Abstract:
An image reading apparatus includes an image reading section and a detection section. The image reading section includes at least two detection units, and performs a reading operation on an image. The at least two detection units have respective spectral characteristics which are different from each other. The detection section detects a condition of an irregularity on an image carrier by comparing a detection result of the image read by the image reading section with an output characteristic. The output characteristic is stored in advance and is a color component obtained from a value obtained by the image reading section reading a test image having a region in at least one color.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2015-132491 filed Jul. 1, 2015. 
       BACKGROUND 
     Technical Field 
       [0002]    The present invention relates to an image reading apparatus, an image forming apparatus, and a non-transitory computer readable medium. 
       SUMMARY 
       [0003]    According to an aspect of the invention, there is provided an image reading apparatus including an image reading section and a detection section. The image reading section includes at least two detection units, and performs a reading operation on an image. The at least two detection units have respective spectral characteristics which are different from each other. The detection section detects a condition of an irregularity on an image carrier by comparing a detection result of the image read by the image reading section with an output characteristic. The output characteristic is stored in advance and is a color component obtained from a value obtained by the image reading section reading a test image having a region in at least one color. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
           [0005]      FIG. 1  is a schematic sectional view of an image forming apparatus according to an exemplary embodiment of the present invention; 
           [0006]      FIG. 2  is a block diagram illustrating the hardware configuration of the image forming apparatus according to the exemplary embodiment of the present invention; 
           [0007]      FIG. 3  is a flowchart for obtaining characteristics of detection units according to the exemplary embodiment of the present invention; 
           [0008]      FIG. 4  is a plan view of an exemplary color sample used in the exemplary embodiment of the present invention; 
           [0009]      FIG. 5  is a diagram illustrating output characteristics obtained when the detection units used in the exemplary embodiment of the present invention are installed and when the detection units are to be adjusted; 
           [0010]      FIG. 6  is a flowchart for dealing with paper wrinkles, according to a first exemplary embodiment of the present invention; 
           [0011]      FIG. 7  is a plan view of testing paper on which a test image used in the first exemplary embodiment of the present invention is formed; 
           [0012]      FIG. 8  is a flowchart for dealing with paper wrinkles, according to a second exemplary embodiment of the present invention; 
           [0013]      FIG. 9  is a flowchart describing the detail of step S 52  in  FIG. 8 ; 
           [0014]      FIG. 10  is a diagram in which outputs obtained by reading a test image by using the detection units are compared with detected outputs, in the second exemplary embodiment of the present invention; and 
           [0015]      FIG. 11  is a plan view of testing paper on which a test image used in another exemplary embodiment of the present invention is formed. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Exemplary embodiments of the present invention will be described in detail with reference to the drawings. 
         [0017]      FIG. 1  is a schematic sectional view of an image forming apparatus  10 . The image forming apparatus  10  includes a user interface (UI) device  12 , an image forming apparatus body  14 , and an image reading apparatus  16 . 
         [0018]    The UI device  12  including a display for displaying information and an input receiving device for receiving input performed by an operator is constituted, for example, by a touch panel. An operator may input operation setting information via the UI device  12 . 
         [0019]    The image forming apparatus body  14  has, for example, three recording-medium supplying cassettes  18 , each of which is provided with a supply head  20 . 
         [0020]    When one of the recording-medium supplying cassettes  18  is selected, a corresponding one of the supply heads  20  is activated, and a recording medium is supplied from the selected recording-medium supplying cassette  18  via a recording-medium supplying path  22  to an image forming unit  24 . 
         [0021]    The image forming unit  24  is provided with yellow, magenta, cyan, and black photoconductors  26  disposed side by side and an intermediate transfer belt  28 . 
         [0022]    Around each of the photoconductors  26 , an exposure apparatus  27  is disposed. In addition, a charging device, a developing device, a first transfer device, a cleaning device, and the like (not illustrated) are disposed. A toner image formed by using each photoconductor  26  is transferred to the intermediate transfer belt  28 . The exposure apparatus  27  is constituted, for example, by a light-emitting diode (LED) and a laser emitting device. The exposure apparatus  27  having, for example, an output resolution of 600 dpi has a configuration in which the amount of light may be adjusted for each dot. 
