information value may be any value that reflects a physical quantity related to the density of each pixel of the original image, and should be interpreted in the broadest sense. Synonyms include reflection density, transmission density, luminance, current / voltage values, and the like. These density information values may be extracted as density information signals by photoelectrically scanning an original image. In the <gradation conversion formula (1)> of the present invention,
The basic light amount value (x) is obtained from an image information value correlated with the light amount on the horizontal axis graduated by the same scaling as the vertical axis of the density characteristic curve (for example, as a portrait of a positive color film,
Although there are those having a density value of 0.2 to 2.70 on the vertical axis, a value on the horizontal axis corresponding to this is adopted. ) And y _H [a gradation intensity value preset for the pixel of the brightest part (H)] and y _S [a gradation intensity value preset for the pixel of the darkest part (S)]. For example, using a pixel coverage of 5% or 95%), the y value [the gradation intensity value set for the pixel on the duplicated image corresponding to an arbitrary pixel on the original image] is calculated as a percentage value. You.

In the operation of the <gradation conversion formula (1)> of the present invention, not only the following modification but also the utilization is used.
It can be freely used after being processed, deformed, or guided. _{y = y H + E (1-10} -kx) (y s -y H) However, in the above equation, E = 1 / (1- β) = 1 / (1-
10 ^-γ ). In the above modification, α = 1. This is a recording paper (base material) for recording duplicate images
Has a surface reflectance of 100%. As the value of α, if the zero point adjustment of the density measuring mechanism is performed with reference to the recording paper, α may be set to 1.0 in practice. Also,
In the case of a luminance image such as a TV image, α = 1 may be set.

According to the modified example (α = 1.0), the brightest portion (H) on the duplicated image by the image forming apparatus has y
The _H, it is possible to set in as was scheduled to y _S to the darkest part (S). This is because x = 0 in the brightest part (H) on the duplicated image, and x in the darkest part (S).
= [X _Sn −X _Hn ], that is, kx = γ · [(X
_Sn− X _Hn ) / (X _Sn −X _Hn )] = γ, and thus −kx = −
It is clear from the fact that γ is obtained.

In the operation of the <gradation conversion formula (1)> of the present invention, α, β, γ (where γ is β =
The β value is defined by 10 ^−γ . The values in parentheses) take various values. In the present invention, by appropriately selecting these numerical values, it is possible to rationally convert the gradation of an image regardless of the quality characteristics of the original image. That is, the tone conversion processing method of the image based on the <tone conversion formula (1)> of the present invention reproduces the density tone and color tone of the original image, that is, the tone of the original image is added to the duplicate image by one. : 1 is very useful for reproducing, but its usefulness is not limited to this. According to the present invention, the <gradation conversion formula (1)
>, Besides faithfully reproducing the characteristics of the original image, α, as easily understood from the characteristics of the <gradation conversion formula (1)>,
beta, gamma value, and further it is extremely useful to modify or change the characteristics of the original image reasonably by selecting y _H, a y _S values as appropriate. It should be noted that among the parameters of the <gradation conversion formula (1)>, in particular, the γ value plays a significant role in adjusting (including correcting or changing) the image characteristics of the duplicated image. It can be easily understood by using the conversion formula (1)>.

When forming a multi-color image using the <gradation conversion formula (1)>, for example, when producing a duplicate image using a color film original, a color separation technique known in the field of printing and the like, That is, reflected light from a color original is separated into blue (B), green (G), and red (R) to obtain a signal correlated with a density information value (D value) for each color, and this is converted into a light amount. The image information is converted into a correlated image information value (X value), and further processed by a gradation adjustment mechanism using the <tone conversion formula (1)>. The image may be formed by adjusting the recording unit. At this time, when the y value relating to the reference color plate (for example, C plate), that is, the gradation characteristic curve of the reference color plate (the y value is calculated and the y value is plotted against the x value, the above-described printing is performed. A tone characteristic curve similar to the halftone dot characteristic curve in the technology is obtained.), And the tone characteristic curves of the other color plates (M plate, Y plate) are set to the y values of the reference color plate. It can be rationally determined by multiplying by an appropriate adjustment value based on the gray balance ratio of each ink, and an image may be formed using these gradation characteristic curves. The gradation characteristic curve for each color plate set as described above is <
Since they are defined by the gradation conversion formula (1)>, not only are the characteristic curves reasonable, but also the correlation between the density curves and the color tone between the characteristic curves is rational and appropriate.

