JP2003032504A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device for employing a calibration method to bring a characteristic of a 1st read means closer to that of a 2nd read means. SOLUTION: The image forming device in an embodiment of this invention obtains RGB-γ conversion tables respectively included in 1st image signal outputted from the 1st read means and 2nd image signal outputted from the 2nd read means resulting from reading the same reference pattern and creates corrected RGB-γ conversion tables so as to decrease a difference between the image signals outputted from both the read means on the basis of the read values after the RGB-γ conversion. Each read means uses the created RGB-γconversion table so that the image forming means can correct the difference between the read values obtained by reading the same original to avoid the difference from being increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a digital copying machine, a printer or a fax machine for correcting an image signal read by an image reading means such as a scanner.

[0002]

2. Description of the Related Art Conventionally, in a color copying machine or the like, a scanner is driven to drive a CCD (Charge Coupled).
Device) and CMOS (Complimentar)
yMetal Oxide Semiconductor
The reflected image of the document is guided to a photoelectric conversion element such as r), the image signal after photoelectric conversion is processed, and visualized in the image forming unit. In the case of a double-sided original, such an image forming apparatus reads the first side (front side) of the original and then reverses the original to read the second side (back side) of the original. On the other hand, recently, a contact type first reading sensor (actual size sensor) for reading a first document surface installed in a sheet-through document feeder (hereinafter referred to as SDF) and a document and a contact glass are sandwiched. A color copying machine that includes a second reading sensor that reads a second original surface that is arranged at a position facing the SDF, and that can read both sides of the original by passing the original between the two reading sensors. Is being developed. This SD
Among those using F, in addition to the scanner, a reading sensor of the same size is installed in the SDF device for reading the original,
There is an image forming apparatus such as a copying machine that can read both sides of a document without reversing the document together with a scanner.

The first reading sensor uses a reduction optical system S.
A contact-type unity-magnification reading sensor is used as the reading means for the structural reason that it is difficult to have in the DF. In addition, the second reading sensor is not only a "thin" document that can use the SDF, but also a document having a thickness such as a book, or a SDF such as a cardboard, an iron plate, or plastic is difficult to pass through. Although it has a scanner (running body) for reading a "hard-to-bend" document, a reduction-type reading sensor is used as the reading means because of the merit that the depth of focus can be increased. An image signal obtained from the same original read by the first reading sensor and the second reading sensor, that is, a first image signal from the first reading sensor and a second image from the second reading sensor. It is desirable that the signal has almost the same value. At the time of factory shipment, it is possible to set the difference between the two values (first reading sensor and second reading sensor) to be small by adjustment at the factory. The reading characteristics may change, and it is necessary to correct this in a simple way in the user environment. In particular, correction is necessary when reading a double-sided original as a scanner.

By the way, Japanese Unexamined Patent Publication No. 2000-196881 has a first reading mode using a sheet-through document feeder and a second reading mode using a pressure plate, and a document can be read in either mode. In the image processing apparatus, which reads and converts the read image information into a digitally converted image signal and processes the digitally converted image signal into an image signal that can be output as a visible image, An image processing apparatus is described, which is provided with image processing means for independently performing optimization of reading correction in two reading modes. In addition, Japanese Examined Patent Publication 7-118756
Japanese Patent Laid-Open Publication No. 2003-242242 discloses a copying apparatus that converts image information obtained by optically scanning an original surface of an original into an electric signal, performs image processing on the electric signal, and then outputs the electric signal to a printer unit. A selection circuit for selecting data of a test pattern signal for generating a test pattern signal of a test sample which is a basis of parameter adjustment according to the present invention and image data obtained by optically scanning the test sample obtained by the test pattern signal. A memory circuit for comparing the image data obtained by optically scanning the test sample with the data of the test pattern signal and storing a conversion table for parameter adjustment obtained based on the difference between the two data. , A copying apparatus characterized by changing parameters relating to image formation based on a conversion table stored in a memory circuit. To have.

[0005]

However, in the conventional image processing apparatus as described above, one reading means is used for reading the sheet-through document feeder (SDF) and for reading on the contact glass surface. Therefore, the configuration does not include the first and second image reading units, and different image processing for correcting the respective characteristics is not performed. Reference data stored in a ROM (Read Only Memory) or a RAM (Random Access Memory) when creating a gradation correction table used when correcting the image signal read by the reading means. To use.
If this reference data is fixed, it is not possible to absorb the setting and the variation of each machine (device) that suits the user's preference and adjust the variation of the result set for each machine. Therefore, when automatic adjustment is performed, the adjustment result will always be different from the user's desired one, or the adjustment result will be different depending on the machine. Will occur.

Further, as described above, the structural reason of the first reading sensor and the second reading sensor, how the line is read, for example, the line is read thick and the line is thin. MTF (Modulation Transfer), which is a characteristic indicating whether or not it can be read
r Function) characteristics and the difference in color sensitivity due to the difference in spectral sensitivity of the reading sensor and the spectral transmittance of the transmission filter, etc., it is accurate even when the same image processing parameters are used and the same document is read. It may not be possible to reproduce a large image. Therefore, a first object of the present invention is to provide an image forming apparatus using a calibration method that brings the characteristics of the first reading unit and the second reading unit close to each other. A second object of the present invention is to provide an image forming apparatus that can exemplify image processing parameters that reflect the execution result of calibration as image correction.

[0007]

According to a first aspect of the present invention, in an image forming apparatus for automatically reading an original set on an automatic original feeding apparatus to form an image, the image forming apparatus is unique to the image forming apparatus during image formation. A reference document output means for forming a reference pattern of image density on a predetermined paper and outputting it as a reference document, and a document or a reference document installed in the automatic document feeder and installed in the automatic document feeder. A first image reading means for reading the image information on the surface of the document and outputting it as a first image signal; and a document or a reference document installed in the automatic document feeder and installed in the automatic document feeder. Second image reading means for reading the image information on the back side and outputting it as a second image signal, and reading by the first image reading means and the second image reading means Image processing means and said image processing said corrected by means the first image signal and the second to correct the first image signal and second image signal
Image forming means for forming an image signal of the image signal on the front surface and the back surface of the paper, respectively, and when the first image reading means or the second image reading means reads the reference document, the image processing means By correcting the image processing parameter or the image reading characteristic of both or one of the first image signal and the second image signal,
The first object is achieved.

According to a second aspect of the present invention, in the first aspect of the present invention, the image processing means is the read value of the image signal of the reference original read by the first image reading means or the second image. By correcting the image processing parameter or the image reading characteristic of either the first image signal or the second image signal based on the read value of the image signal of the reference document read by the reading unit, Achieve the first objective. In the invention according to claim 3, in the invention according to claim 1 or claim 2,
The image processing parameter corrected by the image processing means is R
Either or both of a gradation conversion table for converting GB (red, green, blue) signals and a gradation conversion table for converting YMCK (yellow, magenta, cyan, black) signals are used. Two
Achieve the purpose of.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. In this embodiment, an electrophotographic copying machine (hereinafter referred to as a copying machine) will be described as an example of an image forming apparatus. Figure 1
FIG. 1 is a diagram showing a configuration of the entire copying machine. First, an outline of a mechanism of the copying machine main body 101 will be described with reference to FIG. In FIG. 1, the surface of an organic photoconductor (OPC) drum 102 having a diameter of 120 [mm], which is an image carrier, is disposed substantially at the center of the copying machine body 101, and the surface of the organic photoconductor drum 102 is charged. Charging charger 103,
A laser optical system 104 that irradiates a semiconductor laser beam on the surface of the uniformly charged organic photosensitive drum 102 to form an electrostatic latent image, supplies toner of each color to the electrostatic latent image to develop, and develops each color. Black (K) developing device 105 for obtaining a toner image
And yellow (Y), magenta (M), cyan (C)
Of the three color developing devices 106, 107, 108, the intermediate transfer belt 109 and the intermediate transfer belt 1 for sequentially transferring the toner images of the respective colors formed on the organic photosensitive drum 102.
Bias roller 110 for applying a transfer voltage to 09, cleaning device 111 for removing the toner remaining on the surface of organic photoconductor drum 102 after the transfer, and static eliminator for removing the electric charge remaining on the surface of organic photoconductor drum 102 after the transfer. Part 1
Twelve etc. are arranged in order.

