JP2015154229A - image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can suppress, even upon the occurrence of sub-scanning streaks in output images, a deterioration in quality of the output images due to the sub-scanning streaks without performing cleaning or replacement of units or the like.SOLUTION: An image forming apparatus includes: an operation display unit that receives operations from a user; a screen processing unit 26 that executes screen processing to a first image to create a second image; an image forming unit 5 that performs image formation on a recording sheet on the basis of the second image created by the screen processing unit 26; a streak detection unit 30 that detects sub-scanning streaks on the basis of a third image created by a reading unit (output image reading unit 13) reading the recording sheet on which the image formation is performed by the image forming unit 5; and a screen changing unit 32 that changes the content of the screen processing to an area corresponding to the sub-scanning streaks detected by the streak detection unit 30.

Description

  The present invention relates to an image forming apparatus.

  In an image forming apparatus, due to deterioration over time of members and units (hereinafter referred to as units and the like) such as a developing device, a photosensitive member, and a cleaning member that constitute the image forming device, the developing device is clogged and the photosensitive member is damaged. A cleaning failure occurs due to deterioration of the cleaning member, and these may cause streaks (hereinafter referred to as sub-scanning streaks) in the sub-scanning direction on the output image.

  Once a sub-scanning streak occurs, a sub-scanning streak occurs over the entire surface in the sub-scanning direction at a certain position in the main scanning direction every time image formation is performed. It drops significantly.

  On the other hand, in order to eliminate the sub-scanning streaks, it is necessary to clean and replace the units that cause the sub-scanning streaks. Therefore, the user recognizes the deterioration in the quality of the output image, but puts it up and uses the image forming apparatus.

  In addition, since it is difficult for a general user to accurately identify a unit that causes a sub-scanning line, a unit that is not originally required to be replaced and that is not related to the sub-scanning line is replaced. In some cases, unnecessary costs may be generated.

  Although it is possible to ask a service person in charge of maintenance and inspection of the image forming apparatus to clean or replace the unit, etc., it is necessary to pay the labor cost of the service person. Therefore, the cost increases for the user.

  In addition, when a service person requests a response, it takes a certain amount of time to get the response, and during that time the image forming apparatus cannot be operated. For example, a university or a large company specializes in printing. In an environment where the image forming apparatus is required to be continuously operated in order to finish a large amount of printed matter in a short time, such as a department or a print shop, there is a time that the image forming apparatus cannot be operated, which greatly hinders business.

  With respect to the above-described problems, in Patent Document 1, the image forming apparatus has a recording head in which a plurality of recording elements are arranged in a row in the main scanning direction, and each recording is performed based on an input gradation value. In an image forming apparatus that drives an element and moves a recording head and a recording medium relatively in a direction substantially perpendicular to the main scanning direction to sequentially form a scanning line image on the recording medium, each recording element A driving energy calculation unit that calculates a plurality of stages of driving energy, a random number generation unit that generates a random value corresponding to each gradation value, a driving energy and a random number generation unit calculated by the driving energy calculation unit A driving correction unit that corrects the driving energy based on the random number value generated by the driving correction unit, and a carry-over value for the subsequent scanning line image is calculated based on the correction amount of the driving energy corrected by the driving correction unit. A carry-over value calculation unit, and the drive energy calculation unit calculates drive energy based on the gradation value corresponding to each of the plurality of recording elements and the carry-over value calculated by the carry-over value calculation unit. Has solved the above problem.

Japanese Patent Laid-Open No. 2007-083587

  However, in Patent Document 1, it is possible to suppress sub-scanning streaks by correcting variations in the LED elements used for the exposure means, but taking into account changes over time in units such as developing units, photoconductors, and cleaning members. However, there is a problem that it is not possible to completely prevent the occurrence of sub-scanning streaks that accompany changes with time of the unit or the like.

  The present invention has been made in view of the above problems, and even if a situation in which sub-scanning streaks may occur in an output image due to changes over time of units such as a developing device, a photosensitive member, and a cleaning member, It is an object of the present invention to provide an image forming apparatus capable of suppressing quality degradation of an output image due to a sub-scanning line without cleaning or replacing a unit or the like.

  (1) An operation display unit that receives an operation from a user, a screen processing unit that executes screen processing on the first image, and generates a second image, and a second image generated by the screen processing unit An image forming unit that forms an image on a recording sheet, and a stripe detection unit that detects a sub-scanning line based on a third image generated by a reading unit that reads the recording sheet on which the image forming unit forms an image; An image forming apparatus comprising: a screen changing unit that changes a screen processing content of an area corresponding to the sub-scanning stripe detected by the stripe detecting unit.

  (2) The image forming apparatus according to (1), wherein the screen changing unit changes the number of screen lines in an area corresponding to the sub-scanning stripe.

  (3) The image forming apparatus according to (1) or (2), wherein the screen changing unit changes a screen angle of an area corresponding to the sub-scanning stripe.

  (4) The screen changing unit is characterized in that the number of screen lines in the area corresponding to the sub-scanning stripe is made lower than the number of screen lines in the area other than the area corresponding to the sub-scanning line. The image forming apparatus described.

  (5) The screen changing unit determines the difference in the screen angle of the region corresponding to the sub-scanning stripe with respect to the predetermined angle from the difference in the screen angle of the region other than the region corresponding to the sub-scanning stripe with respect to the predetermined angle. The image forming apparatus as described in (3), wherein

  (6) The operation display unit receives a setting as to whether or not to correct the sub-scanning streak from the user, and the screen change unit screen processing the area corresponding to the sub-scanning streak based on the setting received by the operation display unit. The image forming apparatus according to any one of (1) to (5), wherein the content of the image is changed.

  (7) The operation display unit further receives a setting related to the correction area for correcting the sub-scanning streak from the user, and further includes a correction area determination unit that determines the correction area based on the setting related to the correction area received from the user by the operation display unit. The image forming apparatus according to any one of (1) to (6), wherein the screen change unit changes the content of the screen processing of the correction area determined by the correction area determination unit.

  (8) The image forming apparatus according to (7), wherein the setting relating to the correction area is a setting for changing the width of the correction area.

  (9) The streak detecting unit detects the width of the sub-scanning streak, and the screen changing unit changes the content of the screen processing when the width of the sub-scanning streak satisfies a predetermined condition (1) The image forming apparatus according to any one of (8) to (8).

  (10) The operation display unit receives a parameter setting relating to the screen processing of the area corresponding to the sub-scanning stripe from the user, and the screen changing unit displays the contents of the screen processing of the area corresponding to the sub-scanning stripe based on the parameter. The image forming apparatus according to any one of (1) to (9), wherein the image forming apparatus is changed.

  (11) The screen changing unit changes the content of the screen processing in the area corresponding to the sub-scanning stripe for a predetermined pixel type among the plurality of pixel types, and sets other pixel types other than the predetermined pixel type. The image forming apparatus according to any one of (1) to (10), wherein the content of the screen processing in the area corresponding to the sub-scanning stripe is not changed for the type.

  (12) The image forming apparatus further includes a correction area determination unit that determines a correction area for correcting the sub-scanning stripe, and the correction area determination unit includes a first correction area and a second correction area other than the first correction area as the correction area. In addition to determining the area, a non-correction area other than the correction area is determined, and the screen changing unit screens the first correction area, the second correction area, and the non-correction area with different screen processing contents. The content of processing is changed, The image forming apparatus as described in any one of (1)-(6) characterized by the above-mentioned.