In the present invention, as described above, the X
X-axis to display the _n value (horizontal axis), is plotted the y value corresponding to X _n value and the Xn value to the orthogonal coordinate system Y axis displaying the y value (vertical axis), the X-axis color separation curves can get. In addition,
Conventional color separation curves that emphasize the density information value (D _n )
It is called a D-axis color separation curve to distinguish it from the present invention.

The characteristics of the X-axis separation curve obtained by the present invention and the conventional D-axis color separation curve will be described. The <gradation conversion formula (1)> of the present invention is operated under constant conditions, that is, α, y _H , y _S , and γ values are each kept constant, and the image quality is different as a color film original (that is, each original is different). When a plurality of originals having different density ranges and density information values are used and respective X-axis color separation curves (gradation characteristic curves) are obtained, respective obtained X-axis color separation curves (gradation characteristics The curve) has a property that all the y values (gradation intensity values) of each pixel from the H portion to the S portion of the duplicate image (for example, the print image) as the final product are relatively in the same relation.

The above point is a very important feature of the present invention. In other words, as shown in the embodiments described later, even if the range of the image information value (X value) correlated with the light amount on the X axis of each color film original is different (this is because
This naturally reflects the difference in image quality of the color film original and the density range is different. ), When adjusted to the same predetermined X-axis range, the X-axis obtained by the present invention is obtained.
The axial color separation curve (gradation characteristic curve) has a characteristic feature that it is converged into one (only one). Therefore,
From the shape of each X-axis color separation curve (gradation characteristic curve),
For example, in view of the arrangement state of the halftone dots (when the y value is made to correspond to the halftone dot area% value), it is not necessary to proof (produce a proof) what kind of image quality is finally obtained as a duplicated image. Even in advance, it can be correctly evaluated.

On the other hand, in the conventional D-axis color separation curve, each curve corresponding to the image quality of each color film original is obtained, and as described above, the same D-axis on the D-axis is obtained. Even if adjusted to the range, these do not fit into one (the only one). That is, each D-axis color separation curve merely indicates a choice of gradation conversion, and a desired gradation conversion is performed unless proof printing (proof creation) is performed according to each D-axis color separation curve. It is impossible to accurately determine whether or not a duplicate image of a desired image quality has been produced.

In relation to the above points, the <gradation conversion formula (1)> of the present invention is obtained by changing the values of α, y _H , y _S and γ arbitrarily (particularly by changing the γ value). That is, it is possible to rationally change the shape of the gradation characteristic curve.
(1)> It is possible to arbitrarily adjust (modify and change) the tone of the duplicated image under desired conditions. In other words, the tone conversion is performed under the X-axis color separation curve. The feature is that work can be managed rationally.

As described above, a method for obtaining an image information value (X value) correlated with the light amount of an arbitrary pixel on a document image (subject) is as follows.
The description has been given of the example using the photographic density characteristic curve of the photographic photosensitive material that is the recording medium of the color film original (medium image). In the image forming apparatus of the present invention, the original image is not limited to the above-described color film original (medium image), and all originals that can be read by the image information detecting unit configured by the photoelectric conversion element of the image forming apparatus. The image is of interest.

In the image forming apparatus of the present invention, as is apparent from the above description, the linearity (linearization) of the image information detecting section is maintained, and a desired recording medium (for example, If the characteristic curve of the (photosensitive material) is appropriately functioned, a duplicate image of extremely high image quality or desired image quality can be produced. In this regard, in the prior art approach, the characteristics (photoelectric conversion characteristics and photosensitive characteristics) of various photoelectric conversion elements and recording media (photosensitive materials for photography) are intended to produce high-quality duplicate images.
Efforts have been made actively to improve. In this regard, when a duplicate image is produced according to the present invention, various photoelectric conversion elements and recording media are not necessarily required to have high quality and high performance,
Existing performance (characteristics) are sufficient, which is a great advantage derived from the characteristics of the gradation conversion method employed in the present invention.

