JPH10178551A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a highly accurate ACC by correcting unevenness in a luminous quantity due to a read position of a scanner. SOLUTION: An image forming device has a scanner that reads an image of an original placed at a read position by optical scanning, an image processing circuit that converts the inputted image signal from the scanner into an output image signal with an image signal conversion table to output, a laser optical system 104 that writes information on a photoreceptor drum 102 corresponding to the output image signal, developers 105 to 108 that form an image on transfer paper through the photoreceptor drum 102, an image signal generating means that generates a gradation pattern and a means that generates/selects the image signal conversion table based on a read signal of the gradation pattern read by the scanner and gradation objective data stored in a RAM. In this case, the scanner detects a luminous quantity at or in the vicinity of the read position of the gradation pattern, stores the result of detection in a memory and corrects the read value of the gradation pattern based on the detected result and the detected result stored in the memory.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus such as a digital copying machine, a printer, and a facsimile.

[0002]

2. Description of the Related Art Conventionally, in a digital image forming apparatus, in order to correct output characteristics of an output device (image forming means) such as a printer or to emphasize a specific density area,
Image signal conversion table (Look Up Table:
Hereinafter, referred to as “LUT”). The image forming apparatus generally includes an image reading unit, an image processing unit,
The LUT is formed by an image writing unit, an image forming unit, and the like.
An image signal input from the image reading means to the image processing means is converted and output to the image writing means as an output image signal.

On the other hand, since the LUT reflects the output characteristics of the image forming means such as a printer with respect to the image density, the output characteristics of the printer change due to deterioration or dirt of the image forming means or the like. If it does, it will not play the role of correction.

In order to correct this, one of controls called process control performed inside the image forming apparatus.
First, a plurality of patterns with different image densities are formed on an image carrier such as a photoreceptor or a transfer body, and these patterns are detected by an optical sensor by the reflected light or transmitted light, and the charging potential is determined based on the detection result. The development bias or the exposure amount of the laser is changed, or the gradation correction table for converting the gradation of the image data is changed.

[0005] This correction method has an advantage that the correction can be performed automatically in the apparatus and there is no need for human intervention. However, due to the characteristics of the optical sensor, the correction method is used on the high-density side where the amount of toner adhesion is large. Due to the lack of sensitivity, the correction was performed from a low density with a small amount of toner attached to an intermediate density.
Further, there is a defect that it is not possible to correct a toner amount that fluctuates due to a change over time in the transfer performance of the transfer unit, and to correct a fluctuation in image density due to a change in fixability in the fixing unit.

On the other hand, a pattern image formed on an image carrier is transferred and fixed on a transfer material, and the image is read by a scanner, and a gradation correction table is selected and created based on the read data, and a color correction table is selected. Conversion coefficient, RGB-YMC
A correction method for creating a K color conversion table has also been proposed. This method requires processing by an operator, such as placing the discharged transfer material on a platen by hand, as compared to the correction method using the optical sensor described above.
It is possible to correct a high image density portion where a large amount of toner adheres, and it is possible to correct a change in image density due to a change with time in a transfer portion and a change in fixability in a fixing portion. Such a correction method is disclosed in, for example,
There are JP-A-131266 and JP-A-5-114962.

[0007]

As described above, one of the conditions for obtaining color reproduction faithful to an original is YMC
It is necessary to appropriately set a gradation correction table (γ correction table), which is an LUT for converting an image signal of the K component to form an electrostatic latent image on a photoreceptor with an appropriate amount of laser light. (Auto Color Calibatat
ion; hereinafter, referred to as ACC), an appropriate gradation correction table is selected. However, due to unevenness in light amount or dirt due to the position on the contact glass surface on which the original is placed, originals having the same image density are selected. , The read value may vary, and the adjustment result of the automatic gradation correction may vary from machine to machine.

In the above-mentioned Japanese Patent Application Laid-Open No. 59-131266, information on sensitivity and non-uniformity of illuminance between reading elements obtained by sequentially reading images of uniform density in the main scanning direction and the sub-scanning direction is described. The image signal stored and read by the conversion is corrected according to the image position. This method has the advantage that the entire document can be read relatively faithfully.

However, in order to improve the accuracy of the sensitivity information and the illuminance variation information between the reading elements, a large-capacity memory for storing the correction values is required, which may increase the cost.

On the other hand, as a condition necessary for faithfully reading a color image, when an original having the same density and the same hue is read over the entire reading area, a CCD (Charge Coupled D) constituting a scanner is read.
It is desirable that the RGB ratio, which is the read value of the device, be the same regardless of the read position. However, the ratio of RGB may not always be constant due to slight displacement or distortion of the optical axis of the traveling optical system. Although the cause is not exactly known, it is considered that the spectral transmittance and the reflectance of the reading system change depending on the reading position.

In such a case, Japanese Patent Application Laid-Open No.
The method described in Japanese Patent No. 1266 is basically a method for correcting unevenness in illuminance and a reading element, and is not sufficient as a method for accurately reading a color image into a faithful color.

On the other hand, when trying to store the variation information of the entire reading area for each of R, G, and B, the amount of information increases, so that the processing load increases and a large-capacity memory is required. However, there is a disadvantage that the cost is increased.

Further, even if the gradation correction table is set to an appropriate value when the machine is installed, the photosensitive drum, the developer,
A shift from an appropriate state occurs due to a temporal change of an image forming unit such as a transfer belt. In such a case, in order to set the above tone correction table to an appropriate value again,
A transfer paper on which a tone pattern or a color patch of each color of YMCK is recorded is read by a scanner, and a tone correction table (γ correction table) for correcting tone characteristics of a printer unit is created from the read values. But A
As a condition for setting the tone correction table to an appropriate value again by executing the CC, the read value of the tone pattern or color patch needs to be a value that accurately reflects the characteristics of the image forming unit. is there.

However, even if a document having the same image density is read due to unevenness in light amount or dirt due to the position on the contact glass surface on which the document is placed, the read value varies, and the ACC adjustment result varies from machine to machine. May occur.

Generally, in a digital copying machine scanner,
Correction (shading correction) is performed using the white reference plate at the scanner's home position to correct for differences in light transmittance due to the image height of the lens and unevenness in the main scanning direction due to characteristics of the illumination system. ing. However, unevenness in the light amount due to the position on the contact glass is caused by slight distortion or inclination of the scanner or the rail on which the scanner travels, change in the light amount over time due to the rising time of the halogen lamp as a light source, deterioration of the halogen lamp over time, or Occasionally, the flare may occur over the entire contact glass surface due to a slight flare in the lighting section of the traveling body.

In such a case, the shading correction for correcting only the main scanning direction cannot correct the light amount unevenness on the entire surface of the contact glass, which is the original placing surface. Therefore, even if you read a document with the same image density,
Reading values vary depending on the image position. That is, as shown in FIG. 65 which is a graph showing the read value according to the magnitude of the light amount, the read value differs depending on the magnitude of the light amount. FIG. 66 is a diagram for describing an example of reading positions with different light amounts. In FIG. 65, a) shows a read value at a position with a large amount of light, b) shows a read value at a position with a small amount of light, and c) shows a read value as a result of correction according to the present invention.
The vertical axis indicates the read value of the gradation pattern, and the horizontal axis indicates the image density of the gradation pattern. The image density decreases as going to the left, and increases as going to the right. FIG. 66 is a diagram for explaining the reading position in the reading area, in which a) schematically shows a reading position with a large amount of light and b) a reading position with a small amount of light. The left direction in FIG. 66 is the leading end of the reading area, and the right direction is the rear end of the reading area.

Further, there is another problem that the value read by the scanner reading the gradation correction pattern varies depending on the amount of the fixing oil adhering to the transfer paper. That is, the toner image formed on the photoreceptor is transferred onto the transfer paper, and the toner on the transfer paper is melted and fixed by the fixing device. The fixing device uses a fixing oil such as silicone oil for the purpose of preventing molten toner from adhering to a fixing roller in the fixing device. The fixing oil adheres to the transfer paper at the time of fixing, but also adheres to the fixed toner and the background portion of the transfer paper at the time of forming a gradation pattern for automatic gradation correction.

The fixing oil covers the surface of the transfer paper and the surface of the toner fixed on the surface of the transfer paper. The specular reflectance and the irregular reflectance of the surface differ depending on whether or not the fixing oil is present. come. For this reason, the read value of the scanner and the colorimetric value of the colorimeter differ between the two. This poses a problem in that it causes a mechanical difference and a time-dependent change in image density as described below.

First, the cause of the mechanical difference will be described.
If the amount of fixing oil applied varies from machine to machine, the amount of fixing oil remaining in the automatic gradation correction pattern also varies from machine to machine. Therefore, even when the same amount of toner adheres to the transfer paper and is fixed, the read value of the automatic gradation correction pattern changes depending on the remaining amount of the fixing oil remaining on the transfer paper. As a result, the result adjusted by the automatic gradation correction differs for each machine. As described above, the amount of the fixing oil remaining on the transfer paper causes a variation in the adjustment result of the automatic gradation correction for each machine.

On the other hand, the problem due to the change over time is as follows. That is, the amount of the fixing oil on the transfer paper changes over time from immediately after fixing due to evaporation. In response,
The read value of the gradation pattern of the toner formed on the transfer paper also changes with time. Therefore, the result differs between a tone correction table created from values obtained by reading a tone pattern immediately after fixing and a tone correction table created from values obtained by reading a tone pattern left for a while after fixing. Normally, when executing the automatic gradation correction, the output gradation pattern is immediately read by the scanner and the gradation correction table is created. It is adjusted to an optimum state for the image density immediately after fixing. However, since the user uses the state in which the fixing oil is sufficiently evaporated, the state is adjusted to a state deviated from the optimum state.

Furthermore, when the light amount at the reading position of the gradation pattern is detected by the scanner, the result obtained by the averaging method may be different. In other words, 40 commonly used in digital copiers and the like are used.
In a high-precision scanner equivalent to 0 DPI or more, a CCD that reads an odd-numbered pixel in the main scanning direction is different from a CCD that reads an even-numbered pixel. It differs for each pixel. As a result, for example, the obtained result may be different between the case where the read values of only the odd-numbered pixels are averaged and the case where the read values of the even-numbered pixels are averaged.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances of the prior art, and a first object of the present invention is to provide an image forming apparatus in which ACC is made highly accurate by correcting light amount unevenness due to a reading position of a scanner. Is to provide.

A second object of the present invention is to provide an image forming apparatus which has a high-precision ACC by correcting uneven light amount on a contact glass surface without using a special apparatus.

A third object of the present invention is to provide an image forming apparatus capable of detecting light amount unevenness only on a document on which a gradation pattern is formed.

A fourth object of the present invention is to provide an image forming apparatus which eliminates an error caused by a difference in averaging process between reading a gradation pattern and detecting a light amount.

A fifth object of the present invention is to improve the detection accuracy of light amount unevenness when a document for detecting light amount unevenness uses, for example, a uniform blank sheet having a reflectance in a visible light region of about 70% or more. It is an object of the present invention to provide an image forming apparatus in which the detection accuracy is close to the case where a non-white document such as a pressure plate made of resin is used for detecting unevenness in light amount.

A sixth object of the present invention is to make it possible to select not to perform correction based on the light amount at or near the reading position of the gradation pattern, and to allow the user to adjust the light amount at or near the reading position of the gradation pattern. An object of the present invention is to provide an image forming apparatus capable of detecting a light amount when correction is required.

A seventh object of the present invention is to form an image by which an optimum gradation correction table can be selected and created irrespective of the residual amount of fixing oil remaining on a transfer material on which a gradation pattern is formed. It is to provide a device.

An eighth object of the present invention is to omit the operation of reading a background portion before forming a gradation pattern and simplify the operation when the type of transfer material to be normally used is determined. An object of the present invention is to provide an image forming apparatus.

A ninth object of the present invention is to estimate the adhesion amount of fixing oil when the type of the transfer material read as the state before the formation of the gradation pattern is different from the type of the transfer material actually formed with the gradation pattern. An object of the present invention is to provide an image forming apparatus in which an inappropriate correction is not performed.

A tenth object of the present invention is to provide an image forming apparatus capable of selecting whether or not to correct a fixing oil remaining on a transfer material after forming a gradation pattern.

An eleventh object of the present invention is to provide an image forming apparatus which saves labor at the time of manufacturing by automatically inputting a correction amount of light amount unevenness at the time of manufacturing the apparatus online. .

[0033]

In order to achieve the first object, the first means comprises means for optically scanning a document image placed at a reading position for reading, and input from the reading means. Means for converting an image signal into an output image signal using an image signal conversion table and outputting the image signal, means for writing information on an image carrier in accordance with the output image signal, and an image on a transfer material via the image carrier , A means for generating a gradation pattern, and means for creating and selecting an image signal conversion table based on a read signal of the gradation pattern and gradation target data stored in the storage means. The image forming apparatus includes a unit that detects a light amount at or near the reading position of the gradation pattern, and a unit that stores and holds a detection result. It is characterized by correcting the readings of the gradation pattern based on the detection result stored in that unit.

In order to achieve the second object, the second means includes a means for detecting a light amount in the first means, wherein the means for detecting a light amount of the document having a substantially uniform density placed on a document table is provided with the gradation. The detection is performed by reading the pattern at the reading position by the reading means.

In order to achieve the second object, the third means is characterized in that the original in the second means is constituted by blank paper.

In order to achieve the second object, the fourth means is that the means for detecting the amount of light in the first means detects by reading the blank portion of the gradation pattern by the reading means. Features.

In order to achieve the third object, the fifth means is the first to fourth means for detecting a margin portion of the gradation pattern and storing a detection result of the margin portion. Means for comparing the detection result of the blank portion and the detection result of the blank portion stored in the storage means, based on a result of comparing the read position or the vicinity of the read position of the gradation pattern. It is characterized in that the execution or non-execution of the light amount detection is determined.

In order to achieve the fourth object, the sixth means is that the means for detecting the amount of light in the first to fifth means performs the same averaging process as when reading the gradation pattern. Features.

In order to achieve the fifth object, the seventh means is characterized in that, in the first to sixth means, the correction based on the light amount at or near the reading position of the gradation pattern is performed using blank paper. When performing, the gain of the signal read by the reading unit is changed.

In order to attain the fifth object, the eighth means is characterized in that in the first to sixth means, the correction based on the light amount in the reading position of the gradation pattern or in the vicinity of the reading position is performed by using a blank sheet. When performing, the reflectance of the back surface of the document is made lower than that of the reading means.

In order to achieve the sixth object, the ninth means selects the execution or non-execution of the correction based on the light amount in the reading position of the gradation pattern or in the vicinity of the reading position in the first to sixth means. It is characterized by further comprising means for performing.

In order to achieve the fifth object, the tenth means is to carry out the correction based on the light quantity near or near the reading position of the gradation pattern in the first to ninth means using blank paper. It is characterized by further having a means for selecting whether or not to perform the determination.

In order to achieve the seventh object, the eleventh means comprises means for optically scanning a document image placed at a reading position for reading, and converting an input image signal from the reading means into an image signal. Means for converting and outputting to an output image signal by a table, means for writing information on an image carrier according to the output image signal, means for forming an image on a transfer material via the image carrier, An image forming apparatus comprising: means for generating a tone pattern; and means for creating and selecting an image signal conversion table based on a read signal of the tone pattern and tone target data stored in a storage means. A read value of the background portion of the transfer material before the formation of the gradation pattern is compared with a read value of the background portion of the transfer material after the formation of the gradation pattern, and based on the result, the gradation pattern is read. It is characterized by correcting the readings down.