  (13) The second correction area is determined on both ends of the correction area with respect to the main scanning direction, and the first correction area is determined between the second correction areas (12) The image forming apparatus described in 1.

  (14) The screen changing unit performs screen processing so that the content of the screen processing in the second correction area becomes an intermediate screen line number or / and a screen angle between the first correction area and the non-correction area. The image forming apparatus as described in (12) or (13), wherein the content of the image is changed.

  (15) The image forming apparatus further includes a correction area determining unit that determines a correction area for correcting the sub-scanning stripe, and the correction area determining unit includes a position in the main scanning direction of the boundary at the first position in the sub-scanning direction, and a position in the sub-scanning direction. The correction area is determined so that the position of the boundary at the second position, which is different from the first position, is different from the first position, and the screen changing unit performs screen processing of the correction area determined by the correction area determining unit. The image forming apparatus according to any one of (1) to (6), wherein the content is changed.

  According to the present invention, even when the sub-scanning streak may occur in the output image due to the change over time of the unit such as the developing unit, the photosensitive member, and the cleaning member, the unit or the like is not cleaned or replaced. Sub-scanning lines can be made inconspicuous, and output image quality deterioration due to sub-scanning lines can be suppressed.

1 is a hardware configuration diagram of an image forming apparatus 1 according to an embodiment. 3 is a functional block diagram of functions realized by a storage unit 15. FIG. It is an example of the test pattern used when detecting a sub-scanning line. It is a functional block diagram of the function relevant to subscanning stripe correction. It is an example of profile data corresponding to the gradation of the test patterns K1 to K8. (A) is the figure which made the area | region of the subscanning stripe width | variety centering on a subscanning stripe the correction | amendment area | region. (B) is a diagram showing a correction area including a sub-scanning line width area centered on the sub-scanning stripe and an area adjacent to the area. It is a screen which receives the execution instruction of subscanning stripe detection. It is an alerting | reporting screen of subscanning stripe detection. This is a setting screen that accepts screen parameter settings. It is a screen which receives the setting of the range which performs subscanning stripe correction. It is a screen for selecting the correction strength of the sub-scanning stripe. It is a main routine of processing related to sub-scanning line correction. It is a subroutine which shows the process of setting reception. It is a subroutine showing a sub-scanning streak detection process. It is a subroutine of processing for determining a correction area. It is a subroutine which shows the process regarding the subscanning stripe correction | amendment performed at the time of image formation. (A) is a figure explaining a screen parameter. (B) is a figure explaining a screen angle. It is an example of the determination result of the correction | amendment area | region in the modification 1. It is an example of the determination result of the correction area | region in the modification 2.

  The configuration and operation of the image forming apparatus 1 according to the embodiment of the present disclosure will be described with reference to the drawings.

  The image forming apparatus 1 according to the present embodiment forms an image on a recording sheet based on a test pattern for detecting sub-scanning streaks, and performs sub-scanning based on an image generated by reading the recording sheet on which the test pattern is formed. When a streak is detected and a sub-scanning streak is detected, the screen processing settings for the next and subsequent times are changed so that the sub-scanning streak is not noticeable. In the following, processing for making sub-scanning lines inconspicuous may be referred to as sub-scanning line correction.

  FIG. 1 is a hardware configuration diagram of an image forming apparatus 1 according to an embodiment of the present invention.

  Referring to FIG. 1, an image forming apparatus 1 can be connected to an information processing apparatus 2 such as a personal computer (PC (Personal Computer)) via a network 3 such as a LAN (Local Area Network).

  Referring to FIG. 1, image forming apparatus 1 includes document reading unit 4, image forming unit 5, operation display unit 6, IF (Interface) unit 10, output image reading unit 13, and control unit 14. And a storage unit 15, which are connected via a bus.

  The control unit 14 is, for example, a CPU, and executes a program stored in the storage unit 15, thereby allowing the document reading unit 4, the image forming unit 5, the operation display unit 6, the IF unit 10, and the output image reading. The function of the image forming apparatus 1 is realized by controlling the unit 13 and the storage unit 15.

  The storage unit 15 mainly includes a RAM (Random Access Memory), a ROM (Read Only Memory), a HDD (Hard Disc Drive), and the like. The storage unit 15 stores data necessary for realizing the functions of the image forming apparatus 1 including the program executed by the control unit 14. Specifically, the storage unit 15 stores image data used for image formation, screen parameters related to screen processing, and the like. Details of the information stored in the storage unit 15 will be described later.

  The document reading unit 4 optically reads an image of a document transported to a reading position by an automatic document transport device or a document placed on a platen glass, generates image data, and stores the generated image data in the storage unit 15. Remember me.

  The IF unit 10 includes a LANIF (Local Area Network Interface) 11 and a storage medium IF 12. The LANIF 11 acquires print data transmitted from the information processing apparatus 2 via the network 3 and stores the print data in the storage unit 15. The storage medium IF 12 acquires print data from a portable storage medium such as an HDD, a USB (Universal Serial Bus) memory, an SD card, and stores the print data in the storage unit 15. The print data is data including an image corresponding to a predetermined type including characters, graphics, and images. For example, the print data is data described in a printer language such as PDL (Page Description Language). The print data may be data that can be edited by a general application, such as a PDF format or a TEXT format.

  The control unit 14 also functions as a RIP (Raster Image Processor) unit (not shown) and an image processing unit 22 (see FIG. 4). The RIP unit executes rasterization processing based on the print data acquired by the IF unit 10 and stored in the storage unit 15 to generate raster data. The image processing unit 22 performs image processing on the image data generated by the document reading unit 4 and the raster data generated by the RIP unit. In the following description, the image data generated by the document reading unit 4 and the raster data generated by the RIP unit are collectively referred to as raster data.

  The image processing unit 22 performs image processing on the raster data stored in the storage unit 15 and causes the storage unit 15 to store the image data after the image processing. Details of the image processing executed by the image processing unit 22 will be described later.

  The image forming unit 5 forms an image on the recording paper based on the image data after image processing stored in the storage unit 15. The image forming unit 5 includes print units corresponding to Y (yellow), M (magenta), C (cyan), and K (black) colors, and generates a toner image based on image data corresponding to YMCK colors. Then, an image is formed by transferring the toner image onto the recording paper.

  The output image reading unit 13 reads the image of the recording paper on which the image has been formed via a reading sensor provided on the recording paper conveyance path, and stores the read image in the storage unit 15. The reading sensor is, for example, a CIS type line sensor provided on a conveyance path located upstream of a paper discharge outlet from which recording paper is discharged. The output image reading unit 13 acquires a two-dimensional RGB color image corresponding to the recording paper by performing a reading operation in accordance with the timing at which the recording paper on which the image is formed is discharged. In the following description, data read by the output image reading unit 13 and stored in the storage unit 15 is referred to as output image read data. A reading sensor for reading output image reading data is called an inline sensor.

  The operation display unit 6 includes a display 7, a touch panel 8, and operation keys 9.

  The display 7 is a liquid crystal display (LCD (Liquid Crystal Display)), for example, and can display an operation screen. The operation screen includes, for example, a screen for notifying the user that a sub-scanning streak has occurred, and a screen for receiving screen settings related to screen processing from the user.