In the image forming apparatus of the present invention, the concept of maintaining the linearity (linearization) of the image information detecting section may be utilized in the output system (recording system) of the image forming apparatus. is there. For example, when a halftone image is output on a photosensitive film and developed to produce a printing plate, the linearity of the output system depends on the nonlinearity of the photosensitive film and the chemical reaction in the developing machine. May be performed so as to correct the non-linearity. By ensuring the linearity of the image information detection unit and the output unit, the image forming apparatus of the present invention can produce a high-quality duplicate image (for example, a print image).

As described above, when a duplicate image is formed by the image forming apparatus of the present invention, gradation conversion is performed by the gradation adjustment mechanism section based on the <gradation conversion formula (1)>. By incorporating hardware or software, it is possible to obtain a duplicate image excellent in reproduction of color tone as well as density gradation, or a duplicate image in which the image quality of a document image is arbitrarily corrected or changed.

At this time, the y value (gradation intensity value) obtained by the arithmetic processing of <gradation conversion formula (1)> is converted into a density display method (variable dot method, constant dot method, density dot method) suitable for each image forming apparatus. Needless to say, it is only necessary to correspond to a variable dot) or a luminance display method.

For example, as shown in FIG. 4, in the case of the column shown in FIG. 4A, the distribution of the pixels recorded in a predetermined pixel block changes as the number of recorded pixels increases.
Although they are in a mutually dispersed positional relationship within the pixel block, they may alternatively be spread spirally outward from the center of the pixel block, for example. It will be. In the column of FIG. 4B, halftone dots having an area corresponding to the number of pixels in the column of FIG. 4A are shown. Here, the pixel block has been described as a 4 × 4 matrix type, but 17 gradations are expressed by this. Generally, an n × n matrix type pixel block has n ² +1 levels of gradation (0 to 100%)
Is expressed. As described above, a method of expressing the density gradation of an original image such as a continuous tone image by the distribution of pixels formed in a matrix type pixel block is generally called a "Tiza matrix method" and is well known. (For example, JP-A-58-85434 and JP-A-58-114).
No. 569, No. 59-52969, No. 60-14158
No. 5, No. 62-186663 and the like. ).

Next, application fields of the image forming apparatus of the present invention will be described. Although the present invention has been described above with particular reference to the production of printed images, its application is not limited to equipment associated with producing printed images. In the image forming apparatus of the present invention, the gradation conversion method of the image forming the largest feature point has been described above, particularly in relation to the production of a printed image. However, the image forming apparatus incorporating the gradation conversion method is not limited to a device for producing a printed image. Hereinafter, representative examples of the image forming apparatus of the present invention will be described, but the present invention is not limited thereto.

(I) The size of halftone dots (dots) seen in a printed image such as letterpress, lithographic, halftone gravure, or silk screen, which has already been described in detail, or a piezoelectric ink jet or melt transfer type thermal transfer image. An image forming apparatus that attempts to express the gradation and color tone of a duplicated image by modulating the tone (this is also called an area gradation method).

(Ii). Sublimation transfer type thermal transfer image, (using silver salt) thermal phenomenon transfer image, conventional gravure image, etc., such as a printing ink or the like adhered per pixel (for example, per dot) of a fixed area. An image forming apparatus that attempts to express gradation and color tone by shading of a pigment, dye (dye) or the like (this is also called a density gradation method).

(Iii). Recording density per fixed area, such as digital copying machines (such as color copying machines), printers (such as ink jet printers and bubble jet printers), and facsimile machines, for example, the number of dots and the size of ink particles. An image forming apparatus that attempts to express gradation by changing the number or the like (this is similar to the area gradation in (i) and is also called a density modulation method).

(Iv) An apparatus for producing an image faithful to a subject (affected part, lesion, etc.) as a medical precision image for examination such as an X-ray photograph.

(V). In addition, the dot area% together with the density display
Printing-related equipment such as a densitometer with a density / gradation conversion mechanism that can also display information, such as a color separation preliminary inspection (for example, a color proof for calibration) and a color separation education simulator.

[0086]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

In the production of a duplicate image by the image forming apparatus of the present invention, the gradation conversion of the image, which is a core elemental technology thereof, is performed under the above <gradation conversion formula (1)>. Therefore, first, a setting example of a color separation curve (gradation characteristic curve) that determines the quality of a duplicate image as a final product will be described. Here, the setting example of the X-axis color separation curve of the present invention and the conventional D-axis color separation curve and their differences will be clarified.
Next, the image information detection unit of the present invention, and <gradation conversion type
(1) An image forming apparatus having a gradation adjustment mechanism unit incorporating hardware or software for performing gradation conversion based on <> will be described.