Further, the intermediate transfer belt 109 has a transfer bias roller 113 for applying a voltage for transferring the transferred toner image to the transfer material and a belt cleaning for cleaning the toner image remaining after the transfer on the transfer material. A device 114 is provided. Intermediate transfer belt 10
A fixing device 116 that heats and pressurizes the toner image to fix the toner image is disposed at the end of the exit side of the transport belt 115 that transports the transfer material separated from No. 9, and at the exit of the fixing device 116. A paper discharge tray 117 is attached. On the upper part of the laser optical system 104, a contact glass 118 as a document placing table arranged on the upper part of the copying machine main body 101, an exposure lamp 119 for irradiating a document on the contact glass 118 with scanning light, and a reflected light from the document. Is guided to the imaging lens 122 by the reflection mirror 121, and the CCD image sensor array 1 which is a photoelectric conversion element.
Let light enter 23. CCD image sensor array 123
The image signal converted into an electric signal by means of an image processing device (not shown) controls the laser oscillation of the semiconductor laser in the laser optical system 104.

Further, in the copying machine of the present embodiment, any one of K, C, M and Y plates is prepared according to the judged original. For example, in the case of a single color black (K), when the original image is captured in the image memory by full-color image formation, the CMY plate is created without performing the subsequent scanning. When the original image is larger than the size that can be stored in the image memory, scanning is performed every CMY plate creation. For example, if the image memory size is A4 (210 mm
The size is up to (197 mm), and is performed when the image memory is insufficient, such as when performing full-color image formation of A3. The original size is determined by using the size of the paper specified on the operation unit screen or an original size detection sensor (not shown).

Next, the control system built in the copying machine main body 101 will be described. FIG. 2 is a diagram showing the configuration of the control system of the copying machine. As shown in FIG. 2, the control system is a CPU
(Hereinafter referred to as a main control unit) 130, and a predetermined ROM 131 and RA are provided for the main control unit 130.
The M132 is provided and the main controller 13
0 is an interface I / O (Input / Output
ut)) 133 via laser optical system controller 134, power supply circuit 135, photoelectric sensors 136a-c, toner concentration sensor 137, environment sensor 138, photoconductor surface potential sensor 139, toner supply circuit 140, intermediate transfer belt drive unit. 141 and the operation unit 142 are connected to each other. The laser optical system controller 134 adjusts the laser output of the laser optical system 104. Further, the power supply circuit 135 applies a predetermined charging discharge voltage to the charger 103, and at the same time, the developing devices 105, 106, 107, 10
8 (see FIG. 1) is applied with a developing bias of a predetermined voltage, and a predetermined transfer voltage is applied to the bias roller 110 and the transfer bias roller 113.

The photoelectric sensors 136a to 136c are composed of a light emitting element such as a light emitting diode and a light receiving element such as a photo sensor, which are arranged in the vicinity of the area of the organic photosensitive drum 102 after the transfer, and are arranged on the organic photosensitive drum 102. The amount of toner adhered to the toner image of the formed detection pattern latent image and the amount of toner adhered to the background portion are detected for each color, and the residual potential after the photoconductor is discharged is also detected. Detection output signals from the photoelectric sensors 136a to 136c are applied to a photoelectric sensor control unit (not shown). The photoelectric sensor control unit obtains a ratio between the toner adhesion amount in the detection pattern latent image and the toner adhesion amount in the background portion, compares the ratio value with a reference value, detects a change in image density, and detects the toner density sensor 137. The control value is being corrected. Further, the toner concentration sensor 137 detects the toner concentration based on the change in magnetic permeability of the developer existing in the developing devices 105 to 108. Toner concentration sensor 137
Compares the detected toner density value with a reference value, and when the toner density falls below a certain value and a toner shortage occurs, a toner replenishment signal of a magnitude corresponding to the shortage is supplied to the toner replenishment circuit 140. It has a function to apply to.

The photoconductor surface potential sensor 139 detects the surface potential of the organic photoconductor drum 102 which is an image carrier, and the intermediate transfer belt drive unit 141 controls the drive of the intermediate transfer belt. A black developing device 105, which is a black (K) developing device, contains a developer containing black toner and a carrier, which is agitated by the rotation of a developer agitating member 202 (see FIG. 1) to develop. On the sleeve 201B, the amount of developer drawn up onto the developing sleeve 201B by the developer stirring member 202 is adjusted. The supplied developer is magnetically carried on the developing sleeve 201B,
As a magnetic brush, it rotates in the rotation direction of the developing sleeve 201B. Further, each developing sleeve 201 shown in FIGS.
Y, 201M, and 201C are color developing devices 106 to 1 for yellow (Y), magenta (M), and cyan (C), respectively.
08 developing sleeve.

Next, the image processing section of the copying machine will be described. FIG. 3 is a block diagram showing the configuration of the image processing unit of the copying machine. As shown in FIG. 3, the image processing unit includes a scanner 420, a shading correction circuit 401 for the scanner 420, an area processing circuit 423, a scanner γ conversion circuit 402, an image memory 403, an image separation circuit 404, and M.
TF filter 405, color conversion UCR processing circuit 406, scaling circuit 407, image processing (create) circuit 408, printer γ circuit 409 for image processing, gradation processing circuit 410,
A ROM 414, a CPU 415, a RAM 416, and a pattern generation circuit 421 are provided. The image processing unit also includes a reader 520, a shading correction circuit 501 for the reader 520, an area processing circuit 523 for an image signal from the reader 520, and a reader γ conversion circuit 502. The image processing unit of the copying machine uses the interface (I / F) selector 411 shown in FIG.
12, printer 413, system controller 417,
External computer 418, printer controller 41
9, connected to the pattern generation circuit 422. Also,
The system controller 417 and the CPU 415 are directly serially connected.

One side of the original to be copied is the scanner 420.
Is color-separated into R (red), G (green), and B (blue), and is read as a 10-bit signal as an example. The read image signal is corrected for unevenness in the main scanning direction by the shading correction circuit 401 and output as a 10-bit signal. The area processing circuit 423 generates an area signal for distinguishing which area in the document the image data currently being processed belongs to. The area signal generated by the area processing circuit 423 switches the parameters used in the image processing unit in the subsequent stage. These areas are the color correction coefficient, spatial filter, and gradation conversion table that are most suitable for each document such as characters, silver halide photographs (printing paper), printed documents, inkjets, highlighters, maps, and heat transfer documents. Image processing parameters such as can be set according to the image area. The scanner γ conversion circuit 402 converts the read signal from the scanner 420 from reflectance data to brightness data. The image memory 403 stores the image signal after the scanner γ conversion. The image separation circuit 404 determines the character portion and the photograph portion and determines the chromatic color / achromatic color.

On the other hand, the back side of the document surface read by the scanner 420 is color-separated into R, G, and B by the reader 520 and read by a 10-bit signal as an example. The read image signal is corrected for unevenness in the scanning direction by the shading correction circuit 501 and output as a 10-bit signal. In the area processing circuit 523, the area processing circuit 423
Similarly, the image signal from the reader 520 is switched so that the image processing is different for each area designated by the user. Note that the area processing circuits 423 and 523 are not indispensable for constructing the product, so that for a user who does not need area processing, either one or both of them are incorporated in the function or the configuration. It is also possible not to. The reader γ conversion circuit 502 includes the scanner 4
Similar to the scanner γ conversion circuit 402 for 20, the read signal from the reader 520 is converted from reflectance data to brightness data. Scanner γ conversion circuit 402 and reader γ
The conversion circuit 502 is set with parameters according to the reading characteristics of the scanner 420 and the reader 520 (balance of RGB signals, gradation, etc.). Image memory 40
Reference numeral 3 stores the image signal after the reader γ conversion processing. In this way, the image memory 403 stores the image signal from the scanner 420 and the image signal from the reader 520.
Depending on which of the two sides of the document the printer 413 is going to image, the stored two
Either one of the image signals of the two surfaces is output, and the subsequent processing is performed.

