JP2004034292A - Imaging apparatus and imaging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct a shift between the input pixel value and the output pixel value of an image in the subscanning direction due to eccentricity or distortion of a circulating member in an imaging apparatus. <P>SOLUTION: When the output characteristics are corrected, the control section 11 of the imaging apparatus 1 calculates a measurement curve based on the measurements of the quantity of light reflected from the toner image of a step wedge, further calculates a correction curve having reverse characteristics of the measurement curve and then sets both curves in an LUT incorporated in an output characteristics correcting means at an imaging section 17. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus and an image forming method.
[0002]
[Prior art]
2. Description of the Related Art In an electrophotographic image forming apparatus such as a laser printer, a printing operation is performed through processes of exposure, development, transfer, and fixing. Specifically, first, an electrostatic latent image of an image to be printed on the surface of the photosensitive drum is formed by irradiating a light beam (laser beam) modulated based on image data. It is developed as a toner image by a developing device. The toner image is transferred from the photosensitive drum to a transfer belt rotatably supported between the transfer roller and the photosensitive drum, and then transferred from the transfer belt to a transfer material (recording paper). In this case, an image is formed on the transfer material by fixing the toner image on the transfer material by the fixing heat.
[0003]
2. Description of the Related Art Conventionally, as an image forming apparatus that forms an output image by correcting the gradation of an image, for example, there is a digital copier, which reads a document image with a scanner, and performs image processing such as gradation processing and halftone processing on the read image. To form an output image.
[0004]
[Problems to be solved by the invention]
However, in a conventional image forming apparatus such as a digital copier, the manufacturing accuracy and the mounting accuracy of each component constituting the apparatus are slightly different for each apparatus, and the transfer roller, the photosensitive drum, and the photosensitive drum are electrically conductive. In some cases, the center of the orbiting member such as an elastic roller may be decentered. In addition, the eccentricity of the orbiting member as described above occurs due to the deterioration, and the transfer belt is distorted.
[0005]
When the eccentricity or distortion of the orbiting member occurs, a deviation occurs between an output pixel value of a target image (that is, an input pixel value) and an output pixel value of an actually output image, and the vertical direction (sub This causes a problem that output characteristics in the scanning direction) are partially different. For example, even if images having the same input pixel value are input in the sub-scanning direction, if the transfer roller, the photosensitive drum, the roller used in the developing device, and the like are eccentric, the distance between these rollers may be reduced. Due to the partial difference in the sub-scanning direction, there is a difference in the potential of the photosensitive drum during the charging process, the distance between the photosensitive drum and the transfer belt, or the distance between the photosensitive drum and the roller of the developing device, and the contact of each member. There has been a problem that the contact pressure is not constant, and an image having a partially different output pixel value in the circumferential direction (sub-scanning direction) of the printed matter is output.
[0006]
As described above, in the conventional image forming apparatus, the eccentricity of the orbiting member caused by an error in the manufacturing accuracy of the apparatus and an error in the mounting is reduced by reducing the error in the manufacturing and the mounting. It could only be solved by raising it, which had its limitations. In addition, the problem of eccentricity and distortion of the orbiting member due to deterioration due to use of the image forming apparatus cannot be avoided.
[0007]
An object of the present invention is to correct a shift between an input pixel value and an output pixel value in an image in a sub-scanning direction caused by eccentricity or distortion of a circling member in an image forming apparatus.
[0008]
[Means for Solving the Problems]
The present invention has the following features to solve the above problems.
[0009]
The invention according to claim 1 is
In an image forming apparatus that forms and outputs an image on a circulating member based on input image data,
Test image forming means for forming a test image a plurality of times in the rotation direction of the orbiting member on the orbiting member based on test image data having an arbitrary input pixel value;
Measuring means for measuring the amount of reflected light in the rotation direction of the test image formed on the orbiting member by the test image forming means,
Calculation means for calculating correction data for correcting the input pixel value so that the input pixel value of the test image data matches the reflected light amount measurement result,
Output image forming means for correcting an input pixel value of the input image data by the correction data calculated by the calculating means to form an output image,
It is characterized by having.
[0010]
The invention according to claim 6 is
In an image forming method for forming and outputting an image on a circulating member based on input image data,
Based on test image data having an arbitrary input pixel value, a step of forming a test image a plurality of times in the rotation direction of the orbiting member on the orbiting member,
Measuring the amount of reflected light in the rotational direction of the test image formed on the orbiting member,
A step of calculating correction data for correcting the input pixel value so that the input pixel value of the test image data matches the reflected light amount measurement result,
Correcting the input pixel value of the input image data with the correction data to form an output image;
It is characterized by including.
