JP4517961B2 - Image reading apparatus and image reading method - Google Patents

Description

  The present invention relates to an image reading apparatus and an image reading method, and more particularly, to an image reading apparatus and an image reading method for outputting an image obtained by reading a printed material to an inspection device that performs quality inspection of a printed material printed by a printing device that performs high-speed printing. .

  2. Description of the Related Art Conventionally, as an image reading apparatus that reads an image using a line sensor or the like in which light receiving elements such as CCDs are arranged in a row, there is a device that performs so-called shading correction that corrects variations in sensitivity of each light receiving element of a line sensor. (For example, refer to Patent Documents 1 and 2).

  This shading correction is performed in a period other than the job execution period, such as before the start of the job.

By the way, in the case of form printing such as telephone charges, since it is required to be printed accurately due to the nature of the printed contents, it is normal to read the printed matter with an image reading device and collate this with the original print data. It is inspected whether or not it has been printed. In addition, such a print job requires a large amount of print processing in a short period of time, so that high speed is also required for printers and image reading apparatuses. As an image reading apparatus capable of reading an image at high speed, for example, there is an apparatus using a plurality of line sensors (see, for example, Patent Document 3).
JP 2003-163796 A JP-A-5-236272 Japanese Patent Laid-Open No. 2002-84397

  However, since the print job as described above takes a long time to execute each job, each element is affected by an environmental change such as a deviation of the optical path to the line sensor or a temperature change of each element of the line sensor. There may be a difference in density between the two.

  In this case, there is a problem that the job must be stopped halfway and the shading correction must be executed, resulting in a reduction in processing efficiency.

  The present invention has been made in view of the above-described facts, and provides an image reading apparatus and an image reading method capable of suppressing a density difference between each element of a line sensor and preventing a reduction in processing efficiency. Objective.

In order to solve the above-described problem, an image reading apparatus according to claim 1, wherein a line sensor in which light receiving elements are arranged along a predetermined direction and an image recorded on at least a recording medium in a reading area of the line sensor. first reading and the white reference plate provided respectively in the first and the second read area of both ends of the line sensors other than the region, wherein the second read by the second light receiving element corresponding to the second read area to be read based of the pixel values of the reading area, and a correcting means for correcting in real time the pixel value of the first read area for each line read by the first light receiving element corresponding to the first read area The correction means includes a first correction obtained from a larger pixel value of the read pixel values of the second reading area and a maximum value of a predetermined gradation range. And a first correction unit that corrects a pixel value in the first reading area, and a smaller pixel value of the pixel values in the two second reading areas is corrected by the first correction factor. The first correction means of the first reading area according to the second correction rate obtained from the pixel value after the determination and the maximum value and the position of the first reading area in the predetermined direction And a second correction unit that corrects the pixel value after correction according to (1 ).

According to the present invention, among the reading areas of the line sensor in which the light receiving elements are arranged along the predetermined direction, at least the second readings at both ends of the line sensor other than the first reading area for reading the image recorded on the recording medium. A white reference plate is provided in each reading area.

  Then, the correcting means reads the first light receiving element corresponding to the first reading area based on the pixel value of the second reading area read by the second light receiving element corresponding to the second reading area. The pixel value of the first reading area thus obtained is corrected in real time for each line.

Thus, since the white reference plate is respectively provided in the second read area of the ends of the first line sensor other than the reading region of the image recorded on the recording medium, i.e. while reading the first reading area The pixel values of the image recorded on the recording medium can be corrected by reading the second reference areas at both ends of the white reference plate, that is, the line sensor .

  As a result, correction can be performed without temporarily stopping the reading operation, so that not only the density difference between the light receiving elements of the line sensor can be suppressed, but also a reduction in processing efficiency can be effectively prevented. .

In addition, the correction unit may perform the first correction rate according to a first correction factor obtained from a larger pixel value of the read pixel values of the second reading region and a maximum value of a predetermined gradation range. A first correction unit that corrects a pixel value of one reading region, a pixel value after correcting a smaller pixel value of the pixel values of the two second reading regions by the first correction rate, and According to the second correction factor obtained from the maximum value and the position of the first reading area in the predetermined direction, the pixel value after correction by the first correction unit in the first reading area. And a second correction means for correcting the above .

  By configuring the correcting means in this way, it is possible to effectively suppress the density difference in the predetermined direction of the image recorded on the recording medium.

According to a second aspect of the present invention, a plurality of the line sensors may be provided, and the correction unit may be provided for each line sensor.

  In such a configuration, an image can be read at high speed. However, the present invention can perform correction without stopping the reading operation, and thus is particularly effective when applied to such an apparatus. .

According to a third aspect of the present invention, when the difference between the pixel values in the second reading area read by each of the plurality of line sensors is equal to or greater than a predetermined threshold value, the correcting means provided for each line sensor. Correction may also be executed.

  Here, the predetermined threshold value is a value that may adversely affect the image quality when the difference between the pixel values is equal to or greater than this value, that is, the density difference becomes conspicuous when the images read by the respective line sensors are combined. Set to a value. With such a configuration, it is sufficient to correct only when necessary, and there is no need to always perform correction.

