JP2011223301A - Image processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processor which is able to constrain reduction in accuracy of calibration without being affected by the light transmittance of a test chart printed sheet.SOLUTION: A compound machine mounted with the image processor includes: a printer 12 to create a test chart document by printing density patches on a sheet; a scanner 13 to read the printed test chart document and to output the read value indicating the brightness of the density patches; a calibration part 25 to calibrate by associating the reference value of the density patch with the read value; a transmittance measuring unit 39 to measure the light transmittance of the sheet; and a correction part 24 to correct the read value darker as the light transmittance is higher. The calibration part 25 calibrates by using the corrected read value.

Description

  The present invention relates to an image processing apparatus.

  Conventionally, an image processing apparatus having a function of optically reading a document (scanner function) is widely known. In general, in an image processing apparatus, when a document is read, the document is irradiated with light from the transparent glass table side while the document is sandwiched between a transparent glass table and a back plate. Then, the light reflected on the document enters an image sensor such as a CCD sensor and is converted into an electric signal. As described above, in the image processing apparatus, the original is read by reading the intensity of light reflected by the original with the image sensor.

  In addition, the image processing apparatus outputs the generated read image data to a built-in printer or a printer connected via a network, and the read image data is printed by the output destination printer, thereby copying a document. There is something to do. In general, the characteristics of scanners and printers vary, and this type of image processing apparatus is calibrated so that the colors on the original are accurately reproduced on the copy paper by eliminating the variations. Copy calibration) is performed.

  For example, the image forming apparatus described in Patent Document 1 below reads, with a scanner, read data obtained by reading a reference gradation bar with a scanner and an output gradation bar chart obtained by printing the read data with a printer. Is compared with the read data obtained in this manner, and a correction value for bringing the read data gradation of the output gradation bar chart closer to the read data gradation of the reference gradation bar is determined. Through the above processing, the image forming apparatus described in Patent Document 1 performs calibration.

JP-A-7-273997

  However, in the case of the image forming apparatus described in Patent Document 1, the accuracy of calibration may be reduced depending on the paper on which the read data is printed. In the image processing apparatus, the light incident on the image sensor includes reflected light reflected on the original and reflected light transmitted through the original, reflected on the back plate, transmitted again through the original, and incident on the image sensor. Due to inclusion. That is, the greater the light transmittance of the document, the greater the amount of light that is transmitted through the document and reflected by the back plate. For this reason, when the intensity of the light that is reflected by the back plate, passes through the original again, and is incident on the image sensor is detected by the image sensor, the color tone is read brightly due to the influence of this light. The accuracy may be reduced.

  In general, the light transmittance of a document increases as the thickness of the document decreases. If calibration is performed using a sheet having a thickness equal to or less than a certain level, the accuracy of calibration may be reduced.

  The present invention has been made to solve the above problems, and image processing capable of suppressing a decrease in calibration accuracy regardless of the light transmittance or thickness of the paper on which the test chart is printed. An object is to provide an apparatus.

  The image processing apparatus according to the present invention includes: a reading unit that optically reads a document to generate read image data of the document; and a reading unit that generates read image data of a test chart document on which a density patch is printed. A calibration means for performing calibration by associating a read value indicating the lightness of the density patch obtained from the read image data with a reference value of the density patch; and an acquisition means for acquiring the light transmittance of the test chart document; Correction means for correcting so that the lightness indicated by the read value output by the reading means decreases as the light transmittance of the test chart document acquired by the acquiring means increases, and the calibration means includes the correcting means Calibration is performed using the read value corrected by the above.

  According to the image processing apparatus of the present invention, the density patch is printed and a test chart document is created. Then, the created test chart document is read to generate read image data of the test chart document, and a read value indicating the brightness of the density patch is obtained from the read image data. On the other hand, the light transmittance of the test chart document is acquired, and as the acquired light transmittance is larger, the lightness indicated by the read value is corrected to be lowered. Then, calibration is performed using the corrected reading value. Accordingly, even when the light transmittance of the test chart document is large and the reading value becomes brighter due to the influence of the light reflected on the back plate, it is obtained when the test chart document is not affected by the light reflected on the back plate. Calibration is performed after correction to match the read value. Therefore, it is possible to suppress a decrease in calibration accuracy regardless of the light transmittance of the paper on which the test chart is printed.

