[0001]     This application is a continuation of pending U.S. patent application Ser. No. 10/436,384 filed May 12, 2003 under 35 U.S.C. § 120, which claims priority to Japanese Patent Application No. 2002-139061 filed on May 14, 2002, the entirety of all of which are incorporated herein by reference as if fully set forth herein. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to an image reading technique in a copying machine, scanner, facsimile apparatus, and the like and, more particularly, to a technique of performing shading correction for the light quantity of a light source and variations in luminous intensity distribution in sequential reading of an original.  
       BACKGROUND OF THE INVENTION  
       [0003]     In order to correct the light quantity of a light source and variations in luminous intensity distribution, a conventional image forming apparatus such as a copying machine, scanner, or facsimile apparatus moves an original to a white reference plate for each original or at a predetermined timing, reads the original, and performs shading correction every reading. Alternatively, an end white plate is prepared outside the image region, and monitored to perform correction on the basis of the variation amount.  
         [0004]     In the conventional method, movement to the white reference plate at a predetermined timing greatly decreases the reading efficiency of a contact image sensor (to be referred to as a CIS hereinafter). In the use of the end white plate, the light quantity is monitored at an end portion in the main scanning direction. Variations in luminous intensity distribution in the entire main scanning region cannot be corrected, readily degrading the image.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention has been made to overcome the conventional drawbacks, and has as its object to suppress a decrease in reading efficiency while preventing image degradation.  
         [0006]     To solve the above problem and achieve the above object, according to the first aspect of the present invention, an image reading apparatus is comprising a light source which illuminates an object, a reading device which photoelectrically converts light reflected by the object and reads information on the object, a density reference member which serves as a reference for correcting an image signal obtained by reading an original by the reading device, a roller member which feeds the original to a reading position, a comparison device which compares a second signal obtained by reading the roller member by the reading device and a third signal obtained by reading again the roller member by the reading device, and a correction device which corrects the image signal on the basis of a first signal obtained by reading the density reference member by the reading device, and a comparison result of the comparison device.  
         [0007]     According to the second aspect of the present invention, an image reading apparatus control method of controlling an image reading apparatus having a light source which illuminates an object, a reading device which photoelectrically converts light reflected by the object and reads information on the object, a density reference member which serves as a reference for correcting an image signal obtained by reading an original by the reading device, and a roller member which feeds the original to a reading position is comprising a first reading step of reading the density reference member by the reading device to generate a first signal, a second reading step of reading the roller member by the reading device to generate a second signal, a third reading step of reading again the roller member by the reading device to generate a third signal, a comparison step of comparing the second and third signals, and a correction step of correcting an image signal obtained by reading the original by the reading device on the basis of the first signal, and a comparison result in the comparison step.  
         [0008]     According to the third aspect of the present invention, a program which causes a computer to execute an image reading apparatus control method of controlling an image reading apparatus having a light source which illuminates an object, a reading device which photoelectrically converts light reflected by the object and reads information on the object, a density reference member which serves as a reference for correcting an image signal obtained by reading an original by the reading device, and a roller member which feeds the original to a reading position is comprising a first reading step of reading the density reference member by the reading device to generate a first signal, a second reading step of reading the roller member by the reading device to generate a second signal, a third reading step of reading again the roller member by the reading device to generate a third signal, a comparison step of comparing the second and third signals, and a correction step of correcting an image signal obtained by reading the original by the reading device on the basis of the first signal, and a comparison result in the comparison step.  
