Image forming apparatus and image reading apparatus

Abstract

To provide a technique to accurately read density patches while reducing the influence of flare.SOLUTION: An image forming apparatus comprises: image forming means that forms, on a sheet, density patches each including a plurality of images with different densities; conveying means that conveys the sheet in a first direction; reading means that reads a surface of the sheet on which the density patches are formed and conveyed by the conveying means to output read data; detection means that, based on the read data, detects the amount of skew of the density patches with respect to the first direction; and determination means that, based on the skew amount, for each of the plurality of images of the density patches, determines data, in the read data, which corresponds to a predetermined area of the image used for determining the density of the image.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to a technique for reading an image formed on a sheet for image stabilization control. [Background technology]

[0002] In an image forming apparatus that forms an image by an electrophotographic process, the density of an output image may change due to characteristic changes in the charging, developing, and transfer processes caused by aging or environmental changes. In order to suppress the density change, the image forming apparatus performs image stabilization control. In the image stabilization control, the image forming apparatus forms a density patch on, for example, a photoconductor or an intermediate transfer belt, and adjusts image forming conditions based on the detection result of the density patch by an optical sensor so that the output image has an appropriate density.

[0003] Patent Document 1 discloses a configuration in which a density patch is transferred to a sheet, fixed, and the density patch after fixing on the sheet is detected by an optical sensor to perform image stabilization control. By controlling image formation conditions based on the detection result of the density patch after fixing, it is possible to perform image stabilization control taking into account the effects of transfer and fixing on the sheet. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5423620 Summary of the Invention [Problem to be solved by the invention]

[0005] When a density patch formed on a sheet is read by an optical sensor, a phenomenon called "flare" may occur, in which light reflected around the density patch enters the optical sensor, causing a reading error. To suppress the effects of flare, it is necessary to perform image stabilization control using only the read value of the central area of ​​the density patch. However, if the density patch is tilted with respect to the sheet conveyance direction, the reflected light around the density patch enters the optical sensor, resulting in the effect of flare.

[0006] The present invention provides a technique for suppressing the effects of flare and reading an image with high accuracy. [Means for solving the problem]

[0007] According to one aspect of the present invention , S An image forming apparatus for forming an image on a sheet teeth, an image forming means for forming an image based on image forming conditions; a reading means having a conveying section for conveying a sheet on which a test image has been formed by the image forming means, the reading means reading the sheet on which the test image has been formed while conveying the sheet by the conveying section; a storage means for storing a reading result of the test image read by the reading means, a detection means for detecting an edge of the test image in a direction intersecting with a conveying direction of the conveying unit from the reading result by the reading means, and a determination means for determining a range of data to be stored in the storage means from the reading result of the reading means based on the edge detected by the detection means; The inclination of the test image with respect to the conveying direction of the conveying unit is The edge detected by the detection means and a readout means for reading out data relating to the readout result of the test image based on the inclination acquired by the acquisition means from the range determined by the determination means; and generating means for generating the image forming conditions based on the above. Effect of the Invention

[0008] According to the present invention, it is possible to suppress the influence of flare and read an image with high accuracy. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a functional block diagram of a printing system according to an embodiment. [Diagram 2] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus according to an embodiment. [Diagram 3] FIG. 2 is a functional block diagram of a reading device according to an embodiment. [Figure 4]FIG. 2 is a diagram showing the configuration of a line sensor according to an embodiment. [Diagram 5] FIG. 1 illustrates a test sheet according to one embodiment. [Figure 6] 10 is a flowchart of an adjustment process of an image forming condition according to an embodiment. [Figure 7] FIG. 4 is a block diagram of a concentration detection processing unit according to an embodiment. [Figure 8] 6 is an explanatory diagram of a central region used for calculating an average luminance value and an area stored in a memory. [Figure 9] FIG. 4 is an explanatory diagram of a skew amount calculation process according to an embodiment; [Figure 10] 11 is a flowchart of a calculation process of an average luminance value according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0011] 1 is a functional block diagram of a printing system including an image forming apparatus 100. The printing system includes the image forming apparatus 100 and a host computer 101. The image forming apparatus 100 and the host computer 101 can communicate with each other via a network 105. The network 105 is, for example, a LAN or a WAN. In FIG. 1, one image forming apparatus 100 and one host computer 101 are connected to the network 105, but a plurality of image forming apparatuses 100 and a plurality of host computers 101 can be connected to the network 105.

