Image forming apparatus and information processing apparatus

Abstract

To reduce a burden on a user relating to mount a sheet having a test image formed thereon.SOLUTION: An image formation device forms a test image on only one of the first surface and the second surface of a sheet and respectively reads the first surface and the second surface of the sheet to generate read data of the first surface and that of the second surface. The image formation device analyzes the read data of the first surface and that of the second surface, selects the read data of the first surface or that of the second surface which includes a result of reading the test image, and generates a gradation correction condition on the basis of the selected read data.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to image density control for controlling the density of an output image based on read data regarding a test image printed on a sheet.

Background Art

[0002] In an image forming apparatus that forms an image on a sheet using ink or toner, the density of the image may change depending on changes in the usage environment or changes over time. Therefore, the image forming apparatus forms a test image on the sheet, causes a reading device to read the test image, and corrects gradation correction conditions based on the read data of the test image. This is called gradation correction control, which is a part of calibration for adjusting image quality. In Patent Document 1, gradation correction control is proposed for adjusting gradation correction conditions so as to suppress an image formed on the front surface of a sheet from being transferred onto the back surface of the sheet (so-called reverse transfer). More specifically, the image forming apparatus forms a test image only on the front surface (printing surface) of the sheet and does not form a test image on the back surface. The user places the sheet on the platen of an image reader used for reading a document and causes the image reader to read the test image formed on the front surface of the sheet. Further, the user turns the sheet over and places it on the platen, and causes the image reader to read the back surface of the sheet on which the test image is not formed. Then, the density of the test image that does not cause reverse transfer is determined, and gradation correction conditions are created such that the determined density becomes the maximum density.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] While Patent Document 1 can prevent bleed-through, there is a risk that gradation correction conditions may be created in which the gradation characteristics of the image formed on the surface of the sheet by the image forming apparatus do not match the gradation characteristics of the input image. Some users may prioritize the gradation characteristics of the image formed on the surface over preventing bleed-through. For such users, the calibration in Patent Document 1 is not suitable. Furthermore, in order to flip the front and back of the sheet on the platen, the user must open and close the pressure plate to place the sheet on the platen. This would be troublesome for the user. On the other hand, there is a known system that uses an automatic document feeder (hereinafter referred to as ADF) to automatically transport the document placed on the tray to the reading position and have a reading device read a test image on the sheet. When using an ADF to have a reading device read the sheet, opening and closing the pressure plate is unnecessary, reducing the burden on the user. However, if only one side of the sheet transported by the ADF can be read, the readable side of the sheet is determined when the user places the sheet on the ADF tray. Therefore, if a user mistakenly places the sheet face up or face down in the tray, the reading device cannot read the test image formed on the sheet. Thus, the present invention aims to reduce the burden on the user when placing a sheet with a test image on it into the tray. [Means for solving the problem]

[0005] To solve the above problems, the present invention provides an image forming apparatus comprising: an image forming means for forming an image; a loading tray on which originals are loaded; a transport unit for transporting the originals loaded on the loading tray; a first reading unit for reading the image of the lower surface of the originals on the loading tray while the transport unit transports the originals; a discharge unit for discharging the originals read by the first reading unit; and a discharge tray from which the originals are discharged by the discharge unit; a platen on which originals are placed; and a second reading unit, wherein when reading an original placed on the platen, the second reading unit is moved while the second reading unit reads the original on the platen; when reading an original on the loading tray transported by the transport unit, the second reading unit is kept stationary at the reading position while the second reading unit reads the image of the upper surface of the original on the loading tray; and when reading a test image formed on one side of a sheet by the image forming means while transporting it to the original transport means, While the conveying unit is transporting the sheets on the loading tray, The first reading unit and the second reading unit Using The aforementioned sheet both sides Let it read control means and From the first reading image of the sheet on which the test image was formed by the first reading unit, and the second reading image of the sheet on which the test image was formed by the second reading unit, A determination means for determining the read image of the surface on the sheet on which the test image is formed, and the determination by the determination means Based on the read image, the image quality of the image formed by the image forming means is adjusted. adjustment It is characterized by having means. [Effects of the Invention]

[0006] According to the present invention, the burden on the user when placing the sheet on which the test image has been formed into the tray can be reduced. [Brief explanation of the drawing]

[0007] [Figure 1] Cross-sectional view illustrating an image forming apparatus. [Figure 2] Block diagram illustrating the control unit. [Figure 3] Diagram explaining the test chart [Figure 4]Block diagram illustrating the functions of the CPU. [Figure 5] Diagram explaining edge detection [Figure 6] A flowchart showing how to create a test chart. [Figure 7] Flowchart showing how to generate tone correction conditions [Figure 8] A flowchart showing how to generate tone correction conditions. [Figure 9] A flowchart showing how to generate tone correction conditions. [Figure 10] A schematic cross-sectional diagram illustrating a modified image reader. [Modes for carrying out the invention]

[0008] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments are not intended to limit the invention as defined in the claims. While the embodiments describe multiple features, not all of these features are essential to the invention, and the features may be combined in any way. Furthermore, in the attached drawings, identical or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

[0009] <First Embodiment> [Image forming apparatus] As shown in Figure 1, the image forming apparatus 1 is a multifunction peripheral (MFP) having an electrophotographic printer 100 and an image reader 110. The electrophotographic method is just one example, and other image forming methods such as inkjet may be used.

[0010] ●Printer 100 The image forming unit 50 forms a color image by layering four developer (toner) colors: yellow (Y), magenta (M), cyan (C), and black (K). In Figure 1, the letters YMCK are appended to the end of the reference numbers to indicate the toner colors, but these letters are omitted when explaining something common to all four colors.

[0011] The sheet feeding cassette 2 is a storage for storing the sheet P. The sheet feeding roller 4 feeds the sheet P from the sheet feeding cassette 2 to the conveyance path. The pair of conveyance rollers 5 conveys the sheet P fed from the sheet feeding cassette 2 further downstream in the conveyance direction of the sheet P. The registration roller pair 6 is a conveyance roller for aligning the timing when the sheet P arrives at the secondary transfer roller 19 and the timing when the toner image arrives at the secondary transfer roller 19. The sheet sensor 22 is provided near the registration roller pair 6 and detects the arrival timing of the sheet P.