[0011]
According to the first or sixth aspect of the present invention, it is possible to correct a shift between an input pixel value and an output pixel value in the sub-scanning direction of an image caused by eccentricity or distortion of the orbiting member in the image forming apparatus. This makes it possible to output an image with a target pixel value. Further, the present invention can be implemented without improving the manufacturing accuracy and without significantly changing the structure of the conventional image forming apparatus, so that an increase in manufacturing cost can be suppressed. Further, since an input pixel value of an image can be corrected and output with a desired output pixel value, waste of a transfer material such as recording paper can be prevented.
[0012]
The invention according to claim 2 is the invention according to claim 1,
The test image forming unit forms a plurality of test images in the rotation direction of the orbiting member on the orbiting member based on a plurality of test image data having different input pixel values,
The measuring unit measures the amount of reflected light in the rotation direction of the plurality of test images formed on the orbiting member by the test image forming unit,
The calculation means calculates correction data for correcting the input pixel value so that the input pixel value of the plurality of test image data matches the reflected light amount measurement result,
The output image forming means forms an output image by correcting an input pixel value of the input image data based on the correction data calculated by the calculation means.
[0013]
The invention according to claim 7 is the invention according to claim 6,
Based on a plurality of test image data having different input pixel values, forming a plurality of test images in the rotation direction of the orbiting member on the orbiting member,
Measuring the amount of reflected light in the rotational direction of the plurality of test images formed on the orbiting member,
Calculating correction data for correcting the input pixel value so that the input pixel value of the plurality of test image data matches the reflected light amount measurement result;
Correcting the input pixel value of the input image data with the correction data to form an output image;
It is a feature including.
[0014]
According to the second or seventh aspect of the invention, by forming a test image based on a plurality of test image data having different input pixel values, it is possible to measure the amount of reflected light at multiple points, thereby improving the correction accuracy. Can be done.
[0015]
The invention according to claim 3 is the invention according to claim 1 or 2,
The test image data is composed of a plurality of colors,
The test image forming unit, based on the test image data, forms a test image for each color in the rotation direction of the orbiting member on the orbiting member,
The measuring unit measures the amount of reflected light in the rotation direction of the test image for each color formed on the orbiting member by the test image forming unit,
The calculating means calculates correction data for correcting the input pixel value such that the input pixel value for each color of the test image data matches the reflected light amount measurement result,
The output image forming means forms an output image by correcting an input pixel value for each color of the input image data based on the correction data calculated by the calculation means.
[0016]
The invention according to claim 8 is the invention according to claim 6 or 7,
The test image data is composed of a plurality of colors,
Based on the test image data, forming a test image for each color in the rotating direction of the orbiting member on the orbiting member,
Measuring the amount of reflected light in the rotational direction of the test image for each color formed on the orbiting member,
A step of calculating correction data for correcting the input pixel value such that the input pixel value for each color of the test image data matches the reflected light amount measurement result,
Forming an output image by correcting the input pixel value for each color of the input image data by the correction data calculated by the calculation unit;
It is characterized by including.
[0017]
According to the third or eighth aspect of the invention, when outputting an image composed of a plurality of colors, it is possible to correct a deviation between an input pixel value and an output pixel value for each color.
[0018]
The invention according to claim 4 is the invention according to any one of claims 1 to 3,
It is characterized by comprising one or both of storage means for storing the test image data and generating means for generating the test image data.
[0019]
The invention according to claim 9 is the invention according to any one of claims 6 to 8,
The method is characterized by including one or both of a step of storing the test image data in a storage unit and a step of generating the test image data.
[0020]
According to the fourth or ninth aspect of the present invention, the image correction processing can be executed by using the test image data stored in the storage unit in advance, or by generating and using the test image data. Therefore, the configuration can be changed according to the manufacturing cost of the image forming apparatus and the mounted memory.
[0021]
The invention according to claim 5 is the invention according to any one of claims 1 to 4,
The orbiting member is a transfer member for transferring an output image formed by the output image forming unit to a transfer material.
[0022]
The invention according to claim 10 is the invention according to any one of claims 6 to 9, wherein the orbiting member is a transfer member for transferring the output image to a transfer material.
[0023]
According to the fifth or tenth aspect of the present invention, a test image is formed on a transfer member for transferring an output image to a transfer material, an output pixel value is measured, and an input pixel value is corrected. Since the input pixel value of the image at the final stage can be corrected, there is no risk of deterioration before the corrected image is output, and the correction accuracy can be improved.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Here, in the above claims, a test image is a test pattern for correcting an input pixel value of an image, and a step wedge in the following embodiments corresponds to a test image. Further, the correction curves described in the following embodiments correspond to the correction data described in the above claims. Note that a step wedge in the following embodiments is an image for input pixel value correction in which the input pixel value is changed stepwise in the sub-scanning direction.
[0025]
In the following embodiments, the control unit 11 is a calculating unit described in the claims of the present invention, the storage unit 15 is a storage unit, the image forming unit 17 is a test image forming unit, an output image forming unit, and a generating unit. As means, each of the reflected light amount measuring sensors 5 has a function as a measuring means.
