Abstract:
An image processing apparatus including an input device for inputting image data, a storage device for storing image data from the input device, and a controlling device. The controlling device controls the parallel operations of a) writing image data into the storage device, and 2) reading image data from the storage device. Therefore, fast output is possible. Moreover, in a book copying mode, when copying two facing-pages with a scanner, copies of the first of two facing-pages are printed while the second of the two facing pages is scanned. As a result, this apparatus and the corresponding method enable a document to be changed easily and prevent extended holding times by an operator when using book copy mode.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus such as a digital copier, which generates an image based on image data which is stored in an image memory. 
     2. Discussion of the Background 
     A digital copier which has a scanner, an image memory and a printer is known. In this digital copier, the scanner scans documents, generates image data from the scanned documents, and stores the image data in the image memory. The printer prints an image on a recording medium (e.g., paper) according to the image data from the scanner or the image memory. 
     In digital copiers, editing functions are known. Known editing functions include an image rotating function and a combining function which prints two or more images from original documents onto a single recording medium. In the editing function, the scanner reads original documents and the image data from the scanner is stored into the image memory after processing according to the editing function. Then, after storing the image data, the printer prints the edited image on the recording medium according to the edited image data which is stored in the image memory after editing. 
     However, in this known digital copier, when using the editing function, it takes more time to make copies than compared with copies made without using the editing function because, when using the editing function, the image data is stored into the image memory once after editing, and after storing the image, the stored image is read out and printing is carried out. 
     Also, a book copying mode is known. The book copying mode is a mode for making copies of a book. In the book copying mode, the book is used as an original document which is set on a document glass. The book is spread open so that both pages are on the document glass, and an image of each page is printed on a different recording medium or on different sides of one recording medium. Hereinafter, when two pages of a book are copied sequentially, the layout of the pages will be called two “facing-pages”. 
     When making one copy in the book copying mode, the scanner reads the image of a first page of two facing-pages and the printer prints the image of the first page according to the image data from the scanner. Next, the scanner reads the image of a second page of the two facing-pages and the printer prints the image of the second page according to the image data from the scanner on a different recording medium or on the opposite side of the recording medium on which was printed the first page of the two facing-pages. 
     In general, when making more than two copies of documents with this digital copier, the scanner reads a first original document, and the image data from the scanner is stored in the image memory. In parallel with this storing, the printer prints the image on the first recording medium according to the image data from scanner. After that, the printer prints second or subsequent copies according to the image data which is stored in the image memory. After making copies of a first original document, the operation of making copies of second or subsequent original documents is carried out as in case of the making copies of first document. 
     In the book copying mode, when making more than two copies of a book as original, the scanner reads the image of the first page of two-facing-pages and the image memory stores the image data from the scanner. In parallel with this storing step, the printer prints an image on the first recording medium according to the image data received from scanner. After that, the printer prints the image of the first page of the two facing-pages on a second or subsequent recording medium according to the image data which is stored in the image memory. After the first page of the two facing-pages has printed, the scanner reads the image of a second page of the two facing-pages, and the image data is stored. The image of the second page is printed in the same fashion that the first page of the two facing-pages was printed. 
     However, in this known digital copier, when making more than two copies of a book in the book copying mode, an operator must hold a book on the document glass while 1) reading the first page of two facing-pages, 2) printing a quantity specified by an operator, and 3) reading the second page of the two facing-pages. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an image forming apparatus which copies quickly. 
     It is a further object of the present invention to provide an image forming apparatus which makes changing documents easy and does not require that an operator hold a book open for an extended period of time in book copying mode. 
     The present invention provides an image processing apparatus having an input device for inputting image data, a storage device for storing the image data from the input device, an output device for outputting the image data from the input device or the storage device, and a controller for controlling the parallel operations of 1) writing image data into the storage device, and 2) reading image data from the storage device. 