         [0009]     Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a sectional view showing the schematic arrangement of an image reading apparatus according to an embodiment of the present invention;  
         [0011]      FIG. 2  is a plan view showing the image reading apparatus main body in  FIG. 1  when viewed from the top;  
         [0012]      FIG. 3  is a sectional view showing in detail the sheetfed scanning unit of the image reading apparatus according to the embodiment;  
         [0013]      FIG. 4  is a block diagram showing the arrangement of the control system of the image reading apparatus in  FIG. 1 ;  
         [0014]      FIG. 5  is a block diagram showing the arrangement of the image processing unit of the image reading apparatus according to the embodiment;  
         [0015]      FIG. 6  is a flow chart showing the sheetfed scanning sequence of the image reading apparatus according to the embodiment;  
         [0016]      FIG. 7A  is a graph showing the luminous intensity distribution when a platen roller is read;  
         [0017]      FIG. 7B  is a graph showing the gain value between sampling points;  
         [0018]      FIG. 8  is a flow chart showing an image processing sequence of reading the platen roller between sheets by the image reading apparatus according to the embodiment;  
         [0019]      FIG. 9  is a table showing an example of concrete numerical values when the luminous intensity distribution in  FIG. 7A  is corrected in accordance with the sequence in  FIG. 8 ;  
         [0020]      FIG. 10  is a block diagram showing the arrangement of the image processing unit of the image reading apparatus in  FIG. 5  for explaining the relationship between a black memory  504 , a white memory  505 , and a gain memory  506 ; and  
         [0021]      FIG. 11  is a block diagram showing a modification to  FIG. 10 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]     A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.  
         [0023]      FIG. 1  is a sectional view showing the schematic arrangement of an image reading apparatus according to the embodiment of the present invention.  FIG. 2  is a plan view showing the image reading apparatus main body in  FIG. 1  when viewed from the top.  
         [0024]     In  FIG. 1 , the image reading apparatus comprises an image reading apparatus main body  100 , and an ADF (Auto Document Feeder)  200  which is detachable from the image reading apparatus main body  100 .  
         [0025]     The ADF  200  conveys an original set on a feed tray  205  to a sheetfed scanning glass plate  122  of the image reading apparatus main body  100  by convey rollers  203  and  204 , and then recovers the original. At this time, the original passes between a platen roller  201  attached to the ADF  200  and the sheetfed scanning glass plate  122  of the image reading apparatus main body  100 . During the passage, the original is optically scanned by the image reading apparatus main body  100  to read original information.  
         [0026]     More specifically, the image reading apparatus main body  100  has a contact image sensor (to be referred to as a CIS hereinafter)  110 . The CIS  110  is constituted by integrally storing in a casing  114  a lamp  111  which emits light to the original surface, a lens  112  for guiding, to an image sensor  113 , light reflected by the original that corresponds to light emitted by the lamp  111 , and the image sensor  113  for photoelectrically converting light condensed by the lens  112 .  
         [0027]     The CIS  110  is connected to a motor  125  via a timing belt  126  in  FIG. 2 . By rotating and driving the motor  125 , the CIS  110  moves parallel to a glass original table  121  and the sheetfed scanning glass plate  122 . A position sensor  124  detects the home position of the CIS  110 . The motor  125  is rotated in a normal or opposite direction on the basis of the position of the position sensor  124  serving as a reference. The CIS  110  then moves to optically scan an original on the glass original table  121  and sheetfed scanning glass plate  122 .  
         [0028]     The motor  125  is comprised of a stepping motor. The motor  125  is connected to an encoder  402  (see  FIG. 4 ). An output from the encoder allows recognizing the number of pulses by which the CIS  110  has moved. In other words, the position of the CIS  110  can be grasped on the basis of a detection signal from the position sensor  124  and an encoder pulse from the encoder  402 .  
         [0029]     Light reflected by an original is guided to the SELFOC lens  112 , and condensed on the image sensor  113 . The image sensor  113  photoelectrically converts reflected light containing original information, and outputs an electronic image signal.  
         [0030]     With this arrangement, original information can be read in two modes: an ADF original reading mode in which original information is read while the CIS  110  stops at an original reading position and an original is conveyed by the ADF  200 , and a glass original table original reading mode in which original information is read while the original is stationarily set on the glass original table  121  and the CIS  110  is moved in a subscanning direction.  