[0012] The host computer 101 transmits a print job to the image forming apparatus 100 via the network 105. The print job includes various information necessary for printing, such as image data of the image to be formed, the type of sheet to be printed on, the number of copies to be printed, whether double-sided printing or single-sided printing, etc.

[0013] The image forming apparatus 100 forms an image on a sheet based on a print job received from a host computer 101. The image forming apparatus 100 includes a controller 110, an operation panel 120, a feeding device 140, a printer 150, and a reading device 160, which are capable of communicating with each other via a system bus 116.

[0014] The ROM 112, which is a non-volatile memory of the controller 110, stores various control programs. The RAM 113 is a volatile memory, and functions as a system work memory that reads and stores the control programs stored in the ROM 112. The CPU 114 executes the control programs read into the RAM 113 to centrally control the entire image forming apparatus 100. The HDD 115 is a large-capacity storage device. The HDD 115 stores various data such as the control programs and image data used in the image forming process (printing process). The I / O control unit 111 is an interface that communicates with the host computer 101 and the like via the network 105. Note that these functional blocks in the controller 110 can also communicate with each other via a system bus 116.

[0015] Operation panel 120 provides a user interface and has operation buttons, a numeric keypad, a liquid crystal display, etc. An operator can operate image forming apparatus 100 using operation panel 120 and determine the state of image forming apparatus 100 based on information displayed on operation panel 120.

[0016] The feeding device 140 includes a plurality of feeding units that store sheets, and feeds the sheets from the feeding units to the printer 150. The printer 150 forms an image on the sheet fed by the feeding device 140 based on image data. The configuration of the printer 150 will be described in detail later with reference to FIG. 2. The reading device 160 reads the surface of the sheet and outputs the read data, which is image data, to the controller 110.

[0017] 2 is a configuration diagram of the image forming apparatus 100. The image forming apparatus 100 includes a feeding device 140, a printer 150, a reading device 160, and a finisher 190. The finisher 190 is a post-processing device that performs post-processing on printed materials from the printer 150. The finisher 190 performs, for example, stapling, cutting, sorting, and the like on a plurality of printed materials.

[0018] The printer 150 includes four image forming units that form images of yellow, magenta, cyan, and black. The configuration of each image forming unit is basically the same. The photoconductor 153 of the image forming unit is rotated in the direction of the arrow R1 during image formation. The charger 220 charges the surface of the photoconductor 153. The exposure device 223 exposes the photoconductor 153 based on image data of the image to be formed, and forms an electrostatic latent image on the photoconductor 153. The developer 152 develops the electrostatic latent image on the photoconductor 153 using a developer (toner). As a result, the electrostatic latent image on the photoconductor 153 is visualized, and an image is formed on the photoconductor 153.

[0019] During image formation, the intermediate transfer belt 154 is driven to rotate in the direction of arrow R2. Images formed by the image forming units are transferred to the intermediate transfer belt 154. Note that a full-color image can be formed on the intermediate transfer belt 154 by transferring the images formed by the image forming units onto the intermediate transfer belt 154 in a superimposed manner. The image transferred to the intermediate transfer belt 154 is transported toward a position facing the transfer roller 221.

[0020] The feeding device 140 has feeding units 140a, 140b, 140c, 140d, and 140e that accommodate sheets. The feeding device 140 feeds a sheet from any one of the feeding units to the printer 150. The printer 150 transports the fed sheet toward a position facing the transfer roller 221. The transfer roller 221 transfers the image on the intermediate transfer belt 154 onto the sheet.