In the MTF filter 405, in addition to the processing of changing the frequency characteristic 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 MTF filter 405 changes according to the edge degree of the image signal. Edge enhancement processing (adaptive edge enhancement processing). For example, the edge enhancement is performed on the character edge, and the edge enhancement is not performed on the halftone image, and adaptive edge enhancement is performed on each of the R, G, and B signals. FIG. 4 is a diagram showing an example of the adaptive edge enhancement circuit. The image signal converted from the reflectance data to the brightness data by the scanner γ conversion circuit 402 is smoothed by the smoothing filter circuit 1101. As an example, the coefficient shown in FIG. 4B is used. The differential component of the image data is extracted by the 3 × 3 Laplacian filter 1102 in the next stage. A specific example of the Laplacian filter is shown in FIG. The scanner γ conversion circuit 402
Of the 10-bit image signal that has not been converted, the upper 8 bits (as an example) component is the edge amount detection filter 110.
Edge detection is performed by 3.

FIG. 5 is a diagram showing a specific example of the sub-scanning direction edge detection filter. FIG. 6 is a diagram showing a specific example of the edge detection filter in the main scanning direction. FIG. 7 is a diagram showing the diagonal direction detection filter (1). FIG. 8 is a diagram showing the diagonal direction detection filter (2). 5 to 8
Of the edge amounts obtained by the respective edge detection filters, the maximum value is used as the edge degree in the subsequent image processing. The edge degree is adjusted by the smoothing filter 1 in the subsequent stage, if necessary.
It is smoothed by 104. As a result, the scanner 42
The influence of the sensitivity difference between the even pixel of 0 and the odd pixel is reduced. At that time, a coefficient as shown in FIG. 4D is used as an example. Next, the edge degree obtained by the table conversion circuit 1105 is converted into a table. The values in this table specify the density of lines and points (including contrast and density) and the smoothness of halftone dots. FIG. 9 is a diagram showing an example of the adaptive edge enhancement filter table. The edge degree becomes the largest with black lines and dots on a white background, and becomes smaller as the dots of fine print and the boundaries of pixels become smoother, such as in silver halide photographs and thermal transfer originals. The product (image signal D) of the edge degree (image signal C) converted by the table conversion circuit 1105 and the output value (image signal B) of the Laplacian filter 1102 becomes the image signal (image signal A) after the smoothing process. The signals are added and transmitted as an image signal E to the image processing circuit in the subsequent stage.

The color conversion UCR processing circuit 406 corrects the difference between the color separation characteristic of the input system and the spectral characteristic of the color material of the output system, and calculates the amounts of the color materials Y, M and C required for faithful color reproduction. The color correction processing unit that does not overlap with the portion where the three colors of Y, M, and C overlap
It is composed of a UCR processing unit for replacing with k (black). The color correction processing can be realized by performing a matrix calculation as shown in FIG. here,
R, G, and B indicate the complements of the RGB colors,
The matrix coefficient aij is determined by the spectral characteristics of the input system and the output system (color material). Here, the first-order masking equation is given as an example, but a second-order term such as B2 and BG,
Alternatively, it is possible to perform color correction with higher accuracy by using a higher-order term. Further, the arithmetic expression may be changed depending on the hue, or the Neugebauer equation may be used. Whichever method is used, Y, M, C are B, G,
It can be obtained from the value of R. On the other hand, the UCR process can be executed by calculating using the formula as shown in FIG. In the expression (b) of FIG. 10, α is UC
This is a coefficient that determines the amount of R, and when α = 1, 100% UCR processing is performed. α may be a constant value. For example, in the high density area,
α is close to 1, and 0 in the highlight part (low image density part)
The image in the highlight portion can be smoothed by making the image closer to.

The scaling circuit 407 performs vertical and horizontal scaling, and the image processing (create) circuit 408 performs repeat processing. In the image processing printer γ circuit 409, the image signal is corrected in accordance with the image quality mode such as characters and photographs. In addition, it is possible to simultaneously remove the background. The image processing printer γ circuit 409 has a plurality (10 as an example) of a gradation conversion table that can be switched according to the area signal generated by the area processing circuit 423. This gradation conversion table includes characters, silver halide photographs (printing paper), printed documents, inkjets, highlighters, maps,
An optimum gradation conversion table for each original such as a thermal transfer original can be selected from a plurality of image processing parameters. The gradation processing circuit 410 performs dither processing. The output of the gradation processing circuit 410 is half the pixel frequency.
2 pixels of data at the same time
Image data bus 1 so that it can be transferred to
It has a width of 6 bits (two lines of image data of 8 bits). Interface (I / F) selector 411
Has a switching function for outputting image data read by the scanner 420 for processing by an external image processing device or the like, and for outputting image data from an external host computer or image processing device by the printer 413. is doing.

The operator can specify the mode and other processing conditions from the switches on the operation panel (not shown). In the copy mode using the internal scanner, the internal scanner is operated and the original is sequentially color-separated into R, G, and B and read, and the image processing unit performs shading correction, MTF correction, γ correction, color correction, and UCR processing. That is, multi-valued processing is performed by gradation processing. The multiplexer is for selecting data obtained through an external I / F (interface), and in the copy mode, selects image data based on data from the internal scanner. The data converter is adapted to the characteristics of the output system when data having a different number of bits is input from the outside.

The image forming printer γ (pro computer γ) circuit 412 includes an interface (I / F) selector 41.
The image signal from No. 1 is converted by the gradation conversion table and output to the laser modulation circuit described later. Interface (I /
F) Selector 411, printer γ correction circuit 412 for image formation, printer 413 and system controller 4
The printer unit is configured by 17, and can be used independently of the scanner / IPU. The image signal from the computer 418 is input to the interface (I / F) selector 411 through the printer controller 419,
The tone is converted by the image forming printer γ circuit 412,
By performing image formation by the printer 413,
It can be used as a printer unit. The image processing unit is controlled by the CPU 415 as described above. The CPU 415 has a ROM 414 and a RAM 416.
And BUS (bus) 426. Also, CP
The U 415 is serially connected to the system controller 417, and commands from an operation unit (not shown) or the like are transmitted through the system controller 417. Based on the transmitted image quality mode, density information, area information, and the like, various parameters are set for each circuit of each image processing unit described above. The pattern generation circuits 421 and 422 generate gradation patterns used in the image processing unit and the image forming unit, respectively.

FIG. 11 is a diagram showing the concept of area processing. In FIG. 11, the designated area information on the document is compared with the reading position information at the time of reading the image, and the area processing circuit 423 generates an area signal. The parameters used in the scanner γ conversion circuit 402, the MTF filter 405, the color conversion UCR circuit 406, the image processing circuit 408, the image processing printer γ circuit 409, and the gradation processing circuit 410 are changed based on the area signal. In FIG. 11, the image processing printer γ circuit 409 and the gradation processing circuit 410 are illustrated. In the image processing printer γ circuit 409, the area signal from the area processing circuit 423 is decoded (decoded) by the decoder 1, and the selector 1 selects a corresponding one from a plurality of gradation conversion tables such as characters and inkjets. To do. In the example of the document shown in FIG. 11, an example in which a character region 0, a photographic paper region 1 and an inkjet region 2 are present is illustrated. The gradation conversion table 1 for characters is used for the character area 0, and the gradation conversion table 3 is used for printing paper for the area 1 of photographic paper.
For the inkjet region 2, the inkjet gradation conversion table 2 is selected as an example.

