Optical line sensor, method for manufacturing the same, and correction processing method

Abstract

To provide an optical line sensor configured to properly correct error of an image based on misalignment of imaging elements, a method of manufacturing the optical line sensor, and a correction processing method.SOLUTION: When a correction read image 30 including a line image 31 and an equal-interval image 32 is read by a read processing unit 110, a parameter storage unit 120 stores first and second correction parameters generated based on the correction read image 30. The first correction parameter is generated by dividing the correction read image 30 read by the read processing unit 110 into multiple subdivided images corresponding to imaging elements, respectively, and by calculating, for each of the subdivided images, the amount of misalignment of the line image 31 along a conveyance direction and inclination of the line image 31 in a line direction. The second correction parameter is generated by calculating the amount of misalignment of the equal-interval image 32 along the line direction, based on the correction read image 30 read by the read processing unit 110.SELECTED DRAWING: Figure 5

Description

【Technical Field】 , , 【0004】 , , 【0005】 , , 【0001】 The present invention relates to an optical line sensor that reads an image of an object conveyed along a conveyance direction with a plurality of image pickup elements arranged linearly side by side, a method for manufacturing the same, and a correction processing method. 【Background Art】 【0002】 A contact type optical line sensor (CIS: Contact Image Sensor) as exemplified in Patent Document 1 below generally includes a plurality of light receiving IC chips as image pickup elements. A plurality of photoelectric conversion elements such as photodiodes are arranged in a straight line on each light receiving IC chip. Each light receiving IC chip is arranged along the length direction on a long mounting substrate by a mounting device called a mounter. 【Prior Art Documents】 【Patent Documents】 【0003】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2019-139489 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 With the recent increase in the resolution of contact type optical line sensors, the light receiving IC chips of contact type optical line sensors are becoming mainstream with resolutions of 600 dpi or more, compared to the conventional ones with a resolution of about 300 dpi. Under such circumstances, when a plurality of light receiving IC chips are mounted side by side in the length direction on a mounting substrate by the above-described mounting device, a deviation of about ±50 μm generally occurs during the arrangement of each light receiving IC chip. 【0005】 At a resolution of around 300 dpi, the pixel pitch is approximately 84 μm, so the aforementioned misalignment can be considered negligible. However, at a resolution of around 600 dpi, the pixel pitch becomes approximately 42 μm, and the aforementioned misalignment becomes a misalignment of one or more pixels, making it impossible to ignore. Since such misalignment varies from one contact optical line sensor to another, there is a risk that it may not be possible to stably manufacture high-precision contact optical line sensors. 【0006】 The present invention has been made in view of the above circumstances, and aims to provide an optical line sensor, a method for manufacturing the same, and a correction processing method that can suitably correct image errors due to misalignment of each image sensor in a configuration in which a plurality of high-resolution image sensors are arranged in a line. [Means for solving the problem] 【0007】 (1) The optical line sensor according to the present invention is an optical line sensor that reads an image of an object being transported along a transport direction using a plurality of image sensors arranged in a line, and comprises a reading processing unit, a parameter storage unit, and a correction processing unit. The reading processing unit reads an image of the object based on input signals from the plurality of image sensors. The parameter storage unit stores correction parameters generated based on the correction reading image when a correction reading image, which includes a line image extending in a line direction perpendicular to the transport direction and equally spaced images arranged at equal intervals in the line direction, is read by the reading processing unit as an image of the object. The correction processing unit corrects the image to be read based on the correction parameters when an image to be read that is different from the correction reading image is read by the reading processing unit as an image of the object. 【0008】 The correction parameters include a first correction parameter and a second correction parameter. The first correction parameter is generated by dividing the correction read image read by the reading processing unit into a plurality of segmented images corresponding to each image sensor, and for each segmented image, calculating the amount of displacement of the line image along the transport direction and the inclination of the line image with respect to the line direction. The second correction parameter is generated by calculating the amount of displacement of the equally spaced images along the line direction based on the correction read image read by the reading processing unit. 