In order to achieve the seventh object, the twelfth means may be arranged so that the background reading of the transfer material before the formation of the gradation pattern in the eleventh means is changed before the formation of the gradation pattern. It is characterized in that it is a value that is read.

In order to achieve the eighth object, a thirteenth means is arranged such that a reading value of a background portion of the transfer material before the formation of the gradation pattern in the eleventh means is stored in the storage means in advance. It is characterized by using a certain value.

In order to achieve the ninth object, the fourteenth means includes: a reading value of a background portion of the transfer material before the formation of the gradation pattern in the eleventh to thirteenth means; When a result of comparison with a later read value of the background portion of the transfer material is larger than a predetermined amount, the read value is not corrected.

In order to achieve the fourth object, the fifteenth means may further comprise, in the eleventh to thirteenth means, means for registering a read value of a background portion of the transfer material before the formation of the gradation pattern. It is characterized by having.

In order to achieve the tenth object, a sixteenth
The means of the present invention is characterized in that, in the eleventh to fifteenth means, there is further provided a means for selecting execution / non-execution of correction of the read value of the gradation pattern.

In order to achieve the first object, the seventeenth means comprises means for optically scanning a document image placed at a reading position for reading, and converting an input image signal from the reading means into an image signal. Means for converting and outputting to an output image signal by a table, means for writing information on an image carrier according to the output image signal, means for forming an image on a transfer material via the image carrier, An image forming apparatus comprising: means for generating a tone pattern; and means for creating and selecting an image signal conversion table based on a read signal of the tone pattern and tone target data stored in a storage means. Means for storing the light amount at or near the read position of the gradation pattern, and the read value of the gradation pattern based on the light amount stored in the storage means It is characterized by correcting.

In order to achieve the eleventh object, an eighteenth object
Means, provided in the seventeenth means, outside the image forming apparatus, wherein the external adjustment apparatus obtains the correction amount of the gradation pattern, and the external adjustment apparatus corrects the gradation pattern by the image forming apparatus. Means for inputting an amount.

In order to achieve the sixth object, the nineteenth means selects the execution or non-execution of the correction based on the light amount near the reading position or near the reading position in the seventeenth or eighteenth means. It is characterized by further comprising means for performing.

In order to attain the second object, the twentieth means is characterized in that, in the seventeenth to nineteenth means, means for detecting a light quantity at or near the reading position of the gradation pattern is provided. Features.

In order to achieve the fourth object, the twenty-first means according to the seventeenth to twentieth means, wherein the correction amount of the gradation pattern performs the same averaging processing as when reading the gradation pattern. It is characterized by:

[0054]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which an image forming apparatus of the present invention is applied to an electrophotographic copying machine (hereinafter, simply referred to as a copying machine) will be described below with reference to the drawings. In each embodiment, the same components are denoted by the same reference numerals, and duplicate description will be omitted.

First, an outline of a mechanism of a copying machine main body common to each embodiment and a control system built in the copying machine will be described with reference to FIGS. FIG. 2 is a mechanism diagram schematically showing the mechanism of the copying machine main body, and FIG. 3 is a diagram for explaining a control system of the copying machine main body of FIG. In FIG. 2, the diameter of the image carrier, which is disposed substantially at the center of
Around a 20 mm organic photoconductor (OPC) drum 102, a charging charger 103 for charging the surface of the photoconductor drum, and a semiconductor laser beam is irradiated onto the uniformly charged surface of the photoconductor drum 102 to statically charge the surface. A laser optical system 104 for forming an electrostatic latent image; a black developing device 105 for supplying and developing toner of each color to the electrostatic latent image to obtain a toner image for each color; three color developments of yellow Y, magenta M, and cyan C Apparatus 1
06, 107, 108, an intermediate transfer belt 1 for sequentially transferring toner images of each color formed on the photosensitive drum 102
09, a bias roller 110 for applying a transfer voltage to the intermediate transfer belt 109, and a cleaning device 11 for removing toner remaining on the surface of the photosensitive drum 102 after the transfer.
1. A charge removing unit 112 for removing charges remaining on the surface of the photosensitive drum 102 after transfer is sequentially arranged. Also,
A transfer bias roller 113 for applying a voltage for transferring a toner image transferred along the intermediate transfer belt 109 to a transfer material, and the intermediate transfer belt 109 after transferring the toner image to the transfer material.
A belt cleaning device 114 for cleaning the remaining toner image is provided.

After the toner image on the intermediate transfer belt 109 has been transferred, the toner image is fixed by heating and pressing to the exit end of the transport belt 115 that transports the transfer material separated from the intermediate transfer belt 109. A fixing device 116 is disposed, and an outlet of the fixing device 116 includes:
A paper discharge tray 117 is attached.

Above the laser optical system 104, there are provided a contact glass 118 as an original placing table arranged above the copying machine main body 101, and an exposure lamp 119 for irradiating the original on the contact glass 118 with scanning light. The reflection light from the original is reflected by the reflection mirror 121 into the imaging lens 1.
The light is led to an image sensor array 123 of a CCD which is a photoelectric conversion element. The image signal converted into an electric signal by the image sensor array 123 of the CCD passes through an image processing device (not shown) and controls laser oscillation of the semiconductor laser in the laser optical system 104.

As shown in FIG. 3, the control system includes a main control unit (CPU) 130, and a ROM 131 and a RAM 132 are added to the main control unit 130. The main control unit 130 also has an interface I
/ O 133, laser optical system controller 134, power supply circuit 135, optical sensor 136, toner density sensor 13
7, environment sensor 138, photoconductor surface potential sensor 139,
A toner supply circuit 140, an intermediate transfer belt driving unit 141,
The scanning units 142 are respectively connected. The laser optical system control unit 134 adjusts the laser output of the laser optical system 104. The power supply circuit 135 supplies a predetermined charging discharge voltage to the charging charger 103, and the developing device 105, A developing bias of a predetermined voltage is applied to 106, 107 and 108, and the bias roller 1
A predetermined transfer voltage is applied to the transfer bias roller 113 and the transfer bias roller 113.

The optical sensor 136 is connected to the photosensitive drum 102
A light-emitting element such as a light-emitting diode and a light-receiving element such as a photosensor are disposed in the vicinity of the area after the transfer of the toner, and the toner adhesion amount and the background portion in the toner image of the detection pattern latent image formed on the photosensitive drum 102 Is detected for each color, and the so-called residual potential after the photosensitive member is neutralized is detected.

The detection output signal from the photoelectric sensor 136 is applied to a photoelectric sensor control unit (not shown). The photoelectric sensor control unit obtains the ratio between the amount of toner attached to the detection pattern toner image and the amount of toner attached to the background portion, compares the ratio value with a reference value to detect a change in image density, and detects the change in image density. The control value is being corrected.

Further, the toner density sensor 137 detects the toner density based on the change in the magnetic permeability of the developer present in the developing devices 105 to 108. Toner density sensor 13
Reference numeral 7 compares a detected toner density value with a reference value, and when the toner density falls below a certain value and the toner becomes insufficient, a toner replenishment signal having a magnitude corresponding to the shortage is provided. 140 is provided. The potential sensor 139 detects the surface potential of the photoconductor 102 serving as an image carrier, and the intermediate transfer belt driving unit 141 controls driving of the intermediate transfer belt 109.

For example, a developer containing M toner and a carrier is contained in the magenta developing device 107, and is stirred by the rotation of the developer stirring member 202M.
Adjust developer pumped up to 1M. The supplied developer is magnetically carried on the developing sleeve 201M and rotates as a magnetic brush in the rotation direction of the developing sleeve 201M. The developing sleeve 201 is controlled by a power supply circuit 135 via a current detection circuit 143.

Next, the electrical configuration of the image processing unit according to the first embodiment will be described with reference to the block diagram of FIG.

In FIG. 1, reference numeral 401 denotes a color scanner;
402, a shading correction circuit, 403, an RGB gamma correction circuit, 404, an image separation circuit, 405, an MTF correction circuit, 406, a color conversion-UCR processing circuit, 407, a scaling circuit, 407, an image processing (create) circuit, and 409. M
TF filter, 410 is a gamma correction circuit, 411 is a gradation processing circuit, and 412 is a printer.

An original to be copied is separated into R, G, and B colors by a color scanner (hereinafter, simply referred to as a scanner) 401 and read. Shading correction circuit 40
In 2, the unevenness of the image sensor and the unevenness of the illumination of the light source are corrected. In the RGB γ correction circuit 403, a read signal from the scanner 401 is converted from reflectance data into brightness data. The image separation circuit 404 determines a character portion and a photo portion,
And a chromatic or achromatic color is determined. The MTF correction circuit 405 corrects the deterioration of the MTF characteristics of the input system, particularly in a high frequency range. Color conversion-UCR processing circuit 406
Is a color correction processing unit that corrects the difference between the color separation characteristics of the input system and the spectral characteristics of the color materials of the output system, calculates the amount of the color material YMC necessary for faithful color reproduction, and overlaps the three colors YMC. Part B
UCR processing for replacing with k (black). The color correction processing in the color correction processing unit can be realized by performing the following matrix operation.

[0066]

(Equation 1)

Here, R ゛, G ゛, B ゛ are R, G, B
Shows the complement of. The matrix coefficient a _ij is determined by the spectral characteristics of the input system and the output system (color material). Here, the first-order masking equation is used as an example, but two-dimensional masking equations such as B2 and BG are used.
By using the next term or a higher order term, color correction can be performed more accurately. Further, the arithmetic expression may be changed depending on the hue, or the Neugebauer equation may be used. In any case, Y, M, and C are B
゛, G ゛, R ゛ (or B, G, R).

On the other hand, the UCR process can be performed by performing calculations using the following formula for each color.

Y ′ = Y−α · min (Y, M, C) (2) M ′ = M−α · min (Y, M, C) (3) C ′ = C− α · min (Y, M, C) (4) Bk = α · min (Y, M, C) (5) In these equations (2) to (5), α is the amount of UCR Is a coefficient that determines 100% UCR processing when α = 1. This α may be a constant value. For example, by setting α close to 1 in a high density portion and setting α close to 0 in a highlight portion, an image in the highlight portion can be smoothed.

An image memory 424 and a hue determination circuit 422 are connected between the MTF correction circuit 405 and the color conversion / UCR processing circuit 406. The image memory 424 is for storing image data as needed.
The hue determination circuit 422 determines which hue of RGBCMY the RGB image signal is, and selects a color conversion coefficient corresponding to each hue.

The scaling circuit 407 performs vertical and horizontal scaling, and the image processing (create) circuit 408 performs repeat processing and the like. The MTF filter 409 performs a process of changing the frequency characteristics of the image signal, such as edge enhancement and smoothing, according to the user's preference, such as a sharp image or a soft image. The γ correction circuit 410 corrects an image signal in accordance with the characteristics of the printer 412, and the γ correction circuit 410 can simultaneously perform processing such as background removal. In the gradation processing circuit 411, dither processing or pattern processing is performed.

Interfaces (I / F) 413 and 414 for processing image data read by the scanner 401 by an external image processing device or the like and outputting image data from the external image processing device to the printer 412. Is provided.

The CP for controlling the above image processing circuit
U415, ROM416 and RAM417 are BUS
Connected at 418. The CPU 415 has a serial I
It is connected to the system controller 419 via / F, and commands from an operation unit (not shown) are transmitted. Connected between the I / F 413 and the RGB γ correction circuit 403 is a selector 423 that generates a signal to switch parameters of each circuit according to an image quality mode based on a command from the CPU 415. Although not specifically described, in FIG.
21 is a pattern generation circuit.

Next, the laser modulation circuit according to the first embodiment will be described with reference to the block diagram shown in FIG. It is assumed that the writing frequency is 18.6 MHz and the scanning time of one pixel is 53.8 nsec. The 8-bit image data is represented by γ in a look-up table (LUT) 451.
Conversion can be performed. Pulse width modulation circuit (PWM)
In step 452, the image signal is converted into an 8-level pulse width based on the upper 3 bits of the 8-bit image signal, and the power modulation circuit (P
At (M) 453, 32-level power modulation is performed based on the lower 5 bits of the signal, and the laser diode (LD) 454 emits light based on the modulated signal. The light emission intensity is monitored by a photodetector (PD) 455, and correction is performed for each dot.

The maximum value of the laser beam intensity can be changed to 8 bits (256 steps) independently of the image signal. Also, the beam diameter in the main scanning direction (this beam diameter is defined as the width when the beam intensity at rest is attenuated to 1 / e ² with respect to the maximum value) with respect to the size of one pixel. It is 90% or less, preferably 80%. 400
At a DPI of 63.5 μm per pixel, a desirable beam diameter is 505 μm or less.

The image reading system according to the first embodiment will be described with reference to a block diagram shown in FIG.
The reflected light is radiated by an exposure lamp (not shown), and the reflected light is separated and read by an RGB filter of a CCD 501 constituting a scanner, and is amplified to a predetermined level by an amplifier circuit 502. The CCD driver 509 is a CCD
A pulse signal for driving is supplied. A pulse source necessary for driving the CCD driver 509 is generated by a pulse generator 510 using a signal from a clock generator 511 composed of a crystal oscillator or the like as a reference signal. The pulse generator 510 includes a sample / hold circuit (hereinafter, referred to as an S / H circuit) 503 and a CCD 501.
Supplies the timing pulse required to sample and hold the signal from The analog color signal sampled and held by the S / H circuit 503 is digitized by the A / D conversion circuit 504 into, for example, an 8-bit signal. The black correction circuit 505 reduces the variation of the black level, which is an electric signal when the amount of light is small between the chips of the CCD 501 and between the pixels, and prevents the occurrence of streaks or unevenness in the black portion of the image. The shading correction circuit 506 corrects a white level which is an electric signal when the light amount is large. The white level is determined based on white data obtained when the scanner 401 is moved to the position of a uniform white plate and is irradiated, based on the irradiation system, the optical system, and the CC.
The variation in sensitivity of D501 is corrected. The signal from the shading correction circuit 506 is processed by the image processing unit 507 and output by the printer 412. These circuits are
Controlled by the CPU 514, the ROM 513 and the RA
Data necessary for control is stored in M515. CPU 51
Reference numeral 4 is connected to a system controller 419 that controls the entire image forming apparatus so as to be communicated via a serial I / F, and controls a scanner driving device (not shown) to control driving of the scanner 401. ing.

The amplification amount of the amplification circuit 502 is determined so that the output value of the A / D conversion circuit 504 becomes a desired value for a specific original density. As an example, a document having a document density of 0.05 (0.891 in reflectivity) during normal copying can be obtained as a 240-bit 8-bit signal value. On the other hand, at the time of shading correction, the amplification factor is lowered to increase the sensitivity of shading correction. The reason is that, when the amplification factor at the time of normal copying is large, when there is a large amount of reflected light, there is a case where an error occurs in shading correction because there is no sensitivity in a portion exceeding 255 values in an 8-bit signal.

FIG. 6 is a graph showing a model in which a read signal of an image amplified by the amplifier circuit 502 is sampled and held by the S / H circuit 503. The horizontal axis of the graph indicates the time during which the amplified analog image signal passes through the S / H circuit 503, and the vertical axis indicates the magnitude of the amplified analog signal. The analog signal is sampled and held for a predetermined sample hold time, and the signal is sent to the A / D conversion circuit 504. FIG. 6 shows an image signal obtained by reading the above-mentioned white level. The image signal after amplification is, for example, a value of 240 after A / D conversion at the time of copying and 180 at the time of white correction.
The value is shown.