  In the image processing apparatus according to the present invention, the acquisition unit includes a light projector and a light receiver arranged so as to face each other in the paper thickness direction of the test chart document with the test chart document interposed therebetween, and the light transmittance of the test chart document It is preferably a photoelectric sensor that measures According to this preferable configuration, the light transmittance of the test chart document can be easily measured.

  In the image processing apparatus according to the present invention, it is preferable that the correction unit corrects each read value output by the reading unit using a correction characteristic that defines a relationship between a value before correction and a value after correction. . According to this preferable configuration, a corrected value can be obtained for each read value of the density patch based on the correction characteristic, so that correction suitable for each read value can be performed.

  In the image processing apparatus according to the present invention, the correction unit obtains one correction characteristic based on the light transmittance of the test chart document from among a plurality of correction characteristics set according to the light transmittance of the test chart document. It is preferable to select and perform correction based on the selected correction characteristic.

  According to this preferred configuration, a correction characteristic more suitable for correction can be selected from a plurality of correction characteristics set according to the light transmittance of the test chart document. Therefore, more suitable correction can be performed according to the light transmittance of the test chart document, and it is possible to further suppress a decrease in calibration accuracy.

  The image processing apparatus according to the present invention includes: a reading unit that optically reads a document to generate read image data of the document; and a reading unit that generates read image data of a test chart document on which a density patch is printed. A calibration unit that performs calibration by associating a reading value indicating the brightness of the density patch obtained from the read image data with a reference value of the density patch, a measurement unit that measures the paper thickness of the test chart document, and a measurement And a correction unit that corrects the lightness indicated by the read value output by the reading unit as the paper thickness of the test chart document measured by the unit is smaller. The calibration unit is corrected by the correction unit. It is characterized in that calibration is performed using the read value after the reading.

  According to the image processing apparatus of the present invention, the density patch is printed and a test chart document is created. Then, the created test chart document is read to generate read image data of the test chart document, and a read value indicating the brightness of the density patch is obtained from the read image data. On the other hand, the paper thickness of the test chart document is measured, and as the measured paper thickness is smaller, the lightness indicated by the read value is corrected to decrease, and calibration is performed using the corrected read value. . As a result, even when the test chart document is thin and the reading value becomes brighter due to the influence of the light reflected on the back plate, the reading obtained when the test chart document is not affected by the light reflected on the back plate. After being corrected to match the value, calibration is performed. Therefore, it is possible to suppress a decrease in calibration accuracy regardless of the sheet thickness of the sheet on which the test chart is printed.

  The image processing apparatus according to the present invention includes: a reading unit that optically reads a document to generate read image data of the document; and a reading unit that generates read image data of a test chart document on which a density patch is printed. Calibration means for performing calibration by associating the read value indicating the brightness of the density patch obtained from the read image data with the reference value of the density patch, and accepting information indicating that the paper thickness of the test chart document is thin And a correction means for correcting so as to reduce the lightness indicated by the read value output by the reading means when the information indicating that the paper thickness of the test chart document is thin is received by the receiving means. The means calibrates using the read value after correction by the correction means. To.

  According to the image processing apparatus of the present invention, the density patch is printed on the paper by the printing unit to create the test chart document. Then, the created test chart document is read to generate read image data of the test chart document, and a read value indicating the brightness of the density patch is obtained from the read image data. On the other hand, when information indicating that the paper thickness of the test chart document is thin is received, correction is performed so as to reduce the brightness indicated by the read value, and calibration is performed using the corrected read value. As a result, even when the test chart document is thin and the reading value becomes brighter due to the influence of the light reflected on the back plate, the reading obtained when the test chart document is not affected by the light reflected on the back plate. After being corrected to match the value, calibration is performed. Therefore, it is possible to suppress a decrease in calibration accuracy regardless of the sheet thickness of the sheet on which the test chart is printed.

  According to the present invention, it is possible to suppress a decrease in calibration accuracy regardless of the light transmittance or paper thickness of the paper on which the test chart is printed.