The image reading method according to claim 4, wherein the line sensor in which the light-receiving elements are arrayed along a predetermined direction, among the reading area of the line sensor, other than the first read area for reading an image recorded on at least a recording medium An image reading method executed by an image reading apparatus provided with a white reference plate provided in each of the second reading areas at both ends of the line sensor , wherein the second reading area corresponds to the second reading area. Based on the pixel value of the second reading area read by the light receiving element, the pixel value of the first reading area read by the first light receiving element corresponding to the first reading area for each line The step of correcting in real time , wherein the step of correcting includes a larger pixel value of the read pixel values of the second reading region and a predetermined pixel value. A first correction step of correcting the pixel value of the first reading area according to a first correction factor obtained from the maximum value of the gradation range, and the pixel values of the two second reading areas Depending on the pixel value after correcting the smaller pixel value with the first correction factor and the second correction factor obtained from the maximum value, and the position of the first reading area in the predetermined direction And a second correction step of correcting the pixel value after correction by the first correction means in the first reading area .

  According to the present invention, the correction can be performed without temporarily stopping the reading operation. Therefore, not only can the density difference between the light receiving elements of the line sensor be suppressed, but also a reduction in processing efficiency can be effectively prevented. be able to.

Further, the correction is performed according to a first correction factor obtained from a larger pixel value of the read pixel values of the second reading area and a maximum value of a predetermined gradation range. A first correction for correcting a pixel value in the reading area of the first pixel, a pixel value after correcting a smaller pixel value of the pixel values in the two second reading areas by the first correction factor, and the maximum The pixel value after correction by the first correction unit of the first reading area is corrected according to the second correction rate obtained from the value and the position of the first reading area in the predetermined direction. Second correction to be performed .

For this reason , the density difference in the predetermined direction of the image recorded on the recording medium can be effectively suppressed.

The invention according to claim 5 is characterized in that, when a plurality of line sensors are provided, the correction is executed for each line sensor.

  According to the present invention, an image can be read at high speed. However, the present invention can perform correction without stopping the reading operation. Therefore, the present invention is applied to an apparatus provided with a plurality of such line sensors. It is particularly effective when applied.

The invention according to claim 6 is characterized in that the correction is executed for each of the line sensors when a difference in pixel values of the second reading area respectively read by a plurality of line sensors is equal to or greater than a predetermined threshold value. And

  According to the present invention, it is sufficient to correct only when necessary, and it is not necessary to always perform correction.

  As described above, according to the present invention, it is possible to suppress the density difference between the elements of the line sensor and to prevent the processing efficiency from being lowered.

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

  First, an example of a schematic configuration of a printing system to which a mechanism according to the present invention is applied will be described with reference to FIG.

  The printing system generally includes a host computer 10, a printer controller 20, a printing device 100, a print inspection device 200, and a reading device 260.

  The host computer 10 is a device that creates print data to be printed. The data to be printed may be, for example, data in which an image to be printed is described in a page description language, or may be raster image data indicating an image to be printed. In the case of standard printing such as form printing, a file in which values to be printed in each column of a standard format (form) are arranged in a predetermined format such as CSV (Comma Separated Value) format is created as print data Is done. Print data created by the host computer 10 is input to the printer controller 20 via a data communication network such as a LAN (Local Area Network) or a portable storage medium such as a CD-R / RW.

  The printer controller 20 acquires print data created by the host computer 10, generates image data (for example, raster image data) that can be handled by the printing apparatus 100 from this data, and supplies this to the printing apparatus 100. If the print data is page description language data, the printer controller 20 interprets it and creates image data for each page. In the case of standard printing, the printer controller 20 has data in a standard format (this data is registered in advance by the system operator), and each data value in the print data input from the host computer 10 is stored. Creates and outputs image data that fits the standard format. Image data supplied from the printer controller 20 to the printing apparatus 100 is referred to as “original image data”. The printer controller 20 extracts control data indicating print processing attributes such as paper size and single-sided / double-sided printing from the print data, and supplies the control data to the printing apparatus 100. The printer controller 20 supplies the original image data of each page created from the print data and the corresponding control data to the printing apparatus 100 in the order in which the printing apparatus 100 prints on the paper.

  The printing apparatus 100 receives document image data and control data from the printer controller 20, and prints document image data on a sheet in accordance with a print processing attribute indicated by the control data.

  The reading device 260 optically reads the printed surface of the printed paper 150 printed by the printing device 100, thereby generating inspection image data indicating an image of the printed surface.

  The print inspection apparatus 200 is an apparatus that inspects the quality of print results on paper. Here, as an example, inspection image data obtained by reading by the reading device 260 is collated with document image data supplied from the printer controller 20 (this is a document image for the same page as the inspection image data). A print inspection apparatus 200 of the type that performs print quality inspection is illustrated.

  The outline of the printing system has been described above. Next, details of the printing apparatus 100, the print inspection apparatus 200, and the reading apparatus 260 will be described.

  The printing apparatus 100 includes an image input IF (interface) circuit 105, a print engine 110, a paper transport system 112, a paper discharge destination switching gate 114, a drive motor 116, a normal paper discharge tray 120, an abnormal paper discharge tray 125, and an encoder 130. .