[0026]
First, the configuration will be described.
FIG. 1 is a cross-sectional configuration diagram of an image forming apparatus 1 according to the present embodiment. As shown in FIG. 1, the image forming apparatus 1 includes an image forming apparatus main body GH and an image reading device YS.
[0027]
An image reading device YS including an automatic paper feeding device 201 and a document image scanning exposure device 202 is installed above the image forming device main body GH. A document d placed on a document table of the automatic document feeder 201 is conveyed by a conveying means (not shown), and an image of one side or both sides of the document is scanned and exposed by an optical system of a document image scanning and exposing device 202, and line The data is read into the image sensor CCD.
[0028]
The analog signal photoelectrically converted by the line image sensor CCD is subjected to various image processing such as analog processing, A / D conversion, shading correction, image compression processing, and the like in an image forming unit 17 (see FIG. 3). Send signals to 3Y, 3M, 3C, 3K.
[0029]
The automatic document feeder 201 reads information of one or many documents d fed from the document table at once, and accumulates the information in the storage unit 15 (see FIG. 3).
[0030]
The image forming apparatus main body GH is referred to as a tandem type color image forming apparatus, and includes a plurality of sets of image output units 10Y, 10M, 10C, and 10K, an intermediate transfer belt 6 as an intermediate transfer body, and a sheet feeder. It comprises a transport unit and a fixing device 26 as a fixing unit.
[0031]
The image output unit 10Y that forms a yellow (Y) image includes a photosensitive drum 1Y as an image forming body, a charging unit 2Y, an exposing unit 3Y, a developing device 4Y, and a charging unit 2Y arranged around the photosensitive drum 1Y. An image forming body cleaning unit 8Y is provided. An image output unit 10M that forms a magenta (M) color image includes a photosensitive drum 1M as an image forming body, a charging unit 2M, an exposing unit 3M, a developing device 4M, and a charging unit 2M arranged around the photosensitive drum 1M. An image forming body cleaning unit 8M is provided. An image output unit 10C that forms a cyan (C) color image includes a photosensitive drum 1C as an image forming body, a charging unit 2C, an exposing unit 3C, a developing device 4C, and a charging unit 2C arranged around the photosensitive drum 1C. An image forming body cleaning unit 8C is provided. An image output unit 10K that forms a black (K) color image includes a photosensitive drum 1K as an image forming body, a charging unit 2K, an exposing unit 3K, a developing device 4K, and a photosensitive unit 1K arranged around the photosensitive drum 1K. An image forming body cleaning unit 8K is provided.
[0032]
Further, the intermediate transfer belt 6 is wound around a plurality of rollers and is rotatably supported. The development by the developing devices 4Y, 4M, 4C, and 4K is performed by an inversion phenomenon in which a developing bias in which an AC voltage is superimposed on a DC voltage having the same polarity as the toner polarity to be used is applied.
[0033]
The outline of the image forming process by the image forming apparatus 1 will be described below.
The image of each color formed by the image output units 10Y, 10M, 10C, and 10K is applied by primary transfer rollers 7Y, 7M, 7C, and 7K to which a primary transfer bias (not shown) having a polarity opposite to that of the toner to be used is applied. Are sequentially transferred onto the rotating intermediate transfer belt 6 (primary transfer) to form a combined color image (color toner image). The recording paper P stored in the paper feed cassettes 20A, 20B, and 20C is fed by a feed roller 21 and a paper feed roller 22A provided in the paper feed cassettes 20A, 20B, and 20C, respectively, and is transported by conveyance rollers 22B, 22C, and 22D. Then, the sheet is conveyed to a secondary transfer roller 7A as a secondary transfer means via a registration roller 23, and a color image is collectively transferred to one surface of the recording paper P (secondary transfer).
[0034]
The recording paper P to which the color image has been transferred is subjected to a fixing process by a fixing device 26, nipped by paper ejection rollers 24, and placed on a paper ejection tray 25 outside the machine.
[0035]
The untransferred toner remaining on the peripheral surfaces of the photosensitive drums 1Y, 1M, 1C, and 1K after the transfer is cleaned by the image forming body cleaning means 8Y, 8M, 8C, and 8K, and enters the next image forming cycle.
[0036]
Here, the reflected light amount measuring sensor 5 shown in FIG. 1 will be described. FIG. 2A is a diagram illustrating a positional relationship among the reflected light amount measuring sensor 5, the photosensitive drum 1K, and the intermediate transfer belt 6, and FIG. 2B is an enlarged view of the reflected light amount measuring sensor 5. As shown in FIG. 2A, the toner image formed on the photosensitive drum 1K is transferred to the intermediate transfer belt 6 by the rotation of the photosensitive drum 1K and the intermediate transfer belt 6. The reflected light amount measurement sensor 5 measures the reflected light amount of the toner image formed on the intermediate transfer belt 6 and outputs the measurement result to the control system of the image forming apparatus 1.
