Abstract:
An image reading device having plural image sensors and a reading controller is disclosed. The image reading device is for obtaining image data over a subject by joining sub-image data outputs read by the image sensors, each image sensor comprising: a signal amplifier; and an A/D converter for converting an analog value output from the image sensor to a digital value; whereby the reading controller adjusts an amplification factor of each signal amplifier so that a read value of a white board read by each image sensor becomes a predetermined value.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to image reading devices and method, and image forming apparatus and method. 
   2. Description of the Related Art 
   Prior image forming apparatus compatible with A0 size subject paper uses only one close image sensor (referred to as “CIS” hereinafter). That is, such a prior image forming apparatus uses a CIS having a length of A0 size paper width to read an original subject. However, such prior image forming apparatus is very large and takes high manufacturing cost, resulting in high price of the image forming apparatus. 
   Therefore, as shown in  FIG. 1 , an image forming apparatus having 5 CISs equivalent to A4 size paper arranged zigzag is already known. 
   In order to accurately read the original subject and obtain good results, it is necessary that the image forming apparatus should correctly recognize white color as reference. Accordingly it is required to adjust the image forming apparatus to make it properly recognize the white color that is called “white color reference adjustment”. The white color reference adjustment is a process wherein an output of the CIS reading light generated by a light source is adjusted (gain adjusted) to a predetermined output reference value by an amplifier (or a signal amplifier) before image forming. 
   Since a prior image forming apparatus compatible with A0 size paper has only one large CIS, even if a problem occurs in white reference adjusting, it is easy to re-adjust the white reference for the only one CIS during the following image processing step. 
   Patent Reference 1: Japanese Patent Laid-open Publication 2001-157006 
   However, a prior image forming apparatus compatible with A0 size paper having plural CISs arranged zigzag, has only one amplifier (or signal amplifier), and therefore can adjust one white reference for only one CIS (e.g. CISm shown in  FIG. 2 ), and the other CISs cannot be adjusted, resulting in variations in CIS outputs. 
   As a result, each CIS has a different white color reference, and when the same white color is read by plural CISs, some CISs output grey color, providing bad image forming. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is a general object of the present invention to provide an image reading device and method in which the white reference value for each CIS is adjusted independently to reduce variation in white reference values of plural CISs and provide a white reference value common to each CIS. 
   Features and advantages of the present invention are set forth in the description that follows, and in part will become apparent from the description and the accompanying drawings, or may be learned by practice of the invention according to the teachings provided in the description. Objects as well as other features and advantages of the present invention will be realized and attained by an image reading device and method and an image forming apparatus and method particularly pointed out in the specification in such full, clear, concise, and exact terms as to enable a person having ordinary skill in the art to practice the invention. 
   To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides as follows. 
   According to one feature of the present invention, there is provided an image reading device having plural image sensors and a reading controller for obtaining image data over a subject by joining sub-image data outputs read by the plural image sensors, each image sensor comprising:
         a signal amplifier; and   an A/D converter for converting an analog value output from the image sensor to a digital value;   whereby the reading controller adjusts an amplification factor of each signal amplifier so that a read value of a white board read by each image sensor becomes a predetermined value.       

   According to another feature of the present invention, there is provided an image forming apparatus including the image reading device as explained above, comprising:
         an image processor for forming an image based on read values of the reference white board adjusted for each image sensor.       

   According to another feature of the present invention, there is provided an image reading method in an image reading device having plural image sensors and a reading controller, for obtaining image data over a subject by joining sub-image data outputs read by the plural image sensors, each image sensor comprising:
         a signal amplifier; and   an A/D converter for converting an analog value output from the image sensor to a digital value;   the image reading method comprising:   a reading controlling step for adjusting an amplification factor of each signal amplifier so that a read value of a white board read by each image sensor becomes a predetermined value.       

   According to another feature of the present invention, there is provided an image forming method in an image forming apparatus having plural image sensors and a reading controller, for obtaining an image data over a subject by joining sub-image data outputs read by the plural image sensors, each image sensor comprising:
         a signal amplifier; and   an A/D converter for converting an analog value output from the image sensor to a digital value;   the image reading method comprising:   a reading controlling step for adjusting an amplification factor of each signal amplifier so that a read value of a white board read by each image sensor becomes a predetermined value; and   an image forming step for forming an image based on read values of the reference white board adjusted for each image sensor.       

