JP2019145994A - Magnification fluctuation correction method and image processing device - Google Patents

Abstract

To provide a magnification fluctuation correction method or the like capable of correcting a partial magnification deviation generated in reading only by a sheet to be printed.SOLUTION: An inline reading device 15 includes two reading sensors disposed at a distance in a sheet conveyance direction. An image printing part 13 is configured to print a test chart including a plurality of edge images each having an outline substantially orthogonal to the sheet conveyance direction, and an image processing part 12 is configured to, when the reading device 15 reads the test chart, measure a time difference since each edge image is read by the first reading sensor until it is read by the second reading sensor, and to detect fluctuation of a reading speed at each part of the sheet on the basis of the time difference, and to correct a magnification in the sheet conveyance direction of the image read and obtained by the reading device such that the fluctuation of the reading speed is canceled.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a magnification correction method and an image processing apparatus that perform magnification correction of an image scanned by scanning a document.

  When performing double-sided printing on paper, it is required to align the front and back images. In response to this requirement, conventionally, front and back alignment marks (so-called registration marks) are printed at the four corners of the front and back sides of the paper, read by an inline scanner or the like, and the registration marks at the four corners coincide. In this way, the magnification of the image is corrected.

  However, as shown in FIG. 13, even if the registration marks at the four corners are aligned on the front and back of the paper, the position of the front and back images at the center of the paper etc., the paper conveyance direction (sub-scanning direction: up and down in FIG. Direction) may occur. This is due to the fact that the image size (magnification) changes between the leading edge and the trailing edge of the sheet (exactly each part of the sheet). For example, printing on a sheet is performed while moving the sheet on the conveyance path, but the sheet conveyance speed fluctuates due to the sequential change of the conveyance roller that holds the sheet as the sheet moves. The magnification in the paper conveyance direction of the image formed on the top changes in each part of the paper. In addition, when the fixing device passes through the paper, the way in which moisture escapes and the temperature fluctuate from the front edge to the rear edge of the paper, resulting in changes in the size of each part of the paper, resulting in fluctuations in the partial magnification of the image on the paper. There is also. In FIG. 13, as illustrated, the solid line represents the pattern on the front surface, and the dotted line represents the pattern on the back surface. Since the registration marks at the four corners are in a state in which the front and back sides are combined, the front and back patterns overlap, and the back side pattern represented by the dotted line is invisible.

  In the example of FIG. 13, the entire image is scaled and corrected at a uniform magnification so that the positions of the register marks at the four corners coincide with each other. However, lines that should originally be printed at equal intervals due to a variation in partial magnification (partial magnification deviation). The minute interval is the distance (a) at the leading edge of the paper and the distance (b) at the trailing edge of the paper (b> a).

  In addition, when double-sided printing is performed with the top and bottom of the paper (front and rear edges) switched between front and back printing, the image misalignment caused by the change in partial magnification in the paper transport direction is reversed on the front and back sides. As a result, the image position shift is conspicuous in the central portion.

  In recent years, the importance of double-sided printing on long paper has increased in order to meet the increasing demand for high value-added printed materials such as three-sided folding designs. However, long paper is susceptible to changes in magnification (position The misalignment error increases with the magnification × distance), and, for example, in the above-described three-surface folding design, a crease is given to the middle portion of the paper, so that higher image position accuracy is required and is corrected by each part of the paper. The partial magnification correction that varies the magnification to be performed is more important.

  In general, the correction of the partial magnification deviation in the paper conveyance direction is performed by a method of printing the image information as a print document after deforming it in the reverse direction so that the partial magnification deviation is offset. In order to adopt this method, it is necessary to detect a magnification shift of each part by reading a sheet on which image information to be a printed document is printed with a scanner and comparing the read image with the original image information.

  In recent years, in order to increase the productivity of printing, a reading device that scans both sides of the output paper being conveyed and scans the image is arranged on the conveyance path between the printing press and the stacker. There is a system that corrects image information of a printed document in real time (as needed during printing) based on the read image.

  When an image on a sheet is read with such a system, the resolution of the read image depends on the conveyance speed of the output paper during the continuous reading. For this reason, if there is a change in the conveyance speed (reading speed) at the time of flow reading, the read image includes both a partial magnification shift at the time of flow reading and a partial magnification shift at the time of printing, and a partial magnification at the time of printing. Misalignment cannot be detected correctly.

  In response to this problem, for example, in Patent Document 1 below, two copies of a first method for reading a calibration chart on which an accurate pattern is printed and correcting distortion at the time of scanning, and a chart printed on both sides by printing means are provided. A second method has been proposed that prepares, scans in reverse, and corrects the difference.

JP 2016-158207 A

  However, in the first method described above, a calibration chart reading means is required, and the paper passing performance of the reading means depends on the type of paper (thickness, surface roughness, etc.), so a calibration chart is provided for each type of paper. There were issues such as the need to prepare. Further, in the second method, since the front / back reverse reading of two sheets of double-sided printing is required in one measurement, there is a problem that the adjustment sequence becomes complicated and the apparatus becomes large in size because a paper reversing mechanism is newly provided.

  The present invention is intended to solve the above-described problem, and a magnification variation correction method and image capable of correcting a partial magnification deviation occurring at the time of reading only with a sheet to be printed without using an accurate calibration chart. An object is to provide a processing apparatus.

  The gist of the present invention for achieving the object lies in the inventions of the following items.

[1] A first reading sensor for reading one line in the first direction and a predetermined distance in a second direction perpendicular to the first direction for reading one line in the first direction and the reading position of the first reading sensor. An outline substantially orthogonal to the second direction in a reading device that reads the original in two dimensions by relatively moving a reading section having a second reading sensor whose reading position is a reading position and the original in the second direction. A reading step of reading a document having a plurality of edge images arranged in the second direction;
A measurement step of measuring, for each of the plurality of edge images, a time difference from when the edge image is read by the first reading sensor to when the original is read by the reading device; ,
A reading speed fluctuation detecting step for detecting a fluctuation in relative speed between the original and the reading unit in the second direction when the original is read in the reading step based on a change in time difference measured in the measuring step; ,
A magnification correction step of correcting the magnification in the second direction of the image obtained by reading the original with the reading device so that the fluctuation of the relative speed detected in the reading speed fluctuation detection step is offset;
A magnification variation correction method characterized by comprising:

  In the above invention and the invention described in [11] below, a document in which a plurality of edge images having contours substantially orthogonal to the paper transport direction are arranged in the paper transport direction is read in a first reading position where the reading position is separated in the paper transport direction. When reading by the sensor and the second reading sensor, a time difference between reading of each edge image by the first reading sensor and reading by the second reading sensor is measured. This time difference is proportional to the relative speed (scanning speed) between the original and the reading unit when the edge image passes between the first reading sensor and the second reading sensor, and therefore, from the change in the time difference measured for each edge image. The variation in relative speed (scanning speed) can be detected, and this is used to correct the variation in the magnification in the paper conveyance direction at the time of reading included in the read image.