1 is a block diagram illustrating a configuration of a multifunction machine in which an image processing apparatus according to an embodiment is mounted. It is a figure which shows an example of a test chart original document. FIG. 2 is a schematic diagram illustrating a document transport mechanism included in a multifunction peripheral. FIG. 3 is a block diagram illustrating a configuration of a control unit included in the multifunction peripheral. It is a graph which shows an example of a correction characteristic. It is a formula which shows the function which linked the reading value and the value after amendment. 6 is a flowchart illustrating a calibration processing procedure by the multifunction peripheral.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. First, the configuration of the multifunction machine 1 in which the image processing apparatus according to the present embodiment is mounted will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration of the multifunction machine 1.

  The multifunction device 1 has a document reading function in addition to a printing function and a FAX function. The multifunction device 1 also has a function of performing calibration in order to improve the color tone reproducibility of the document in the copy process. Calibration is performed using a test chart printed on a sheet by the multifunction device 1. Since the read value obtained by reading the test chart changes depending on the light transmittance of the paper on which the test chart is printed, the multifunction device 1 calibrates using the value obtained by correcting the read value according to the light transmittance of the paper. I do.

  As shown in FIG. 1, the multifunction device 1 includes an operation panel 10, a display 11, a printer 12, a scanner 13, an image memory 14, a LAN interface 15, an NCU 16, a modem 17, and a control unit 20.

  The operation panel 10 includes a plurality of operation buttons that are used by the user to operate the multifunction device 1. The display 11 displays various setting contents. The user can perform various operations by referring to the display on the display 11 and using the operation panel 10.

  The printer 12 is an electrophotographic printer, and prints various image data on paper. When performing calibration, the printer 12 generates a test chart document by printing test data on a sheet. The test data may be stored in advance as image data, or a program for generating test data may be stored, and the test data may be generated by the stored program. When test data is generated by a program, the program is executed to generate test data when performing calibration.

  FIG. 2 shows an example of the test chart document 50. The test chart document 50 has a plurality of (seven in this embodiment) density patches 52 printed on a sheet 51. The plurality of density patches 52 have gray gradations that differ in stages from the brightest white to the darkest black. In FIG. 2, the gray gradation difference is indicated by the hatching interval. A reference value indicating a gradation value is determined for each of the plurality of density patches 52 and stored in the storage unit 22 described later. The reference value may be calculated by a stored program. Each density patch 52 is printed by the printer 12 based on this reference value.

  Returning to FIG. 1, the description will be continued. The scanner 13 is composed of a light source, a CCD sensor 13a, and the like, and reads a document set on the multifunction machine 1. The CCD sensor 13a is a line type color sensor that scans an original in a line shape and separates and reads the image information of the original into three primary colors of red, green, and blue (RGB). The read image data output from the CCD sensor 13a includes data indicating the intensity of light of each RGB color.

  The scanner 13 scans the entire document and converts the read image data obtained from the CCD sensor 13a from the RGB color space to the YCC color space to generate read image data. The YCC color space is a color space represented using luminance (Y) and color difference (Cb, Cr). In the present embodiment, the luminance is indicated using gradation values from 0 to 255. The read image data generated by the scanner 13 is subjected to image processing by the control unit 20 and stored in the image memory 14 as output image data.

  Normally, the scanner 13 reads a general document different from the test chart document 50 and generates read image data. On the other hand, when calibration is performed, the test chart document 50 is read by the scanner 13, and read image data of the test chart document 50 is generated. The generated read image data of the test chart document 50 is output to the control unit 20. The read image data of the test chart document 50 includes a read value indicating the luminance (brightness) of each density patch 52. The scanner 13 functions as a reading unit described in the claims.

  The test chart document 50 is read while being transported by the document transport mechanism. Here, the document transport mechanism will be described with reference to FIG. FIG. 3 is a schematic diagram illustrating a document transport mechanism included in the multifunction machine 1. The document transport mechanism functions as an auto document feeder (ADF), and transports the document from the document tray 31 to the discharge tray via the reading position 32 along the transport path 33. When performing calibration, the above-described test chart document 50 is conveyed. In FIG. 3, the conveyance path 33 from the document tray 31 to the discharge tray is represented by a straight line. However, in an actual multifunction machine, the conveyance path 33 is curved and a discharge tray is provided below the document tray 31. ing.