[0012] In the image forming unit 50, the photosensitive drum 11 is an image carrier that carries an electrostatic latent image and a toner image. The charging roller 12 charges the surface of the photosensitive drum 11 so that the potential on the surface of the photosensitive drum 11 becomes a uniform potential. The exposure device 13 forms an electrostatic latent image by irradiating light on the surface of the photosensitive drum 11. The developing device 15 develops the electrostatic latent image using toner to form a toner image. The primary transferrer 16 transfers the toner image to the intermediate transfer member 17. The secondary transfer roller 19 transfers the toner image from the intermediate transfer member 17 to the sheet P. The fixing device 20 fixes the toner image to the sheet P using heat and pressure. The discharge roller 21 discharges the sheet P to a tray provided outside the image forming apparatus 1.

[0013] ● Image reader The image reader 110 has a reading unit 70 and a document feeder 80. The reading unit 70 has a platen 71 on which a document (sheet) is placed, and an image sensor 72 that reads the document (sheet) placed on the platen 71. Since the image sensor 72 reads the document (sheet) placed on the platen 71, it reads the document (sheet) while moving from the right to the left in the drawing directly below the platen. The image sensor 72 of the present embodiment has an LED as a light source and optical components including a lens, and reads the surface of the document (sheet) lying on the platen 71 by receiving the reflected light from the document (sheet). Note that the reading unit 70 may have a housing equipped with an LED and optical components, and the image sensor 72, and may be configured such that the housing equipped with the LED and optical components moves while the image sensor 72 does not move. Note that the document feeder 80 is rotatable with respect to the reading unit 70 so that the user can place a document (sheet) on the platen.

[0014] Also, a configuration in which the user reads a document (sheet) without placing the document (sheet) on the platen 71 will be described below. When the sheet sensor 82 detects that a document (sheet) is placed on the document tray 81, the pickup roller 83 rotates and takes in the sheet into the conveyance path of the document feeder 80. When a plurality of sheets are drawn from the document tray 81, the separation roller 84 separates one sheet from the plurality of sheets and conveys it to the conveyance rollers 85 and 86 located further downstream. The conveyance rollers 85 and 86 correct the skew of the sheet by abutting the leading edge of the sheet against the registration roller 87. When the registration roller 87 starts rotating, the sheet is conveyed to the reading unit 70. The conveyance belt 88 conveys the sheet along the platen 71. At this time, the image sensor 72 is stationary at the document reading position and reads the image formed on the sheet conveyed along the platen 71. The conveyance belt 88 and the paper discharge roller 89 discharge the sheet to the paper discharge tray 91. Note that the paper discharge sensor 90 detects that the sheet has been discharged to the paper discharge tray 91.

[0015] ● Control unit As shown in Figure 2, the control unit 10 comprehensively controls the entire image forming apparatus 1. The control unit 10 is connected to the printer 100 via the device IF 116 and controls the printer 100 to form an image on a sheet. The control unit 10 is also connected to the image reader 110 via the device IF 116 and acquires image data (read data) of the original document generated by the image reader 110. The CPU 111 controls the image forming apparatus 1 based on a control program stored in the storage unit 112. The storage unit 112 includes RAM, ROM, and a hard disk drive. The CPU 111 receives print jobs from a host computer or the like via the network IF 115. The CPU 111 displays messages on the display device of the operation unit 150, which is connected via the operation unit IF 117, and accepts user instructions from the input device of the operation unit 150. The image processing unit 118 performs predetermined image processing on the print data (image data for printing) received via the network IF 115. The image processing unit 118 expands the print data into bitmap data, converts the color space of the bitmap data (RGB → YMCK), and then performs gradation correction based on gradation correction conditions. The image processing unit 118 converts the color space (RGB → YMCK) of the image data received from the image reader 110 and then performs gradation correction based on gradation correction conditions. The image memory 119 is a high-speed memory that temporarily holds image data for image processing. The gradation correction conditions are, for example, a one-dimensional table used to convert the image signal values ​​contained in the image data. The gradation correction conditions are used to correct the gradation characteristics of the image formed by the printer 100 to ideal gradation characteristics. The image data converted by the image processing unit 118 is transferred to the exposure device 13 of the printer 100. The exposure device 13 controls the light that exposes the photosensitive drum 11 based on the transferred image data.

[0016] [Surface judgment] The image reader 110 has a fixed reading mode and a continuous reading mode. In fixed reading mode, the document transport device 80 is opened and the sheet is placed on the platen 71, and then the document transport device 80 is closed. The lower surface of the document transport device 80 is a pressure plate that presses the sheet against the platen 71. In this case, the user places the sheet on the platen 71 with the side on which the test image is formed facing the platen 71. On the other hand, in continuous reading mode, the image on the sheet is read while the sheet placed on the document tray 81 of the document transport device 80 is transported by the document transport device 80. In this case, the user often wonders whether to place the sheet on the document tray 81 with the test image facing up or with the test image facing down. If the front and back of the sheet are mistaken, the CPU 111 cannot create the correct gradation correction conditions. Therefore, this embodiment allows the user to place the sheet on the document tray 81 without intending to determine the front and back of the test image. In this embodiment, the image reader 110 reads both the first and second sides of the sheet. Here, the first side is the side that is first read by the image reader 110. The second side is the side that is read by the image reader 110 after the first side. The user may place the sheet in the document tray 81 so that the test image is visible first, and then place the sheet in the document tray 81 so that the test image is not visible. Alternatively, the user may place the sheet in the document tray 81 so that the test image is not visible first, and then place the sheet in the document tray 81 so that the test image is visible. The CPU 111 analyzes the reading data from the first side and the reading data from the second side and selects the reading data that includes the reading result of the test image. Furthermore, the CPU 111 creates gradation correction conditions based on the selected reading data. This reduces the burden on the user regarding the placement of the sheet on which the test image has been formed.

