Abstract:
The present invention provides an image reading device and image reading method which reduce the total reading time and do not produce color drift when reading a plurality of documents comprising a mix of color and monochrome documents. The present invention provides for reading all documents by moving the documents during reading past a fixed position reader. If the documents are determined to be color documents, the documents are read by moving the reader during reading past fixed position documents. The present invention also provides an image forming apparatus, which reduces the total reading time when reading a mix of color and monochrome documents. The present invention additionally provides a computer program product for use in an image reading system to operate the system in the prescribed manner.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is related to application number JP(A) 11-114782, filed in Japan, the entire contents of which are hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to an image reading device capable of selecting a first reading method for reading a document by moving the document while the reading means is stationary, a second reading method for reading a document by moving the reading means while the document is stationary, an image reading method, a computer program product for storing an image reading sequence, and an image forming apparatus. 
     BACKGROUND OF THE INVENTION 
     Conventionally, the reading methods used in image reading devices include a sheet-through scanning method for reading a document while the document moves relative to a stationary reading unit, and a flatbed scanning method for reading a document while the reading unit moves relative to the stationary document. 
     The sheet-through scanning method is suitable for high-speed reading because the documents are sequentially fed at high-speed to a reading unit, but are unsuitable for reading color documents due to the difficulty of achieving high-precision document transport control due to differences in thickness and friction coefficient corresponding to the type of document. The flatbed scanning method is appropriate for reading color documents due to the ease of achieving high-precision control of the movement of the reading unit, but is inappropriate for high-speed reading because the reading unit must be moved and has considerable weight. 
     Conventional art utilizing the mutual advantages of the two methods include, for example, Japanese-Laid-Open Patent Application No. HEI 9-261417, which discloses a reading device which performs a preliminary scan of a plurality of documents via a sheet-through method, and after determining whether each document is a color document or a monochrome document, scans the color documents via the flatbed scan method, and scans the monochrome documents via the sheet-through method. Japanese Laid-Open Patent Application No. HEI 7-273952 discloses a reading device which determines whether or not a document is a color document before reading the document, and reduces the document transport speed for color documents so as to improve the reading accuracy of color documents by the sheet-through scan method. 
     In the art of the former disclosure, however, a disadvantage arises in that extra time is required to conduct a preliminary scan of all the documents to determine whether the document is a color document or a monochrome document. Moreover, in the art of the latter disclosure, it is difficult to read a document via the sheet-through method at greater accuracy than the flatbed scan method even when the document transport speed is reduced due to differences in friction coefficient and document type, thereby leading to the possibility of color shift in the case of color documents. 
     SUMMARY OF THE INVENTION 
     A first object of the present invention is to provide an image reading device and an image reading method for utilizing the respective advantages of the sheet-through and flatbed scan methods which reduce the entire reading time when reading a mixture of color and monochrome documents. A second object of the present invention is to provide an image reading device and an image reading method which do not produce color-shifts in color documents. A third object of the present invention is to provide a computer program product for storing image reading instructions. Another object of the present invention is to provide an image forming apparatus that utilizes this image reading device. 
     These objects of the present invention-are attained by the means described below. 
     In a first aspect of the present invention, an image reading device includes a reader for reading a document thereby obtaining image data. The position of the reader can be moved relative to the document being read. The image reading device further includes a controller that operates the reader in one of two modes. The first reading mode moves the document relative to the reader while the reader is stationary. The second mode moves the reader relative to the document while the document is stationary. After the document is read in the first mode, a decision unit determines whether the obtained image data correspond to color image data or monochrome image data. An output controller then outputs the image data if the image data is monochrome image data. If the image data is color image data, the document is read by the second mode, and the second mode image data is output. 
     In a second aspect of the present invention, an image reading method is disclosed. This method includes reading a document by moving a document relative to a stationary reader to obtain image data. The resultant image data is then determined to represent either monochrome image data or color image data. If the image data represent monochrome image data, the image data is outputted. However, if the image data represent color image data, the document is read a second time by moving the reader relative to a stationary document to obtain image data. The image data from the second reading is then output. 
     In a third aspect of the present invention, a computer program product is disclosed. This product includes instructions for recording image data. The instructions include first instructions to read a document that moves relative to a reader that is stationary in order to obtain image data. The second instructions are to determine whether the image data obtained by the first instruction represent a color image or a monochrome image. If the second instructions determine the image data represent monochrome data, the third instructions are executed which output the image data from the first instructions, and no more instructions are executed. If the second instructions determine the image data represent color image data, the fourth instructions are executed. The fourth instructions are to read the document that is stationary by a reader that moves relative to the document in order to obtain image data. The fifth instructions are to output the image data from the fourth instructions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the mechanical construction of the reading device of the present invention; 
     FIG. 2 is a block diagram showing the structure of the controller of the reading device; 
     FIG. 3 is a block diagram showing the structure of the image processor provided within the controller; 
     FIG. 4 is a main flow chart showing the control sequence of the reading device; 
     FIG. 5 is a subroutine flow chart showing the sequence of the reading control; 
     FIG. 6 is a flow chart continuing FIG. 5; 
     FIG. 7 shows an example of a document; and 
     FIG. 8 compares the reading time of the present invention and the reading time of the conventional art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments of the present invention are described hereinafter with reference to the accompanying drawings. 