  The touch panel 8 is provided on the screen of the liquid crystal display and detects a coordinate position pressed with a pen, a finger, or the like.

  The operation key 9 is, for example, a hard key and includes a numeric keypad and a start key. The numeric keypad is a key for accepting input of numbers and symbols, and accepts numerical input related to screen settings. The start key accepts an instruction to start the operation of the image forming apparatus 1.

  FIG. 2 shows a functional block diagram of functions realized by the storage unit 15. The storage unit 15 functions as a print data storage unit 16, raster data storage unit 17, output image read data storage unit 18, test pattern storage unit 19, screen parameter storage unit 20, and sub-scanning streak correction flag storage unit 21.

  The print data storage unit 16 stores the print data acquired by the IF unit 10. The raster data storage unit 17 stores raster data generated by the document reading unit 4 or the RIP unit. The output image reading data storage unit 18 stores the output image reading data read by the output image reading unit 13.

  The test pattern storage unit 19 stores a test pattern used when detecting a sub-scanning line. The test pattern is YMCK data, and as shown in FIG. 3, is composed of gradation patterns corresponding to each of the YMCK colors whose gradation (density) changes in the sub-scanning direction (vertical direction). That is, the test pattern is a pattern having the same gradation in the main scanning direction (left-right direction) when viewed for each of YMCK. In FIG. 3, the Y-color pattern is composed of eight kinds of gradations corresponding to Y1 to Y8. The M color, the C color, and the K color are also composed of eight kinds of gradations as in the Y color. The test pattern shown in FIG. 3 is formed on, for example, an A3 size recording paper, and is read as output image reading data by the output image reading unit 13, whereby the sub-scanning streak is detected for each of the YMCK colors. The size of the test pattern in the main scanning direction is preferably a size corresponding to the effective area in the main scanning direction of the image forming apparatus 1 with the aim of detecting sub-scanning lines throughout the main scanning direction.

  Note that the test pattern shown in FIG. 3 is merely an example, and the number of gradations may be more or less than eight as long as the sub-scanning streaks for each YMCK color can be detected. May be a pattern in which an image is formed on different recording papers.

  The screen parameter storage unit 20 stores screen parameters used for screen processing. A detailed description of the screen parameters will be described later.

  The sub-scanning line correction flag storage unit 21 stores a sub-scanning line correction flag indicating whether the sub-scanning line correction function is enabled or disabled. Details of the sub-scanning streak correction flag will be described later.

  FIG. 4 is a functional block diagram of functions related to sub-scanning line correction. Functions related to sub-scanning line correction include an execution instruction receiving unit 33, an image processing unit 22, an image forming unit 5, an output image reading unit 13, a screen control unit 29, a notification unit 34, and a setting reception. Part 35 is included. At least the execution instruction reception unit 33, the image processing unit 22, the screen control unit 29, the notification unit 34, and the setting reception unit 35 are realized by the control unit 14 executing the program stored in the storage unit 15.

  The execution instruction receiving unit 33 receives a sub-scanning line detection execution instruction from the user. The execution instruction receiving unit 33 displays the screen shown in FIG. 7 on the operation display unit 6 and receives an execution instruction for sub-scanning streak detection from the user. When “Yes” is selected on the screen shown in FIG. 7, sub-scanning streak detection is executed.

  The execution instruction reception unit 33 may display the screen shown in FIG. 7 in response to the user performing a predetermined operation on the operation display unit 6 or by performing sub-scanning line detection first. May be automatically displayed in response to execution of image formation a predetermined number of times or more.

  Returning to FIG. 4, the image processing unit 22 performs image processing on the raster data generated by the document reading unit 4 and the RIP unit, and generates data for the image forming unit 5 to perform image formation. The image processing unit 22 executes image processing on the test pattern stored in the storage unit 15 when the image formation of the test patch is performed in order to detect the sub-scanning streak. Data for forming is generated.

  The image processing unit 22 includes a YMCK conversion unit 23, a γ correction unit 24, a filter processing unit 25, and a screen processing unit 26.

  The YMCK conversion unit 23 performs color conversion processing on raster data that is RGB data, and generates YMCK data.

  The γ correction unit 24 performs gradation correction (γ correction) on the YMCK data generated by the YMCK conversion unit 23. Specifically, based on the YMCK data generated by the YMCK conversion unit 23, a preset lookup table (LUT (Look Up Table)) is referred to and replaced with data stored in the LUT. Adjust the tone.

  The filter processing unit 25 performs sharpness processing and smoothing processing on the YMCK data after γ correction. The filter processing unit 25 performs a filter process corresponding to the type of image on each of the character area, the photographic area, and the graphic area included in the image data. For example, sharpness processing is performed on edge portions included in a character region, and smoothing processing is performed on a photographic region or a graphic region.

  Note that the image processing unit 22 uses an area determination unit (not shown) as to whether a pixel to be processed is included in a character area, a photographic area, or a graphic area (which image type corresponds to). The area determination unit performs area determination processing based on RGB data before color conversion by the YMCK conversion unit 23 or YMCK data after color conversion, and based on the result, the pixel to be processed Can be determined as a character area, a photograph area, or a graphic area. In the case of processing for print data acquired by the IF unit 10, the print data itself often includes attribute information indicating a character area, a photo area, and a graphic area, and is therefore included in the print data. Based on the attribute information, it may be determined whether a pixel to be processed is included in a character area, a photograph area, or a graphic area.

  The screen processing unit 26 performs screen processing on the YMCK data subjected to the filter processing. Specifically, threshold values are set in advance as a two-dimensional matrix, and the pixel values to be output to the image forming unit 5 are compared by comparing the pixel values to be processed with the threshold values corresponding to the pixel coordinates. decide.

  The screen is specified by a screen parameter including a screen line number indicating the fineness of the screen and a screen angle indicating the screen angle. The screen corresponding to each of the YMCK colors is a screen specified by a screen parameter with a different screen line number or / and a screen angle.

  Referring to FIG. 17A, screen parameters corresponding to three types of screens (screens 1 to 3) are shown. The screen 1 has a Y-color screen with a line number of 150.0 lpi and an angle of 90 °, an M-color screen with a line number of 166.4 lpi and an angle of 56.3 °, and a C-color screen with a line number of 166.4 lpi and an angle of −56. .3 °, K-color screen shows a line number of 189.7 lpi and an angle of −71.6 °. A detailed description of the screens 2 and 3 will be omitted.

  lpi is a unit of the number of screen lines, and indicates the number of patterns repeated per inch. The smaller the lpi value, the lower the screen resolution (coarse).

  FIG. 17B is a diagram for explaining the screen angle of the screen 1 shown in FIG. Referring to FIG. 17B, the screen angle indicates an angle formed between the horizontal axis and the screen pattern when the horizontal axis is the main scanning direction. The reference of the screen angle shown as the horizontal axis in FIG. 17B can be an arbitrary direction. For example, it can be the sub-scanning direction instead of the main scanning direction.

  In the three types of screens shown in FIG. 17A, the screen line number of the screen 1 is the lowest, and the screen line number increases as going to the screen 2 and the screen 3.