[0021] The printer 150 has a first fixing device 155 and a second fixing device 156 that heat and pressurize an image transferred to a sheet to fix the image on the sheet. The first fixing device 155 has a fixing roller having a heater therein and a pressure belt for pressing the sheet against the fixing roller. These rollers are driven by a motor (not shown) to transport the sheet. The second fixing device 156 is disposed downstream of the first fixing device in the sheet transport direction. The second fixing device 156 is provided to increase the gloss of the image on the sheet that has passed through the first fixing device 155 and to ensure fixability. The second fixing device 156 has a fixing roller having a heater therein and a pressure roller having a heater therein. Depending on the type of sheet, it is not necessary to use the second fixing device 156. In this case, the sheet is transported to the transport path 130 and does not pass through the second fixing device 156. The flapper 131 switches between guiding the sheet to the transport path 130 or to the second fixing device 156.

[0022] The flapper 132 switches between guiding the sheet to the transport path 135 and guiding the sheet to the discharge path 139. For example, in a double-sided printing mode, the flapper 132 guides a sheet having an image formed on its first side to the transport path 135. Also, for example, in a face-up discharge mode, the flapper 132 guides a sheet having an image formed on its first side to the discharge path 139. Also, for example, in a face-down discharge mode, the flapper 132 guides a sheet having an image formed on its first side to the transport path 135.

[0023] The sheet conveyed to the conveying path 135 is conveyed to the inversion unit 136. After being conveyed to the inversion unit 136, the conveying direction of the sheet is reversed. Then, the flapper 133 switches whether to guide the sheet at the inversion unit 136 to the conveying path 138 or to the conveying path 135. For example, the flapper 133 guides the sheet to the conveying path 138 in a double-sided printing mode. Also, for example, the flapper 133 guides the switched-back sheet to the conveying path 135 in a face-down discharge mode. The sheet conveyed to the conveying path 135 by the flapper 133 is guided to the discharge path 139 by the flapper 134. The sheet conveyed to the conveying path 138 by the flapper 133 is conveyed again to a position facing the transfer roller 221, whereby images are formed on both sides of the sheet.

[0024] The sheet guided to the transport path 139 is transported along a transport path 313 of the reading device 160. The document detection sensor 311 of the reading device 160 detects the leading edge in the transport direction of the test sheet transported along the transport path 313. The document detection sensor 311 is, for example, an optical sensor having a light emitting element and a light receiving element. The line sensor unit 312a reads one side of the sheet, and the line sensor unit 312b reads the other side of the sheet. The controller 110 controls the reading timing of the line sensor units 312a and 312b based on the detection timing of the leading edge of the sheet by the document detection sensor 311.

[0025] FIG. 3 is a functional block diagram of the reading device 160. The line sensor units 312a and 312b have the same configuration, and each includes a memory 300, a line sensor 301, and an analog-to-digital converter (ADC) 302. The line sensor 301 is, for example, a contact image sensor (CIS). FIG. 4 is a configuration diagram of the line sensor 301. The LEDs 400a and 400b are light sources and emit white light. The LEDs 400a and 400b are disposed at different ends in the longitudinal direction of the light guide 402a. The line sensor 301 is disposed so that the longitudinal direction is perpendicular to the sheet conveying direction. Hereinafter, the longitudinal direction is also referred to as the main scanning direction, and the sheet conveying direction is also referred to as the sub-scanning direction. The light emitted by the LEDs 400a and 400b is diffused in the main scanning direction inside the light guide 402a, and the sheet is irradiated from the entire main scanning direction of the light guide 402a. The light reflected from the sheet is incident on a plurality of light receiving elements 401a arranged along the main scanning direction via a lens array 403a. The position on the sheet where the reflected light incident on each light receiving element 401a is reflected is also called a pixel. The light receiving elements 401a are arranged in three lines coated with red (R), green (G), and blue (B) color filters. The line sensor 301 of this embodiment has a "double-sided illumination configuration" in which light is irradiated from both sides of the lens array 403a in the sub-scanning direction.