  The test chart document 50 set on the document tray 31 is picked up by a pickup roller 34 disposed on the document tray 31. The picked-up test chart document 50 is fed to the conveyance path 33 by a paper feed roller 35 disposed on the downstream side of the pickup roller 34. The test chart document 50 fed to the conveyance path 33 is detected by a first document detection sensor 37 disposed along the conveyance path 33.

  In the conveyance path 33, three pairs of conveyance rollers 38 are arranged along the conveyance path 33. The test chart document 50 is transported by the three pairs of transport rollers 38 toward the paper discharge tray on the transport path 33. During the conveyance, the light transmittance of the test chart document 50 is measured by the transmittance measuring device 39. The transmittance measuring device 39 includes a light projecting device 39a and a light receiving device 39b arranged so as to face each other in the sheet thickness direction of the test chart document 50 with the test chart document 50 conveyed on the conveyance path 33 interposed therebetween. It is a sensor. The transmittance measuring device 39 functions as an acquisition unit described in the claims. Note that visible light, infrared light, or the like can be used as the light projected by the light projector 39a and the light received by the light receiver 39b.

  After the light transmittance is measured, when the leading edge of the test chart document 50 reaches the reading position 32, the leading edge of the test chart document 50 is detected by the second document detection sensor 40. Subsequently, the reading operation of the test chart document 50 by the scanner 13 is started. At the reading position 32, the transparent glass 43 and the white back plate 44 are arranged to face each other with the conveyance path 33 interposed therebetween, and the test chart document 50 is conveyed between the transparent glass 43 and the back plate 44. Then, light is irradiated from the transparent glass 43 side, and the light reflected from the original enters the CCD sensor 13a. Further, the light transmitted through the test chart document 50 and reflected by the back plate 44 and again transmitted through the test chart document 50 also enters the CCD sensor 13a.

  When the rear end of the test chart document 50 is detected by the second document detection sensor 40 and passes through the reading position 32, the reading operation ends. When the leading edge of the test chart document 50 that has passed the reading position 32 reaches near the end of the conveyance path 33, the leading edge of the test chart document 50 is detected by the third document detection sensor 41. Then, the test chart document 50 is conveyed to the discharge tray by the discharge roller 42 disposed at the end of the conveyance path 33.

  As described above, the test chart document 50 is conveyed via the reading position 32 of the scanner 13, whereby the test chart document 50 is read, and read image data including the reading value of the density patch 52 is generated. Further, while the test chart document 50 is being conveyed, the light transmittance of the test chart document 50 is measured on the upstream side of the reading position 32.

  The control unit 20 shown in FIG. 1 includes a CPU 18, a ROM 19 that stores a control program, and a RAM. The control unit 20 controls the above-mentioned hardware constituting the multifunction machine 1 in an integrated manner by executing a control program.

  The control unit 20 will be described with reference to FIG. FIG. 4 is a block diagram illustrating a configuration of the control unit 20. The control unit 20 functions as a comparison unit 21, a storage unit 22, an acquisition unit 23, a correction unit 24, and a calibration unit 25. The arrows shown in FIG. 4 indicate the flow of data between functional blocks, and the hardware configuring the control unit 20 can be configured regardless of the arrows shown in FIG.

  The comparison unit 21 compares the light transmittance of the test chart document 50 output by the transmittance measuring device 39 with the reference value stored in the storage unit 22, and outputs the comparison result to the correction unit 24. More specifically, the transmittance measuring device 39 samples a predetermined area of the test chart document 50 a plurality of times while the test chart document 50 passes between the projector 39a and the light receiver 39b. The predetermined area where light is projected by the projector 39a is preferably an area where the density patch 52 is not printed. For this reason, when the density patch 52 is printed by the printer 12, it is preferable to print the density patch 52 so that the position of the scanner 13 in the test chart document 50 in the main scanning direction is different from the predetermined area. It is preferable to print the density patch 52 at a position different from the sampling position of the transmittance measuring device 39 in the scanning direction.

  The comparison unit 21 inputs a plurality of sampling results from the transmittance measuring device 39 and sets the most frequently used sampling result as the light transmittance of the test chart document 50. Further, the comparison unit 21 outputs an error when the obtained light transmittance is out of the predetermined range. When an error is output, the calibration process is stopped. The predetermined range is set to a range of light transmittance of white paper. Thereby, for example, when the paper 51 of the test chart document 50 is a colored sheet, or when characters or pictures are written at the sampling location of the transmittance measuring device 39 in the test chart document 50, the light transmittance is predetermined. Since it is out of range, the calibration process is stopped.