     The present invention provides an image processing apparatus which has a book copying mode for copying two facing-pages, the apparatus includes a scanner for scanning two facing-pages and producing image data of the two facing-pages that were scanned, a storage device for storing the image data from the scanner, a mode selector for selecting the book copying mode, and a controller for controlling, when the book copying mode is selected by the mode selector, 1) scanning the first page of two facing-pages, and 2) scanning the second page of the two facing-pages, wherein the two scannings by the scanner are sequential. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
     FIG. 1 is a diagram illustrating the construction of a digital copier in one embodiment of the present invention; 
     FIG. 2 is a block diagram of a control unit of the digital copier in one embodiment of the present invention; 
     FIG. 3 is a diagram of an operating unit of the digital copier in one embodiment of the present invention; 
     FIG. 4 is a sample screen of a liquid crystal display (LCD) in the an operating unit of the digital copier in one embodiment of the present invention; 
     FIG. 5 is a block diagram of an image processing unit of the digital copier in one embodiment of the present invention; 
     FIG. 6 is a timing diagram of control signals of an image processing unit of the digital copier in one embodiment of the present invention; 
     FIG. 7 is a diagram of a memory controller and an image memory of the digital copier in one embodiment of the present invention; 
     FIG. 8 is a diagram showing an example of how multiple copies are created from one set of originals according to one embodiment of the present invention; 
     FIG. 9 is diagram showing the copying steps that create the multiple copies of FIG. 8; 
     FIG. 10 is a diagram showing a second example of copying according to one embodiment of the present invention; 
     FIG. 11 is diagram showing the copying steps that create the facing-pages copies of FIG. 10; 
     FIG. 12 is a diagram showing a third example of copying according to one embodiment of the present invention; 
     FIG. 13 is a diagram showing a fourth example of copying according to one embodiment of the present invention; 
     FIG. 14 is diagram showing the copying steps that create the multiple copies shown in the third example depicted in FIG. 12; 
     FIG. 15 is diagram showing the copying steps that create the multiple copies shown in the fourth example depicted in FIG. 13; 
     FIG. 16 is a flowchart showing the control process performed by the control unit in one embodiment of the present invention; and 
     FIG. 17 is a flowchart for displaying the status of the digital copies according to one embodiment of the resent invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, FIG. 1 is a drawing of a section of the digital copier according to a described embodiment of present invention. As would be evident to one of ordinary skill in the art in light of this disclosure, other embodiments are possible; however, for clarity, a single embodiment is described throughout. In an ADF (automatic document feeder)  1 , documents are set on a document tray  2  and fed to a predetermined position on a document glass  6  by a feed roller  3  and a feed belt  4 . After scanning by a scanner unit  50 , the document on the document glass  6  is ejected using the feed belt  4  and an ejection roller  5 . 
     The scanner unit  50  includes an illuminating lamp  51 , a first mirror  52 , a second mirror  55 , a third mirror  56 , a, lens  53  and CCD (charge-coupled device)  54 . The scanner unit  50  scans an image of the document on the document glass  6 . The document which is set on the document glass  6  is illuminated by the illuminating lamp  51 . Light reflected from the document is directed at the CCD  54  by the first mirror  52 , the second mirror  55 , the third mirror  56  and the lens  53 . The CCD  54  converts a light signal from the document to an electric signal and outputs the electric signal to an image processing unit. The illuminating lamp  51 , the first mirror  52 , the second mirror  55  and the third mirror  56  are moved, and the scanner unit  50  reads the entire image of the document. 
     A writing unit  57  includes a laser unit  58 , a lens unit  59  and a mirror  60 , and exposes a photoconductive element  15  according to the image data received at the image processing unit. The laser unit  58  includes a laser diode and a polygon mirror which rotates at high speed. A laser light emitted from the laser diode in a laser unit  58  is reflected by the polygon mirror in such a way as to scan, and the laser light is directed at the photoconductive element  15  by the lens unit  59  and the mirror  60 . By this exposing, an electrostatic image is formed on the photoconductive element  15 . In addition, the laser light is detected by a synchronous detector, and control signals are generated for illuminating the laser diode and inputting/outputting image data. 
     A printer unit is placed under the writing unit  57 . A recording medium (e.g., paper, transparency, envelope) carried by a first tray  8 , a second tray  9  or a third tray  10  is fed to the photoconductive element  15  by a first transport  11 , a second transport  12 , a third transport  13  and a vertical transport  14 . The first tray  8 , the second tray  9  and the third tray  10  each carry different size (A4, 8.5×11, envelope) recording media. 