The image signal whose gradation has been converted by the image processing printer γ circuit 409 is decoded again by the decoder 2 in the gradation processing circuit 410 in correspondence with the area signal, and based on this decoded signal. The selector 2 switches the gradation processing to be used. As usable gradation processing, processing without using dither, processing with dither, error diffusion processing and the like are performed. The error diffusion process is performed on the inkjet document. The decoder 3 selects the line 1 or the line 2 of the image signal after the gradation processing based on the reading position information. Line 1 and line 2 are switched every time one pixel differs in the sub-scanning direction. The data of the line 1 is stored in the FIFO (First
It is temporarily stored in the In First Out memory and the data of line 1 and line 2 is output. As a result, the pixel frequency can be reduced to 1/2 and input to the interface (I / F) selector 411.

FIG. 12 is a block diagram showing the structure of the laser modulation circuit. The writing frequency is 1 as an example
8.6 [MHz], and the scanning time for one pixel is 53.
It is assumed that it is 8 [nsec]. 8-bit image data can be subjected to γ conversion by a look-up table (LUT) 451. Pulse width modulation circuit (PWM) 452
Is converted into an 8-value pulse width on the basis of the upper 3-bit signal of the 8-bit image signal, and the power modulation circuit (P
M) 453 performs 32-value power modulation on the lower 5 bits, and the laser diode (LD) 454 emits light based on the modulated signal. Photodetector (PD) 455
The emission intensity is monitored with and the correction is performed for each dot. The maximum value of the intensity of laser light can be changed to 8 bits (256 steps) independently of the image signal. With respect to the size of one pixel, the beam diameter in the main scanning direction (this is defined as the width when the beam intensity at rest is attenuated to 1 / e ² with respect to the maximum value) is 600 dpi, 1 Pixel 42.
At 3 [μm], the beam diameter is 50 [μm] in the main scanning direction,
The sub-scanning direction 60 [μm] is used. A laser modulation circuit is prepared for each of the image data of line 1 and line 2 in FIG. Line 1 and line 2
Image data is synchronized and is scanned on the photoconductor in parallel in the main scanning direction.

FIG. 13 is a block diagram showing the structure of the image reading system. Further, FIG. 14 is a diagram showing an example of a scanner optical system having a sheet-through document feeder. The original is the exposure lamp 5501 (see FIG.
The light reflected by the document is emitted by the CCD 5
It is color-separated by the RGB filter 401 and read, and amplified to a predetermined level by the amplifier circuit 5402. The CCD driver 5409 supplies a pulse signal for driving the CCD 5401. CCD driver 54
The pulse source needed to drive 09 is generated by pulse generator 5410. The pulse generator 5410 uses a clock generator 5411 including a crystal oscillator as a reference signal. Pulse generator 5
Reference numeral 410 supplies a timing necessary for the sample hold (S / H) circuit 5403 to sample and hold the signal from the CCD 5401. The analog color image signal sample-held by the S / H circuit 5403 is digitized by the A / D conversion circuit 5404 into an 8-bit signal (an example).

The black correction circuit 5405 reduces variations in black level (electric signal when light amount is small) between the chips of the CCD 5401 and between pixels, and prevents streaks and unevenness from occurring in the black portion of the image. Shading correction circuit 5406
Corrects the white level (electrical signal when the amount of light is large). The white level is based on the white data when the scanner 420 is moved to a uniform white plate position and is irradiated,
The sensitivity variations of the optical system and CCD 5401 are corrected. FIG. 15 is a diagram showing the concept of image signals for white correction / black correction. The signal from the shading correction circuit 5405 is
The image is processed by the image processing unit 5407 and output by the printer 413. Such a circuit is controlled by the CPU 5414 and stores data required for control in the ROM 5413 and the RAM 5415. The CPU 5414 communicates with a system controller 417 that controls the entire image forming apparatus by serial I / F. CPU 541
Reference numeral 4 controls a scanner driving device (not shown) to control driving of the scanner 420.

The amplification amount of the amplification circuit 5402 is determined so that the output value of the A / D conversion circuit 5404 becomes a desired value for a certain specific document density. As an example, a document having an original density of 0.05 (reflectance of 0.891) can be obtained as an 8-bit signal value of 240 during normal copying. On the other hand, at the time of shading correction, the amplification factor is lowered to increase the sensitivity of shading correction. This is because when the amount of reflected light is large at an amplification factor during normal copying, an image signal having a size of more than 255 with an 8-bit signal is 255.
This is because the value is saturated and an error occurs in shading correction. FIG. 16 is a schematic diagram in which the image signal is sampled and held. FIG. 16 shows a schematic diagram in which the read signal of the image amplified by the amplifier circuit 5402 is sampled and held by the S / H circuit 5403. The horizontal axis is
The vertical axis represents the magnitude of the amplified analog signal, which is the time taken for the amplified analog image signal to pass through the S / H circuit 5403. The analog signal is sampled and held at a predetermined sample and hold time 5501, and the A / D conversion circuit 5
A signal is sent to 404. FIG. 16 shows an image signal obtained by reading the above-described white level. The image signal after amplification is 240 values as a value after A / D conversion when copying, for example.
This is an example of the image signal after amplification, which is set to 180 during white correction.

Next, the reading operation of the double-sided original will be described with reference to FIG. Note that FIG. 17 is a diagram showing the entire operation unit of the copying machine, and FIG. 18 is a diagram showing the liquid crystal screen of the operation unit. When the start button of the operation unit (see FIGS. 17 and 18) is pushed down, the scanner 4
20 and the reader 520 each perform a shading operation. The original at the position of the original A is fed by a roller 5601 and driven by a roller 5602, which is a white belt 560.
Roller 5604 and glass window 56 facing 3
The position of the document B between 05 is passed. When the document passes, the position of the document B is illuminated by the exposure lamp 5606, and the reflected light passes through the lens 5607 and is photoelectrically converted by the unity magnification sensor 5608 including a photoelectric element such as CCD to be converted into an image signal. Before the original reaches the reading position of the normal magnification sensor 5608, the normal magnification sensor 5608 receives the reflected light of the white belt 5603, and the shading correction of the uniform magnification sensor 5608 is performed based on the reflected light. The original that has passed the position of the original B is conveyed by the transport roller 56.
The sheet C is conveyed to the position of the document C by 09. At this time, the light from the exposure lamp 5501 of the traveling system 5502 of the scanner 420 is reflected by the position of the document C, the reflected light is reflected by the second mirror 5503, the first mirror 5504, and the third mirror 5506 of the traveling system 5505. It is condensed by the lens 5507 and photoelectrically converted by the CCD 5401. In the above operation, the traveling system 5502 and the traveling system 5505 do not travel and are stationary at a fixed position. However, the traveling system 5502, up to the position where the white plate 5508 is read before the original reaches the position of the original C, It is assumed that the traveling system 5505 is moving and is performing shading correction.

Next, the operation and processing of automatic correction will be described. Automatic gradation correction of image density (gradation) (AC
C: Auto Color Calibration)
The operation will be described based on the flowchart of FIG.
When the ACC menu is called on the liquid crystal screen of the operation unit (see FIG. 18), a screen for setting the correction content of the automatic gradation correction as shown in FIG. 20 is displayed. When [Execution] of the automatic gradation correction is selected when using a copy or when using a printer, a screen (1) displayed during execution of ACC as shown in FIG. 21 is displayed. When the copy use is selected, the tone correction table used when the copy is used is displayed, and when the printer is used, the tone correction table when the printer is used is displayed, and the change is performed based on this reference data. When the print start key is selected, a plurality of density gradation patterns corresponding to YMCK colors and character and photo image quality modes, which are gradation patterns on the transfer paper output when executing ACC as shown in FIG. 22, are transferred. It is formed on the material (step 1).

