JP2018182529A - Image reading apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reading apparatus that can suppress accuracy degradation of shading compensation when an image printed in a web is read while avoiding waste of the web or degradation of printing productivity in a printing apparatus which prints in the web.SOLUTION: A reading control unit 63 controls an image reading unit 23 to read both end parts of a white reference roller to generate end part reading data when an image printed in a web is read, generates inner side white reference data being the white reference data of an inner side area than both ends in a width direction of the web on the basis of pre-existing white reference data and end part reading data which are obtained by the image reading unit 23 by reading the white reference roller in a state in which there is no web between the image reading unit 23 and the white reference roller in advance, and performs shading compensation to the read image data which is obtained by the image reading unit 23 by reading the image printed in the web W using inner side white reference data.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image reading apparatus which photoelectrically reads an image printed on a web.

  In the image reading apparatus, shading correction is performed to prevent unevenness in the read image due to uneven light intensity of the light source or temporal change, variation in light reception sensitivity of the reading element of the line sensor, and the like. Shading correction is performed by correcting read image data based on white reference data acquired by reading a white reference plate provided in the image reading apparatus.

  By the way, in a printing apparatus for printing on a long web, an image reading apparatus may be provided to read an image printed on the web. In such an image reading apparatus, the white reference plate may be disposed to face the image reading unit having the light source and the line sensor with the web interposed therebetween.

  In this case, while the image of the web being conveyed is being read, since the web is present between the image reading unit and the white reference plate, the white reference plate can not be read.

  On the other hand, the light quantity of the light source of the image reading unit may change under the influence of ambient temperature or the like. When the light amount of the light source is changing, it is desirable to use white reference data according to the light amount change of the light source for the shading correction.

  However, as described above, the white reference plate can not be read while the web image is read, and white reference data can not be obtained according to the change in the light amount of the light source, which may lower the accuracy of shading correction. There is.

  On the other hand, Patent Document 1 discloses a technique in which a blank area where nothing is recorded is provided on the web, and this blank area is read instead of the white reference plate to acquire white reference data.

JP, 2015-51612, A

  However, in the technique of Patent Document 1, since a blank area is provided on the web, waste of the web and a decrease in productivity of printing occur. When the web is of a type having a strong specular reflection such as glossy paper, the read image becomes dark, and therefore, the white reference plate is not used instead, and the shading correction accuracy may be lowered.

  The present invention has been made in view of the above, and it is possible to reduce the accuracy of shading correction when reading an image printed on a web while avoiding waste of the web in a printing apparatus printing on the web and a decrease in printing productivity. It is an object of the present invention to provide an image reading apparatus capable of suppressing

  In order to achieve the above object, a first feature of the image reading apparatus according to the present invention is a light source, and a line in which a plurality of reading elements are arranged along a width direction of a web being conveyed over a width longer than the width of the web. An image reading unit having a sensor, emitting light from the light source toward the web, and reading light from the web side by the line sensor to read an image printed on the web; A white white reference member disposed opposite to the image reading unit, which is longer than the width of the web and protrudes to both sides in the width direction of the web, and the white reference member at the time of reading the image printed on the web. The image reading unit is controlled to read both ends of the web protruding to the outer side of the web to generate edge read data, and the white is not generated in advance in a state where there is no web between the image reading unit and the white reference member. Reference member Inner white reference data, which is white reference data of an area inside both ends in the width direction of the web, is generated based on the pre-white reference data obtained by reading by the image reading unit and the end read data. The image reading unit may further include a control unit that performs shading correction on read image data obtained by reading an image printed on the web using inner white reference data.

  A second feature of the image reading apparatus according to the present invention is that the control unit controls the image reading unit to read both ends of the white reference member at predetermined time intervals, and the image reading unit The inner white reference data is generated based on the end reading data obtained by reading the both ends of the white reference member and the preliminary white reference data, and the first reading is performed after the generation of the latest inner white reference data. From the page to be started, the latest one is set as the inner white reference data to be used for shading correction to the read image data.

  A third feature of the image reading apparatus according to the present invention further comprises a drive unit for moving the white reference member so as to shift the read area of the white reference member by the image reading unit, the control unit It is determined whether or not dirt is present on at least one of both end portions of the white reference member based on partial read data, and the drive is determined when it is determined that dirt is present on at least one of both end portions of the white reference member. After moving the white reference member so as to shift the read area by the unit, the image reading unit is controlled to read again both ends of the white reference member.

  According to the first aspect of the image reading device of the present invention, the control unit reads the both ends of the white reference member protruding to the outside of the web and reads the end when reading the image printed on the web. The image reading unit is controlled to generate read data, and inner white reference data that is white reference data of an area inside both ends in the width direction of the web is generated based on the pre-white reference data and the edge read data. Then, the control unit performs shading correction on the read image data obtained by reading the image printed on the web by the image reading unit using the inside white reference data.