[0026] Returning to FIG. 3, the memory 300 stores correction information for correcting the light amount variation of the plurality of light receiving elements 401a of the corresponding line sensor 301. The line sensor 301 corrects the amount of light received by each light receiving element 401a with the correction information, and outputs the corrected amount of light received by each light receiving element 401a to the ADC 302 in order as the amount of light received by the pixel. The ADC 302 converts the analog signal output by the corresponding line sensor 301 into a digital signal, and outputs it to the density detection processing unit 305 as read data. The read data indicates the luminance values ​​of red (R), green (G), and blue (B) of each pixel. The line sensor 301 reads the image of the entire sheet by repeatedly reading the image of one line in the main scanning direction while the sheet is being conveyed. The processing in the density detection processing unit 305 will be described later. The image memory 303 is used as a storage unit that stores the read data when the density detection processing unit 305 performs processing.

[0027] The image forming apparatus 100 forms a test sheet for image stabilization control and has the reading device 160 read it. Here, the test sheet is a sheet on which an image formed by a user (hereinafter, a user image) and a density patch are formed. Fig. 5(A) to Fig. 5(C) show an example of the test sheet. The left-right direction in Fig. 5(A) to Fig. 5(C) is the main scanning direction, and the up-down direction is the sub-scanning direction. The shaded area in Fig. 5(A) to Fig. 5(C) is the area where the user image is formed (hereinafter, a user image forming area). On the test sheet, density patches of each of the four colors used for image formation are formed outside the user image forming area in the sheet. The density patches of each color include a plurality of images (hereinafter, patches) whose densities are changed stepwise. In this embodiment, the density of the patches at both ends of one density patch in the direction in which the multiple patches are continuous is made higher than the density of the other patches in the density patch. For example, the patch at one end of one density patch can be made the highest density, and the patch at the other end can be made the second highest density. The densities of the patches at the two ends of one density patch may be the same. The area where the density patch is formed is ultimately an area that is cut and removed by, for example, the finisher 190, so the density patch is not included in the final product for the user. The density patch may be formed on both sides of the sheet or on only one side of the sheet, regardless of whether the user image is formed on only one side or both sides of the sheet.

[0028] In Fig. 5(A), density patches of four colors are arranged along the sub-scanning direction at one end of the sheet in the main scanning direction. In Fig. 5(B), density patches of two colors are arranged along the sub-scanning direction at one end of the sheet in the main scanning direction, and density patches of the remaining two colors are arranged along the sub-scanning direction at the other end. In Fig. 5(C), density patches of two colors are arranged along the main scanning direction at one end of the sheet in the sub-scanning direction, and density patches of the remaining two colors are arranged along the main scanning direction at the other end.

[0029] When the test sheet is read by the reading device 160, the line sensor unit 312a and the line sensor unit 312b output the read data including the user image and the density patch to the density detection processing unit 305. The density detection processing unit 305 determines the average luminance value of each of the density patches of each color based on the read data. Then, the density detection processing unit 305 outputs the average luminance value to the controller 110. The controller 110 obtains the detected density of each patch from the average luminance value of each patch, and sets the image formation conditions related to the density based on the density of the formed patch and the detected density. Note that the controller 110 uses the luminance value of the complementary color to obtain the density of each patch. For example, the density detection processing unit 305 determines the average luminance value of the cyan, magenta, and yellow patches from the luminance values ​​of red, green, and blue, respectively. Note that the controller 110 determines the average luminance value of the black patch from the luminance value of green. The density detection processing unit 305 may be configured, for example, with an FPGA and / or an ASIC.