     Further, the electrostatic image on the photoconductive element  15  is developed into a toner image by a developing unit  27 . The recording medium which is fed by the vertical transport  14  is fed by transferring belt  16  with the same speed as the photoconductive element  15 . The toner image on the photoconductive element  15  then is transferred to the recording medium. The recording medium is fed to a fixing unit  17 , and the toner image which was transferred to the recording medium is fixed on the recording medium by the fixing unit  17 . 
     During single-sided copying, after fixing, the recording paper is fed to a finishing unit  100  by an ejection unit  18  and fed to a stacking roller  102  or a stapler roller  105  by a multi-drop apparatus  101 . The multi-drop apparatus  101  is a movable apparatus. To feed the stacking roller  102 , the multi-drop apparatus  101  rotates down which directs the recording media up, and to feed the stapler roller  105 , the multi-drop apparatus  101  rotates up which directs the recording media down. The stacking tray  104  is an output tray which is able to move back-and-forth and sorts recording media by each original document or sorts each copy by using an image memory. 
     The recording media fed to the stapler roller  105  are ejected to a staple tray  108  by a stapler feed roller  107 . On the stapler tray  108 , the recording media are evened at the edges by a jogging unit  109  and stapled by a stapling unit  106 . The recording media which are stapled are stored in a stapled output tray  110 . 
     On the other hand, for double-sided copying, the recording medium with a formed image (i.e., that has been copied on one side) is guided to a double-sided tray  111  by the multi-drop apparatus  112  and stacked temporarily. Next, the recording medium which is stacked in the double-sided tray  111  is fed to the photoconductive element  15  again and, after image forming, is output to the finishing unit  100 . 
     FIG. 2 is a block diagram of control units of the digital copier according to this embodiment. A main control unit  20  controls other units including: an operating unit  30  which controls displaying information to an operator and inputting commands by the operator; an image processing unit  49  which controls the scanner  50  and controls access to an image memory; and an ADF  1 . Further, the main control unit  20  controls a main motor  25 , clutch (CL)  21 , CL  22 , CL  23  and CL  24 . These clutches control transferring power from the main motor  25  to each apparatus, for example, the photoconductive elements  15 , the developing unit  27 , each roller, etc. 
     FIG. 3 is a diagram of an operating unit of this embodiment. The operating unit  30  includes a LCD  31 , number keys  32 , a clear/stop key  33 , a print key  34 , a clear mode key  35  and a system setting mode key  36 . The LCD  31  includes a touch panel on the surface and displays function keys, a quantity selected, and messages of the condition of the apparatus. 
     FIG. 4 shows a sample screen of the LCD  31 . By touching a function key displayed on the LCD  31 , the function indicated on the function key is selected and the selected key is displayed in reverse video. To specify details of the selected function, for example, to select a value by which to reduce or enlarge when the operator selects reduction/enlargement, a detail setting screen is displayed after touching a function key. On the sample screen shown in FIG. 4, a message area  41  is displayed. In the message area  41 , a message is displayed, for example “READY” or “WAIT”. Also displayed are a quantity number display area  42 ; an auto image density key for selecting a function of auto image density; an auto paper select key  44  for selecting a function of auto paper selecting; and a full size (100%) key  45  for selecting normal size. Additionally displayed are a staple key  46  for selecting a stapling function; a stack key  47  for selecting a stacking function; a sort key  48  for selecting a sorting function; a stamp key  90  for selecting a function of stamping some characters, for example, date and/or page number; a combine key for selecting a combining function; a duplex/series copy key for selecting a duplex function; and a reduce/enlarge key  93  for selecting reduction or enlargement. 
     FIG. 5 is a block diagram of an embodiment the image processing unit  49 . The CCD  54  converts the reflected light from the document to image data, and the image data is converted from analog data to digital data by an A/D converter  61 . Next, after shading correction by a shading correcting unit  62 , the image data is sent to an image processor  63 . At the image processor, an MTF correction and a gamma correction are carried out. 