【0009】 With this configuration, first and second correction parameters are generated based on the corrected read image, and errors in the read image due to the misalignment of each image sensor can be suitably corrected based on these correction parameters. 【0010】 (2) The parameter storage unit and the correction processing unit may be configured as a PLD that stores the correction parameters and corrects the image to be read, which is read by the reading processing unit based on the correction parameters. 【0011】 With this configuration, different correction parameters can be written to the PLD for each optical line sensor, and the error in the image being read can be suitably corrected based on these correction parameters. 【0012】 (3) The PLD may be configured using an FPGA. 【0013】 With this configuration, correction parameters can be pre-programmed into the FPGA, and the corrected image to be read can be output by the FPGA. 【0014】 (4) The first correction parameter may be generated by using a linear function to calculate the amount of displacement of the line image along the transport direction and the inclination of the line image with respect to the line direction. 【0015】 With this configuration, the first correction parameter can be appropriately calculated using a linear function, thereby more effectively correcting errors in the read image caused by the misalignment of each image sensor. 【0016】 (5) The correction processing unit may perform sub-pixel processing based on the correction parameters. 【0017】 With this configuration, subpixel processing can be used to further suitably correct errors in the image being read due to misalignment of each image sensor. 【0018】 (6) A method for manufacturing an optical line sensor according to the present invention is a method for manufacturing an optical line sensor, comprising a correction reading step, a parameter generation step, and a writing step. In the correction reading step, the reading processing unit reads the correction reading image as an image of the object. In the parameter generation step, correction parameters are generated based on the correction reading image. In the writing step, the correction parameters are written to the parameter storage unit. 【0019】 With this configuration, it is possible to manufacture optical line sensors in which different correction parameters are pre-written in the parameter storage unit for each optical line sensor. When an image to be read is read using such an optical line sensor, the error in the image to be read can be suitably corrected based on the correction parameters. 【0020】 (7) The correction processing method according to the present invention is a correction processing method for an optical line sensor, comprising a reading step and a correction step. In the reading step, the reading processing unit reads the reading image as an image of the object. In the correction step, the correction processing unit corrects the reading image based on the correction parameters. 【0021】 With this configuration, errors in the image to be read can be suitably corrected based on correction parameters pre-written in the parameter storage unit. 【Effect of the Invention】 【0022】 According to the present invention, in a configuration in which a plurality of high-resolution imaging elements are arranged side by side in a line, it is possible to suitably correct an image error based on the deviation of each imaging element. 【Brief Description of the Drawings】 【0023】 [Figure 1] It is a schematic cross-sectional view showing an example of the configuration of a close-contact type optical line sensor in an embodiment of the present invention. [Figure 2] It is a schematic cross-sectional view showing a modified example of the configuration of a close-contact type optical line sensor. [Figure 3A] It is a schematic diagram showing an example of the configuration of a light receiving part. [Figure 3B] It is a schematic diagram showing a modified example of the configuration of a light receiving part. [Figure 4] It is a diagram showing an example of a correction reading image. [Figure 5] It is a block diagram showing a part of the electrical configuration of a close-contact type optical line sensor. [Figure 6] It is a diagram for explaining an aspect when generating correction parameters. <00001​​​​​​​​​​​​​​​​​Figure 1 is a schematic cross-sectional view showing an example of the configuration of a contact-type optical line sensor 100 in one embodiment of the present invention, but embodiments of the present invention are not limited to contact-type. This contact-type optical line sensor (CIS: Contact Image Sensor) 100 reads an image of an object being transported along the transport direction (y direction) and has the function of correcting and outputting the read image. Paper sheets can be given as examples of objects, but it is not limited to this and is possible to read images of any object. 【0025】 This close-contact optical line sensor 100 comprises a housing 16, a line illumination light source 10 for illuminating an object, a lens array 11 for guiding the light emitted from the line illumination light source 10 toward the focal plane 20 and reflected by the object, and a light receiving unit 12 mounted on a CIS substrate 13 for receiving light transmitted through the lens array 11. The object is transported in one direction (y direction) along the focal plane 20. These housing 16, line illumination light source 10, light receiving unit 12, and lens array 11 extend in the x direction, that is, in the direction perpendicular to the plane of the paper in Figure 1, and Figure 1 shows a cross-section perpendicular to the x direction. 