         [0031]      FIG. 3  is a view showing an arrangement near the CIS  110  used in the embodiment. The ADF  200  of the embodiment comprises a white sheet member  210  on the upstream side of the platen roller  201  in the original convey direction. The white sheet member  210  is arranged almost parallel to the sheetfed scanning glass plate  122 . A distal end position  211  where the white sheet member  210  comes closest to the platen roller  201  is set such that the white sheet member  210  covers part of the platen roller  201  in almost the entire image reading range of the CIS  110  in the main scanning direction when the platen roller  201  and white sheet member  210  are viewed from a lower portion in  FIG. 3 . The reading position of the CIS  110  in the ADF original reading mode is set to a position where the surface of the platen roller  201  is read when no original is conveyed. The glass original table  121  has a white reference plate  127 . A jump table  123  has a mechanism which scoops, along the shape of the jump table, an original conveyed by the platen roller  201  and the like. The jump table  123  is effective for conveying a sheet.  
         [0032]      FIG. 4  is a block diagram showing the schematic arrangement of the control system of the image reading apparatus according to the embodiment.  
         [0033]     In  FIG. 4 , the image reading apparatus comprises the platen roller  201 , a feed roller  202 , and the convey rollers  203  and  204  that convey an original, the lamp  111  which emits light to an original surface, the motor  125  which moves the CIS  110  in the subscanning direction to scan an original, the image sensor  113  which photoelectrically converts light reflected by an original surface, an A/D conversion circuit  401  which A/D-converts an output signal from the image sensor  113 , an encoder  402  which is connected to the motor  125 , the position sensor  124  for positioning the CIS  110  at the home position, a backup RAM  403  for setting a normal original reading position in the ADF original reading mode, and a scanner controller  404 .  
         [0034]     The scanner controller includes a ROM  405  which stores various programs such as a program corresponding to the flow charts of the following drawings.  
         [0035]      FIG. 5  is a block diagram showing the arrangement of the image processing unit of the image reading apparatus according to the embodiment.  
         [0036]     In  FIG. 5 , an image signal from the image sensor undergoes known shading correction by a shading correction unit  501 , and undergoes, by a luminance intensity distribution variation correction unit  502 , luminance intensity distribution variation correction which is a feature of the present invention and is to be described later.  
         [0037]      FIG. 6  is a flow chart showing the sheetfed scanning sequence of the image reading apparatus according to the embodiment.  
         [0038]     The CIS  110  reads the white reference plate  127  serving as a color density reference member at the home position, obtaining shading correction data (step S 1 ). The CIS  110  moves below the jump table  123  to the reading position (step S 2 ), and reads the background member (more specifically the surface of the platen roller  201 ), obtaining luminous intensity distribution variation correction data (step S 3 ). After that, the CIS  110  reads an original (step S 4 ). In the presence of the next original, the CIS  110  reads the background member again between originals (step S 3 ), and reads the original. In the absence of the next original, the processing ends. Note that the white reference plate and background member (more specifically, platen roller) are different in density.  
         [0039]     The platen roller can be read while being rotated, and the influence of contamination of the platen roller on reading can be reduced. Also, the mechanical arrangement of the platen roller allows conveying a sheet without fluttering it.  
         [0040]     One of the reasons why the CIS  110  does not return to the white reference plate  127  after moving to the reading position in step S 1  is as follows. If the CIS  110  moves to the home position in order to read the white reference plate  127  again after moving to the reading position, the CIS  110  must move below the jump table  123  again. To reduce restrictions on the return time, variation correction data is obtained in step S 3 . Since shading data is obtained in step S 1 , the data need not be acquired during reading as far as the arrangement considers changes along with sequential reading. This will be explained below. The luminance intensity distribution variation correction unit  502  will be described with reference to  FIGS. 7A and 7B .  