This density gradation pattern is stored and set in advance in the ROM of the scanner / IPU.
The written value of the pattern is 00h, 11 in hexadecimal notation.
16 patterns of h, 22h, ..., EEh, FFh. In FIG. 22, patches for 5 gradations are displayed excluding the background portion, but among the 00h-FFh 8-bit signals,
Any value can be selected. In character mode, one dot 256 is used without performing dither processing such as pattern processing.
A pattern is formed with gradation, and in the photographic mode, the writing value of the laser is formed by distributing the sum of the writing values of every two adjacent pixels in the main scanning direction. That is, dither in units of 2 pixels in the main scanning direction and 2 pixels in the sub scanning direction can be processed as follows.

Output image signal m [i] [j] [n] (i = 0,1: pixel number in the main scanning direction, j = 0,1: sub) for input image signal n (0≤n≤255) Pixel number in the scanning direction) (0 ≦ m [i] [j] [n] ≦ 255), for 0 ≦ n <32, m [0] [0] [n] = 4 × n, m [ 0] [1] [n] = m [1] [0] [n] = m
For [1] [1] [n] = 0, 32 ≦ n <64, m [0] [0] [n] = 127, m [0] [1] [n] = 4 × (n−32 ) +1 m [1] [0] [n] = m [1] [1] [n] = 0, for 64 ≦ n <128, m [0] [0] [n] = 127, m [0 ] [1] [n] = 127, m [1] [0] [n] = m [1] [1] [n] = 2 ×
(N−64) +1, 128 ≦ n ≦ 255 m [0] [1] [n] = m [1] [0] [n] = m
Dither processing such as [1] [1] [n] n is used. In addition to the dither processing described above, the pattern processing actually used at the time of image formation is used.

After the pattern is output to the transfer material, the transfer material is transferred to the sheet through document feeder (SDF) 5
A screen (2) displayed during execution of ACC as shown in FIG. 23 is displayed on the liquid crystal screen of the operation unit so as to be mounted on 701 (see FIG. 14). When the transfer material on which the reference pattern is formed is placed on the SDF5701, and the reading start is selected (step 2), the transfer paper on which the ACC pattern is formed is fed and the original C is read at the position (see FIG. 14). The stationary scanner 420 reads the RGB data of the YMCK density pattern (step 3). At this time, 1
The image memory 403 stores the RGB image signal obtained by reading the area including the pattern portion and the background portion of the transfer material when the original is passed once. The image signal of the reference pattern is extracted based on the image signal of the image memory 403. This means that the average of the sum of the image signals in the area of about 5 mm square of each density area of the reference pattern is stored in the memory as a value having an accuracy of about 12 bits. Then, the machine difference of the read signal of the scanner 420 is corrected using the machine difference correction value described later, and the read value of the corrected pattern is stored (step 4).

When it is set to perform the processing using the background data (step 5; Y), the background data processing for the read data is executed (step 6). If it is set to correct the reference data (step 7; Y), the high image density portion of the reference data is processed (step 8). Create YMCK gradation correction table
A selection is made (step 9). Until correction is performed for each color of YMCK (step 10; Y) and until correction is performed for each image quality mode of photograph and character (step 1)
1; Y), the processes of steps 5 to 9 are repeated.
Next, when the screen (3) displayed during execution of the ACC as shown in FIG. 24 is displayed on the liquid crystal screen of the operation unit, the transfer paper on which the reference pattern is formed is turned upside down with respect to the direction in which the transfer paper was previously placed. And place it on the SDF5701 (step 12). When the "Start reading" soft key displayed on the liquid crystal screen is selected, the transfer sheet placed on the SDF5701 is fed and the reader 520 causes the YMCK density when passing to the position of the document B (see FIG. 14). The RGB data of the pattern is read (step 13). The image memory 403 stores an RGB image signal obtained by reading an area including the pattern portion and the background portion of the transfer material when the document is passed once.

Then, similarly to step 4, the image signal of the reference pattern is extracted based on the image signal of the image memory read by the reader 520, and the reader 520 is used by using the machine difference correction value for the reader. Is corrected and the read value of the corrected pattern is stored (step 14). Based on the corrected read value of the scanner 420 stored in step 4, the reader γ correction table used in the reader γ conversion circuit 502 and the read value of the reader 520 are corrected. As a result, the read value from the scanner 420 after the scanner γ conversion processing and the gradation of the read value of the reader 520 after the reader γ conversion processing are matched. Whether or not to perform the correction is determined based on the set value, and background correction processing is executed (step 1
5). Similar to step 5 and step 6, when it is set to perform the process using the background data (step 15; Y), the background data process for the read data is performed (step 16).

Similarly to steps 7 and 8, when it is set that the reference data is corrected (step 17; Y), the high image density portion of the reference data is processed (step 18). Then, a YMCK gradation correction table is created and selected (step 19). YM
Until correction is performed for each color of CK (step 20;
Y) and the processes of steps 15 to 19 are repeated until correction is made for each image quality mode of photograph and character (step 21; Y). The result of performing the YMCK gradation correction table after the correction processing for each color of YMCK and the correction for each image quality mode of the photograph and the character is completed (step 20; Y, step 21; Y). If it is not desired, the [Return] key is displayed on the liquid crystal screen of the operation unit so that the YMCK gradation correction table before processing can be selected.

Next, the background correction in steps 5 and 15 in the flowchart of FIG. 19 will be described. There are two purposes of background correction processing. First,
This is to correct the whiteness of the transfer material used during ACC. This is because even if an image is formed on the same machine at the same time, it is necessary to correct it because the value read by the scanner differs depending on the whiteness of the transfer material used. As a problem in the case where this is not corrected, for example, when recycled paper or the like having low whiteness is used for ACC, recycled paper generally has many yellow components. Need to be corrected so that In this state, when copying is performed next with art paper having a high degree of whiteness, an image having a small amount of yellow component may be obtained and desired color reproduction may not be obtained.

Another reason is that when the thickness of the transfer paper used during ACC (paper thickness) is thin, the color of the pressure plate for pressing the transfer material may be transparent and read by the scanner. For example, instead of the pressure plate, ADF (Auto
When an automatic document feeder called Document Feeder) is installed, a belt is used to convey the original, but the whiteness is low and it becomes slightly grayish depending on the rubber material used. There is something.
Therefore, the read image signal is also read as an image signal that is apparently higher than that of the YMCK image.
When creating the gradation correction table, the gradation correction table is created so as to be lighter. In this state, this time the paper thickness is thick,
When a transfer paper having poor transparency is used, an image having a low overall density is reproduced, and therefore a desired image cannot always be obtained.

In order to prevent the above problems, it is necessary to correct the read image signal of the pattern portion from the read image signal of the background portion of the paper based on the image signal of the background portion of the paper. There is an advantage even when the background is not corrected, and when using transfer paper with a large amount of yellow components, such as recycled paper, it is better not to perform color reproduction for colors containing yellow components. You can do well. Further, when only the transfer paper having a thin paper thickness is always used, there is also an advantage that the gradation correction table is created in a state adapted to the thin paper. In the image forming apparatus of the present embodiment, the correction of the background portion is turned ON / O according to the user's situation and preference.
FF (off) can be performed.

Next, the machine difference correction in steps 4 and 14 in the flowchart of FIG. 19 will be described. The writing value of the gradation pattern (see FIG. 22) formed on the transfer paper is LD [i] (i = 0, 1, ..., 9),
The value read by the scanner of the formed pattern is v [t] [i] ≡ (r [t] [i], g [t] in vector format.
[I], b [t] [i]) (t = Y, M, C, or
K, i = 0, 1, ..., 9). (R, g,
Instead of b), lightness, saturation, hue angle (L *, C *, h
*) Or brightness, redness, blueness (L *, a *, b)
*) Etc. may be used. A reference white read value stored in advance in the ROM 414 or the RAM 416 is defined as (r [W], g [W], b [W]).