  The image processing unit 22 does not execute the processes by the YMCK conversion unit 23, the γ correction unit 24, and the filter processing unit 25 when executing test pattern image formation to detect the sub-scanning streak. Only the screen processing by the screen processing unit 26 is executed on the test pattern (YMCK data) stored in FIG.

  The image forming unit 5 forms an image on the recording paper based on the YMCK data subjected to the screen processing.

  The output image reading unit 13 reads an image of the recording sheet on which an image has been formed via a reading sensor (not shown) provided on the recording paper conveyance path, and the storage unit 15 uses the read image as output image reading data. Remember me.

  The screen control unit 29 detects a sub-scanning streak based on the output image read data, and changes the screen parameter as sub-scanning streak correction when the sub-scanning streak is detected.

  The screen control unit 29 includes a streak detection unit 30, a correction area determination unit 31, and a screen change unit 32. The streak detection unit 30 detects sub-scanning streaks using output image reading data of recording paper on which an image is formed based on a test pattern. Further, when the sub-scanning streak is detected, the streak detection unit 30 detects the position of the sub-scanning streak (in the main scanning direction) and the width of the sub-scanning streak.

  The streak detector 30 detects a sub-scanning streak based on the luminance value. The streak detection unit 30 converts output image read data, which is RGB data, into luminance data. Specifically, as shown in the equation (1), each of the RGB data values is multiplied by a predetermined coefficient (x, y, z), and these values are added together to obtain a luminance value for each pixel. Is calculated.

    V = R × x + G × y + B × z (1)

  As shown in FIG. 3, since the test pattern is a pattern having the same gradation in the main scanning direction, in an ideal situation where there is no sub-scanning streak, the test pattern in the main scanning direction at a predetermined position in the sub-scanning direction is used. Pixel values should be equal. On the other hand, in a situation where sub-scanning streaks occur, pixel values in the main scanning direction vary. Specifically, the luminance value (pixel value) is low at a position where a black line occurs, and the pixel value is high at a position where a white line occurs.

  The streak detection unit 30 calculates data as shown in FIG. 5 by accumulating the respective pixel values in the main scanning direction in the sub-scanning direction for each region having the same gradation in the test pattern. In FIG. 5, the horizontal axis indicates the position in the main scanning direction, and the vertical axis indicates the luminance value integration result. In the following, data as shown in FIG. 5 calculated by integration is referred to as profile data. FIG. 5A shows an example of profile data corresponding to the K1 gradation of the test pattern shown in FIG. Similarly, FIGS. 5B to 5H show examples of profile data corresponding to the gradations K2 to K8, respectively.

  The streak detection unit 30 detects the presence or absence of a sub-scanning streak based on the profile data. Specifically, the streak detection unit 30 detects the presence or absence of a sub-scanning streak by performing peak detection in the profile data. Since a known method can be used for the peak detection method, a detailed description thereof is omitted here. The streak detection unit 30 performs peak detection in profile data corresponding to each of a plurality of gradations (in the case of K color, each of FIGS. 5A to 5H) to detect sub-scanning streaks. The reason for performing peak detection for each of a plurality of gradations is that the visibility (degree of occurrence) of black and white stripes depends on the gradation, so by detecting the occurrence of stripes at multiple gradations, This is because the accuracy of streak detection can be improved.

  The streak detection unit 30 detects that a sub-scanning streak has occurred when a peak is detected at any of a plurality of gradations. In FIG. 5, a white peak is detected at position a in the main scanning direction in the profile data corresponding to the gradations K1 to K4, and at the position a in the main scanning direction with the profile data corresponding to the gradations K7 to K8. An example in which a black peak is detected is shown. In this case, a white peak is detected at a position and a black peak is detected at a position. The streak detection unit 30 detects that a sub-scanning streak has occurred when a peak is detected in any of the YMCK colors.

  When a peak is detected, the streak detection unit 30 detects the coordinates in the main scanning direction at the center of the peak as the sub-scanning streak position. The streak detection unit 30 detects the peak width as the sub-scanning streak width. When peaks are detected at the same position in profile data corresponding to a plurality of gradations in each of the YMCK colors, the peak appears most prominently among the plurality of peaks detected at the same position (white peak). In this case, the peak width in the profile data of gradation is detected as the sub-scanning stripe width. Here, as the peak width, for example, a half-value width (a peak width at a position half the height of the peak) can be used. In FIG. 5, one black streak and one white streak are detected. The white streak has a sub-scanning streak position a and a sub-scanning streak width α, and the black streak has a sub-scanning streak position a. The scanning stripe width is β. The peak width is not limited to the half width as described above.

  The correction area determination unit 31 determines an area where the sub-scanning stripe is generated as a correction area for executing the sub-scanning stripe correction. Specifically, an area having a sub-scanning stripe width centered on the sub-scanning stripe position is determined as a correction area. When a sub-scanning streak is detected based on the profile data shown in FIG. 5, as shown in FIG. 6 (a), an area of α width centering on a in the main scanning direction and a in the main scanning direction are centered. And a β-width region is detected as a correction region.

  Here, as shown in FIG. 6B, the correction area determination unit 31 determines the correction area including the area of the sub-scanning stripe width centered on the sub-scanning stripe position and the area close to the area. May be. For example, the correction area determination unit 31 determines, as a correction area, an area that is a combination of a sub-scanning stripe width area centered on the sub-scanning stripe position and a predetermined number of pixels (for example, 50 pixels) on both sides of the area. Also good. The correction area determination unit 31 determines an area other than the correction area as a non-correction area.

  The screen changing unit 32 changes the screen parameter based on the determination result of the correction area. Specifically, the screen changing unit 32 changes the screen parameter in the screen processing unit 26 based on whether it is a correction region or a non-correction region.

  The screen changing unit 32 changes the screen parameters so that the number of screen lines in the correction area is lower than the number of screen lines in the non-correction area. By reducing the number of screen lines in the correction area, the sub-scanning stripe can be made inconspicuous. Here, if the number of screen lines is made lower, the effect of making the sub-scanning streak inconspicuous is greater. In the following, the fact that the effect of making the sub-scanning lines inconspicuous is large is referred to as the high correction strength of the sub-scanning lines.

  Further, the screen changing unit 32 sets an angle that is 0 °, 90 °, + 45 °, or −45 ° with respect to the main scanning direction as a predetermined angle, and the difference in screen angle in the correction region with respect to the predetermined angle is The screen parameter is changed so as to be larger than the difference of the screen angle in the non-correction area with respect to the predetermined angle. The sub-scanning stripe can be made inconspicuous by changing so that the difference in the screen angle in the correction area with respect to the predetermined angle becomes large. If the difference in the screen angle in the correction area with respect to the predetermined angle is made larger, the correction intensity of the sub-scanning stripe becomes larger.

  A plurality of angles can be used among the angles of 0 °, 90 °, + 45 °, and −45 ° with respect to the main scanning direction. For the sake of explanation, if 0 ° and 90 ° are set to a predetermined angle, the sub-scanning streak is made by bringing the screen angle close to + 45 ° or −45 ° at which the difference between 0 ° and 90 ° is maximum. The correction intensity can be increased.

  Note that the predetermined angle may be an angle other than the angles of 0 °, 90 °, + 45 °, and −45 ° with respect to the main scanning direction. The screen changing unit 32 may change both the screen line number and the screen angle in the correction area, or may change either the screen line number or the screen angle.