         [0041]      FIG. 7A  is a graph showing the luminous intensity distribution in the main scanning direction when the platen roller  201  is read between originals.  
         [0042]     The luminous intensity distribution is almost flat after shading correction (0 min), but varies after 2 min. Shading correction has conventionally been executed between originals. However, if the CIS arrangement is moved to the white reference plate  127  again, the reading efficiency greatly decreases. The gain may be applied uniformly in the main scanning direction by using an end white plate. This method cannot completely correct variations in luminance intensity when the light quantity decrease amount is different between the center and the end in the main scanning direction.  
         [0043]      FIG. 8  is a flow chart showing operation of reading the platen roller  201  between originals by the image reading apparatus according to the embodiment.  
         [0044]     If the platen roller  201  serving as a reference is read, m main scanning pixels and n subscanning pixels are sampled at a plurality of points in the main scanning direction, and data are averaged at each point (step S 11 ). The data averaged in step S 11  are backed up in a memory as the average luminance level of the reference platen roller  201 . In reading a plurality of originals, m main scanning pixels and n subscanning pixels are sampled at a plurality of points by the same method as that in step S 11  upon reading the platen roller  201  between originals, and data are averaged at each point (step S 12 ). By using the average value calculated at each point, the decrease ratio is calculated (step S 13 ): 
 
Decrease ratio=(average luminance level of platen roller between originals)/(average luminance level of reference platen roller) 
 
         [0045]     The gain value at each point is calculated from the decrease ratio (step S 14 ): 
 
Gain value=1/(decrease ratio) 
 
         [0046]      FIG. 9  shows the concrete numerical values of  FIGS. 7A and 7B  along the flow chart.  
         [0047]     As shown in  FIG. 7B , the gain value between a plurality of points is obtained by approximating gain values at two points by a linear equation. The gain values of all pixels can be calculated by monotone increase or monotone decrease from gain values at two points without any special memory. Luminous intensity distribution variation correction calculation is executed using the data (step S 15 ).  
         [0048]     Luminous intensity distribution variation correction may be done between originals every time each original is read or for a predetermined number of originals. It is also possible to perform luminous intensity distribution variation correction at an early timing on an early stage with a relatively large lamp variation amount, and perform luminous intensity distribution variation correction at an interval when the light quantity of the lamp becomes stable upon the lapse of a predetermined time.  
         [0049]     When the productivity increases (the number of originals read per unit time increases) in luminous intensity distribution variation correction for a predetermined number of originals, the time between originals becomes shorter, and the time used for calculation or the like also becomes shorter. Considering other processes between originals, a plurality of processes may fail between sheets. To prevent this, for example, process A is done between even-numbered sheets, and process B is done between odd-numbered sheets. This enables a plurality of control operations between sheets.  
         [0050]     In luminous intensity distribution variation correction upon the lapse of a predetermined time, correction is done for each original till 60 sec immediately after the lamp is turned on because of a high decrease ratio. After the decrease ratio of the lamp becomes low over 60 sec, correction is done for a predetermined number of originals. This processing control can prevent wasteful calculation.  
         [0051]     It is also possible to monitor the decrease ratio, and if a decrease equal to or larger than a threshold is detected, make luminous intensity distribution variation correction effective for subsequent originals. Also in this case, wasteful calculation at a low decrease ratio can be avoided, similar to correction upon the lapse of a predetermined time.  
         [0052]     A larger number of sampling points (six points in the embodiment) to be averaged is effective because the luminous intensity distribution can be approximated at a higher precision. However, the luminous intensity distribution may be approximated even with a small number of sampling points depending on the lamp characteristic. The number of sampling points and sampling point positions can be changed. A decrease in the number of sampling points leads to an increase in processing speed and reduction in memory capacity. In the sampling point region, m main scanning pixels (256 pixels in the embodiment) and n subscanning pixels (64 pixels in the embodiment) are averaged to reduce the influence of roller contamination and the electrical noise component. When the sampling position is not contaminated, the noise component by contamination can be reduced by sampling m main scanning pixels.  