[2] The magnification variation correction method according to [1], wherein the edge image is formed in a predetermined range at least from the front and rear edges of the document.

  In the above invention and the invention described in [12] below, the leading edge and the trailing edge of the document are places where the relative speed between the document and the reading unit is likely to change. Therefore, at least the edge image is arranged to arrange the relative speed. Detect fluctuations.

[3] The reading unit is a color line sensor that reads a line in the first direction and has a plurality of line sensors with different reading colors arranged in the second direction, and one of the plurality of line sensors is The first reading sensor, and another one of the plurality of line sensors is the second reading sensor,
The magnification variation correction method according to [1] or [2], wherein the edge image has a color that can be read by both the first reading sensor and the second reading sensor.

  In the above-described invention and the invention described in [13] below, the reading position of the line image sensor for each color of the color line image sensor is slightly apart in the paper transport direction, so that the line image sensor for one color is first read. A line image sensor of another color is used as the second reading sensor. The edge image is a color detected by both of these two line image sensors. The color line image sensor referred to here may include a line image sensor that detects an arbitrary color such as an infrared color or an ultraviolet color in addition to RGB.

[4] The magnification variation correction method according to [3], wherein the edge image is black.

  In the above invention and the invention described in [14] below, if the edge image is black, it can correspond to each color detected by the color line image sensor. In addition, the use of a material having a characteristic of absorbing infrared light, such as including general carbon blacks as a black coloring material, is particularly suitable when an infrared color is included.

[5] The first reading sensor and the second reading sensor are two line sensors whose reading positions are most distant in the second direction among the plurality of line sensors. [3] or The magnification fluctuation correction method according to [4].

  In the above invention and the invention described in [15] below, the measurement accuracy of the time difference (scanning speed) is improved as the reading positions of the first reading sensor and the second reading sensor are separated from each other. Two line sensors whose positions are farthest in the sheet conveyance direction are used.

[6] The reading unit is a two-dimensional image sensor, and the reading position of the first reading sensor and the reading position of the second reading sensor are separated in the second direction of the two-dimensional image sensor. The magnification variation correction method according to any one of [1] to [5], wherein the magnification is replaced by a reading position.

  In the above invention and the invention described in [16] below, both the first reading sensor and the second reading sensor are replaced with one two-dimensional image sensor.

[7] The reading unit includes a first reading unit that reads the front surface of the document and a second reading unit that reads the back surface of the document at different positions in the second direction,
The plurality of edge images are arranged in the second direction on the front and back surfaces of the document,
Based on the change in the time difference measured when the first reading unit reads the plurality of edge images on the surface of the document, the image of the surface of the document read by the first reading unit in the second direction. Correct the magnification,
Based on the change in the time difference measured when the second reading unit reads the plurality of edge images on the back side of the document, the image on the back side of the document read by the second reading unit in the second direction. To correct the magnification,
The magnification variation correction method according to any one of [1] to [6].

  In the above invention and the invention described in [17] below, a change in reading speed when each part is read on each of the front side and the back side of the document is detected, and paper conveyance is performed so that the reading speed fluctuation is offset for each of the front and back sides. Correct the direction magnification.

[8] The document is obtained by simultaneously printing a magnification variation measurement image for measuring magnification variation in the second direction and the plurality of edge images on a sheet by a predetermined printing device.
The plurality of edge images are arranged in different positions in the first direction with respect to the magnification variation measurement image in a range in the second direction including the magnification variation measurement image.
In the reading step, the magnification variation measurement image and the edge image are read,
In the magnification correction step, the magnification in the second direction of the magnification variation measurement image obtained by reading by the reading unit is corrected,
Printing by the printing apparatus so that the magnification fluctuation in the second direction of the magnification fluctuation measurement image corrected in the magnification correction step with respect to the original image of the magnification fluctuation measurement image used for printing is offset The magnification variation correction method according to any one of [1] to [7], further including a second magnification correction step of calculating a correction value of the magnification in the second direction of the print data to be printed.

  In the above-described invention and the invention described in [18] below, the image obtained by reading the magnification variation measurement image printed simultaneously with the edge image with the reading device has a distortion in the sheet conveyance direction and a variation in the reading speed generated during printing. Although both of the accompanying distortions in the paper conveyance direction are included, the distortion accompanying the fluctuations in the reading speed is corrected by detecting the fluctuations in the reading speed based on the edge image. Since the distortion remaining in the image after correction is generated at the time of printing, a magnification correction value for correcting the print data is obtained so as to cancel the distortion.

[9] The magnification variation measurement image includes a plurality of position measurement marks arranged at a distance in the second direction.
The position measurement mark includes an oblique line inclined with respect to the first direction, a wedge shape having a tip directed in the first direction, a ladder pattern in which a plurality of line segments in the first direction are arranged in the second direction with a gap therebetween, The magnification fluctuation correction method according to [8], comprising one or more of the above.

  In the above-mentioned invention and the invention described in [19] below, the position measurement mark is an oblique line, a wedge shape, or a ladder pattern, so that an average of a plurality of measurements can be taken and can be detected by the position measurement mark. The accuracy of the correct position can be increased.

[10] The document printed by the printing apparatus is recorded with a mark for identifying the leading and trailing edges, and when there is a front and back, a mark for identifying the front and back is further recorded [8] ] Or the magnification variation correction method according to [9].

  In the above invention and the invention described in [20] below, when reading an original with an off-line reading device, it is possible to recognize the rear end of the front end and the top and bottom, and correct them correctly.

[11] A first reading sensor that reads one line in the first direction and a predetermined distance in the second direction that reads one line in the first direction and is perpendicular to the first direction with respect to the reading position of the first reading sensor. A reading device that reads the original two-dimensionally by relatively moving a reading section having a second reading sensor whose reading position is a reading position and the original in the second direction;
When the reading device reads a document in which a plurality of edge images having contours substantially orthogonal to the second direction are arranged in the second direction, the edge image is read by the first reading sensor and then the first image is read. A measuring unit that measures a time difference until the reading by the two reading sensors for each of the plurality of edge images;
A reading speed fluctuation detecting section that detects a fluctuation in relative speed between the original and the reading section in the second direction when the reading apparatus reads the original based on a change in time difference measured by the measuring section; ,
A magnification correction unit that corrects the magnification in the second direction of an image obtained by reading the original with the reading device so that the variation in the relative speed detected by the reading speed variation detection unit is offset;
An image processing apparatus comprising:

[12] The image processing apparatus according to [11], wherein the edge image is formed in a predetermined range at least from the front and rear edges of the document.