【0026】 The line illumination light source 10 is a unit that emits light toward an object located at the focal plane 20. The types of light emitted are, for example, visible light and ultraviolet light, and infrared light may also be emitted. However, it is also possible to configure the line illumination light source 10 to emit only visible light toward the object. 【0027】 The line illumination light source 10 is provided with a transparent light guide 1 extending along the x-direction (longitudinal direction). Each outer side of the light guide 1 is held by a cover member 2. A light source (not shown) is provided at one or both ends of the light guide 1 in the x-direction. Light entering the light guide 1 from the light source is diffused by a light diffusion pattern P and emitted from the side of the light guide 1 that is not covered by the cover member 2. 【0028】 Light emitted from the line illumination light source 10 passes through the protective glass 14 and is focused at the focal plane 20. The protective glass 14 is not strictly necessary and can be omitted, but it is desirable to install it to protect the line illumination light source 10 and lens array 11 from scattering of dust and scratches during use. The material of the protective glass 14 can be any material that transmits the light emitted from the line illumination light source 10, such as a transparent resin such as acrylic resin or cycloolefin resin, or white glass or borosilicate glass. 【0029】 A light source substrate 5 for fixing the light source unit is installed opposite the bottom surface of the line lighting light source 10. This light source substrate 5 is a thin insulating board made of phenol, glass epoxy, etc., and a wiring pattern made of copper foil is formed on its back surface. By inserting the terminals of the light source unit into holes formed at various locations on the light source substrate 5 and joining them to the wiring pattern on the back surface of the light source substrate 5 with solder, the light source unit can be mounted and fixed to the light source substrate 5, and power can be supplied to the light source unit from a predetermined drive power supply (not shown) through the wiring pattern on the back surface of the substrate. 【0030】 The lens array 11 is an optical element that forms an image of light reflected from an object onto the light-receiving unit 12, and can be composed of a rod lens array. In this embodiment, the magnification of the lens array 11 is set to 1 (erect). An ultraviolet light blocking filter film 15 may be provided at any position from the focal plane 20 to the light-receiving unit 12 to block ultraviolet light by reflecting or absorbing it, so that ultraviolet light does not enter the light-receiving unit 12. 【0031】 The light-receiving unit 12 is mounted on the CIS substrate 13 and includes multiple photoelectric conversion elements that receive reflected light from an object and read an image by photoelectric conversion. The material and structure of the photoelectric conversion elements are not particularly limited and may include photodiodes or phototransistors made of amorphous silicon, crystalline silicon, CdS, or CdSe. In this embodiment, a light-receiving IC (Integrated Circuit) chip in which multiple photoelectric conversion elements are arranged in a straight line in the x-direction is arranged along the length direction (x-direction) on a long CIS substrate 13. In addition, if necessary, electrical circuits such as drive circuits or amplification circuits, A / D converters, or connectors for extracting signals to the outside can also be mounted on the CIS substrate 13. 【0032】 In the above embodiment, a reflective, close-contact optical line sensor 100 was described, which irradiates light from a line illumination light source 10 toward an object and receives the light reflected by the object. However, the present invention is not limited to the reflective, close-contact optical line sensor 100, but can also be applied to a transmissive, close-contact optical line sensor, as shown in Figure 2, in which the line illumination light source 10 is positioned on the opposite side of the focal plane 20 from the light receiving unit 12, and the light emitted from the line illumination light source 10 toward the object and transmitted through the object is received. In this case, the only difference from the arrangement in Figure 1 is that the position of the line illumination light source 10 is below the focal plane 20, but the configuration of the line illumination light source 10 itself is the same as the configuration in Figure 1. 【0033】 2. Configuration of the light-receiving section Figure 3A is a schematic diagram showing an example of the configuration of the light-receiving unit 12. Figure 3A shows a bottom view of the light-receiving unit 12 and the CIS substrate 13 as viewed along the z-direction. 【0034】 The light-receiving unit 12 is equipped with multiple light-receiving IC chips 121 as image sensors. The multiple light-receiving IC chips 121 are arranged in a line along the x-direction. Here, "line" is not limited to a configuration in which multiple light-receiving IC chips 121 are arranged on a straight line along the x-direction as shown in Figure 3A, but also includes a configuration in which multiple light-receiving IC chips 121 are arranged in a staggered pattern on two straight lines parallel to the x-direction as shown in Figure 3B. When multiple light-receiving IC chips 121 are arranged in a staggered pattern as shown in Figure 3B, the ends of each light-receiving IC chip may be arranged so that they overlap with the ends of adjacent light-receiving IC chips in the y-direction. 