  As a result, even when there is a web between the image reading unit and the white reference member, the inner white reference data can be acquired as white reference data according to the change in the amount of light of the light source by reading both ends of the white reference member. For this reason, it is possible to suppress the decrease in the shading correction accuracy. In addition, since the web does not have a substitute area for the white reference member, it is possible to avoid waste of the web and a decrease in the productivity of printing. Therefore, according to the first feature of the image reading apparatus according to the present invention, it is possible to reduce the shading correction accuracy when reading an image printed on the web while avoiding waste of the web and a decrease in the productivity of printing. It can be suppressed.

  According to the second feature of the image reading apparatus according to the present invention, the control unit controls the image reading unit to read both ends of the white reference member at predetermined time intervals, and the image reading unit performs the white reference Inner white reference data is generated based on the end read data obtained by reading both ends of the member and the pre-white reference data. Then, the control unit sets the latest as inner white reference data to be used for shading correction on the read image data from the page which is first started reading after the generation of the latest inner white reference data. As a result, it is possible to prevent the image quality deterioration of the read image data due to the switching of the inner white reference data while the page is read, while sequentially updating the inner white reference data to improve the accuracy of the shading correction.

  According to the third aspect of the image reading device relating to the present invention, when the control unit determines that at least one of the both end portions of the white reference member is dirty, the white portion is shifted by the drive unit. After moving the reference member, control is performed to read again both ends of the white reference member by the image reading unit. As a result, by reading the dirt on both ends of the white reference member, it becomes possible to suppress the inside white reference data from becoming inappropriate data and to further suppress the decrease in the shading correction accuracy.

1 is a schematic configuration diagram of a printing system provided with a printing apparatus provided with an image reading apparatus according to an embodiment. (A), (b) is a perspective view of the image reading part of the printing apparatus in the printing system shown in FIG. (A), (b) is a top view of the image reading part of the printing apparatus in the printing system shown in FIG. It is a control block diagram of a printing system shown in FIG. It is a flow chart of prior standard data acquisition processing. It is a figure which shows an example of the read data of a white reference | standard roller. It is a figure which shows an example of the read data of a white reference | standard roller in case a dirt is in a white reference | standard roller. It is a flowchart of white reference data acquisition processing at the time of reading. It is a flowchart of white reference data acquisition processing at the time of reading. It is a figure which shows an example of edge part read data. It is explanatory drawing of the method of producing | generating inside white reference | standard data. It is a figure which shows an example of full width white reference data.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same or equivalent parts or components are denoted by the same or equivalent reference numerals throughout the drawings.

  The embodiment shown below exemplifies an apparatus etc. for embodying the technical idea of this invention, and the technical idea of this invention is the material, shape, structure, arrangement etc. of each component. Does not specify the following. Various changes can be added to the technical idea of the present invention within the scope of the claims.

  FIG. 1 is a schematic configuration diagram of a printing system provided with a printing apparatus provided with an image reading apparatus according to an embodiment of the present invention. 2A and 2B are perspective views of the image reading unit of the printing apparatus in the printing system shown in FIG. 3A and 3B are plan views of the image reading unit of the printing apparatus in the printing system shown in FIG. FIG. 4 is a control block diagram of the printing system shown in FIG. In the following description, the direction perpendicular to the paper surface of FIG. 1 is referred to as the front-rear direction, and the front direction of the paper surface is referred to as the front. Further, the top, bottom, left, and right of the paper surface in FIG.

  As shown in FIGS. 1 and 4, the printing system 1 according to the present embodiment includes an unwinding device 2, a printing device 3, and a winding device 4.

  The unwinding device 2 unwinds the web W, which is a long printing medium made of film, paper or the like, to the printing device 3. The unwinding device 2 includes a web roll support shaft 11, a brake 12, and an unwinding device control unit 13.

  The web roll support shaft 11 rotatably supports the web roll 16. The web roll support shaft 11 is formed in a long shape extending in the front-rear direction. The web roll 16 is a web W wound in a roll.

  The brake 12 applies a brake to the web roll support shaft 11. As a result, tension is applied to the web W between the web roll 16 and a transport roller 43 of the printing apparatus 3 described later.

  The unwinding device control unit 13 controls the brake 12. The unwinding device control unit 13 is configured to include a CPU, a memory, a hard disk, and the like.

  The printing device 3 prints an image on the web W while conveying the web W unwound from the unwinding device 2. The printing apparatus 3 includes a transport unit 21, printing units 22A and 22B, image reading units 23A and 23B, white reference rollers 24A and 24B, white reference roller rotation motors 25A and 25B, and four edge sensors 26. An operation panel 27 and a printing apparatus control unit 28 are provided. The suffixes of the alphabets in the reference numerals of the printing units 22A, 22B, etc. may be omitted and collectively described. The image reading device provided in the printing device 3 includes an image reading unit 23, a white reference roller (white reference member) 24, a white reference roller rotation motor (drive unit) 25, an edge sensor 26, and a reading control unit A control unit 63 and a storage unit 64 described later are included.