  The screen changing unit 32 may change the screen in all the correction regions, or may change the screen only for pixels corresponding to a predetermined image type in the correction region. Specifically, the screen may be changed only for an area other than the character area among the character area, the photograph area, and the graphic area included in the correction area. Whether the pixel to be processed is included in a character area, a photographic area, or a graphic area, as described above, the determination result by the area determination unit may be used, or the attribute data included in the print data You may judge using.

  When the sub scanning line is detected, the notification unit 34 notifies the user through the operation display unit 6 that the sub scanning line has been detected. For example, the notification unit 34 displays a notification screen as shown in FIG. 8 on the operation display unit 6 to notify the user that a sub-scanning streak has been detected. The notification screen includes a message for notifying that a sub-scanning streak has been detected and a button for accepting a setting as to whether to enable sub-scanning streak correction from the user. That is, the operation display unit 6 receives a setting as to whether or not to correct the sub-scanning streak. In the screen shown in FIG. 8, when the “Yes” button is pressed, the sub-scanning line correction is enabled, and when the “No” button is pressed, the sub-scanning line correction is disabled.

  The setting receiving unit 35 receives a setting of a screen parameter in the correction area (hereinafter also referred to as a correction area screen parameter). In other words, the operation display unit 6 receives a setting relating to a correction area for correcting the sub-scanning stripe. Specifically, the setting of the screen line number and the screen angle corresponding to each of the YMCK colors is accepted. For example, the setting reception unit 35 displays a setting screen as illustrated in FIG. 9 on the operation display unit 6 and receives an input to the setting box, thereby receiving a screen parameter setting. The setting accepting unit 35 may accept input of numerical values of the screen line number and the screen angle via the numeric keypad. For example, a plurality of screen parameters as shown in FIG. A plurality of options regarding the number and the screen angle may be displayed, and a selection may be accepted from the options. The setting accepting unit 35 may individually accept the setting (selection) of the screen parameters for each of the YMCK colors. Alternatively, the setting accepting unit 35 may register a combination of a plurality of YMCK color screens in advance. You may accept the selection.

  The setting receiving unit 35 may receive the setting of the screen parameter in the non-correction area (hereinafter also referred to as the non-correction area screen parameter) together with the setting of the screen parameter in the correction area.

  When the sub-scanning line correction is performed, there is a merit that the sub-scanning line can be made inconspicuous, but a demerit such as a decrease in resolution may occur. Therefore, by setting the screen parameters in the correction area by the user, the user can determine the balance between the advantages and disadvantages of the sub-scanning stripe correction.

  The setting receiving unit 35 receives a setting of a range in which sub-scanning line correction is executed. The setting accepting unit 35 accepts a setting (selection) as to whether to perform sub-scanning streak correction on the entire image or only to the correction area when sub-scanning streaks are detected. In addition, when the sub-scanning line correction is performed only on the correction area, the setting reception unit 35 receives a setting (selection) on how wide the width of the correction area is with respect to the sub-scanning line width.

  For example, the setting reception unit 35 displays the screen illustrated in FIG. 10 on the operation display unit 6 and receives a setting of a range (sub-scanning line correction width) for performing sub-scanning line correction. When “entire surface” is selected on the screen shown in FIG. 10, the sub-scanning line correction is executed on the entire image when the sub-scanning line is detected. When “narrow” is selected, the width of the correction area is made equal to the sub-scanning stripe width. That is, the sub-scanning line correction is performed only on the area having the sub-scanning line width. When “medium” is selected, the width of the correction region is set to a region combining the sub-scanning stripe width region and a predetermined number of pixels (for example, 50 pixels) on both sides thereof. That is, the sub-scanning line correction is performed on an area wider than the sub-scanning line width. When “wide” is selected, sub-scanning line correction is performed on an area wider than “medium” (for example, an area having a sub-scanning line width and 100 pixels on both sides).

  The user selects one of “narrow”, “medium”, “wide”, and “entire surface” on the screen shown in FIG. 10 to set a range (sub-scanning line correction width) for executing sub-scanning line correction. be able to. Here, if the sub-scanning line correction width is further increased, the correction intensity of the sub-scanning line is increased.

  The setting receiving unit 35 receives a predetermined condition as the setting of the sub-scanning stripe width that is the target of sub-scanning line correction. If the sub-scanning line width is too large, even if the screen parameter is changed and the sub-scanning line correction is performed, the effect of the correction is low, and only the image quality deterioration (decrease in resolution) caused by changing the screen parameter is conspicuous. become. Therefore, for example, the setting reception unit 35 displays the screen illustrated in FIG. 10 on the operation display unit 6 and receives a selection as to whether or not to set the upper limit value of the sub-scanning stripe width that is the target of sub-scanning line correction. When “no upper limit” is selected, correction areas are set corresponding to all detected sub-scanning stripes, and sub-scanning stripe correction is executed. When “with upper limit” is selected, a correction area is set only for the sub-scanning stripes having a width equal to or smaller than the line width specified in the box, and the sub-scanning line correction is executed. In other words, even if there is a sub-scanning line having a width wider than the line width specified in the box, the correction area is not set, and the sub-scanning line correction for the sub-scanning line is not executed. In the case of the example in FIG. 10, sub-scanning line correction is executed for sub-scanning lines having a width of 8 mm or less, and sub-scanning line correction is not executed for sub-scanning lines having a width wider than 8 mm.

  In this way, sub-scanning streak correction is not performed for sub-scanning streaks having a low effect on sub-scanning streak correction. In other words, sub-scanning only for sub-scanning streaks having the effect of sub-scanning streak correction is performed. By executing the line correction, it is possible to suppress useless image quality deterioration (resolution reduction).

  12 to 16 are flowcharts illustrating processing related to sub-scanning line correction, which is executed by the image forming apparatus 1. The control unit 14 executes the processes shown in FIGS. 12 to 16 by executing the program stored in the storage unit 15.

  FIG. 12 is a main routine of processing related to sub-scanning line correction. The image forming apparatus 1 accepts settings related to sub-scanning streak correction from the user (step S101), performs sub-scanning streaking (sub-scanning streak detection) based on the settings accepted from the user (step S102), and performs image formation. Sub-scanning line correction (sub-scanning line correction) is performed (step S103).

  FIG. 13 is a subroutine showing a setting reception process. The image forming apparatus 1 receives the setting of the correction area screen parameter from the user (step S201). For example, the setting screen as shown in FIG. 9 is displayed on the operation display unit 6 and the setting of the screen parameter is accepted by accepting the input to the setting box.

  The image forming apparatus 1 receives a setting of a range for performing the sub-scanning line correction from the user (step S202). For example, the screen shown in FIG. 10 is displayed on the operation display unit 6 and the setting of the range in which the sub-scanning line correction is executed is accepted.

  The image forming apparatus 1 receives the setting of the sub-scanning stripe width that is the target of sub-scanning stripe correction from the user (step S203). For example, the screen shown in FIG. 10 is displayed on the operation display unit 6, and a setting as to whether or not to set the upper limit value of the sub-scanning stripe width that is the sub-scanning stripe correction target is accepted from the user. When the upper limit value is set, the setting of the stripe width (line width) as the upper limit value is also accepted.