     A selector  64  selects output units, a superimposing unit  73  or a memory controller  65 . When the superimposing unit  73  is selected, the image data is sent to a reduction/enlargement unit  71  by way of the superimposing unit  73 . After reducing or enlarging at the reduction/enlargement unit  71 , the image data is sent to the writing unit  57  in printer  80 . 
     A central processing unit (CPU)  68 , and controls reading and writing image data using the memory controller  65 . Moreover, the CPU  68  controls the scanner  50  and the writing unit  57 . A ROM  69  is a read-only memory and stores data which includes a control program for the CPU  68 . A RAM  70  is a random access memory and stores data temporarily. 
     A stamp image generator  74  is connected to a CPU bus and generates character image data for printing page numbers and image data of a chosen stamp image. An example of a stamp image is an image displaying “CONFIDENTIAL” or “DRAFT”. The image data which is generated by the stamp image generator is sent to a superimposing unit  72 ,  73  and superimposed upon the image data from the image processor or the memory controller  65 . 
     FIG. 6 is a timing diagram of control signals of an embodiment of the image processing unit  49 . A /LSYNC signal (“/” indicates an active low signal) is a main scanning synchronization signal. A /FGATE signal is a frame gate signal and sets a valid range for sub-scanning. A /LGATE signal is a line gate signal and sets a valid range of main scanning. The /LSYNC, /FGATE and /LGATE are synchronized with VCLK and one pixel of image data is sent every pulse of VCLK. The image processing unit  49  has generators for /LSYNC, /FGATE and /LGATE for inputting and outputting each. 
     FIG. 7 is a diagram of the memory controller  65  and the image memory  66 . The memory controller  65  includes an input data selector  81 , an image overlaying unit  82 , a first compression and decompression unit  82 , an output data selector  84  and a second compression and decompression unit  85 . Each unit is controlled by the CPU  68 . 
     The image memory  66  includes a first memory unit  86  and a second memory unit  87 . The first memory unit  86  includes a memory (e.g., SRAM or DRAM) which can be accessed quickly and synchronized with data transfers, i.e., when writing image data and reading image data. The first memory unit  86  is divided into a number of banks according to a size of an image, and reading image data and writing image data is carried out in parallel. More specifically, the memory controller  65  and the image memory  66  are connected by two sets of address and data buses. The first set is for reading image data and the second set is for writing image data. Therefore, it is possible to write image data to bank 1  and read data from bank 2  in parallel. 
     The second memory unit  87  is used for image overlaying, sorting and ordering by storing image data from the scanner unit  50 . The second memory, for example, a HDD (hard disk drive) or a magento-optic (MO) disk, includes a slower, lower cost memory but includes a large amount of storage. Reading and writing data is carried out away from the first memory unit  86 . Therefore, reading, writing and editing a large amount of image data is possible at a low cost. 
     To quickly write image data into the image memory  66 , the input data selector  81  receives data from the image data which is sent from the scanner unit  50  by way of the image processing unit  49 . The image data which is received by the input data selector  81  is transferred to the image overlaying unit  82 . In image overlaying unit  82 , the transferred image data is overlayed with the image data which is stored in the image memory  66  as necessary. After that, the image data is output to the first compression/decompression unit  83 . 
     In the first compression and decompression unit  83 , image data is compressed and afterwards, compressed image data is written into the first memory unit  86  in the image memory  66 . The data stored in the first memory unit  86  is, as necessary, compressed further in the second compression and decompression unit  85 , and compressed image data is written into the second memory unit  87 . 
     To read image data from the image memory  66 , when image data is stored in the first memory unit  86 , the image data which was read is sent to the first compression and decompression unit  83  and decompression is carried out. After decompression, decompressed image data or decompressed image data which is overlaid with an image data from the scanner unit  50  is selected by the output data selector and selected image data is output. 
     The image overlaying unit  82  overlays the image data from the image memory  66  and the image data from the scanner unit  50  with aligned and selects output units from 1) the first compression and decompression unit  83 , 2) the output data selector  84 , or 3) both. 
     When read image data is stored in the second memory unit  87 , after having read the image data, the read image data is sent to the second compression and decompression unit  85  and is decompressed. After decompression, decompressed image data is stored as the first image data  86  and the above process is carried out. 
