Patent Publication Number: US-8970932-B2

Title: Decolorizing device, sheet decolorizing method, and recording medium for recording decolorizing process program

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of application Ser. No. 13/432,584 filed on Mar. 28, 2012, which is based upon and claims the benefit of priority from U.S. provisional application 61/472,670, filed on Apr. 7, 2011; the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to a technique of a decolorizing process for an image formed by a decolorable colorant. 
     BACKGROUND 
     There has been known a decolorizing device for decolorizing an image on a sheet by subjecting the sheet including the image formed thereon with a decolorable colorant to a decolorizing process such as heating so as to turn the decolorable colorant in a colored state into a decolorized state. Some of such decolorizing devices read an image on a sheet and save the image data before performing the decolorizing process. Moreover, in some of such decolorizing devices, a side having been subjected to the decolorizing process is read after the decolorizing process of the image, and a destination of sheet discharge is sorted into either a reusable sheet stacking section for stacking reusable sheets or a rejected sheet stacking section for stacking non-reusable sheets based on determination if there is an undecolorized portion or not. 
     In order to perform both of the image data saving before the decolorizing process and the determination regarding the existence of an undecolorized portion, image reading needs to be performed before and after the decolorizing process. In such a case, however, there is a problem of an increase in time to finish the series of decolorizing processes. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a sheet transfer path in a decolorizing device according to a first embodiment. 
         FIG. 2  is a block diagram showing the hardware configuration of the decolorizing device. 
         FIG. 3  is a flow chart for explaining a decolorizing process conducted by the decolorizing device. 
         FIG. 4  is a flow chart for explaining a process of determining if the decolorizing process is necessary or not. 
         FIG. 5  is a flow chart for explaining a determination process of a second embodiment. 
         FIG. 6  is a flow chart for explaining a determination process of a third embodiment. 
         FIG. 7  is a diagram illustrating a rectangular region on an upper left side of a sheet in image data. 
         FIG. 8  is a flow chart for explaining a decolorizing process of a sixth embodiment. 
         FIG. 9  is a diagram showing an upper region of a sheet in image data. 
         FIG. 10  is a diagram showing a lower region of the sheet in image data. 
     
    
    