[13] The reading unit is a color line sensor having a plurality of line sensors that read one line in the first direction and that have different reading colors arranged in the second direction, and one of the plurality of line sensors is The first reading sensor, and another one of the plurality of line sensors is the second reading sensor,
The image processing apparatus according to [11] or [12], wherein the edge image has a color that can be read by both the first reading sensor and the second reading sensor.

[14] The image processing device according to [13], wherein the edge image is black.

[15] The first reading sensor and the second reading sensor are two line sensors whose reading positions are most distant in the second direction among the plurality of line sensors. [13] or [14] The image processing apparatus according to [14].

[16] The reading unit is a two-dimensional image sensor, and the reading position of the first reading sensor and the reading position of the second reading sensor are separated in two directions separated from each other in the second direction of the two-dimensional image sensor. The image processing apparatus according to any one of [11] to [15], wherein the image processing apparatus is replaced with a reading position.

[17] The reading unit includes a first reading unit that reads the front surface of the document and a second reading unit that reads the back surface of the document at different positions in the second direction,
The plurality of edge images are arranged in the second direction on the front and back surfaces of the document,
Based on the change in the time difference measured when the first reading unit reads the plurality of edge images on the surface of the document, the image of the surface of the document read by the first reading unit in the second direction. Correct the magnification,
Based on the change in the time difference measured when the second reading unit reads the plurality of edge images on the back side of the document, the image on the back side of the document read by the second reading unit in the second direction. To correct the magnification,
The image processing apparatus according to any one of [11] to [16].

[18] The document is an image in which a magnification variation measurement image for measuring magnification variation in the second direction and the plurality of edge images are simultaneously printed on a sheet by a predetermined printing device,
The plurality of edge images are arranged in different positions in the first direction with respect to the magnification variation measurement image in a range in the second direction including the magnification variation measurement image.
The reading device reads the magnification variation measurement image and the edge image,
The magnification correction unit corrects the magnification in the second direction of the magnification variation measurement image obtained by reading by the reading unit,
Printing by the printing apparatus so that the magnification fluctuation in the second direction of the magnification fluctuation measurement image corrected by the magnification correction unit with respect to the original image of the magnification fluctuation measurement image used for printing is offset The image processing apparatus according to any one of [11] to [17], further including a second magnification correction unit that calculates a correction value of the magnification in the second direction of the print data to be printed.

[19] The magnification variation measurement image includes a plurality of position measurement marks arranged at a distance in the second direction.
The position measurement mark includes an oblique line inclined with respect to the first direction, a wedge shape having a tip directed in the first direction, a ladder pattern in which a plurality of line segments in the first direction are arranged in the second direction with a gap therebetween, The image processing apparatus according to [18], wherein the image processing apparatus includes one or more of the above.

[20] The document printed by the printing apparatus is recorded with a mark for identifying the leading and trailing edges, and when there is a front and back, a mark for identifying the front and back is further recorded [18] ] Or the image processing apparatus according to [19].

  According to the magnification variation correcting method and the image processing apparatus according to the present invention, it is possible to correct the partial magnification deviation occurring at the time of reading only with the paper to be printed, without using an accurate calibration chart.

1 is a diagram illustrating a schematic configuration of an image processing apparatus according to an embodiment of the present invention. FIG. 6 is a diagram illustrating a sheet passing path in a reading device. FIG. 6 is a diagram illustrating a conveyance state at each position when a sheet is read through a reading device. FIG. 10 is a diagram illustrating a change in a conveyance state when each position on the front and back sides of a sheet is read. It is a figure which shows an example of the test chart for detecting the fluctuation | variation of reading speed and performing magnification correction. It is a figure which shows each component arrange | positioned at a test chart. It is a figure which shows the reading position of each color line image sensor of the reading part (color line image sensor) of a reader. It is a figure which shows the change of the signal strength of the line image sensor of each color when one edge image is read. It is a figure which shows the reading position of each color line image sensor and IR sensor in case a reading part has a color line image sensor and IR sensor. It is a figure which shows an example of the reading range in case a reading part is a two-dimensional image sensor. It is a figure which shows the structure which a reading part (color line image sensor) moves, and scans the paper on platen glass, and the reading position of each color line image sensor. It is a figure which shows the flow of operation | movement in adjustment mode. FIG. 10 is a diagram illustrating a printing example in which the registration marks are aligned on both front and back surfaces, but the image is misaligned in the center of the sheet.

  Hereinafter, various embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a schematic configuration of an image processing apparatus 10 according to an embodiment of the present invention. The image processing apparatus 10 includes an image input unit 11 that inputs an image to be printed, an information storage unit 16 that stores an input image, a program, various data, and the like, and an image for magnification correction or the like for the image to be printed. An image processing unit 12 that performs processing, an image printing unit 13 that can print a full-color image on both sides of the paper, and a paper (output paper) printed by the image printing unit 13 as a paper discharge destination. A stacker 14 that stores and holds, an inline reader 15 that optically reads images on both sides of the paper by scanning both sides of the output paper that is conveyed on the conveyance path from the image printing unit 13 to the stacker 14, and the like. Yes.

  The image printing unit 13 forms an image on a sheet by, for example, electrophotography. In the duplex printing method, after forming an image on the front side of the paper, the front and back sides of the paper are reversed to form an image on the back side of the paper. It is a method. Note that the double-sided printing method is not limited to the above method, and for example, a method in which the front and rear ends of the paper are not reversed when the front and back sides are reversed may be used. In the case of the latter, the partial magnification error on the front and back of the paper is synchronized between the front and back, so it is unlikely that the partial magnification will appear as a difference between the front and back sides. Therefore, the present invention can be used effectively even in the latter case.

  The reading device 15 is fixed at a specific position on the conveyance path, and the output paper to be conveyed is moved relative to the reading position of the reading device 15 so that the output paper is scanned (flow-reading) and read. It is done. Therefore, the fluctuation in the conveyance speed of the output paper when passing the reading position of the reading device 15 becomes the fluctuation in the reading speed (scanning speed) of the reading device 15. The paper transport direction is the sub-scanning direction, and the direction perpendicular to this on the paper is the main scanning direction. The reading device 15 reads the paper two-dimensionally by repeating reading in units of lines in the main scanning direction with respect to the paper conveyed in the sub-scanning direction.

  The image processing unit 12 includes a CPU (Central Processing Unit), reads a program stored in the information storage unit 16, and executes various processes and functions as the CPU operates according to the program. A part of the function of the image processing unit 12 may be executed by a circuit such as an ASIC.