     FIG. 8 is a diagram showing an example of creating multiple copies from one set of originals according to this embodiment, and FIG. 9 is a diagram showing the copying steps that create the multiple copies of FIG.  8 . In FIG. 8, the operator selects to generate two rotated copies of two original documents by selecting the rotate function from the operating unit  30 . 
     In FIG. 9, the scanner unit  50  is indicated with a box labeled S, the image memory  66  is indicated with a box labeled M, and the printer  80  is indicated with a box labeled P. The number above the box labeled S indicates an image number of the original documents which is being scanned by the scanner unit  50 . The legend at the upper left of the box labeled M indicates into which memory bank of image memory  66  an image is written, and the legend at the upper right of the box labeled M indicates from which memory bank of image memory  66  an image is read. 
     FIG. 9 starts with step S 101 , where, after two original documents are set on the ADF  1  and the print key  34  (shown in FIG. 3) is selected, a first original document is fed by ADF  1  and read by the scanner unit and then the read image data is written into bank B 1  of the image memory  66 . At step S 102 , the image data which was written into bank B 1  of the image memory  66  is read out, rotated, and sent to the printer, thereby generating a first rotated copy of the first image shown in FIG.  8 . Next, at step S 103 , a second original document is read by the scanner unit  50  and the image data read by the scanner unit  50  is written into bank B 2  of the image memory  66 . In parallel with writing to bank B 2 , the first original document image data which was written into bank B 1  of the image memory is read out, rotated and sent to the printer again, generating a second copy of the first image. At steps S 104  and S 105 , the second original document image data which was written into bank B 2  of the image memory  66  (in step S 103 ) is rotated and sent to the printer. 
     FIG. 10 is a diagram showing a second example of copying according to this embodiment, and FIG. 11 is a diagram showing the copying steps that create the facing-pages copies of FIG.  10 . In FIG. 10, the operator selects to generate two copies of four original documents by selecting the combine function from the operating unit  30 . Using the combine function, two original documents are combined and printed on one side of a single recording medium. 
     FIG. 11 shows step S 201  where, after four original documents are set on the ADF  1  and the print key  34  (shown in FIG. 3) is selected, a first original document is fed by ADF  1  and read by the scanner unit  50 , and then the read image data is written into bank B 1  of the image memory  66 . At step S 202 , a second original document is fed by ADF  1  and read by the scanner unit, and its corresponding image data also is written into bank B 1  of the image memory  66 . 
     At step S 203 , the image data of the first and second original documents which was written into bank B 1  of the image memory  66  (in steps S 201  and S 202 ) is read out and sent to the printer. The printer prints the image of the first and second original documents on one recording medium according to the data of bank B 1  to create the first facing-pages copy. 
     Next, at step S 204 , two parallel sub-steps are performed whereby 1) a third original document is read by the scanner unit  50  and the read image data is written into bank B 2  of the image memory, and 2) the image data of the first and second original documents previously written into bank B 1  of the image memory (in steps S 201  and S 202 ) is read out and sent to the printer. The sub-step 2) produces the second facing-pages copy. 
     At step S 205 , a fourth original document is fed by ADF  1  and read by the scanner unit  50 , and then the read image data is written into bank B 2  of the image memory  66 . At steps S 206  and S 207 , the image data of the third and forth original documents which was written into bank B 2  of the image memory (in steps S 204  and S 205 ) is read out and sent to the printer, thereby creating the second two facing-pages copies shown in FIG.  10 . 
     FIGS. 12 and 13 are diagrams showing the third and fourth examples of copying in the book copying mode according to this embodiment. In FIGS. 12 and 13, L indicates a left side page of two facing-pages of an original document and R indicates a right side page of the two facing-pages of the original document. FIG. 14 is a diagram showing the copying steps that create the individual copies shown in FIG. 12, and FIG. 15 is a diagram showing the copying steps that create the groups of individual copies shown in FIG.  13 . In FIG. 12, the operator selects three copies of the same two original documents which are facing-pages by selecting the book copying mode from the operating unit  30 , and in FIG. 13, the operator selects three copies of the same original documents using the operating unit  30 . 