     DETAILED DESCRIPTION 
     According to an embodiment, a decolorizing device typically includes a first reading section, a decolorizing section, a second reading section and a controller. The first reading section reads a first side of the sheet. The decolorizing section is configured to perform a decolorizing process on the sheet that has been read by the first reading section. The second reading section is configured to read the first side of the sheet that has been processed by the decolorizing section. The controller is configured to determine if the decolorizing process is necessary or not on the first side based on first image data of the first side read by the first reading section, to read the first side of the sheet having been subjected to the decolorizing process at the decolorizing section by the second reading section if it is determined that the decolorizing process is necessary, and to avoid reading of the first side of the sheet by the second reading section if it is determined that the decolorizing process is unnecessary. 
     Embodiments will be described below with reference to the drawings. 
     First Embodiment 
       FIG. 1  is a diagram showing a sheet transfer path in a decolorizing device  100 . 
     The decolorizing device  100  performs a decolorizing process on a sheet on which an image is formed with a decolorable colorant so as to turn the decolorable colorant in a colored state into a decolorized state, thereby decolorizing the image on the sheet. In the present embodiment, it is assumed that the image on the sheet to be decolorized by the decolorizing device  100  is formed by a powdered decolorable toner or a liquid decolorable ink capable of being decolorized when heated. Moreover, in the present embodiment, the sheet is heated as the decolorizing process and the image on the sheet is thereby decolorized. However, the decolorizing device may be alternatively configured to irradiate, as a decolorizing process, a sheet with light such as near-infrared light so as to decolorize an image on the sheet. In this case, the image on the sheet is formed by a decolorable toner or a decolorable ink capable of being decolorized by the irradiation of light such as near-infrared light. The decolorable toner or the decolorable ink capable of being decolorized by the light irradiation may be a toner or an ink which is decolorized by light in the vicinity of a wavelength of 820 nm, for example, but does not respond to light in the vicinity of a wavelength of 600 nm irradiated from a fluorescent lamp. 
     The decolorizing device  100  includes a sheet feeding cassette  11 , a reusable sheet cassette  12  (reusable sheet stacking section), a rejected sheet cassette  13  (rejected sheet stacking section), a transferring section  2 , a reading section  14  (a first reading section and a second reading section), a decolorizing section  15 , and sensors  16 . 
     The sheet feeding cassette  11  accommodates sheets on which images have been formed by decolorable colorants. A sheet size thereof may vary, for example, A4, A3, B5, or LTR. 
     A sheet made reusable as a result of the image docoloring is discharged to the reusable sheet cassette  12  from the transferring section  2 . 
     A non-reusable sheet due to the presence of an image in a colored state is discharged to the rejected sheet cassette  13  from the transferring section  2 . 
     Although the reusable sheet stacking section and the rejected sheet stacking section are in the form of cassettes in the present embodiment, they may not be cassettes as long as they can stack sheets thereon. For example, they may be trays or sections in a body of the decolorizing device provided so as to be accessible to the outside and capable of stacking sheets thereon. 
     The transferring section  2  transfers sheets. The transferring section  2  includes a transfer path  30  for guiding a sheet, a pickup roller  21  for picking up a sheet onto the transfer path  30  from the sheet feeding cassette  11 , flappers  22  for sorting a sheet into any one route of the branching transfer path  30 , and transferring rollers  23  for transferring a sheet on the transfer path  30 . 
     The transfer path  30  includes transfer paths  311 ,  312 ,  321 , and  322 . 
     The transfer path  312  is in the form of a ring. The transfer path  311  connects between the sheet feeding cassette  11  and the transfer path  312 . The transfer path  321  connects between the transfer path  312  and the reusable sheet cassette  12 . The transfer path  322  is connected to a midway of the transfer path  321  and connects between the transfer path  321  and the rejected sheet cassette  13 . 
     The transferring roller  23  is formed by a pair of a driving roller and a driven roller. The transferring roller  23  includes a sheet feeding roller  231  and a separation roller  232 . The sheet feeding roller  231  and the separation roller  232  are provided as a pair. When the pickup roller  21  sends a plurality of sheets to the transfer path  311  from the sheet feeding cassette  11 , the sheet feeding roller  231  and the separation roller  232  separate a sheet from the plurality of sheets and send it to the transfer path  311 . 
     The transferring section  2  including the above-described elements can be functionally divided into a transferring section  31  for decolorizing, which is for decolorizing an image, and a transferring section  32  for discharge, which is connected to the transferring section  31  for decolorizing and is for discharging sheets to the outside of the transferring section  2  (the cassettes  12  and  13 ). The transferring section  31  for decolorizing includes the transfer paths  311  and  312 , the flappers  22 , and the transferring rollers  23 . The transferring section  32  for discharge includes the transfer paths  321  and  322 , the flapper  22 , and the transferring rollers  23 . 
     The ring-shaped transfer path  312  is provided with a junction P 1  with the transfer path  311  for transferring sheets from the sheet feeding cassette  11  to the transfer path  312 . The ring-shaped transfer path  312  is also provided with a branching point P 2  from which the transfer path  321  for discharging sheets to the cassettes  12  and  13  is branched. In the transfer path  312 , a sheet transferring direction is counterclockwise in  FIG. 1 . 
     The reading section  14  is placed between the junction P 1  and the branching point P 2  on the transfer path  312  in the sheet transferring direction. The reading section  14  includes two reading units  141  and  142  such as a CIS (contact image sensor), a CCD (charge coupled device image sensor), or a CMOS (complementary metal oxide semiconductor) provided along the transfer path  312 . The reading section  14  reads an image on a first side of a sheet and an image on a second side, which is the reverse side of the first side, i.e., images on the both sides of the sheet at once. Image data obtained by the reading section  14  is stored in a memory  43  to be described later. According to the present embodiment, the image data before performing the decolorizing process is stored in the memory  43 , thereby being able to reproduce the image recorded on the sheet even after performing the decolorizing process. Thus, the convenience thereof is improved. 