[0030] FIG. 6 is a flowchart of the generation process of the image forming conditions. The process of FIG. 6 is started, for example, when the user inputs an instruction to start image formation via the operation panel 120. In S10, the controller 110 forms a test sheet. Specifically, the controller 110 generates a user image on a sheet based on image data and forms density patches of each color on the sheet. In S11, the controller 110 causes the reading device 160 to read the test sheet. Note that the reading timing by the reading device 160 is determined based on the timing when the document detection sensor 311 detects the test sheet. In S12, the density detection processing unit 305 outputs the average luminance value of each patch to the controller 110, and the controller 110 detects the density of each patch. In S13, the controller 110 determines whether image formation has been completed, that is, whether images have been formed on all sheets specified in the instruction to start image formation. If image formation has not been completed, the controller 110 repeats the process from S10. On the other hand, when image formation is completed, the controller 110 sets image formation conditions for adjusting the density based on the density detection result of the density patch in S12.

[0031] It is not necessary to form density patches on all sheets on which user images are formed. In other words, a configuration may be adopted in which density patches are formed on some of the sheets on which user images are formed and used as test sheets. In this case, the process of S13 is a process for determining whether or not all test sheets have been formed.

[0032] Next, the process performed by the density detection processing unit 305 will be described. FIG. 7 is a block diagram of the density detection processing unit 305. Note that the process for the read data input from the line sensor units 312a and 312b is similar, so in FIG. 7, the process for the read data input from one of the two line sensor units will be described. Note that, as described above, the line sensor 301 reads the surface of the sheet conveyed in the sub-scanning direction line by line, but in the following description, it is assumed that the line sensor reads line by line from the top to the bottom of FIG. 5. Also, the line sensor outputs the luminance value of each pixel of one line in order, but in the following description, it is assumed that the output is in the order from the left side to the right side of FIG. 5. Furthermore, in the following description, the upper side, lower side, right side, and left side correspond to the upper side, lower side, right side, and left side of FIG. Also, the number of the line is the order in which the line sensor 301 reads, and the number of the pixel in one line is the order in which the line sensor outputs. Therefore, the topmost line is the first line, and the bottommost line is the last line. Also, the leftmost pixel on a line is the first pixel, and the rightmost pixel is the last pixel.

[0033] The read data is input to a color selection unit 305a1 and a writing unit 305a4. The color selection unit 305a1 selects a color to be used by the downstream edge detection unit 305a2 for edge detection, and outputs the read data of the selected color to the edge detection unit 305a2. To improve the accuracy of edge detection, the color selection unit 305a1 can select a color to be used for edge detection according to, for example, the background color of the sheet.

[0034] The edge detection unit 305a2 detects one of two edges along the sub-scanning direction of the density patch based on the read data input from the color selection unit 305a1. In this embodiment, the edge to be detected first among the two edges along the sub-scanning direction of the density patch, that is, the left edge (hereinafter, the left edge), is detected. For example, the edge detection unit 305a2 determines the luminance value for each line in order from the first pixel. The luminance of the density patch is lower than the luminance of the background part of the white sheet. Therefore, the edge detection unit 305a2 can detect the left edge of the density patch by detecting the falling edge of the luminance value in the main scanning direction. Note that instead of detecting the left edge for each line, the left edge may be detected for each predetermined number of consecutive lines in the sub-scanning direction and the left edge may be detected by averaging the positions in the main scanning direction of the edges detected for the predetermined number of lines. Note that in this case, the position of the edge in the sub-scanning direction is set to the average position in the sub-scanning direction of the predetermined number of lines used for averaging.