  The transport unit 21 transports the web W unwound from the unwinding device 2. The conveyance unit 21 includes guide rollers 31 to 40, twenty head lower support members 41, a meander control unit 42, a pair of conveyance rollers 43, and a conveyance motor 44.

  The guide rollers 31 to 40 guide the web W conveyed in the printing apparatus 3. The guide rollers 31 to 40 are driven to rotate by the web W being conveyed. The guide rollers 31 to 40 are formed in a long cylindrical shape extending in the front-rear direction.

  The guide rollers 31, 32 guide the web W between the unwinding device 2 and the meander control unit 42. The guide roller 31 is disposed at the lower left end of the printing apparatus 3. The guide roller 32 is disposed between the guide roller 31 and a meander control roller 47 of a meander control unit 42 described later.

  The guide rollers 33 to 39 guide the web W between the meander control unit 42 and the conveyance roller 43. The guide roller 33 is disposed to the left of the meander control roller 48 of the meander control unit 42 described later. The guide roller 34 is disposed above the guide roller 33. The guide roller 35 is disposed at the same height as the guide roller 34 and to the right of the guide roller 34. The guide roller 36 is disposed below the guide roller 35 and higher than the guide roller 33. The guide roller 37 is disposed on the left side of the guide roller 36 and in the vicinity of the right side of the web W between the guide rollers 33 and 34 and at a position substantially the same height as the guide roller 36. The guide roller 38 is disposed at the lower right of the guide roller 37. The guide roller 39 is disposed below and slightly to the right of the guide roller 38.

  The guide roller 40 guides the web W between the transport roller 43 and the winding device 4. The guide roller 40 is disposed at the lower right end of the printing apparatus 3.

  The lower head supporting member 41 supports the web W under the head unit 51 described later between the guide rollers 34 and 35 and between the guide rollers 36 and 37. The lower head support member 41 is formed in a long shape extending in the front-rear direction. Ten head lower support members 41 are disposed between the guide rollers 34 and 35 and between the guide rollers 36 and 37, respectively. The two lower head supporting members 41 are disposed immediately below each of the head units 51.

  The meander control unit 42 corrects the meandering of the web W. The meander control unit 42 includes meander control rollers 47 and 48 and a meander control motor 49.

  The meander control rollers 47 and 48 guide the web W and correct the meander of the web W. The meandering control rollers 47 and 48 are formed in a long cylindrical shape extending in the front-rear direction. The meandering control rollers 47 and 48 are driven to rotate by the web W being conveyed. The meandering control rollers 47 and 48 are configured so as to be adjustable in angle with respect to the width direction (front-rear direction) of the web W in the axial direction. The meandering control roller 47 is disposed to the right of the guide roller 32. The meander control roller 48 is disposed above the meander control roller 47.

  In order to adjust the angle of the meandering control rollers 47 and 48 in the axial direction of the meandering control rollers 47 and 48 with respect to the width direction (longitudinal direction) of the web W, meandering control rollers 47 and 48 are arranged around an axis parallel to the lateral direction. Rotate.

  The pair of transport rollers 43 transports the web W toward the winding device 4 while nipping the web W. The transport roller 43 is formed in a long cylindrical shape extending in the front-rear direction. The pair of conveyance rollers 43 is disposed between the guide rollers 39 and 40.

  The conveyance motor 44 rotationally drives the conveyance roller 43.

  The printing units 22A and 22B print images on the front and back surfaces of the web W, respectively. The printing unit 22A is disposed in the vicinity of the upper side of the web W between the guide rollers 34 and 35. The printing unit 22B is disposed in the vicinity of the upper side of the web W between the guide rollers 36 and 37. The printing units 22A and 22B each include five head units 51.

  The head unit 51 discharges the ink to the web W to print an image. In the printing unit 22, the five head units 51 respectively eject ink of different colors.

  The image reading units 23A and 23B photoelectrically read the images printed by the printing units 22A and 22B. The image reading units 23A and 23B are disposed above the web W near the downstream side of the printing units 22A and 22B in the transport direction of the web W, respectively. As shown in FIGS. 3A and 3B, the image reading unit 23 includes a light source 56 and a line sensor 57.

  The light source 56 emits light toward the web W. The light source 56 is formed in a long shape extending in the main scanning direction (front-rear direction) which is the width direction of the web W. The light source 56 is formed of a cold cathode tube, an LED or the like.

  The line sensor 57 has a plurality of reading elements arranged over a range longer than the width of the web W along the main scanning direction. The line sensor 57 receives the light from the web W side (lower side) by the reading element, and generates read data. The reading element of the line sensor 57 is formed of, for example, a CCD (Charge Coupled Device).