  The image input IF circuit 105 is an interface circuit for receiving document image data and control data from the printer controller 20. The received document image data is supplied to the print engine 110. The received control data is supplied to a control unit (not shown) that controls the overall operation of the printing apparatus 100. This control unit executes various controls according to the control data, such as selecting a paper feed tray to be used and switching a paper transport path in duplex / single-sided printing. Further, the image input IF circuit 105 supplies at least document image data among the data supplied from the printer controller 20 to the document image processing unit 210 of the print inspection apparatus 200.

  The print engine 110 is a device for printing a document image on a sheet 150 based on document image data input via the image input IF circuit 105. The present invention does not matter the format of the print engine 110. Various types such as an electrophotographic system and an inkjet system can be used. The electrophotographic print engine 110 includes a photoconductor, an exposure device, a developing device, a transfer mechanism, a fixing mechanism, and a cleaner mechanism.

  The paper transport system 112 is a mechanism for transporting paper within the printing apparatus 100 for printing. The paper transport system 112 takes out the paper from a paper feed tray (not shown) and transports it to the print engine 110, and the paper on which an image is printed by the print engine 110 is transferred from the normal paper discharge tray 120 to the abnormal paper discharge tray 125. Transport. In the case of double-sided printing, the paper on which the front surface has been printed is turned over and conveyed to the print engine 110 again. The paper transport system 112 is configured by a roller or a belt that is rotationally driven by a drive motor 116.

  The normal paper discharge tray 120 is a tray in which printed sheets determined as non-defective products by the inspection of printed sheets by the print inspection apparatus 200 are accumulated. On the other hand, the abnormal paper discharge tray 125 is a tray in which printed sheets determined to be defective by the inspection are accumulated.

  The paper discharge destination switching gate 114 is a switching mechanism for switching the paper discharge destination of the printed paper between the normal paper discharge tray 120 or the abnormal paper discharge tray 125. The discharge destination switching gate 114 is controlled by the control unit of the printing apparatus 100 based on the inspection result signal supplied from the print inspection apparatus 200.

  The encoder 130 is a rotary encoder for measuring the rotation of the drive motor 116, and outputs an encoder pulse having a pulse width corresponding to the rotation speed of the drive motor 116. This encoder pulse is used as a basis for determining the paper conveyance speed when the printed paper passes the reading position of the reading device 260. In other words, the drive motor 116 to be measured needs to be a motor that drives a roller or a belt near the reading position of the paper transport system 112. Therefore, further, the encoder 130 may measure the rotation of the paper transport roller at the position immediately before or immediately after the reading position (or both) instead of the motor.

  Next, the reading device 260 will be described. The reading device 260 is provided at a position downstream of the print engine 110 and upstream of the paper discharge destination switching gate 114 in the paper transport system 112 of the printing apparatus 100. The reading device 260 includes an illumination light source that illuminates the printing surface of the printed paper 150, an imaging device, and an imaging optical system that links reflected light from the printing surface with respect to the illumination to the imaging surface of the imaging device. In a preferred example, a CCD (charge coupled device) line sensor as a light receiving element can be used as the imaging device. In this case, the line sensor and the imaging optical system are arranged so that a line in a direction perpendicular to the sheet conveyance direction (referred to as a main scanning direction) at the position of the reading device 260 can be read at a time by the line sensor. Then, the inspection image data for one page is created by reading the lines in the main scanning direction line by line with the line sensor in synchronization with the sheet conveyance. In the following example, a configuration using a line sensor as an imaging device will be described as a main example.

  As shown in FIG. 3, white reference plates 30A and 30B are provided at both ends of the paper transport system 112 in the direction perpendicular to the paper transport direction A. The line sensor 265 is arranged so that both ends thereof are positioned on the white reference plates 30A and 30B. Of the light receiving elements of the line sensor 265, light receiving elements other than the light receiving elements that read the white reference plates 30A and 30B are assigned as the first light receiving elements, and the light receiving elements that read the white reference plates 30A and 30B are the first light receiving elements. Assigned as an element.

  An image when the printed paper 150 is read by the line sensor 265 while the printed paper 150 is conveyed by the paper conveyance system 112 is an image as shown in FIG. As shown in FIG. 4, both ends of the image image 34 become white reference image regions (images read from the second reading region) taken by reading the white reference plates 30 </ b> A and 30 </ b> B, and are sandwiched between these white reference image regions. The area thus obtained is a conveyance path image area obtained by reading the paper conveyance system 112, and the inside thereof is a paper image area obtained by reading the printed paper 150 (an image obtained by reading the first reading area).

  The white reference plates 30A and 30B ideally have whiteness with a density of “0” when read by the line sensor 265. Accordingly, the pixel value (luminance value) in the white reference image region is “FF” in hexadecimal in the ideal state, for example, when the gradation range of the pixel value is 256 gradations. In the present embodiment, a case where the gradation range is 256 gradations will be described.