[0017] [Test image] Figure 3(A) shows a test image 301 formed on the printed surface 300a of sheet P. Figure 3(B) shows the non-printed surface 300b of sheet P. On the non-printed surface 300b, the bleed-through image 302 is an image in which the test image 301 formed on the printed surface 300a is visible through the non-printed surface 300b. The bleed-through image 302 is more likely to occur as the density of the test image 301 increases. In other words, the bleed-through image 302 corresponding to the low-density region of the test image 301 is less likely to occur. In this embodiment, a test image is formed on the printed surface 300a, and no test image is formed on the non-printed surface 300b. Furthermore, the CPU 111 can detect edges, marks, or histograms from the read data and distinguish between the printed surface 300a and the non-printed surface 300b based on these detection results. The method for distinguishing between the printed surface 300a and the non-printed surface 300b will be described in detail later.

[0018] As shown in Figure 3(C), a mark 303a may be formed on the printed surface 300a along with the test image 301. As shown in Figure 3(D), a mark 303b may be formed on the printed surface 300a along with the test image 301. Marks 303a and 303b are not formed on the non-printed surface 300b. Alternatively, marks 303a and 303b may be formed on the printed surface 300a, and a mark different from marks 303a and 303b may be formed on the non-printed surface 300b. Alternatively, no marks may be formed on the printed surface 300a, and marks may be formed on the non-printed surface 300b. Note that if marks are formed only on the printed surface 300a, the image forming apparatus 1 only needs to perform single-sided printing, thus shortening the test chart formation time. A test chart is the sheet P on which the test image 301 is formed. If marks are formed on the non-printed surface 300b, the image forming apparatus 1 must perform double-sided printing, thus increasing the test chart formation time.

[0019] [CPU Functions] Figure 4 shows the functions realized by the CPU 111 executing the control program. However, all or part of these functions may be implemented by hardware circuits such as ASICs or FPGAs.

[0020] The calibration unit 400 generates gradation correction conditions based on the reading results of the test image 301. The test image unit 401 either generates test data 451 or reads test data 451 from the storage unit 112 and sends it to the image processing unit 118. The test data 451 is image data for forming the test image 301 on sheet P. The mark unit 402 is optional and either generates image data for forming marks 303a and 303b on sheet P or reads image data from the storage unit 112 and sends it to the image processing unit 118. The generation unit 403 generates gradation correction conditions (correction table 452) based on the reading results of the test image 301. The UI unit 404 displays calibration guidance messages on the display device of the operation unit 150 and accepts user instructions from the input device. The calibration unit 400 controls the image reader 110 to read both the first and second sides of sheet P on which the test image 301 is formed. The calibration unit 400 stores the first reading data 453, which is the reading result of the first side from the image reader 110, and the second reading data 454, which is the reading result of the second side, in the storage unit 112.

[0021] The selection unit 410 analyzes the first read data 453 and the second read data 454 to select the read data that includes the reading result of the test image 301 from among the first read data 453 and the second read data 454. The analysis unit 420 analyzes the first read data 453 and the second read data 454 in order to select the read data that includes the reading result of the test image 301. The reduction unit 421 reduces the first read data 453 to generate the first reduced data 455. The reduction unit 421 reduces the second read data 454 to generate the second reduced data 456. The first read data 453 and the second read data 454 are high-resolution images because they are used for calibration. On the other hand, such high-resolution images are not necessary to determine the printed surface 300a on which the test image 301 is formed. Therefore, a reduction unit 421 may be used to speed up the analysis processing of the analysis unit 420. In other words, the analysis unit 420 analyzes the first reduced data 455 and the second reduced data 456 instead of the first read data 453 and the second read data 454. In the following description, the descriptions of the first read data 453 and the second read data 454 also apply to the first reduced data 455 and the second reduced data 456. The edge detection unit 422 detects edges contained in the first read data 453 and the second read data 454.

[0022] Figure 5 schematically shows the image data of the test image 301 that the CPU 111 has loaded into the image memory 119. The edge detection unit 422 references the pixel values ​​of a plurality of pixels 502 to 505 that are separated by a predetermined interval d from the leading edge of the image data loaded into the image memory 119, in the direction indicated by the arrow 501. The pixel values ​​may be brightness values ​​or density values. The edge detection unit 422 finds the difference between the pixel values ​​of two adjacent pixels among the plurality of pixels 502 to 505. The edge detection unit 422 determines whether this difference exceeds a threshold. If this difference exceeds the threshold, the edge detection unit 422 determines that an edge exists between the two pixels. If this difference does not exceed the threshold, the edge detection unit 422 determines that there is no edge between the two pixels. According to Figure 5, it is determined that there is an edge between pixel 503 and pixel 504. The edge detection unit 422 determines whether the position of the edge or the position of pixel 504 is within a predetermined range. The edge detection unit 422 determines that the read data includes the test image 301 if the position of the edge or the position of the pixel 504 is within a predetermined range. The edge detection unit 422 determines that the read data does not include the test image 301 if the position of the edge or the position of the pixel 504 is not within the predetermined range. Even if bleed-through occurs as shown in Figure 3(B), the CPU 111 determines that the read data does not include the test image 301 because the position of the edge or the position of the pixel 504 is not within the predetermined range. This is because, as shown in Figures 3(A) and 3(B), the high-density test image that causes bleed-through is formed to be located outside the predetermined range.

[0023] The mark detection unit 423 analyzes the first read data 453 and the second read data 454 and determines whether the mark 303a (or 303b) is included in either the first read data 453 or the second read data 454. The mark 303a (or 303b) is also formed at a predetermined position on the sheet P. Therefore, the mark detection unit 423 selects the first read data 453 if the mark 303a (or 303b) is formed at a predetermined position in the first read data 453. The mark detection unit 423 selects the second read data 454 if the mark 303a (or 303b) is formed at a predetermined position in the second read data 454. Note that the mark 303a (or 303b) may be formed to a low density so as not to cause bleed-through. With this configuration, the CPU 111 can select the read data containing the test image from the first read data and the second read data based on the detection result (selection result) of the mark detection unit 423. Alternatively, the mark detection unit 423 may compare the brightness of the area where the mark 303a (or 303b) is predicted to be formed and make a decision based on the brightness comparison result. If the brightness of the pixels in the predicted area of ​​the first read data is lower than the brightness of the pixels in the predicted area of ​​the second read data, the mark detection unit 423 selects the first read data 453. On the other hand, if the brightness of the pixels in the predicted area of ​​the second read data is lower than the brightness of the pixels in the predicted area of ​​the first read data, the mark detection unit 423 selects the second read data 454.

