JP2020106555A - Image forming device - Google Patents

Abstract

To provide an image forming device capable of performing satisfactory image formation with constantly small concentration variation and color variation without lowering the productivity of image forming operation or excessive consumption of the developer.SOLUTION: The image forming device includes: image forming means that forms a toner image on an image carrier on the basis of the image signal; and density detection means for detecting the density of the toner image on the image carrier. The image forming device also includes control means configured to: determine an area to detect the density in a normal image formed by the image forming means; and control the image forming conditions on the basis of the value obtained by weighting and integrating the image data of the detection area according to the sensor characteristics and the detection result of the area detected by the concentration detection means.SELECTED DRAWING: Figure 11

Description

The present invention relates to an image forming apparatus.

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer that employs an electrophotographic method, it is desired that an image having a constant density is reproduced on a transfer material for the same image data. For this reason, the image forming apparatus is started up, and after the warm-up operation is completed, the density detection development image (patch) having a specific pattern is exposed during the image forming preparation step before the image forming step, that is, during the pre-rotation. The image is formed on an image carrier such as a body drum, and the density of the formed pattern is read, and based on the read density value, the charge amount, the exposure amount, the image information conversion table of the image forming apparatus, a so-called lookup table (hereinafter , "LUT"), image control (pre-rotation image control) that stabilizes the quality of an image to be formed by changing various parameters that determine image forming conditions such as a developing electric field and a developer replenishment amount. It has been implemented.

Furthermore, due to changes in environmental conditions and characteristics of the image forming apparatus that change every moment when image formation is performed for a long time, even when gradation characteristics change, a patch is formed again on the image carrier, By reading and feeding back to various parameters that determine the image forming condition again, the image quality can be stabilized according to the variation.

As described in Patent Document 1, after repeating the image forming process, one or a plurality of predetermined gradation patterns as patches are formed on a predetermined number of sheets on the image carrier, and the density of the gradation pattern is increased. Is known, and so-called post-rotation image control is known.

Further, as described in Patent Document 2, one or a plurality of predetermined gradation patterns are provided between image formations during continuous image formation in which a plurality of images are continuously formed, that is, between papers, as described above. There is also known a method of forming an image on an image carrier, reading the density of the gradation pattern, and controlling various parameters according to the value, so-called inter-sheet image control.

However, in the above-described post-rotation image control, the image control is executed after a predetermined number of sheets, so that the image formation cannot be executed during the execution, which lowers the productivity of the user. Further, in the above-mentioned sheet-to-sheet image control, since a patch is formed between sheets, it is necessary to lengthen the sheet-to-sheet time correspondingly, which is a factor that reduces the number of image forming sheets that can be produced at the same processing speed. It was In either image control method, since an image pattern different from the formed image desired by the user is formed as a patch in the image forming process, excessive consumption of the developer and the image forming apparatus It was a cause of increasing dirt inside.

Therefore, a method is disclosed in which the normal image output by the user is detected instead of the patch, and the image forming condition is changed to suppress the consumption of the excessive developer. As described in Patent Document 3, a determination unit that determines whether or not a predetermined region of the toner image formed based on the image information input to the image data input unit is suitable as a detection target of the image density. Was established. Then, when the determination unit determines that the image density of the predetermined area is determined to be suitable as a detection target, the toner density control target value is corrected based on the result of detection by the optical sensor. Configured the controller. In addition, as described in Patent Documents 4, 5, and 6, methods for extracting a region of image data suitable as a substitute for a patch are disclosed.

JP-A-2000-238341 JP, 2003-202711, A JP, 2014-186311, A JP, 2014-115517, A JP-A-2007-20111 JP, 2005-148716, A

However, in the above method, since the area where the image density is suitable is limited, the frequency of obtaining necessary information is low and sufficient control cannot be performed.

An object of the present invention is to provide an image forming apparatus capable of always carrying out good image formation with little variation in density and variation in tint without causing a decrease in productivity of image forming operation and excessive consumption of developer. Especially.

In order to achieve the above object, the image forming apparatus according to the present invention,
An image forming condition control (gradation control) for forming an image pattern on an image carrier (photosensitive drum), reading the image pattern with a reading means (patch sensor), and changing the image forming condition (γLUT) is provided. In the image forming apparatus, the image data in the range corresponding to the reading area (detection spot) in the reading means is corrected according to the characteristics (light amount distribution) of the reading means (representative value) and the detection value by the reading means. The image forming condition is controlled according to the above.