         [0023]    The toner images on the intermediate transfer belt  28  are transferred by a second transfer roller  30  onto a recording medium which has been conveyed, and are fixed by a fixing device  32 . The recording medium on which the toner images are fixed is discharged to a discharge unit  36  through a recording-medium discharge path  34 . The image transferred onto the intermediate transfer belt  28  is read by a belt-image reading unit  38 . 
         [0024]    When a setting for duplex printing is set, the recording medium on which the toner image is fixed by the fixing device  32  is conveyed from the recording-medium discharge path  34  to a reversing device  40 , and is reversed by the reversing device  40 . Then, the recording medium is conveyed to a recording-medium reversing path  42 , is conveyed back to the recording-medium supplying path  22  again, and is conveyed to the image forming unit  24 , whereby printing is performed on the surface on the back. A fixed-image reading unit  44  is provided downstream of the fixing device  32 . The fixed-image reading unit  44  reads the image fixed on the recording medium. 
         [0025]    The image reading apparatus  16  includes a document supply unit  46  to which a document is supplied, a document-image reading unit  48  which reads the image of the document, a document feeding device  50  which feeds the document from the document supply unit  46  to the document-image reading unit  48 , and a document discharge unit  52  which discharges the document from which the image has been read by the document-image reading unit  46 . 
         [0026]      FIG. 2  is a block diagram illustrating the hardware configuration of the image forming apparatus  10 . The document-image reading unit  48  described above has, for example, three detection units  48   r,    48   g,  and  48   b  each of which includes, for example, a charge-coupled device (CCD) or the like covered with a filter, and each of which has a different spectral characteristic from each other. That is, the first detection unit  48   r  reads red components; the second detection unit  48   g  reads green components; and the third detection unit  48   b  reads blue components. Each of these detection units  48   r,    48   g,  and  48   b  detects a density as an analog signal, in the subscanning direction with respect to a document, for example, with a resolution of 600 dpi. Then, each of the detection units  48   r,    48   g,  and  48   b  converts the analog signal into a digital signal through an analog-digital (A/D) converter, and outputs the data obtained through the conversion to a main controller  54 . 
         [0027]    The main controller  54  having a central processing unit (CPU) and the like controls the UI device  12  and a drive controller  56  on the basis of programs. The drive controller  56  controls drive of the image forming apparatus  10 . A storage unit  58  stores data which is output from the main controller  54 , and outputs stored data to the main controller  54  through access from the main controller  54 . 
         [0028]    The image forming apparatus  10  obtains output characteristics of the detection units  48   r,    48   g,  and  48   b  of the document-image reading unit  48 , for example, when the image forming apparatus  10  is installed. That is, as illustrated in  FIG. 3 , in step S 10 , the main controller  54  transmits an instruction to transmit, for example, a color sample  60  (color chart) illustrated in  FIG. 4  to the document-image reading unit  48  so that the color sample  60  is read by using the detection units  48   r,    48   g,  and  48   b.  The color sample  60  is formed in which, for example, a yellow row  62 Y, a magenta row  62 M, and a cyan row  62 C are formed parallel with one another in the subscanning direction and in which each of the yellow row  62 Y, the magenta row  62 M, and the cyan row  62 C extends in the main scanning direction so that its density is gradually changed in a predetermined rate. In the next step S 12 , relationships of G-R, R-B, and B-G are obtained on the basis of the detected values obtained through the reading in step S 10 . For example, as illustrated by using a solid line in  FIG. 5 , the values obtained by reading the cyan row  62 C by using the detection unit  48   r  and the detection unit  48   g  are plotted so that the relationship between red output values and green output values is shown. The values thus plotted are subjected to linear regression so that the relationship is obtained. In the next step S 14 , each of the relationships of G-R, R-B, and B-G which are obtained by reading the yellow row  62 Y, the magenta row  62 M, and the cyan row  62 C are stored in the storage unit  58  described above, and the process ends. 