[0035] The range determination unit 305a3 determines the data range to be stored in the memory 305a5 from the read data based on the size of the density patch and the position in the sub-scanning direction of the left edge of the first patch detected by the edge detection unit 305a2, and notifies the writing unit 305a4. FIG. 8(A) and FIG. 8(B) show one density patch. The vertical direction in FIG. 8(A) and FIG. 8(B) is the sub-scanning direction. The cross-hatched area in FIG. 8(A) shows the central area (predetermined area) used to calculate the average luminance value. As described above, in order to suppress the influence of flare, the central area of ​​each patch of the density patch is used to calculate the average luminance value, and the area other than the cross-hatched area, that is, the edge area including the edge, is not used to calculate the average luminance value. The diagonal-hatched area in FIG. 8(B) shows the range of pixels to be stored in the memory 305a5 by the range determination unit 305a3. As shown in FIG. 8B, the range determining unit 305a3 determines to store in the memory 305a5 the read data corresponding to a range that is the same as the central area used to calculate the average luminance value in the sub-scanning direction and includes the entire area of ​​the density patch in the main scanning direction. The range in the main scanning direction stored in the memory 305a5 is expanded from the range used to calculate the average luminance value in consideration of the inclination of the density patch, as described later. Therefore, more specifically, the range in the main scanning direction stored in the memory 305a5 can be determined in consideration of the maximum amount of skew that can occur. The reason why the range is not expanded in the sub-scanning direction is that the effect of the inclination is small and can be ignored. However, it is also possible to configure the range to be expanded in the sub-scanning direction. The writing unit 305a4 writes the read data of the pixels in the range determined by the range determining unit 305a3 into the memory 305a5. In this way, the range determination unit 305a3 does not store the luminance values ​​of all pixels on the test sheet, but stores the luminance values ​​of only a specified area of ​​the density patch that takes into account the amount of skew, thereby reducing the capacity required for the memory 305a5.

[0036] The edge detection unit 305a2 also outputs the detected left edge to the edge determination unit 305b1. The edge determination unit 305b1 writes the positions of the two left edges into the memory 305b3 based on the left edges detected by the edge detection unit 305a2 on the lines in the main scanning direction. The two left edges can be, for example, the left edge on one line in the first patch of one density patch and the left edge on one line in the last patch. For example, the left edge detected first and the left edge detected last in one density patch can be the two left edges written into the memory 305b3. Also, the average position of the left edges of the lines detected for the first patch of one density patch and the average position of the left edges of the lines detected for the last patch of one density patch can be written into the memory 305b3 as the two left edges. As described above, the density of the first patch and the last patch of a density patch is higher than that of the other patches of the same density patch, so the detection accuracy of the left edges of the first patch and the last patch is higher than that of the other patches.

[0037] The skew amount calculation unit 305b4 reads the positions of the two left edges from the memory 305b3 and calculates the amount of skew of the density patch. FIG. 9 is an explanatory diagram of a method of calculating the amount of skew. As shown in FIG. 9, it is assumed that the skew amount calculation unit 305b4 reads the positions of two left edges, a first left edge and a second left edge, from the memory 305b3. According to FIG. 9, the position of the first left edge in the main scanning direction is X1, and the position in the sub-scanning direction is Y1. Also, according to FIG. 9, the position of the second left edge in the main scanning direction is X2, and the position in the sub-scanning direction is Y2. The skew amount calculation unit 305b4 obtains the amount of skew θ as the inclination of the left edge of the density patch with respect to the sub-scanning direction. That is, according to FIG. 9, The amount of skew is θ=(X2-X1) / (Y2-Y1). As described above, the first left edge and the second left edge are the left edges of a patch with a high density, so that their detection accuracy is high, and therefore the amount of skew can be determined with high accuracy.

[0038] Based on the skew amount θ calculated by the skew amount detection unit 305b, the reading unit 305c determines the read data corresponding to the central region of each patch (see FIG. 8A) from the read data stored in the memory 305a5. Specifically, the memory 305a5 stores the read data of the cross-hatched region of FIG. 8B. Therefore, based on the skew amount θ, the reading unit 305c determines the range in the main scanning direction corresponding to the central region of each patch from the cross-hatched region of FIG. 8B. For this reason, the reading unit 305c moves the left position in the main scanning direction of the central region by S to the right from the reference position according to the position of the line in the sub-scanning direction. Specifically, if the position in the sub-scanning direction is Y, then S = (Y-Y1) × θ Here, the reference position corresponds to, for example, the distance in the main scanning direction from the position X1 of the first left edge in the main scanning direction to the left side of the central region of the patch. Note that the length read from the left position S toward the right in the main scanning direction is predetermined based on the size of the patch in the main scanning direction. The read unit 305c reads the determined read data from the memory 305a5 and outputs it to the average calculation unit 305d.