     The decolorizing section  15  is placed between the branching point P 2  and the junction P 1  on the transfer path  312  in the sheet transferring direction. In the ring-shaped transfer path  312 , a distance between the reading section  14  and the decolorizing section  15  in the sheet transferring direction and a distance between the decolorizing section  15  and the reading section  14  in the sheet transferring direction are respectively longer than a length (297 mm) of a long side of an A4-size sheet (210 mm×297 mm). The decolorizing section  15  includes two decolorizing units  151  and  152  provided along the transfer path  312 . In the decolorizing section  15 , the decolorizing units abut against the both sides of the sheet and heat them so as to decolorize the images on the both sides of the sheet at once. In a case where an image on a sheet is formed by a decolorable colorant capable of being decolorized by light irradiation, the decolorizing section may be a section that irradiates the sheet with light so as to decolorize the image on the sheet. 
     Among sheets transferred to the transfer path  321  from the ring-shaped transfer path  312 , reusable sheets on which images have been decolorized are discharged to the reusable sheet cassette  12  from the transfer path  321 . The transfer path  321  is provided with a junction P 3  with the transfer path  322  whose end is connected to the rejected sheet cassette  13 . Non-reusable sheets with colored images thereon are transferred to the downstream side of the junction P 3  on the transfer path  321 , and then switch back-transferred to the transfer path  322  side and discharged to the rejected sheet cassette  13  from the transfer path  322 . 
     The sensors  16  are of a contact or non-contact type and provided at various positions along the transfer path  30  to detect sheets. The sensors  16  are provided before and after the reading section  14  in the transferring direction or before and after the decolorizing section  15  in the transferring direction on the transfer path  312 , for example. 
       FIG. 2  is a block diagram showing the hardware configuration of the decolorizing device  100 . 
     The decolorizing device  100  includes a controller  4 , an operation inputting section  17 , a display section  18 , and a communication section  19  in addition to the reading section  14 , the decolorizing section  15 , the sensor  16 , and the transferring section  2  described above. The elements  14  to  19 ,  2 , and  4  are connected with each other via a bus B. 
     The controller  4  includes a processor  41 , an ASIC  42  (application specific integrated circuit), the memory  43 , and an HDD  44  (hard disk drive), and controls the whole decolorizing device  100 . 
     The operation inputting section  17  includes the touch-panel type display section  18  and operation keys such as a numeric keypad, a stop key, and a start key, and accepts operation inputs from a user. 
     The display section  18  displays a setting information, an operation status, and a log information of the decolorizing device  100 , and notification to a user. 
     The communication section  19  is an interface to obtain connection with an external device. The communication section  19  communicates with an external device  200  on a network in a wireless or wired manner. 
     The decolorizing device  100  reads an image on a sheet before the decolorizing process is performed on the sheet under the control of the controller  4 , stores the read image data in the memory  43  once, and determines if the decolorizing process is necessary or not based on the image data read out from the memory  43 . The decolorizing device  100  has a plurality of decolorizing modes having different processing steps in the determination and after the determination. 
     The decolorizing device  100  has a first decolorizing mode for turning ON the decolorizing section to perform the decolorizing process on a sheet after the completion of the above-described determination and for performing a process of decolorizing an image formed on a white sheet whose base color is white. The decolorizing device  100  has a second decolorizing mode for performing a process of decolorizing an image on a color sheet whose base color is a chromatic color. The decolorizing device  100  has a third decolorizing mode for reading an image on a sheet in gray-scale. 
     The decolorizing device  100  has a fourth decolorizing mode for determining if the decolorizing process is necessary or not based on a color of an image on a sheet. The decolorizing device  100  has a fifth decolorizing mode. In the fifth decolorizing mode, the decolorizing device  100  specifies a range where an image exists based on the image data, and determines if an undecolorized portion exists or not only in the above-described specified range after the decolorizing process. 
     The decolorizing device  100  has a sixth decolorizing mode for transferring a sheet to the decolorizing section  15  in an ON state and performing the decolorizing process on the sheet even if the determination if the decolorizing process is necessary or not has not been completed. 
     A decolorizing process by the decolorizing device  100  will be described below with reference to a flow chart of  FIG. 3 . In the present embodiment, the decolorizing device  100  is set in the first decolorizing mode for performing the process of decolorizing an image on a white sheet. 
     The controller  4  takes out one sheet from the sheet feeding cassette  11  and transfers the sheet to the reading section  14 . The controller  4  reads images on both sides of the sheet at the reading section  14  (Act 1 ). At that time, the controller  4  performs the reading at the reading section  14  at a low resolution or thins out pixel components from the image data obtained by the reading section  14  to reduce the resolution thereof in order to shorten data processing time. Then, the image data (first image data) is stored in the memory  43 . 
     The controller  4  determines if an image exists or not on the first side of the sheet, i.e., determines if the decolorizing process is necessary or not on the first side of the sheet based on the image data of the first side, which has been stored in the memory  43  (Act 2 ). Such determination will be specifically described below with reference to a flow chart of  FIG. 4 . 
     First, as referenced in the following expression (1), the controller  4  extracts, as non-white pixels, pixels in each of which any one of brightness values R, G, and B thereof is less than a threshold thR, thG, or thB based on the image data of the first side (Act 21 ).
 