     FIG. 1 shows the mechanical construction of a reading device of the present invention, and FIG. 2 is a block diagram showing the structure of the control unit of the reading device. 
     The reading device  100  mainly comprises an Automatic Document Feeder (ADF)  101  for feeding documents one sheet at a time, and a scanner  102  for reading the document image. 
     The ADF  101  is provided with a document tray  103  for holding a plurality of document sheets, pick-up roller  104  for extracting the document set in the document tray  103  sheet by sheet, feed roller  105  for transporting a fed sheet at constant speed to a transport belt  107 , transport belt  107  for transporting a document at constant speed, discharge roller  108  for ejecting a sheet transported by the transport belt  107 , and a discharge tray  109  for accommodating ejected documents. The ADF  101  is further provided with a sensor (not illustrated) for detecting the presence/absence of a document on the document tray  103 , and a standard position sensor  106  disposed anterior to the transport belt  107  for detecting a document being transported. 
     The scanner  102  is provided with a platen  110  disposed at a position opposite the transport belt  107 , and a reading unit  111  capable of reciprocating reading below the platen  110 . The reading unit  111  is provided with an illumination lamp  112  for illuminating a document surface, mirror-lens optical system  113 , and CCD photoreceptor unit  114  comprising a charge-coupled device line image sensor for reading the image of each color red (R), green (G), and blue (B), wherein the light reflected from a document surface illuminated by the illumination lamp  112  is directed to the CCD photoreceptor unit  114  by the mirror-lens optical system  113 . 
     The reading-device  100  is capable of consecutively reading via a sheet-through scan method (first reading method), and reading via a flatbed scan method (second reading method). 
     When the sheet-through scan method is used, the reading unit  111  is stopped at a home position  115 , and reading starts at the moment when the leading edge of a transported document is detected at the standard position by the standard position sensor  106 , and reading ends at the moment when the trailing edge of the document is detected by the standard position sensor  106 . 
     When the flatbed scan method is used, after a document is transported to a predetermined position on the platen  110  via the ADF  101 , the reading unit  111  is moved relative to the document and reads the document. After the reading unit  111  has moved to an end position  116 , it is returned to the home position  115 . 
     The control unit of the reading device, as shown in FIG. 2, comprises a CPU  201  for controlling each part of the reading device by executing specific programs, a ROM  202  for storing the programs required for control, a RAM  203  having a work area for the CPU  201  and a storage area for image data, a Small Computer Systems Interface (SCSI-I/F)  204  for transferring data to an external computer or the like, an A/D converter  206  for converting analog image data output from the CCD photoreceptor unit  114  to digital image data, an image processor  207  for processing of the image data and determining whether a document is a color document or a monochrome document, a drive controller  208  for controlling the various drive units, and an ADF signal input interface  210  for receiving signal input from the various sensors provided in the ADF  101 . The various parts are mutually connected via a bus line  209  to transfer signals. 
     As shown in FIG. 3, the image processor  207  comprises an input interface  301 , shading correction unit  302 , gradient converter  303 , color/monochrome switch  304 , color pixel discriminator unit  305 , color pixel counter  306 , color document determining unit  307 , and output interface  308 . 
     In the image processor  207 , the input interface  301  receives the image data of each color R, G, and B after digital conversion, the shading correction unit  302  corrects characteristic dispersion of each pixel of the CCD line sensor and illumination irregularities, and the gradient converter  303  performs gradient conversion when the read gradients differ from the output gradients (e.g., R, G, and B color image data input when the read gradient is 12-bits and the output gradient is 8-bits, are output as 8-bit data). After gradient conversion, the R, G, and B color image data are input to the color/monochrome switch  304 . 
     The color/monochrome switch  304  switches the image data output in accordance with instructions from the CPU  201 . When color image data output is specified, R, G, and B color image data are output, whereas only G image data are output when monochrome image data output is specified. The G image data are output as monochrome image data because the G image data are nearest the sensitivity characteristics of the human eye. 
     The image data output from the color/monochrome switch  304  are stored in RAM  203  via the output interface  308 . The image data stored in the RAM  203  are suitably read out and output from the SCSI-I/F  204  to an external computer or the like in accordance with instructions from the CPU  201 . 