  In FIG. 4, the number of pixels in the image image 34 in the direction perpendicular to the paper conveyance direction A is 5000 pixels, the number of pixels in the white reference image region in the vertical direction is 10 pixels, and the conveyance path image in the vertical direction. The case where the number of pixels in the area is 4980 pixels is shown.

  In the present embodiment, the line sensor 265 is fixed, and the printed paper 150 is read by the paper transport system 112 while the printed paper 150 is transported. However, the printed paper 150 is fixed. Alternatively, the line sensor 265 may be moved to read an image printed on the printed paper 150. In this case, the white reference plates 30 </ b> A and 30 </ b> B may have a shape in which the moving direction of the line sensor 265 is the longitudinal direction and has a length at least longer than the moving range of the line sensor 265.

  The print inspection apparatus 200 includes an original image processing unit 210, an original image buffer 215, an inspection image processing unit 220, an inspection image buffer 225, a collation unit 230, an inspection information storage device 235, a display control unit 240, a display device 245, and a UI ( A user interface) unit 250 is provided.

  The document image processing unit 210 is a functional module that receives document image data branched by the image input IF circuit 105 and performs image processing necessary for collation with inspection image data on the document image data. A representative example of image processing necessary for collation is resolution conversion. Of course, this is merely an example, and other image processing may be performed. In addition, a plurality of image processing may be performed on the document image data. These various image processing functions can be configured as a hardware circuit. Of course, a plurality of image processing functions can be incorporated into one hardware circuit.

  The document image buffer 215 is a buffer memory that temporarily stores document image data processed by the document image processing unit 210.

  The inspection image processing unit 220 is a functional module that performs image processing necessary for collation with the document image on the inspection image data generated by the reading device 260. Image processing executed by the inspection image processing unit 220 includes shading correction, exposure correction, positional deviation correction, magnification correction, binarization, and the like.

  The inspection image processing unit 220 has a function of controlling an image reading operation by the reading device 260. That is, the inspection image processing unit 220 receives an encoder pulse from the encoder 130, obtains a paper conveyance speed at the reading position of the reading device 260 from the encoder pulse, generates a line synchronization signal based on the paper conveyance speed, The image signal is read line by line from the line sensor of the reading device 260 in synchronization with the line synchronization signal.

  Such an image processing function and control function executed by the inspection image processing unit 220 can be configured as a hardware circuit as in the case of the document image processing unit 210. The inspection image processing unit 220 can be configured as an aggregate of these hardware circuits.

  The inspection image buffer 225 is a buffer memory that temporarily stores inspection image data processed by the inspection image processing unit 220.

  The collation unit 230 reads out the original image data in the original image buffer 215 and the inspection image data in the inspection image buffer 225 and collates them, so that the print quality of the printed paper corresponding to the inspection image data is good or bad. Determine. Of the processes of the collation unit 230, the comparison of both the original image data and the inspection image data and the quality determination process can use conventional processes, and thus the description thereof is omitted. Although there is a difference between the timing at which the print inspection apparatus 200 acquires document image data and the timing at which inspection image data corresponding to the document image data is acquired, the document image buffer 215 provided in the print inspection apparatus 200. The buffer function such as the inspection image buffer 225 can absorb the difference until the collation by the collation unit 230.

  The collation unit 230 supplies a signal indicating the result of the quality determination to the printing apparatus 100. The control unit of the printing apparatus 100 switches and controls the discharge destination switching gate 114 according to this signal, so that the printed paper determined to be non-defective is transferred to the normal discharge tray 120, and the printed paper determined to be defective is The paper is discharged to the abnormal paper discharge tray 125.

  Further, the collation unit 230 registers the original image data and the inspection image data for the printed paper determined to be defective as a result of the collation processing in the inspection information storage device 235. These document image data and inspection image data indicate information indicating which page of which job corresponds to the print result (in the case of double-sided printing, whether the sheet number is front or back). Information may be registered).

  The inspection information storage device 235 is configured by a large-capacity storage medium such as a hard disk. The document image data and the inspection image data stored in the inspection information storage device 235 can be referred to for the purpose of confirming the inspection contents later. In the above, only the data on the printed paper determined to be defective is registered in the inspection information storage device 235. However, if the capacity of the inspection information storage device 235 allows, the data on all printed paper is registered. You may do it. In this case, it is preferable to register the determination result for each printed sheet together with a determination result as a non-defective product or a defective product.

  The display control unit 240 is a functional module that generates a display screen for displaying various types of information regarding the print inspection. The display control unit 240 has a function of generating a display image in which document image data and inspection image data held in the document image buffer 215 and the inspection image buffer 225 are displayed side by side or overlaid for comparison. The generated display image is displayed on the display device 245.

  Further, the display control unit 240 has a function of generating a display image showing document image data and inspection image data registered in the inspection information storage device 235. When the user wants to know about the printed paper determined to be defective, the user displays the inspection image data on the screen on the display device 245 by this function, and if necessary, displays the corresponding original image data on the screen. Can be displayed.

  The UI unit 250 is a user interface unit for operating the print inspection apparatus 200. The UI unit 250 includes mechanical keys and buttons for input, a pointing device, and the like. For example, the user operates the UI unit 250 to display the current image of the original image buffer 215 and the inspection image buffer 225, or to display the inspection image or the original image stored in the inspection information storage device 235. Can be selected.