 R&lt;thR  or  G&lt;thG  or  B&lt;thB   (1)
 
     Next, the controller  4  extracts, from among the non-white pixels, pixels successively existing in a sub-scanning direction, which is the sheet transferring direction, by an amount equal to or greater than a threshold Nx as non-white pixels coupled in the sub-scanning direction. The controller  4  extracts, from among the non-white pixels coupled in the sub-scanning direction, pixels successively existing in a scanning direction perpendicular to the sub-scanning direction by an amount equal to or greater than a threshold Ny as non-white coupled pixels (Act 22 ). 
     The controller  4  determines that the first side contains no images, i.e., determines that the decolorizing process is unnecessary on the first side if the number of the non-white coupled pixels is lower than or equal to a threshold thN (Act 23 : NO, Act 2 : NO). The controller  4  determines that the first side contains an image, i.e., determines that the decolorizing process is necessary if the number of the non-white coupled pixels is greater than the threshold thN (Act 23 : YES, Act 2 : YES). 
     After it is determined if the decolorizing process is necessary or not on the first side, the controller  4  similarly determines if the decolorizing process is necessary or not on the second side (Act 3  or Act 4 ). The controller  4  makes the sheet waited between the reading section  14  and the decolorizing section  15  until the completion of the above-described determination. 
     If it is determined that the decolorizing process is necessary on any side (Act 3 : YES, Act 3 : NO, ACT 4 : YES), the controller  4  turns ON only the decolorizing unit  151  or  152  corresponding to the side determined to require the decolorizing process and transfers the sheet to the decolorizing section  15 . The controller  4  heats only the side determined to require the decolorizing process with the decolorizing unit  151  or  152  so as to perform the process of decolorizing the image on the side (Act 5  (Act 51  to Act 53 )). Note that the controller  4  may constantly turn ON both of the decolorizing units  151  and  152  and may control the decolorizing section  15  so as to be able to decolorize an image even if the image is on any side of the sheet. In this case, it is possible to perform the decolorizing process regardless of the result of the determination if the decolorizing process is necessary or not on the first side or the result of the determination if the decolorizing process is necessary or not on the second side. 
     The controller  4  transfers the sheet having been subjected to the decolorizing process to the reading section  14 , turns ON only the reading unit  141  or  142  corresponding to the side determined to require the decolorizing process, and reads only the image on the side determined to require the decolorizing process (Act 6 ). Then, the controller  4  controls the reading section  14  to perform the reading at a resolution higher than that before the decolorizing process. 
     Based on the image data of the side having been subjected to the decolorizing process, the controller  4  determines if there exists or not an image with a size equal to or greater than the threshold on the side using a method similar to that in Act 2 , i.e., determines if there is an undecolorized portion or not on the side having been subjected to the decolorizing process (Act 7 ). In particular, in a case where the decolorizing process is performed on the both sides of the sheet, the controller  4  determines if there is an undecolorized portion or not on each of the both sides of the sheet. In a case where the decolorizing process is performed only on one side of the sheet, the controller  4  determines if there is an undecolorized portion or not only on the one side. 
     If the controller  4  determines that there is an undecolorized portion at least on one of the sides subjected to the decolorizing process (Act 7 : YES), the sheet is discharged to the rejected sheet cassette  13  from the ring-shaped transfer path  312  through the transfer path  321  (Act 8 ). 
     If it is determined that no images exist on both sides of the sheet before performing the decolorizing process (Act 4 : NO), the controller  4  makes the sheet pass through the decolorizing section  15  and the reading section  14  in an OFF state (Act 9 ), and then discharges the sheet to the reusable sheet cassette  12  through the transfer paths  321  and  322  (Act 10 ). Also, if it is determined that there is no undecolorized portion on the side having been subjected to the decolorizing process (Act 7 : NO), the controller  4  discharges the sheet to the reusable sheet cassette  12  through the transfer paths  321  and  322  (Act 10 ). 
     In the present embodiment, when determining if there exists an undecolorized portion or not on the side having been subjected to the decolorizing process, only the image data regarding the side subjected to the decolorizing process is transferred to the memory  43 . Thus, when compared with a case where image data regarding the both sides of a sheet is always transferred to the memory  43 , the present embodiment makes it possible to shorten time required for the determination process and eventually time required for the decolorizing process. 
     In the present embodiment, when determining if there exists an undecolorized portion or not on the side having been subjected to the decolorizing process, only the image data regarding the side subjected to the decolorizing process is analyzed. Thus, when compared with a case where image data regarding the both sides of a sheet is always analyzed, the present embodiment makes it possible to shorten the analysis time and eventually time required for the decolorizing process. 
     Second Embodiment 
     In the present embodiment, the decolorizing device  100  is set in the second decolorizing mode for performing the process of decolorizing an image on a color sheet. The present embodiment differs from the first embodiment in Act 2  to Act 4  and Act 7  for determining if an image exists on a sheet or not. Processes in Act 2  to Act 4  and Act 7  of the present embodiment will be briefly described below with reference to a flow chart of  FIG. 5  and the above-described flow chart of  FIG. 3 . 
     The controller  4 , for example, reads 128 lines from an upstream side in the sub-scanning direction (from the head of the sheet) in the image data on the sheet which has been read before the decolorizing process, and calculates averages aveR, aveG, and aveB of the brightness values R, G, and B of pixels existing in this range (Act 201 ). 
     The controller  4  extracts, as non-uniform pixels, pixels in each of which any one of absolute values of differences between the brightness values R, G, and B thereof and the averages aveR, aveG, and aveB is greater than a threshold thR′, thG′, or thB′ as referenced in the following expression (2) (Act 202 ). Such extraction is performed for pixels on the whole page.
 