【0035】 Each light-receiving IC chip 121 has multiple photoelectric conversion elements (not shown) arranged in a straight line along the x-direction. Specifically, each light-receiving IC chip 121 is equipped with 300 photoelectric conversion elements and can perform readings with 300 pixels. In this embodiment, 10 such light-receiving IC chips 121 are arranged in a line. However, the number of light-receiving IC chips 121 and the number of photoelectric conversion elements provided in each light-receiving IC chip 121 are not limited to the numbers described above. 【0036】 3. An example of a reading image for correction. In this embodiment, when manufacturing the contact-type optical line sensor 100, a correction parameter is generated by having the light-receiving unit 12 read a correction reading image. When reading an image to be read (the actual object to be read) that is different from the correction reading image, a correction process is performed based on the pre-generated correction parameter. 【0037】 Figure 4 shows an example of a correction image 30. In this example, a black correction image 30 is displayed on a plain white (monochromatic) surface. By transporting a sheet of paper with such a correction image 30 along the focal plane 20 and reading the correction image 30, correction parameters can be generated. 【0038】 Specifically, the correction reading image 30 includes a line image 31 extending in the x-direction (line direction) and equally spaced images 32 arranged at equal intervals in the x-direction. The line image 31 is represented in a straight line with a uniform thickness along the x-direction. The equally spaced images 32 are line-shaped images extending along the y-direction, and multiple equally spaced images 32 are represented parallel to each other at regular intervals in the x-direction. 【0039】 The pitch between the multiple equally spaced images 32 corresponds to the number of pixels on each light-receiving IC chip 121, for example, 300 pixels. One end of each equally spaced image 32 is joined to a line image 31. As a result, multiple T-shaped images continuously joined in the x-direction are represented as the correction reading image 30. The number of T-shaped images corresponds to the number of light-receiving IC chips 121 (for example, 10). 【0040】 However, the correction reading image 30 is not limited to the image shown in Figure 4. For example, the equally spaced image 32 does not have to be joined to the line image 31, and it may extend along a direction that is inclined with respect to the y direction. Also, the equally spaced image 32 may not be a line image, but a dotted image or the like. Thus, the correction reading image 30 is not limited to an image formed by joining multiple T-shaped images. Furthermore, the correction reading image 30 is not limited to black, and the plane on which the correction reading image 30 is represented may be a single color other than white or multiple colors. 【0041】 4. Electrical configuration of a contact-type optical line sensor Figure 5 is a block diagram showing a part of the electrical configuration of the contact-type optical line sensor 100. In addition to the CIS substrate 13 described above, the contact-type optical line sensor 100 includes an FPGA substrate 17 and the like. 【0042】 The CIS board 13 constitutes the reading processing unit 110. The reading processing unit 110 is a functional component of the contact-type optical line sensor 100, and the CIS board 13 functions as a reading processing unit 110 that reads an image of an object based on input signals from multiple light-receiving IC chips 121. As shown in Figure 5, when the correction reading image 30 is read by the reading processing unit 110 as an image of an object, data representing the correction reading image 30 is output from the CIS board 13 to the FPGA board 17. 【0043】 The FPGA board 17 constitutes a parameter storage unit 120 and a correction processing unit 130. The parameter storage unit 120 and the correction processing unit 130 are functional configurations provided in the contact-type optical line sensor 100, respectively. The FPGA board 17 functions as a parameter storage unit 120 that stores correction parameters generated based on the correction reading image 30, and as a correction processing unit 130 that corrects the image to be read based on the correction parameters. 【0044】 An FPGA (Field-Programmable Gate Array) is mounted on the FPGA board 17. An FPGA is an integrated circuit that can be programmed by the purchaser or designer after manufacturing, and in a broad sense, it is a type of PLD (Programmable Logic Device). As shown in Figure 5, when the correction reading image 30 is read by the reading processing unit 110 as an image of the target object, data representing the correction reading image 30 is output from the CIS board 13 to the correction terminal 200 via the FPGA board 17. 【0045】 The correction terminal 200 is configured, for example, as a personal computer and can communicate with the contact-type optical line sensor 100 via wired or wireless connection. When data representing the correction reading image 30 is input to the correction terminal 200, it performs a process to generate correction parameters based on that data. The correction parameters generated by the correction terminal 200 are written to and stored in the FPGA on the FPGA board 17, which serves as the parameter storage unit 120. 