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows an arrangement of plural CISs in an image reading device; 
       FIG. 2  shows a chart illustrating signal levels of plural CISs; 
       FIG. 3  generally shows an image forming apparatus to which the present invention may be applied; 
       FIG. 4  is a block diagram of an example of an image forming apparatus according to a first embodiment of the present invention; 
       FIG. 5  is a cross-sectional view of the image reading device cut by A-A′ plane in  FIG. 1 ; 
       FIG. 6  is a chart illustrating signal levels of plural CISs that are adjusted by the reading controller  106 ; 
       FIG. 7  is a flow chart showing procedure for the white reference adjustment processing in the reading controller and image forming processing in the image processor; 
       FIG. 8  is a block diagram illustrating a structure of an image forming apparatus according to a second embodiment of the present invention; 
       FIG. 9  is a flowchart showing another example of procedure for the white reference adjustment processing in the reading controller and image forming processing in the image processor; and 
       FIG. 10  is a block diagram of an image forming apparatus according to another embodiment. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the following, embodiments of the present invention are described with reference to the accompanying drawings. 
   First Embodiment 
     FIG. 3  generally shows an image forming apparatus to which the present invention may be applied. As shown in  FIG. 3 , the image forming apparatus  1  comprises an image reader  10 , an image writer  11 , an image forming unit  12 , a manual paper feeder  13 , a roll paper feeder  14 , and a cassette paper feeder  15 . 
   The image reader  10  corresponds to an image reading device  50  (explained later), and reads image data and the like. The image writer  11  responds to image data read by the image reader  10 , and writes the image on a paper fed by the roll paper feeder  14 . The image forming unit  12  forms an image based on the image data ready by the image reader  10 , to write it on a paper fed by the roll paper feeder  14 . The manual paper feeder  13  is used when a user manually feeds a sheet of paper to the image forming apparatus  1 . The roll paper feeder  14  supplies a sheet of paper contained in the cassette paper feeder  15  to the image writer  11 . The cassette paper feeder  15  stores sheets of papers put by the user. 
     FIG. 4  is a block diagram of an example of an image forming apparatus  1  according to a first embodiment of the present invention. 
   The image forming apparatus  1  shown in  FIG. 4  comprises an image reading device  50 , an image processor  108 , and a controller  109 . The image reading device  50  comprises plural CISs  100 ˜ 104  and light sources  200 ˜ 204 . The CISs and the light sources are arranged zigzag. Each of the CISs has N reading pixels, and each CIS  100 ˜ 104  has a signal amplifier  1 ˜ 5 , and an A/D converter  1 ˜ 5 . The image reading device  50  further comprises an image memory  105 , a reading controller  106  and an interface  107 . 
   The light sources  200 ˜ 204  emit light in response to a request from the reading controller  106  and others. The CISs  100 ˜ 104  are image sensors that convert light signals (pixels) to electric signals. The amplifiers  1 ˜ 5  amplify electric signals. The A/D converters  1 ˜ 5  convert analog values (signals) output from corresponding CIS  100 ˜ 104  and amplified by corresponding amplifier  1 ˜ 5  to digital values (signals). 
   The image memory  105  relates to image reading and processing, and stores image data. The reading controller  106  performs white reference adjustment processing, which is explained later. The interface circuit  107  connects the image reading device  50  to the image forming apparatus  1 , or connects the reading controller  106  of the image reading device  50  to an image processor  108  of the image forming apparatus  1 . 
   A controller  109  controls the image forming apparatus overall. The image processor  108  forms an image, based on the reading value of the reference white board adjusted by the reading controller  106  for each CIS. 
   The white reference adjustment processing is performed by the reading controller  106  each time whenever the image forming apparatus  1  is first started (powered-on) by the user in the morning, or resumed or woken up from sleeping mode. The white reference adjustment process is performed so that the reading controller  106  makes the CISs read a white board  22  shown in  FIG. 5 . In this embodiment, it is assumed that the CISs of the image reading device  50  are arranged zigzag as shown in  FIG. 1 , which does not limit the scope of the present invention. 
   A cross section of the image reading device  50  cut by A-A′ plane in  FIG. 1  is shown in  FIG. 5 . The cross-sectional view of the image reading device  50  shown in  FIG. 5  corresponds to a portion indicated by A in  FIG. 3 . 
   As shown in  FIG. 5 , the image reading device  50  includes conveying rollers  21 , a reference white board  22  and CIS  1 ˜ 5 . 
   The conveying rollers  21  convey an original paper. The reference white board  22  is a white board used for white reference adjustment processing. 
     FIG. 6  shows an example of signal levels of plural CISs, wherein their signal outputs are adjusted (amplification factor adjustment or white reference adjustment) by the reading controller  106 . 