| R −ave R|&gt;thR′  or | G −ave G|&gt;thG′  or
 
| B −ave B|&gt;thB′   (2)
 
     The controller  4  extracts, from among the non-uniform pixels, pixels successively existing in the sub-scanning direction by an amount equal to or greater than the threshold Nx as non-uniform pixels coupled in the sub-scanning direction. The controller  4  extracts, from among the non-uniform pixels coupled in the sub-scanning direction, pixels successively existing in the scanning direction by an amount equal to or greater than the threshold Ny as non-uniform coupled pixels (Act 203 ). 
     If the number of the non-uniform coupled pixels is smaller than or equal to the threshold thN, the controller  4  determines that no images exist on the first side, i.e., determines that the decolorizing process is unnecessary on the first side (Act 204 : NO, Act 2 : NO). If the number of the non-uniform coupled pixels is greater than the threshold thN, the controller  4  determines that an image exists on the first side, i.e., determines that the decolorizing process is necessary (Act 204 : YES, Act 2 : YES). 
     Thereafter, the controller  4  similarly determines if an image exists or not on the second side (Act 3  and Act 4 ). If an image exists at least on one side, the decolorizing process is performed on the side (Act 5 ). Subsequently, the controller  4  reads only the side subjected to the decolorizing process (Act 6 ) and determines if an image exists or not on the side subjected to the decolorizing process using a method similar to the above-described method, i.e., determines if an undecolorized portion exists or not on the side subjected to the decolorizing process (Act 7 ). 
     Third Embodiment 
     In the present embodiment, the decolorizing device  100  is set in the third decolorizing mode in which an image on a sheet is read in gray-scale. The present embodiment differs from the first embodiment in Act 2  to Act 4  and Act 7  for determining if an image exists or not on a sheet. Processes in Act 2  to Act 4  and Act 7  of the present embodiment will be briefly described below with reference to a flow chart of  FIG. 6  and the above-described flow chart of  FIG. 3 . 
     The controller  4  determines if an image on the first side is a monochrome image or a color image containing a chromatic color based on the image data (Act 2001 ). In particular, the controller  4  first extracts, as color pixels, pixels in each of which any one of absolute values |R−G|, |G−B|, and |B−R| of differences between the brightness values R, G, and B thereof is greater than a threshold th as referenced in the following expression (3).
 
| R−G|&gt;th  or | G−B|&gt;th  or | B−R|&gt;th   (3)
 