  The white reference rollers 24A and 24B are read in order to obtain the later-described advance white reference data and the like used to perform shading correction on the read image data. The white reference rollers 24A and 24B are disposed to face the image reading units 23A and 23B with the web W interposed therebetween. The white reference rollers 24A and 24B are white rollers longer than the width of the web W. The white reference rollers 24A and 24B are disposed so as to project on both outer sides (front and rear sides) in the width direction of the web W. The white reference rollers 24A and 24B are not driven to rotate by the web W, and are rotated by the white reference roller rotation motors 25A and 25B.

  The white reference roller rotation motors 25A and 25B rotate the white reference rollers 24A and 24B, respectively.

  The edge sensor 26 detects the position of the end of the web W in the width direction (front-rear direction). As shown in FIGS. 2A and 3A, two edge sensors 26 are disposed in the vicinity of the upstream side of the image reading unit 23A in a pair. The two edge sensors 26 detect the positions of the front end and the rear end of the web W near the upstream side of the image reading unit 23A.

  Further, as shown in FIGS. 2B and 3B, the other two edge sensors 26 are disposed in the vicinity of the upstream side of the image reading unit 23B in a pair. The two edge sensors 26 detect the positions of the front end and the rear end of the web W near the upstream side of the image reading unit 23B.

  The operation panel 27 displays various input screens and the like, and accepts an input operation by the user. The operation panel 27 includes a display unit having a liquid crystal display panel and the like, and an input unit (not shown) having various operation keys, a touch panel and the like.

  The printing device control unit 28 controls the overall operation of the printing device 3. The printing apparatus control unit 28 includes a conveyance control unit 61, a print control unit 62, a reading control unit 63, and a storage unit 64. Each part of the printing apparatus control unit 28 can be realized as software or hardware by a CPU, a RAM, a ROM, a hard disk and the like.

  The conveyance control unit 61 causes the conveyance motor 43 to drive the conveyance roller 43 to convey the web W.

  The print control unit 62 controls the head units 51 of the printing units 22A and 22B to print an image on the web W.

  The reading control unit 63 controls the image reading units 23A and 23B to read an image printed on the web W in a printing and reading operation described later.

  Further, when reading an image printed on the web W in the printing and reading operation, the reading control unit 63 reads the both ends 24a and 24b of the white reference roller 24 and generates end reading data at specified time intervals. The image reading unit 23 is controlled. Here, the end 24 a of the white reference roller 24 is a portion projecting outward from the web W on the front side, and the end 24 b is a portion projecting outward on the rear side from the web W.

  When the image reading unit 23 reads the both ends 24 a and 24 b of the white reference roller 24 and generates the edge reading data, the reading control unit 63 generates the edge reading data, and the following white reference data stored in the storage unit 64 and the edge reading Based on the data, generate inner white reference data. The inside white reference data is white reference data of the area inside the both ends in the width direction of the web W. Details of the process of generating the inner white reference data will be described later.

  Then, the reading control unit 63 performs shading correction on the read image data obtained by reading the image printed on the web W by the image reading unit 23 using the inside white reference data.

  The storage unit 64 stores the pre-white reference data and the black reference data. The pre-white reference data is white reference in a state where the light source 56 is lighted by the image reading unit 23 in a state where there is no web W between the image reading unit 23 and the white reference roller 24 by prior reference data acquisition processing described later. The read data is generated by reading the roller 24. The pre-white reference data is used to generate the inner white reference data described above. The black reference data is read data generated by reading the white reference roller 24 in a state in which the image reading unit 23 turns off the light source 56 by the prior reference data acquisition process. The black reference data is used for shading correction on the read image data.

  The winding device 4 winds the web W printed by the printing device 3. The winding device 4 includes a winding shaft 71, a winding motor 72, and a winding device control unit 73.

  The winding shaft 71 winds and holds the web W. The winding shaft 71 is formed in a long shape extending in the front-rear direction.

  The winding motor 72 rotates the winding shaft 71 clockwise in FIG. The web W is wound around the winding shaft 71 by the rotation of the winding shaft 71.

  The winding device control unit 73 controls the driving of the winding motor 72. The winding device control unit 73 includes a CPU, a memory, a hard disk, and the like.

  Next, advance reference data acquisition processing in the printing apparatus 3 will be described.

  The prior reference data acquisition process is a process for acquiring the above-described prior white reference data and black reference data prior to a print reading operation in which the image reading unit 23 reads the printed image while printing the image on the web W It is.

  FIG. 5 is a flowchart of prior reference data acquisition processing. The prior reference data acquisition processing is performed in a state where there is no web W between the image reading unit 23 and the white reference roller 24. The absence of the web W between the image reading unit 23 and the white reference roller 24 is, for example, when the web roll 16 is replaced. The prior reference data acquisition process is performed for each of the image reading units 23A and 23B.