[0037]
As shown in FIG. 2B, a phototransistor and an LED (Light Emitting Diode) are provided inside the measurement sensor 5, the LED emits light, and the emitted light is reflected on a toner image. When the light enters the transistor, the phototransistor outputs the measurement result of the reflected light amount to the control system of the image forming apparatus 1 as the reflected light amount measurement result. The image forming apparatus 1 calculates the amount of reflected light of the toner image formed on the intermediate transfer belt 6 based on the measurement result of the amount of reflected light input from the reflected light amount measuring sensor 5.
[0038]
The reflected light amount measuring sensor 5 is configured to measure not only the black toner image formed by the photosensitive drum 1K but also the yellow, magenta, and cyan toner images transferred onto the intermediate transfer belt 6 by the photosensitive drums 1Y, 1M, and 1C. Measure the amount of reflected light. Further, in the present embodiment, the configuration is described in which the reflected light amount of the toner image transferred to the intermediate transfer belt 6 is measured by the reflected light amount measuring sensor 5, but at the time when the toner image is formed on the photosensitive drum 1 The reflected light amount of the toner image on the photosensitive drum 1 may be measured.
[0039]
Next, the functional configuration of the image forming apparatus 1 shown in FIG. 1 will be described in detail. FIG. 3 is a block diagram illustrating a functional configuration of the image forming apparatus 1. As shown in FIG. 3, the image forming apparatus 1 includes a control unit 11, an input unit 12, a display unit 13, a RAM 14, a storage unit 15, an image reading unit 16, an image forming unit 17, an output unit 18, a reflected light amount measuring sensor 5, And each unit is connected by a bus 19.
[0040]
The control unit 11 reads various programs stored in the storage unit 15 and develops them in the RAM 14, and performs centralized control of each unit according to the programs. Specifically, the control unit 11 executes an output characteristic correction process described later in accordance with the output characteristic correction processing program stored in the storage unit 15, stores the processing result in the RAM 14, and displays the processing result on the display unit 13. . Then, the processing result stored in the RAM 14 is stored in a predetermined area in the storage unit 15.
[0041]
The control unit 11 reads from the storage unit 15 a test image for image correction in which the input pixel value in the sub-scanning direction is changed stepwise in the output characteristic correction process, that is, data of the step wedge, and the output unit 18 By driving the means 3Y, a step wedge toner image is continuously formed on the photosensitive drum 1Y twice or more. This toner image is transferred from the photosensitive drum 1Y to the intermediate transfer belt 6. The control unit 11 acquires the measurement result of the reflected light of the toner image transferred onto the intermediate transfer belt 6 measured by the reflected light amount measurement sensor 5 from the reflected light amount measurement sensor 5 in synchronization with the position of the step wedge. Then, based on the acquired measurement result and the input pixel value of the step wedge, a function (hereinafter, referred to as a measurement curve) indicating the reflected light amount measurement result is calculated by using the least squares method or spline interpolation, and the input pixel value and the reflection are calculated. A function (hereinafter, referred to as a correction curve) having an inverse characteristic of the measurement curve for correcting a difference from the light amount measurement value (hereinafter, referred to as output characteristic deviation) is calculated, and an LUT and an output characteristic correction unit (see FIG. 5) Set to. The control unit 11 calculates a correction curve for each color of M (magenta), C (cyan), and K (black) other than Y (yellow) in the same procedure as described above, and sets the correction curve in the output characteristic correction unit. I do.
[0042]
Here, the output characteristic correction processing by the control unit 11 will be described in more detail with reference to FIGS. As described above, the control unit 11 repeats and outputs the step wedge twice or more, and corrects the output characteristic deviation based on the measurement result of the amount of reflected light of the toner image of the step wedge formed by the step wedge. As the method, there are two methods, a method of continuously outputting the same step wedge two or more times and a method of outputting two or more types of step wedges having different input pixel values. The step wedge is output by any method according to the instruction input.
[0043]
Here, assuming that the peripheral length of the intermediate transfer belt 6 is L, the length of the step wedge is S, and the number of repetitions of the step wedge is N, (S × N ÷ L) is set to an approximate integer, so that the intermediate transfer belt 6 and the like are obtained. The periodic fluctuation of the output characteristics due to the eccentricity or distortion of the orbiting member is averaged. However, the effect is improved when the output characteristic deviation is within 1/4 of the length S of the step wedge. Explaining with actual numerical values, for example, in the case where S = 45 mm step wedge is repeatedly output twice on the photosensitive drum 1 having a circumferential length L = 90 mm, an output characteristic deviation of 1/4 of the circumferential length due to eccentricity (11.25 mm) ) Occurs, (S × N ÷ L) becomes 45 × 2 ÷ (90− (output characteristic deviation when the photosensitive drum 1 makes one rotation: 11.25 × 2)) = 1.33.