     Then, if the number of the color pixels is greater than or equal to the threshold, the controller  4  determines that the image on the first side is a color image (Act 2001 : NO). In this case, the controller  4  determines if the base color of the sheet is white or a chromatic color using the known method (see Japanese Patent Application Laid-Open No. H04-90258) (Act 2002 ). If it is determined that the base color of the sheet is white (Act 2002 : YES), the controller  4  determines if an image exists or not on the first side using processes similar to those in Act 21  to Act 23  of the first embodiment. If it is determined that the base color of the sheet is a chromatic color (Act 2002 : NO), the controller  4  determines if an image exists or not on the first side using processes similar to those in Act 201  to Act 204  of the second embodiment. 
     If the number of the color pixels is less than the threshold, the controller  4  determines that the image on the first side is a monochrome image (Act 2001 : YES). In this case, the controller  4  determines if the base color of the sheet is white or a chromatic color using the known method (Act 2003 ). If it is determined that the base color of the sheet is white (Act 2003 : YES), the controller  4  extracts, as non-white pixels, pixels in each of which a brightness value K thereof is less than a threshold thK as referenced in the following expression (4) (Act 21 A). Such extraction is performed for pixels on the whole page. Regarding the brightness value K, K being zero means black, and K being 255 means white.
 
 K&lt;thK   (4)
 
     The brightness value K of each pixel may be obtained by the conversion from the brightness values R, G, and B of the pixel. Alternatively, the reading section  14  may include a line sensor for K with no color film in addition to three R, G, and B line sensors having R, G, and B films, respectively, and the reading section  14  may obtain the brightness value K of each pixel by the line sensor for K. The following processes, i.e., the processes of extracting an aggregate of non-white coupled pixels from the extracted non-white pixels and determining if an image exists or not on the sheet based on the number of the non-white coupled pixels, and the like, are similar to those in the first embodiment (Act 22 , Act 23 , and the like). 
     When it is determined that the base color of the sheet is a chromatic color (Act 2003 : NO), the controller  4 , for example, reads 128 lines from the head of the sheet and calculates an average aveK of the brightness values K of pixels existing in this range (Act 201 ) as in the second embodiment. Then, the controller  4  extracts, as non-uniform pixels, pixels in each of which the absolute value of a difference between the brightness value K thereof and the average aveK is greater than the threshold thK as referenced in the following expression (5). Such extraction is performed for pixels on the whole page.
 
| K −ave K|&gt;thK   (5)
 