[0039] Based on the read data read by the read unit 305c, the average value calculation unit 305d determines the luminance value of each pixel in the central region of each patch, and averages them to calculate the average luminance value of each patch. If one density patch includes seven different patches as shown in Fig. 8(A), seven average luminance values ​​are calculated from one density patch.

[0040] 10 is a flowchart of the process in the density detection processing unit 305. In S20, the density detection processing unit 305 initializes a density patch counter M to 0. In S21, the density detection processing unit 305 initializes a line counter H to 0. When the density detection processing unit 305 detects a left edge in S22, the density detection processing unit 305 increments the counter H by 1 in S23. In S24, the density detection processing unit 305 determines whether the counter H is equal to or greater than a first set value. The first set value is a value obtained by converting the length of one density patch in the sub-scanning direction into the number of lines, and is set in advance in the density detection processing unit 305. If the line counter H is less than the first set value, it means that all the left edges of one density patch have not been detected, so the density detection processing unit 305 repeats the process from S22. On the other hand, if the counter H is equal to or greater than the first set value, this means that all left edges of one density patch have been detected, and the density detection processing unit 305 calculates the amount of skew as described in S25 using Figure 9.

[0041] In S26, the density detection processing unit 305 reads out the read data determined based on the amount of skew from the memory 305a5, and in S27 calculates the average luminance value of each patch. This completes the process for one density patch. Thereafter, in S28, the density detection processing unit 305 increments the counter M by 1, and in S29, determines whether the counter M is equal to or greater than a second set value. The second set value corresponds to the number of density patches formed in the sub-scanning direction on one recording material, and is set in advance in the density detection processing unit 305. If the counter M is less than the second set value, this means that all density patches have not been detected, and therefore the density detection processing unit 305 repeats the process from S21. On the other hand, if the counter M is equal to or greater than the second set value, this means that all density patches have been detected, and therefore the density detection processing unit 305 completes the process of FIG. 10.

[0042] The average luminance value of each patch output by the density detection processing unit 305 is output to the controller 110. The controller 110 converts the average luminance value of each patch of the density patch for each color into a density based on the luminance density conversion table. That is, the density of each patch is obtained for each color. Then, the controller 110 determines the density characteristics (tone characteristics) of the printer 150 for each color based on the density of each patch. Based on the determined (current) density characteristics of the printer 150, the controller 110 generates a one-dimensional tone correction table for each color that converts the input value of the image data so that the density characteristics of the printer 150 become ideal. The controller 110 converts the image data based on the tone correction table, and causes the printer 150 to form an image based on the converted image data. With this configuration, it is possible to reduce the difference between the density characteristics of the user image formed by the printer 150 and the ideal density characteristics.

[0043] The image forming conditions to be adjusted are not limited to the gradation correction table, and other image forming conditions related to density may be adjusted. For example, the controller 110 may be configured to control at least one of the charging bias of the charger 220 of the printer 150, the exposure intensity of the exposure device 223, and the developing bias of the developer 152 based on the detection result of the density patch.

[0044] Furthermore, in this embodiment, the luminance value indicated by the read data is converted into density, and then the image forming conditions are generated using the density. However, it is also possible to configure the image forming conditions to be generated directly from the average luminance value.