[0024] The histogram unit 424 calculates histograms for both the first read data 453 and the second read data 454. A test image 301 is formed on the printed surface 300a of sheet P, but not on the non-printed surface 300b. In other words, the histogram of the non-printed surface 300b should be similar to the histogram of a blank sheet. Alternatively, the histogram of the printed surface 300a should be a unique histogram derived from the test image 301. Therefore, based on the histogram, the histogram unit 424 may select the read data from the first read data 453 and the second read data 454 that includes the reading result of the test image 301.

[0025] Based on the analysis results from the analysis unit 420, the determination unit 430 determines which of the first read data 453 and the second read data 454 contains the test image 301. The determination unit 430 notifies the generation unit 403 which of the first read data 453 and the second read data 454 should be used.

[0026] [Calibration flowchart] ● Create a test chart Figure 6 shows how the CPU 111 creates a test chart according to the control program. Calibration is divided into the process of creating the test chart and the process of creating the gradation correction conditions. When the CPU 111 receives a calibration execution command from the operation unit 150 or the like, it executes the following processes. In S601, the CPU 111 (test image unit 401) instructs the printer 100 to start printing. Upon receiving the instruction to start printing, the printer 100 performs the necessary preparatory operations to execute the print job and waits for the image data (image signal) to be output from the control unit 10. In S602, the CPU 111 (test image unit 401) generates test data 451, which is image data of the test image. This process involves writing the test data 451 as image data to the image memory 119. The test data 451 may be stored in the storage unit 112 beforehand. The test image unit 401 may generate the test data 451 according to the control program. In S603, the CPU 111 (test image unit 401) supplies the test data 451, which has been expanded in the image memory 119, to the printer 100 via the device IF 116, causing the printer 100 to create a test chart. The printer 100 creates the test chart by forming the test image 301 on sheet P. • In S604, CPU111 (test image unit 401) instructs printer 100 to finish printing.

[0027] ●Generating tone correction conditions Figure 7 shows how the CPU 111 generates the gradation correction conditions to be executed according to the control program. Once the test chart creation is complete, the CPU 111 performs the following processes. ·In S701, the CPU 111 (calibration unit 400) instructs the image reader 110 to start reading. The CPU 111 may also display a message on the display device of the operation unit 150 prompting the user to place the test chart on the document tray 81. The user may place the test chart on the document tray 81 so that the test image 301 is visible, or so the user may place the test chart on the document tray 81 so that the test image is not visible. In S702, the CPU 111 (calibration unit 400) obtains the reading result of the first side of the test chart from the image reader 110. For example, the CPU 111 receives the first reading data 453 output by the image reader 110 and stores it in the storage unit 112. As described above, the CPU 111 may also reduce the first reading data 453 to generate first reduced data 455 and store it in the storage unit 112. The CPU 111 may also display a message on the operation unit 150 prompting the user to flip the test chart over and place it on the document tray 81. In S703, the CPU 111 (calibration unit 400) obtains the reading result of the second side of the test chart from the image reader 110. For example, the CPU 111 receives the second reading data 454 output by the image reader 110 and stores it in the storage unit 112. As described above, the CPU 111 may also reduce the second reading data 454 to generate second reduced data 456 and store it in the storage unit 112. In S704, the CPU 111 (analysis unit 420) analyzes the first read data 453. Instead of the first read data 453, the first reduced data 455 may be analyzed. These read data may be expanded into the image memory 119 to speed up the analysis process. The analysis results should be information useful for determining the presence or absence of the test image 301, such as edge detection results (e.g., presence or absence of edges and edge positions), mark detection results, and histogram calculation results. In S705, the CPU 111 (determination unit 430) determines, based on the analysis results, whether the first read data 453 includes the test image reading results. If the first read data 453 includes the test image reading results, the CPU 111 proceeds to S706. If the first read data 453 does not include the test image reading results, the CPU 111 proceeds to S710.

[0028] ●When the first read data 453 includes the reading result of the test image In S706, the CPU 111 (generation unit 403) performs sampling on the first read data 453 to create gradation correction conditions. The test image 301 has multiple gradation patterns (patch images), each with a different gradation. Therefore, the generation unit 403 performs sampling for each of the multiple gradation patterns. In S707, the CPU 111 (generation unit 403) updates the tone correction conditions based on the sampling results. For example, the tone correction conditions for a certain tone are updated by comparing the sampling results for that tone with the test data 451 for that tone. As described above, the tone correction conditions may also be a tone correction table (correction table 452). The generation unit 403 creates a new correction table 452 based on the sampling results and overwrites the old correction table 452 stored in the storage unit 112. • In S708, the CPU 111 (UI unit 404) notifies the user that the calibration is complete. For example, the UI unit 404 may display a message indicating the completion of the calibration on the operation unit 150. In S708, the CPU 111 (generation unit 403) deletes the read data (e.g., first read data 453, second read data 454, first reduced data 455, second reduced data 456) from the storage unit 112 and the image memory 119.

[0029] ● If the first read data 453 does not include the reading result of the test image • In S710, the CPU 111 (analysis unit 420) analyzes the second read data 454. The second reduced data 456 may be analyzed instead of the second read data 454. These read data may be expanded into the image memory 119 to speed up the analysis process. The analysis results should be information useful for determining the presence or absence of the test image 301, such as edge detection results (e.g., presence or absence of edges and edge positions), mark detection results, and histogram calculation results. In S711, the CPU 111 (determination unit 430) determines, based on the analysis results, whether the second read data 454 contains the test image reading results. If the second read data 454 contains the test image reading results, the CPU 111 proceeds to S706. In this case, S706 to S709 are executed for the second read data 454. If the second read data 454 also does not contain the test image reading results, the CPU 111 proceeds to S712.