     The following processes, i.e., the processes of extracting an aggregate of non-uniform coupled pixels from the extracted non-uniform pixels and determining if an image exists or not on the sheet based on the number of the non-uniform coupled pixels, and the like, are similar to those in Act 202  to Act 204  of the second embodiment. 
     The controller  4  performs the decolorizing process on the sheet determined to require the decolorizing process (Act 5 ), then reads only the side subjected to the decolorizing process (Act 6 ), and determines if an undecolorized portion exists or not on the side (Act 7 ). 
     At that time, the controller  4  performs the determination if an image exists or not on the side having been subjected to the decolorizing process using a method in accordance with the determination method for the side before being subjected to the decolorizing process. That is, in a case where the first side is determined to have a color image and the second side is determined to have a monochrome image before performing the decolorizing process, the controller  4  uses the brightness values R, G, and B for the determination if an undecolorized portion exists or not on the first side and uses the brightness value K for the determination if an undecolorized portion exists or not on the second side. 
     In the present embodiment, the brightness value K is used to determine if an undecolorized portion exists or not on the side determined to have a monochrome image before performing the decolorizing process. Thus, when compared with a case where the three brightness values R, G, and B are used for such determination, it is possible to shorten time required for the determination and eventually time required for the decolorizing process. 
     Fourth Embodiment 
     In the present embodiment, the decolorizing device  100  is set in the fourth decolorizing mode in which determination if the decolorizing process is necessary or not is made based on a color of an image on a sheet. An image formation using a decolorable colorant is often performed using a decolorable colorant of only one color such as cyan, for example. Thus, if it is determined before the decolorizing process that an image exists on a sheet and the color of the image is the predetermined specified one color such as cyan, for example, based on the image data, the controller  4  determines that the decolorizing process is necessary. When it is determined that no images exist on a sheet or the color of an image is not the specified one color, the controller  4  determines that the decolorizing process is unnecessary. The other processes are similar to those in the above-described first embodiment. 
     Even if a sheet including an image formed thereon by an indecolorable colorant is mixed into the sheet feeding cassette  11 , the present embodiment makes it possible to prevent the sheet from being subjected to the decolorizing process. Thus, time required for the decolorizing process can be shortened and an energy loss can be thus suppressed. 
     Fifth Embodiment 
     In the present embodiment, the decolorizing device  100  is set in the fifth decolorizing mode, specifies a range where an image exists based on the image data, and determines if an undecolorized portion exists or not only in the above-described specified range after the decolorizing process. The present embodiment also differs from the first embodiment in Act  2  to Act 4  and Act  7  for determining if an image exists or not on a sheet. The processes will be briefly described below with reference to the flow chart of  FIG. 3 . 
     In Act 2  before the decolorizing process, the controller  4  specifies a range where an image exists based on the image data of the first side of the sheet. As shown in  FIG. 7 , the controller  4  determines that an image exists in a rectangular region L 1  at the upper left side of the sheet, for example (Act 2 : YES). 
     The controller  4  similarly determines the position of an image on the second side (Act 3  and Act 4 ), and then performs the decolorizing process on the side determined to have an image thereon at Act 2  to Act 4  (Act 5 ). In the present embodiment, it is herein assumed that an image exists only on the first side and the controller  4  performs the decolorizing process only on the first side. The controller  4  reads the first side at a high resolution after the decolorizing process (Act 6 ). 
     The controller  4  analyzes only a rectangular region L 1  in the image data of the first side having been subjected to the decolorizing process corresponding to the rectangular region L 1  in the low-resolution image data before performing the decolorizing process, and determines if an image exists or not in the rectangular region L 1  (Act  7 ). 
     According to the present embodiment, the process of determining if an undecolorized portion exists or not is performed only on the region L 1  where the image existed before the decolorizing process. Thus, the determination processing time can be further shortened. 
     Sixth Embodiment 
     In the present embodiment, the decolorizing device  100  is set in the sixth decolorizing mode. The decolorizing device  100  transfers a sheet to the decolorizing section  15  in an ON state and performs the decolorizing process on the sheet even if the determination if the decolorizing process is necessary or not has not been completed yet. The decolorizing process in the sixth decolorizing mode will be described below with reference to a flow chart of  FIG. 8 . Parts of processes similar to those in the first embodiment will be briefly described below. 
     The controller  4  reads images on both sides of a sheet at a low resolution (Act 601 ). 
     The controller  4  determines if the decolorizing process is necessary or not on each of the both sides of the sheet using a process similar to that in the first embodiment (Act 602 ). 
     The controller  4  transfers the read sheet to the decolorizing section  15  without making it waited between the reading section  14  and the decolorizing section  15 . In a case where the above-described determination process has been completed before an elapse of a threshold amount of time since the reading of the image on the sheet at the reading section  14  (Act 603 : YES) and it is determined that the decolorizing process is unnecessary for both sides of the sheet (Act 604 : NO), the controller  4  transfers the sheet to the decolorizing section  15  while keeping the decolorizing section  15  in an OFF state (Act 605 ). Then, after making the sheet pass through the decolorizing section  15  and the reading section  14 , the controller  4  discharges the sheet to the reusable sheet cassette  12  through the transfer path  321  (Act 609 ). 
     In a case where the above-described determination process has been completed before the elapse of the threshold amount of time since the reading of the image on the sheet at the reading section  14  (Act 603 : YES) and it is determined that the decolorizing process is necessary for any side of the sheet (Act 604 : YES), the controller  4  turns ON the decolorizing unit  151  or  152  corresponding to the side determined to require the decolorizing process and transfers the sheet to the decolorizing section  15 . Then, the controller  4  performs the decolorizing process by the decolorizing section  15  on the side determined to require the decolorizing process (Act 606 ). 