[0045] As described above, the image forming apparatus of this embodiment detects the amount of skew of the density patch relative to the line sensor unit, and determines the central area of ​​each patch of the density patch based on the amount of skew. With this configuration, it is possible to suppress the influence of flare and read the density patch with high accuracy. Furthermore, by adjusting the image forming conditions based on the read data corresponding to the central area, it is possible to output an image with stable density. According to the present invention, an image reading apparatus is provided. The image reading apparatus corresponds to the reading apparatus 160, detects the amount of skew of the density patch relative to the line sensor unit, and determines the central area of ​​each patch of the density patch based on the amount of skew. Then, it outputs an average luminance value of each patch based on the luminance value of the central area. Furthermore, the image reading apparatus can also generate image forming conditions by converting the average luminance value into density.

[0046] [Other embodiments] The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions.

[0047] The invention is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0048] 312a, 312b: line sensor unit, 305b4: skew amount calculation unit, 305c: reading unit

Claims

1. An image forming apparatus for forming an image on a sheet, an image forming means for forming an image based on image forming conditions; a reading means for reading the sheet on which the test image is formed while the sheet is being conveyed by the conveying means; a storage means for storing the result of reading the test image read by the reading means; a detection unit that detects an edge of the test image in a direction intersecting with a conveying direction of the conveying unit from a reading result by the reading unit; a determining means for determining a range of data to be stored in the storing means from the read result of the reading means based on the edge detected by the detecting means; an acquisition means for acquiring an inclination of the test image with respect to a conveying direction of the conveying unit based on the edge detected by the detection means; a readout means for reading out data relating to a result of reading the test image based on the inclination acquired by the acquisition means from the range determined by the determination means; a generating unit that generates the image forming conditions based on the data read by the reading unit; An image forming apparatus comprising:

2. 2. The image forming apparatus according to claim 1, wherein the image forming conditions are conditions for adjusting the density of the image formed by the image forming means.

3. 3. The image forming apparatus according to claim 1, wherein the test images are a series of images having a plurality of gradations formed along the transport direction.

4. The image forming apparatus according to claim 1 , wherein the conveying direction is a direction in which the conveying section conveys the sheet.

5. the reading means has a line sensor having a plurality of pixels arranged thereon as a reading element for reading the sheet, 5. The image forming apparatus according to claim 1, wherein the line sensor is provided such that a longitudinal direction of the line sensor intersects with the transport direction.

6. The image forming apparatus according to claim 1 , wherein the test image is formed outside an area where a user image is to be formed.

7. the reading means has a line sensor having a plurality of pixels arranged thereon as a reading element for reading the sheet, 7. The image forming apparatus according to claim 1, wherein the transport direction is a direction intersecting a longitudinal direction of the line sensor.

8. a reading means for reading the sheet on which the test image is formed while the sheet is being conveyed by the conveying means; a storage means for storing the result of reading the test image read by the reading means; a detection unit that detects an edge of the test image in a direction intersecting with a conveying direction of the conveying unit from a reading result by the reading unit; a determining means for determining a range of data to be stored in the storing means from the read result of the reading means based on the edge detected by the detecting means; an acquisition means for acquiring an inclination of the test image with respect to a conveying direction of the conveying unit based on the edge detected by the detection means; an output means for outputting data on a result of reading the test image based on the inclination acquired by the acquisition means from the range determined by the determination means; An image reading device having the above structure.

9. 9. The image reading device according to claim 8, wherein the test image is a series of images having a plurality of gradations formed along the transport direction.

10. The image reading device according to claim 8 , wherein the conveying direction is a direction in which the conveying unit conveys the sheet.

11. the reading means has a line sensor having a plurality of pixels arranged thereon as a reading element for reading the sheet, 11. The image reading device according to claim 8, wherein the line sensor is provided such that a longitudinal direction of the line sensor intersects with the transport direction.

12. 12. The image reading device according to claim 8, wherein the test image is formed outside an area where a user image is to be formed.

13. the reading means has a line sensor having a plurality of pixels arranged thereon as a reading element for reading the sheet, 13. The image reading device according to claim 8, wherein the transport direction is a direction intersecting a longitudinal direction of the line sensor.

Images