[0030] ● If the second read data 454 also does not include the reading result of the test image. In S712, the CPU 111 (UI unit 404) notifies the user of the error. For example, the UI unit 404 may display a message on the operation unit 150 indicating that an error has occurred. It is not usually the case that both the first read data 453 and the second read data 454 do not contain the test image. However, such an error may occur if the user forgets to flip the front and back of the test chart.

[0031] <Second Embodiment> Figure 8 shows another method for generating gradation correction conditions executed by the CPU 111 according to the control program. The difference between Figure 8 and Figure 7 is that S705, S706, S710, and S711 are replaced by S801 to S805. Here, we will mainly explain S801 to S805. To avoid repetition of explanations regarding matters already explained in Figure 7, explanations will be omitted. When S704 is completed, the CPU 111 proceeds to S801. In S801, CPU 111 analyzes the second read data 454. S801 is the same process as S710. In S802, the CPU 111 determines, based on the analysis results of the first read data 453 and the second read data 454, whether either the first or second face of the test chart contains the test image 301. In other words, the CPU 111 determines whether either the first read data 453 or the second read data 454 contains the reading result of the test image 301. As described above, the presence or absence of the test image 301 may also be determined based on edges, marks, or histograms. If either the first read data 453 or the second read data 454 contains the reading result of the test image 301, the CPU 111 proceeds to S803. If neither the first read data 453 nor the second read data 454 contains the reading result of the test image 301, the CPU 111 proceeds to S712. In step S803, the CPU 111 determines whether the first surface contains the test image 301. For example, the determination unit 430 determines whether the first read data 453 contains the reading result of the test image 301 based on the analysis result of the first read data 453. As described above, the presence or absence of the test image 301 may be determined based on edges, marks, or histograms. If the first surface contains the test image 301, the CPU 111 proceeds to S804. If the first surface does not contain the test image 301 (if the second surface contains the test image 301), the CPU 111 proceeds to S805. In S804, the CPU 111 (generation unit 403) performs sampling on the first read data 453 to create gradation correction conditions. S804 is the same process as S706. In S805, the CPU 111 (generation unit 403) performs sampling on the second read data 454 to create gradation correction conditions. S805 is the same process as S706.

[0032] <Third Embodiment> Figure 9 shows yet another method for generating gradation correction conditions that the CPU 111 executes according to the control program. The difference between Figure 9 and Figure 7 is that S703 to S705 are replaced with S901 to S903. Here, we will mainly explain S901 to S903. To avoid repetition of explanations regarding matters already explained in Figure 7, explanations will be omitted. When S702 is completed, the CPU 111 proceeds to S901. In S901, CPU 111 analyzes the first read data 453. S901 is the same process as S704. In step 902, the CPU 111 (determination unit 430) determines, based on the analysis results, whether the first read data 453 includes the test image reading results. If the first read data 453 includes the test image reading results, the CPU 111 proceeds to S706. If the first read data 453 does not include the test image reading results, the CPU 111 proceeds to S903. In S903, CPU111 obtains the reading result of the second side of the test chart from image reader 110. S903 is the same process as S703. After that, CPU111 proceeds to process S710.

[0033] As shown in Figure 9, the reading process for the second surface is performed only if the test image 301 is not formed on the first surface. If the test image 301 is formed on the first surface, the reading process for the second surface is skipped. Compared to Figures 7 and 8, the time from the start to the end of calibration will be reduced in Figure 9.

[0034] <Other Embodiments> The image forming apparatus 1 may have an image reader 110 as shown in Figure 10 instead of the image reader 110 shown in Figure 1. The configuration of the image reader 110 in Figure 10 will be described in detail. The image reader 110 in Figure 10 has a document transport device 80 and a reading unit 70. The document transport device 80 of the image reader shown in Figure 10 is different from the document feeding device 80 of the image reader 110 shown in Figure 1. The image sensor 72A has the same configuration as the image sensor 72 in Figure 1.

[0035] The pickup roller 83 feeds the documents (sheets) loaded on the document tray 81 into the document transport device 80. The rotation of the separation roller 84 is controlled to prevent multiple documents (sheets) from being fed simultaneously by the pickup roller 83. The documents (sheets) fed into the transport path are transported toward the reading position A by the transport rollers 85 and 86a. Here, the reading unit 70 has a transparent glass 73 at a position opposite to the reading position A. The glass 73 is provided separately from the platen 71, but a part of the platen 71 may overlap with the reading position A.

[0036] An opening is formed in the document transport device 80 so that the document (sheet) transported by the document transport device 80 is pressed against the glass 73 of the reading unit 70 at reading position A. When the image sensor 72A reads the document (sheet) transported by the document transport device 80, the image sensor 72A of the reading unit 70 moves directly below the glass 73. When the image sensor 72A reads the document (sheet) transported by the document transport device 80, the image sensor 72A remains directly below reading position A. As a result, the document (sheet) is read by the image sensor 72A as it passes through reading position A by the document transport device. Hereafter, the surface of the document (sheet) read by the image sensor 72A will be referred to as the first surface.

[0037] The document transport device 80 has a sensor upstream of the reading position A in the document (sheet) transport direction that detects the leading edge of the document (sheet) being transported along the transport path. The control unit 10 controls the timing at which the image sensor 72A starts reading the document (sheet) based on the timing when the sensor detects the leading edge of the document (sheet). The document transport device 80 also has backup rollers to suppress flapping of the document (sheet) as it passes through the reading position A.

[0038] The original document (sheet) that has passed through reading position A is transported toward reading position B by transport roller 86b. The document transport device 80 has an image sensor 72B that reads the original document (sheet) being transported toward reading position B. The image sensor 72B has its longitudinal direction from front to back in Figure 10. The image sensor 72B further includes an LED and optical components. The longitudinal direction of the image sensor 72B is perpendicular to the direction in which the sheet is transported. The image sensor 72B has multiple pixels that receive R (red), G (green), and B (blue) light in its longitudinal direction. The image sensor 72B reads the second side, which is the back side of the first side of the original document (sheet) that is read by the image sensor 72A.