【0046】 Thus, when manufacturing the contact-type optical line sensor 100, the correction reading image 30 is read by the reading processing unit 110 as an image of the target object (correction reading step). Then, a predetermined operation is performed on the correction terminal 200, which has data representing the correction reading image 30 as input, and correction parameters are generated based on the correction reading image 30 (parameter generation step). 【0047】 The correction parameters generated at the correction terminal 200 are input from the correction terminal 200 to the contact-type optical line sensor 100 and written to the FPGA on the FPGA board 17 that constitutes the parameter storage unit 120 (writing process). The correction parameters written and stored in the FPGA as the parameter storage unit 120 are read out when the FPGA functions as a correction processing unit 130. 【0048】 5. Generation of correction parameters Figures 6 and 7 illustrate the process for generating correction parameters. When the correction reading image 30 is read by the reading processing unit 110, a portion of the line image 31 may be shifted in the y-direction due to misalignment of the placement of each light-receiving IC chip 121, as shown in Figure 6. Similarly, the pitch P between the equally spaced images 32 may be shifted in the x-direction due to misalignment of the placement of each light-receiving IC chip 121. The generated correction parameters include a first correction parameter for correcting the misalignment in the y-direction and a second correction parameter for correcting the misalignment in the x-direction. 【0049】 The first correction parameter is generated by dividing the correction reading image 30 read by the reading processing unit 110 into multiple (10) segmented images corresponding to each light receiving IC chip 121, as shown by the dashed line in Figure 6, and calculating the amount of displacement of the line image 31 along the y direction and the slope of the line image 31 with respect to the x direction for each segmented image. 【0050】 At this point, the first correction parameter is generated using the linear function y = ax + b. "b" represents the amount of displacement of the line image 31 along the y-direction, and "a" represents the slope of the line image 31 with respect to the x-direction. The first correction parameter can be generated by substituting the x and y coordinates of the line image 31 in each segmented image into the above linear function. 【0051】 The second correction parameter is generated by the reading processing unit 110, based on the correction reading image 30 read and the generated first correction parameter, by generating a corrected image 40 with corrected displacement and tilt in the y-direction, and by calculating the displacement of the equally spaced images 42 along the x-direction. In other words, the second correction parameter is generated so that the pitch P between the equally spaced images 42 is constant in the x-direction. 【0052】 6. Correction Processing Method Figure 8 is a block diagram illustrating the manner in which the correction process is performed. In Figure 8, the electrical configuration of the contact-type optical line sensor 100 is the same as in Figure 5. 【0053】 When a user uses the contact-type optical line sensor 100, the user allows the reading processing unit 110 to read the image to be read 50 as an image of the target object (image to be read process). At this time, data representing the image to be read 50 is output from the CIS board 13 to the FPGA board 17. 【0054】 As described above, correction parameters are pre-programmed into the FPGA on the FPGA board 17. The FPGA, acting as the correction processing unit 130, corrects the image to be read based on these correction parameters (correction process). Specifically, the y-direction shift of the image to be read is corrected by the first correction parameter, and the x-direction shift of the image to be read is corrected by the second correction parameter. 【0055】 The corrected image to be read (corrected image) is output to the user terminal 300. The user terminal 300 is, for example, a personal computer and can communicate with the contact-type optical line sensor 100 via wired or wireless connection. The corrected image may be displayed or printed on the user terminal 300 upon receiving the input. 【0056】 Figure 9 is a diagram illustrating a specific example of the correction process. Figure 9(a) shows a portion of the image 50 to be read by the reading processing unit 110, and Figure 9(b) shows a corrected image in which a portion of the image 50 to be read in Figure 9(a) has been corrected by the FPGA. In Figures 9(a) and 9(b), the hatched pixels represent a portion of the corrected reading image 30 (line image 31). 【0057】 When a corrected image is output from the FPGA, the data of each pixel is sequentially read in an order based on the correction parameters (first correction parameter and second correction parameter) pre-written to the FPGA, and output to the user terminal 300. As a result, the user terminal 300 obtains a corrected image of the read image (corrected image) with the misalignment corrected, as shown in Figure 9(b). 