[0044]
FIG. 4A is a table showing input pixel values for each sub-scanning position when the same step wedge is repeatedly output to the intermediate transfer belt 6 three times, and FIG. 4B is a table showing the input pixels of FIG. FIG. 7 is a diagram showing a measurement curve of the reflected light amount of the step wedge actually formed on the intermediate transfer belt 6 based on the values, and FIG. 9C is a diagram showing a correction curve calculated based on the measurement curve of FIG. .
[0045]
In the example shown in FIG. 4A, the control unit 11 repeatedly outputs the same step wedge three times. When the control unit 11 outputs the step wedge A as shown in FIG. 4A, the control unit 11 inputs the pixel input points (0, 64, 128, 192, 255, 0, 64, 128, 192, 255, 0, 64). , 128, 192, 255), the measurement result of the reflected light is acquired from the reflected light amount measurement sensor 5 and the measurement curve is calculated. Then, when the calculated measurement curve becomes the curve shown in FIG. 4B, the control section 11 determines that there is an output characteristic deviation because the measurement curve does not match the target output pixel value, and determines the inverse characteristic of the measurement curve. The correction curve shown in FIG. 4C is calculated.
[0046]
FIG. 5A is a table showing input pixel values for each sub-scanning position when three types of step wedges having different input pixel values are successively output to the intermediate transfer belt 6, and FIG. 7A and 7B are diagrams showing measurement results of the reflected light amount of the step wedge actually formed on the intermediate transfer belt 6 according to the input pixel values of FIG. 7C, and FIG. 9C is a diagram showing a correction curve having the inverse characteristic of the measurement curve of FIG. It is.
[0047]
In the example illustrated in FIG. 5A, the control unit 11 outputs three different types of step wedges A, B, and C whose input pixel values are similar. According to this example, utilizing the fact that outputting a step wedge of an approximated input pixel value also approximates the periodic variation of the output pixel value, not only averaging the circular variation of the output pixel value, but also By increasing the number of measurement points of the amount of reflected light in accordance with the point increase, the accuracy of data interpolation can be improved.
[0048]
When the control unit 11 outputs the step wedges A, B, and C as shown in FIG. 5A, the input unit (0, 54, 108, 162, 216, 18, 18, 72, 126, 180, 234) of the pixel is output. , 36, 90, 144, 198, 255), the measurement result of the reflected light is acquired from the reflected light amount measuring sensor 5 at the timing synchronized with the timing, and the measurement curve is calculated. In this case, the number of types of numerical values of the measurement points is increased as compared with the example shown in FIG. When the calculated measurement curve becomes the curve shown in FIG. 5B, the control unit 11 determines that there is an output characteristic deviation because the measurement curve does not match the target output pixel value, and determines the inverse characteristic of the measurement curve. The correction curve shown in FIG. 5C is calculated.
[0049]
The input unit 12 includes a keyboard having cursor keys, numeric input keys, various function keys, and the like, and outputs a press signal corresponding to a key pressed on the keyboard to the control unit 11. Note that the input unit 12 may be provided with a touch panel or the like integrally with the display unit 13 as necessary, or may include another input device.
[0050]
The display unit 13 includes an LCD (Liquid Crystal Display), an EL (Electro Luminescence), and the like, and displays image data, text data, and the like on a screen in accordance with an instruction of a display signal input from the control unit 11.
[0051]
The RAM 14 forms a temporary storage area for programs, input or output data, parameters, and the like read from the storage unit 15 in various processes executed and controlled by the control unit 11.
[0052]
The storage unit 15 is configured by a nonvolatile semiconductor memory such as an EEPROM (Electrically Erasable Programmable Read-Only Memory), and stores various programs executable by the image forming apparatus 1 and setting contents according to functions. Specifically, the storage unit 15 stores an output characteristic correction processing program and data of a plurality of types of step wedges having different input pixel values.
[0053]
The image reading unit 16 is provided with a scanner below a contact glass on which a document is placed, and reads image data of the document. The image reading device YS shown in FIG. The scanner includes a light source, a lens, a CCD (Charge Coupled Device), and the like. The scanner reads a document image by forming reflected light of light that has been illuminated from the light source onto the document and photoelectrically converts the image. Output to the image forming unit 17. Here, the image data includes not only image data such as figures and photographs but also text data such as characters and symbols.
[0054]
The image forming unit 17 includes a gate array circuit including a density conversion unit, a color correction unit, an output characteristic correction unit, a gradation characteristic correction unit, and a halftone processing unit illustrated in FIG. The image forming unit 17 performs scaling, rotation, and position change on image data input from the image reading unit 16 according to an instruction from the control unit 11. In the image correction processing, image processing such as density conversion processing, color correction processing, output characteristic correction processing, gradation characteristic correction processing, halftone processing, and the like are performed on image data input from the image reading unit 16, and as a result, The obtained output data is output to the output unit 18.