  The image processing unit 12 functions as a measurement unit 21, a reading speed variation detection unit 22, a first magnification correction unit 23, and a second magnification correction unit 24. The image processing unit 12 also has a function as a control unit that controls the operation of the entire image processing apparatus 10.

  The image processing unit 12 is connected to an instruction input unit 17 for receiving various operations and instructions from an operator, and a display unit 18 for displaying an operation screen, a screen for notifying the operation state of the apparatus, and the like.

  The image processing apparatus 10 prints a predetermined test chart by the image printing unit 13, and based on a read image obtained by reading the predetermined test chart by the reading device 15, fluctuations in the reading speed in the paper conveyance direction when reading the test chart. Is detected. In the test chart, a plurality of edge images (line segments and the like) having an outline substantially orthogonal to the paper conveyance direction are arranged in the paper conveyance direction (see the speed fluctuation measurement pattern 43 in FIG. 5). Note that image information for printing the test chart may be input from the image input unit 11 or may be stored in advance in the information storage unit 16. Alternatively, it may be created by the image processing unit 12.

  The reading device 15 reads the printed test chart in accordance with an instruction from the image processing unit 12. The reading unit of the reading device 15 includes a first reading sensor that reads one line in the main scanning direction (first direction), and reads one line in the main scanning direction, and in the sheet conveyance direction with respect to the reading position of the first reading sensor. A second reading sensor having a reading position at a position separated by a predetermined distance downstream is provided.

  The measurement unit 21 of the image processing unit 12 measures a time difference from when one edge image on the test chart is read by the first reading sensor to when the edge image is read by the second reading sensor. This time difference corresponds to the sheet moving speed (reading speed) when the reading unit reads the edge image. The reading speed fluctuation detection unit 22 detects fluctuations in the reading speed from the difference in time difference when each edge image measured by the measurement unit 21 is read.

  The first magnification correction unit 23 of the image processing unit 12 corrects the magnification (partial magnification) of each part (front end, center, rear end, etc.) of the read image in the paper conveyance direction so that the fluctuation in the reading speed is offset. . Further, the second magnification correction unit 24 of the image processing unit 12 corrects distortion (partial magnification fluctuation) of the image in the paper transport direction that occurs during printing based on the read image corrected by the first magnification correction unit 23. The correction value is calculated. Here, the second magnification correction unit 24 corrects the print data (partial magnification value) so that the image is not misaligned at each part (front, center, rear end) on both the front and back sides when double-sided printing is performed. ) Is derived.

  Instead of the in-line reading device 15, an offline reading device 19 may be used to read the test chart image. In this case, an operation procedure is displayed on the display unit 18, and the user takes out a test chart from the stacker according to the operation procedure, sets the test chart on the reading device 19, and inputs an instruction to start the reading operation by the reading device 19. I do. The offline reading device 19 may be shared by a plurality of systems, and may be instructed and controlled by a control unit different from the image processing unit 12 of the image processing device 10. The read image is analyzed by the image processing unit 12 in the same manner as in the case of using the reading device 15, the fluctuation of the reading speed is obtained, the read image is corrected so as to cancel this, and the front and back image positions are printed. A process of deriving a correction value (partial magnification value) for aligning is performed.

  FIG. 2 shows a sheet passing path in the reading device 15. Since the reading device 15 reads both sides of the paper in one pass, the upper surface side line image sensor 31 that reads the front surface of the paper and the lower surface side line image sensor 32 that reads the back surface of the paper are spaced apart from each other in the paper transport direction. They are located at different positions. In this example, the lower surface line image sensor 32 is arranged upstream of the upper surface side line image sensor 31 in the paper conveyance direction.

  In front of and behind each of the line image sensors 31, 32, there is a paper transport mechanism for holding and transporting the paper. The paper transport mechanism is usually composed of a pair of transport rollers arranged to face each other. In the example of FIG. 2, a pair of first transport rollers 35 is provided in the vicinity of the upstream side in the sheet transport direction of the lower surface side line image sensor 32, and a pair of first transport rollers 35 are disposed between the lower surface side line image sensor 32 and the upper surface side line image sensor 31. A pair of third conveying rollers 37 is disposed in the vicinity of the downstream side of the upper surface side line image sensor 31.

  Here, the distance from the first conveying roller 35 to the reading position of the lower surface side line image sensor 32 is d4, the distance from the reading position of the lower surface side line image sensor 32 to the second conveying roller 36 is d3, and the second conveying roller 36. The distance from the reading position of the upper surface side line image sensor 31 to the reading position of the upper surface side line image sensor 31 is d2, and the distance from the reading position of the upper surface side line image sensor 31 to the third conveying roller 37 is d1.

  FIG. 3 shows a conveyance state at each sheet passing position when the sheet is read through the reading device 15. FIG. 4A shows a state a in which the leading edge of the sheet is between the first conveyance roller 35 and the second conveyance roller 36. FIG. 2B shows a state b in which the leading edge of the sheet is between the second conveyance roller 36 and the third conveyance roller 37. FIG. 2C shows a state c in which the sheet is held by all of the first conveyance roller 35, the second conveyance roller 36, and the third conveyance roller 37. FIG. 4D shows a state d in which the trailing edge of the sheet is between the first conveyance roller 35 and the second conveyance roller 36. FIG. 4E shows a state e in which the trailing edge of the sheet is between the second conveyance roller 36 and the third conveyance roller 37. Since the paper transport state (states a to e in FIG. 3) changes depending on the paper position, the paper transport speed may be slightly different in each.

  When the conveyance state changes as shown in FIG. 3, the reading characteristics differ as shown in FIG. 4 depending on the front and back sides of the paper and the scanning position. That is, when the lower surface side line image sensor 32 reads the back side of the sheet, the state a is read while reading the distance d3 from the leading edge of the sheet, the state b is read while the following distance (d1 + d2) is read, and the central portion of the image is read. The state of paper conveyance changes such as state c when reading and state d when reading from a position d4 away from the rear edge of the paper to the rear edge of the paper.

  On the other hand, when the upper surface side line image sensor 31 reads the surface of the paper, the state b during reading from the front edge of the paper to the distance d1, the state c when reading a predetermined period (the central part of the paper) following this, and the back of the paper The sheet conveyance state changes such that the state d is obtained while the distance (d3 + d4) is read from the front position by the distance (d3 + d4 + d2) from the end, and then the state e is obtained when reading the rear end of the sheet.

  As described above, since the center of the sheet is read in the state c on both sides of the sheet, the scanning state (reading speed) of the front and back sides coincides, but the scanning state (reading speed) is different between the front and back of the sheet. For this reason, it is important to accurately recognize the variation in the reading speed at the leading and trailing edges of the sheet in order to perform front and back alignment during duplex printing.