  When the image forming apparatus 1 receives the setting of the sub-scanning streak width that is the target of sub-scanning streak correction (step S203), the image forming apparatus 1 returns to the main routine shown in FIG. 12 and executes the sub-scanning streak detection process (step S102). .

  FIG. 14 is a subroutine showing sub-scanning line detection processing. The image forming apparatus 1 waits until receiving a sub-scanning line detection execution instruction from the user (step S301). The screen shown in FIG. 7 is displayed on the operation display unit 6, and when “Yes” is selected, it is determined that a sub-scanning line detection execution instruction has been received (YES in step S 301).

  When the image forming apparatus 1 receives a sub-scanning line detection execution instruction (YES in step S301), the image forming apparatus 1 executes image formation based on the test pattern (step S302). For example, the image forming apparatus 1 forms an image on an A3 size recording sheet based on the test pattern shown in FIG.

  The image forming apparatus 1 reads an image of a recording sheet on which an image is formed based on a test pattern, acquires output image reading data (step S303), and executes sub-scanning streak detection based on the output image reading data (step S303). Step S304).

  When the image forming apparatus 1 detects the sub-scanning line (YES in step S305), the image forming apparatus 1 notifies the user that the sub-scanning line has been detected (step S306). For example, the image forming apparatus 1 displays the screen illustrated in FIG. 8 on the operation display unit 6 to notify the user that a sub-scanning line has been detected.

  The image forming apparatus 1 determines a correction area for the detected sub-scanning stripe (step S307). FIG. 15 is a subroutine of processing for determining a correction area. The image forming apparatus 1 determines whether or not the upper limit value of the sub-scanning stripe width that is the target of sub-scanning line correction is set (step S401). When the upper limit value of the sub-scanning stripe width to be corrected is set (YES in step S401), it is determined whether or not the detected sub-scanning stripe width is equal to or smaller than the upper limit value (step S402).

  When the detected sub-scanning stripe width is equal to or smaller than the upper limit value (YES in step S402), the image forming apparatus 1 sets any of “narrow”, “medium”, “wide”, and “entire surface” on the screen shown in FIG. A correction area is determined according to whether it has been done (step S403). When “Narrow” is set, the sub-scanning stripe width is determined as a correction area (step S404). When “Medium” is set, the area of the sub-scanning stripe width and the 50 pixels on both sides are corrected. An area is determined (step S405), and when “wide” is set, an area including the sub-scanning stripe width area and 100 pixels on both sides thereof is determined as a correction area (step S406), and “entire surface” is set. If so, the entire image is determined as a correction area (step S407).

  When it is determined in step S401 that the upper limit value of the sub-scanning line width that is the target of sub-scanning line correction is not set (NO in step S401), the image forming apparatus 1 determines the sub-scanning line width in step S402. Without determination, the process proceeds to step S403. That is, correction areas are determined for all detected sub-scanning stripes.

  If it is determined in step S402 that the detected sub-scanning stripe width is larger than the upper limit (NO in step S402), the image forming apparatus 1 proceeds to step S408 without setting a correction area.

  Since a plurality of sub-scanning lines may be detected, the image forming apparatus 1 determines in step S408 whether or not the processing for all detected sub-scanning lines has been completed, and the remaining sub-scanning lines are detected. If there is, the process returns to step S401, and the processes of steps S401 to S408 are repeated until the processes for all detected sub-scanning stripes are completed. When the processing for all the detected sub-scanning lines is completed (YES in step S408), the process returns to the sub-scanning line detection subroutine shown in FIG.

  Referring to FIG. 14, in step S308, image forming apparatus 1 displays the screen shown in FIG. 8 on operation display unit 6, and accepts a setting as to whether or not to enable sub-scanning line correction from the user. When a setting for enabling the sub-scanning line correction is received from the user (YES in step S308), the sub-scanning line correction flag is set to be effective (step S309).

  When no sub-scanning streak is detected in step S305 (NO in step S305), or when a setting indicating that sub-scanning streak correction is not enabled is accepted in step S308 (NO in step S308), sub-scanning streak correction is performed. The flag is set to be invalid (step S310).

  When the above processing ends, the image forming apparatus 1 returns to the main routine shown in FIG.

  Referring to FIG. 12, in step S103, image forming apparatus 1 performs sub-scanning line correction when performing image formation in accordance with an instruction from the user (step S103). FIG. 16 is a subroutine showing processing relating to sub-scanning streak correction executed at the time of image formation.

  When the image forming apparatus 1 executes the screen process for the processing target pixel, it is determined whether or not the sub-scanning streak correction flag is valid (step S501). When the sub-scanning streak correction flag is valid (YES in step S501), the image forming apparatus 1 determines whether the image type of the processing target pixel is a predetermined type (step S502). Specifically, it is determined whether the image type of the pixel to be processed is a character area, a photograph area, or a graphic area other than the character area.

  When the processing target pixel is outside the character area (YES in step S502), it is determined whether or not the processing target pixel is included in the correction area (step S503). When the pixel to be processed is included in the correction area (YES in step S503), the image forming apparatus 1 selects the correction area screen parameter and executes screen processing (step S504).

  On the other hand, when it is determined in step S501 that the sub-scanning streak correction flag is not valid (NO in step S501), in step S502, it is determined that the image type of the processing target pixel is a character area (NO in step S502). ) When it is determined in step S503 that the processing target pixel is not included in the correction area (NO in step S503), the image forming apparatus 1 selects the non-correction area screen parameter and executes the screen process (step S503). S505).

  In step S506, the image forming apparatus 1 determines whether or not processing for all pixels has been completed. If processing for all pixels has not been completed (NO in step S506), the process returns to step S501. The processing in steps S501 to S506 is repeated until the processing for all the pixels is completed, and when the processing for all the pixels is completed (YES in step S506), the processing returns to the main routine shown in FIG.

  The image forming apparatus 1 according to the present embodiment performs screen processing on a test pattern (first image), generates a screen-processed image (second image), and performs screen processing. Output image read data (first image) generated by an image forming unit 5 that forms an image on a recording sheet based on the image (second image) and a reading unit (output image reading unit 13) that reads the recording sheet on which the image has been formed. 3), and a screen changing unit 32 that changes the content of the screen processing in the area corresponding to the sub-scanning line detected by the streak detecting unit 30. Thus, it becomes possible to change the contents of the screen processing of the area corresponding to the sub-scanning line based on the detection result of the sub-scanning line, without requiring cleaning or replacement of the unit or the like. Since can be corrected subscanning streaks, without depending on the environment, over a long period of time, it is possible to suppress the quality degradation of an output image due to the sub-scanning stripes.

  Changing the screen has the effect of making the sub-scanning lines inconspicuous, but may have the side effect of reducing the resolution, for example. Also, depending on the type of image, there are some that have a large effect of making sub-scanning lines inconspicuous, and some that have a small side effect but large side effects.

  Therefore, in the image forming apparatus 1 according to the present embodiment, the screen changing unit 32 changes the content of the screen processing in the area corresponding to the sub-scanning stripe for a predetermined pixel type among the plurality of pixel types, For other pixel types other than the predetermined pixel type, by not changing the contents of the screen processing in the area corresponding to the sub-scanning streak, side effects due to the screen change are suppressed, and the sub-scanning streak is inconspicuous can do.