Here, a method of generating a gradation conversion table (LUT) performed by the γ conversion processing unit at the time of executing ACC will be described. Pattern read value v [t] [i]
≡ (r [t] [i], g [t] [i], b [t]
In [i]), the image signals of the complementary colors of YMC toner are b [t] [i], g [t] [i], and r [t], respectively.
Since it is [i], only image signals of respective complementary colors are used. Here, in order to facilitate the later description, a
[T] [i] (i = 0, 1, ..., 9; t = C,
M, Y, or K) is used to create a gradation conversion table, which simplifies the process. Note that for the black toner, sufficient accuracy can be obtained by using any of the RGB image signals, but here, the G (green) component is used.

The reference data is the read value v0 of the scanner.
[T] [i] ≡ (r0 [t] [i], g0 [t]
[I], b0 [t] [i]) and the corresponding laser writing value LD [i] (i = 0, 1, ..., M). Similarly, using only the YMC complementary color image signals, A [t] [n
[I]] (0 ≦ n [i] ≦ 255; i = 1, 2, ...
., M; t = C, M, Y, or K).
Note that m is the number of reference data. FIG. 25 is a diagram showing an example of the machine difference correction value. The values in Fig. 25 are Black.
(G), Cyan (R), Magenta (G), Ye
The correction values corresponding to the respective toners of low (B) are shown in (), and the signals of Red (R), Green (G), and Blue (B) of the scanner used at the time of automatic gradation correction are shown. K for each color toner
(0) and k (1023) represent correction values for the reference data value 0 and the reference data value 1023 (10-bit signal). The value of the corrected reference data is A1 [t] [n
As [i], the reference data A [t] [n [i]] is corrected according to the following equation. A1 [t] [n [i]] = A1 [t] [n [i]] +
(K (1023) −k (0)) × n [i] / 1023 +
k (0) FIG. 26 is a diagram showing an example of a graph of the correction value, and represents the above-mentioned function. The correction value in FIG. 25 is set at the time of manufacture and is held in the machine. In the following, A1 [t] [n [i]] in the above equation is
It is used as a new A [t] [n [i]].

Next, the creation / selection of the YMCK gradation correction table in steps 9 and 19 in the flowchart of FIG. 19 will be described. The YMCK gradation correction table is obtained by comparing the a [LD] described above with the reference data A [n] stored in the ROM 414. Here, n is an input value to the YMCK gradation correction table, and the reference data A [n] is the input value n
It is the target value of the read image signal obtained by reading the YMC toner pattern output by the laser writing value LD [i] after the CK gradation correction by the scanner. Here, the reference data is a reference value A [n] that is corrected according to the image density that can be output by the printer, and a reference value A [n] that is not corrected.
It consists of a kind value. The determination as to whether or not to perform the correction is made based on the determination data, which will be described later, stored in the ROM 414 or the RAM 416 in advance.

By obtaining the LD corresponding to A [n] from a [LD], the laser output value LD [n] corresponding to the input value n to the YMCK gradation conversion table can be obtained. The input value i = 0, 1, ..., 255 (8
The gradation correction table can be obtained by obtaining the gradation correction table. At that time, input values n = 00h, 01h, ... for the YMCK gradation correction table
.., ni = 0, 11h, 2 instead of performing the above processing for all values for FFh (hexadecimal number)
2h, ..., FFh, the above-described processing is performed on the discrete values, and interpolation is performed on the other points with a spline function, or the ROM 4 is used in advance.
In the YMCKγ correction table stored in 14, the (0, LD [0]), (11
h, LD [11h]), (22h, LD [22h]),
.., (FFh, LD [FFh]) is selected, the closest table is selected.

Here, the arithmetic processing of the above-mentioned ACC will be described with reference to FIG. The horizontal axis of the first quadrant (a) of FIG. 27 is the input value n to the YMCK gradation correction table, and the vertical axis is the reading value (after processing) of the scanner, which represents the above-mentioned reference data A [i]. ing. The value read by the scanner (after processing) is the RGBγ conversion (not converted here) with respect to the value read by the scanner for the gradation pattern, and the averaging processing and addition processing of the read data at several points in the gradation pattern. This is a later value and is processed here as a 12-bit data signal in order to improve calculation accuracy.
The horizontal axis of the second quadrant (b) in FIG. 27 represents the reading value (after processing) of the scanner, like the vertical axis.

The vertical axis of the third quadrant (c) is the laser beam (L
D) represents the written value. This data a [LD]
Represents the characteristics of the printer unit. In addition, the writing value of the LD of the pattern actually formed is 00h (background), 1
There are 16 points of 1h, 22h, ..., EEh, FFh, which show discrete values, but here, the detection points are interpolated and treated as a continuous graph. The graph (d) of the fourth quadrant represents the YMCK gradation conversion table LD [i], and the purpose is to find this table. The vertical axis and horizontal axis of the graph (f) are the same as the vertical axis and horizontal axis of the graph (d). When forming a gradation pattern for detection, the YMCK gradation conversion table (g) shown in the graph (f) is used. The horizontal axis of the graph (e) is the same as that of the third quadrant (c), and the writing value of the LD at the time of creating the gradation pattern and the reading value of the gradation pattern scanner (after processing)
For convenience, a linear transformation is represented to represent the relationship with. Reference data A [n] is obtained for a certain input value n, and LD [n], which is an LD output for obtaining A [n], is read using a gradation pattern read value a [LD] in the figure. Along the arrow (1).

When compared with the graph when the RGBγ conversion is performed, the graphs of the printer characteristics of the third quadrant match, but the characteristics of the RGBγ conversion table of the second quadrant differ. In accordance with this, it is necessary to change the reference data of the first quadrant, but the final result is that the characteristics of the YMCK gradation correction table LD [n] are the same. In this way, the reference data is changed depending on whether the processing based on the RGBγ conversion table is performed or not. Next, the arithmetic processing will be described with reference to FIGS. 27 and 28. FIG. 28 is a flowchart showing the ACC calculation procedure. First, an input value required to obtain the YMCKγ gradation correction table is determined (step 101).
Here, n [i] = 11 (h) × i (i = 0, 1, ...
.., imax = 15). Then, machine difference correction is performed (step 102). This processing is as described above. The reference data A [n] is corrected according to the image density that can be output by the printer (step 103). This is step 8 and step 18 of the flowchart of FIG.
This is the same as the processing in.

It is assumed that the writing value of the laser capable of obtaining the maximum image density that can be created by the printer unit is FFh (hexadecimal notation), and the reading value m [FFh] of the pattern at this time is mmax. Reference data A [i] (i = 0, 1, i) that is not corrected from the low image density side to the intermediate image density side
, I1), reference data A [i] (i = i2 + 1, ..., imax-1) without correction on the high image density side
(I1 ≦ i2, i2 ≦ imax−1), and reference data A [i] (i = i1 + 1, ..., i2) to be corrected. Hereinafter, a specific calculation method will be described assuming that the image signal is proportional to the document reflectance without RGB-γ conversion. Of the reference data not corrected, the reference data A [i2 + 1] having the lowest image density in the high image density portion
And the reference data A with the lowest image density in the low image density part
The difference Δref between the data is obtained from [i1], that is, Δref = A [i1] −A [i2 + 1].
Here, in the case of reflectance data or brightness data that is not subjected to the RGB-γ conversion that is the inversion process, Δref>
It means 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 unit. That is, Δdet = A [i
1] -mmax. Thus, the reference data A [i] (i = i1 + 1, ...
2), A [i] = A [i1] + (A [i] −A [i
1]) × (Δdet / Δref). Where i =
It is assumed that i1 + 1, i1 + 2, ..., i2-1, i2. The scanner read image signal m [i] corresponding to n [i] is obtained from the reference data A [n] (step 1
04). Actually, the reference data A [n [j]] (0 ≦ n [j] ≦ 255, j = corresponding to the discrete n [j])
0, 1, ..., jmax, n [j] ≦ n [k] for
j ≦ k) is set as follows.