Embodiment 1 (Setting of X-axis Color Separation Curve) Photo Density Characteristic Curve Used in the Experiment The photo density characteristic curve shown in FIG. 1 (DX orthogonal coordinate system) (manufactured by Company F, Fujichrome) was used. In FIG. 1, the D axis (vertical axis) indicates the density value of the color original image. On the other hand, the X-axis shows the exposure amount (logE = logI × t) in the photographic density characteristic curve, but here, it was quantified by the same scaling as the D-axis. The functions shown in Table 1 were used as the function formulas of the photographic density characteristic curve. 2. Image of experimental manuscript Image quality of color film manuscript (medium image) generally varies depending on the exposure conditions at the time of photographing, such as standard (appropriate exposure) and non-standard (over / under exposure). Everything is different. In order to verify whether the present invention can reasonably respond to these various color film originals, the density range of the color film original (Density
(Range = DR) was different (the concentration range on the D axis was different). 3. Using the function of tables 1 function expression the photographic characteristic curve calculations Figure 1 of the setting data of the X-axis color separation curve, the D _n values on the D axis of the various color film original on the X-axis X _n Converted to a value. Next, the _Xn value was converted into a gradation intensity value (y value) by <gradation conversion formula (1)>. The operation conditions of the <gradation conversion formula (1)> are as follows. x = X _n −X _Hn , y _H = 5%, y _s = 95%, γ = 1.
00, β = 10 ^−γ = 0.1, α = 1.00, k = γ /
X _sn -X _Hn . (In the case of Table 2 (1) below, X _Hn = 0.4781, X _Sn =
2.2300. In other cases, see Table 2. )

Table 2 shows the results. In Table 2, of Table 2
(1) to (3) are overexposed (light originals).
(4) to (7) show the results close to the proper exposure, and (8) to (10) in Table 2 show the underexposure (dark original).

[0090]

[Table 2 (1)]

[0091]

[Table 2 (2)]

[0092]

[Table 2 (3)]

[0093]

[Table 2 (4)]

[0094]

[Table 2 (5)]

[0095]

[Table 2 (6)]

[0096]

[Table 2 (7)]

[0097]

[Table 2 (8)]

[0098]

[Table 2 (9)]

[0099]

[Table 2 (10)]

4. X-axis color separation curve The data in Table 2 are shown in FIGS. Note that in both FIGS. 2 and 3, the ordinate represents the y value in both figures, but it should be noted that the abscissas in FIGS. 2 and 3 have different characteristics. That is, the horizontal axis in FIG. 2 is the image information value (X _n value) correlated with the light amount.
The horizontal axis in FIG. 3 indicates the density value (D
_n value). In graphing the data in Table 2,
For convenience of comparison, the ranges (dynamic range) relating to the light amount value and the density value were adjusted to be the same. In the case of the present example, it was adjusted to 2.5000. In addition,
Needless to say, the adjustment range is 1.000.
It may be adjusted to a desired range such as 0. This is because the y value (halftone dot area% value in the present embodiment) changes relative to each other according to the size of the adjustment range. When the adjustment range is set to 1.0000, the calculation load is greatly reduced due to the characteristics of <tone conversion formula (1)> of the present invention. The value after this adjustment is (D _n →) D _n ′ in Table 2,
(X _n →) X _n ′. In the case of Table 2 (1), the adjustment from D _n → D _n ′ is D _n ′ = (D _n −1.800) ×
[(Adjustment range) / DR _n ] = (D _n −1.800) ×
What is necessary is just to calculate by (2.50 / 2.52). Similarly, X _n → X _n 'adjustment to _{the, X n' = (X n} -0.4781)
X (2.500 / 1.7519).

FIG. 2 shows a gradation characteristic curve according to the present invention, that is, an X-axis color separation curve (the relationship between X _n 'and y as described above), and FIG. 3 shows a D-axis color separation curve (as described above). This shows the relationship between D _n ′ and y, which can be regarded as an example of setting a conventional color separation curve.)