  The printing system of this embodiment has been described above. In the system described above, when printing is performed on a sheet by the print engine 110 of the printing apparatus 100, the printing surface of the sheet is read by the reading device 260, and the inspection image data obtained by the reading is checked for verification. After various necessary processes are performed by the inspection image processing unit 220, the collation unit 230 performs comparison with the document image data.

  Next, the details of the inspection image processing unit 220 will be described with reference to FIG. As shown in the figure, the circuits constituting the inspection image processing unit 220 can be roughly divided into a control signal generation unit 300 and an image processing unit 320.

  The control signal generation unit 300 is a circuit that generates control signals such as a line synchronization signal for controlling image reading and a signal indicating a sheet conveyance speed.

  In the control signal generation unit 300, an encoder pulse is input to the counter 302 from the encoder 130 of the printing apparatus 100. The counter 302 counts input encoder pulses for a predetermined unit time, and outputs a signal indicating the count value per unit time. This signal corresponds to the paper conveyance speed at the reading position of the reading device 260.

  The count correction circuit 304 is a circuit for correcting the count value output from the counter 302. This is for correcting an error in the count value caused by individual differences or differences in the installation environment of the printing apparatus 100. The parameter storage unit 304m has a non-volatile storage device, and stores parameter values used for calculation of this correction. The output of the count correction circuit 304 is supplied to the image processing unit 320 and the synchronization signal generation circuit 306 as a conveyance speed signal.

  The synchronization signal generation circuit 306 generates a line synchronization signal based on a signal indicating the sheet conveyance speed supplied from the count correction circuit 304. The line synchronization signal is a signal that is at the H (high) level only during the period when the image signal of one line is present, and is at the L (low) level during the other periods (of course, a signal having the opposite polarity may be used). The synchronization signal generation circuit 306 generates the line synchronization signal so that the interval between adjacent H level sections in the line synchronization signal becomes smaller as the sheet conveyance speed is higher. As a result, image signals having the same number of lines are acquired if the length in the direction of paper conveyance speed is the same regardless of the size of the paper conveyance speed. The line synchronization signal generated by the synchronization signal generation circuit 306 is supplied to the image processing unit 320.

  Next, the image processing unit 320 will be described. The image processing unit 320 reads out the image signal line by line from the imaging device (line sensor 265) of the reading device 260 in accordance with the line synchronization signal generated by the control signal generation unit 300, and the collation unit 230 collates the image signal. The necessary image processing is performed. The image signal output from the line sensor 265 is converted into digital data by an A / D conversion circuit (not shown) and then input to the image processing unit 320. The image processing executed by the image processing unit 320 is basically for eliminating an error factor mixed during reading. Examples of such image processing include exposure correction and misalignment correction. Of course, the image processing executed by the image processing unit 320 is not limited to this. For example, when the collation processing in the collation unit 230 is performed by comparing binarized images, binarization processing is necessary as image processing. In the example of FIG. 2, the image processing unit 320 exemplifies a unit that performs shading correction, exposure correction, density unevenness correction, positional deviation correction, magnification correction, and binarization.

  The shading correction circuit 322 performs shading correction on the input digital image signal. The shading correction is a process for correcting low-frequency unevenness in the inspection image due to uneven illumination of the reading device 260. The details of the shading correction process are well known and will not be described in detail. The calculation of shading correction requires parameters such as a white reference value (indicating white brightness as the background color of the paper). This parameter is stored in the parameter storage unit 322m.

  The exposure correction circuit 324 is a circuit that performs exposure correction on the shading-corrected image data. This exposure correction is a process of correcting the luminance value of each pixel on the line in accordance with the conveyance speed of the sheet when the sheet passes the reading position of the reading device 260. That is, the higher the paper conveyance speed at the reading position, the shorter the exposure time of the line to be read and the smaller the exposure amount, so that the brightness of the image is lowered. Therefore, in the exposure correction, the luminance value of each pixel on the line is corrected so as to increase as the paper conveyance speed increases. This exposure correction is executed based on the paper speed signal supplied from the control signal generator 300. This exposure correction also requires parameters such as reference values and coefficients for obtaining correction values, and these parameters are stored in the parameter storage unit 324m.

  The density unevenness correction circuit 325 is a circuit that performs processing for correcting the luminance value of the pixel in the paper image area based on the luminance value of the pixel in the white reference image area for each line image read by the line sensor. As described above, the pixel value in the white reference image region should be 'FF' in an ideal state. However, when the apparatus is operated continuously for a long time, the position of the light source is, for example, due to vibration of the apparatus. Environmental changes such as optical path shifts due to subtle shifts and temperature changes of each element of the line sensor occur. In this case, there may be a difference in reading density between each element of the line sensor. Therefore, the density unevenness correction circuit 325 corrects the luminance value of the pixel in the paper image area for each line in real time without stopping the job.

  The density unevenness correction will be specifically described below.

  FIG. 5 shows an example of pixel values (luminance values) of a line image for one line read by the line sensor. In FIG. 5, the pixel value of the left white reference image region is a pixel value obtained by reading the white reference plate 30A, and the pixel value of the right white reference image region is a pixel value obtained by reading the white reference plate 30B. .