  Then, the comparison unit 21 compares the light transmittance of the test chart document 50 with a predetermined reference value. This reference value is set to, for example, the light transmittance of the paper that is below the level at which the light reflected by the back plate 44 and transmitted again through the paper is detected by the CCD sensor. Accordingly, it is possible to determine whether or not the test chart document 50 is brightly read by the light reflected by the back plate 44 and transmitted through the paper again by the comparison by the comparison unit 21.

  The acquisition unit 23 acquires the reading value of each density patch 52 by processing the read image data output from the scanner 13. Specifically, the acquisition unit 23 extracts a plurality of RGB reading values in the region where the density patch 52 is located from the read image data, and calculates an average of the extracted reading values for each RGB. . The calculated value is used as the read value of the density patch 52. In this way, the acquisition unit 23 acquires RGB read values for each density patch 52. Then, the acquisition unit 23 outputs the obtained reading value to the correction unit 24.

  When the comparison result indicating that the light transmittance of the test chart document 50 is equal to or less than the reference value is input, the correction unit 24 outputs the reading value of each density patch 52 to the calibration unit 25 without correcting it. When the comparison result indicating that the light transmittance of the test chart document 50 is greater than the reference value is input, the acquisition unit 23 corrects the read value of each density patch 52 and then outputs the correction value to the calibration unit 25.

  When the light transmittance of the test chart document 50 is larger than the reference value, the read value is corrected and then output to the calibration unit 25 because the read value by the scanner 13 becomes brighter as the light transmittance increases. . This is because as the light transmittance of the test chart document 50 increases, the amount of light transmitted through the test chart document 50, reflected by the back plate located on the back surface, and transmitted again through the test chart document 50 and incident on the CCD sensor 13a. Because it grows.

  The correction unit 24 corrects the read value based on the correction characteristic that defines the relationship between the value before correction and the value after correction of the read value output from the acquisition unit 23. FIG. 5 is a graph showing an example of correction characteristics. The horizontal axis indicates the read value output from the acquisition unit 23, and the vertical axis indicates the value after correction. The read value and the correction value indicate that the lightness is higher (brighter) as the gradation value from 0 to 255 is larger.

  For example, when the read value “a” is corrected based on the correction characteristics of FIG. 5, the corrected value becomes (a−α), and is corrected to be smaller by α. That is, the correction unit 24 corrects the luminance (lightness) indicated by the read value so as to decrease. In order to perform correction based on this correction characteristic, a function in which the read value and the corrected value are associated with each other may be used, or a lookup table may be used. A function in which the read value and the corrected value are associated with each other is expressed by, for example, the equation of FIG. In the equation of FIG. 6, when γ <1, the function becomes a downwardly convex curve. The correction unit 24 functions as a correction unit described in the claims.

  The calibration unit 25 performs calibration using the read value of each density patch 52 output from the correction unit 24. Here, calibration refers to associating a value before correction and a value after correction with respect to a reading value obtained by the scanner 13 so that the color on the original is accurately reproduced on the copy paper at the time of copy processing. This is a process of creating a lookup table for tone correction (for gamma correction).

  The storage unit 22 stores a gradation value (reference value) indicating the luminance of each density patch 52. The calibration unit 25 uses the read value of the density patch 52 and the target value (reference value) to create a lookup table for tone correction.

  The look-up table for gradation correction can be generated using the following method. For example, when the read values xi (i = 1, 2,..., 7) of the seven density patches 52 are obtained, the value y (xi) obtained by substituting the read values xi into the function y (x). ) And the target value are determined using the least square method so as to minimize the difference between the target value and the target value. Then, the correction value y (xi) calculated by the function y (x) is associated with the read value xi, and a lookup table for gradation correction can be created.

  Further, for example, a lookup table for gradation correction may be created by associating read values with one-to-one correspondence with target values of a plurality of density patches 52. In this case, it is preferable to interpolate values between read values obtained from the plurality of density patches 52 by performing an interpolation process.