As is apparent from FIGS. 2 and 3, a very surprising fact can be found. That is, according to the gradation conversion method of the present invention, no matter what color film original is used, α, y _H , y _{s in} <gradation conversion formula (1)>
, Γ values are the same, it is a surprising fact that each X-axis color separation curve fits into one and the same curve as shown in FIG. This is the fact that the tone of the duplicated image is uniformly displayed. In other words, according to the gradation characteristic curve (X-axis color separation curve) setting technique of the present invention, regardless of the image quality of a color film original, the H section
As a result, a gradation characteristic curve that can produce a duplicate image of the same quality with the same y value (gradation intensity value) of each pixel reaching the portion is obtained. In addition, an operator who intends to produce a duplicate image by the image forming apparatus may change the x-axis color separation curve obtained as described above by changing the parameters in the <gradation conversion formula (1)>, particularly the γ value. Can be changed to a desired shape. That is, gradation can be rationally managed based on the X-axis color separation curve so that desired image quality and tone can be obtained.

On the other hand, in the setting example of the conventional color separation curve shown in FIG. 3, although a D-axis color separation curve corresponding to the image quality of each color film original is obtained, it is manufactured after the color separation. It is not possible to know in advance from the respective D-axis color separation curves whether or not the tone of the color print image is all the same. That is, under the conventional D-axis color separation curve, proof printing (creation of proof) is actually performed.
However, if the evaluation is not carried out, it is difficult to determine whether the image quality and condition of the final product are appropriate. This requires a setup work in which an appropriate color separation curve must be selected from a large number of color separation curves in the color separation work by the image forming apparatus, and a grouping work of color documents in a pre-process of the setup work. It means there is. That is, it means that the conventional D-axis color separation curve setting technique cannot efficiently perform or rationally manage the tone conversion work.

Embodiment 2 (Regarding Image Forming Apparatus) An image forming apparatus according to the present invention will be described with reference to FIGS.

FIG. 5 is a block diagram of the image forming apparatus according to the first embodiment of the present invention. As shown in FIG. 5, the image forming apparatus of the present invention converts transmitted light or reflected light of a document image into R light.
(Red), G (green), and B (blue). The image information detecting unit 1 reads and outputs signals of the image information detecting unit 1 to Y (yellow), M (magenta), C (cyan), A color separation unit 2 for converting a color separation signal into a K (black) color separation signal, a gradation adjustment unit 3 for obtaining a density gradation based on an appropriate pixel distribution using <tone conversion formula (1)>, An output unit 4 for exposing the electrophotographic photosensitive member with a laser beam based on an output signal of the adjusting unit 3; a latent image formed on the photosensitive member is developed in a developing unit to become a toner image; The image is transferred and fixed in the fixing unit. In order to form a color image, an independent photoconductor and a developing unit are provided for each component color, and the formed toner images are sequentially transferred to a recording sheet, or a latent image of the component color is formed on one photoconductor. Is formed and developed to form a toner image, then transferred to a recording sheet, and this process is repeated for each color component.

The image information detecting section 1 detects the transmitted light or the reflected light of each pixel of the original image 5 by a photoelectric conversion element such as a photomultiplier or a solid-state imaging device (CCD), and outputs R,
G, B, and USM signals are output, and the A / V converter 6 converts the signals into voltage signals. The color separation unit 2 uses the R, G, B, U of the image information detection unit 1 in the log amplifier 7.
Each voltage signal (image information) of the SM is logarithmically calculated and converted into a density. In a basic masking (BM) 8, a black (K) component is separated from the density, and Y,
Separate each component of M and C. That is, in the image forming apparatus of the present invention, first, image information is read from a duplication target (original image) by an image information reading mechanism including a photomultiplier, a CCD, and the like of the image information detecting unit 1, , Image information for each of the Y, M, and C color components is obtained.

In the present invention, the detection unit 1 maintains linearity (linearization) using an LUT (Look Up Table) not shown. The density information value (D _n ) detected from the detection unit 1 is
An image information value ( _Xn ) correlated with the light amount is changed using a characteristic curve (such as a photographic density characteristic curve) of the recording medium on which the original image is recorded. These may be performed by software or hardware (not shown).