[0055]
The output unit 18 includes an image output unit 10 illustrated in FIG. 1, a paper feed unit including a paper feed cassette 20, a feed roller 21, a paper feed roller 22A, transport rollers 22B to 22D, a registration roller 23, and toners TY, TM, A transfer unit including TC, TK, an intermediate transfer belt 6, a primary transfer roller and a secondary transfer roller 7, a fixing device 26, and a paper discharge unit including a paper discharge roller 24 and a paper discharge tray 25. Is done. The output unit 18 converts the step wedge read from the storage unit 15 or the electrostatic latent image of the image data input from the image forming unit 17 into the photosensitive drums 1Y, 1M, 1C, Exposure to 1K causes toner to be attracted to the electrostatic latent image to form a toner image. The output unit 18 prints the toner image on the recording paper P.
[0056]
Here, a procedure from reading of image data to output thereof will be described with reference to FIG.
As described above, the image forming unit 17 includes the image forming unit 17 including the density conversion unit, the color correction unit, the output characteristic correction unit, the gradation characteristic correction unit, and the halftone processing unit. Further, the output characteristic correction means includes a built-in LUT (Look Up Table) (not shown), and the control unit 11 sets the correction curve calculated in the output characteristic correction process in this LUT, thereby generating the image data in the image forming apparatus 1. Correct the output characteristic deviation.
[0057]
As shown in FIG. 6, when the data of the document d placed on the image reading device YS is read by the image reading unit 16 to generate RGB image data, the density conversion unit converts the data into linear density image data. The color conversion means converts the image data into CMYK image data. Next, the output characteristic correction unit corrects the output characteristic deviation of the CMYK image data by using the LUT on which the correction curve is set, and corrects the output characteristic deviation in the sub-scanning direction. Subsequently, the gradation characteristic correction unit corrects the gradation characteristics of the CMYK image data input from the output characteristic correction unit. Then, the halftone processing means performs halftone processing on the CMYK image data input from the tone characteristic correction means to generate output data. As the halftone processing, for example, a dither method can be used, but since these methods are general, description thereof is omitted. Then, the control unit 11 outputs the output data to the output unit 18 and prints it on the recording paper P.
[0058]
Next, the operation will be described.
As a premise of the description of the operation, a program for realizing the output characteristic correction processing is stored in the storage unit 15 in the form of a computer-readable program code, and the control unit 11 performs an operation according to the program code. Execute sequentially.
[0059]
FIG. 7 is a flowchart showing the output characteristic correction processing by the control unit 11. In the output characteristic correction processing, the control unit 11 sets the LUT of the output characteristic correction means of FIG. 6 to through (step S1). Next, the step wedge selected through the input unit 12 shown in FIG. 4A or 5A is read from the storage unit 15, and the read step wedge data is subjected to density conversion processing by the density conversion unit. After the color correction processing is performed by the color correction means, the image data is passed through the output characteristic correction means, the gradation correction is performed by the gradation characteristic correction means, the halftone processing is performed by the halftone processing means, and output to the output unit 18. Thus, a step wedge toner image is formed on the photosensitive drum 1 (step S2).
[0060]
Next, the control unit 11 uses the reflected light amount measurement sensor 5 to measure the reflected light amount of the step wedge toner image formed on the photoconductor drum 1 and uses the reflected light amount measurement result and the input pixel value of the step wedge to measure the curve. Is calculated (step S3). Subsequently, the control unit 11 calculates a correction curve based on the measurement curve (step S4), sets the calculated correction curve in the LUT of the output characteristic correction unit (step S5), and ends the output characteristic correction processing. I do. By setting the correction curve in the output characteristic correction unit in this manner, the density of the data of the image read by the image reading unit 16 is corrected, and the output can be performed with a desired output pixel value.
[0061]
As described above, according to the above-described embodiment, the control unit 11 of the image forming apparatus 1 performs the output characteristic correction process based on the reflection light amount measurement result of the step wedge toner image and the input pixel value of the step wedge. A measurement curve is calculated, and a correction curve having an inverse characteristic of the measurement curve is calculated and set in an LUT built in the output characteristic correction unit of the image forming unit 17.
[0062]
Therefore, sub-scanning of output image data generated due to errors in manufacturing the image forming apparatus 1 or mounting members, and eccentricity caused by deterioration of the cylindrical members such as the photosensitive drum 1 and the intermediate transfer belt 6. Output characteristic deviation in the direction can be corrected. In addition, by executing the output characteristic correction processing periodically at the time of maintenance of the image forming apparatus 1 or the like, it is possible to always output an image with desired output characteristics, and to prevent waste of recording paper.