  The calibration unit 25 outputs the created lookup table to the storage unit 22, and the gradation correction lookup table is stored in the storage unit 22. This look-up table for tone correction is used for tone correction of read image data obtained when the original is read later.

  Further, the control unit 20 performs gamma correction on the read image data of the document generated by the scanner 13 using the tone correction lookup table generated by the calibration unit 25 during the copy process. Is provided. When performing the copy process, the document is read by the scanner 13, and read image data of the document is output from the scanner 13 to the image processing unit 26. The image processing unit 26 includes a gamma correction unit 26 a, and the gamma correction unit 26 a performs gamma correction of the read value included in the read image data using the gradation correction lookup table stored in the storage unit 22. Do. The image processing unit 26 performs various image processing so that the printer 12 can print the read image data, and outputs the processed image data to the printer 12. The printer 12 prints the read image data of the output document on paper.

  In addition, the LAN interface 15 shown in FIG. 1 is connected to a LAN (local area network) and controls input / output of information between the LAN and the multi-function peripheral 1. The NCU 16 controls the connection between the modem 17 and the public switched telephone network (PSTN) 90 and controls the FAX transmission / reception function.

  Subsequently, the operation of the multifunction machine 1 will be described with reference to FIG. FIG. 7 is a flowchart illustrating a calibration processing procedure by the multifunction machine 1.

  First, when the user sets the paper 51 in the paper tray and receives an input to perform calibration from the user, the multifunction device 1 is set to the calibration mode in step S101. In step S102, the test chart is printed on the paper 51, and the test chart document 50 is generated. When the generated test chart document 50 is set on the document tray 31 and an input for performing a reading operation is received from the user, in step S103, conveyance of the test chart document 50 is started.

  In step S104, the light transmittance of the test chart document 50 is measured by the transmittance measuring device 39. In step S <b> 105, each density patch 52 of the test chart document 50 is read by the scanner 13 during conveyance of the test chart document 50. In step S106, the light transmittance of the test chart document 50 measured in step S104 is compared with the reference value. As a result of the comparison, if the light transmittance of the test chart document 50 is equal to or less than the reference value, the process proceeds to step S108.

  As a result of the comparison in step S106, when the light transmittance of the test chart document 50 is larger than the reference value, the process proceeds to step S107. In step S107, the read value of each density patch 52 is corrected darkly based on the correction characteristics. Subsequently, in step S108, a lookup table is created using the read value and target value of each density patch 52. That is, when the reading value is not corrected, calibration is performed using the reading value obtained by the acquisition unit 23. When the reading value is corrected, calibration is performed using the corrected reading value. Thereby, even when the light transmittance of the test chart document 50 is large, a look-up table obtained when a sheet having a reference light transmittance is used can be obtained.

  In the MFP 1 described above, the light transmittance of the test chart document 50 is measured, and when the light transmittance is larger than the reference value, the read value is corrected darkly, and calibration is performed using the corrected read value. Is called. As a result, even when the light transmittance of the paper 51 of the test chart document 50 is larger than the reference, it is corrected so as to coincide with the read value obtained when the paper having the reference light transmittance is used. Calibration is performed. Therefore, it is possible to suppress a decrease in calibration accuracy regardless of the light transmittance of the paper on which the test chart is printed. As a result, even if the user performs calibration using a paper having a light transmittance larger than the light transmittance that is a reference for calibration, it is possible to suppress a decrease in calibration accuracy.

  Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications can be made. Hereinafter, modified examples will be described.

  In the above embodiment, there is one correction characteristic, but the present invention is not limited to this. For example, a plurality of correction characteristics may be set according to the light transmittance of the test chart document 50. In this case, the light transmittance of the test chart document 50 and the correction characteristics are stored in association with each other. Then, the correction unit 24 selects a correction characteristic based on the light transmittance of the test chart document 50 measured by the transmittance measuring device 39. With this configuration, the read value can be corrected using a more suitable correction characteristic in accordance with the light transmittance of the test chart document 50 to be read. That is, when the light transmittance of the test chart document 50 is equal to or higher than the reference value, the lightness indicated by the read value can be corrected so as to decrease as the light transmittance of the test chart document 50 increases. Further, regardless of whether or not the light transmittance of the test chart document 50 is equal to or higher than a reference value, the lightness indicated by the read value may be corrected to decrease as the light transmittance of the test chart document 50 increases.