  In step S1 of FIG. 5, the reading control unit 63 resets the contamination detection number count value C. Here, the stain detection number count value C is a value indicating the number of times it is determined that the white reference roller 24 has dirt in step S4 of FIG. 5 and step S26 of FIG. 8 described later. The contamination of the white reference roller 24 occurs, for example, when the ink mist generated by the ink discharge in the printing unit 22 adheres. The latest value of the dirt detection number count value C is stored in the storage unit 64.

  Next, in step S2, the reading control unit 63 turns on the light source 56 of the image reading unit 23.

  Next, in step S3, the reading control unit 63 controls the image reading unit 23 to read the white reference roller 24.

  Here, an example of read data of the white reference roller 24 by the image reading unit 23 is shown in FIG. In the example of FIG. 6, the variation of the light receiving sensitivity of the reading element of the line sensor 57, the difference in the light quantity between the reflected light by the end of the white reference roller 24 and the reflected light by the inner part, the influence of ambient temperature etc. The reading value changes depending on the position in the main scanning direction due to the uneven light amount.

  Next, in step S4, the reading control unit 63 determines whether the white reference roller 24 has a stain based on the read data of the white reference roller 24 read in step S3 described above.

  Here, an example of the read data of the white reference roller 24 when the white reference roller 24 is contaminated is shown in FIG. When the white reference roller 24 is soiled, local reading drops occur in the read data of the white reference roller 24, as shown in FIG.

  Therefore, for example, the reading control unit 63 scans the read data of the white reference roller 24 and determines that the white reference roller 24 is dirty when there is a pixel whose change rate of read values for adjacent pixels is equal to or greater than a threshold. . It may be determined that the white reference roller 24 is dirty when there is a pixel whose difference in read value with respect to the adjacent pixel is equal to or greater than a threshold.

  When it is determined that the white reference roller 24 is not soiled (step S4: NO), in step S5, the reading control unit 63 reads the read data of the white reference roller 24 as shown in FIG. 6 by the reading operation of step S3. It is stored in the storage unit 64 as prior white reference data.

  Next, in step S6, the reading control unit 63 turns off the light source 56 of the image reading unit 23.

  Next, in step S7, the reading control unit 63 controls the image reading unit 23 to read the white reference roller 24, acquires the generated read data as black reference data, and stores the read data in the storage unit 64. Thus, the prior reference data acquisition process is completed.

  If it is determined in step S4 that the white reference roller 24 is dirty (YES in step S4), the reading control unit 63 counts up the dirt detection number count value C in step S8. That is, the reading control unit 63 adds “1” to the dirt detection number count value C.

  Next, in step S9, the reading control unit 63 determines whether the dirt detection number count value C has reached the threshold Cth. Here, the threshold value Cth is a value set in advance as the number of times of contamination detection that requires cleaning of the white reference roller 24.

  If it is determined that the dirt detection number count value C has not reached the threshold Cth (step S9: NO), the reading control unit 63 causes the white reference roller 24 to rotate the white reference roller 24 by a predetermined angle in step S10. Rotate. As a result, the white reference roller 24 is moved so as to shift the area to be read by the image reading unit 23. As a result, it is possible to allow the image reading unit 23 to read an area on the surface of the white reference roller 24 without stains. Thereafter, the reading control unit 63 returns to step S3.

  If it is determined in step S9 that the dirt detection number count value C has reached the threshold Cth (step S9: YES), the reading control unit 63 cancels the prior reference data acquisition process in step S11. At this time, the reading control unit 63 turns off the light source 56 and causes the operation panel 27 to display a message prompting cleaning of the white reference roller 24, and ends the prior reference data acquisition process.

  Next, the print reading operation in the printing apparatus 3 will be described.

  The print reading operation is an operation of reading the printed image by the image reading unit 23 while printing the image on the web W as described above. The print reading operation is performed, for example, for inspection of print quality and the like. In a print reading operation for inspection of print quality and the like, images of a plurality of pages such as test pattern images are continuously printed.

  When the print reading operation is started, the conveyance control unit 61 of the printing apparatus control unit 28 starts driving of the conveyance motor 44. Further, the winding device control unit 73 starts driving of the winding motor 72. Thereby, conveyance of the web W is started. After the start of the transport of the web W, when the transport speed of the web W reaches a predetermined printing transport speed, the unwinding device control unit 13 starts the driving of the brake 12. Thereby, the web W is conveyed while tension is applied to the web W. After the transport speed of the web W reaches the print transport speed, the transport speed of the web W is maintained at the print transport speed until printing is completed.

  After the transport speed of the web W reaches the print transport speed, the print control unit 62 of the printing apparatus control unit 28 discharges ink from the head units 51 of the printing units 22A and 22B to print an image on the web W.