         [0029]      FIG. 6  illustrates an operation flow for dealing with paper wrinkles, according to a first exemplary embodiment. 
         [0030]    As illustrated in  FIG. 7 , in step S 20 , testing paper  64  on which a halftone image with a predetermined density is formed on the entire surface is prepared. The testing paper  64  is conveyed to the document-image reading unit  48 , and the test image (the entire halftone image) on the testing paper  64  is read by using the detection units  48   r,    48   g,  and  48   b.  In the next step S 22 , relationships of G-R, R-B, and B-G are obtained on the basis of the detected values obtained through the reading in step S 20 . For example, if the test image is a cyan halftone image, as illustrated by using a dotted line in  FIG. 5 , the values obtained through reading using the detection unit  48   r  and the detection unit  48   g  are subjected, for example, to linear regression so that the relationship between red output values and green output values is obtained. 
         [0031]    In the next step S 24 , the relationship characteristics of G-R, R-B, and B-G which are stored in the storage unit  58  are retrieved, and are compared with the relationship characteristics obtained in step S 22 . In theory, the relationship characteristics of G-R, R-B, and B-G which are stored in the storage unit  58  are to match the relationship characteristics obtained in step S 22  in the density range of the halftone image. 
         [0032]    However, when paper wrinkles are present on the testing paper, irregularities occur on the test image. The irregularities on the test image cause spectral characteristics of light reflected by the irregularities on the test image to be changed, and a difference between the relationship characteristics of G-R, R-B, and B-G which are stored in the storage unit  58  and the relationship characteristics obtained in step S 22  arises. 
         [0033]    Therefore, in step S 26 , it is determined whether or not the difference between the relationship characteristics is large. If the difference is large (such as if the number or ratio of pixels whose values are larger than a determined threshold is larger than a predetermined number or ratio, or if the difference between the averages over the halftone image is larger than a predetermined threshold), the process proceeds to step S 28 , and a control instruction is output to the drive controller  56  described above so that the operation performed by the document-image reading unit  48  is aborted. In the next step S 30 , if it is determined that the difference is small in step  26 , a message such as “You may continue the operation.” is displayed. If the operation performed by the document-image reading unit  48  is aborted in step S 28 , an instruction is transmitted to the UI device  12  so that a message such as “Read an image again.” is displayed, and the process ends. 
         [0034]      FIGS. 8 and 9  illustrate an operation flow for dealing with paper wrinkles, according to a second exemplary embodiment. 
         [0035]    In step S 40 , an instruction to print a test image is displayed on the UI device  12 . In the next step S 42 , a user presses a print switch of the UI device  12  in accordance with the instruction displayed in step S 40 . In the next step S 44 , a control instruction is output to the drive controller  56  so that the test image (test pattern) is printed. The test image is the halftone image used in the first exemplary embodiment. In the next step S 46 , an instruction to read the test image obtained through printing in step S 44  is displayed on the UI device  12 . In the next step  48 , the user presses a reading button of the UI device  12  in accordance with the instruction displayed in step S 46 . In the next step S 50 , a control instruction is output to the drive controller  56  so that the test image is read. In the next step S 52 , paper wrinkles are detected and a correction process is performed. In the next step S 54 , density unevenness in the paper feeding direction (main scanning direction) is corrected, and the process ends. 
         [0036]    The process in step S 52  will be described in detail. As illustrated in  FIG. 9 , in step S 522 , the R signal data for the testing paper  64  which is obtained through reading using the detection unit  48   r  is converted into G′ data by using the linear regression data in  FIG. 5 . That is, in the case where the test image is a cyan halftone image, when R is data obtained by using the detection unit  48   r  performing a reading operation in the subscanning direction at a certain position in the main scanning direction, R is converted into G′ on the basis of the R-G characteristics diagram stored in the storage unit  58  as illustrated in  FIG. 10 . If no paper wrinkles are present, G′ is to match G data detected by the detection unit  48   g.    