   When the image forming apparatus  1  is powered on by a user, the reading controller  106  turns on only the light source  200  corresponding to the CIS  100 , and performs the white reference adjustment for the light from the light source  200 . This white reference adjustment processing is processing wherein the reading controller  106  adjusts an amplification factor of the amplifier  1  so as to change a peak of a value (or output value) of the white reference  22  read by CIS  100  to a predetermined output value (for example, an output value A as shown in  FIG. 6 ). The output value (or analog value) of the CIS after the white reference adjustment processing is converted to a digital value (for example, a digital value of 220 when 8-bit processing is carried out) by an A/b converter. 
   After the adjustment (white reference adjustment) of the amplification factor of the amplifier  1  corresponding to the CIS  100 , the reading controller  106  turns off the light source  200  corresponding to the CIS  100 . At that time, since the light sources  201 ˜ 204  corresponding to other CIS  101 - 104  are also off, A/D converted output values from the CIS  100 ˜ 104  are zero or close to zero (digital value equivalent to black). 
   Next, the reading controller  106  turns on only the light source  201  corresponding to the CIS  101 , and performs the white reference adjustment processing against the amplifier  2  corresponding to the CIS  101 . The reading controller  106  performs the same processing against the CIS  102 ˜ 104  (or the amplifiers  3 ˜ 5  corresponding the CIS  102 ˜ 104 ). Then the white reference adjustment is finished for all the CISs (or all the amplifiers). As a result, the peak value of each CIS output value is changed to the reference value A and therefore there becomes no variation in the white reference values. 
   Since white paper reference values have no variation, image forming disorder or variation can be suppressed in the image processor  108 . That is, by reducing the variation in the white paper reference values, the reading controller  106  can reduce the output unevenness over all pixels of the plural CISs to an extent that can be corrected by the image processor  108 . 
   In the above explained embodiment, the reading controller  106  performs white reference adjustment on the CIS  100  to begin with. However, it is possible to begin with another CIS for performing white reference adjustment processing. No specific order is required in this and other embodiments. 
     FIG. 7  is a flowchart showing a procedure for the white reference adjustment processing in the reading controller  106  and image forming processing in the image processor  108 . 
   When the image forming apparatus  1  is turned on, the image controller  106  starts its procedure with step S 10 , where the image controller sets 1 to a counter N. 
   The procedure goes from step S 10  to step S 11 , where the reading controller  106  turns on only the light corresponding to the Nth CIS. 
   The procedure goes from the step S 11  to a step S 12 , where the reading controller  106  performs the white reference adjustment processing on the Nth CIS. That is, the reading controller  106  makes the Nth CIS read the reference white board  22 , and adjusts the amplification factor of the amplifier corresponding to the Nth CIS so that the peak of the read values becomes a predetermined output value. 
   After the white reference adjustment processing is completed, the procedure goes from step S 12  to step S 13 , where the reading controller  106  turns off the light corresponding to the Nth CIS. 
   The procedure goes from step S 13  to step S 14 , where the reading controller  106  increases the counter N by one. 
   The procedure goes from step S 14  to step S 15 , where the reading controller  106  determines if the counter N is larger than Nmax (that is the number of the CISs included in the image reading device  50 ). If the reading controller  106  determines that the counter N is larger than Nmax (YES at the step S 15 ), the procedure goes to step S 16 . If the reading controller  106  determines that the counter N is equal to or smaller than Nmax (NO at step S 15 ), the procedure returns to step S 11 , and repeats the above mentioned steps. 
   At step S 16 , the image processor  108  forms an image based on read values (white reference values) of the reference white board  22 , which have been adjusted for each CIS by the reading controller  106 . 
   The above processing is performed and there becomes no variation in the white reference values and no variation or disorder in image formation. 
   Second Embodiment 
   Other examples of the image forming apparatus  1 , the white reference adjustment processing carried out by the reading controller  106  and image forming processing carried out by the image processor  108  are shown in a second embodiment. Mainly different points from the first embodiment are explained below. 
     FIG. 8  is a block diagram illustrating a structure of an image forming apparatus according to the second embodiment of the present invention. The image forming apparatus  1  in the second embodiment further includes a memory  110 . 
   The memory  110  stores adjustments values, etc., explained below, in response to a request from the reading controller  106 . 
   When the image forming apparatus  1  is powered on by a user, the reading controller  106  turns on all the lights. Then the reading controller  106  begins the white reference adjustments with the CIS  100  (or the amplifier  1  corresponding to the CIS  100 ). When the reading controller  106  performs the white reference adjustment on the CIS  100  (or the amplifier  1  corresponding to the CIS  100 ), it forcibly minimizes the white reference adjustment values of other amplifiers  2 ˜ 5  corresponding to other CISs  101 ˜ 104 . If the white reference adjustment is done in the range of 1 times˜10 times, the reading controller  106  first forcibly makes the white reference adjustment values of the amplifiers  2 ˜ 5  corresponding to the CIS 101 ˜ 104  “1 times” (that is 0 dB, the lowest sensitivity), and then performs the white reference adjustment on CIS  100  (or the amplifier  1  to CIS  100 ). 