  When an image is printed on the web W, the reading control unit 63 of the printing device control unit 28 causes the image reading units 23A and 23B to read the image printed on the web W. Here, the reading control unit 63 determines the position of each printed page on the web W based on the printing timing of each page under the control of the printing control unit 62 and the number of output pulses of an encoder (not shown), and reads the image. The sections 23A and 23B can read an image of each page.

  The reading control unit 63 subjects the read image data generated by reading the image printed on the web W by the image reading unit 23 to various image processing including shading correction, and the read image data after the image processing is subjected to inspection. Output to an external device that performs image analysis.

  After printing and reading of the image are completed, the unwinding device control unit 13 causes the brake 12 to stop, the printing device control unit 28 causes the conveyance motor 44 to stop, and the winding device control unit 73 causes the winding motor 72 to stop. . As a result, the transport of the web is completed, and the printing and reading operation is completed.

  Next, a reading white reference data acquisition process performed during the above-described print reading operation will be described.

  The reading-time white reference data acquisition process is a process for sequentially updating the white reference data used for shading correction during the print reading operation. 8 and 9 are flowcharts of the reading white reference data acquisition process. The reading white reference data acquisition process is performed for each of the image reading units 23A and 23B. The processes of the flowcharts of FIGS. 8 and 9 are started by the start of the print reading operation.

  In step S21 of FIG. 8, the reading control unit 63 resets the dirt detection number count value C.

  Next, in step S22, the reading control unit 63 turns on the light source 56 of the image reading unit 23. The lighting of the light source 56 is performed to read an image printed on the web W.

  Next, in step S23, the reading control unit 63 determines whether the current time is before the start of reading the image of the first page printed on the web W.

  If it is determined that the current time is before the start of reading of the first page image printed on the web W (step S24: YES), the reading control unit 63 instructs the edge sensor 26 in the width direction of the web W in step S25. Detect the position of both ends.

  Next, in step S25, the reading control unit 63 controls the image reading unit 23 to read both ends 24a and 24b of the white reference roller 24 outside the positions of both ends in the width direction of the web W detected by the edge sensor 26. Do. The image reading unit 23 reads the both end portions 24a and 24b of the white reference roller 24, and generates end portion read data as shown in FIG.

  Next, in step S26, the reading control unit 63 determines whether or not there is a stain on at least one of the both end portions 24a and 24b of the white reference roller 24, based on the end reading data. The method of determining whether or not the end portions 24a and 24b of the white reference roller 24 are dirty is the same as the method described in step S4 of FIG. 5 described above.

  If it is determined that neither of the end portions 24a and 24b of the white reference roller 24 is dirty (step S26: NO), the reading control unit 63 stores the end portion read data in the storage unit 64 in step S27. Inner white reference data is generated based on the pre-white reference data.

  Here, a method of generating the inside white reference data will be described with reference to FIG.

  In FIG. 11, the end reading data is distributed in the range of the 0th to Nth pixels and the range of the Mth to Xth pixels. Here, X is the number of the final pixel.

  In the example of FIG. 11, the end reading data is darker than the pre-white reference data. This is because the light amount of the light source 56 is read at the time of reading the both end portions 24a and 24b of the white reference roller 24 at the time of generating the edge reading data compared to the reading of the white reference roller 24 at the time of generating the white reference data. Because it decreased. The light amount of the light source 56 is larger at the time of reading of both end portions 24a and 24b of the white reference roller 24 at the time of generating the edge reading data than at the reading of the white reference roller 24 at the time of generating the white reference data. If it does, the edge reading data becomes brighter than the pre-white reference data.

  As shown in FIG. 11, it is assumed that the read value of the Nth pixel of the preliminary white reference data is P (N) and the read value of the Nth pixel of the end scan data is Q (N). Further, a read value of the Mth pixel of the pre-white reference data is P (M), and a read value of the Mth pixel of the end reading data is Q (M). Further, the rate of change from P (N) to Q (N) is N ′, and the rate of change from P (M) to Q (M) is M ′.

  Also, let J be the distance in the main scanning direction between the (N + α) -th pixel and the N-th pixel, which is an arbitrary pixel in an area inside the both ends of the web W (within the existence range of the web W) The distance between the (N + α) th pixel and the Mth pixel in the main scanning direction is K.

  In addition, the read value of the (N + α) th pixel when the entire white reference roller 24 is read by the light amount of the light source 56 at the time of reading the both ends 24a and 24b of the white reference roller 24 when generating the edge reading data Let the estimated value be Q (N + α).

  Also, let α ′ be a predicted change rate from P (N + α), which is a read value at the (N + α) -th pixel of the pre-white reference data, to Q (N + α). Calculated from M ′ and distances J and K by interpolation. Specifically, the predicted change rate α 'is calculated by the following equation (1).