         [0037]    However, when irregularities such as paper wrinkles are present on an image, a difference between the detected G data and the G′ data obtained through conversion arises. That is, when irregularities are present on an image, hues and densities detected by the two detection units  48   r  and  48   g  are changed, and a difference between the detected G data and the G′ data obtained through conversion arises. In step S 524 , the difference between the data G and the data G′ is detected, and the condition of the irregularities on the test image is detected. This detection of the condition of the irregularities is performed in the entire subscanning and main scanning directions. 
         [0038]    In the next step S 526 , it is determined whether or not large paper wrinkles are present, on the basis of the difference data G′-G obtained in step S 524 . The determination is made, for example, on the basis of whether or not the number of pixels having difference data G′-G which is equal to or larger than a predetermined threshold is equal to or larger than a predetermined number, or whether or not difference data G′-G which is equal to or larger than a predetermined threshold occupies an area whose ratio is equal to or larger than a predetermined ratio. 
         [0039]    In step S 526 , if it is determined that large paper wrinkles are present, the process proceeds step S 528 , and the operation of the document-image reading unit  48  is aborted. Then, the UI device  12  is instructed to display a message such as “Read again.”, and the process ends. 
         [0040]    In step S 526 , if it is determined that large paper wrinkles are not present, the process proceeds to step S 530 , correction values for data G and R are set for each dot in the subscanning direction and the main scanning direction, and the process ends. That is, a correction value is set for data G on the basis of the difference data G′-G obtained in step S 524 . The data G′-G may be set as a correction value without conversion. Alternatively, for example, the data G′-G may be multiplied by a factor, for example, 0.8, and the resulting value may be set as a correction value. Instead, data obtained from another detection unit may be used to set a correction value. Similarly to data G, for data R, R′-R is obtained, and a correction value is set on the basis of the data R′-R. 
         [0041]    In the above-described exemplary embodiments, the detection units  48   r  and  48   g  are used to read a cyan halftone image. A similar process is performed for yellow and magenta. That is, in the case of yellow, the determination for paper wrinkles is made on the basis of outputs from the detection units  48   r  and  48   b  or the detection units  48   g  and  48   r;  and in the case of magenta, on the basis of outputs from the detection units  48   r  and  48   g  or the detection units  48   g  and  48   b.    
         [0042]    Correction values for outputs from the detection units  48   r,    48   g,  and  48   b  may be set by using, in a comprehensive manner, the data which is obtained by reading cyan, yellow, and magenta halftone images. A document may be read by the document-image reading unit  48  with less adverse effects from paper wrinkles by using the above-described correction values to correct outputs from the detection units  48   r,    48   g , and  48   b.  When a document is to be copied, outputs from the detection units  48   r,    48   g,  and  48   b  are corrected by the main controller  54 , and are converted into yellow/magenta/cyan/black (YMCK), whereby the amount of light emitted from the exposure apparatus  27  is changed. 
         [0043]    In the above-described exemplary embodiments, a halftone image is formed on the entire surface of the testing paper  64  as a test image. However, the present invention is not limited to this. For example, as illustrated in  FIG. 11 , a test image in which a cyan pattern and a magenta pattern are alternately formed in the main scanning direction may be used. Alternatively, the condition of paper wrinkles may be determined by using one color, and the result may be used for the other colors. Instead, by using a white test image, variations (such as a standard deviation) of output values from the detection units  48   r,    48   g,  and  48   b  may be measured, and the magnitude of the area for paper wrinkles may be determined. 
         [0044]    In the above-described exemplary embodiments, application to the document-image reading unit  48  is described. However, the present invention is not limited to this. For example, the present invention may be applied to the belt-image reading unit  38 , and floppiness of the intermediate transfer belt may be detected. Alternatively, the present invention may be applied to the fixed-image reading unit  44 , and paper wrinkles on a recording medium holding a fixed image may be detected. 
         [0045]    In the above-described exemplary embodiments, output values from the detection units  48   r,    48   g,  and  48   b  are corrected in accordance with the condition of irregularities on a test image. When a document is to be copied, output values obtained in the image forming apparatus  10  may be corrected. 
         [0046]    The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.