FIG. 5 shows a color correction (CC) unit 9 and a UCR / UCA unit 10 as the configuration of the color separation unit 2. The CC unit 9 includes R, G, B and Y,
The Y component, the M component, and the C component are controlled for each of the M and C original colors. Further, the UC of the UCR / UCA unit 10
R (under color removal) or UCA (under color
addition) determines the ratio of expressing the black component of the document image by three components of Y, M, and C.

As described above, the Y, M, C, and K components converted into image information values (X _n ) correlated with the light amount are shown in FIG.
The gradation is converted by the adjustment unit 11 as shown in FIG. In addition,
Conventionally, in a gradation control unit in a gradation adjustment unit (IMC), the area ratios ye ', me', ce ', and ke' of the pixels occupied by each component are determined, and further, these are subjected to inverse log conversion in an inverse log conversion unit. ing. In this embodiment, an adjustment unit 11 is used instead of the gradation control unit and the inverse log conversion unit.
Conversion from M, C, K to ye ', me', ce ', ke' is performed. The adjustment unit 11 internally has an algorithm of <gradation conversion formula (1)>, applies <gradation conversion formula (1)> to each of Y, M, C, and K, and adjusts ye ′, me ′,
Find ce 'and ke'.

As the adjusting unit 11, <gradation conversion formula (1)>
Owns the algorithm of A /
A general-purpose computer having a D / D / A I / F (interface), an electric circuit embodied by a general-purpose IC using an algorithm as internal logic, an electric circuit including a ROM holding an operation result of the algorithm, and an algorithm implemented as internal logic Various forms such as a PAL, a gate array, a custom IC, and the like can be adopted.

The pixel area ratio (gradation intensity value) obtained by the adjustment unit 11 is input to the color channel selector 12, and the color channel selector 12
e ', ce', and ke 'are sequentially and selectively output. This output is A / D converted by the A / D converter 13 and input to the output unit 4. The output unit 4 controls the laser beam oscillator 15 in the dot control unit 14 based on the output of the gradation adjustment unit 3.

FIG. 6 shows an image forming apparatus according to a second embodiment of the present invention, in which the conventional inverse log converter 16 is used as it is.
', Me', ce ', ke' are output. As a result, the <gradation conversion formula (1)> can be applied only by converting one component of the conventional device, and the existing system is remodeled to the system according to the present system by changing fewer devices than in the first embodiment. can do.

FIG. 7 shows an image forming apparatus according to a third embodiment of the present invention, in which the conventional gradation control (IMC) section 17 is left and the gradation control section 17 can be used in combination. is there. An adjustment unit 11 similar to that of the second embodiment, that is, an adjustment unit 11 that outputs ye ′, me ′, ce ′, and ke ′ in a logarithmic format is employed. The adjustment unit 11 takes the Y, M, C, and K signals from the preceding stage of the gradation control unit 17 and outputs the value after gradation conversion to the inverse log conversion unit 16.

FIG. 8 shows an image forming apparatus according to a fourth embodiment of the present invention, in which a conventional inverse log conversion unit 16 and gradation control (IMC) unit 17 are left, and these can be used in combination. Things. Then, the adjustment unit 11 takes the Y, M, C, and K signals from the preceding stage of the gradation control unit 17 and is directly connected to the color channel selector 12, and ye ', me', c
It is possible to obtain ye ', me', ce ', and ke' in the same optimal processing mode as in the adjusting unit 11 of the first embodiment without restricting e 'and ke' to the conventional system. it can. And the fourth embodiment of the present invention is the third embodiment.
As in the embodiment, the system of the present invention can be realized with a slight modification of the conventional system.

FIG. 9 shows an image forming apparatus according to a fifth embodiment of the present invention, in which the entire conventional tone conversion unit is configured as a new adjustment unit 11, and this adjustment unit 11 performs a <tone conversion. Equation (1)> can be used.

The image forming section of the image forming apparatus shown in FIGS. 5 to 9 is of an electrophotographic type for forming an electrostatic latent image on a photoconductive photoreceptor by scanning with a laser beam. However, as a method of forming a duplicate image based on the distribution of pixels, other methods such as an electrostatic recording method and a magnetic recording method can be adopted.