α ′ = N ′ × (K / L) + M ′ × (J / L) (1)
Then, Q (N + α) is calculated by multiplying P (N + α) by the predicted change rate α ′ as in the following equation (2).

Q (N + α) = P (N + α) × α ′ (2)
The inner white reference data corresponds to each of the (N + 1) th pixel to the (M-1) th pixel, that is, Q (N + .alpha.) Corresponding to each of .alpha. = 1 to (M-1-N). It consists of values.

  The reading control unit 63 generates inner white reference data as shown in FIG. 12 by calculating the value of Q (N + α) corresponding to each of α = 1 to (M−1−N).

  In the example of FIG. 11, the reading value of the pixel at the position (Nth and Mth) of the end on the web W side among the end reading data is used for generation of the inner white reference data. Readings of pixels at other positions of data may be used.

  Returning to FIG. 8, in step S28, the reading control unit 63 determines whether the image reading unit 23 is in the middle of reading a page when the generation of the inner white reference data ends. If the image reading unit 23 determines that the page is being read (YES in step S28), the reading control unit 63 repeats step S28.

  The image reading unit 23 is not in the middle of reading a page, that is, before the start of reading of the first page, or the reading target position of the image reading unit 23 is at the position of a break between pages, or after reading the last page If it is (step S28: NO), in step S29, the read control unit 63 determines whether the reading of the last page is completed.

  When it is determined that the reading of the last page is not completed (step S29: NO), in step S30, the reading control unit 63 sets the latest full-width white reference data as the white reference data used for the shading correction. Here, the full-width white reference data is, as shown in FIG. 12, composed of the inside white reference data generated in step S27 and the end reading data acquired in step S25. After step S30, the reading control unit 63 returns to step S23.

  When it is determined in step S29 that the reading of the last page is completed (step S29: YES), the reading control unit 63 turns off the light source 56 in step S31, and ends the reading white reference data acquisition process.

  If it is determined in step S23 that the present time is after the start of reading the first page image printed on the web W (step S23: NO), the read control unit 63 resets the time count value T in step S32. Do. Here, the time count value T is a count value of time for determining the timing at which the both ends 24 a and 24 b of the white reference roller 24 are read.

  Next, in step S33, the reading control unit 63 counts up the time count value T. That is, the reading control unit 63 adds “1” to the time count value T. The count up of the time count value T is performed, for example, every one second.

  Next, in step S34, the read control unit 63 determines whether the time count value T has reached a specified value (specified time). If it is determined that the time count value T has not reached the specified value (step S34: NO), the reading control unit 63 returns to step S33.

  If it is determined that the time count value T has reached the specified value (step S34: YES), the reading control unit 63 proceeds to step S24.

  If it is determined in step S26 that at least one of the end portions 24a and 24b of the white reference roller 24 is dirty (step S26: YES), the reading control unit 63 proceeds to step S35 in FIG.

  The processes of steps S35 to S37 are the same as steps S8 to S10 of FIG. 5 described above. After step S37, the reading control unit 63 returns to step S25 in FIG.

  If it is determined in step S36 that the dirt detection number count value C has reached the threshold Cth (step S36: YES), the reading control unit 63 cancels the reading white reference data acquisition processing in step S38. At this time, the reading control unit 63 turns off the light source 56 and causes the operation panel 27 to display a message prompting the cleaning of the white reference roller 24, and ends the reading white reference data acquisition process. At this time, the print reading operation itself is also canceled.

  By the reading white reference data acquisition process as described above, the image reading unit 23 reads the both ends 24 a and 24 b of the white reference roller 24 during the printing reading operation (steps S 32 to S 34, S25). Also, each time the image reading unit 23 reads the both ends 24a and 24b of the white reference roller 24, inner white reference data is generated based on the end read data and the pre-white reference data (step S27). Then, the latest page is set as the inside white reference data to be used for the shading correction to the read image data from the page which is first started to be read after the generation of the latest inside white reference data (steps S28 to S30).

  Shading correction is performed based on full-width white reference data (inner white reference data, edge reading data) generated in reading white reference data acquisition processing and black reference generated in advance reference data acquisition processing and stored in the storage unit 64. It is done using the data. Specifically, assuming that the read image data is D, the full width white reference data is Wk, and the black reference data is B, the read image data Ds after the shading correction is calculated by the following equation (3).

Ds = (D−B) × tone value / (Wk−B) (3)
By such an operation, for example, when the read data has 8-bit gradation, shading correction is performed so that the read value of the white reference roller 24 is converted to the maximum lightness 255 as shown in FIG. It will be.

  It is desirable that shading correction be performed for each of the RGB channels in order to increase the correction accuracy.