  More specifically, the image forming apparatus 1 of the present embodiment performs sub-scanning line correction when the type of pixels included in the correction area is a predetermined type. For character images, the image quality is less likely to deteriorate due to sub-scanning lines compared to other image types, but the side effect (decrease in resolution) caused by changing the screen is large. By executing the sub-scanning line correction when the area is out of the area, the side-scanning streaks can be made inconspicuous while suppressing the side effects caused by changing the screen.

  Note that the image forming apparatus 1 of the present embodiment displays the screen shown in FIG. 10 on the operation display unit 6, and when “medium” is set, the sub-scanning stripe width region and 50 pixels on both sides thereof are combined. The area is determined as the correction area (step S405), and when “wide” is set, the area including the sub-scanning stripe width area and 100 pixels on both sides is determined as the correction area (step S406). The numerical values such as 50 pixels and 100 pixels included in the correction area are merely examples, and can be appropriately changed according to the conditions to be implemented.

(Modification 1)
In the above embodiment, the area is set to either the correction area or the non-correction area and the screen is changed. However, in the present modification, the first correction area and the second correction area are used as the correction areas. The screen processing is performed using different screen parameters for the first correction area, the second correction area, and the non-correction area.

  FIG. 18 shows an example of the correction area determination result of the correction area determination unit 31 in this modification. When the sub-scanning streak shown in FIG. 6A is detected, the correction region determining unit 31 in the present modification first performs a first correction on a region corresponding to the sub-scanning streak width (a region indicated by black in FIG. 18). An area of a predetermined number of pixels (for example, 50 pixels) on both sides of the sub-scanning stripe width is determined as a second correction area, and the other areas are determined as non-correction areas. That is, the correction area determination unit 31 determines the second correction area on both ends of the correction area, and determines the first correction area between the second correction areas.

  The screen control unit 29 in the present modification performs screen processing using different screen parameters for the first correction area, the second correction area, and the non-correction area. Specifically, the screen of the second correction area is a screen having a correction intensity lower than that of the screen of the first correction area. In other words, the number of lines and the angle of the screen in the second correction area are set to intermediate values between the screen in the first correction area and the screen in the non-correction area.

  If the number of screen lines and the screen angle are significantly changed, the boundary where the screen is changed is noticeable, and the image quality may be deteriorated. As in this modification, by changing the number of lines and the angle of the screen in stages, the boundary where the screen is changed can be made inconspicuous, and deterioration in image quality can be suppressed.

(Modification 2)
In the above embodiment, as shown in FIGS. 6A and 6B, the correction region is set at the same position in the main scanning direction along the sub scanning direction. However, as shown in FIG. A correction area is set so that the position in the main scanning direction is different along the line. In FIG. 19, when a gray area is detected as the sub-scanning stripe width, an area wider than the sub-scanning stripe width is set as a correction area, and the boundary between the correction area and the non-correction area in the main scanning direction is set. The correction area is set so that the position is at least partially different. In FIG. 19, a region obtained by combining a region indicated by gray and a region indicated by black is a correction region. That is, the correction area determination unit 31 determines that the position in the main scanning direction of the boundary at a certain position (first position) in the sub-scanning direction is different from the certain position in the sub-scanning direction (second position). The correction area is determined so that the position of the boundary in the main scanning direction is different.

  Note that, as in Modification 1, the gray area in FIG. 19 is set as the first correction area, the black area is set as the second correction area, and the first correction area and the second correction area are set. Different screens may be used in the correction area.

  In the example of FIG. 19, the width of the correction area in the main scanning direction at each position in the sub-scanning direction is constant, and the correction area and the non-correction area in the main scanning direction are changed by changing the position of the correction area. The boundary position is changed along the sub-scanning direction. By changing the size of the correction area in the sub-scanning direction, the boundary position between the correction area in the main scanning direction and the non-correction area is changed in the sub-scanning direction. You may make it change along.

  If the positions in the main scanning direction for changing the number of screen lines and the screen angle are aligned along the sub-scanning direction, the boundary where the screen is changed may be noticeable and the image quality may be deteriorated. As in this modification, by changing the position of the screen change point in the main scanning direction along the sub-scanning direction, the boundary where the screen is changed can be made inconspicuous, and deterioration in image quality can be suppressed. it can.

(Modification 3)
In the above embodiment, as shown in FIG. 9, the setting receiving unit 35 receives the setting of the screen line number and the screen angle in the correction area. However, as shown in FIG. You may accept the selection. In this case, screen parameters and sub-scanning stripe correction widths corresponding to the correction strengths of the respective sub-scanning stripes are registered in advance, and screen parameters and sub-scanning stripe correction widths corresponding to the correction strength selected by the user are set. The In the example of FIG. 11, the user can select a correction strength from three options “weak”, “medium”, and “strong” for the correction strength of the sub-scanning streak.

  In this way, even if the user has insufficient knowledge about the screen parameters by accepting the selection of the intensity of the sub-scanning streak from the user and automatically setting the screen parameter and the sub-scanning streak correction width according to the intensity. A desired sub-scanning streak correction strength can be easily set.

(Modification 4)
In the above embodiment, the streak detection unit 30 detects the sub-scanning streak without distinguishing the YMCK color when a peak is detected in any of the profile data of YMCK color, and the screen changing unit 32 detects the peak. The screen of the area corresponding to the sub-scanning line is changed. For example, even when a sub-scanning streak is detected only with an image corresponding to M color, the YMCK color screen is changed together.

  One of the factors that determine the combination of the YMCK color screens, such as the screens 1 to 3 in FIG. 17A, is moiré suppression. For example, if any one of the YMCK colors is changed, moiré characteristics are obtained. May get worse. By collectively changing the YMCK color screen, it is possible to suppress the deterioration of the moire characteristics.

  In this modification, the streak detection unit 30 detects sub-scanning streaks individually for each of the YMCK colors, and the screen changing unit 32 does not change all the YMCK color screens, but detects the sub-scanning streaks among the YMCK colors. Change at least one screen containing the rendered color.

  At this time, the screen changing unit 32 replaces the screen of the color in which the sub-scanning streak is detected with the screen of the color in which the sub-scanning streak is not detected while maintaining the combination of the screens before the change. If there are multiple colors for which no sub-scanning streak has been detected, the screen with the color for which the sub-scanning streak has been detected is the screen with the sub-scanning streak that has the highest correction strength. Change to a larger screen. Also, when there are multiple colors for which sub-scanning streaks have been detected, it is determined which color and which color screen are to be replaced according to the degree of sub-scanning streaks (sub-scanning stripe width and the number of sub-scanning streaks) You may do it. For example, a screen with the highest (bad) color of the sub-scanning streak is replaced with a screen with the highest correction strength of the sub-scanning streak among the screens where the sub-scanning streak is not detected. Of the screens in which the sub-scanning streak is not detected, the large color screen is replaced with the screen having the second largest correction intensity of the sub-scanning streak.

  Further, the screen changing unit 32 may change the screen of the color in which the sub-scanning streak is detected to a screen that is not included in the original screen combination.

(Modification 5)
In the above embodiment, the streak detection unit 30 changes the screen of the area corresponding to the detected sub-scanning streak to a screen set in advance by the user.

  In this modification, the streak detection unit 30 detects sub-scanning streaks individually for each of the YMCK colors, and the screen changing unit 32 determines a predetermined screen combination based on the sub-scanning streak detection results for each of the YMCK colors. The screen of the area corresponding to the detected sub-scanning stripe may be automatically determined from the above.