[0039] The image sensor 72B reads the second side of the original document (sheet) as follows. Specifically, an LED, acting as a light source, illuminates the second side of the original document (sheet). The reflected light from the original document (sheet) passes through the glass and reaches the optical component. The optical component guides the reflected light from the original document (sheet) to the image sensor 72B. The image sensor 72B outputs analog reading data based on the received reflected light. The image sensor 72B simultaneously reads one line of image along its longitudinal direction. Therefore, the image sensor 72B acquires analog reading data for one page of the original document (sheet) by performing readings multiple times while transporting the original document (sheet). The analog reading data is converted into digital reading data (second reading data) by an A / D conversion circuit (not shown) of the image sensor 72B and output to the control unit 10.

[0040] Furthermore, the timing at which the image sensor 72B begins reading is controlled based on the timing at which the sensor detects the leading edge of the document (sheet). The document (sheet) that has passed through reading position B is ejected to the output tray 91 by the output roller 89.

[0041] Furthermore, the image sensor 72A of this embodiment has an LED as a light source and an optical component including a lens, and reads the surface of the document (sheet) placed face down on the platen 71 by receiving reflected light from the document (sheet). The reading unit 70 has a housing equipped with an LED and optical component and an image sensor 72, and the housing equipped with the LED and optical component may move while the image sensor 72 does not move.

[0042] Next, the method for generating gradation correction conditions executed by the CPU 111 of this embodiment according to the control program will be explained, focusing on the differences from Figure 7 of the first embodiment. In step S702, the CPU 111 (calibration unit 400) of this embodiment acquires the reading result of the first surface of the test chart from the image sensor 72A, and in step S703, acquires the reading result of the second surface of the test chart from the image sensor 72B. The CPU 111 acquires the first reading data 453 acquired from the image sensor 72A and the second reading data 454 acquired from the image sensor 72B, and stores them in the storage unit 112. The CPU 111 may also generate first reduction data 455 from the first reading data 453 and second reduction data 456 from the second reading data 454. At this time, the CPU 111 stores the first reduction data 455 and the second reduction data 456 in the storage unit 112. The processing of the other steps is the same as in Figure 7, so the explanation here is omitted.

[0043] Furthermore, if the sheet sensor 82 does not detect that a document (sheet) has been placed in the document tray 81, and a reading start instruction is issued, it is presumed that the document (sheet) is placed on the platen 71. Therefore, the image reader 70 performs a known fixed-document reading. Since fixed-document reading is a known technique, a detailed explanation will be omitted.

[0044] The document transport device 80 in Figure 1 does not have a reading unit to read the second side of the document (sheet) opposite to the first side of the document (sheet) read by the reading unit 70. Therefore, with the image reader 110 in Figure 1, the user had to place the sheet that had been ejected to the output tray 91 back onto the document tray 81 in order to obtain reading data for both sides of the sheet. On the other hand, the image reader 110 in Figure 10 has a reading unit in the document transport device 80 that reads the second side of the sheet. As a result, the user does not need to place the sheet that has been ejected to the output tray 91 back onto the document tray 81. Furthermore, with the image reader 110 in Figure 10, there is no need to re-place a sheet that has had one side read, so the problem of both the first and second reading data being reading data for the non-printed side where the test image 301 is not formed does not occur.

[0045] Furthermore, in the first to third embodiments and other embodiments, a configuration has been described in which a test chart used to generate gradation correction conditions is transported and read by the document transport device 80. However, the test chart transported and read by the document transport device 80 is not limited to one that generates gradation correction conditions, but may also be, for example, a test chart for adjusting transfer conditions for transferring a toner image. In the case of a test chart for adjusting transfer conditions for transferring a toner image, test images with different transfer conditions are formed on only one side (printing surface 300a) of the first and second sides of the sheet P.

[0046] A test chart for adjusting the transfer conditions for transferring toner images is, for example, a sheet P on which multiple test images with different transfer conditions are formed. Here, the transfer condition is, for example, the transfer voltage applied to the secondary transfer roller 19. The resistance values ​​of the secondary transfer roller 19 and the intermediate transfer body 17 change due to temperature, humidity, and cumulative operating time. If the resistance values ​​of the secondary transfer roller 19 and the intermediate transfer body 17 change, the transfer efficiency decreases, and the density of the output image formed by the image forming apparatus 1 changes. Therefore, the control unit 10 adjusts the image quality of the output image formed by the image forming apparatus 1 by adjusting the transfer conditions based on the reading data related to the test chart for adjusting the transfer conditions for transferring toner images.

[0047] <Technical concepts and their effects derived from the first to third embodiments> [Perspective 1] As shown in Figure 1, the printer 100 functions as an image forming means that forms a test image 301 for determining gradation correction conditions on only one side (printing surface 300a) of the first and second sides of the sheet P. The image reader 110 functions as a reading means that generates reading data for the first side (first reading data 453) and reading data for the second side (second reading data 454) by reading the first and second sides of the sheet P, respectively. The selection unit 410 functions as a selection means that analyzes the reading data for the first side and the reading data for the second side and selects the reading data that includes the reading result of the test image 301 from the reading data for the first side and the reading data for the second side. The generation unit 403 functions as a generation means that generates gradation correction conditions (e.g., correction table 452) based on the selected reading data. Thus, according to this embodiment, both the front and back sides of the sheet P are basically read. In particular, during the initial scanning process, the user may place the sheet P on the document tray 81 so that the printed surface 300a is visible, or they may place the sheet P on the document tray 81 so that the printed surface 300a is not visible. Therefore, the user's burden regarding the placement of the sheet P on which the test image has been formed is reduced. The image forming apparatus 1 also selects the scanned data, including the scanning result of the test image 301, and generates gradation correction conditions based on the selected scanned data. By using the generated gradation correction conditions, the image forming apparatus 1 can correct the gradation characteristics of the output image formed by the image forming apparatus 1 to ideal gradation characteristics.