Here, the procedure for creating a gradation conversion table (LUT) performed by the gamma correction circuit 410 of FIG. 1 is shown in FIG.
A description will be given based on the flowchart of FIG. That is, in this creation procedure, first, the entire curvature is selected (step 1001), and the curvature of a low image density (highlight) portion and the curvature of a high image density (shadow) portion are selected (step 1002). 1003). Then, a tone conversion curve is created by multiplying the whole by the coefficient IDMAX so that the image density becomes a desired value (step 1004).

The processing in step 1001 will be described in detail with reference to FIG. FIG. 8 is a diagram for explaining selection of the degree of overall curvature. For the gradation curve A as a reference, gradation conversion for changing the overall curvature is B, and gradation conversion for changing the curvature in the highlight area (low density area) is C.
1. The gradation conversion for changing the curvature of the shadow area (high density area) is defined as C2. Then, a gradation curve obtained by performing gradation conversion on the gradation curve A by the gradation conversion B is represented by E, which is represented by E = B and (A).

This is specifically described in outline using the format of the programming language C.

[0082]

(Equation 2)

Can be expressed as follows. Here, B is a function for changing the curvature of A.

As an example of this function, in the case of an 8-bit image signal, 0 = B (0, n), 255 = B (255,
n) (n is an arbitrary integer), a quadratic Bezier function can be used.

The Bezier function that satisfies the above condition is the starting point P
0 (0, 0) and a straight line P0P1 connecting the end point P1 (255, 255), a straight line L intersecting with the straight line P0P1, and a distance d from the intersection of the straight line P0P1 and the straight line L existing on the straight line L Is expressed as a second-order Bezier curve from the control point P2 having the parameter

In the above function, the degree of curvature can be changed by making the distance d proportional to the integer curvature, which is an argument of the function B. As an example, the straight line P0
An example for a straight line L1 orthogonal to P1 and an example for a straight line L2 parallel to the vertical axis of the figure will be described.

The control points in the first example are defined as both end points P0,
Center point PC of line segment P0P1 created by P1 = (P0 + P1)
/ 2 = 127.5, 127.5) or (127, 1
27) or (128, 128), when the distance d to this point is used as a parameter, the control point P2 is P2 (d) = PC + (− d / √2, d / √2) = (127.5− d / √2, 127.5 + d / √2) (6) (FIG. 9). Thereby, the gradation conversion curve P
(D, t) is given by P (d, t) = P0 · t 2 +2 · P 2 (d) · t · (1-t) + P1 · (1-t) 2 ··· (7) . Here, t is a parameter satisfying 0 ≦ t ≦ 1. P (d, t) is an input x and an output y to the gradation conversion curve.
Is given as a set (x, y), t is obtained from the above equation (7), where x = A from the integer A given as an argument to the function B (), and the obtained t is again expressed by the equation ( 7) to obtain an output value y.

In practice, instead of performing the above calculation every time, all the sets of (x, y) (0 ≦ x ≦ 255) are set in advance.
Is calculated and stored in the ROM 416 as a table, so that the calculation time can be omitted. Several sets (or tens of sets) of this gradation correction table are stored in the ROM 416 while changing the degree of curvature. The degree of curvature is calculated by using the argument "curvatur" to the function B () described above.
e.

Thus, <List 1> is rewritten as follows.

[0090]

(Equation 3)

In the above example, since Table_max = 9, the number of tables having different degrees of curvature is set to nine. In the above example, a Bezier curve is used. However, a higher-order function, an exponential / logarithmic function, or the like can be used as needed.

Next, the above steps 1002 and 100
Explaining the process No. 3, the curvature of the low image density (highlight) area and the high image density (shadow) area can be changed in the same manner as described above. That is, if <List 1> is rewritten in a more general form, it becomes as follows.

[0093]

(Equation 4)

When the conversion of the highlight conversion curve CH (h) and the shadow conversion curve CS (s) is executed,

[0095]

(Equation 5)

Can be expressed as follows. In this, curv
where ature, h, and s are the whole, the highlight part,
This value determines the degree of curvature of the shadow portion. Note that the curves of the highlight portion and the shadow portion are created independently of each other.

A gradation conversion curve for changing the curvature of a specific density area, such as a highlight area and a shadow area, is generated as follows.

That is, a straight line P0P1 connecting the start point P0 and the end point P1, a straight line L intersecting the straight line P0P1, and a distance d from the intersection of the straight line P0P1 and the straight line L existing on the straight line L are used as parameters. From the control point P2, a gradation conversion curve is generated using a cubic Bezier curve.

Here, as an example, the case of a straight line L1 orthogonal to the straight line P0P1 and the case of a straight line L2
Will be described below.

As shown in FIG. 10, a conversion curve for changing the gradation characteristic of the highlight area is generated as follows as an example. The start point P0 and the end point P1 are P0 = (0,
0), P1 = (255, 255), and the first control point P
2 is set to P2 = (32, 32). The control point P3 in the first example is defined as P3 (d) = (16, 1) using the distance d from the intersection of the straight line P0P1 and the straight line L1 as a parameter.
6) + (− d / √2, d / √2). Further, the control point P3 in the second example is expressed by P3 (d) =
(16, 16) + (0, d). These P0 to P3
Using. Gradation conversion curve P (d, t) is, P (d, t) = P0 · t 3 +3 · P2 · t 2 · (1-t) +3 · P3 (d) · t · (1-t) 2 + P1 · (1-t) ³ ... (8)

Here, as the end point, P1 = (255,
255), but the end point P1 may be a point on the line segment m: (0, 0)-(255, 255) such as P1 = (64, 64). At this time, a line segment on the line segment m that is not included in the line segment P0P1 is used as it is as the gradation conversion as the identity conversion, and the other region is a specific density region such as a highlight region and a shadow region. And acts as a gradation conversion curve for changing the degree of curvature.

Next, automatic gradation correction of image density (gradation) (ACC: Auto Color Calibration)
n, hereinafter referred to as ACC).
This will be described with reference to the drawings. FIG. 11 is a flowchart showing the operation of ACC for image density, FIG. 12 is a plan view showing an operation unit, FIG. 13 is a plan view showing a display screen of the operation unit when the ACC menu is called, and FIG. AC
FIG. 15 is a plan view showing a display screen of the operation unit when the execution of C is selected, FIG. 15 is a plan view showing a display screen of the operation unit in ACC, and FIG. FIG. 17 is a plan view showing a density gradation pattern on the transfer paper when the print start key is selected, FIG. 18 is a plan view showing a display screen of the operation unit after the pattern is output on the transfer paper, FIG. 19 is a plan view showing a display screen of the operation unit during the ACC process.

As shown in FIG. 12, a start button 301, a clear / stop button 302, a ten-key 303 for setting the number of copies, etc. are provided on the upper side of the copying machine main body 101 as shown in FIG. A plurality of operation buttons 304 for performing various operations such as / mode clear, memory call, interrupt operation, color adjustment / registration, program, option, and area processing are provided. A display screen 305 of the liquid crystal display device is provided so as to be surrounded by these buttons. The display screen 305 has a tablet function of outputting a signal by pressing a display location or touching the display location.

First, an operation screen for selecting an ACC function will be described. When the ACC menu is called on the display screen 305 of the operation unit 142 shown in FIG.
The screen shown in FIG. 13 is displayed. If you select [Execute] of ACC for copy use or printer use,
The display on the display screen 305 switches as shown in FIG. In FIG. 13, when the use of copy is selected, the gradation correction table used at the time of use of copy is changed based on the reference data. If the result of image formation using the changed YMCK tone correction table is not desirable, a [Restore] key is displayed in the screen of FIG. 13 so that the YMCK tone correction table before processing can be selected. Is displayed.

The other items on the screen will be described with reference to FIG. 13. When the [Execute] key for detecting the unevenness in the light amount is selected, the unevenness in the light amount is detected. When the [SET] key of the automatic gradation correction setting is selected, the display screen 305 is switched as shown in FIG. 15, and the background correction, the correction of the high density portion, the correction of the RGB ratio, and the correction of the light amount unevenness described later. Each [Execute],
[None] can be selected. In FIG.
When the [SET] key for the setting of the light amount unevenness detection is selected, the display screen 305 selects whether the original used for the correction of the light amount unevenness is white or non-white, as shown in FIG. And the [non-white] key are displayed. Note that these selections are not always necessary, and may be always executed.

Next, the operation of the ACC will be described with reference to the flowchart of FIG. When "Execute" of automatic gradation correction for copy use or printer use is selected on the display screen 305 of the operation unit 142 shown in FIG. 12, the display on the display screen 305 switches as shown in FIG. Here, in the display screen 305 of FIG.
When is selected, as shown in FIG. 17, a plurality of density gradation patterns 311 corresponding to each color of YMCK and each image quality mode of characters and photographs are formed on the transfer paper 310 (step 2001 in FIG. 11). Reference numeral 312 denotes a position designation mark. This density gradation pattern 311 is
Are stored and set in the ROM of the computer 420. The write value of the pattern is 00 in hexadecimal notation.
h, 11h, 22h,... EEh, FFh. In FIG. 17, patches for gradations are displayed except for the background portion, but an arbitrary value can be selected from the 8-bit signal of 00h-FFh. In the character mode, dither processing such as pattern processing is not performed, and a pattern is formed at 256 gradations per dot. In the photo mode, the writing value of the laser is distributed by distributing the sum of the writing values of two adjacent pixels in the main scanning direction. Is formed.

That is, the write value of the first pixel is n
When the writing value of the first and second pixels is n2, the pattern processing is as follows: n1 + n2 ≦ 255, the writing value of the first pixel: n1 + n2, the writing value of the second pixel: 0, n1 + n2> 255, Write value of the first pixel: 255, Write value of the second pixel: n
1 + n2-255 or n1 + n2 ≦ 128, the write value of the first pixel: n1 + n2, the write value of the second pixel: 0, if 128 <n1 + n2 ≦ 256, the write value of the first pixel: 128, the write of the second pixel Value: n
1 + n2-128 When 256 <n1 + n2 ≦ 383, the write value of the first pixel: n1 + n2-128, the write value of the second pixel: 128 383 <n1 + n2, the write value of the first pixel: 255, the writing of the second pixel Value: n
1 + n2-255 and so on. In addition, the pattern processing actually used at the time of image formation is used.

After the pattern is output on the transfer paper 310,
So that the transfer paper 310 is placed on the platen 118,
The display on the display screen 305 switches as shown in FIG. According to the display, the transfer paper 310 on which the pattern is formed is placed on the document table 118 (step 2002), and [Reading Start] is selected on the display screen 305 of FIG. 18 or [Cancel] is selected (FIG. 18). Step 2003).
If [Cancel] is selected, the process ends (step 2
004), when [Read Start] is selected, the scanner 401 travels and reads RGB data of a YMCK density pattern (step 2005). At this time, the data of the pattern portion and the data of the background portion of the transfer paper 310 are read.

It is determined whether the data in the pattern portion has been read normally (step 2006). If the data has been read normally, the screen shown in FIG. 18 is displayed again. If the reading is not successful twice, the process ends (step 2).
007). On the other hand, when the data of the pattern portion is normally read, it is determined whether or not the correction of the light amount unevenness is selected on the display screen of FIG. 15 (step 2008). If it is selected to execute the light amount unevenness correction, the pattern read value is corrected using the light amount unevenness correction data stored in advance (step 2009).

The document for detecting the light amount unevenness may be any document as long as the document density near the pattern reading position is substantially uniform. However, the document having a low surface reflectivity and the high saturation can be used. For the original, the S / N of the RGB read signal
Since the ratio is fixed, the image density is 0.01 to 1.0.
It is desirable to use a document having a color saturation of about 0 and a low saturation such as, for example, a saturation C * of about 20 or less, and an almost achromatic color. Note that the document need only have a document density in the vicinity of the pattern reading position that is substantially uniform, and does not need to have a uniform density over the entire surface.

Next, the read value of the pattern is
Whether the correction of the read signal ratio of 01 (correction of the RGB ratio) is performed or not is determined based on the result selected on the display screen 305 of FIG. 15 (step 2010). When the [Execute] key for the correction of the RGB ratio is selected, the ratio of the read value of the scanner 401 is corrected (step 201).
1). Similarly, execution or non-execution of the process using the background data is determined based on the result selected on the screen of the display screen 305 in FIG. 15 (step 2012), and the [Execute] key of the process using the background data is selected. In this case, background data processing is performed on the read data (step 201).
3). Further, execution of correction of the high image density portion of the reference data,
Non-execution is determined based on the result selected on the screen of the display screen 305 in FIG. 15 (step 2014). When the [Execute] key for correcting the high image density portion of the reference data is selected, the high The processing of the image density section is performed (Step 2015).

Next, a YMCK gradation correction table is created and selected (step 2016), and the above processing is performed by YMCK.
(Step 2017). Further, the above processing is performed for each image quality mode of a photograph and a character (step 2).
018). If the processing has not been performed for each color or has not been performed for each image quality mode in steps 2017 and 2018, the process returns to step 2008.

While these processes are being performed, the display on the display screen 305 is switched as shown in FIG. If the result of image formation using the YMCK tone correction table after the processing is not desirable, a [Return to Original Value] key is pressed so that the YMCK tone correction table before the processing can be selected. As shown in FIG.
5 is displayed.

Next, the operation of detecting uneven light quantity will be described with reference to FIGS. FIG. 20 is a flowchart showing the operation of detecting uneven light quantity, and FIG. 21 is a plan view showing a display screen of the operation unit when the detection of uneven light quantity is performed.

The display screen 30 of the operation unit 142 shown in FIG.
When [Execute] of the detection of the unevenness of the light amount is selected in 5, the display on the display screen 305 is switched as shown in FIG. Here, according to the display on the display screen 305 in FIG. 21, a document for detecting unevenness in light amount is placed on the document table 118 (step 3001). After that, the user selects the [Read Start] key on the operation unit 142 (step 3002).
If the [Cancel] key is selected, the process ends (step 3003). If cancel is not selected, the manuscript on the manuscript table 118 is read by the scanner 401 (step 3004), and his judgment that the data of the pattern portion of the manuscript is normally read is made (step 300).
5). If the reading is not performed normally, the display screen 305 shown in FIG. 21 is displayed again. If the reading is not successful twice, the process ends (step 3006).
If the reading is normal, the reading is stored in a memory for recording and holding, for example, the RAM 417 (step 3).
007). It should be noted that whether or not the reading has been performed normally is determined that the reading has been performed normally when the difference between the reading value at a certain point or the average value of a certain area is not smaller than a predetermined value compared to the average value of the entire reading value. to decide.

Here, the correction of the read value of the pattern by the light amount unevenness detection data will be described. The read value of the formed pattern by the scanner is (r [t]).
[I], g [t] [i], b [t] [i]) (t = Y,
M, C or K, i = 0, 1,... 9), and the read values after correction are expressed as (rl [t] [i], gl [t] [i], b
l [t] [i]) (t = Y, M, C or K, i = 0,
1,... 9), and the reference white value is (Wr [0], W
g [0], Wb [0]). Note that (r, g, b)
Instead of brightness, saturation, hue angle (L ^* , c ^* ,
h ^* ), or lightness, redness and bluishness (L ^* , a ^* ,
b ^* ). Also, the measured light quantity at the pattern reading position is expressed as (Wr [t] [i], Wg [t]
[I], Wb [t] [i]) (t = Y, M, C or K, i = 0, 1,..., 9), the correction of the pattern read value by the light intensity measurement data is as follows. Equation (9) shows.