According to the image forming apparatus of the present invention, it is possible to always provide a good image with a small density or tint variation without causing a decrease in productivity and without consuming excess developer. ..

FIG. 1 is a diagram showing a schematic configuration of a color image forming apparatus according to an embodiment. FIG. 3 is an exemplary functional block diagram of a document reading unit according to the embodiment. FIG. 3 is an exemplary functional block diagram of an image forming unit according to the embodiment. FIG. 6 is a diagram showing the spectral characteristics of the yellow toner according to the embodiment. FIG. 6 is a diagram showing a spectral characteristic of the magenta toner according to the embodiment. FIG. 6 is a diagram showing spectral characteristics of cyan toner according to the embodiment. FIG. 3 is a diagram showing spectral characteristics of black toner according to the embodiment. It is a figure which shows the relationship between the sensor output and output image density which concern on embodiment. It is a figure which shows the relationship between the sensor output and input signal which concern on embodiment. 6 is an exemplary flowchart of first gradation control according to the embodiment. It is a figure which shows the weighting filter which concerns on embodiment. It is a figure which shows the relationship between the image data and patch substitution part which concern on embodiment. 6 is an exemplary flowchart of image data extraction according to the embodiment. It is a figure which shows the relationship between the sensor output and input signal which concern on embodiment. 6 is an exemplary flowchart of second gradation control according to the embodiment. It is a figure which shows the alignment sequence image data which concerns on embodiment. It is a figure which shows the relationship between the sensor output and a vertical line position which concern on embodiment. 6 is an exemplary flowchart of an alignment sequence according to an embodiment.

Hereinafter, modes for carrying out the present invention will be described with reference to the drawings.

[System configuration]
FIG. 1 is a diagram showing a schematic configuration of a color image forming apparatus according to an embodiment. The color image forming apparatus 100 shown in FIG. 1 includes a document reading unit 101 for reading a document and an image forming unit 150 for forming an image on a recording medium.

(leader)
The document reading unit 101 is generally arranged above the color image forming apparatus 100 in many cases. The original 102 is placed in the platen cover 103. The lamp 104 is a light source that irradiates the document surface with light. The mirror 105 guides the reflected light from the lamp 104 reflected by the original 102 to the mirror 106. The mirror 106 guides the light reflected by the mirror 105 to the lens 108. The lamp 104 and the mirror 105 are installed on the optical stand 112. The mirror 106 and the mirror 107 are installed on the optical stand 113.

The optical benches 112 and 113 move by rotating the motor 111 forward or backward. By moving the optical tables 112 and 113, the original 102 can be scanned in the sub-scanning direction. The lens 108 focuses the reflected light from the document surface guided by the optical stands 112 and 113 onto the CCD 109. The CCD 109 receives the light from the surface of the document collected by the lens 108 and performs photoelectric conversion. It is assumed that the CCD 109 is installed on the substrate 110. The reference white plate 114 is used when measuring the light amount variation of the lamp 104 and the sensitivity variation of the CCD 109. The CCD 109 has three line sensors.

Each line sensor corresponds to RED, GREEN, BLUE (hereinafter RGB) in order to read a color image. For example, if the number of pixels of each sensor in the main scan is 7,500, an A3 original can be read at 600 dpi.

<Original scanning>
FIG. 2 is an exemplary functional block diagram of the document reading unit according to the embodiment.

The document reading controller 201 transfers the image data read by the CCD 109 to the image forming controller 300 of the image forming unit 150. More specifically, when an instruction to read a document is given from the operation unit 308 or the like shown in FIG. 3, the document reading controller 201 controls the motor 111 to move the optical table 112 to a position for reading the reference white plate 114. And 113 are moved.

Next, the document controller 201 turns on the lamp 104 and causes the CCD 109 to read the reference white plate 114. From the reading result of the reference white plate 114, the eye light controller 201 corrects the light amount variation of the lamp 104 and the sensitivity variation of the CCD 109 (so-called shading correction). The document controller 201 further controls the motor 111 to sub-scan the document 102, and transfers the acquired RGB image data to the image forming controller 300.

(Printer)
Referring again to FIG. 1, it can be seen that the image forming unit 150 is disposed below the color image forming apparatus 100. The recording paper 153 placed on the paper feeding unit 152 is fed by the pickup roller 154 one by one. The recording paper 153 is conveyed to the transfer roller 159 via the paper feed roller 155, the guide plate 156 and the registration roller 157.