     FIG. 14 begins with step S 301  where, after a first original two facing-pages document is set on the document glass  6  (FIG. 1) and the print key  34  (FIG. 3) is selected, the right side page of the two facing-pages on the document glass  6  is read by the scanner unit. The image data is printed on a first recording medium and written into bank B 1  of the image memory. The image data is written to bank B 1  in case of a paper jam or other error in the printer. When a printer error occurs, re-scanning is not necessary since reprinting is carried out by using the image data which was stored in the image memory. 
     Next, at step S 302 , the left side page of the first original two facing-pages document on the document glass  6  is read by the scanner unit  50 . The image data read by the scanner is written into bank B 2  of the image memory and printed on a second recording medium. 
     In step S 303 , the second original two facing-pages document is set on the document glass  6  (FIG. 1) and the print key  34  (FIG. 3) is selected, the right side page of the second original document is read by the scanner unit  50 . The image data read by the scanner is written into bank B 3  of the image memory and printed on a third recording medium. Next, at step S 304 , the left side page of the second original document is read by the scanner unit:  50 . The image data read by the scanner unit is written into bank B 4  of the image memory and printed on a fourth recording medium. In FIG. 14, it is not necessary to read out image data from the image memory and write data into the image memory in parallel. 
     FIG. 15 starts with step S 401 , where, after the first original facing-pages document is set on the document glass and the print key  34  is selected, the right side page of the first original document on the document glass  6  is read by the scanner unit  50 . The image data read by the scanner unit  50  is written into bank B 1  of the image memory and printed on a recording medium as a first copy. 
     At step S 402 , the left side of the first original document is read by the scanner unit  50  and the image data read by the scanner unit  50  is written into bank B 2  of the image memory, and the right side page of the first original document which was written into bank B 1  of the image memory (in step S 401 ) is read out and printed on a recording medium as a second copy. The system carries out in parallel the above sub-steps of 1) writing into bank B 2  of the image memory and 2) reading out from bank B 1  of the image memory. 
     At step S 403 , the image of the right side of the first original document is printed on a recording medium as a third copy using the image data which is stored in bank B 1 . At step S 404 , the image of the left side of the first original document is printed on a recording medium as first copy according to the image data which is stored in bank B 2 . At steps S 405  and S 406 , second and third copies of the image of the left side of the first original document are printed on respective recording media using the image data which was stored in bank B 2 . 
     During steps S 403  through S 406 , the scanning unit is idle and an operator has sufficient time to change from the first original document to a second original facing-pages document. 
     After changing from the first original document to the second original document, at step S 407 , the right side page of the second original document on the document glass  6  is read by the scanner unit  50 . The image data read by the scanner unit is written into bank B 3  of the image memory and a first copy is printed on a recording medium. 
     At step S 408 , the left side of the second original document is read by the scanner unit and the image data is written into bank B 4  of the image memory. Simultaneously, the right side page of the second original document (which was written into bank B 3  of the image memory in step S 407 ) is read out and printed on a recording paper as a second copy. The system carries out in parallel the sub-steps of 1) writing into bank B 4  of the image memory, and 2) reading out from bank B 3  of the image memory. 
     At step S 409 , a third copy of the right side of the second original document is printed on a recording medium using the image data which was stored in bank B 3 . At step S 410 , a first copy of the image of the left side of the second original document is printed on a recording paper using the image data which is stored in bank B 4 . At steps S 411  and S 412 , second and third copies of the image of the left side of the second original document are printed on respective recording media using the image data which is stored in bank B 4 . After S 407 , the scanning unit is idle and an operator is not required to hold the book on the document glass. 
     FIG. 16 is a flowchart showing the internal control process of the control unit of this embodiment. In the flowchart, the scanner  5  can transfer image data to both the memory M and the printer P simultaneously, or to either individually. In FIG. 16, the transfer labeled S→MP indicates that the image data which is read by scanning unit is sent to both the image memory and the printer, wherein it is written into the image memory and printed on a recording medium. One example of this process step is step S 401  shown in FIG.  15 . The transfer labeled S→M indicates that the image data which is read by scanning unit is written into the image memory. One example of this process step is step S 101  shown in FIG.  9 . The transfer labeled M→P indicates that the image data which is stored in the image memory is read out and printed on a recording medium. 