[0048] [Perspective 2] The document transport device 80 is an example of an automatic document transport device. The document tray 81 is an example of a loading means on which a sheet P is placed. The transport roller 85 is an example of a transport means that transports the sheet placed on the loading means to the reading means. After the sheet is placed on the loading means so that the first side is read by the reading means, the sheet is placed on the loading means so that the second side is read by the reading means. In other words, once the first reading process is complete, the user only needs to flip the front and back of the sheet P for the second reading process.

[0049] [Perspective 3] The display device of the operation unit 150 may also function as an output means that outputs a message prompting the user to flip the sheet over and place it on the placement means when the first side is read by the reading means. This would allow the user to perform the sheet flipping operation without hesitation.

[0050] [Perspective 4] As explained in relation to Figure 5, the selection unit 410 may perform edge detection on the read data of the first surface and select the read data of the first surface if an edge exists at a predetermined position. The selection unit 410 may also perform edge detection on the read data of the second surface and select the read data of the second surface if an edge exists at a predetermined position. As shown in Figure 5, an edge exists on the outer periphery of the test image 301. Therefore, the presence or absence of the test image 301 may be determined by focusing on the edge.

[0051] [Perspective 5] There are cases where an edge does not exist at a predetermined position in the data read from the first side, and an edge does not exist at a predetermined position in the data read from the second side. For example, this can occur if the user forgets to flip the sheet or places a different sheet than the test chart on the document tray 81. In this case, the selection unit 410 will not select either the data read from the first side or the data read from the second side. This will make it less likely for incorrect gradation correction conditions to be generated.

[0052] [Perspective 6] The printer 100 may form the test image and the first marks (e.g., marks 303a, 303b) on only one of the two surfaces, the first or the second. The selection unit 410 may analyze the read data from the first surface and the read data from the second surface and select the read data from the first surface and the read data from the second surface that includes the first marks. By forming such marks, the printed surface 300a and the non-printed surface 300b will be easily distinguishable.

[0053] [perspective 7] As shown in Figure 3(C) and other figures, the printer 100 may form the first mark at a position away from the test image 301. This would reduce the influence of the first mark on the creation of the gradation correction conditions.

[0054] [Perspective 8] The printer 100 may form a second mark different from the first mark on the other of the two surfaces, without forming the test image 301 on the other surface. By forming such a mark, the printable surface 300a and the non-printable surface 300b will be easily distinguishable.

[0055] [Perspective 9] The selection unit 410 may obtain a histogram for the data read from the first side, and if the histogram obtained for the data read from the first side is a histogram specific to a blank page, it may select the data read from the second side. The selection unit 410 may obtain a histogram for the data read from the second side, and if the histogram obtained for the data read from the second side is a histogram specific to a blank page, it may select the data read from the first side. In this embodiment, the test image 301 may be formed only on the printed surface 300a, and the non-printed surface 300b may be left blank. Therefore, the printed surface 300a and the non-printed surface 300b can be easily distinguished based on the histogram.

[0056] [Perspective 10] The selection unit 410 may obtain a histogram for the data read from the first surface, and if the histogram obtained for the data read from the first surface is a histogram specific to the test image, it may select the data read from the first surface. The selection unit 410 may obtain a histogram for the data read from the second surface, and if the histogram obtained for the data read from the second surface is a histogram specific to the test image, it may select the data read from the second surface. In this embodiment, the test image 301 may be formed only on the printed surface 300a, and the non-printed surface 300b may be left blank. Therefore, the printed surface 300a and the non-printed surface 300b can be easily distinguished based on the histogram.

[0057] [Perspective 11] The tone correction conditions may be a one-dimensional tone correction table (e.g., correction table 452) that converts the tone characteristics of the input image data to generate output image data. The image processing unit 118 uses the tone correction table to convert the tone characteristics of the input image data to generate output image data. The input image data is generated by an image reader or by unpacking a print job. Alternatively, the input image data may be generated by converting the color space of these image data. The output image data is image data generated for supply to a printer. This will bring the tone characteristics of the input image and the tone characteristics of the output image formed on sheet P closer together.

[0058] [Perspective 12] As shown in Figure 7 and other figures, the selection unit 410 may analyze the reading data of the first surface and select the reading data of the first surface if it includes the reading result of the test image 301. The generation unit 403 may generate gradation correction conditions based on the reading data of the first surface selected by the selection means. If the reading data of the first surface does not include the reading result of the test image, the selection unit 410 may analyze the reading data of the second surface and select the reading data of the second surface if it includes the reading result of the test image. The generation unit 403 may generate gradation correction conditions based on the reading data of the second surface selected by the selection means.

[0059] [Perspective 13] As shown in Figure 8, the selection unit 410 may analyze the reading data from the first surface and the reading data from the second surface, respectively, and determine which of the two sets of reading data contains the test image reading result. The selection unit 410 may then select the reading data containing the test image reading result. The generation unit 403 generates gradation correction conditions based on the reading data selected by the selection means.

[0060] [Perspective 14] As shown in Figure 9, if the selection unit 410 selects the data to be read from the first side, the image reader 110 may skip reading the second side of the sheet. This will reduce the time required for calibration.

[0061] [Perspective 15] As shown in Figure 4, the reduction unit 421 functions as a reduction means that generates first reduced data obtained by reducing the read data of the first surface and second reduced data obtained by reducing the read data of the second surface. The analysis unit 420 functions as an analysis means that analyzes the first reduced data and the second reduced data. The selection unit 410 may select the read data from the read data of the first surface and the read data of the second surface that includes the read result of the test image, based on at least one of the analysis results of the first reduced data and the analysis results of the second reduced data. By analyzing the read data whose size has been reduced in this way, the analysis time will be shortened.