FIG. 10 shows an image forming section of the image forming apparatus using the electrostatic recording method. This method is shown in FIG.
As shown in FIG. 2, a voltage is applied to each electrode of a recording head in which a large number of electrodes are arranged in a direction perpendicular to the moving direction by approaching or in contact with a moving recording body made of a sheet-shaped dielectric, and statically applied. An electrostatic latent image is formed. The steps after the step of adding toner to the latent image and developing the same are the same as those of the electrophotographic type. A voltage as an output signal corresponding to an image to be recorded is applied from the dot control unit 14 of the output unit 4 to the recording head as an aggregate of electrodes.

In the case of the magnetic recording system, for example, a recording body in which a surface of a drum body is uniformly coated with a magnetic substance is used, and a voltage as an image information signal is applied to a magnetic recording head in contact with the surface. The magnetic latent image is formed on the recording medium surface by moving the magnetic recording head and the recording medium surface relatively while applying the voltage. To develop this latent image, a toner made of a magnetic material is used, but otherwise, the development is performed in the same manner as in the case of the electrophotographic method.

By modifying the gradation adjusting section of the conventional device as described above, it is possible to combine <Gray scale conversion formula (1)> with other processing, and to increase the speed by optimizing the system. ,
Compactness can be realized, and cost performance per system can be improved. In the above-described embodiment, the color separation unit has the same configuration as that of the related art, but in the present invention, the <gradation conversion formula (1)>
, A high-quality duplicated image can be obtained. Therefore, the conventional color correction (CC) unit 9, USR /
The UCA unit 10 may be omitted from the color separation unit. Also,
A configuration for obtaining, for example, a blur mask or a sharpness effect, which is not directly related to the present invention, is omitted in the embodiment relating to the image forming apparatus described above, but a configuration for obtaining these other effects is added. It goes without saying that it may be done.

[0120]

The present invention has the following excellent effects. 1). Density values of predetermined pixels on an original image such as a continuous tone image and a duplicate image to be produced (an image recorded by pixel distribution), which are the most basic elemental technologies for producing a duplicate image. In determining the correlation with the gradation intensity value of the corresponding pixel above, an irrational method has conventionally been used, which is based solely on the experience and intuition of the worker, or based on a limited number of data on predetermined conditions. there were. On the other hand, in the present invention, under any precondition, this can be rationally determined based on the <gradation conversion formula (1)>.

2). When converting an original image such as a continuous tone image into a duplicate image based on pixel distribution, what is the most important elemental technology, gradation management (gradation conversion, modification or change)? In addition, it is directly related not only to the density gradation of the image but also to the color tone of the image. For this reason,
According to the present invention, the density gradation and the color tone can be simultaneously and rationally managed.

3). The image forming apparatus in which the algorithm of the <gradation conversion formula (1)> of the present invention is adopted in the gradation adjustment mechanism is as follows.
The color separation work and the gradation conversion work can be systematized theoretically and rationally, and the work can be simplified, and the effect is extremely large.

4) A means (linearization means) for preventing deterioration (degradation) of image information due to the characteristics of the photoelectric conversion element of the detection system is incorporated in the image information detecting section of the image forming apparatus. By adopting the algorithm of the tone conversion formula (1)> into the tone adjustment mechanism of the image forming apparatus,
The image forming apparatus can be streamlined and simplified, and the manufacturing cost can be reduced. Also, the operation has been simplified and clarified, and re-make has been extremely reduced.
The consumption of consumable materials can be greatly reduced, and the performance of the image forming apparatus can be greatly improved. In particular, in the performance of the image forming apparatus, there is a great merit that a reproduced image excellent in density gradation and color tone can be formed regardless of the quality of a document image.

5). The gradation adjustment mechanism adopting the algorithm of <gradation conversion formula (1)> rationally and easily separates the image information of the original image from the image information of the original image to improve the quality of the recorded image by the pixel distribution. Evaluation criteria can be defined. Therefore, it is possible to rationally respond to the diversified needs of customers.

6). By adopting the <gradation conversion formula (1)>, the education and training of technicians, which are required with the advancement of image production equipment such as printers and copiers at present, are as follows.
Through the operation of the gradation conversion formula (1)>, it can be performed effectively, and unnecessary labor in daily work can be omitted, and time margin for new creative development can be secured.

[Brief description of the drawings]

FIG. 1 shows a photographic density characteristic curve of a color film.

FIG. 2 shows an X-axis color separation curve (used in gradation conversion of the present invention) set based on the photographic density characteristic curve of FIG.