         [0053]     The gain value by the luminance intensity distribution variation correction unit is stored in a memory different from that for the shading unit. These memories are illustrated in  FIG. 10 .  FIG. 10  is a block diagram showing the arrangement of the image processing unit of the image reading apparatus in  FIG. 5  according to the embodiment for explaining the relationship between a black memory  504 , a white memory  505 , and a gain memory  506 .  
         [0054]     The white reference plate  127  has a managed density and serves as a reference for an original to be read. That is, the shading correction gain value need not be rewritten. A value calculated by reading the white reference plate  127  serving as the first density reference member is held in the white memory  505 , and a value calculated by the luminance intensity distribution variation correction unit is held in the gain memory  506 . When the memory of the luminance intensity distribution variation correction unit cannot be ensured, the arrangement may be modified as follows. That is, as shown in  FIG. 11 , the gain value of the white memory  505  of the shading unit is rewritten into a gain value which considers luminous intensity distribution variation correction.  
         [0055]     In this arrangement, proper shading data can be obtained without any temporal restrictions such that the CIS  110  moves below the jump table  123  during reading and reads again the white reference plate  127  serving as a color reference member. As a result, appropriate image reading can be achieved.  
         [0056]     The luminance intensity distribution variation correction unit of the embodiment applies the gain to a read signal. For a controllable light source, the light quantity of the light source may be corrected.  
         [0057]     As described above, according to the embodiment, the light quantity of the light source and variations in luminous intensity distribution can be corrected by reading the platen roller at the reading position between originals without decreasing the productivity. Degradation of the image quality by the light quantity and variations in luminous intensity distribution can be prevented.  
         [0058]     Note that the surface of the platen roller  201  is read in the above embodiment, but the white sheet member  210  may be read. In this case, high productivity can be ensured because the distance is shorter in reading the white sheet member from the reading position than in reading the first density reference member.  
       Other Embodiment  
       [0059]     The object of the embodiment is also achieved when a storage medium (or recording medium) which stores software program codes for realizing the functions of the above-described embodiment is supplied to a system or apparatus, and the computer (or the CPU or MPU) of the system or apparatus reads out and executes the program codes stored in the storage medium. In this case, the program codes read out from the storage medium realize the functions of the above-described embodiment, and the storage medium which stores the program codes constitutes the present invention. The functions of the above-described embodiment are realized when the computer executes the readout program codes. Also, the functions of the above-described embodiment are realized when an OS (Operating System) or the like running on the computer performs part or all of actual processing on the basis of the instructions of the program codes.  
         [0060]     The functions of the above-described embodiment are also realized when the program codes read out from the storage medium are written in the memory of a function expansion card inserted into the computer or the memory of a function expansion unit connected to the computer, and the CPU of the function expansion card or function expansion unit performs part or all of actual processing on the basis of the instructions of the program codes.  
         [0061]     When the present invention is applied to the storage medium, the storage medium stores program codes corresponding to the above-described flow charts.  
         [0062]     As has been described above, the present invention can suppress a decrease in reading efficiency while the invention is not limited to the specific embodiments thereof except as defined in the appended claims.
An object of this invention is to suppress a decrease in reading efficiency while preventing image degradation. To achieve this object, an image reading apparatus includes a light source which illuminates an object, a sensor which photoelectrically converts light reflected by the object and reads information on the object, a first density reference member which serves as a reference for correcting an image signal obtained by reading an original by the sensor, a second density reference member which is different from the first density reference member, a comparison unit which compares the second signal obtained by reading the second density reference member by the sensor and the third signal obtained by reading again the second density reference member by the sensor, and a correction unit which corrects the image signal on the basis of the first signal obtained by reading the first density reference member by the sensor, and the comparison result of the comparison device.