[0063]
Further, the circuit for executing the image correction processing in the image forming apparatus 1 can be realized by a hardware configuration such as a gate array, and it is necessary to improve the manufacturing accuracy of the image forming apparatus itself and to significantly change the structure. Therefore, it can be realized without incurring much cost.
[0064]
The reflection light amount measuring sensor 5 measures the reflection light amount of the toner image formed on the intermediate transfer belt 6 immediately before being transferred to the recording paper. Even if a deviation, an eccentricity, a distortion, or the like in accuracy occurs in the orbiting member, the control unit 11 can calculate a correction curve that comprehensively corrects these deviations.
[0065]
In the above-described embodiment, the circuit for correcting the image read by the image reading unit 16 is configured by the gate array. Instead, the image correction processing program is stored in the storage unit 15. Of course, it is also possible to configure the image forming apparatus such that the control unit 11 performs the image correction processing according to the image correction processing program.
[0066]
Further, in the above embodiment, the image forming apparatus for processing a color image has been described, but the present invention is also applicable to an image forming apparatus for processing a monochrome image.
[0067]
In the above embodiment, the toner image is transferred from the photosensitive drum 1 to the intermediate transfer belt 6 and then transferred from the intermediate transfer belt 6 to recording paper. However, the toner image is directly transferred from the photosensitive drum 1 to recording paper. May be configured.
[0068]
Further, in the above-described embodiment, an example has been described in which the measurement sensor 5 measures the reflected light amount of the toner image of the step wedge formed on the intermediate transfer belt 6 to correct the output characteristic deviation. The output characteristic deviation may be corrected by measuring the reflected light amount of the formed toner image and calculating the measurement curve and the correction curve.
[0069]
In addition, the detailed configuration and detailed operation of the image forming apparatus 1 to which the present invention is applied can be appropriately changed without departing from the spirit of the present invention.
[0070]
【The invention's effect】
According to the first or sixth aspect of the present invention, it is possible to correct a shift between an input pixel value and an output pixel value in the sub-scanning direction of an image caused by eccentricity or distortion of the orbiting member in the image forming apparatus. This makes it possible to output an image with a target pixel value. Further, the present invention can be implemented without improving the manufacturing accuracy and without significantly changing the structure of the conventional image forming apparatus, so that an increase in manufacturing cost can be suppressed. Further, since an input pixel value of an image can be corrected and output with a desired output pixel value, waste of a transfer material such as recording paper can be prevented.
[0071]
According to the second or seventh aspect of the present invention, by forming a test image based on a plurality of test image data having different input pixel values, output pixel values at multiple points can be measured. Can be improved.
[0072]
According to the third or eighth aspect of the invention, when outputting an image composed of a plurality of colors, it is possible to correct a deviation between an input pixel value and an output pixel value for each color.
[0073]
According to the fourth or ninth aspect of the present invention, the image correction processing can be executed by using the test image data stored in the storage unit in advance, or by generating and using the test image data. Therefore, the configuration can be changed according to the manufacturing cost of the image forming apparatus and the mounted memory.
[0074]
According to the fifth or tenth aspect of the present invention, a test image is formed on a transfer member for transferring an output image to a transfer material, an output pixel value is measured, and an input pixel value is corrected. Since the input pixel value of the image at the final stage can be corrected, there is no risk of deterioration before the corrected image is output, and the correction accuracy can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional configuration diagram of an image forming apparatus 1.
2A is a perspective view showing a positional relationship among a reflected light amount measuring sensor 5, a photosensitive drum 1K, and an intermediate transfer belt 6 shown in FIG. 1, and FIG. 2B is an enlarged view of the reflected light amount measuring sensor 5. is there.
FIG. 3 is a block diagram illustrating a functional configuration of the image forming apparatus 1 of FIG. 1;
4A is a table showing input pixel values for each sub-scanning position when the same step wedge is repeatedly output to the intermediate transfer belt 6 three times, and FIG. 4B is a table showing the input pixels of FIG. FIG. 7 is a diagram showing a measurement curve of the reflected light amount of the step wedge actually formed on the intermediate transfer belt 6 based on the values, and FIG. 9C is a diagram showing a correction curve calculated based on the measurement curve of FIG. .
FIG. 5A is a table showing input pixel values for each sub-scanning position when three types of step wedges having different input pixel values are successively output to the intermediate transfer belt 6, and FIG. 7A is a diagram showing a measurement curve of the reflected light amount of the step wedge actually formed on the intermediate transfer belt 6 based on the input pixel value of FIG. 7A, and FIG. 9C is a correction curve calculated based on the measurement curve of FIG. FIG.