  In the above embodiment, the light transmittance of the test chart document 50 is measured in order to obtain the light transmittance of the test chart document 50. However, the light transmittance of the test chart document 50 may be estimated. For example, the front surface (printing surface) and the back surface of the test chart document 50 are read by the scanner 13 to generate read image data of the front surface and the back surface. When the back surface is read by the scanner 13, the pattern printed on the front surface is thinly reflected on the back surface, so that the thinly reflected pattern is read by the scanner 13. The light transmittance of the test chart document 50 can be estimated based on the read image data on the front surface and the read image data on the back surface.

  In the above embodiment, the light transmittance of the test chart document 50 is measured in order to obtain the light transmittance of the test chart document 50. However, in order to obtain the light transmittance of the test chart document 50, the test chart document 50 is obtained. The opacity of may be measured. The opacity of the paper is measured by the opacity test method for paper and paperboard (JIS standard number JISP8149) and has a correlation with the light transmittance of the paper. Opacity is reduced. Therefore, by measuring the opacity, the degree of influence on the gradation value by the reflected light that is transmitted through the test chart document 50, reflected by the back plate, transmitted through the test chart document 50 again, and incident on the CCD sensor is measured. Can be estimated.

  In the above embodiment, whether or not to correct the reading value is determined based on the light transmittance of the test chart document 50. However, the present invention is not limited to this. Any device that can estimate the degree of influence on the reading value by the reflected light that passes through the test chart document 50 and enters the CCD sensor may be used. For example, generally, as the paper thickness of the test chart document 50 becomes thinner, the intensity of reflected light incident on the CCD sensor increases and the degree of influence on the read value increases. Therefore, for example, a measurement unit that measures the paper thickness of the test chart document 50 may be provided, and the reading value may be corrected when the paper thickness of the test chart document 50 is equal to or less than a reference value. As a measuring means for measuring the paper thickness of the test chart document 50, for example, a displacement sensor for measuring the displacement amount of the pair of conveying rollers 38 can be used. Since the test chart document 50 is conveyed while being sandwiched between a pair of conveyance rollers 38, the paper thickness of the test chart document 50 can be measured during conveyance. An ultrasonic sensor or the like can also be used as a measuring unit that measures the paper thickness of the test chart document 50.

  Further, instead of the comparison result by the comparison unit 21, the read value may be corrected when an input indicating that the paper thickness is thin is received from the operation panel 10. For example, when an input indicating that the paper thickness is thin is received from the user, the read value may be corrected. In this case, the operation panel 10 functions as a receiving unit described in the claims.

  In the above embodiment, the case where the image processing apparatus according to this embodiment is mounted on a multifunction peripheral has been described. However, the present invention is not limited to this. A device equipped with the image processing apparatus of the present embodiment may not have a print, FAX, IFAX, or network function. For example, the image processing apparatus of this embodiment may be mounted on a device having only a copy function, or may be mounted on a device having only a scan function.

  When only the scan function is provided, the image processing apparatus is connected to a printer via a network, and performs calibration using a test chart document 50 printed by the connected printer. As a result, calibration of copy processing performed by the scanner 13 and a printer connected via a network can be performed. When performing copy processing, read image data of a document generated by the scanner 13 is subjected to image processing including gamma correction by the image processing unit 26, and is output to a printer via a network. Then, the read image data of the original is printed by a network-connected printer.

  In the above embodiment, the transmittance measuring device 39 is provided separately from the first to third document detection sensors 37, 40, 41. However, any one of the first to third document detection sensors 37, 40, 41 is detected. The sensor may function as a transmittance measuring device that measures the light transmittance of the document 33. The first to third document detection sensors 37, 40, 41 are composed of a projector and a light receiver, and when the value detected by the light receiver becomes a value greater than the reference value to a value less than the reference value, This is a sensor for detecting that the tip of the test chart document 50 has reached the detection position. In this case, it is not necessary to provide the transmittance measuring device 39 separately.

  In the above embodiment, the light transmittance of the test chart document 50 is measured in order to obtain the light transmittance of the test chart document 50. However, in order to obtain the light transmittance of the test chart document 50, the light output from the projector 39a is obtained. The amount of light transmitted through the test chart document 50 may be measured in a state where the amount of light transmitted is constant.