  The density unevenness correction circuit 325 compares the pixel values of the white reference image regions on both sides, and corrects each pixel value of the line image based on the larger pixel value (reference pixel value). In FIG. 5, the pixel value of the left white reference image region is “F0” in hexadecimal, the pixel value of the right white reference image region is “E0”, and the pixel value of the left white reference image region is Therefore, each pixel value of the line image is corrected based on this pixel value.

  In FIG. 5, the pixel values of the respective white reference image areas are the same, but there may be variations. In this case, the density unevenness correction circuit 325 obtains representative values of the pixel values of the white reference image areas on both sides. This representative value may be, for example, the maximum value or the average value of the pixel values in the white reference image area. Then, the representative values of the pixel values of the white reference image regions on both sides are compared, and each pixel value of the line image is corrected based on the larger representative value (reference pixel value).

  For correction of each pixel value of the line image, the reference pixel value is A, the maximum value of the gradation range of the pixel value is M (in this embodiment, “FF”), the pixel value before correction of the correction target pixel is B, The corrected pixel value is set as B ′ and the following equation is used.

B ′ = (M / A) × B (1)
By correcting each pixel value of the line image by the above equation (1), the pixel value of each region is corrected as shown in FIG. That is, in the correction according to the above equation (1), the pixel value of the pixel in the left white reference image region is A = B, so that it is corrected to the maximum value M in the gradation range, and the pixel value of the pixel in the other region The value is corrected according to the correction rate (M / A: first correction rate) of the pixel value of the pixel in the left white reference image region.

  Here, when the pixel value “E0” in the white reference image area on the right side is corrected by the above equation (1), it is corrected to “EF” as shown in FIG. 6, but it satisfies the original pixel value “FF”. Absent.

  For this reason, the density unevenness correction circuit 325 corrects each pixel value of the line image in the region other than the white reference image region based on the pixel value of the white reference image region on the right side after the correction according to the equation (1). .

  Specifically, the corrected pixel value of the right-side white reference image region according to the above equation (1) is set as B1 ′, and the maximum value M is divided by B1 ′, thereby correcting C (= M / B1 ′: No. 2). The number of pixels (4980 in this embodiment) of the area other than the white reference image area, that is, the area including the conveyance path image area and the paper image area is corrected by P, the pixel No. of the area is corrected by N, and the above equation (1). The corrected pixel value B ″ is obtained by the following equation, where B ′ is the subsequent pixel value.

B ″ = (((C−1) / P) × N) +1) × B ′ (2)
The pixel numbers are numbered from 1 for the regions other than the white reference image region in order from the white reference image region side selected as the correction reference, that is, the left white reference image region side. That is, in the case of FIG. 6, the pixel No. of the leftmost pixel in the left conveyance path image area is “1”, and the pixel No. of the rightmost pixel in the right conveyance path image area is 4980. Incidentally, in the example shown in FIG. 6, the pixel values after correction by the equation (1) on the right side of the white reference image area is 'EF', C = (FF ) 16 / (EF) 16 ≒ 1.07 It becomes.

  As a result, as shown in FIG. 7, the pixel values at both ends of the image image 34 are corrected to the maximum value M, and the pixel values in the paper image area are corrected accordingly. It is possible to correct the density unevenness in. Further, since the white reference plates 30A and 30B are installed at both ends of the paper conveyance system 112, it is not necessary to stop the job and correct the density unevenness, and the image can be read and corrected for each line. it can. Therefore, processing efficiency can be improved. In addition, if there is basically a memory for storing an image for one line, density unevenness can be corrected in real time, so that the memory capacity can be reduced. Therefore, the apparatus can be configured to be simple and inexpensive.

  The positional deviation correction circuit 326 performs positional deviation correction on the image data that has been corrected by the density unevenness correction circuit 325. The misregistration correction is a process for correcting misregistration in the main scanning direction (predetermined direction) of the inspection image data due to individual apparatus differences. That is, the attachment position relationship between the paper conveyance system 112 and the reading device 260 is slightly different in each system. As a result, the position of the read inspection image data in the main scanning direction is different in each system. is there. In order to correct this positional deviation, parameters such as a correction amount corresponding to the amount of positional deviation from the normal state are necessary, and the value of this parameter is stored in the parameter storage unit 326m.

  The magnification correction circuit 328 is a circuit that performs magnification correction processing on the image data that has been corrected by the positional deviation correction circuit 326. Here, the magnification correction is a process of correcting the magnification in the main scanning direction of the inspection image data. For example, in the case of a configuration corresponding to a reading target of a different paper size by changing the position of the imaging device with respect to the reading target, the size of the reading target corresponding to one pixel of the inspection image data varies depending on the paper size. Therefore, this is corrected by this magnification correction. The magnification correction circuit 328 acquires a paper selection signal indicating the size of the printed paper corresponding to the inspection image data from the printing apparatus 100, and performs magnification correction according to the paper size indicated by the paper selection signal. The paper selection signal is included in control data that the printing apparatus 100 receives from the printer controller 20. Timing when document image data and control data corresponding thereto are input to the printing apparatus 100, timing when printed paper corresponding to the document image data is read by the reading device 260, and input to the inspection image processing unit 220 Although there is a time difference, the paper selection signal is delayed by this time difference and supplied to the magnification correction circuit 328.