  Although this example is a case of simultaneous reading on both sides, even when the line image sensor is arranged on only one side and the reading of the front and back sides is performed with two paper passes, a speed difference is similarly generated. In particular, when the front end of the reading is in the reverse direction on the front side and the back side (this is preferable because the reading condition in the main scanning direction is the same on the front and back sides), as in FIG. Will occur.

  Note that a paper reading mechanism other than an inline device such as the reading device 15 may be used. For example, the double-sided reading mechanism equipped for copy printing has the same configuration as that shown in FIG. 3 except that the paper path is bent to reduce the size and improve the workability, and the same problem occurs. However, a similar technique can be applied.

  FIG. 5 shows an example of a test chart 40 for detecting a change in reading speed and performing magnification correction. FIG. 6 shows the components arranged in the test chart 40. On the test chart 40, an image position measurement pattern 41, a magnification measurement pattern 42, and a speed variation measurement pattern 43 are arranged. Further, a print state measurement pattern 44 and a top / bottom front / back identification pattern 45 are also arranged.

  The image position measurement pattern 41 is a so-called cross mark called a registration mark, and is arranged at the four corners of the paper. The image position measurement pattern 41 is a reference for measuring the image position from the sheet edge (see FIG. 6A).

  The magnification measurement pattern 42 is used to measure the magnification generated during printing from the distance between adjacent patterns (see FIG. 6B). The magnification measurement pattern 42 is obtained by arranging a plurality of patterns in the paper conveyance direction at predetermined equal intervals on the original image (print data). Here, a magnification measurement pattern 42 is arranged from the leading edge to the trailing edge of the paper.

  In order to increase the accuracy of magnification measurement in a short distance, the magnification measurement pattern 42 may be a pattern as shown in FIG. If the magnification measurement pattern 42 is a ladder type in which a plurality of fine lines in a direction orthogonal to the paper conveyance direction are arranged at a slight interval in the paper conveyance direction, the measurement can be repeated for each fine line, and the average etc. If it takes, accuracy can be raised.

  For the wave shape and the wedge shape, the measurement can be repeated many times while changing the measurement position in the main scanning direction. These are more preferable because the position of the edge to be measured changes almost continuously, and is not easily affected by minute vibrations or minute repetition errors of the beam pitch. In this case, it is preferable that the inclination of the pattern edge with respect to the main scanning direction is about ± 20 degrees because the influence of the main scanning position deviation at the time of pattern reading and the variation of the image edge due to, for example, toner granularity can be reduced. .

  The speed variation measurement pattern 43 is a pattern in which a plurality of edge images (here, line segments orthogonal to the paper transport direction) having an outline substantially orthogonal to the paper transport direction are arranged in the paper transport direction. It is used for detecting fluctuations in reading speed in the reading device 15. The speed variation measurement pattern 43 is arranged at least at the leading edge and the trailing edge of the sheet where the reading speed is predicted to change. Each speed variation measurement pattern 43 is arranged at least from the leading edge or the trailing edge of the sheet toward the center of the sheet until it can be determined that the reading speed is stable (the state c in FIGS. 3 and 4). The

  Further, the edge image of the speed variation measurement pattern 43 is located in a range in the paper transport direction including at least two continuous magnification measurement patterns 42, and in a different position in the main scanning direction with respect to the magnification measurement pattern 42 (aligned in the main scanning direction). ). In the example of FIG. 5, the edge image of the speed variation measurement pattern 43 is arranged in a slightly wider range before and after the range where the two magnification measurement patterns 42 on the front end side of the sheet (and the two magnification measurement patterns 42 on the rear end side) exist. Has been.

  The interval between the edge images in the paper conveyance direction need not be constant. As the interval between the edge images is made finer, the fluctuation in the reading speed can be recognized more finely.

  The print state measurement pattern 44 is a halftone patch image or the like. Check if the printing status is stable. Details will be described later.

  The top / bottom front / back identification pattern 45 is a mark for identifying the front / back and top / bottom (front and rear ends) of the test chart 40. This is used when the offline reader 19 is used.

  Next, a method for detecting a fluctuation in reading speed from reading each edge image of the speed fluctuation measuring pattern 43 will be described.

  For example, as illustrated in FIG. 7, the reading unit of the reading device 15 is a color line image sensor 51. The color line image sensor 51 is configured by arranging line image sensors of R, G, and B colors that read one line in the main scanning direction in the paper conveyance direction. Therefore, the reading position where the line image sensor of each color reads the image on the paper is slightly away in the paper conveyance direction, and the timing when the line image sensor of each color reads one edge image drawn on the conveyed paper There is a difference.

  For example, the reading position of the R color line image sensor and the reading position of the B color line image sensor are separated from each other by a certain distance in the paper transport direction, so that as shown in FIG. From the time when one edge image is read (time T1 when the R color signal intensity peaks) to the time when the B color line image sensor reads the edge image (time T2 when the B color signal intensity peaks) A time difference occurs. This time difference is proportional to the distance between the sensors and inversely proportional to the paper conveyance speed, but since the distance between the sensors is fixed, the time difference changes inversely proportional to the paper conveyance speed.

  That is, the measured time difference changes in inverse proportion to the sheet conveyance speed (reading speed) when the edge image moves from the reading position of the R line image sensor to the reading position of the B line image sensor.

  Therefore, the time difference is measured for each of the plurality of edge images arranged in the paper conveyance direction on the test chart 40, and the change in the reading speed is detected by observing the change.

  As described above, since the change in the reading speed is likely to be particularly large in the front and rear end areas of the paper, in the present embodiment, as shown in FIG. 5, only in the front end area and the rear end area of the test chart 40. A speed fluctuation measurement pattern 43 is provided to measure a change in reading speed in the front and rear end regions of the paper. Of course, the speed fluctuation measurement pattern 43 may be provided in an arbitrary area where the reading speed is likely to change, or may be provided in all areas from the leading edge to the trailing edge of the paper.

  In addition, since the measurement of the time difference requires high accuracy, it is preferable to repeatedly measure each line of the ladder pattern and reduce the error by averaging these lines. Each line (edge image) of the speed variation measurement pattern 43 may be a pattern having an edge in the main scanning direction (perpendicular to the paper conveyance direction). However, when the line is orthogonal to the paper conveyance direction, the edge is formed. There is a high possibility that a pixel is drawn by one specific element, and there is a possibility that the pixel is directly affected by the characteristics of the element and the minute vibration of the image printing unit 13 at the moment when the element is drawn. Therefore, the edge image may be composed of diagonal lines and wavy lines that are substantially orthogonal to the paper conveyance direction. The substantially orthogonal range varies depending on the system, but is preferably set to, for example, orthogonal ± 20 degrees.