The developing units 160y to 160k store different developers (hereinafter referred to as toners). The photosensitive drums 163y-k uniformly charged by the chargers 162y-k are exposed by the exposure units 161y-k according to the image data. The electrostatic latent images formed on the photosensitive drums 163y-k are developed by the developing units 162y-k. The toner images on the photosensitive drums 163y to 163k are multi-transferred (primarily transferred) onto the intermediate transfer belt 158. It should be noted that primary transfer chargers 166y-k are provided at positions facing the photosensitive drums 163y-k.

The transfer roller 159 is pressed against the intermediate transfer belt 158 with an appropriate pressure. The toner image carried on the intermediate transfer belt 158 is secondarily transferred to the recording paper 153 by the transfer roller 159. The fixing unit 164 has a roller provided with a heat source such as a halogen heater inside. The fixing unit 164 melts and fixes the toner image on the recording paper 153.

The patch sensor is a sensor that reads the density (toner amount) of the image pattern formed on each of the photosensitive drums 163Y to 163K, and is provided between the developing position and the transfer position on each drum. The position in the scanning direction is the position where the sensor detection spot is at the center of the image forming area. The patch sensor is a photo sensor including an LED and a photodiode, and detects the reflected light of the light applied to the drum. As described above, by adopting the configuration in which the toner image on each photosensitive drum can be individually read, it becomes easy to individually detect the input/output characteristics of each of CMYK.

(Patch sensor)
Reference numerals 40 to 42 in FIG. 3 denote processing circuits for processing a signal from the patch sensor 40, which includes the LED 10 and the photodiode 11 facing the photosensitive drum 163. The reflected light (near infrared light) from the photosensitive drum 163 that has entered the patch sensor 40 is converted into an electric signal by the patch sensor 40, and the electric signal is converted into an output voltage of 0 to 5 V by the A/D conversion circuit 41. It is converted into a digital signal of 255 levels. Then, the density conversion circuit 42 converts the density.

The toners used in the present embodiment are yellow, magenta, and cyan color toners, and are formed by dispersing color materials of respective colors using a styrene-based copolymer resin as a binder.

As for the spectral characteristics of the yellow, magenta, and cyan toners, the reflectance of near infrared light (960 nm) emitted by the LED 10 is 80% or more, as shown in FIGS. 4, 5, and 6 in this order. Further, in forming these color toner images, a two-component developing method which is advantageous in color purity and transparency is adopted. On the other hand, in the present embodiment, although the black toner is of the same two-component developing system as the black toner, carbon black is used as the coloring material in order to produce pure black. The reflectance at 960 nm) is about 10%.

Further, the photosensitive drum 163 is an OPC drum, the reflectance (960 nm) of near infrared light is about 40%, and an amorphous silicon drum or the like may be used as long as the reflectance is about the same.

FIG. 8 shows the relationship between the output of the patch sensor 40 and the output image density when the density on the photosensitive drum 163 is gradually changed according to the area gradation of each color. The output of the patch sensor 40 in the state where the toner does not adhere to the photosensitive drum 163 is set to 2.5 V, that is, 128 level. As can be seen from FIG. 8, as the area coverage of the yellow, magenta, and cyan toners increases and the image density increases, the output of the patch sensor 40 becomes larger than that of the photosensitive drum 163 alone.

On the other hand, as the area coverage of black toner increases and the image density increases, the output of the patch sensor 40 becomes smaller than that of the photosensitive drum 163 alone. By using these characteristics to create the density conversion table 42a for converting the sensor output signal on the photosensitive drum dedicated to each color to the image density value on the paper, the image density for each color can be accurately obtained.

The spot diameter of the light emitted from the LED 10 formed on the photosensitive drum 163 (the area until the light amount reaches 1/e2 of the peak) is 3 mm, and the light intensity distribution can be a Gaussian distribution. The detection area of the photodiode is arranged so as to include the irradiation spot of the LED.

The patch sensor output characteristics shown in FIG. 8 are characteristics when there is a patch image of uniform density in the LED irradiation spot. When the patch density in the LED spot is not uniform, the integrated value of the reflected light amount determined by the density at each position in the spot and the irradiation light amount becomes the output value of the patch sensor.

(Image forming controller)
FIG. 3 is an exemplary functional block diagram of the image forming unit according to the embodiment.

The image forming controller 300 mainly includes the following components. The image input I/F unit 301 receives image data transferred from the document reading unit 101 or image data transferred from the PC terminal 350 or the like. The image input I/F unit 301 can switch which image data is stored in the image memory 302. The CPU 320 is a control circuit that comprehensively controls each unit of the image forming controller 300.