  The binarization circuit 330 is a circuit that performs binarization processing on the inspection image data corrected by the magnification correction circuit 328. Binarization is a process of converting multi-value inspection image data generated by the reading device 260 into binary image data of 1 bit per pixel. When it is attempted to detect missing or smeared images in the printing result, this binarization can simplify the detection process. The binarization circuit 330 executes binarization processing using the parameters stored in the parameter storage unit 330m. The parameters used here include a binarization threshold value that is a pixel value that serves as a boundary between whether the binarization result is white or black.

  As described above, some examples of the image processing executed by the inspection image processing unit 220 have been shown. However, the inspection image processing unit 220 does not have to execute all the image processings exemplified above. The illustrated image processing is only an example, and the inspection image processing unit 220 may perform other image processing such as skew correction, for example.

  The control signal generation unit 300 and the image processing unit 320 described above can be configured as a hardware circuit such as an application specific IC (ASIC) or a field programmable gate array (FPGA). Here, the method of dividing the control signal generation unit 300 and the image processing unit 320 is merely for convenience. Therefore, all of the circuits 302, 304, 304m, 306, 322, 322m, 324, 324m, 326, 326m, 328, 330, 330m included in them may be configured as one ASIC or the like. The inspection image processing unit 220 may be configured by a plurality of ASICs or ICs by appropriately allocating a circuit to a plurality of ASICs or the like.

  Each of the parameter storage units 304m and 322m to 330m is a nonvolatile rewritable memory element such as an EEPROM (Electrically Erasable Programmable Read-Only Memory) or an SRAM (Static Random Access Memory) with a battery backup. For example, at the time of printing system shipment, inspection at the time of printing system installation, or periodic inspection by a customer engineer, for example, by operating the system while shaking the value of each parameter within a certain range, Optimum values are obtained and stored in the parameter storage units 304m and 322m to 330m.

  In the above example, parameters used for each image processing or processing for generating a signal such as a conveyance speed signal that is the basis of the image processing are stored in the parameter storage units 304m and 322m to 330m and used. He said. However, the data stored in the memory element in the inspection image processing unit 220 is not limited to this. For example, in general, ASIC and FPGA designs are improved as needed to expand functions and deal with problems. Therefore, there are cases in which versions of ASIC and the like differ depending on the shipping time even for devices of the same model. Such version information, such as ASIC, is one important piece of information for specifying the cause of print result failure determination or the like. Therefore, in this embodiment, version information of each ASIC or the like is stored in a non-volatile memory such as each ASIC that constitutes the inspection image processing unit 220.

  The inspection image processing unit 220 has been described above. Next, the document image processing unit 210 will be described with reference to FIG. The document image processing unit 210 illustrated in FIG. 8 is an example in which resolution conversion is performed as image processing for document image data, and includes a resolution conversion circuit 405 and a parameter storage unit 405m. In this case, it is assumed that document image data of a binary image is supplied from the printer controller 20.

  The resolution conversion circuit 405 is a circuit that converts the resolution of document image data so that it has the same resolution as the inspection image data. In general, since the original image data is an image printed on paper, it is a relatively high resolution image such as 400 dpi (dot per inch) or 600 dpi, whereas the inspection image data is read in real time in synchronization with printing. Since the image needs to be processed, the image has a relatively low resolution. For this reason, the resolution of the document image data is lowered to match the inspection image data in order to make it possible to compare the pixels. The parameter storage unit 405m stores data serving as resolution conversion parameters such as the resolution value of the inspection image data. The resolution conversion circuit 405 acquires the resolution value of the document image data from the control data input via the image input IF circuit 105, and converts the image of this resolution into the resolution of the inspection image data. Since the processing contents of resolution conversion are well known, description thereof will be omitted.

  Although the resolution conversion has been exemplified above, the image processing executed by the document image processing unit 210 is not limited to this. An example of image processing other than resolution conversion is binarization. It is effective to compare the binarized document image with the inspection image to determine whether the printed part is missing or dirty in the print inspection. When such a method is used, the original image data is In the case of multi-valued image data, the document image processing unit 210 has a binarization processing function for document image data.

  The embodiment described above is merely an example, and various modifications can be made within the scope of the present invention.

  For example, in the above example, the case where the inspection image processing unit 220 and the document image processing unit 210 execute all the processes by the hardware circuit is taken as an example. It is also conceivable that everything is executed by software.

  In the above example, the print inspection apparatus 200 evaluates the quality of the print result by comparing the inspection image data with the document image data, but this is one example. A method of performing a print inspection only from inspection image data without performing comparison with original image data is also conceivable. For example, in the printing of a form mainly composed of characters and ruled lines, the edge of an image to be printed is basically clear, but the stain due to ink / toner scattering often makes the edge unclear. Therefore, in such a case, the contamination can be detected to a considerable extent by obtaining the edge strength of each part of the inspection image. As described above, the print quality may be evaluated by the feature calculation for the inspection image, and the method of the present embodiment can be applied to such a case.