FIG. 3 shows a D-axis color separation curve (used in gradation conversion of a conventional example) set based on the density characteristic curve of FIG.

FIG. 4A shows an example in which an original image having continuous tones is represented by a density gradation by a distribution of unit pixels in a pixel block, and FIG. FIG. 4 is a diagram showing an example in which density gradation is expressed by halftone dot sizes in photolithography corresponding to ()).

FIG. 5 is a block diagram of the image forming apparatus according to the first embodiment of the present invention.

FIG. 6 is a block diagram of an image forming apparatus according to a second embodiment of the present invention.

FIG. 7 is a block diagram of an image forming apparatus according to a third embodiment of the present invention.

FIG. 8 is a block diagram of an image forming apparatus according to a fourth embodiment of the present invention.

FIG. 9 is a block diagram of an image forming apparatus according to a fifth embodiment of the present invention.

FIG. 10 is an explanatory diagram of an image forming unit of an electrostatic recording type applied to the image forming apparatus of the present invention.

[Explanation of symbols]

 1 image information detecting section 2 color separating section 3 gradation adjusting section 4 output section 5 original image

Claims (5)

[Claims] An image forming apparatus for forming a duplicate image from a document image having an image information detecting section and a gradation adjusting section, comprising: (i) an image information detecting section of the image forming apparatus; . Input image information value (IP) and output image information value (O
(I) The image information detector detects a predetermined characteristic curve [image information value (D _n ) correlated with density and image information correlated with light amount. (A curve defining the correlation between the values (X _n )) and the image information value (D _n ) correlated with the density of the document image recorded on the recording medium, and (i) -3. correlated image information values in the (D _n), and configured to convert the recorded image information values of the characteristic curve was correlated to the amount by use of the medium _{(X n), (ii)} . floors of the image forming apparatus The tone adjustment unit calculates an image information value (X _n ) correlated to the amount of light input to the recording medium for recording the original image obtained as described above, by the following <gradation conversion formula (1)>. Tone intensity value (y
(1) an image forming apparatus for forming a replicated image having excellent tone reproducibility from a document image. < ^Tone conversion formula (1)> y = y _H + [α (1-10− ^kx ) / (α−β)] · (y
_S− y _H ) However, in the above <gradation conversion formula (1)>, each symbol means the following. x: represents ( _{Xn- XHn} ). This is because the image information value (X _n ) correlated with the light amount of the corresponding pixel obtained from the density information value (D _n value) of an arbitrary pixel (n point) on the original image using the characteristic curve of the recording medium. ), An image correlated with the light amount of the corresponding brightest portion (H portion) obtained from the density information value (D _Hn ) of the brightest portion (H portion) on the original image using the characteristic curve of the recording medium. This is the basic light amount value after subtracting the information value (X _Hn ). y: A gradation intensity value set for a pixel on the duplicate image corresponding to an arbitrary pixel on the original image. y _H: a preset tone intensity value that is in the brightest part of the duplicated image corresponding to the brightest portion of the document image (H section) (H unit). y _S : A gradation intensity value preset for the darkest part (S part) on the duplicate image corresponding to the darkest part (S part) on the original image. α: surface reflectance of an image expressing medium for forming a duplicate image. β: Numerical value determined by β = 10− ^γ . k: k = γ / (X _Sn −X _Hn ) where (X _Sn ) is obtained from the density information value (D _Sn ) of the darkest portion (S portion) on the original image using the characteristic curve of the recording medium. The image information value (X _Sn ) correlated with the obtained light amount of the corresponding darkest part (S part) is shown. γ: arbitrary coefficient. 2. The image forming apparatus according to claim 1, wherein the linearity between the input image information value (IP) and the output image information value (OP) utilizes an LUT (Look Up Table). Image forming device. 3. The reproduced image according to claim 2, wherein the linearity of the input image information value (IP) and the output image information value (OP) is maintained using the linear gray step data. An image forming apparatus for forming. 4. The image forming apparatus for forming a duplicate image according to claim 1, wherein the image information detecting section is constituted by a photomultiplier, a photodiode, or a photoelectric conversion element such as a CCD. 5. The image forming apparatus according to claim 1, wherein the recording medium for the original image is a photographic photosensitive material, and the characteristic curve is a photographic density characteristic curve.