  As described above, in the printing apparatus 3, when reading an image printed on the web W, the reading control unit 63 reads the both ends 24 a and 24 b of the white reference roller 24 and generates end reading data The image reading unit 23 is controlled. Thereafter, the reading control unit 63 generates inner white reference data based on the pre-white reference data and the end reading data. Then, using the inside white reference data, the image reading unit 23 performs shading correction on the read image data obtained by reading the image printed on the web.

  As a result, even when the web W is present between the image reading unit 23 and the white reference roller 24, by reading the both end portions 24a and 24b of the white reference roller 24, white reference data corresponding to the light amount change of the light source 56 is obtained. Internal white reference data can be acquired. For this reason, it is possible to suppress the decrease in the shading correction accuracy.

  In addition, since the web W is not provided with a region that is substituted for the white reference member, it is possible to avoid waste of the web W and a decrease in productivity of printing.

  Therefore, according to the printing apparatus 3, it is possible to suppress a decrease in the accuracy of shading correction when reading an image printed on the web W while avoiding waste of the web W and a decrease in the productivity of printing.

  Further, in the printing apparatus 3, the reading control unit 63 controls the image reading unit 23 to read the both ends 24 a and 24 b of the white reference roller 24 at every predetermined time, and the image reading unit 23 controls the white reference roller 24. The inside white reference data is generated based on the end reading data obtained by reading the both ends 24a and 24b of the image data and the pre-white reference data. Then, the reading control unit 63 sets the latest as inner white reference data to be used for shading correction from the page which is first started reading after the generation of the latest inner white reference data.

  As a result, it is possible to prevent the image quality deterioration of the read image data due to the switching of the inner white reference data while the page is read, while sequentially updating the inner white reference data to improve the accuracy of the shading correction.

  Further, in the printing apparatus 3, when the reading control unit 63 determines that at least one of the both end portions 24 a and 24 b of the white reference roller 24 is dirty, the white reference roller 24 is rotated and the image reading unit 23 Shift the reading area. Thereafter, the reading control unit 63 controls the image reading unit 23 to read the both ends 24 a and 24 b of the white reference roller 24 again. As a result, by reading the dirt on both ends 24 a and 24 b of the white reference roller 24, it is possible to suppress the inside white reference data from becoming inappropriate data and to further suppress the decrease in the shading correction accuracy.

  Although the white reference roller 24 is used as the white reference member in the embodiment described above, the present invention is not limited to this, and a plate-shaped white reference member may be used. In this case, for example, by moving the plate-like white reference member in the sub-scanning direction, it is possible to shift the area to be read by the image reading unit 23.

  The present invention is not limited to the above embodiment as it is, and in the implementation stage, the constituent elements can be modified and embodied without departing from the scope of the invention. In addition, various inventions can be formed by appropriate combinations of a plurality of components disclosed in the above-described embodiment. For example, some components may be deleted from all the components shown in the embodiment.

DESCRIPTION OF SYMBOLS 1 printing system 2 unwinding apparatus 3 printing apparatus 4 take-up apparatus 23, 23A, 23B image reading part 24, 24A, 24B white reference roller 24a, 24b edge part 25, 25A, 25B white reference roller rotation motor 56 light source 57 line sensor 63 reading control unit 64 storage unit

Claims (3)

A light source and a line sensor in which a plurality of reading elements are disposed along the width direction of the web being conveyed over a width longer than the width of the web, and light is emitted from the light source toward the web An image reading unit that reads an image printed on the web by reading light of the light by the line sensor;
A white white reference member disposed opposite to the image reading unit with a web interposed therebetween, which is longer than the width of the web and protrudes to both outer sides in the width direction of the web;
When reading an image printed on the web, the image reading unit is controlled to read the both protruding ends of the white reference member on both sides of the web to generate edge read data;
Based on prior white reference data obtained by the image reading unit reading the white reference member in a state where there is no web between the image reading unit and the white reference member in advance, and the edge reading data, Generate inner white reference data, which is white reference data of an area inside both ends in the width direction of the web,
An image reading apparatus comprising: a control unit that performs shading correction on read image data obtained by the image reading unit reading an image printed on a web using the inside white reference data; . The control unit
The end reading data obtained by reading the both ends of the white reference member by the image reading unit while controlling to read the both ends of the white reference member by the image reading unit at every specified time Generating the inner white reference data based on the pre-white reference data;
2. The method according to claim 1, wherein the latest page is set as the inner white reference data to be used for shading correction on read image data from a page which is first started to be read after generation of the latest inner white reference data. Image reader. The white reference member further includes a drive unit that moves the white reference member so as to shift a reading area of the white reference member by the image reading unit.
The control unit
If it is determined based on the end reading data whether at least one of both ends of the white reference member is dirty, it is determined that at least one of the ends of the white reference member is dirty,
3. The apparatus according to claim 1, wherein after the white reference member is moved so as to shift the read area by the drive unit, the image reading unit is controlled to read both ends of the white reference member again. Image reader as described.