Rl [t] [i] = r [t] [i] × Wr [0] / Wr [t] [i] (t = Y, M, C or K, i = 0, 1,...) 9) gl [t] [i] = g [t] [i] × Wg [0] / Wg [t] [i] (t = Y, M, C or K, i = 0, 1,...) 9) bl [t] [i] = b [t] [i] × Wb [0] / Wb [t] [i] (t = Y, M, C or K, i = 0, 1,...) · 9) · · · (9) Next, the correction of the background will be described.

There are two purposes for the background correction processing. One is to correct the whiteness of the transfer paper 310 used at the time of ACC, and the other is to correct show-through. That is, in the former, even when an image is formed on the same apparatus at the same time, the value read by the scanner 401 differs depending on the whiteness of the transfer paper 310 used. The disadvantage of not correcting this is that, for example, when recycled paper having a low whiteness is used for this ACC, the recycled paper generally has a large amount of yellow components, so that when a yellow gradation correction table is created, the yellow component is reduced. Correction as follows. In this state, when the image is copied next with an art winding having the highest whiteness, an image having a small yellow component may be obtained, and a desired color reproduction may not be obtained.

In the latter case, when the thickness (paper thickness) of the transfer paper 310 used at the time of ACC is small, the color of a pressure plate or the like that presses the transfer paper 310 is read by the scanner 401 and copied in some cases. That's why. For example, instead of a pressure plate, an ADF (AutoDocument Fee)
When an automatic document feeder called der) is mounted, a belt is used for conveying the document. However, the whiteness is low due to the rubber material used for the belt.
May have a slight gray tint. In the case of such a color, the read image signal is also read as an image signal that is apparently increased as a whole. Therefore, when creating the YMCK gradation correction table, the YMCK gradation correction table is created so as to be thinner accordingly. . In this state, if the transfer paper 310 having a large paper thickness and poor transparency is used, an image having a low density is reproduced as a whole, so that a desired image is not necessarily obtained.

Therefore, in order to prevent the above inconvenience,
The reading image signal of the pattern portion is corrected based on the image signal of the background portion of the paper.

However, there is a merit even when the above correction is not performed. That is, when the transfer paper 310 which always has a large amount of yellow component such as recycled paper is used, it may be possible to improve color reproduction with respect to the color containing the yellow component by not performing the correction. Further, the transfer paper 31 having a small thickness is used.
When only 0 is used, there is a merit that a gradation correction table is created in a state in which the table is adjusted to thin paper.

As described above, the display screen 305 displays the correction of the background as shown in FIG. 15 so that the correction of the background can be turned ON / OFF according to the situation and preference of the user. The key to perform or not perform is displayed.

The write value of the gradation pattern formed on the photosensitive member is LD (i) (where i = 0, 1,... 9).
On the other hand, the reference data is the input value n to the gradation conversion table.
(N = 0, 1, 2,..., 255) and the reading value (rl [t] [i],
gl [t] [i], bl [t] [i]).

The reference data is represented as follows.

Ar [t] [n] (0 ≧ n ≦ 255, t = Y, M, C or K) Ag [t] [n] (0 ≦ n ≦ 255, t = Y, M, C or K) Ab [t] [n] (0 ≦ n ≦ 255, t = Y, M, C or K) (10) where Ar, Ag and Ab are Red signal and Gr, respectively.
Reference data for the eeb signal and the Blue signal.
M, C, and K each represent a toner color. In addition,
Instead of (r, g, b), lightness, saturation, hue angle (L ^* , c ^* , h ^* ), or lightness, redness, and blueness (L
^* , A ^* , b ^* ).

The above expression (10) is a value that can be taken as an input value to the gradation conversion table in 8-bit signal processing, that is, 0
Reference data corresponding to 256 values from
It indicates that it is held in the memory. By storing 256 pieces of reference data in the memory as described above, the processing described later can be simplified. In this case, in order to save the amount of memory for storing the reference data, n [0] = 0, n [i] = 26 × I_5 (I =
Some examples of n [i] taking 1, 2,... 10) as an example
N [i] (0 ≦ n [i] ≦ 255, i = 0, 1, 2,...) Which is a set of (16 in this case) values and corresponding reference data (expression) 10) Ar [t] [n [i]] (0 ≦ n [i] ≦ 255, i = 0, 1, 2,... 10, t = Y, M, C or K) Ag [t] [ n [i]] (0 ≦ n [i] ≦ 255, i = 0, 1, 2,... 10, t = Y, M, C or K) Ab [t] [n [i]] (0 ≦ n [i] ≦ 255, i = 0, 1, 2,... 10, t = Y, M, C or K) (11) is stored in the memory, and n [i] ( i = 1,2, ...
Reference data Ar [t] [n [i]] for n other than 10) (n = 1 to 20 in the above example) may be calculated by performing interpolation, as described later.
As an example, n satisfying n [i] ≦ n ≦ n [i + 1]
[I], n [i + 1] (for n = 1 to 20, i =
0, n [0] = 0, n [1] = 21), reference data Ar, g, b [t] [n [i]], Ar, g, b
It is obtained by performing interpolation using [t] [n [i + 1]].

Next, the correction of the ratio of the read signal of the scanner 401 will be described. In the RAM 417 of FIG.
For each of the YMCK toners, the ratio of the magnitude of the RGB component of the read value of the pattern, K “s” “t” ｛s = R, G or B; t = Y, M, C
Alternatively, K｝ is stored. k [s] [t] means taking a value around 1, but is stored as integer data inside the copying machine as follows: K “s” “t” = kl [ s] [t] / 2 ⁿ (kl [s]
[T] is an integer. For example, n = 10, 2 ⁿ = 1024, and the like. K [s] which is the correction value of the RGB signal thus obtained
Table 1 shows the values of [t].

[0128]

[Table 1]

The correction data of the RGB signals shown in Table 1 above is displayed on the display screen 305 of the operation unit of the copying machine main body 101 as shown in FIG. 22, and the corresponding portion of the display location is pressed with a finger. By doing so, you can enter those numerical values. The input data is stored in the RAM 417.

Here, the case where t = C (cyan) will be described as an example. R of cyan toner reading
The GB component is Arl [C] [n [i] = Ar [W] + (Ar [C] [n [i]]-Ar [W]) × k [r] [C] Agl [C] [n [I] = Ag [W] + (Ar [C] [n [i]] − Ar [W]) × k [g] [C] AbI [C] [n [i] = Ab [W] + ( Ar [C] [n [i]] − Ar [W]) × k [b] [C] (12) Here, i = 0, 1, 2,... 10 and (Arl [C] [n [i]], Agl [C] [n
[I]] and Abl [C] [n [i]]) respectively represent the RGB components of the corrected reference data, and (Ar [T]
[N [i]], Ag [t] [n [i]], Ab [t]
[N [i]) is reference data before correction. Ar
[W], Ag [W], and Ab [W] are RGB signals when white (the lightest color for the scanner used) is read, respectively.

When the read value is an 8-bit signal, the value of this correction value is in the range of 0 to 255 values.
The value is the darkest image density (the amount of light detected by the CCD of the scanner when an object with low reflectance or transmittance is read), and the 255 value is the brightest image density (the amount of light when the object with high reflectance or transmittance is read). (Light amount detected by the CCD of the scanner) and has a value around 255. The accuracy of this correction is slightly reduced, but in actual use, Ar [W] = Ar [C] [0] Ag [W] = Ag [C] [0] Ab [W] = Ab [C] [ 0]. Here, Ar [C] [0], Ag [C]
[0] and Ab [C] [0] are values obtained by reading the background portion of the paper. Note that when reading the background of the paper, several sheets of paper are stacked on the back of the paper (so-called white back), and care is taken not to darken the back of the paper, thereby preventing the accuracy of the background reading from lowering. be able to.

On the other hand, the above correction may be processed by the following equation (15).

Arl [C] [n [i]] = Ar [C] [n [i]] × k [r] [C] Agl [C] [n [i]] = Ag [C] [n [ i]] × k [g] [C] Ab1 [C] [n [i]] = Ab [C] [n [i]] × k [b] [C] (13) where i = 1, 2,..., 10. Where i
= 0, n [0] = 0, that is, when the input value to the gradation correction table is 0, the correction by the above equation (13) is not performed. K [r] [C] in equation (15),
The values of k [g] [C], k [b] [C] and k [r] [C], k [g] [C], k [b] used in equation (14)
[C] is not the same numerical value, and it is necessary to change the numerical value to an appropriate value depending on the formula used. In order to simplify the processing, (Arl [C] [n [i]], A
gl [C] [n [i]], Abl [C] [n [i]])
To the new (Ar [t] [n [i]], Ag [t] [n
[I]] and Ab [t] [n [i]]).

Next, a method of generating a gradation conversion table (LUT) performed by the γ correction circuit 410 as the γ conversion processing unit when ACC is executed will be described.

The image signals of the complementary colors of the respective YMC toners are blue, green, and red, respectively. Therefore, in order to simplify the processing, the above-described reference data Ar [t] [i], A
g [t] [i], Ab [t] [i], reference data Ab [t] [i],
Ag [t] [i] and Ar [t] [i] are used. This is effective when the spectral (reflectance) characteristics of the toner used do not change significantly, that is, when the color does not change.

To simplify the following description, A [t] [n
[I]] (0 ≦ n [i] ≦ 255; i = 1, 2,...)
., 10; t = C, M, Y). For the black toner, sufficient accuracy can be obtained by using any of the RGB image signals, but a G (green) component is used here.

Similarly, the read signal is a [t] [i] (i = 1, 2,..., 9;
t = C, M, Y). In addition, a certain color toner t (t
= C, M, Y, K) reference data A [t] [i]
And the write value a [t] [i] of the LD,
They are abbreviated as [i] and a [i].

The YMCK gradation conversion table is based on a
[LD] is obtained by comparing the reference data A [n] stored in the ROM 416. here,
n is an input value to the YMCK gradation conversion table,
The reference data A [n] obtained by correcting the B signal is obtained by converting the input value n into YM
This is the target value of the read image signal obtained by scanning the YMC toner pattern output with the laser writing value LD [i] after the CK gradation conversion. There are two types of reference data A [n] obtained by correcting the RGB signals: reference data that performs correction in accordance with the image density that can be output by the printer, and reference data that does not perform correction. The determination as to whether or not to perform the correction is made based on determination data described later stored in the ROM 416 or the RAM 417 in advance. This correction will be described later.

L corresponding to the above-mentioned reference data A [n]
By obtaining D, a laser output value LD [n] corresponding to the input value n to the YMCMK gradation conversion table is obtained. .., 255 (8
(In the case of a bit signal), a gradation conversion table can be obtained.

At this time, instead of performing the above processing on all the values for the input values n = 00h, 01h,... FFh (hexadecimal) for the YMCK gradation conversion table. The above processing is performed for discrete values such as n [i] = 0, 11h, 22h,... FFh, and for other points, interpolation is performed using a spline function or the like, or stored in the ROM 416 in advance. YM
Among the CKγ correction tables, (0, L
D [0], [11h, LD [11h]]), (22h,
LD [22h]]),..., (FFh, LD [FF
h]])).

The above processing will be described with reference to a graph shown in FIG. FIG. 23 is a graph for explaining the correction of the background. The horizontal axis of the first phenomenon (a) in FIG. 23 is the input value n to the YMCMK gradation conversion table, and the vertical axis is the read value of the scanner 401 (after processing), and the above-described reference data A [i].
Represents The value read by the scanner 401 (after processing) is calculated by comparing the value obtained by reading the gradation pattern with the scanner 401 with R
This is a value after the GBγ conversion (no conversion is performed here) and the averaging processing and addition processing of read data at several places in the gradation pattern, and is processed here as 12-bit data in order to improve calculation accuracy. The horizontal axis of the second phenomenon (b) is
As with the vertical axis, the read value of the scanner 401 (post-processing)
Is represented. The vertical axis of the third phenomenon (c) indicates the laser light (L
D) represents the write value. This data a [LD] represents the characteristics of the printer. The write value of the laser light (LD) of the pattern actually formed is 00h (background), 11
h, 22h,... EEh, FFh, which are 16 points, which indicate intermittent values. In this case, interpolation is performed between the detection points and treated as a continuous graph. The graph of the fourth phenomenon (d) is Y
The vertical and horizontal axes of the MC graph (f) are the graph (d)
Are the same as the vertical and horizontal axes. When forming a gradation pattern for detection, a YMCK gradation conversion table (G) shown in a graph (f) is used. The horizontal axis of the last graph (e) is the same as the third phenomenon (c), and indicates the relationship between the LD write value and the gray pattern read value (post-processing) of the gray pattern when the gray pattern is created. For convenience, a linear transformation for convenience is shown. Reference data A [n] is obtained for a certain input value n from the graph of FIG.
Is obtained along the arrow (l) in the figure, using the read value a [LD] of the gradation pattern.

Next, the calculation procedure will be described with reference to FIG. FIG. 24 is a flowchart showing a calculation procedure of the gradation conversion table when ACC is executed.

First, input values necessary for obtaining a YMCKγ correction table are obtained (step 4001). Here, n [i] = 11 [h] × i (i = 0, 1,...)
., Imax = 15). Next, the reference data is corrected using the correction values of the RGB signals according to the procedure described above (step 4002). Next, the reference data A [n] is corrected according to the image density that can be output by the printer 412 (step 4003). Here, the read value of the laser that can obtain the maximum image density that can be created by the printer 412 is FF.
h (hexadecimal notation), and the pattern reading m [FFh] at this time is mmax. Reference data A [i] (i = 0, 1,..., I1) for which no correction is performed from the low image density side to the intermediate image density side, and reference data A [i] (for which no correction is performed on the high image density side) i = i2 + 1,
..., imax-1) (i2≥i1, i2≤imax
-1), reference data A [i] to be corrected (i = i1 +
1,... I2).

In the following, a specific calculation method will be described assuming that the image signal is in proportion to the original reflectance without performing RGBγ conversion. Among the reference data not subjected to correction, reference data A [i2 + having the lowest image density in the high image density portion
1] and the reference data A [i1] having the highest image density in the low image density portion, a difference Δref between the data is obtained.
That is, Δref = A [il] −A [i2 + l] (14)

On the other hand, in the case of the reflectance linear or the brightness linear without performing the RGBγ conversion as the inversion processing, Δr
ef> 0. On the other hand, the difference Δdet is similarly obtained from the read value mmax of the pattern that can obtain the maximum image density that can be created by the printer 412. That is, Δdet = A [il] -mmax (15)

From the above equations (14) and (15), the reference data A [i] (i = i1 +
1,..., I2) as A [i] = A [il] + (A [i] −A [il] × (△ det / △ ref) (16) where i = i1 + 1, i1 + 2,..., i
2-1 and i2.

Next, n [i] obtained in step 4001
Is obtained from the reference data A [n] from the read image signal m [i] of the scanner 401 (step 4004).
Actually, reference data A corresponding to discrete n [i]
[N [j]] (0 ≦ n [j] 255, j = 0, 1,...)
Jmax, n [j] ≦ n [k] forj ≦ k) is as follows. That is, n [j] ≦ n [i] <n [j +
1] (0 ≦ j ≦ jmax).

In the case of an 8-bit image signal, n [0] = 0,
n [jmax] = 255, n [jmax + 1] = n [j
If the reference data is obtained assuming that [max] +1, A [jmax + 1] = A [jmax], the calculation is simplified.

From j obtained as described above, m [i]
Is calculated from the following equation.

M [i] = A [j] + (A [j + 1] −A [i]) · (n [i] −n [j]) / (n [j + 1] −n [j]) (17) Further, as for the interval of the reference data, the smaller the interval n [j] is, the higher the accuracy of the gamma correction table finally obtained becomes.

Here, the interpolation is performed using a linear expression, but the interpolation may be performed using a higher-order function, a spline function, or the like. In that case, m [i] = f (n [i]). In the case of a k-th order function,

[0152]

(Equation 6)

And so on.