     Ina case where the determination process on both sides of the sheet has not been completed before the elapse of the threshold amount of time since the reading of the image on the sheet at the reading section  14  (Act 603 : NO), the controller  4  turns ON the decolorizing unit  151  or  152  corresponding to the side for which the determination has not been completed yet and the decolorizing unit  151  or  152  corresponding to the side for which it has been determined that the decolorizing process is necessary. Then, the controller  4  performs the decolorizing process by the decolorizing section  15  on the side for which the determination if the decolorizing process is necessary or not has not been completed yet and the side already determined to require the decolorizing process (Act 606 ). 
     As shown in  FIG. 9 , it is herein assumed that the controller  4  has completed the determination process only on an upper half region L 2  in the image data of the first side obtained before the decolorizing process and has not completed the determination process on a lower half region L 3 . It is also assumed that the upper half of the first side has been determined to have no image. If the process of determining if the decolorizing process is necessary or not has not been completed yet when the threshold amount of time is elapsed, the determination process is stopped at that moment. 
     In a case where the above-described determination process has already been completed when the sheet is detected by the sensor  16  provided between the reading section  14  and the decolorizing section  15  and on the upstream side of the decolorizing section  15  in the transferring direction (Act 603 : YES) and it has been determined that the decolorizing process is unnecessary for both sides of the sheet (Act 604 : NO), the controller  4  may transfer the sheet to the decolorizing section  15  while keeping the decolorizing section  15  in an OFF state (Act 605 ). Alternatively, in a case where the above-described determination process has not been completed yet when the sheet is detected by the sensor  16  placed on the upstream side of the decolorizing section  15  in the transferring direction (Act 603 : NO), the decolorizing process may be performed on the side for which the determination has not been completed (Act 606 ). In this case, the process of determining if the decolorizing process is necessary or not is stopped when the sheet is detected by the sensor  16  placed on the upstream side of the decolorizing section  15  in the transferring direction. 
     After Act 606 , the controller  4  reads the image on the side having been subjected to the decolorizing process at a resolution higher than that used when the first side is read before the decolorizing process (Act 607 ). 
     The controller  4  determines if a decolorized portion exists or not based on the image data of the side having been subjected to the decolorizing process (Act 608 ). The controller  4  determines if an undecolorized portion exists or not on the side already determined to require the decolorizing process as with Act 7  (Act 2 ) in the first embodiment. Regarding the side for which the determination if the decolorizing process is necessary or not has not been completed yet, the controller  4  performs the process of determining if an undecolorized portion exists or not only on the region L 3  where the process of determining if the decolorizing process is necessary or not has not been completed (see  FIG. 10 ). Note that the region L 3  in the high resolution image data used for the determination process after the decolorizing process corresponds to the lower half region L 3  in the low resolution image data of the first side obtained at the determination process before the decolorizing process. 
     If it is determined that both sides thereof have no undecolorized portions (Act 608 : NO), the controller  4  discharges the sheet to the reusable sheet cassette  12  (Act 609 ). If it is determined that one of the sides thereof has an undecolorized portion (Act 608 : YES), the controller  4  discharges the sheet to the rejected sheet cassette  13  (Act 610 ). 
     In the present embodiment, a sheet is transferred to the decolorizing section  15  before the completion of the process of determining if the decolorizing process is necessary or not, whereby time required for the decolorizing process can further be shortened. 
     In the present embodiment, regarding the side for which the determination if the decolorizing process is necessary or not has not been completed yet, the process of determining if an undecolorized portion exists or not is performed only on the region L 3  where the process of determining if the decolorizing process is necessary or not has not been completed yet. Thus, it is possible to shorten time required for the decolorizing process sufficiently. 
     The resolutions of the image data used in the determination processes before and after the decolorizing process may be equal to each other. 
     The determination process performed based on the low resolution image data before the decolorizing process may be performed by the ASIC  42 , and the determination process performed based on the high resolution image data after the decolorizing process may be performed by the processor  41 . 
     The sheet transfer path used by the transferring section for decolorizing may not be in the form of a ring. Non-ring-shaped transferring section for decolorizing may include a first reading section, a decolorizing section, and a second reading section different from the first reading section in this order from the downstream side in the transferring direction. In this case, the transferring section positioned in a portion between the first reading section and a section which is a destination of sheet discharged from the transferring section (cassette or tray, or sheet stacking sections in the body of the decolorizing device) functions as the transferring section for discharge. 
     The series of determination processes or the control of the various sections of the decolorizing device may be performed by the external device  200 . 
     The recording medium may be in any form as long as it is capable of storing a program therein and being read by a computer. In particular, examples of the recording medium include an internal memory internally mounted in a computer such as a ROM or a RAM, a portable storage medium such as a CD-ROM or a flexible disk, a DVD disk, a magneto optical disk, or an IC card, a database for storing a computer program, and other computers and databases thereof. A function which can be obtained by installation or downloading may be the function realized in cooperation with an OS inside the device or the like. A part of the program or the entire program may be an execute module dynamically generated. 
     The order of the processes in each of the above-described embodiments may be different from that shown by way of example in each of the above-described embodiments. 
     As described above in detail, according to the technique described in this specification, it is possible to provide a technique capable of shortening time required for the decolorizing process. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of invention. Indeed, the novel apparatus, methods and system described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the apparatus, methods and system described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.