  In order to improve the measurement accuracy, it is desirable to select two of the plurality of line image sensors whose reading positions are farthest in the sheet conveyance direction and measure the time difference.

  Depending on the purpose of image reading, in addition to RGB color images, for example, IR (infrared) or UV (ultraviolet) images can be collected (scratches, dirt, and paper types can be monitored). May be provided in the reading device 15. In this case, the RGB image sensor has a single unit configuration, whereas the sensor for detecting an IR (infrared) or UV (ultraviolet) image often has a separate unit configuration (see FIG. 9). For the measurement of the time difference described above, using two sensors separated as much as possible leads to improvement in measurement accuracy. Therefore, when using a reading unit configured as shown in FIG. It is desirable to detect by a combination (R and IR in the example of FIG. 9).

  In addition, as the reading unit of the reading device 15, as shown in FIG. 10, a two-dimensional image sensor 53 that reads a predetermined range in the paper conveyance direction at a time may be used. In this case, as the two reading sensors for measuring the above-described time difference, two reading positions separated from each other in the sheet conveyance direction in the two-dimensional image sensor may be used.

  In addition, if the two-dimensional image sensor 53 is used to capture a moving image of a paper passing state or a plurality of still images with a short interval, and the movement distance of a specific pattern such as an edge image between them is determined, the specific pattern The sheet passing speed (reading speed) in the vicinity of the imaging location can be detected.

  In the case of the off-line reading device 19, as shown in FIG. 11, the paper is fixedly arranged on the platen glass, and the reading unit (color line image sensor 51 or the like) moves to scan the paper. It doesn't matter. At this time, if the moving speed of the reading unit is uneven, the reading magnification is shifted. However, as in the case of FIG. 7, the fluctuation of the reading speed is changed based on the time difference between the two line image sensors detecting the edge image. It is possible to detect and correct the read image.

  The edge image has a color that can be read by either of the two line image sensors used for measuring the time difference. Considering the case where an IR sensor is used, the edge image color is preferably black made of a material that also absorbs infrared light, such as general carbon blacks.

  Next, the operation in the adjustment mode performed by the image processing apparatus 10 will be described. The adjustment mode is an operation different from normal printing, and a test chart 40 for deriving a magnification correction value used for front / back position alignment during double-sided printing is printed, and this is read to perform image analysis or the like.

  FIG. 12 shows the flow of operation in the adjustment mode. The adjustment mode may be activated by a user's instruction, or may be activated by a trigger such as after a certain number of sheets have passed, a certain amount of time has elapsed, a predetermined amount of environmental fluctuation has been detected, tray paper has been replaced, etc. good.

  In addition, when correcting the magnification correction value for front and back alignment in real time during a normal printing operation, the image position measurement pattern 41 and the magnification measurement pattern 42 are formed in the margin of the print image (the portion cut in the subsequent process). Alternatively, the adjustment process may be performed by forming the speed variation measurement pattern 43 or the like. Alternatively, at the time of real-time adjustment, only the positional deviation amount of the sheet intermediate portion may be simply monitored, and if a change appears in the deviation amount, the adjustment mode may be entered to perform detailed measurement and adjustment.

  In FIG. 12, when the adjustment mode is activated (step S101), the image processing unit 12 generates an image of the test chart 40 or reads it from the information storage unit 16 or the like (step S102), and prints it on the image printing unit 13. Output (step S103). The test chart 40 is printed on both sides of the paper.

  Further, the image processing unit 12 causes the in-line reading device 15 to read both sides of the test chart 40 printed out by the image printing unit 13 (step S104, reading step), and analyzes the image obtained by the reading device 15 reading ( Step S105). The image analysis in step S105 includes a measurement step and a reading speed fluctuation detection step. In the measurement step, the time difference between the timings when two line image sensors (for example, the R color line image sensor and the B color line image sensor in FIG. 7) read one edge image is measured for each edge image. Further, the magnification measurement pattern 42 is detected, and the time difference when the adjacent magnification measurement patterns 42 are read is sequentially measured.

  These image analysis processes are desirably performed in real time together with the reading operation. Note that a time stamp may be added to the image, and a time difference may be obtained later based on this.

  In the reading speed fluctuation detecting step of the image analysis, the reading speed fluctuation is detected from the change state of the time difference measured for each edge image.

  Thereafter, the magnification of each part in the paper conveyance direction of the read image is corrected based on the change in the reading speed obtained in the reading speed fluctuation detection step (step S106, magnification correction step). Here, the time difference (distance between patterns) when adjacent magnification measurement patterns 42 are read is corrected based on the relative reading speed.

For example,
The time when one magnification measurement pattern 42 on the test chart 40 is detected is Ta,
The time when the next magnification measurement pattern 42 is detected is Tb,
・ Standard paper transport speed is V,
The average value of the relative reading speed between time Ta and time Tb is V ′,
When
The distance L between adjacent magnification measurement patterns 42 before correction is
L = (Tb−Ta) × V,
The inter-pattern distance L ′ after correcting the fluctuation of the relative reading speed is
L ′ = L × (V / V ′)
Can be obtained as
Note that the reference sheet conveyance speed V may be a relative reading speed when the relative reading speed is stable (for example, the center of the sheet, state c).

  The image analysis in step S105 and the magnification correction in step S106 are performed for each of the front surface and the back surface. That is, the surface of the test chart 40 is read based on a change in time difference measured when each edge image of the speed variation measurement pattern 43 printed on the surface of the test chart 40 is read by the upper surface side line image sensor 31 of the reading unit. The magnification of the image in the paper conveyance direction (distance between the magnification measurement patterns 42) is corrected, and each edge image of the speed variation measurement pattern 43 printed on the back surface of the test chart 40 is read by the lower surface side line image sensor 32 of the reading unit. Based on the change of the time difference measured at the time, the magnification of the read image on the back surface of the test chart 40 on the rear side of the sheet conveyance is corrected.

  Further, the image processing unit 12 performs partial magnification correction for correcting the print data so that the front and back image positions coincide with each part of the paper during double-sided printing based on the distance between the magnification measurement patterns 42 corrected in step S106. A value is obtained (step S107, second magnification correction step), and the process ends. In the subsequent printing, by correcting the magnification of the print data in the paper conveyance direction with the partial magnification correction value obtained in step S107, an output result in which the image positions coincide with each other on both the front and back sides can be obtained.

  When reading the printed test chart 40 with the offline reading device 19, it may be necessary to read one test chart 40 a plurality of times. In this case, each reading needs to be performed by a correct reading method (front and back of the test chart 40 or top and bottom). Therefore, the test chart 40 is provided with a mark (such as the top / bottom front / back identification pattern 45 in FIG. 5) that can identify the reading direction and the chart reading direction on the platen, or various measurement patterns with patterns that can identify the reading direction and the like. It is preferable to configure.