Next, m obtained in step 4004
The write value LD [i] of the LD for obtaining [i] is obtained by the same procedure as in step 4004 (step 40).
05). (J> k): That is, when processing image signal data that has not been subjected to RGBγ conversion, LD
As the value of becomes larger, a [LD] becomes smaller.
That is, for LD [k] <LD [k + 1], a [L
D [k]] ≧ a [LD [k + 1].

Here, the value at the time of pattern formation is represented by LD [k].
= 00h, 11h, 22h, ..., 66h, 88h,
AAh, FFh, (k = 0, 1,... 9) were set to 10 values. This is because, at an image density with a small amount of toner adhesion, a change in the reading value of the scanner 401 with respect to the amount of toner adhesion is large. Therefore, the interval between the write values LD [k] of the pattern is made small. This is because the change in the read value of the scanner 401 with respect to the attached amount is small, so that the reading is performed with the interval increased.

As a merit of this, LD [k]
= 00h, 11h, 22h, ..., EEh, FFh
(Total 16 points) and the like, the toner consumption can be suppressed as compared with the case where the number of patterns is increased, and in the high image density region, the change with respect to the LD writing value is small, the potential unevenness on the photoconductor, the toner Since the read value is likely to be reversed due to the influence of adhesion unevenness and potential unevenness, the pattern is formed with the LD write value as described above because narrowing the interval between the LD write values is not necessarily effective in improving the accuracy. doing.

Here, a [LD [k]] ≧ m [i]> a
For LD [k] that becomes [LD [k + 1]], LD [i] = LD [k] + (LD [k + 1] -LD
[K]) · (m [i] −a [LD [k]]) / (aLD
[K + 1] -a [LD [k]]).

When 0 ≦ k ≦ kmax [kmax> 0], when a [LD [kmax]> m [i] (when the image density of the target value obtained from the reference data is high), LD [ i] = LD [k] + (LD [kmax] −LD
[Kmax-1]) · (m [i] -a [LD [kmax
-1]]) / (a [LD [kmax]]-a [LD [k
]]) Is predicted by extrapolation using a linear equation. This may be extrapolated by other methods such as taking a logarithm in addition to the linear expression.

Thus, a set [n [i], L of the input value n [i] and the output value LD [i] to the YMCKγ correction table is obtained.
D [i]] (i = 0, 1,..., 15) is obtained.

Then, the obtained [n [i], LD
[I]] (i = 0, 1,..., 15) to perform interpolation using a spline function or the like, or select a γ correction table stored in the ROM 416 (step 40).
06).

Next, a method of selecting a γ correction table stored in the ROM 416 will be described with reference to FIG. FIG. 25 is a flowchart showing a procedure for selecting a gradation conversion table when executing ACC.

First, the coefficient I applied to the entire γ correction table
DMAX [%] is obtained (step 5001). Here, when n [imax] = FFh, IDMAX =
LD [imax] / FFh × 100 [%]. Also, here, LD ′ [i] = LD [i] × 100 / I
Output value L to YMCKγ correction table as DMAX
Replace D [i]. This eliminates the need to consider IDMAX when selecting the γ correction table.

Next, the curvature, h, and s, which are indices of the curved portions of the whole, the highlight portion, and the shadow portion, are selected. Therefore, first, the entire curvature m is selected (step 5002). The basic concept of the selection is that the finally obtained gradation conversion curve E [j] (0 ≦ j ≦ 25)
5) and the input value n [i] to the YMCKγ correction table
(N [i], LD [i]) (0
≤ i ≤ 15) sum of squares of error error = {wi · (LD [i] -Ε [n [i]])
² Select m so as to minimize (hereinafter, referred to as an error). Here, wi is a weight for the input value to the i-th YMCKγ correction table. At this time, if the error in the highlight portion is large, a desired result cannot be obtained. Therefore, the weight wi of the highlight portion is particularly increased, and the error is reduced as much as possible.

Similarly, the curvature h of the highlight portion which minimizes the error is determined (step 5003), and the curvature s of the shadow portion which minimizes the error is determined (step 50).
04). (H_min, m_m
in, s_min) and IDMAX are used as the curvature of the new correction gradation curve.

Next, an original for detecting unevenness in light amount for detecting the light amount at the reading position of the gradation pattern will be further described. As described above, a document for detecting unevenness in light amount is desirably a document which has a low saturation such that the document density near the pattern reading position is almost uniform and has a saturation C ^{* of} about 20 or less, and is almost achromatic. As a manuscript satisfying this, it is easy to use a blank sheet used as the transfer sheet 310 because of availability or the like. However, the scanner 401 determines that the read value is 0 to 255 of 8
Bit signals can be output, and 25
When the value is set to about 5 to 240, when a blank sheet is read, the read value of the scanner 401 saturates to 255, and the sensitivity setting may be inappropriate for correcting the light amount unevenness.

This will be described with reference to FIG. FIG. 26 is a graph for explaining the relationship between the read value of the scanner and the frequency at which pixel data is included. In this figure, a region a) is a region where the background portion of the paper has a high reflectance or a large amount of light is applied, and a region b) is a background portion of the paper having a normal reflected light amount. A blank sheet corresponds to the area a), and since the amount of reflected light during copying is high, most of the peaks reach a saturation point of 255 or more.

A method for dealing with such a case is shown in FIGS. 27 and 28. FIG. 27 is an explanatory diagram schematically showing a unit for making a document black back, and FIG. 28 is an explanatory diagram schematically showing another unit for making a document black back.

In FIG. 27, transfer paper 310 is placed on a document table (not shown) on the upper part of copying machine main body 101, and black paper 602 is overlaid on transfer paper 310. Then, the pressing plate or the document feeder 603 (hereinafter simply referred to as the pressing plate 603) is closed. Thereby, the transfer paper 3
A black paper 602 is pressed against the back surface of the transfer paper 10, which is the same as the black paper (Black Back) processing of the transfer paper 310. In FIG. 28, the transfer paper 310 is placed on a document table, and reading is performed with the pressure plate 603 opened. Since there is no pressure plate 603 on the back surface of the transfer paper 310, most of the light is scattered and there is no reflected light amount, so that the same state as when the transfer paper 310 has been subjected to the black back processing can be obtained. In addition, even if the reflectance of the pressure plate 603 is reduced to, for example, 50% or less, the transfer paper 31
0 can be set to a black back state. 60
1 is an operator.

On the other hand, the black paper 60
2 and 5 to 10 blank sheets (not shown), and a state in which the pressure plate 603 is closed is a white background (White B).
Assuming that the state is ACK), the difference between the white back state and the black back state will be described with reference to FIGS. 29 and 30. FIG. 29 is a graph for explaining the relationship between the value read by the scanner and the frequency at which pixel data is included, and FIG. 30 is a diagram for explaining the area read by the scanner.

In the graph of FIG. 29, a region having a blank portion, that is, a background portion of the paper, for example, 100 pixels in the main scanning direction and 100 pixels in the sub-scanning direction as shown in FIG. Are plotted on the horizontal axis, and the vertical axis is the number of pixels whose frequency includes the image data. In the state in which the black back is set as compared with the state in which the white back is set, the scanner 40
Since the read value of 1 shifts from the 255-value side to the 0-value side, it is possible to avoid the inconvenience of the above-described 255 value and saturation.

The reason will be described with reference to FIG. FIG.
FIG. 1 is a diagram schematically showing a reading system of a copying machine. Illumination light from an exposure lamp 119 composed of a halogen lamp is reflected by a reflection plate 610 and reflected by the surface of the original 611 and reflected by the pressure plate 603 after passing through the original 611, respectively. The light is reflected by the second mirror 612, the first mirror 613, and the third mirror 614, and is read by the CCD 123 via the lens 122. Of these,
The amount of reflected light reflected on the document surface does not change so much in the black back state and the white back state. However, the amount of light reflected by the pressure plate 603 is smaller in the black-back state than in the white-back state, so that the amount of light incident on the CCD 123 decreases, the read value decreases, and the read value shifts. It is. Reference numeral 615 denotes a lamp shade, 616 denotes a first traveling system for moving the exposure lamp 119, the reflection plate 610, the second mirror 612, and the like.
Denotes a second traveling system for moving the first mirror 613, the third mirror 614, and the like.

The reflectance of the back side of the document can be reduced by using the pressure plate 603 whose reflectance on the reflection surface side is 10% or less, preferably about 5%. This can be realized by mirror finishing, black coating, or the like, or by using a black material. This makes it possible to reduce the read value of the scanner 401 to an appropriate value even when blank paper is used for correcting unevenness in the light amount, prevent saturation to 255 values (in the case of an 8-bit signal), and Accuracy can be obtained. This is not limited to the 8-bit processing, and is effective even when the number of bits is larger.

When blank paper is used for correcting light amount unevenness, the amplification circuit 502 of the scanner 401 shown in FIG.
, The output of the scanner 401 when a blank transfer sheet is read in the copy mode becomes
As an example, when an 8-bit signal is set to 250 values, it can be changed to output 180 values.

The procedure for changing the amplification factor of the scanner 401 will be described with reference to the flowchart of FIG. The change procedure is as follows. First, according to the display on the display screen 305 in FIG. 21, a blank sheet is placed on a document table as a document for detecting unevenness in light amount (step 6001).
5, the user selects the [Read Start] key (step 6002). If the [Cancel] key is selected, the process ends (step 6003). On the display screen 305 in FIG. 16, when “white” is selected as the original to be used for the correction of the light amount unevenness (step 600).
4) The amplification factor of the amplifier circuit 502 of the scanner 401 is reduced as compared with the normal copy, and the amplification factor of the analog signal of the scanner 401 is reduced (step 6005). Next, the original platen is read by the scanner 401 (step 600).
6) It is determined whether the data of the pattern portion has been read normally (step 6007). If the image is not read normally, it is displayed again on the display screen 305 as shown in FIG. If it is not read twice correctly, the process ends (step 6008).

When the data of the pattern portion is normally read, and when the document is selected as [white] on the display screen 305 of FIG. 16 (step 6009), the amplification of the amplification circuit 502 of the scanner 401 is performed. The ratio is changed to the setting at the time of copying (step 6010), and the read value is stored in the RAM for storage (step 6011). If the document is selected as [non-white], step 6011 is executed. It should be noted that whether or not the reading was normal was determined that the reading was normal if the difference between the reading at a certain point or the average of a certain area did not exceed a predetermined value compared to the average of the entire reading. to decide.

Next, the case where the light amount in the blank portion of the gradation pattern is read by the scanner 401 will be described with reference to FIGS. FIG. 33 is a plan view showing a part of the transfer paper on which a gradation pattern is formed, FIG. 34 is a plan view showing a part of the transfer paper on which a gradation pattern with a small margin is formed, and FIG. 35 is a gradation pattern. 36 is a graph for explaining the relationship between the reading value of the scanner and the frequency at which the pixel data is included, and FIG. 37 is a view showing a part of the transfer paper on which another gradation pattern is formed. FIG. 38 is a flowchart for explaining a procedure of reading a margin.

The gradation pattern formed on the transfer paper 310 will be described with reference to FIG. 33. The color patches 1 to 3 have different gradations of yellow, magenta, cyan, and black formed with a margin portion therebetween. It has a pattern. As the read values of these color patches 1 to 3, the scanner 40 in the area of a1-0 to a3-0 in the figure is used.
The average of one reading is used.

In order to correct the light quantity unevenness in the color patch areas a1-0 to a3-0, in the above-described embodiment, the transfer paper 310 on which no pattern is formed is replaced with a1-0 to a3-0. The amount of reflected light at the portion corresponding to a3-0 was read by the scanner 401. In the modification of FIG. 32, for example, in order to obtain the amount of reflected light from the scanner 401 of a3-0 of the color patch 3, the color patch 3
Margins a3-1 to a3-2, a3-3 to a3
The scanner 401 reads the reflected light amount of the scanner lamp at -4 or any of a3-1 to a3-4. The positions of the centers of the margins a3-1 and a3-2 exist on a straight line passing through the center of a3-0, and a3-0
If they are separated from each other by l3-1 and l3-2,
The reflected light amount a3-0 of the scanner lamp at the position a3-0
Is a3-0 = (13-2.a3-1 + l3-1.a3-
2) Obtained as / (l3-1 + l3-2).

Similarly, the center positions of the margins a3-3 and a3-4 exist on a straight line passing through the center of a3-0, and a3
-3, 13-4, respectively, the reflected light amount a3--3 of the scanner lamp at the position a3-0.
0 is a3-0 = (13-4.a3-3 + 13-3.a3-
4) Obtained as / (13-3 + 13-4).

Alternatively, when the read values of the margins a3-1 to a3-4 are obtained, the following is performed.

A3-0 = (1/2). (13-2.a3
-1 + l3-1 · a3-2) / (l3-1 + l3-2)
+ (1/2). (13-4.a3-3 + 13-3.a3
-2) / (l3-3 + l3-4) On the other hand, FIG. 34 shows a case where the margin between the color patches 1 to 3 is small, and also in this case, a3-0 = (l3-2a3- 1 + l3-1 · a3-
2) Calculate a3-0 as / (l3-1 + l3-2).

Further, the amount of reflected light of the scanner lamp in the margin around the gradation pattern may be read by the scanner 401, and the read value may be used as it is. That is, any of the values a3-1 to a3-4 in FIG. 32 is used as it is as the value of a3-0 without performing the above processing.
That is, a3-0 = a3-1 and the like. This is a3
For each of -1 to a3-4, l3-1 to l3-
The closer each value of 4 is to 0, the smaller the error handled as the value of a3-0. This is represented by the following equation.

A3-0 = lima3-1 for l3-1 → 0 In this example, lim represents a limit value when l3-1 approaches 0.

Another modification of the gradation pattern will be described with reference to FIG. In this example, the reading areas a1-1 to a3-1 of the color patches 1 to 3 include a color patch and a blank portion as illustrated. This reading area a1
For example, -1 to a3-1 read a range of 100 pixels in the main scanning direction × 50 pixels in the sub-scanning direction.

FIG. 36 shows an example of the read result. In the figure, the horizontal axis represents the read value of the pixel, and the vertical axis represents the frequency of the pixel from which the read value is obtained. From this figure, two peaks, that is, the read value of the color patch and the read value of the margin, are obtained. By calculating the peak value of each peak or the average value of each peak, the read value of the color patch is obtained. And the read value of the margin can be obtained.

FIG. 37 shows still another modification of the gradation pattern, which has a blank portion inside the color patches 1 to 3.
The margins of the color patches are formed in the main scanning direction, but may be formed in the sub-scanning direction. Further, the number of pixels in the color patch portion and the margin portion may be about 4 pixels or more. For pixels smaller than that, the peaks of the read values of the color patch portion and the blank portion in FIG. 36 approach, making it difficult to detect an accurate value.

The procedure for reading the margin will be described with reference to the flowchart of FIG. First, of the image data in the reading area taken into the image memory, the number of pixels having the same image data value is counted, and FIG.
(Step 7001). At this time, even if the values are not exactly the same, they may be integrated in a binary unit (the number of pixels having a value of 0 and 1), a 4-value unit (the number of pixels having a range of values from 0 to 3), or the like. . Thereafter, as a read value of the color patch, a peak value of the number of pixels or a moving average value of several read values is calculated from the 0 side in FIG. 36 (step 7002), and the peak value is calculated as in c) of FIG. It is determined (step 7003), and the determined peak value or moving average value is stored as a read value of the color patch section (a in FIG. 35) (step 7004).