     After gradient conversion, the R, G, and B image data are input to the color pixel discriminator unit  305 . The color pixel discriminator unit  305  discriminates each pixel as a color pixel or a monochrome pixel. Specifically, the color pixel discriminator unit  305  discriminates whether or not difference in the gradient value of each R, G, and B color comprising a single pixel is below a predetermined value. For example, when the R, G, and B image data are 8-bit data, the color pixel discriminator unit  305  performs the calculation (|Ri−Gi|&gt;32), or (|Gi−Bi|&gt;32), or (|Bi−Ri|&gt;32), and discriminates a pixel as a color pixel when the calculation result is true. In the above equations, Ri, Gi, and Bi are gradient values of the image data of each color R, G, and B. The previously mentioned predetermined value may be a variable value changeable by the CPU  201 . 
     The discrimination result of each pixel is input to the color pixel counter  306 . The color pixel counter  306  counts the number of color pixels based on the discrimination result. 
     The color pixel count value is input to the color document determination unit  307 , and the color document determination unit  307  compares the color pixel count value to a predetermined threshold value, then either determines the document is a color document when the count value meets or exceeds the threshold value, or determines the document is a monochrome document when the count value is less than the threshold value. The threshold value may be a variable value changeable by instruction from the CPU  201 . The determination result of either a color document or a monochrome document is input to the CPU  201  via the output interface  308 . 
     The drive controller  208  controls the motor M 1  for moving the reading unit  111 , the motor M 2  for the transport belt  107  within the ADF  101 , and the pick-up motor M 3  in accordance with instructions from the CPU  201 . 
     The operation of the reading device  100  is described below with reference to the flow charts of FIGS. 4,  5 , and  6 . 
     FIG. 4 is a main flow chart showing the control sequence for the operation of the reading device  100 . 
     First, the CPU  201  reads the programs stored within the ROM  202  to RAM  203 , and sets the various types of necessary initial settings simultaneously with the start of the processing (S 1 ). Then, the SCSI-I/F  204  is controlled to receive setting information from a connected computer or the like, or outputs image data to the computer if output data are present (S 2 ). Next, the state of the reading device is determined from the signals of the various sensors within the reading device  100  (S 3 ). The state of the reading device  100  includes, for example, whether or not a document has been set, or whether or not a document has reached the standard position determined from the ON/OFF signal of the standard position sensor  106 . Then, parameters such as reading resolution and reading area are set based on the setting information input from the computer (S 4 ). Thereafter, the document is moved by reading control, and read based on the set parameters (S 5 ). Reading control is described later. Next, a set time period is measured by a loop counter, and after the count ends, the routine returns to step S 2 , and the subsequent steps S 2 -S 6  are repeated. 
     FIGS. 5 and 6 are subroutine flow charts of the reading control. 
     In reading control, first, a determination is made as to whether or not the on-going scan flag is set, i.e., whether or not a document is currently being read (S 501 ). If a document is not currently being read (S 501 : NO), then a determination is made as to whether or not a document is placed on the document tray  103  (S 502 ). If a document is placed in the document tray (S 502 : YES), the on-going scan flag is set to indicate a document is currently being read (S 503 ). If a document is not set in the document tray (S 502 : NO), the subroutine returns to the main routine. 
     On the other hand, if a document is currently being read (S 501 : YES), a determination is made as to whether or not the on-going flatbed scan flag is set (S 504 ). If the on-going flatbed scan flag is not set (S 504 : NO), feeding of a document from the document tray  103  starts because there is no document present on the platen  110  (S 505 ). If the on-going flatbed scan flag is set (S 504 : YES), the routine advances to step S 518 , and a determination is made as to whether or not reading via the flatbed scan method has ended. 
     When the document transport begins, a determination is made as to whether or not the on-going sheet-through scan flag is set (S 506 ). If the on-going sheet-through scan flag is set (S 506 : YES), the routine advances to step S 510 , and a determination is made as to whether or not reading via the sheet-through scan method has ended. 
     If the on-going sheet-through scan flag is not set (S 506 : NO), a determination is made as to whether or not the leading edge of the document has been transported to the standard position sensor  106  in accordance with whether or not an ON-edge signal, (i.e., a signal changing the sensor from OFF to ON) is detected from the standard position sensor  106  (S 507 ). If the leading edge of the document has been transported to the standard position sensor  106  (S 507 : YES), the on-going sheet-through scan flag is set (S 508 ), and reading via the sheet-through scan method starts together with monochrome image instructions (S 509 ). On the other hand, if the leading edge of the document has not reached the standard position (S 507 : NO), the subroutine returns to the main routine. 
     The color/monochrome switch output is switched to monochrome via the monochrome image instruction, and the read image data are stored in RAM  203  as monochrome image data. A determination is then made as to whether or not the document read by the sheet-through scan method is a color document via the color document determination unit  307 . 