In the analysis processing of the image obtained by reading the test chart 40 with the reading device 15 or the like, from the time when the edge position of each edge image of the speed variation measurement pattern 43 or the gravity center position of each edge image is read by one line image sensor. A time difference between times read by the other line image sensor (actually, a time difference detected by two line image sensors that are the farthest apart) is obtained, and the time difference is used as a color shift amount. This color misregistration amount is calculated for each edge image of the speed variation measurement pattern 43. The relative reading speed at each location on the test chart 40 is expressed by the following equation.
(Relative reading speed) = 1 / (color misregistration amount)

  The amount of color shift depends on the interval between the two line image sensors used for measuring the time difference, but the interval between the two line image sensors may be considered unchanged during the reading time. In calculating the speed, it is not necessary to consider the value of this interval. In other words, the absolute value of the reading speed is not necessary, and it is only necessary to detect the relative fluctuation of the reading speed. Therefore, there is no need to consider the absolute distance between the two line image sensors used for measuring the time difference. .

  In the configuration example of the present invention, the speed fluctuation measurement pattern 43 is arranged only at the front and rear edges of the paper. The measured distance of the image of the magnification measurement pattern 42 at the leading and trailing edges of the paper is calculated from the measurement of the time difference between a plurality of edge images arranged in the same range in the paper conveyance direction as the magnification measurement pattern 42 in the speed fluctuation measurement pattern 43. Correction is performed using the average value of the relative reading speeds (when the edge images of the speed fluctuation measurement pattern 43 are arranged at equal intervals. In the case of unequal intervals, the weighted average may be used at each interval). Specifically, the corrected distance may be obtained by dividing the actually measured distance on the image by the average value of the relative reading speed.

  Since it can be predicted that there is no large difference in speed between the front and back sides of the paper center portion where the speed fluctuation measurement pattern 43 does not exist, the front-back difference may be calculated using the measured distance as it is. The correction may be performed based on the relative reading speed obtained from the edge image close to (closest to) the center.

  Further, the speed variation measurement pattern 43 may be arranged over the entire sheet, and the entire pattern may be corrected.

<Other configurations>
In the test chart 40 of FIG. 5, a print state measurement pattern 44 for monitoring the print state is arranged in parallel with the speed fluctuation measurement pattern 43 (side by side in the main scanning direction). The print state measurement pattern 44 is, for example, a halftone patch of an AM screen having a relatively high number of lines, and monitors a density change in the patch. In places where the density change suddenly occurs, there is a high possibility that a rapid change occurs in the sheet conveyance and a local magnification shift occurs. Such a rapid magnification shift causes a positional deviation between the front and back images at the center of the sheet. Although the front / back position deviation can be eliminated by the method described in the present invention, it is difficult to correct the local magnification deviation (sometimes called a step deviation because a sudden change appears as a step). Is likely to be defective.

  Therefore, when density unevenness of a predetermined value or more occurs in the printing state measurement pattern 44, the adjustment mode may be terminated and the check of the paper conveyance state may be promoted or the operation mode for adjusting the paper conveyance state may be shifted. . Similarly, if there is an abrupt change in the amount of color misregistration obtained from each edge image of the speed variation measurement pattern 43, a reading device abnormality may be considered, so a check of the scan conveyance state is promoted or the scan conveyance state is adjusted. You may make it transfer to operation mode.

  As described above, according to the present invention, it is possible to correct the partial magnification deviation accompanying the fluctuation of the reading speed at the time of reading without using an accurate calibration chart printed separately. Therefore, for example, if a measurement pattern such as the magnification measurement pattern 42 and the speed fluctuation measurement pattern 43 is printed on a part of the paper to be printed (a part to be cut and discarded later), the reading is performed only on the paper to be printed. The magnification correction value can be obtained by correcting the fluctuation of the speed to obtain the magnification correction value for matching the display image position at the time of duplex printing.

  The embodiment of the present invention has been described with reference to the drawings. However, the specific configuration is not limited to that shown in the embodiment, and there are changes and additions within the scope of the present invention. Are also included in the present invention.

  In the embodiment, an example in which two different line image sensors or IR sensors of the color line image sensor 51 are used as two reading sensors separated in the paper conveyance direction has been described. However, two independent reading sensors are used. It doesn't matter.

DESCRIPTION OF SYMBOLS 10 ... Image processing apparatus 11 ... Image input part 12 ... Image processing part 13 ... Image printing part 14 ... Stacker 15 ... Reading apparatus (inline)
16 ... Information storage unit 17 ... Instruction input unit 18 ... Display unit 19 ... Reading device (offline)
DESCRIPTION OF SYMBOLS 21 ... Measuring part 22 ... Reading speed fluctuation | variation detection part 23 ... 1st magnification correction part 24 ... 2nd magnification correction part 31 ... Upper surface side line image sensor 32 ... Lower surface side line image sensor 35 ... 1st conveyance roller 36 ... 2nd conveyance Roller 37 ... Third transport roller 40 ... Test chart 41 ... Image position measurement pattern 42 ... Magnification measurement pattern 43 ... Speed fluctuation measurement pattern 44 ... Printing state measurement pattern 45 ... Top / bottom identification pattern 51 ... Color line image sensor 53 ... Two-dimensional Image sensor

Claims (20)