On the other hand, for the read value of the margin, 2
From 55 values, a peak value or a moving average value for several read values is obtained (step 7005), and a peak value is obtained as shown in d) of FIG. 36 (step 7006). This is stored as a blank portion or a paper background portion (step 700).
7).

Next, at the same time as reading the ACC pattern at the reading position of the gradation pattern, the background portion near the reading position is read, and the amount of unevenness in the light amount of the pattern portion is predicted. The procedure for making the selection will be described with reference to the flowcharts shown in FIGS. FIG. 39 shows the first part of a flowchart showing the procedure for creating and selecting a gradation correction table by estimating the amount of light amount unevenness in the pattern portion. FIG. 40 shows the second part connected to terminal B in FIG. Is shown.

On the display screen 305 of the operation unit 142 shown in FIG. 14, a [Print Start] key is selected, and a plurality of density gradations corresponding to each color of YMCK and each image quality mode of characters and photographs as shown in FIG. A pattern is formed on transfer paper 310 (step 8001). After the density gradation pattern is output to the transfer paper 310, the display screen 30 of the operation unit 142
As shown in FIG. 18, the transfer paper 310
18 is displayed. According to this screen display, the transfer paper 310 on which the pattern is formed is placed on the platen 118.
(Step 8002), and the display screen 3 of FIG.
When the [Read Start] key is selected in 05, the scanner 401 travels and reads the RGB data of the YMCK density pattern (step 8003). At this time, the data of the pattern portion, the data of the background portion of the transfer paper 310, and the value of the margin around the pattern are read. When the data of the pattern portion is normally read, the display screen 3 shown in FIG.
At 05, it is determined whether or not the [Execute] key for correcting the unevenness of the light amount is selected (step 8004).

When the correction of the light amount unevenness is selected, the amount of the light amount unevenness of the pattern portion is predicted from the read value of the margin around the pattern portion by the above-described method (step 8005), and called out from the memory. The value of the light amount unevenness is called (step 8006). The difference between the value of the light amount unevenness retrieved from the memory and the value of the light amount unevenness calculated from the margin around the pattern is calculated, and it is determined whether the difference is within a predetermined value (step 8007). If the difference is larger than the predetermined value, a message as shown in FIG.
5 and the user makes a selection from the display screen of FIG. 40 (step 8009). In other words, on the screen, [detection] and [cancel] of the light amount unevenness, [execute with stored value] for correcting the pattern reading value based on the stored light amount unevenness amount, and the pattern were read at the same time. [Execute with predicted amount] to execute correction with the value of light amount unevenness predicted from the value of the margin, [Do not perform correction] of light amount unevenness
Can be selected. In order to increase the accuracy of ACC, it is desirable to perform detection, but detection time is required. Therefore, in practice, it is sufficient to select execution with a stored value or execution with a predicted value. In the display on the display screen 305 in FIG. 41, the selection is made by the operation unit 142. However, since it is troublesome for the user to determine which to select, when the difference between the stored value and the predicted value is large, May be executed with a predicted value.

If the [Execute detection] key is selected (Step 8010), the detection of light amount unevenness is executed (Step 8011), and the read value of the pattern is corrected using the detected value (Step 8012). If the [Cancel] key is selected, the process ends there (step 8013). When the “do not perform correction” key is selected (step 8014), step 8017 in FIG.
If the key is selected (step 8015), a step 8012 of correcting the pattern read value with the light amount correction data stored in the memory in advance is executed.
If the “Execute with predicted amount” (other than correction with stored value) key is selected (Step 8015), the pan reading is corrected with the predicted value from the periphery of the pattern (Step 801).
6).

Next, the execution or non-execution of the correction of the ratio of the read values (RGB ratio) of the scanner 401 is determined based on the result selected on the display screen 305 in FIG. 15 (step 80).
17) If the [Execute] key is selected, the ratio of the read values of the scanner 401 is corrected (step 801).
8). Similarly, execution or non-execution of the process using the background data is determined based on the result selected on the display screen 305 of FIG. 15 in FIG. 13 (step 8019), and the [Execute] key of the process using the background data is pressed. If selected, background data processing values for the read data are performed (step 80).
20).

Further, the execution or non-execution of the correction of the high image density portion of the reference data is determined based on the result selected on the display screen 305 in FIG. 15 (step 8021), and when the [Execute] key is selected, the reference is made. The data is processed in the high image density portion (step 8022). Then, a YMCK gradation correction table is created and selected (step 802).
3).

The above-described correction processing is performed for each color of YMCK and each image quality of photographs and characters. During these processes, the display screen becomes the screen shown in FIG. YMCK after processing
If the result of image formation using the gradation correction table is not desirable, the [Return to Original Value] key is pressed in FIG. 1 so that the YMCK gradation correction table before processing can be selected.
3 is displayed on the display screen 305.

When reading the reflected light amount of the document for correcting the unevenness in light amount, the same averaging process as in reading the gradation pattern is performed. Therefore, the averaging process will be described next.

The read values of the RGB signals of the pattern are stored in the image memory 424 shown in FIG. 1 and are averaged by the CPU 415. The averaging process is performed by the CPU 41
Instead of 5, a circuit for the averaging process may be separately provided.

When averaging is performed using the image memory 424, the RGB γ correction circuit 403 sets a through (non-conversion) gradation conversion table, and the MTF correction circuit 40
5 is a smoothing filter of 5 pixels in main scanning × 3 pixels in sub-scanning:

[0199]

(Equation 7)

Is used.

As a first example of the averaging process, 100 pixels of main scanning (1/4 inch at 400 dpi, approximately 6.4 mm) included in the read position of the gradation pattern ×
The average value of the read values of 100 pixels in the sub-scanning direction (a total of 10,000 pixels) is used as the read value of each pattern (FIG.
0). The size is not limited to this, and may be reduced to about several tens of pixels. When a 400 dpi scanner is used, CCD elements are different between even-numbered pixels and odd-numbered pixels in the main scanning direction. In such a case,
Since the read values are slightly different from the even-numbered and odd-numbered pixels, it is necessary to take an average value for the even-numbered pixels in the main scanning direction. In this example, as shown in FIG. 42 showing the relationship between pixels in the main scanning direction and the sub-scanning direction, 32 pixels in the main scanning direction,
An average value of a total of 96 pixels of three pixels is used with three pixels in the sub-scanning direction.

The procedure of the averaging process will be described below with reference to the flowchart of FIG. First, the RGB gamma correction table is set to through (step 9001), and the MTF is set.
A smoothing filter is set in the correction circuit 405 (step 9002). Next, the scanner 401 is moved to read the gradation pattern (step 9003), and the read pattern data is stored in the image memory 424 (step 9).
004), an RGB gamma correction table for copying is set (step 9005). Next, an MTF filter for copying is set (step 9006), and finally an averaging process is performed (step 8009).

Such processing is used in the flow chart of FIG. 11 and subsequent flowcharts in the processing of reading the transfer paper or the original for detecting unevenness in the light amount by the scanner. When the averaging process is not performed, the read pixel value is used.

Next, a second embodiment of the present invention will be described with reference to FIG.
FIG. In this second embodiment,
Transfer paper 310 on which gradation pattern is formed in ACC
The optimum gradation correction table is selected and created without being affected by the residual amount of the fixing oil remaining on the upper side. Note that the configurations of the image processing unit, the laser modulation circuit, and the image reading system are the same as those in the first embodiment, and a duplicate description will be omitted. Further, in the case where the display contents of the display screen of the operation unit are the same, the description will be made using the display screen in the first embodiment.

First, the operation of the ACC of the image density in the second embodiment will be described with reference to FIGS. 44 to 49. FIG. 44 shows AC in the second embodiment.
45 is a flowchart showing the operation of C, FIG. 45 is a plan view showing a display screen of the operation unit when the ACC menu is called, and FIG. 46 is an operation unit when the execution of ACC for copy use or printer use is selected. 47 is a plan view showing a display screen of the operation unit after reading the background, FIG. 48 is a plan view showing a display screen of the operation unit after reading the pattern, and FIG. 49 is a print start key. FIG. 7 is a plan view showing a density gradation pattern on transfer paper when is selected.

First, the selection of the ACC function of the image density will be described. This selection is made by calling the automatic gradation menu on the display screen 305 of the operation unit 142 in FIG. 12 in the first embodiment described above.
Displays a screen as shown in FIG. Here, when the [Execute] key of the automatic gradation correction for use of copy or use of the printer is selected, the display screen 305 is switched to a screen as shown in FIG. When the use of copy is selected, the gradation correction table used at the time of use of the copy is changed based on the reference data, and when the use of the printer is selected, the gradation correction table at the time of use of the printer is changed based on the reference data. If the result of image formation using the changed YMCK tone correction table is not desirable, the [Restore] key is displayed in FIG. 45 so that the YMCK tone correction table before processing can be selected. It is displayed in the screen 305.

Explaining other display items on the display screen 305 in FIG. 45, if "Execute" of the automatic gradation correction setting is selected, the display screen switches as shown in FIG. Correction, high density part correction,
[Execution] and [Non-execution] of the correction of the RGB ratio, the correction of the light amount unevenness, and the correction according to the gloss can be selected by using keys. These selections are not always necessary and may always be executed. Further, in the automatic gradation menu, the setting of ACC can be selected, and in the detection menu, detection of unevenness in light amount and registration of the background of the paper can be selected.

Next, the operation of the ACC will be described with reference to the flowchart of FIG. Display screen 305 shown in FIG.
When the user selects the [Execute] key for automatic tone correction for use in copying or using a printer, the display on the display screen 305 is switched as shown in FIG. According to the screen display, the transfer paper 310 for forming the gradation pattern is
46 (step 10001), and
When the [Reading Start] key is selected on the display screen 305 of FIG.
Is read (step 10002). Scanner 4
47 reads the background of the transfer paper 310, as shown in FIG. 47, the display on the display screen 30 is switched, so that the transfer paper 310 on the document table 118 is fed according to the screen table. Copy), and select the [Print Start] key on the screen (step 1000).
3).

When the [Print Start] key is depressed, a plurality of density gradation patterns 311 corresponding to the YMCK colors and the image quality modes of characters and photographs are formed on the transfer paper 310 as shown in FIG. 49 (step 10004). ). This density gradation pattern 311 is stored in advance in the computer 420 of FIG. 1 in the same manner as in the first embodiment.
The data is stored and set during the OM.

After the pattern is output on the transfer paper 310,
So that the transfer paper 310 is placed on the platen 118,
The display on the display screen 305 switches as shown in FIG. According to the display on the screen, the transfer paper 310 on which the pattern is formed is placed on the document table 118 (step 1000).
5) On the display screen 305 of FIG. 18, select the [Reading Start] key or select the [Cancel] key (step 10006). If the [Cancel] key is selected, the process ends (step 10007). If the [Reading Start] key is selected, the scanner 401 runs and
The RGB data of the YMCK density pattern is read (step 10008). At this time, the data of the pattern portion and the data of the background portion of the transfer paper 310 are read. In FIG. 49, the reading position 320 of the pattern is indicated by a dotted line, taking the case of yellow as an example. Although not shown, the reading position is located substantially at the center of the upper two high-density patterns.

It is determined whether the data in the pattern portion has been read normally (step 10009). If the data has not been read normally, the screen shown in FIG. 18 is displayed again. If the reading is not successful twice, the process ends (step 10010). If the data of the pattern portion has been read normally, it is determined whether or not “correction of light amount unevenness” on the display screen 305 of FIG. 48 has been selected (step 10011). If it is selected to execute the light amount unevenness correction, the pattern read value is corrected using the light amount unevenness correction data stored in advance (step 10012).

Next, it is determined whether the [Execute] key for the correction according to the gloss on the display screen 305 in FIG. 48 has been selected (step 10013), and if the [Execute] key has been selected, Then, the background read value read before forming the gradation pattern is compared with the background read value read after forming the gradation pattern, and the read value is corrected based on the comparison result (step 10014). The correction processing according to the gloss will be described later.

Similarly, execution or non-execution of the correction of the ratio of the read signal of the scanner 401 (correction of the RGB ratio) of the read value of the pattern is determined based on the result selected on the display screen 305 of FIG. 48 (step 10015). In the case of execution, the ratio of the read value of the scanner 401 is corrected (step 10016).

Whether the correction according to the background density is to be performed or not is determined based on the result selected on the display screen 305 of FIG. 48 (step 10017). Then, correction according to the background density is performed (step 10018).

Further, the execution or non-execution of the correction of the high image density portion of the reference data is determined based on the result selected on the display screen 305 of FIG. 48 (step 10019), and when the execution of the correction is selected, the reference is made. The process of the high image density portion is performed on the data (step 10020).

Next, a YMCK gradation correction table is created.
Is selected (step 10021), and the above processing
(Step 10022). Further, the above processing is performed for each image quality mode of a photograph and a character (step 10023). While these processes are being performed, the display on the display screen 305 is switched as shown in FIG.
If the result of image formation using the YMCK gradation correction table after processing is not desirable,
The [Return to Original Value] key is pressed on the display screen 3 as shown in FIG. 45 so that the gradation correction table can be selected.
05 is displayed.

Next, the principle of correcting uneven gloss will be described with reference to FIGS. 50 and 51. FIG. FIG. 50 is a diagram for explaining how the toner surface becomes smooth due to the attachment of the fixing oil, and FIG. 51 is a diagram for explaining a state where the toner surface becomes rough due to a decrease in the amount of the fixing oil. . In the following description, the amount of the fixing oil is described, but the contribution of the fixing oil and the contribution of the gloss (this also depends on the fixing temperature at the time of fixing) are not clearly distinguished. The value including the contribution will be described as the amount of the fixing oil.

FIG. 50 shows a fixing oil (silicone oil).
Shows that the surface of the toner is covered with a layer of fixing oil (not shown) due to the adhesion, and the surface becomes smooth. As a result of the smooth surface, a specular component increases with respect to incident light, and gloss is generated. The geometry of a non-integrating sphere (spectral) colorimeter, that is, the positional relationship between the angle of light incident for measurement and the angle of light to be measured is 0/45 ° or 45/0 °. used. The geometry 0/45 ° is incident (0 °) perpendicularly (normal direction) to the measurement surface, and 45 ° to the normal direction.
Measure the light reflected in the ° direction. 50 and 51
Is a schematic diagram for the case of a geometry 45/0 °, where the measured light does not contain a specular reflection component.

As shown in FIG. 50, when the surface of the toner is covered with the fixing oil, the surface of the toner becomes apparently smooth, the regular reflection component for incident light increases, and the irregular reflection component decreases. . Therefore, the amount of light incident on the colorimeter decreases. This is because the specular reflection component is not read even by the scanner of the copying machine, so that the same result is obtained.

On the other hand, as shown in FIG. 51, when the amount of the fixing oil is small, the toner surface becomes rough, the specular reflection component is reduced, and the irregular reflection component is increased. Amount increases. The same applies to a scanner of a copying machine.

From the above description, it can be explained that the spectral reflectance of the colorimeter and the amount of light read by the scanner change due to the change in the surface state due to the presence of the fixing oil even if the amount of toner adhered is the same. This is shown in FIGS.
This will be described next. 52 is a graph showing the spectral reflectance of the transfer paper read by the spectral colorimeter, FIG. 53 is a graph showing the spectral reflectance of the yellow toner read by the spectral colorimeter, and FIG. 54 is read by the spectral colorimeter. FIG. 55 is a graph showing the spectral reflectance of magenta toner, FIG. 55 is a graph showing the spectral sensitivity of RGB of the CCD, and FIG. 56 is a graph showing how the read value changes depending on the amount of fixing oil on the transfer paper or toner. .