【0058】 The correction method may include so-called subpixel processing. Subpixel processing may include bilinear processing, which calculates the brightness value after movement from the brightness values ​​of the pixel position before movement and the four surrounding pixels, or bicubic processing, which calculates the brightness value after movement from the brightness values ​​of the pixel position before movement and the sixteen surrounding pixels. Alternatively, the correction method may include non-subpixel processing such as nearest neighbor processing, which moves the pixel by an integer number of pixels based on the amount of displacement. 【0059】 7. Effects (1) In this embodiment, first correction parameters and second correction parameters are generated based on the correction reading image 30, and errors in the reading image 50 due to the misalignment of each light receiving IC chip 121 can be suitably corrected based on these correction parameters. 【0060】 (2) In this embodiment, different correction parameters are written to the PLD for each contact-type optical line sensor 100, and the error of the image to be read 50 can be suitably corrected based on these correction parameters. In particular, since the PLD is made up of an FPGA, the correction parameters can be written to the FPGA in advance, and the corrected image to be read 50 can be output by the FPGA. 【0061】 (3) In this embodiment, when generating the first correction parameters based on the correction reading image, the first correction parameters can be appropriately calculated by calculation using a linear function, so that errors in the reading image 50 due to the misalignment of each light-receiving IC chip 121 can be corrected more effectively. Furthermore, if the correction is performed by subpixel processing, the errors in the reading image 50 due to the misalignment of each light-receiving IC chip 121 can be corrected even more effectively. [Explanation of symbols] 【0062】 12 Light receiving section 13 CIS substrates 17 FPGA boards 30 Correction reading image 31 Line Images 32 equally spaced images 40 Corrected Images 42 equally spaced images 50 Images to be read 100 Close-contact optical line sensors 110 Reading Processing Unit 120 Parameter storage unit 121 Light-receiving IC chip 130 Correction Processing Unit

Claims

[Claim 1] An optical line sensor that reads images of an object being transported along the transport direction using multiple image sensors arranged in a line, A reading processing unit reads an image of the object based on input signals from the plurality of image sensors, When a correction reading image, which includes a line image extending in a line direction perpendicular to the transport direction and equally spaced images arranged at equal intervals in the line direction, is read by the reading processing unit as an image of the object, a parameter storage unit stores correction parameters generated based on the correction reading image, The system includes a correction processing unit that corrects the image to be read based on the correction parameters when the reading processing unit reads an image to be read that is different from the correction reading image as an image of the object, The aforementioned correction parameters include: The reading processing unit divides the correction reading image read by the reading processing unit into a plurality of segmented images corresponding to each image sensor, and for each segmented image, the amount of displacement of the line image along the transport direction and the inclination of the line image with respect to the line direction are calculated to generate a first correction parameter, This includes a second correction parameter generated by calculating the amount of displacement of the equally spaced images along the line direction based on the correction reading image read by the reading processing unit, The first correction parameter is generated by calculating "b," which is the amount of displacement of the line image along the transport direction, and "a," which is the inclination of the line image with respect to the line direction, using the linear function equation y = ax + b, in an optical line sensor. [Claim 2] The optical line sensor according to claim 1, wherein the parameter storage unit and the correction processing unit are configured with a PLD on which the correction parameters are written and which corrects the image to be read, which is read by the reading processing unit based on the correction parameters. [Claim 3] The optical line sensor according to claim 2, wherein the PLD is composed of an FPGA. [Claim 4] The optical line sensor according to any one of claims 1 to 3, wherein the correction processing unit corrects the correction based on the correction parameters by sub-pixel processing. [Claim 5] The optical line sensor according to any one of claims 1 to 4, wherein the optical line sensor is of the contact type. [Claim 6] A method for manufacturing an optical line sensor according to any one of claims 1 to 5, A correction reading step in which the correction reading image is read by the reading processing unit as an image of the object, A parameter generation step of generating correction parameters based on the correction reading image, A method for manufacturing an optical line sensor, comprising a writing step of writing the correction parameters to the parameter storage unit. [Claim 7] A correction processing method for an optical line sensor according to any one of claims 1 to 5, A reading image step in which the reading image is read by the reading processing unit as an image of the object, A correction processing method comprising a correction step of correcting the image to be read in the correction processing unit based on the correction parameters.

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