     As part of a main control loop, the system executes a first subroutine that includes the steps of FIG.  16 . After returning to the main control loop, a second subroutine which includes the steps of FIG. 17 is executed. After returning from the last step of FIG. 17, the main control loop restarts and re-executes the first subroutine. In the first subroutine, at step S 501 , it is determined whether or not the next transfer is to both the memory and the printer. When the next step is an S→MP transfer, control transitions to step S 502 . At step S 502 , when the scanner unit status is ready, control transitions to step S 503 . At step S 503 , when the memory writing status is ready, control transitions to step S 504 . At step S 504 , when the printer status is ready, control transitions to step S 505 . At step S 505 , the S→MP transfer is carried out and control transitions to step S 506 . At step S 506 , the scanner unit status, the memory writing status and the printer status are set to busy, and the first subroutine returns control to the main control loop. In addition, when any one of the scanner unit status, the memory writing status and the printer status is not ready, the first subroutine returns to the main control loop. 
     At step S 501 , when the next transfer step is not a S→MP process, control transitions to step S 507 . At step S 507 , when the next transfer step is a S→M process, control transitions to step S 508 . At step S 508 , when the scanner unit status is ready, control transitions to step S 509 . At step S 509 , when the memory writing status is ready, control transitions to step S 510 . At step S 510 , the S→M transfer is carried out and control transitions to step S 511 . At step S 511 , the scanner unit status and memory writing status are set busy, and the first subroutine returns. When at least one of the scanner unit status and the memory writing status is not ready, the first subroutine returns. 
     At step S 507 , when the next step is determined not to be a S→M transfer, control transitions to step S 512 . At step S 512 , when the next step is a M→P transfer, control transitions to step S 513 . At step S 513 , when memory reading status is ready, control transitions to step S 514 . At step S 514 , when the printer status is ready, control transitions to step S 515 . At step S 515 , when output image data exists, control transitions to step S 516 . At step S 516 , the M→P transfer is carried out and control transitions to step S 517 . At step S 517 , the memory reading status and the printer status are set busy, and the first subroutine returns. When at least one of the memory reading status and the printer status is not ready, or when the output image data does not exist, the first subroutine returns. 
     In this flowchart, after an M→P transfer starts, and when the next step is a S→M transfer, the S→M process is carried out immediately because at steps S 508  and S 509 , the scanner unit status and the memory writing status are ready. Therefore, M→P process and S→M process are carried out in parallel. 
     FIG. 17 is a flowchart showing how the status is updated in this embodiment. At step S 601 , when a scanner operation finishes, control transitions to step S 602 . At step S 602 , the scanner status is set ready and control transitions to step S 603 . At step S 603 , when a printer operation finishes control transitions to step S 604 . At step S 604 , the printer status is set ready and control transitions to step S 605 . At step S 605 , when a memory writing operation completes, control transitions to step S 606 . At step S 606 , the memory writing status is set ready and control transitions to step S 607 . At step S 607 , when a memory reading operation completes, control transitions to step S 608 . Lastly, at step S 608 , the memory reading status is set ready and the second subroutine returns. In an alternate embodiment of the main control loop and the first and second subroutines, the first and second control are interleaved into a single subroutine or made part of the main control loop such that if a device is not ready then the device is polled until the device is ready. For example, in a modified step S 514 , if the printer is not ready, then control would pass to a waiting step rather than to the step which causes the first subroutine to return. By waiting, the system avoids the rechecking steps of S 501 , S 507 , S 512 , and S 513 . 
     This invention may be conveniently implemented using a conventional general purpose digital computer or a microprocessor programmed according to the teachings of the present specification, as will be apparent to those skilled in the computer art. Appropriate software coding can readily be prepared by skilled programmers based on the teachings of the present disclosure, as will be apparent to those skilled in the software art. The invention may also be implemented by the preparation of an application specific integrated circuit or by interconnecting an appropriate network of conventional components, as will be readily apparent to those skilled in the art. 
     This application is based on Japanese patent application 8-72851 filed in the Japanese Patent Office on Mar. 27, 1996 and Japanese patent application 8-308442 filed in the Japanese Patent Office on Nov. 19, 1996 the entire contents of which are hereby incorporated by reference.