First, n [j] ≦ n [i] <n [j + 1]
J (0 ≦ j ≦ jmax) is obtained. In the case of an 8-bit image signal, n [0] = 0, n [jmax] = 255,
n [jmax + 1] = n [jmax] +1, A [jma
If reference data is obtained with x + 1] = A [jmax], the calculation becomes easy. The reference data interval is n
The accuracy of the finally obtained γ correction table is higher when [j] is as small as possible. From j obtained as described above, m [i] is given by the following equation, m [i] = A [j] +
(A [j + 1] -A [i]). (N [i] -n [j])
/ (N [j + 1] -n [j]) (step 1
04). Here, the interpolation is performed by a linear expression, but the interpolation may be performed by a higher-order function, a spline function, or the like. In that case, m [i] = f (n [i]). In the case of a kth-order function, the formula is as shown in FIG.

Next, the write value LD [i] of the LD for obtaining m [i] is obtained by the same procedure (step 1
05). When processing image signal data that has not been subjected to RGB-γ conversion, as the value of LD increases,
a [LD] becomes smaller. That is, LD [k] <LD
For [k + 1], a [LD [k]] ≧ a [LD [k
+1]]. Here, the value at the time of pattern formation is LD
[K] = 00h, 11h, 22h, ..., 66h, 8
1 of 8h, AAh, FFh (k = 0, 1, ..., 9)
It was set to 0 value. This is because the change in the reading value of the scanner with respect to the toner adhesion amount is large at the image density where the toner adhesion amount is small, so the intervals of the pattern writing values LD [k] are made close, and at the image density where the toner adhesion amount is large, the toner is This is because there is a small change in the reading value of the scanner with respect to the adhered amount, and it is necessary to increase the interval for reading.

As an advantage of this, LD [k] = 0
0h, 11h, 22h, ..., EEh, FFh (total 1
The toner consumption can be suppressed as compared with the case of increasing the number of patterns such as (6 points). Further, in the high image density area, the read value is likely to be reversed due to the small change with respect to the LD writing value, the potential unevenness on the photoconductor, the toner adhesion unevenness, the fixing unevenness, the potential unevenness, and the like.
The pattern is formed with the LD write value as described above because the narrowing of the LD write value interval is not always effective in improving the accuracy.

Further, a [LD [k]] ≧ m [i]> a
For LD [k] that is [LD [k + 1]], LD
[I] = LD [k] + (LD [k + 1] -LD [k])
-(M [i] -a [LD [k]]) / a ([LD [k +
1]]-a [LD [k]]). 0 ≦ k ≦ kmax
When (kmax> 0), a [LD [kmax]]
> M [i] (when the image density of the target value obtained from the reference data is high), LD [i] = LD [k] + (l
d [kmax] -LD [kmax-1]). (m [i]
-A [LD [kmax-1]]) / (a [LD [kma
[x]]-a [LD [kmax-1]]), the prediction is performed by extrapolation using a linear expression. This may be extrapolated by another method such as taking a logarithm other than the linear expression. As a result, the input value n [i] to the YMCKγ correction table is
And the output value LD [i] (n [i], LD [i]) (i
= 0, 1, ..., 15) (step 10)
6). Calculated (n [i], LD [i]) (i = 0,
1, ..., 15), interpolation is performed by a spline function or the like, or a γ correction table stored in the ROM is selected.

Next, the correction of the reader γ correction table used in the reader γ conversion circuit 502 based on the corrected read value of the scanner 420 in step 14 in the flowchart of FIG. 19 and the correction of the read value of the reader 520 will be described. This will be described with reference to the 30-dimensional quaternary chart. Figure 3
0 is a diagram showing a quaternary chart for explaining the reader RGB-γ conversion table. The horizontal axis of the first quadrant in FIG. 30A is the read value aS [n] obtained by reading the reference pattern with the scanner 420, and the vertical axis is the read value aR [n] obtained by reading with the reader 520. , And when they match, the graph in e) is obtained. here,
It is assumed that the characteristics shown in the graph of (f) can be obtained. In addition,
It is assumed that both aS [n] and aR [n] are corrected by the above-described machine difference correction value.

The second quadrant (b) is a conversion characteristic for correcting the value obtained by reading the reference pattern with the reader 520. In the case where the read values of the reference pattern are the same in the scanner 420 and the reader 520. Is the characteristic of g). The vertical axis of the third quadrant (c) is the characteristics after the scanner 420 or reader RGB-γ conversion, and this graph is a reference RGB-γ conversion table. The fourth quadrant is RGB
-Γ conversion table, i) is a scanner γ conversion circuit 402
It is a scanner γ conversion table used in. i) is the reader 520 when the reference pattern of the first quadrant is read.
In the RGB-γ conversion table in the case of e) in which the value read by the above and the value read by the scanner 420 match,
In the case of characteristics like f), RG with characteristics like j)
The B-γ conversion table is used by the reader γ conversion circuit 502.

On the other hand, the second quadrant h) is a conversion table for correcting the read value (corrected by the above-described machine difference correction value) obtained by reading the reference pattern by the reader 520. When the ACC is executed, by correcting the read value of the reference pattern obtained by the reader 520, the color correction coefficient obtained on the assumption that the reader RGB-γ conversion table of the characteristic of f) is used, and the AC
A preferable value can be set in combination with the printer printer γ characteristic obtained by executing C. Also,
FIG. 31 is a diagram showing a liquid crystal screen of the operation unit when a correction value is input. Thus, the correction value as shown in FIG. 25 can be input on the liquid crystal screen of the operation unit. The input data is stored in the RAM as a storage hold.

The input of this correction value will be described. First, the number of the correction gradation curve is selected by selecting the density key or the like. The corrected gradation curve may exist in the ROM 414 or may be newly generated.
Further, the selection of the density key may be performed by the operation unit or by an external controller connected online. On the image forming apparatus side, a copy start signal is obtained by the above-mentioned operation of the operator.
The copy start signal may also be generated by pressing the start button of the operation unit or by an external controller connected online. A corrected gradation curve is calculated, and interpolation processing is performed if necessary. Then, filter processing is performed, the basic gradation conversion curve is converted using the corrected gradation curve, and image formation is performed. It should be noted that these processes are set for each YMCK color and for each mode such as photo and character.

The operation of determining the document type will be described. Select the document type determination mode and place the document on the platen. When copy start is executed, the document is read by the scanner and stored in the image memory. Then, the feature amount of the image is extracted. The feature amount of the extracted image is compared with the feature amount of the registered image. At that time, it is determined whether or not the feature amount of the registered image matches within the allowable level. In the case of the registered document type, the registered image processing parameter is set. If the document type is not registered, it is determined whether the document type is set in advance so that it can be determined. When the document type is determined, the image processing parameter is set according to the determination result. When the judgment cannot be made, the image processing parameter of the default image quality mode is usually set. A copying operation is performed using the set image processing parameters. In addition to the procedure described above, the document type determination may be performed during prescanning or during image formation for the first color.

As described above, in the image forming apparatus of the present embodiment, the reference pattern formed by the image forming section is read by each of the first image reading means and the second image reading means, and the read signal is outputted. Since the reading characteristics are corrected based on the above, it is possible to bring the characteristics of the first image reading means and the second image reading means having different characteristics close to each other. Further, the first image signal output from the first image reading unit and the second image signal output from the second image reading unit are processed independently by the image processing unit, which is different. Since the processing is performed with the image processing parameter, it is possible to correct the difference between the reading characteristics of the first and second reading means. Among the differences, the difference in MTF characteristics can be corrected by the spatial filter parameter, and the color sensitivity can be corrected by the color correction coefficient.