The LOG conversion circuit 303 converts the RGB image data (luminance data for each RGB) stored in the image memory 302 into CMYK density data. The extraction unit 309 extracts the CMYK density data of the area detected by the patch sensor in the normal image formed by the image forming unit 150.

The output γ correction unit 304 functions as a density correction unit. That is, the output γ correction unit 304 converts into CMYK image data according to a γ correction table (γLUT) created by the control described later.

The input selector 305 selects and outputs either CMYK image data output from the output γ correction unit 304 or patch image data output from the patch image generation unit 312. The patch image data is used in gradation control described later.

The binarization processing unit 306 binarizes the image data output from the input selector 305 by halftone processing. The image output control unit 307 controls each unit of the image forming unit 150 according to the binarized image data.

[Special sequence gradation control: first gradation control]
Next, the special sequence gradation control will be described as the first gradation control of the image forming apparatus in this embodiment.

The first gradation control and the second gradation control which will be described later are means for stably achieving the reproduction of the output density and gradation of the image forming apparatus, and by detecting the patch pattern on the photosensitive drum 163. The γ characteristic of the printer engine is detected, and the aforementioned γLUT (output γ correction unit) for converting the image data according to the detected γ characteristic is created.

The patch pattern used for the first gradation control is a patch group of 10 gradations for each color of Y, M, C, and Bk. When the first gradation control is activated, the image forming apparatus forms a patch group as a patch pattern on the photosensitive drum, and the patch sensor 40 detects the patch group. The density value detected by the patch sensor 40 is stored in the memory by storing the relationship between the input signal of the patch pattern and the detected density in the γLUT creation unit 500 by associating the input signal level of each patch pattern with the patch formation position. Γ characteristic data can be obtained from this detected value. The patch detection density data is shown in FIG.

The horizontal axis of FIG. 9 is the input signal (gradation level), the vertical axis is the detected density, and in the figure the number of gradations is reduced for simplification, but it is actually a 10 gradation patch pattern.

The data between the patches is interpolated to form an 8-bit γ characteristic table of 0 to 255, a correction LUT that is inversely converted is created for the target table stored in advance, and this is set as the γLUT in the output γ correction unit 304. In this embodiment, since the target table is linear, the γLUT can be created simply by exchanging the inputs and outputs of the printer γ characteristics.

[Control flow]
Next, the control operation in the first gradation control according to the present embodiment will be described based on the flowchart of FIG. Note that this processing flow is realized by being executed by the CPU 320 included in the image forming controller 300.

In the present embodiment, since the stabilization of the density is performed by the second gradation control using a normal image described later, the first gradation control is not periodically performed, but an instruction from the operation unit and the second gradation control are performed. It is activated at the end of print JOB (at the time of post-rotation) when more than 1000 sheets are output in the state where the γ correction in the gradation control is not performed.

When an instruction to activate the first gradation control is issued (S101), patch image data is input from the patch image generation unit 312 via the input selector 305 (S102). The patch image data is subjected to halftone processing in the binarization processing unit 306 (S103) and is transmitted to the image output control unit 307. The image output control unit 307 forms a patch image on the photosensitive drum by the laser, and on the drum. The patch density is detected using the patch sensor 40 (S104).

For the density value detected by the patch sensor 40, the gradation level of the patch image and the position where the patch image is created are made to correspond to each other, and the relationship between the gradation level of the patch image and the detected density is stored in the memory to obtain the γ characteristic. It is detected (S105). An LUT in which the input and output of the detected printer γ characteristics are exchanged is created, and this is set as the γLUT in the output γ correction unit 304 (S106).

Next, the method of extracting the image data that substitutes the patch in the gradation control using the normal image that is the second gradation control and the method of creating the representative value of the image data that substitutes the input signal value of the patch will be described. To do.

As described above, since the spot of the patch sensor used for detection has a light amount distribution, the sensor output value is the integrated value of the reflected light amount according to the light amount distribution. Therefore, the input image signal corresponding thereto can be obtained by weighting the input image density data at each position in the spot by the light amount distribution and integrating, and using a value divided by the number of pixels as a representative value of the region.

Since the detection spot is a circle having a diameter of 3 mm and its light quantity distribution can be a Gaussian distribution, the weighting filter for the input image density data at each position in the spot is shown in FIG. 11 in this embodiment. The filter size is 9×9, and one square corresponds to 8×8 pixels in 600 dpi image data. Therefore, the input image data corresponding to one patch pattern has 72×72 pixels, that is, 5184 pixels.