[0062] [Perspective 16] The printer 100 functions as an image forming means that forms an image based on image data. The image reader 110 has a tray on which a sheet is placed and a transport unit that transports the sheet on the tray, and functions as a reading means that reads the sheet transported by the transport unit. The control unit 10 functions as an acquisition means that causes the image forming means to form a test image on one side of a sheet, transports the sheet with the test image formed on it to the transport unit, acquires first reading data relating to the reading result of the first side of the sheet with the test image formed on it, and acquires second reading data relating to the reading result of a second side of the sheet with the test image formed on it, which is different from the first side. The selection unit 410 functions as a selection means that selects reading data relating to the reading result of the test image from the first reading data and second reading data acquired by the acquisition means. The CPU 111 functions as a control means that controls the density of the output image formed by the image forming means based on the reading data selected by the selection means.

[0063] The image processing unit 118 may function as a conversion means for converting image data based on gradation correction conditions. The control means (e.g., CPU 111) may generate gradation correction conditions based on the read data selected by the selection means. The image forming means (e.g., printer 100) may form an output image based on the image data converted by the conversion means.

[0064] The image forming means (e.g., printer 100) may be controlled based on image forming conditions (e.g., transfer conditions). The control means (e.g., CPU 111) may determine the image forming conditions based on the read data selected by the selection means.

[0065] As illustrated in Figure 10, the reading means may include a first sensor (e.g., 72A) for reading the first surface of the sheet conveyed by the conveying unit, and a second sensor (e.g., 72B) for reading the second surface of the sheet.

[0066] The control unit 10 is an example of an information processing device. The control unit 10 may be implemented by a personal computer (PC). The control unit 10 may function as an acquisition means to acquire first reading data relating to the reading result of the first side of a sheet output from a reader, and second reading data relating to the reading result of a second side of the sheet, which is different from the first side, output from the reader. The control unit 10 may function as a selection means to select reading data relating to the reading result of a test image printed on one side of the sheet by a printer from the first reading data and the second reading data. The control unit 10 may function as a generation means to generate gradation correction conditions for correcting the gradation characteristics of an image formed by a printer, based on the reading data selected by the selection means. As shown in Figure 10, the control unit 10 may acquire first reading data output from a first sensor of the reader, and second reading data output from a second sensor of the reader.

[0067] The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, claims are attached to make the scope of the invention public. [Explanation of Symbols]

[0068] 1: Image forming apparatus, 10: Control unit, 100: Printer, 110: Image reader

Claims

1. Image forming means for forming an image, A document transport means comprising: a loading tray on which documents are loaded; a transport unit for transporting the documents loaded on the loading tray; a first reading unit for reading an image of the underside of the documents on the loading tray while the transport unit transports the documents; a discharge unit for discharging the documents read by the first reading unit; and a discharge tray from which the documents are discharged by the discharge unit. The reading means comprises a platen on which a document is placed, and a second reading unit, wherein when reading a document placed on the platen, the second reading unit is moved while reading the document on the platen, and when reading a document on the stacking tray transported by the transport unit, the second reading unit is kept stationary at the reading position while reading the image of the upper surface of the document on the stacking tray by the second reading unit. When reading a test image formed on one side of a sheet by the image forming means while transporting it to the document transport means, a control means is provided to transport the sheet on the loading tray to the transport unit while reading both sides of the sheet using the first reading unit and the second reading unit. A determination means for determining the read image of the surface on the sheet on which the test image is formed, based on a first read image of the sheet on which the test image is formed by the first reading unit and a second read image of the sheet on which the test image is formed by the second reading unit, An image forming apparatus characterized by having an adjustment means for adjusting the image quality of an image formed by the image forming means based on the read image determined by the determination means.

2. The system further includes a conversion means for converting image data based on tone correction conditions, The adjustment means generates the grayscale correction conditions based on the read image determined by the determination means. The image forming apparatus according to claim 1, characterized in that the image forming means forms an image based on the image data converted by the conversion means.

3. The image forming means is controlled based on the image forming conditions, The image forming apparatus according to claim 1, characterized in that the adjustment means determines the image forming conditions based on the read image determined by the determination means.

4. The image forming apparatus according to claim 1, further comprising a notification means for notifying an error when the determination means determines that neither the first read image nor the second read image is a read image of the surface on which the test image is formed.

5. An information processing device that can communicate with an image forming apparatus that forms an image, The image forming apparatus is A document transport means comprising: a loading tray on which documents are loaded; a transport unit for transporting the documents loaded on the loading tray; a first reading unit for reading an image of the underside of the documents on the loading tray while the transport unit transports the documents; a discharge unit for discharging the documents read by the first reading unit; and a discharge tray from which the documents are discharged by the discharge unit. The reading means comprises a platen on which a document is placed, and a second reading unit, wherein when reading a document placed on the platen, the second reading unit is moved while reading the document on the platen, and when reading a document on the stacking tray transported by the transport unit, the second reading unit is kept stationary at the reading position while reading the image of the upper surface of the document on the stacking tray by the second reading unit. When reading a test image formed on one side of a sheet by the image forming apparatus while it is being transported to the document transport means, the transport unit transports the sheet on the loading tray while the first reading unit and the second reading unit are used to read both sides of the sheet. It is equipped with, The aforementioned information processing device is A determination means for determining the read image of the surface on the sheet on which the test image is formed, based on a first read image of the sheet on which the test image is formed by the first reading unit and a second read image of the sheet on which the test image is formed by the second reading unit, An information processing apparatus characterized by having an adjustment means for adjusting the image quality of an image formed by an image forming apparatus based on the read image determined by the determination means.

6. The system further includes a conversion means for converting image data based on tone correction conditions, The adjustment means generates the grayscale correction conditions based on the read image determined by the determination means. The image forming apparatus is characterized in that it forms an image based on the image data converted by the conversion means, as described in claim 5.

7. The image forming apparatus is controlled based on image forming conditions. The information processing apparatus according to claim 5, characterized in that the adjustment means determines the image formation conditions based on the read image determined by the determination means.

8. The information processing apparatus according to claim 5, further comprising a notification means for notifying an error when the determination means determines that neither the first read image nor the second read image is a read image of the surface on which the test image is formed.

Images