A first reading sensor that reads one line in the first direction and a position that reads one line in the first direction and is separated from the reading position of the first reading sensor by a predetermined distance in a second direction orthogonal to the first direction. Is a reading apparatus that reads a document in a two-dimensional manner by relatively moving a reading unit having a second reading sensor at a reading position and the document in the second direction, and has a plurality of contours substantially orthogonal to the second direction. A reading step of reading a document in which edge images of the image are arranged in the second direction;
A measurement step of measuring, for each of the plurality of edge images, a time difference from when the edge image is read by the first reading sensor to when the original is read by the reading device; ,
A reading speed fluctuation detecting step for detecting a fluctuation in relative speed between the original and the reading unit in the second direction when the original is read in the reading step based on a change in time difference measured in the measuring step; ,
A magnification correction step of correcting the magnification in the second direction of the image obtained by reading the original with the reading device so that the fluctuation of the relative speed detected in the reading speed fluctuation detection step is offset;
A magnification variation correction method characterized by comprising: The magnification variation correction method according to claim 1, wherein the edge image is formed in a predetermined range at least from the front and rear edges of the document. The reading unit is a color line sensor having a plurality of line sensors having different reading colors arranged in the second direction for reading one line in the first direction, and one of the plurality of line sensors is the first line sensor. A reading sensor, and another one of the plurality of line sensors is the second reading sensor,
The magnification variation correction method according to claim 1, wherein the edge image has a color that can be read by both the first reading sensor and the second reading sensor. The magnification variation correction method according to claim 3, wherein the edge image is black. The first reading sensor and the second reading sensor are two line sensors whose reading positions are most distant from each other in the second direction among the plurality of line sensors. Magnification variation correction method. The reading unit is a two-dimensional image sensor, and the reading position of the first reading sensor and the reading position of the second reading sensor are two reading positions separated in the second direction of the two-dimensional image sensor. The magnification fluctuation correction method according to claim 1, wherein the magnification fluctuation correction method is used. The reading unit has a first reading unit for reading the front side of the document and a second reading unit for reading the back side of the document at different positions in the second direction,
The plurality of edge images are arranged in the second direction on the front and back surfaces of the document,
Based on the change in the time difference measured when the first reading unit reads the plurality of edge images on the surface of the document, the image of the surface of the document read by the first reading unit in the second direction. Correct the magnification,
Based on the change in the time difference measured when the second reading unit reads the plurality of edge images on the back side of the document, the image on the back side of the document read by the second reading unit in the second direction. To correct the magnification,
The magnification fluctuation correction method according to claim 1, wherein the magnification fluctuation correction method is performed. The document is an image in which a magnification variation measurement image for measuring magnification variation in the second direction and the plurality of edge images are simultaneously printed on a sheet by a predetermined printing device,
The plurality of edge images are arranged in different positions in the first direction with respect to the magnification variation measurement image in a range in the second direction including the magnification variation measurement image.
In the reading step, the magnification variation measurement image and the edge image are read,
In the magnification correction step, the magnification in the second direction of the magnification variation measurement image obtained by reading by the reading unit is corrected,
Printing by the printing apparatus so that the magnification fluctuation in the second direction of the magnification fluctuation measurement image corrected in the magnification correction step with respect to the original image of the magnification fluctuation measurement image used for printing is offset The magnification fluctuation correction method according to claim 1, further comprising a second magnification correction step of calculating a correction value of the magnification in the second direction of the print data to be printed. The magnification variation measurement image is a plurality of position measurement marks arranged at a distance in the second direction,
The position measurement mark includes an oblique line inclined with respect to the first direction, a wedge shape having a tip directed in the first direction, a ladder pattern in which a plurality of line segments in the first direction are arranged in the second direction with a gap therebetween, The magnification fluctuation correction method according to claim 8, wherein the magnification fluctuation correction method is configured by one or more of the following. 10. The document printed by the printing apparatus is recorded with a mark for identifying the leading and trailing edges, and when there is a front and back, a mark for identifying the front and back is further recorded. The magnification fluctuation correction method described in 1. A first reading sensor that reads one line in the first direction and a position that reads one line in the first direction and is separated from the reading position of the first reading sensor by a predetermined distance in a second direction orthogonal to the first direction. A reading device having a second reading sensor having a reading position as a reading position and a reading device that relatively moves a document in the second direction to read the document two-dimensionally;
When the reading device reads a document in which a plurality of edge images having contours substantially orthogonal to the second direction are arranged in the second direction, the edge image is read by the first reading sensor and then the first image is read. A measuring unit that measures a time difference until the reading by the two reading sensors for each of the plurality of edge images;
A reading speed fluctuation detecting section that detects a fluctuation in relative speed between the original and the reading section in the second direction when the reading apparatus reads the original based on a change in time difference measured by the measuring section; ,
A magnification correction unit that corrects the magnification in the second direction of an image obtained by reading the original with the reading device so that the variation in the relative speed detected by the reading speed variation detection unit is offset;
An image processing apparatus comprising: The image processing apparatus according to claim 11, wherein the edge image is formed in a predetermined range at least from the front and rear ends of the document. The reading unit is a color line sensor having a plurality of line sensors having different reading colors arranged in the second direction for reading one line in the first direction, and one of the plurality of line sensors is the first line sensor. A reading sensor, and another one of the plurality of line sensors is the second reading sensor,
The image processing apparatus according to claim 11, wherein the edge image has a color that can be read by both the first reading sensor and the second reading sensor. The image processing apparatus according to claim 13, wherein the edge image is black. The first reading sensor and the second reading sensor are two line sensors whose reading positions are most distant in the second direction among the plurality of line sensors. Image processing apparatus. The reading unit is a two-dimensional image sensor, and the reading position of the first reading sensor and the reading position of the second reading sensor are two reading positions separated in the second direction of the two-dimensional image sensor. The image processing apparatus according to claim 11, wherein the image processing apparatus is replaced. The reading unit has a first reading unit for reading the front side of the document and a second reading unit for reading the back side of the document at different positions in the second direction,
The plurality of edge images are arranged in the second direction on the front and back surfaces of the document,
Based on the change in the time difference measured when the first reading unit reads the plurality of edge images on the surface of the document, the image of the surface of the document read by the first reading unit in the second direction. Correct the magnification,
Based on the change in the time difference measured when the second reading unit reads the plurality of edge images on the back side of the document, the image on the back side of the document read by the second reading unit in the second direction. To correct the magnification,
The image processing apparatus according to claim 11, wherein the image processing apparatus is an image processing apparatus. The document is an image in which a magnification variation measurement image for measuring magnification variation in the second direction and the plurality of edge images are simultaneously printed on a sheet by a predetermined printing device,
The plurality of edge images are arranged in different positions in the first direction with respect to the magnification variation measurement image in a range in the second direction including the magnification variation measurement image.
The reading device reads the magnification variation measurement image and the edge image,
The magnification correction unit corrects the magnification in the second direction of the magnification variation measurement image obtained by reading by the reading unit,
Printing by the printing apparatus so that the magnification fluctuation in the second direction of the magnification fluctuation measurement image corrected by the magnification correction unit with respect to the original image of the magnification fluctuation measurement image used for printing is offset The image processing apparatus according to claim 11, further comprising a second magnification correction unit that calculates a correction value of the magnification in the second direction of the print data to be printed. The magnification variation measurement image is a plurality of position measurement marks arranged at a distance in the second direction,
The position measurement mark includes an oblique line inclined with respect to the first direction, a wedge shape having a tip directed in the first direction, a ladder pattern in which a plurality of line segments in the first direction are arranged in the second direction with a gap therebetween, The image processing apparatus according to claim 18, wherein the image processing apparatus is composed of one or more of the above. 20. The document printed by the printing apparatus is recorded with a mark that can identify front and rear edges, and when there is front and back, a mark that can further identify front and back is recorded. An image processing apparatus according to 1.