The graphs shown in FIG. 52 to FIG. 54 show the spectral reflectance in the case where the surface of the toner or the transfer paper 310 is glossy due to the presence of the fixing oil, and in the case where there is no gloss. In these figures, the horizontal axis represents the wavelength, and the vertical axis represents the spectral reflectance of the transfer paper 310 or the toner. These spectral reflectances are the measurement results of a spectral colorimeter, and the values read by the scanner are the results obtained by integrating the spectral reflectance of the toner by various spectral characteristics such as the spectral sensitivity of RGB of the CCD shown in FIG. Is obtained as In FIG. 55, the horizontal axis is wavelength, and the vertical axis is the spectral transmittance (relative value) of the CCD.
It is. Therefore, the value read by the scanner also changes depending on the amount of the fixing oil on the toner surface. In FIG. 56, the horizontal axis is the toner adhesion amount on the transfer paper 310, and the vertical axis is the read value of the scanner. This graph is for the yellow toner, and is the read value of blue as a complementary color signal. When the value of the horizontal axis is 0, it indicates a read value of the background of the transfer paper 310 when there is no toner on the transfer paper 310. Further, a) is a case where the transfer paper 310 is glossy.
B) when the amount of the fixing oil remaining on the toner is large (large), b) when the amount of the fixing oil remaining on the transfer paper 310 or the toner is small (small), and c) before fixing. The figure shows a read value when the amount of the fixing oil remaining on the toner on the transfer paper 310 is almost nil. This figure 5
As shown in FIG. 6, the read value changes in accordance with the amount of the remaining fixing oil on the transfer paper 310 and the toner. Therefore, using this point, the correction of the read value in accordance with the amount of the remaining fixing oil is performed. Do.

This correction will be described with reference to the flowchart shown in FIG. FIG. 57 is a flowchart showing a procedure for correcting the read value according to the amount of the remaining fixing oil.

First, the difference Δa (0) between the read values of the background portion of the transfer paper 310 before and after fixing is obtained (step 1100).
1). Δa (0) represents the difference between the read values when the toner adhesion amount to the transfer paper 310 is 0, and Δa (0) is obtained as follows.

△ a (0) = (read value of background of transfer paper before fixing) − (read value of background of transfer paper after fixing) Next, from the result of step 11001, the remaining amount of fixing oil per unit area The quantity M is predicted as follows (step 11002).

M = fl (△ a (0)) Here, fl (△ a (0)) represents a function that gives the amount of remaining fixing oil with △ a (0) as an argument.

A correction amount Δa of the read value is obtained from the amount of the fixing oil obtained in the above step 11001 and the read value a of the putter (step 11003). That is, Δa = f2 (a, M). f2 (a, M) is a function that takes a and M as arguments and obtains the amount of correction of the read value.

Next, the read value a is corrected using the correction amount obtained in step 11003 as follows (step 11004), and the corrected read value is set to a + △ a. Finally, from step 11003 to step 1100
4 is repeated for all patterns. Note that M = fl
The functional relationship between (△ a (0)) and △ a = f2 (a, M) is obtained in advance.

In the description so far, the operation of reading the background of the transfer paper 310 before forming the gradation pattern was necessary. However, when the type and lot of the transfer paper 310 to be used are determined, the transfer paper 310 The reading of the background does not change much. In such a case, the operation of reading the background of the transfer paper 310 is omitted, and the contribution of the amount of the fixing oil adhering to the transfer paper 310 and the gloss is determined by using the read value of the background of the transfer paper 310 stored in advance. May be predicted.
FIG. 58 is a flowchart showing the operation of the ACC in this case.
Shown in This drawing corresponds to FIG. 44 described above, and Steps 12001 to 1220 correspond to Steps 10004 to 10023 in FIG. 44, and thus detailed description thereof will be omitted. That is, FIG.
This is the same as FIG. 44 except that steps 10001 to 10003 in FIG. 44 are omitted. This processing is shown in FIG.
Step 4 is performed in step 10003 and subsequent steps.

On the other hand, the transfer paper 310 storing the read values
Is different from the type of the transfer paper 310 on which the gradation pattern is formed, the read value of the background greatly differs. In such a case, when the amount of oil remaining on the transfer paper 310 is estimated from the difference between the background reading values before and after the formation of the gradation pattern, the amount of the remaining fixing oil is predicted to be extremely large. In order to prevent this, if the read value (any one of the RGB image signals) of the scanner 401 that reads the background portion of the transfer paper 310 before and after forming the gradation pattern is significantly different from the reference value, Even if the type of the transfer paper 310 used is different, the correction according to the fixing oil and gloss is not performed.

Such a correction will be described with reference to the flowchart of FIG. FIG. 59 is a flowchart showing another procedure for correcting the read value according to the amount of the remaining fixing oil.

First, the difference between the read values of the background portion of the transfer paper 310 before and after fixing (Δr [0], Δg [0], Δb
[0]) (step 13001). That is,
The read value of the background of the transfer paper 310 read before forming the gradation pattern is (r1 [0], g1 [0], b1 [0]).
The read values of the background of the transfer paper 310 read after forming the gradation pattern are (r2 [0], g2 [0], b2
[0]), Δr [0] = r1 [0] −r2 [0] Δg [0] = g1 [0] −g2 [0] Δb [0] = b1 [0] −b2 [0 ].

Next, (△ r [0], △ g [0], △ b
[0]) is a predetermined reference value ($ r1, $ g1, $ b1),
(△ r2, △ g2, △ b2).

If △ r1 ≦ △ r [0] ≦ △ r2 Δg1 ≦ △ g [0] ≦ △ g2 Δb1 ≦ △ b [0] ≦ △ b2, the processing after step 13003 is performed. If the above equation does not hold, the subsequent processing is not performed. In step 13003, the amount M of the remaining fixing oil per unit area is predicted from the result of step 13001. The amount M of the fixing oil is M = f1 (△ r [0], △ g [0], △ b [0]) where f1 (△ r [0], △ g [0], △ b [0] ])
Represents a function that gives the amount of remaining fixing oil by using (△ r [0], △ g [0], △ b [0]) as arguments.

Next, the amount M of the fixing oil obtained in step 13001 and the value (r2
[I], g2 [i], b2 [i]) (i = 1, 2,...)
., N; n = the number of patterns) to determine the correction value of the read value (ｉr2 [i], △ g2 [i], △ b2 [i]) (step 13004).

Δr2 [i] = fr (r2 [i], M) Δg2 [i] = fg (g2 [i], M) Δb2 [i] = fb (b2 [i], M) , Fr (r [i], M), fg (g [i],
M) and fb (b [i], M) are (r2 [i], g2
[I], b2 [i]) and M are used as arguments to obtain a correction value of a read value.

The read values (r2 [i], g2 [i], b2 [i] are obtained using the correction amounts (△ r2 [i], △ g2 [i], △ b2 [i]) obtained in step 13003. )
(I = 1, 2,..., N; n = the number of patterns) is corrected (step 13005). The corrected reading (r
[I], g [i], b [i]) (i = 1, 2,...,
n; n = number of patterns), r [i] = r2 [i] + △ r [i] g [i] = g2 [i] + △ g [i] b [i] = b2 [i] + Δb [i] is used in the subsequent processing.

Finally, Step 13003 to Step 1
Step 3004 is repeated for all the YMCK patterns (step 13006). Note that M = f1 (△ a
(0)) and the function of △ a = f2 (a, M) are obtained in advance.

If the user selects “execute” for registration of the background of the paper on the display screen 305 of the operation unit 142 shown in FIG. 45, the read value of the background of the transfer paper 310 can be registered. This registration operation will be described with reference to FIG. FIG. 60 is a flowchart for explaining the operation in the case of registering the read value of the background of the transfer paper.

First, on the display screen 305 in FIG. 45, when the [Execute] key is pressed to select registration of the background of the paper (step 14001), the screen in FIG. 46 is displayed. FIG.
In accordance with the instruction on the screen 6, the transfer paper 310 for forming the gradation pattern is placed on the document table 118 (step 14002), and the [Reading Start] key in FIG. 46 is selected. As a result, the scanner 401 starts, separates the background of the transfer paper 310 (step 14003), and stores the read image in the image memory (step 140).
04). The above-mentioned averaging process is performed on the read image in the image memory (step 14005), and the result of the averaging process is stored in the RAM (step 1400).
6), the registration operation ends.

Note that procedures such as creation, generation, and calculation of a tone conversion table, procedures for creating a tone conversion table, and procedures for detecting and correcting unevenness in light amount are the same as those in the first embodiment. Therefore, the description is omitted.

Next, a third embodiment of the present invention will be described with reference to FIGS. Also in the third embodiment, the configurations of the laser modulation circuit and the image reading system are the same as those of the above-described first embodiment. In the case where the display contents of the display screen of the operation unit are the same, description will be made based on the display screen in the first embodiment. FIG. 61 is a block diagram illustrating an electrical configuration of an image processing unit according to the third embodiment of the present invention. FIG. 62 is an explanatory diagram schematically illustrating a connection relationship between an image forming apparatus and an external adjustment device. 62 is an explanatory diagram schematically showing the electrical configuration of FIG. 62, and FIG. 64 is a flowchart for explaining an operation procedure of generating the light amount unevenness correction data by the external adjustment device.

The configuration of the image processing section shown in FIG. 61 is such that an external adjustment device 701 is added to the configuration of the image processing section of FIG. 1 in the first embodiment. The external adjustment device 701 includes a computer 702 and an image memory 7
03. Then, the interface (I /
F) 413, a connector 705 is connected via an image data bus 704, and the connector 703 is connected to the image memory 70 of the external adjustment device 701 via an external bus 706.
3 are connected. The computer 702 of the external adjustment device 701 is connected to the image forming apparatus 70 such as a copying machine by a serial cable 707 of a serial interface.
8 system controller 419. The other configuration is the same as the configuration of the image processing unit according to the above-described first embodiment, and a duplicate description will be omitted.

The image data bus 706 has an image data width of 32 bits and can simultaneously receive RGB 8-bit signals. This image data bus 706 is shared so that the interface 413 can simultaneously read and write YMCK image signals. In addition,
The image data width is not limited to the above-described 32 bits, but may be a 64-bit width so that two pixels or two lines can be simultaneously read and written. By increasing the width of the image data in this manner, the communication time of the image data can be reduced. 62 and 63.
Denotes an original for detecting unevenness in light amount. The original 709 may be the white transfer paper 310 as described above.

Next, the procedure for creating the light amount unevenness detection data by the external adjustment device 701 will be described with reference to FIG.
The original 708 for correcting the light amount unevenness is placed on the original table 710 of the image forming apparatus 708 (step 15001). next,
A read start command of the scanner 401 is sent from the external adjustment device 701 to the image forming device 708 via the serial cable 707 (step 15002). As a result, the scanner 401 travels and reads the document 709 placed on the document table 710 (step 15003).
The read image data (image signal) is transmitted to the interface 413, the image data bus 704, the connector 705,
The image data is taken into the image memory 703 in the external adjustment device 701 via the image data bus 706 (step 1500).
4).

The image data corresponding to the reading position of the ACC pattern is averaged by the computer 702 from the image data fetched into the image memory 703 in the same manner as described above, and an average value of the light quantity unevenness is obtained (step 15005). . In the second embodiment, two types of dither processing for characters (no dithering), dither processing for photographs, four types of YMCK toner,
The average value of a total of 80 locations of the pattern is obtained once. The 80 locations include portions where the background of the paper is read without toner adhered when ACC is performed, and one of these locations is set as a reference reading position.

Next, the ratio between the average value of the image data corresponding to the read values of the 80 patterns and the read value at the above-described reference read position is obtained, and is set as the correction value of the effect unevenness (step 15006). The above 80 ratios are transmitted from the computer 702 in the external adjustment device 701 to the system controller 419 via the serial cable 707 (step 15007). Then, the image forming apparatus 70
8 is stored in a storage RAM (not shown) connected to the system controller 419 (step 1500).
8).

After reading the reflected light amount of the original 709 for light amount unevenness correction from the image memory 703 of the external adjusting device 701, the same averaging process as that of the image forming device 708 at the time of reading the gradation pattern is performed. When the image forming apparatus is a copying machine, the read values of the RGB signals of the pattern are as shown in FIG.
1 stored in the image memory 703 and the computer 702
The averaging process is performed in the same manner as described above.

The third embodiment has the same configuration as that of the first embodiment except that the external adjustment device is provided as described above. , The procedure of setting and operation of ACC, the procedure of detecting and correcting the unevenness in light amount, and the like are the same as those in the first embodiment described above, and the description thereof will be omitted.

[0250]

As is apparent from the above description, according to the first aspect of the present invention, the amount of light at the reading position of the gradation correction pattern used in ACC is detected before and after reading the gradation pattern or simultaneously, The read value of the gradation pattern can be corrected with the detected light amount. As described above, the read value of the gradation pattern is corrected based on the detected result and the result of the previously performed detection, and a gradation correction table is created based on the corrected read value of the gradation pattern. Accordingly, it is possible to eliminate the variation in the ACC adjustment result for each machine, and to adjust the image density with high accuracy.

According to the second aspect of the present invention, since the original has a substantially uniform density, the difference in the read value due to the difference in the reading position can be considered to be uneven light amount or stain on the contact glass surface. Therefore, by correcting the read value of the gradation pattern according to the read value of a document having a substantially uniform density, it is possible to correct the light amount unevenness on the contact glass surface. With such a simple method, the user can correct the light amount unevenness on the contact glass surface without requiring a special device, and the adjustment of the image density by the ACC can be performed with high accuracy.

According to the third aspect of the present invention, the original can be composed of white paper such as transfer paper, the unevenness in the amount of light on the contact glass surface can be corrected very easily, and the adjustment of the image density by ACC can be performed with high precision. Can be.

According to the fourth aspect of the invention, when reading the gradation pattern, the background portion of the transfer material around the gradation pattern can be read, and the illumination light amount of the gradation pattern portion can be predicted. The ACC can be executed by correcting the read value of the gradation pattern based on the ACC. This makes it easy and without the need for special equipment,
The user can correct the uneven light amount on the contact glass surface,
It is possible to reduce variations in the image density adjustment by ACC from machine to machine and changes over time, and to make the adjustment highly accurate. Further, the number of times of placing the document can be reduced, and the user's trouble can be saved.

According to the fifth aspect of the present invention, ACC can be executed in the same manner as in the fourth aspect of the present invention, and the user can correct the uneven light amount on the contact glass surface without requiring any special device. Thus, it is possible to reduce a variation in image density adjustment by ACC for each machine and a change with the passage of time, and to increase the accuracy of the adjustment. Further, since the number of times of placing the document can be reduced, the trouble of the user can be saved.

According to the sixth aspect of the present invention, the averaging process at the time of reading the gradation pattern and at the time of detecting the light amount can be made the same, so that an error caused by the difference in the averaging process is eliminated, and the image density by ACC is reduced. Can be prevented from being different for each machine, and the accuracy can be improved.

According to the seventh aspect of the invention, when a blank sheet is used as the document for detecting unevenness in the light amount, the amplification factor of the analog signal in the scanner is reduced, and when the blank sheet is not used, the copy machine is used. Uses the amplification factor during normal copying. As a result, the detection sensitivity of the scanner can be made close to the case where blank paper is used for correcting unevenness in light amount and the case where a document other than blank paper is used, and the accuracy of correction can be improved.

According to the eighth aspect of the present invention, similarly to the seventh aspect of the invention, the detection sensitivity of the scanner is different between when a blank sheet is used for correcting unevenness in light amount and when a document other than a blank sheet is used. Can be brought closer to each other, and the accuracy of correction can be increased.