FIG. 6 is a block diagram illustrating a functional configuration unit that executes an image correction process and is built in the image forming unit 17 of FIG. 3;
FIG. 7 is a flowchart illustrating an output characteristic correction process performed by a control unit 11 of FIG. 3;
[Explanation of symbols]
1 Image forming apparatus
1Y, 1M, 1C, 1K Photoconductor drum
2Y, 2M, 2C, 2K Charging means
3Y, 3M, 3C, 3K exposure means
4Y, 4M, 4C, 4K developing device
5 Reflection light amount measurement sensor
6 Intermediate transfer belt
7A secondary transfer roller
7Y, 7M, 7C, 7K primary transfer roller
8A Intermediate Transfer Member Cleaning Means
8Y, 8M, 8C, 8K Image Forming Body Cleaning Means
10Y, 10M, 10C, 10K Image output unit
11 Control part
12 Input section
13 Display
14 RAM
15 Memory
16 Image reading unit
17 Image forming unit
18 Output section
19 bus
20A, 20B, 20C paper cassette
21 Feeding roller
22A, 22B, 22C, 22D transport rollers
23 Registration roller
24 paper ejection rollers
25 Output tray
26 Fixing device
201 Automatic Document Feeder
202 Document Image Scanning Exposure Device
YS image reading device
GH image forming device body
d manuscript
P Recording paper

Claims (10)

In an image forming apparatus that forms and outputs an image on a circulating member based on input image data,
Test image forming means for forming a test image a plurality of times in the rotation direction of the orbiting member on the orbiting member based on test image data having an arbitrary input pixel value;
Measuring means for measuring the amount of reflected light in the rotation direction of the test image formed on the orbiting member by the test image forming means,
Calculation means for calculating correction data for correcting the input pixel value so that the input pixel value of the test image data matches the reflected light amount measurement result,
Output image forming means for correcting an input pixel value of the input image data by the correction data calculated by the calculating means to form an output image,
An image forming apparatus comprising: The test image forming unit forms a plurality of test images in the rotation direction of the orbiting member on the orbiting member based on a plurality of test image data having different input pixel values,
The measuring unit measures the amount of reflected light in the rotation direction of the plurality of test images formed on the orbiting member by the test image forming unit,
The calculation means calculates correction data for correcting the input pixel value so that the input pixel value of the plurality of test image data matches the reflected light amount measurement result,
The image forming apparatus according to claim 1, wherein the output image forming unit forms an output image by correcting an input pixel value of the input image data based on the correction data calculated by the calculation unit. The test image data is composed of a plurality of colors,
The test image forming unit, based on the test image data, forms a test image for each color in the rotation direction of the orbiting member on the orbiting member,
The measuring unit measures the amount of reflected light in the rotation direction of the test image for each color formed on the orbiting member by the test image forming unit,
The calculating means calculates correction data for correcting the input pixel value such that the input pixel value for each color of the test image data matches the reflected light amount measurement result,
The image according to claim 1, wherein the output image forming unit forms an output image by correcting an input pixel value for each color of the input image data based on the correction data calculated by the calculation unit. Forming equipment. The image forming apparatus according to claim 1, further comprising one or both of a storage unit configured to store the test image data and a generation unit configured to generate the test image data. The image forming apparatus according to claim 1, wherein the orbiting member is a transfer member configured to transfer an output image formed by the output image forming unit to a transfer material. In an image forming method for forming and outputting an image on a circulating member based on input image data,
Based on test image data having an arbitrary input pixel value, a step of forming a test image a plurality of times in the rotation direction of the orbiting member on the orbiting member,
Measuring the amount of reflected light in the rotational direction of the test image formed on the orbiting member,
A step of calculating correction data for correcting the input pixel value so that the input pixel value of the test image data matches the reflected light amount measurement result,
Correcting the input pixel value of the input image data with the correction data to form an output image;
An image forming method comprising: Based on a plurality of test image data having different input pixel values, forming a plurality of test images in the rotation direction of the orbiting member on the orbiting member,
Measuring the amount of reflected light in the rotational direction of the plurality of test images formed on the orbiting member,
Calculating correction data for correcting the input pixel value so that the input pixel value of the plurality of test image data matches the reflected light amount measurement result;
Correcting the input pixel value of the input image data with the correction data to form an output image;
The image forming method according to claim 6, comprising: The test image data is composed of a plurality of colors,
Based on the test image data, forming a test image for each color in the rotating direction of the orbiting member on the orbiting member,
Measuring the amount of reflected light in the rotational direction of the test image for each color formed on the orbiting member,
A step of calculating correction data for correcting the input pixel value such that the input pixel value for each color of the test image data matches the reflected light amount measurement result,
Forming an output image by correcting the input pixel value for each color of the input image data by the correction data calculated by the calculation unit;
The image forming method according to claim 6, further comprising: The image forming method according to claim 6, further comprising one or both of a step of storing the test image data in a storage unit and a step of generating the test image data. The image forming method according to claim 6, wherein the orbiting member is a transfer member for transferring the output image to a transfer material.

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