  Specifically, for example, when five types of screens are registered in advance as sub-scanning streak correction screens, and a sub-scanning streak is detected only with an image corresponding to M color, a sub-scanning streak of M color is detected. Change to the screen with the largest reinforcement strength.

  The screen changing unit 32 automatically sets a screen on which no sub-scanning streaking occurs, so that even a user who does not have sufficient knowledge about screen parameters can easily set a desired sub-scanning streak correction intensity. it can.

(Other variations)
In the above-described embodiment, settings are accepted from the user via the operation display unit 6 or notification to the user is executed. However, the information processing apparatus 2 connected to the image forming apparatus 1 via the network 3 is an input device. It is also possible to receive settings from the user via the user or to notify the user via a display device (for example, a display screen of a PC) provided in the information processing device 2.

  In the above-described embodiment, the output image reading unit 13 performs the reading operation in accordance with the timing at which the image-formed recording paper is discharged and generates (acquires) output image reading data. The recording paper on which the test pattern is formed may be read to generate (acquire) output image reading data.

  In the above embodiment, the output image reading unit 13 performs the reading operation in accordance with the timing at which the image-formed recording paper is discharged, and generates (acquires) the output image reading data. The sensor may read the recording paper on which the test pattern is formed and generate (acquire) output image reading data.

  In the above embodiment, the reading sensor provided on the transport path positioned upstream of the paper discharge outlet from which the recording paper is discharged reads the recording paper. However, the reading sensor can be changed as appropriate according to the embodiment. For example, a reading sensor may be provided on an intermediate transfer member provided in the image forming apparatus or on a photosensitive member. When a reading sensor is provided on the intermediate transfer member or the photoconductor, the reading sensor reads a toner image formed by the intermediate transfer member or the photoconductor.

  The image forming apparatus 1 in the above embodiment is a so-called multi-function image forming apparatus 1 (MFP) that includes the document reading unit 4 and the image forming unit 5, but an image that does not include the document reading unit 4 such as a printer. The forming apparatus 1 may be used.

  In addition, although this embodiment and the modification which concerns on this embodiment were demonstrated separately, it can be implemented combining embodiment and the modification which can be combined among embodiment and the modification.

  Note that the screen displayed on the operation display unit 6 of the image forming apparatus 1 in the present embodiment and the modification according to the present embodiment is not limited to this form and message. Modifications can be made as appropriate without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Information processing apparatus 3 Network 4 Document reading part 5 Image forming part 6 Operation display part 7 Display 8 Touch panel 9 Operation key 10 IF part 11 LANIF
12 Storage media IF
13 Output image reading unit 14 Control unit 15 Storage unit 16 Print data storage unit 17 Raster data storage unit 18 Output image read data storage unit 19 Test pattern storage unit 20 Screen parameter storage unit 21 Sub-scanning streak correction flag storage unit 22 Image processing unit 23 YMCK conversion unit 24 γ correction unit 25 Filter processing unit 26 Screen processing unit 29 Screen control unit 30 Line detection unit 31 Correction area determination unit 32 Screen change unit 33 Execution instruction reception unit 34 Notification unit 35 Setting reception unit Scanning stripe position A Black stripe subscanning stripe position α White stripe subscanning stripe width β Black stripe subscanning stripe width

Claims (15)

An operation display that accepts user operations;
A screen processing unit that performs screen processing on the first image and generates a second image;
An image forming unit that forms an image on a recording sheet based on the second image generated by the screen processing unit;
A line detection unit that detects a sub-scanning line based on a third image generated by a reading unit that reads the recording paper on which the image forming unit has formed an image;
A screen changing unit that changes the content of the screen processing in the area corresponding to the sub-scanning stripe detected by the stripe detection unit;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the screen changing unit changes the number of screen lines in an area corresponding to the sub-scanning stripe.   The image forming apparatus according to claim 1, wherein the screen changing unit changes a screen angle of an area corresponding to the sub-scanning stripe.   3. The screen change unit according to claim 2, wherein the number of screen lines in an area corresponding to the sub-scanning stripe is set lower than the number of screen lines in an area other than the area corresponding to the sub-scanning stripe. The image forming apparatus described.   The screen changing unit is configured to determine a difference in screen angle of an area corresponding to the sub-scanning stripe with respect to a predetermined angle, and a difference in screen angle of an area other than the area corresponding to the sub-scanning stripe with respect to the predetermined angle. The image forming apparatus according to claim 3, wherein the image forming apparatus is larger than the image forming apparatus. The operation display unit receives a setting as to whether or not to correct the sub-scanning streak from a user,
The said screen change part changes the content of the said screen process of the area | region corresponding to the said subscanning stripe based on the setting which the said operation display part received, The any one of Claims 1-5 characterized by the above-mentioned. The image forming apparatus described in 1. The operation display unit receives a setting related to a correction area for correcting the sub-scanning streak from a user,
A correction region determining unit that determines the correction region based on the setting related to the correction region received from the user by the operation display unit;
The image forming apparatus according to claim 1, wherein the screen changing unit changes the content of the screen processing of the correction area determined by the correction area determining unit.   The image forming apparatus according to claim 7, wherein the setting relating to the correction area is a setting for changing a width of the correction area. The stripe detection unit detects the width of the sub-scanning stripe,
The image forming apparatus according to claim 1, wherein the screen changing unit changes the content of the screen processing when a width of the sub-scanning stripe satisfies a predetermined condition. . The operation display unit receives a parameter setting related to the screen processing in an area corresponding to the sub-scanning line from a user,
The image forming apparatus according to claim 1, wherein the screen changing unit changes the content of the screen processing in an area corresponding to the sub-scanning line based on the parameter. .   The screen changing unit changes the content of the screen processing in an area corresponding to the sub-scanning stripe for a predetermined pixel type among a plurality of pixel types, and other pixels other than the predetermined pixel type The image forming apparatus according to claim 1, wherein the content of the screen processing in the area corresponding to the sub-scanning stripe is not changed. A correction area determining unit that determines a correction area for correcting the sub-scanning stripe;
The correction area determination unit determines a first correction area and a second correction area other than the first correction area as the correction area, and determines a non-correction area other than the correction area,
The screen changing unit changes the contents of the screen processing so that the contents of the screen processing in the first correction area, the second correction area, and the non-correction area are different from each other. The image forming apparatus according to claim 1. The second correction area is determined on both ends of the correction area with respect to the main scanning direction,
The image forming apparatus according to claim 12, wherein the first correction area is determined between the second correction areas.   The screen changing unit is configured so that the content of the screen processing in the second correction area is the number of screen lines intermediate between the first correction area and the non-correction area, and / or the screen angle. 14. The image forming apparatus according to claim 12, wherein the content of the screen processing is changed. A correction area determining unit that determines a correction area for correcting the sub-scanning stripe;
The correction area determination unit is configured to detect the boundary in the main scanning direction at the first position in the sub-scanning direction, and the boundary in the main scanning direction at the second position different from the first position in the sub-scanning direction. Determine the correction area so that the position is different,
The image forming apparatus according to claim 1, wherein the screen changing unit changes the content of the screen processing of the correction area determined by the correction area determining unit.