As a result, it is not necessary to limit the image area that can be used as a patch, and in the present invention, a large amount of data can be detected using a normal image.

FIG. 12 shows the relationship between the normal image data and the patch substitute section. FIG. 12 shows A4 size image data, and a region surrounded by a dotted line is a patch substitute portion. The area of the patch substitute portion is detected by the patch sensor, and the representative value of the image data corresponding to the area is used as the input image signal of the area for the second gradation control.

(Extracting input image data and creating representative values)
FIG. 13 is an exemplary flowchart of the substitute image extracting process according to the embodiment. The process of extracting the representative value of the partial image (substitute image) to be used as a patch from the data of the normal image will be described in detail below with reference to FIG.

When the image formation starts, the extraction unit 309 sequentially reads out the CMYK density data converted by the Log conversion unit 303 (S801).

From the read image density data, the image data at the position detected by the patch sensor described later is stored in the memory for each patch substitute (S802). As described above, one patch has 5184 pixels for each of the main and sub 72 pixels, and these are stored at intervals of 72 lines.

The 72×72 pixel data is subjected to the above-mentioned weighting filter (S803), the integrated value of all pixels is obtained and divided by the number of pixels, and this is set as the representative value of this area (S804). This representative value becomes the input signal when the γ characteristic is created. The extraction unit 309 stores and holds information indicating the area of the partial image corresponding to the patch image and the representative value in a memory or the like (S805).

[Gradation control using normal image: Second gradation control]
Generally, the charge amount of the developer changes depending on various conditions such as environmental changes. If the charge amount changes, the density of the formed image becomes unstable. Therefore, in the present embodiment, the patch sensor detects an image area in which a patch extracted from a general normal image (original copy image, a print image transmitted from a personal computer) is detected, and the detected value is used as an image signal of the image area. The γ characteristic of the printer is detected by using the representative value of 1 as an input signal when that area is used as a patch, and a γLUT is created. The gradation control using this normal image is referred to as second gradation control. The sensor detection is performed at the timing when the center of the patch area passes the detection spot center. The image output control unit 307 controls the timing of image formation and sensor detection.

In the detection of the image area and the creation of the γLUT by the second gradation control, one set corresponds to 10 A4-size output sheets. That is, if the size is A4 horizontal, detection of 65 patches per page can be performed, and therefore the γLUT is created at the timing when data corresponding to 650 patches are prepared. When 650 pieces of detection data are prepared, γ characteristic data is created from the relationship with the input signal that is substituted by the representative value of the image data.

In this example, as shown in FIG. 14, (0, 0) (255, 255) was set as a fixed point, and after linearly interpolating the data of 650, a γ characteristic table was created by moving average processing. Of the 650 data, if the input signal is the same, the detected value was changed to its average value and then linear interpolation was performed. It is desirable to set the reference area in the moving average processing according to the characteristics of the image forming apparatus. In this embodiment, the area of the input signals 32 to 223 is set to 65 data, and other than that, the number of data is reduced toward the end. .. After the γ characteristic table is created, it is similar to the first gradation control, and the γLUT created by inversely converting the target is set in the output γ correction unit 304.

[Actual image Cal. flow]
FIG. 15 is an exemplary flowchart of the density correction according to this embodiment.

When the normal image output is activated, the image forming controller 300 performs the image forming process as usual (S701), and at the same time, the extracting unit 309 extracts the patch substitute image data and creates the representative value (S702). Upon receiving the transmission of the image data from the image forming controller 300, the image output control unit 307 also forms a normal image on the drum as usual (S703), and the patch sensor detects the image (S704). The γ creating unit 500 detects the γ characteristic table according to the read detected density data and the image data representative value of the substitute image (S705), and outputs the table in which the input/output values are replaced as the γLUT to the output γ correcting unit 304. The setting is made (S706).

It should be noted that when the change in the density level of the representative value is small, the detection accuracy of the γ characteristic in the entire density range deteriorates. Therefore, in this embodiment, the input signal is equally divided into four, and the four divided areas are If there is a region where the detected value is 0 in any one or more, the γLUT is not corrected.