   The reading controller  106 , as shown in the first embodiment, adjusts the amplification factor of the amplifier  1  so that the peak of the read values (or the output values) of the reference white board  22  read by the CIS  100  becomes a predetermined output (output reference A in  FIG. 6 ). After the white reference adjustments are completed, the reading controller  106  stores the amplification factor values (adjusted values) after the white reference adjustments into the memory  110 . 
   The reading controller  106  performs the white reference adjustments on all the CISs (or the amplifiers corresponding to the CISs) in a similar manner. After the completion of the white reference adjustments of all the CISs (or the amplifiers), the reading controller  106  transfers the adjusted values stored in the memory  110  to the corresponding amplifiers  1 ˜ 5 , and turns off all the lights. The reading controller  106  may transfer the adjusted values to the corresponding amplifiers  1 ˜ 5  after turning off all the lights. 
   As a result of the above white reference adjustment processing according to the second embodiment, the peak values of the CISs are set at the reference value A, that is there becomes no variation in the white reference values, as shown in  FIG. 6  of the first embodiment. 
   Since there is no variation in white paper reference value, disorder or variation in image forming in the image processor  108  can be suppressed. That is, the reading controller  106  can remove variation in paper reference values, and reduce the output unevenness of all the pixels of plural CISs to a level that can be corrected by the image processor  108 , etc. 
     FIG. 9  is a flow chart showing another example of procedure for the white reference adjustment processing in the reading controller  106  and image forming processing in the image processor  108 . 
   When the image forming apparatus  1  is turned on, the image controller  106  starts its procedure with step S 20 , where the image controller  106  sets 1 to a counter N. 
   The procedure goes from step S 20  to step S 21 , where the reading controller  106  turns on all the lights. 
   The procedure goes from step S 21  to step S 22 , where the reading controller  106  forcibly minimizes the white reference adjustments of the amplifiers (e.g. amplifiers  2 ˜ 5 ) corresponding to any CISs (e.g. CIS 101 ˜CIS 104 ) other than the Nth CIS (e.g. CIS 100 ). 
   The procedure goes from step S 22  to step S 23 , where the reading controller  106  performs the white reference adjustment processing on the Nth CIS. That is, the reading controller  106  makes the Nth CIS read the reference white board  22 , and adjusts the amplification factor of the amplifier corresponding to the Nth CIS so that the peak of the read values becomes a predetermined output value. 
   The procedure goes from step S 23  to step S 24 , where the reading controller  106  stores (registers) the adjusted amplification factor (the adjusted value) into the memory  110 . 
   The procedure goes from step  24  to step  25 , where the reading controller  106  increases the counter N by one. 
   The procedure goes from step S 25  to step S 26 , where the reading controller  106  determines if the counter N is larger than Nmax (that is the number of the CISs included in the image reading device  50 ). If the reading controller  106  determines that the counter N is larger than Nmax (YES at the step S 26 ), the procedure goes to step S 16 . If the reading controller  106  determines that the counter N is equal to or smaller than Nmax (NO at step S 26 ), the procedure returns to step S 21 , and repeats the above mentioned steps. 
   At step  27 , the image processor  108  transfers the adjusted values stored in the memory  110  to the corresponding amplifiers (e.g. amplifiers  1 ˜ 5 ). 
   The procedure goes from step  27  to step S 28 , where the image processor  108  forms an image based on read values (white reference values) of the reference white board  22 , which has been adjusted for each CIS by the reading controller  106 . 
   The above processing is performed and there becomes no variation in the white reference values and no variation or disorder in image formation. 
   In the second embodiment, each of the CISs does not have to have a separate light. 
     FIG. 10  is a block diagram of an image forming apparatus according to another embodiment. The image forming apparatus  1  shown in  FIG. 10  comprises only one light  200 , whereby manufacturing cost can be reduced to lower the price of the image forming apparatus. 
   As explained above, according to the embodiments of the present invention, there becomes no variation in the white reference values of the CISs, and it is possible to adjust so that each CIS has a common white reference value. 
   The present invention is not limited to these embodiments, but various variations and modifications may be made without departing from the scope of the present invention. 
   The present application is based on Japanese Priority Applications No. 2003-410577 filed on Dec. 9, 2003, and No. 2004-324893 filed on Nov. 9, 2004 with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.