  In the above-described embodiment, the image processing apparatus according to the present invention is applied when the test chart document 50 is read by ADF. However, the test chart document 50 may be applied when read by an FBS (flat bed scanner). In the case of FBS, the gap between the back plate and the transparent glass is smaller than in the case of ADF. For this reason, in the case of FBS, the distance between the test chart document 50 and the back plate is smaller than in the case of ADF. Therefore, in the case of FBS, the intensity of light reflected on the back plate and transmitted again through the test chart document 50 and incident on the CCD sensor is higher than that in the case of ADF. The influence is large and the reading is bright. Therefore, at the time of calibration, it is preferable to switch the correction characteristic for correcting the read value between when the test chart document 50 is read by ADF and when it is read by FBS. In this case, the correction characteristic used in the case of FBS is a correction characteristic that corrects the reading value smaller than the correction characteristic used in the case of ADF. As a result, even if the reading is brighter than ADF in the case of FBS, it can be corrected to an appropriate gradation value.

  In the above embodiment, the case where the read image data of the test chart document 50 is color has been described. However, the read image data obtained by the scanner may be monochrome. Monochrome read image data can be generated by a scanner having a CCD sensor that reads only one component color. In addition, when a scanner having a CCD sensor that decomposes and reads RGB three components is used, monochrome read image data can be generated by acquiring image data of any one of the RGB three components.

DESCRIPTION OF SYMBOLS 1 Multifunction machine 10 Operation panel 12 Printer 13 Scanner 20 Control part 21 Comparison part 22 Storage part 23 Acquisition part 24 Correction part 25 Calibration part 26 Image processing part 39 Transmittance measuring device

Claims (6)

Reading means for optically reading a document to generate read image data of the document;
When the read image data of the test chart document on which the density patch is printed is generated by the reading unit, the read value indicating the lightness of the density patch obtained from the read image data is associated with the reference value of the density patch. Calibration means for performing calibration,
Obtaining means for obtaining the light transmittance of the test chart document;
Correction means for correcting so as to reduce the lightness indicated by the read value output by the reading means, as the light transmittance of the test chart document acquired by the acquiring means is large;
With
The image processing apparatus according to claim 1, wherein the calibration unit performs calibration using a reading value corrected by the correction unit.   The acquisition means is a photoelectric sensor that includes a projector and a light receiver arranged to face each other in the paper thickness direction of the test chart document with the test chart document interposed therebetween, and is a photoelectric sensor that measures the light transmittance of the test chart document. The image processing apparatus according to claim 1, wherein the image processing apparatus is provided.   The correction means corrects each read value output by the reading means using a correction characteristic that defines a relationship between a value before correction and a value after correction. An image processing apparatus according to 1.   The correction means selects and selects one correction characteristic based on the light transmittance of the test chart document from the plurality of correction characteristics set according to the light transmittance of the test chart document. The image processing apparatus according to claim 3, wherein correction is performed based on correction characteristics. Reading means for optically reading a document to generate read image data of the document;
When the read image data of the test chart document on which the density patch is printed is generated by the reading unit, the read value indicating the lightness of the density patch obtained from the read image data is associated with the reference value of the density patch. Calibration means for performing calibration,
Measuring means for measuring the paper thickness of the test chart document;
Correction means for correcting so that the lightness indicated by the read value output by the reading means decreases as the paper thickness of the test chart document measured by the measuring means decreases,
With
The image processing apparatus according to claim 1, wherein the calibration unit performs calibration using a reading value corrected by the correction unit. Reading means for optically reading a document to generate read image data of the document;
When the read image data of the test chart document on which the density patch is printed is generated by the reading unit, the read value indicating the lightness of the density patch obtained from the read image data is associated with the reference value of the density patch. Calibration means for performing calibration,
Receiving means for receiving information indicating that the test chart document is thin;
When the information indicating that the paper thickness of the test chart document is thin is received by the reception unit, a correction unit that corrects the brightness indicated by the read value output by the reading unit,
With
The image processing apparatus according to claim 1, wherein the calibration unit performs calibration using a reading value corrected by the correction unit.

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