     Then a determination is made as to whether or not the reading of the document has ended based on the detection of an OFF-edge signal (i.e., a signal changing the sensor from ON to OFF) from the standard position sensor  106  (S 510 ), and if reading has ended (S 510 : YES), the on-going sheet-through-scan flag is reset (S 511 ). On the other hand, if document reading has not ended (S 510 : NO), the subroutine returns to the main routine. 
     When reading of the entire surface of a single document sheet via the sheet-through scan method ends, and after a predetermined time has elapsed from the detection of the OFF-edge signal from the standard position sensor  106 , the document transport is stopped (S 512 ), and the document is set stationary at a predetermined position on the platen  110 . 
     Then a determination is made as to whether or not the read document is a color document from the determination result of the color document determination unit  307  (S 513 ). If the read document is not a color document (S 513 : NO), instructions for outputting the monochrome image data stored in RAM  203  are set (S 514 ), and the document is discharged (S 521 ). Thereafter, the on-going scan flag is reset (S 522 ). 
     The monochrome image data set for output are output from the SCSI-I/F  204  by the process of the previously mentioned step S 2  after the subroutine returns to the main routine. 
     On the other hand, when a color document is determined in step S 513  (S 513 : YES), the monochrome image data stored in the RAM  203  are annulled (S 515 ), and the on-going flatbed scan flag is set (S 516 ). Then, the reading is started via the flatbed scan method together with the color image instruction (S 517 ). 
     The output of the color/monochrome switch  304  is switched to color via the color image instruction, and the read image data are stored in RAM  203  as color image data. 
     Next, a determination is made as to whether or not reading via the flatbed scan method has ended (S 518 ). If reading has not ended (S 518 : NO), the subroutine returns to the main routine. 
     If reading has ended S 518 : YES), the ongoing flatbed scan flag is reset (S 519 ), the color image data output instruction is set (S 520 ), and the document is discharged (S 521 ). Thereafter, the on-going scan flag is reset (S 522 ). 
     The color image data set for output are output from the SCSI-I/F  204  by the process of previously mentioned routine returns to the main routine. 
     The reading operation of the reading device  100  is described below by way of examples. 
     The document to be read comprises 10 sheets, including a mix of 8 sheets of monochrome documents and 2 sheets of color documents, as shown in FIG.  7 . 
     FIG. 8 shows the time required when consecutively reading the 10 sheets shown in FIG. 7 by the reading device  100 , and shows the time required by the conventional art for reading after determining the color documents and monochrome documents via a preliminary scan. As can be understood from FIG. 8, reading by the reading device  100  of the present invention requires less total reading time compared to the conventional art by omitting the preliminary scan. 
     In the reading device  100 , the reading speed is stable and color shift does not occur because color documents are read by the flatbed scan method. 
     In the previously described control sequence, color image data are temporarily stored in RAM  203  so as to be output therefrom when a color document is read by the flatbed scan method, and may be output directly without being stored in RAM  203  after various image correction such as shading correction and gradient conversion. In this instance, the image data storage area in the RAM  203  may use a capacity for storing one document sheet of monochrome image data. 
     Although the present invention has been described by way of an embodiment applying the invention to a simple reading device, the invention is not limited to this arrangement. 
     Another embodiment pertains to control from a computer when the reading device is connected, for example, to a personal computer or the like. When the reading device is controlled from a personal computer, the documents may be fed and read consecutively by the sheet-through scan method and flatbed scan method in the same way as the previously described reading device  100 . Then, all the image data read by the sheet-through scan method may be output without storing in the reading device. The image data output from the reading device are all R, G, and B image data. In this case, the reading device need not have a memory for storing the image data. On the other hand, the personal computer can determine whether a document is a color document or monochrome document from the R, G, and B image data obtained by reading via the sheet-through scan method, and store only the G image data among the R, G, and B image data as monochrome image data. The personal computer saves the stored monochrome image data when the determination result is a monochrome document, or annuls the stored monochrome image data when the determination result is a color document, and instructs the reading device to read the document using the flatbed scan method. Then, the reading device reads the document using the flatbed scan method based on the aforesaid instruction, and outputs the R, G, and B color data again to the personal computer. Accordingly, when a plurality of documents comprising a mixture of color documents and monochrome documents are consecutively read, the total reading time is reduced in the same way as when reading a document by a simple reading device. When the reading device is controlled by a computer and reads a document, the present invention can be realized by storing programs generated based on the aforesaid control sequence on a computer-readable storage medium. 
     Another embodiment of the image reading device applies the present invention to, for example, a color digital copier provided with an ADF  101 . In this case, a reading device identical to the previously described embodiment may be provided as the reading unit in a copier. Furthermore, the reading device  100  of the previously described embodiment may be directly connected to a printer so as to print the image data output from the reading device  100  and used as an image forming apparatus. 
     Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless such changes and modifications otherwise depart from the scope of the present invention, they should be construed as being included herein.