Since it is not desirable that the state in which the density correction cannot be executed continues for a long time, in this embodiment, when the γLUT cannot be updated during the output of 1000 or more sheets corresponding to the A4 landscape, that is, during the second gradation control of 100 sets. Activates the first gradation control so that the γLUT can be appropriately maintained. Even in this case, the frequency of forming the patch image is significantly reduced as compared with the conventional technique. Therefore, it goes without saying that the various advantages described above can be enjoyed.

[Alignment sequence]
Since it is a feature of the present invention that the representative value of the image data is created by multiplying the detected image data by the detected spot characteristic, it is important to accurately grasp the detection position of the patch sensor with respect to the image data. Therefore, in this embodiment, the alignment sequence for grasping the image data detection position is provided as a special sequence. This alignment sequence is activated by instructions from the operation unit at the time of factory shipment, installation at the user's site, or replacement of related parts.

The alignment sequence is performed by forming the image data shown in FIG. 16 and detecting it by the patch sensor. The image data consists of horizontal lines for detecting the sub-scanning position and vertical lines for detecting the main-scanning position. The width of each line is 8 pixels for 600 dpi image data, and the length is 144 pixels. The vertical line is formed by shifting the main scanning by 8 pixels for every 144 pixels in the sub scanning, and the position is an area of ±76 pixels from the center of the image forming area, and is sequentially formed from the position of −76 pixels from the center. There are a total of 19 lines at the center of the formation area and at a position offset from it by 8 pixels.

The horizontal line is formed at the position of -72 pixel from the center of the image forming area, and 72 pixels for one spot are opened between the horizontal line and the vertical line. The peak position of the sensor output when each line is detected is set as the center of the detection spot, the detection timing is determined from the horizontal line, and the image data extraction position is determined from the vertical line. FIG. 17 shows an example of vertical line detection. In the case of FIG. 17, since there is a peak of the sensor output at the position of +8 pixels, the +8 pixel position from the center of the image data is set as the center of the detection spot, and image data extraction and weighting filter multiplication are performed.

(Alignment sequence flow)
The flow of the alignment sequence will be described with reference to FIG.

When an instruction to activate the alignment sequence is issued from the operation unit (S901), the line image data for alignment is input from the patch image generation unit (S902). Next, the line image data is transmitted to the image output control unit 307, is formed on each photosensitive drum by the image output control unit 307, and is detected by the patch sensor (S903). The extracted image position is determined based on the position where the detected sensor output value is maximum (S904).

[effect]
As described above, according to this embodiment, the partial image included in the normal image is used as a patch. As a result, the process of outputting a dedicated test pattern for density detection can be omitted. Further, conventionally, since a test pattern is output during density correction, formation of a normal image is stopped. On the other hand, according to the present embodiment, since the normal image formation can be continued, the throughput of image formation is improved. Further, since the images that can be substituted are not limited, the frequency of γLUT update can be set high. Furthermore, according to the present embodiment, the operator does not need to have a high level of knowledge regarding density correction, which is very convenient.

[Other Embodiments]
In the above-described embodiment, the case where the substitute image is extracted and used as the patch image for correcting the data of the γ correction table has been described. However, the present invention may be realized as a method of extracting and using a substitute image as a patch image for adjusting the toner density in the developing device 160.

Generally, in the toner density correction in the developing device 160, a patch image having a predetermined density is formed on the photoconductor 163 at an appropriate timing, the density is measured, and the replenishment of the developer is controlled according to the difference from the reference value. It is realized by doing. Therefore, if the above-described embodiment is applied to the patch image at this time, a substitute image of the patch image can be extracted from the normal image. If the normal image cannot be extracted, a patch image may be created based on the data from the patch image generation unit 312, as in the above-described embodiment.

100 color image forming apparatus, 101 original reading section, 150 image forming section

Claims (4)

An image pattern is formed on the image carrier, the image pattern is read by the reading means, and the image pattern is placed in the image forming apparatus having the image forming condition control for changing the image forming condition. An image forming apparatus characterized by controlling an image forming condition according to a value obtained by correcting image data according to a characteristic of a reading unit and a value detected by the reading unit. 2. The image forming apparatus according to claim 1, wherein a plurality of image patterns having a width smaller than a reading area of the reading unit are formed and detected by changing the positions in order to detect the detection position of the reading unit. .. 3. The image forming apparatus according to claim 1, wherein a plurality of image patterns each having a width smaller than a reading area of the reading unit are detected by changing a position in order to detect the characteristic of the reading unit. The image forming apparatus according to claim 1, wherein the image pattern detected for changing the image forming condition is a part of an output image arbitrarily selected by the user.