  Further, in the present embodiment, the case of a configuration in which an image is read by one line sensor has been described. However, the present invention is applied to a high-speed image reading apparatus that reads images at high speed using a plurality of line sensors and combines the images. can do. For example, the above-described high-speed image reading apparatus may be used when a large amount of printing is performed in a short period of time, such as in the case of form printing such as telephone charges, but the present invention does not stop the job. Since density unevenness can be corrected, the effect is particularly remarkable when applied to such a high-speed image reading apparatus.

  In this case, for example, a shading correction circuit 322, an exposure correction circuit 324, a density unevenness correction circuit 325, a positional deviation correction circuit 326, a magnification correction circuit 328, and a binarization circuit 330 are provided for each line sensor, and the same processing is performed for each line sensor. Just do it.

  In addition, in a high-speed image reading apparatus that reads an image at high speed using a plurality of line sensors, the degree of light irradiation from the light source may be different in each line sensor, and even if an image with the same density is read, the density difference As described above, the density difference between the line sensors can be suppressed by correcting the density unevenness for each line sensor as described above.

  If the density difference between the line sensors is equal to or greater than a predetermined threshold value that adversely affects the image quality, instead of constantly correcting the density unevenness, for example, the difference in pixel values of the white reference plate read by each line sensor is predetermined. If the threshold value is equal to or greater than the threshold value, density unevenness correction may be performed on the image read by each line sensor.

1 is a block diagram illustrating a schematic configuration of an example of a printing system to which the present invention is applied. It is a block diagram which shows the internal structure of the Example of a test | inspection image process part. It is a top view of a paper conveyance system and a white reference plate. It is an image figure which shows a picture image. It is an image figure which shows the pixel value of the line image for 1 line. It is an image figure which shows the pixel value of the line image for 1 line. It is an image figure which shows the pixel value of the line image for 1 line. It is a block diagram which shows the internal structure of the Example of a manuscript image process part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Host computer 20 Printer controller 30A, 30B White reference board 34 Image image 100 Printing apparatus 110 Print engine 112 Paper conveyance system 150 Printed paper (recording medium)
200 Print inspection device 260 Reading device 265 Line sensor 320 Image processing unit 322 Shading correction circuit 324 Exposure correction circuit 325 Density unevenness correction circuit (correction means)
326 Position shift correction circuit 328 Magnification correction circuit 330 Binary circuit

Claims (6)

A line sensor in which light receiving elements are arranged along a predetermined direction;
A white reference plate provided in each of the second reading areas at both ends of the line sensor other than the first reading area for reading at least an image recorded on the recording medium among the reading areas of the line sensor ;
Based on the pixel value of the second reading area read by the second light receiving element corresponding to the second reading area, the reading by the first light receiving element corresponding to the first reading area Correction means for correcting the pixel value of the first reading area for each line in real time;
With
The correction unit is configured to select the first correction factor according to a first correction factor obtained from a larger pixel value of the read two pixel values of the second reading region and a maximum value of a predetermined gradation range. A first correction unit that corrects a pixel value in the reading region; a pixel value after correcting a smaller pixel value of the pixel values in the two second reading regions by the first correction factor; and the maximum value The pixel value after correction by the first correction unit of the first reading area is corrected according to the second correction rate obtained from the value and the position of the first reading area in the predetermined direction. And a second correction unit . It said line sensor with a plurality providing an image of claim 1 Symbol mounting characterized by comprising the correcting means for each of said line sensor reader. The correction by a correction unit provided for each of the line sensors is executed when a difference between pixel values of the second reading areas read by a plurality of line sensors is equal to or greater than a predetermined threshold value. Item 3. The image reading apparatus according to Item 2 . A line sensor in which light receiving elements are arranged along a predetermined direction; and a second sensor at both ends of the line sensor other than a first reading area for reading an image recorded on a recording medium among reading areas of the line sensor . An image reading method executed by an image reading device provided with a white reference plate provided in each reading area,
Based on the pixel value of the second reading area read by the second light receiving element corresponding to the second reading area, the reading by the first light receiving element corresponding to the first reading area step of correcting in real time the pixel value of the first read area for each line
Including
In the correcting step, the first correction rate is obtained according to a first correction factor obtained from a larger pixel value of the read pixel values of the second reading area and a maximum value of a predetermined gradation range. A first correction step for correcting the pixel value in the reading region of the first pixel, a pixel value after correcting the smaller pixel value of the pixel values in the two second reading regions with the first correction factor, and the In accordance with the second correction factor obtained from the maximum value and the position of the first reading area in the predetermined direction, the pixel value after correction by the first correction unit of the first reading area is determined. A second correction step of correcting the image. The image reading method according to claim 4 , wherein the correcting step is executed for each of the line sensors when a plurality of the line sensors are provided. If the difference between the respective read pixel value of the second read area by a plurality of line sensors exceeds a predetermined threshold value, according to claim 5, wherein the performing the step of said correction for each of the line sensors Image reading method.

Images