Further, since the reading position of the first reading means and the reading position of the second reading means are different, the time and timing for starting the image processing are different, and the image processing corresponding to each is different. It is easier to control by means. Also, like when performing area processing,
Same ASIC (Application specific IC; Applicat
Ion Specific Integrated C
ircuits), the first image signal from the first image reading unit and the second image signal from the second image reading unit are image-processed with different image processing parameters. Good. In that case, the first image signal from the first reading unit and the second image signal from the second reading unit are used by using an image memory or the like.
The processing timings will be matched.

As described above, in the image forming apparatus according to the present embodiment, the first image signal from the first reading means and the second reading means obtained by reading the same reference pattern are obtained. An RGB-γ conversion table output by each reading unit is obtained from the second image signal,
The difference between the image signals output from the reading means of the read values after the RGB-γ conversion is small so that the RGB values of the RGB and γ-converted RGB values are small.
-Create a γ conversion table. By using the created RGB-γ conversion characteristics of the respective reading means, it is possible to correct that the reading value obtained by reading the same document has a large difference between the two reading means. You can In addition, when the degree of coincidence of the characteristics after each RGB-γ conversion is high, there is an advantage that substantially the same values can be used in the image processing parameters such as the color correction coefficient and the printer γ conversion table, which are in the subsequent stage. Further, since the image processing parameters are different between the back side and the front side of the document, it is possible to reduce image differences, background stains, and inconsistency in highlight reproducibility. Further, in the image forming apparatus of the present embodiment, a gradation conversion table for converting RGB signals by calibration, or Y
Since the MCK signal is reflected in the gradation conversion table for conversion, it is possible to reduce the difference between the image on the back side and the image on the front side of the double-sided copy created based on the image signal obtained by simultaneously reading the double-sided original.

[0063]

According to the first aspect of the invention, when the first image reading means or the second image reading means reads the reference document set in the automatic document feeder, the image processing means sets the first image reading means to the first document reading means. Since the image processing parameter or the image reading characteristic of both or one of the image signal and the second image signal is corrected, the reading characteristic can be approximated by performing processing with different image processing parameters.

According to the second aspect of the invention, the image processing means reads the read value of the image signal of the reference original read by the first image reading means or the image signal of the reference original read by the second image reading means. Since the image processing parameter or the image reading characteristic of either the first image signal or the second image signal is corrected based on the value, the difference between the reading values obtained by reading the same original becomes large. Can be prevented and corrected.

According to the third aspect of the present invention, the image processing parameters corrected by the image processing means are gradation conversion tables for converting RGB (red, green, blue) signals, or YMCK (yellow, magenta, cyan, black). ) By using one or both of the gradation conversion tables for converting signals, the difference between the image on the back side and the image on the front side of a double-sided copy created based on an image signal obtained by simultaneously reading a double-sided original is reduced. be able to.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an entire copying machine.

FIG. 2 is a diagram showing a configuration of a control system of a copying machine.

FIG. 3 is a block diagram showing a configuration of an image processing unit of a copying machine.

FIG. 4 is a diagram showing an example of an adaptive edge enhancement circuit.

FIG. 5 is a diagram showing a specific example of a sub-scanning direction edge detection filter.

FIG. 6 is a diagram showing a specific example of a main scanning direction edge detection filter.

FIG. 7 is a diagram showing an oblique direction detection filter (1).

FIG. 8 is a diagram showing an oblique direction detection filter (2).

FIG. 9 is a diagram showing an example of an adaptive edge enhancement filter table.

FIG. 10 is a diagram showing an arithmetic expression for color correction processing.

FIG. 11 is a diagram showing the concept of area processing.

FIG. 12 is a block diagram showing a configuration of a laser modulation circuit.

FIG. 13 is a block diagram showing a configuration of an image reading system.

FIG. 14 is a diagram showing an example of a scanner optical system having a sheet-through document feeder.

FIG. 15 is a diagram showing the concept of an image signal for white correction / black correction.

FIG. 16 is a schematic diagram in which an image signal is sampled and held.

FIG. 17 is a diagram showing the entire operation unit of the copying machine.

FIG. 18 is a diagram showing a liquid crystal screen of the operation unit.

FIG. 19 is a flowchart showing an operation procedure of automatic gradation correction of image density (gradation).

FIG. 20 is a diagram showing a screen for setting correction contents of automatic gradation correction.

FIG. 21 is a diagram showing a screen (1) displayed during execution of ACC.

FIG. 22 is a diagram showing a gradation pattern on a transfer sheet that is output when ACC is executed.

FIG. 23 is a diagram showing a screen (2) displayed during execution of ACC.

FIG. 24 is a diagram showing a screen (3) displayed during execution of ACC.

FIG. 25 is a diagram showing an example of a machine difference correction value.

FIG. 26 is a diagram showing an example of a graph of correction values.

FIG. 27 is a quaternary chart showing a method of calculating ACC.

FIG. 28 is a flowchart showing a calculation procedure of ACC.

FIG. 29 is a diagram showing an expression in the case of a kth-order function.

FIG. 30 is a diagram showing a quaternary chart illustrating a reader RGB-γ conversion table.

FIG. 31 is a diagram showing a liquid crystal screen of the operation unit when a correction value is input.

[Explanation of symbols]

401 Shading correction circuit 402 Scanner γ conversion circuit 403 image memory 404 Image separation circuit 405 MTF filter 406 color conversion UCR circuit 407 Variable magnification circuit 408 Image processing (create) circuit 409 Image processing printer γ circuit 410 gradation processing circuit 411 Interface (I / F) selector 412 Image forming printer γ circuit 413 printer 414 ROM (Read Only Memory) 415 CPU 416 RAM (random access memory) 420 scanner 423, 523 area processing circuit 502 Reader γ conversion circuit 520 leader

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/04 107 H04N 1/40 D 5C077 1/19 1/04 103E 5C079 1/46 1/12 Z / / G03B 27/72 1/46 ZF term (reference) 2H027 DA09 DB01 DE07 EA18 EB04 EC03 EC20 HB05 2H028 BA03 BC03 2H076 AA46 AA58 BA83 BA94 BB06 EA24 2H110 CE03 CE08 5C072 AA01 BA19 EA05 LA18 RA18 WA04 WA02 RA05 NA18 WA02 QA20 RA20 NA01 WA02 QA20 5C077 MM03 MM27 MP08 PP15 PP32 PP33 PP37 PP38 PQ23 5C079 HB01 HB03 HB12 JA23 LA12 LA21 LB02 LB04 LB06 MA04

Claims (3)

[Claims] 1. An image forming apparatus for automatically reading a document set on an automatic document feeder to form an image, wherein a reference pattern of image density specific to the image forming apparatus during image formation is formed on a predetermined sheet. Then, a reference document output means for outputting as a reference document and a first image, which is installed in the automatic document feeder and reads image information on the surface of the document or the reference document installed in the automatic document feeder, First output as a signal
A second image reading means, which is installed in the automatic document feeder and reads image information on the back surface of the original document or the reference document set in the automatic document feeder and outputs it as a second image signal.
Image reading means, image processing means for correcting the first image signal and the second image signal read by the first image reading means and the second image reading means, and correction by the image processing means Image forming means for forming an image of the first image signal and the second image signal thus formed on the front surface and the back surface of the sheet, respectively.
Image reading unit or the second image reading unit reads the reference document, the image processing unit causes the image processing parameter or the image of one or both of the first image signal and the second image signal. An image forming apparatus characterized by correcting reading characteristics. 2. The image processing means reads the image signal of the reference original read by the first image reading means or the read value of the image signal of the reference original read by the second image reading means. The image forming apparatus according to claim 1, wherein the image processing parameter or the image reading characteristic of either the first image signal or the second image signal is corrected based on the above. 3. The image processing parameter corrected by the image processing means is a gradation conversion table for converting RGB (red, green, blue) signals or YMCK (yellow, magenta, cyan, black) signals. 3. The image forming apparatus according to claim 1, wherein one or both of the gradation conversion tables are used.