According to the ninth aspect of the present invention, the user can select whether to execute or not execute the correction. If the result obtained by executing or not executing the correction does not greatly differ, the processing time may be reduced. Can be shortened.

According to the tenth aspect of the present invention, the user can select whether to use a blank sheet or a document other than a blank sheet as a document for detecting unevenness in light amount, and use the blank sheet for correcting unevenness in light amount. It is possible to make the detection sensitivity of the scanner close to the case where a document other than a blank sheet is used, and to improve the accuracy of correction.

According to the eleventh aspect, a gradation correction table is created by using a gradation pattern read value corrected in accordance with the amount of the remaining fixing oil, so that the adjustment result of the ACC can be obtained. A
The result of adjusting the image density by executing the CC can be adjusted to an optimum state after the fixing oil has evaporated.

According to the twelfth aspect of the present invention, for the same transfer material, the background is read before and after the formation of the gradation pattern, and the amount of the fixing oil adhering to the fixing material is determined from the change in the value before and after the formation. Prediction can be made with high accuracy. Therefore, the adjustment of the image density by executing the ACC can be performed with high accuracy.

According to the thirteenth aspect of the present invention, for a normally used transfer material or a transfer material recommended by a manufacturer, a value stored in advance is used instead of reading the background of the transfer material every time ACC is executed. Use this,
The reading operation of the background portion before forming the gradation pattern can be omitted, and the operation can be simplified.

According to the fourteenth aspect, improper correction is prevented when the type of the transfer material read before forming the gradation pattern and the type of the transfer material read after forming the gradation pattern are different. be able to.

According to the fifteenth aspect, the sixth aspect is provided.
As in the case of the described invention, the averaging process at the time of reading the gradation pattern and the amount of light detection can be made the same, eliminating errors caused by the different averaging processes, and adjusting the image density by ACC for each machine. Therefore, it is possible to improve the accuracy.

According to the sixteenth aspect of the invention, it is possible to select whether or not to perform the correction of the fixing oil remaining on the transfer material after the formation of the gradation pattern. If a result without correction is preferred, it can be made selectable.

According to the seventeenth aspect, in the first aspect,
Similarly to the described invention, the gradation pattern read value is corrected based on the detected result and the result of the previously performed detection, and a gradation correction table is created based on the corrected gradation pattern read value. According to the invention described in claim 18, it is possible to eliminate the variation of the ACC adjustment result for each machine and to achieve high-precision adjustment of the image density.
The correction amount of the pattern due to the uneven light amount can be automatically input, for example, online, the operation unit and the like of the image forming apparatus can be saved, and the manufacturing time and the manufacturing cost can be reduced.

According to the invention set forth in claim 19, claim 9 is
Similarly to the described invention, the user can select execution / non-execution of the correction, and when the result obtained by execution / non-execution of the correction does not largely differ, the processing time can be reduced. .

According to the twentieth aspect, the second aspect is provided.
Similar to the described invention, the original has a substantially uniform density, and the difference in the read value due to the difference in the reading position can be considered to be uneven light amount or stain on the contact glass surface. By correcting the read value of the gradation pattern in accordance with the read value, the light amount unevenness on the contact glass surface can be corrected. As described above, the user can correct the light amount unevenness on the contact glass surface without requiring a special device, and can adjust the image density by ACC with high accuracy.

According to the twenty-first aspect of the present invention, the averaging process of the correction value of the light amount unevenness of the gradation pattern by the external adjusting device is the same as the averaging process at the time of reading the gradation pattern. In addition, it is possible to eliminate the error at the time of correcting the light amount unevenness caused by the different averaging process,
Of the image density adjustment result for each machine, thereby improving the accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an electrical configuration of an image processing unit according to a first embodiment of the present invention.

FIG. 2 is a mechanism diagram schematically showing a mechanism of a copying machine main body to which the image forming apparatus of the present invention is attached.

FIG. 3 is a diagram for explaining a control system of the copying machine main body of FIG. 2;

FIG. 4 is a block diagram illustrating a laser modulation circuit according to the first embodiment of the present invention.

FIG. 5 is a block diagram illustrating an image reading system according to the first embodiment of the present invention.

FIG. 6 is a graph showing a model in which a read signal of an image amplified in FIG. 5 is sampled and held;

FIG. 7 is a flowchart illustrating a procedure for creating a gradation conversion table.

FIG. 8 is a diagram for explaining selection of the degree of overall curvature.

FIG. 9 is a diagram for explaining selection of a selected curvature.

FIG. 10 is a diagram illustrating an example of a conversion curve that changes the gradation characteristics of a highlight area.

FIG. 11 is a flowchart illustrating an operation of ACC for image density.

FIG. 12 is a plan view showing an operation unit of the copying machine.

FIG. 13 is a plan view showing a display screen of the operation unit when the ACC menu is called.

FIG. 14 is a plan view showing a display screen of the operation unit when execution of ACC is selected when using the printer.

FIG. 15 is a plan view showing a display screen of the operation unit during an ACC operation.

FIG. 16 is a plan view showing a display screen of the operation unit during a process of detecting light amount unevenness.

FIG. 17 is a plan view showing a density gradation pattern on transfer paper when a print start key is selected.

FIG. 18 is a plan view showing a display screen of the operation unit after a pattern is output on a transfer sheet.

FIG. 19 is a plan view showing a display screen of the operation unit during ACC processing.

FIG. 20 is a flowchart illustrating a procedure for detecting light amount unevenness.

FIG. 21 is a plan view showing a display screen of the operation unit when the detection of light amount unevenness is performed.

FIG. 22 is a plan view showing a display screen of an operation unit on which correction data of an RGB signal is shown.

FIG. 23 is a graph for explaining background correction.

FIG. 24 is a flowchart illustrating a calculation procedure of a gradation conversion table when ACC is executed.

FIG. 25 is a flowchart showing a procedure for selecting a gradation conversion table when executing ACC.

FIG. 26 is a graph for explaining a relationship between a reading value of a scanner and a frequency at which pixel data is included.

FIG. 27 is an explanatory diagram schematically showing a unit for setting a document to black back.

FIG. 28 is an explanatory view schematically showing another means for making a document black back.

FIG. 29 is a graph illustrating a relationship between a reading value of a scanner and a frequency at which pixel data is included.

FIG. 30 is a diagram illustrating an area read by a scanner.

FIG. 31 is a diagram schematically showing a reading system of a copying machine.

FIG. 32 is a flowchart showing a procedure for changing the amplification factor of the scanner.

FIG. 33 is a plan view showing a part of the transfer paper on which a gradation pattern is formed.

FIG. 34 is a plan view showing a part of the transfer paper on which a gradation pattern having a small margin is formed.

FIG. 35 is a plan view showing a modification of the gradation pattern.

FIG. 36 is a graph for explaining a relationship between a reading value of a scanner and a frequency at which pixel data is included.

FIG. 37 is a plan view showing a part of the transfer paper on which another gradation pattern is formed.

FIG. 38 is a flowchart illustrating a procedure of reading a margin.

FIG. 39 is a flowchart showing a procedure for predicting the amount of light amount unevenness in a pattern portion and creating and selecting a gradation correction table, showing a preceding stage thereof.

40 is a flowchart of a latter part connected to the terminal B in the flowchart of FIG. 39.

FIG. 41 is a plan view showing a display screen of the operation unit in the case.

FIG. 42 is a diagram illustrating a relationship between pixels in a main scanning direction and a sub-scanning direction.

FIG. 43 is a flowchart illustrating a procedure of an averaging process.

FIG. 44 is a flowchart showing an operation of the ACC according to the second embodiment of the present invention.

FIG. 45 is a plan view showing a display screen of an operation unit when an ACC menu is called in the second embodiment.

FIG. 46 is a plan view showing a display screen of the operation unit when execution of ACC for use of copying or use of a printer is selected in the second embodiment.

FIG. 47 is a plan view showing a display screen of an operation unit after reading a background portion in the second embodiment.

FIG. 48 is a plan view showing a display screen of an operation unit after pattern reading according to the second embodiment.

FIG. 49 is a plan view showing a density gradation pattern on transfer paper when a print start key is selected in the second embodiment.

FIG. 50 is a diagram for explaining a state in which the toner surface is smoothened by the attachment of the fixing oil.

FIG. 51 is a view for explaining a state in which the amount of fixing oil is reduced and the toner surface is roughened.

FIG. 52 is a graph showing the spectral reflectance of transfer paper read by a spectrophotometer.

FIG. 53 is a graph showing the spectral reflectance of yellow toner read by a spectrophotometer.

FIG. 54 is a graph showing the spectral reflectance of magenta toner read by a spectrophotometer.

FIG. 55 is a graph showing the RGB spectral sensitivities of the CCD.

FIG. 56 is a graph showing how a read value changes depending on the amount of fixing oil on transfer paper or toner.

FIG. 57 is a flowchart showing a procedure for correcting a read value according to the amount of remaining fixing oil.

FIG. 58 is a flowchart showing an ACC operation when the contribution of the amount of fixing oil adhered to transfer paper and the contribution of gloss are predicted.

FIG. 59 is a flowchart showing another procedure for correcting a read value according to the amount of remaining fixing oil.

FIG. 60 is a flowchart for explaining an operation when registering a background reading value of a transfer sheet;

FIG. 61 is a block diagram illustrating an electrical configuration of an image processing unit according to a third embodiment of the present invention.

FIG. 62 is an explanatory diagram schematically showing a connection relationship between an image forming apparatus and an external adjustment device according to the third embodiment.

FIG. 63 is an explanatory diagram schematically showing the electrical configuration of FIG. 62;

FIG. 64 is a flowchart for describing creation of light amount unevenness correction data by the external adjustment device according to the third embodiment of the present invention.

FIG. 65 is a graph illustrating an example of a change in a read value depending on the magnitude of a light amount.

FIG. 66 is a diagram for describing an example of reading positions with different light amounts.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Copier main body 102 Photoreceptor drum 103 Charging charger 104 Laser optical system 105, 106, 107, 108 Developing device 130 Main control unit 310 Transfer paper 401 Color scanner 402 Shading correction circuit 403 RGBγ correction circuit 404 Image separation circuit 405 MTF correction circuit 406 color conversion-UCR processing circuit 407 scaling circuit 408 image processing (create) circuit 409 MTF filter 410 gamma correction circuit 411 gradation processing circuit 412 printer 415 CPU 416 ROM 417 RAM 419, 702 computer 424, 703 image memory 501 CCD 503 S / H circuit 505 A / D conversion circuit 507 Image processing unit 514 CPU 701 External adjustment device 707 Serial cable

Claims (21)

[Claims] A means for optically scanning a document image placed at a reading position to read the image; a means for converting an input image signal from the reading means into an output image signal by an image signal conversion table and outputting the output image signal; Means for writing information on an image carrier in accordance with the output image signal, means for forming an image on a transfer material via the image carrier, means for generating a gradation pattern, Means for creating and selecting an image signal conversion table based on the read signal and the gradation target data stored in the storage means, wherein a light amount at or near the read position of the gradation pattern is detected. And a means for storing and holding the detection result. The tone pattern is stored on the basis of the detected result and the detection result stored in the storage and holding means. Image forming apparatus and correcting the readings. 2. The method according to claim 1, wherein the light amount detecting unit detects an original having a substantially uniform density placed on an original table by reading the original at a reading position of the gradation pattern. The image forming apparatus according to claim 1. 3. The image forming apparatus according to claim 2, wherein the original is a blank sheet. 4. The image forming apparatus according to claim 1, wherein the means for detecting the light amount detects by reading a blank portion of the gradation pattern by the reading means. 5. The image processing apparatus further comprises: means for detecting a blank portion of the gradation pattern; and means for storing a result of the detection of the blank portion, wherein the result of the detection of the blank portion and the means for storing are stored. 5. The execution of the detection of the light amount in the reading position of the gradation pattern or in the vicinity of the reading position is determined based on a result of comparison with the detection result of the margin portion. The image forming apparatus according to claim 1. 6. The image forming apparatus according to claim 1, wherein the means for detecting the amount of light performs the same averaging process as when reading the gradation pattern. 7. The method according to claim 1, wherein when the correction based on the light amount at or near the reading position of the gradation pattern is performed using blank paper, the amplification factor of the signal read by the reading unit is changed. Item 7. The image forming apparatus according to any one of Items 1 to 6. 8. The method according to claim 1, wherein the correction based on the light amount at or near the reading position of the gradation pattern is performed by using a blank sheet so that the reflectance of the back surface of the document relative to the reading unit is reduced. The image forming apparatus according to claim 1. 9. The apparatus according to claim 1, further comprising means for selecting execution / non-execution of correction based on the light amount near the reading position of the gradation pattern or near the reading position. Image forming device. 10. The apparatus according to claim 1, further comprising means for selecting whether or not to perform the correction based on the light amount at or near the reading position of the gradation pattern using blank paper. The image forming apparatus according to claim 1. 11. A means for optically scanning and reading an original image placed on a reading position, means for converting an input image signal from the reading means into an output image signal by an image signal conversion table, and outputting the output image signal. Means for writing information on an image carrier in accordance with the output image signal, means for forming an image on a transfer material via the image carrier, means for generating a gradation pattern, Means for creating and selecting an image signal conversion table based on a read signal and tone target data stored in a storage means, wherein a background portion of the transfer material is read before the tone pattern is formed. And comparing a read value of the background portion of the transfer material after the formation of the gradation pattern, and correcting the read value of the gradation pattern based on a result of the comparison. Image forming apparatus. 12. The image forming apparatus according to claim 11, wherein the read value of the background portion of the transfer material before the formation of the gradation pattern is a value read before the formation of the gradation pattern. . 13. The image forming apparatus according to claim 11, wherein a read value of a background portion of the transfer material before the formation of the gradation pattern uses a value stored in the storage unit in advance. 14. A result of comparing a read value of a background portion of the transfer material before the formation of the gradation pattern with a read value of a background portion of the transfer material after the formation of the gradation pattern is larger than a predetermined amount. 14. The image forming apparatus according to claim 11, wherein the correction of the read value is not performed in the case. 15. The image forming apparatus according to claim 11, further comprising means for registering a read value of a background portion of the transfer material before the formation of the gradation pattern. 16. The image forming apparatus according to claim 11, further comprising: means for selecting execution / non-execution of correction of the read value of the gradation pattern. 17. A means for optically scanning and reading an original image placed on a reading position, means for converting an input image signal from the reading means into an output image signal by an image signal conversion table and outputting the output image signal; Means for writing information on an image carrier in accordance with the output image signal, means for forming an image on a transfer material via the image carrier, means for generating a gradation pattern, Means for creating and selecting an image signal conversion table based on the read signal and the tone target data stored in the storage means, wherein the read position of the tone pattern or the amount of light near the read position is stored. An image forming apparatus for correcting the read value of the gradation pattern based on the amount of light stored in the storage unit. 18. A device provided outside the image forming apparatus,
18. The image forming apparatus according to claim 17, further comprising: an external adjustment device that obtains the correction amount of the gradation pattern; and a unit that inputs the correction amount of the gradation pattern from the external adjustment device to the image forming apparatus. apparatus. 19. The apparatus according to claim 17, further comprising means for selecting execution / non-execution of correction based on the light amount near or at the read position of the gradation pattern.
19. The image forming apparatus according to any one of claims 18 and 18. 20. The image forming apparatus according to claim 17, further comprising means for detecting a light amount at or near the reading position of the gradation pattern. 21. The image forming apparatus according to claim 17, wherein the correction amount of the gradation pattern is subjected to the same averaging process as when reading the gradation pattern.