Abstract:
The present invention can reflect precisely a user&#39;s demand by outputting a warning so as to change setting of a compression method and a compression rate when sufficient image quality cannot be obtained with a currently set compression rate in color copying.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to an image forming apparatus such as a full color copying machine or a color printer. 
   A so-called 4-series-tandem type full color copying machine has been conventionally known as an image forming apparatus which outputs a color image. In a four-tandem full color copying machine, four image forming units which respectively form yellow (Y), magenta (M), cyan (C) and black (BK) toner images on the basis of a color-separated image signal are disposed along a conveying belt. 
   Each color image forming unit includes a photo-sensitive drum which rotatably contacts a conveying belt, a charging device which charges a drum surface to a predetermined potential, an exposure device which exposes the drum surface with light to form an electrostatic latent image, a development device which supplies toner to the electrostatic latent image on the drum surface to develop the electrostatic latent image, and a transfer device which transfers the developed toner image to a recording sheet which is being adsorbed and conveyed on the conveying belt. In this way, the recording sheet adsorbed on the conveying belt is conveyed through four image forming units (process units). Color toner images are transferred to the recording sheet in a superposed manner, and the recording sheet is fed to a fixing device. At the fixing device, the color toner images are fixed onto the recording sheet so as to form a color image. 
   The above-described four-tandem color copying machine is configured by a scanner section, an image processing section, an image compression section, an image register section (HDD), an image expansion section and a printer section. 
   Recently, in accordance with an increase in the capacity of the image register section (HDD), at the time of performing color copy, a scanned image is compressed and then stored in an HDD or the like. The compressed image is read out and re-formed. Then, the re-formed image is printed. 
   If the compression is performed with a low compression rate (high image quality), the amount of compressable image data is increased. As the result, the copy speed becomes low. If the compression is performed with a high compression rate, the image quality is deteriorated, but the copy speed is increased. 
   When a user designates the compression rate (in operation, the user designates “high image quality”, “normal” or the like) and then scanning is performed, a sufficient image quality may be maintained by the compression rate or may not be maintained by the compression rate. In order to solve the problem, a pre-scanning is performed so as to automatically set an optimized compression rate. However, there may be a case in which a user does not need a high image quality (low compression rate). Therefore, a user&#39;s demand cannot be reflected precisely. 
   BRIEF SUMMARY OF THE INVENTION 
   An object of the present invention to reflect precisely a user&#39;s demand by outputting a warning so as to change setting of a compression rate when sufficient image quality cannot be obtained with the currently set compression rate in color copying. 
   In order to accomplish the object, the present invention provides an image forming apparatus which comprises: a scanner section which reads an original image to output image data of various colors; a setting section which sets a compression rate of the image data outputted from the scanner section; a compression section which compresses the image data outputted from the scanner section at the compression rate set by the setting section; a register section which registers the image data outputted from the compression section and the compression rate; an expansion section which expands the image data registered in the register section on the basis of the compression rate corresponding to the image data; an image forming section which performs image formation with respect to the image data expanded in the expansion section on an image-formed medium; reading means for reading in advance the original image by the scanner section; a determination section which determines whether or not a predetermined image quality can be obtained at the time of forming an image on the image-formed medium in the image forming section by a state of the original image read by the reading means and the compression rate set by the setting section; and an inform section which informs an operator that the predetermined image quality cannot be obtained when the determination section determines that the predetermined image quality cannot be obtained. 
   Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention. 
       FIGS. 1 and 2  are cross-sectional views showing a schematic structure of an image forming apparatus; 
       FIG. 3  is a diagram showing a display example of a liquid crystal display portion; 
       FIG. 4  is a block diagram showing the schematic structure of the image forming apparatus; and 
       FIGS. 5A and 5B  show a flow chart for explaining a print processing. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. 
     FIGS. 1 and 2  are cross-sectional views showing a schematic structure of a color digital copying machine  1  which is an example of the image forming apparatus of the present invention. 
   As shown in  FIGS. 1 and 2 , the digital copying machine  1  comprises a main body  10 . A scanner section  11  serving as reading means and a color printer section  12  which functions as image forming means are provided within the main body  10 . 
   An automatic document feeder (hereinafter referred to as ADF)  17  which serves as a document cover and automatically feeds sheet-like documents one-by-one is provided at an upper portion of the main body  10  so as to be opened and closed. In place of the ADF  17 , a platen may be mounted to the upper portion of the main body  10  as the document cover. An operation panel (not shown) including various types of operation keys for instructing copy conditions or start of copying, various displays and the like is provided at an upper front portion of the main body  10 . 
   A detector  100  which detects opening or closing of the ADF  17  is provided at the main body  10  in the vicinity of a portion to which the ADF  17  is mounted. The detector  100  detects opening or closing of the platen when the platen is mounted instead of the ADF  17 . 
   A sheet feeding cassette  57  which can store a small number of sheets, and a large capacity sheet feeding cassette  55  which can store a large number of sheets are detechably provided at a right side portion of the main body  10 . The sheet feeding cassette  57  has a manual feeding tray  56  for manually supplying sheets. 
   Sheet feeding cassettes  52 ,  53  and  54  are detachably provided at a lower portion of the main body  10 . Each sheet feeding cassette stores sheets having the different size in longitudinal and lateral directions. Any of the cassette is selected as the occasion demands. A finisher  80  for receiving copied sheets is provided at a left side portion of the main body  10 . 
   An original document mount  13  formed of a transparent glass on which an object to be read, i.e., an original document D is mounted and the ADF  17  for automatically feeding the original document on the document table  13  are disposed on an upper surface of the main body  10 . The ADF  17  is provided so as to open or close relative to the document table  13 , and also functions as an original cover for fitting the original document D placed on the original document mount  13  and the original document mount  13  close together. 
   The ADF  17  comprises: an original document tray  8  on which the original document D is set; an empty sensor  9  for detecting the presence or absence of the original document, a pick-up roller  14  for picking up the original document D one by one from the original document tray  8 ; a sheet feeding roller  15  for conveying the picked up original document D; a pair of aligning rollers  16  for aligning a distal edge of the original document D; an aligning sensor (not shown) provided on an upstream side of the pair of aligning rollers  16  for detecting reach of the original document D; a size sensor (not shown) for detecting the size of the original document D; and a conveying belt  18  disposed so as to cover substantially the entire original document mount  13 . A plurality of original documents set on the original document tray  8  so as to face upward are successively picked up from a bottom page, i.e., a last page and aligned by the pair of aligning rollers  16 . Then, the documents are conveyed by the conveying belt  18  to a predetermined position on the original document mount  13 . 
   In the ADF  17 , an inversion roller  20 , a non-inversion sensor  21 , a flapper  22  and a discharge roller  23  are disposed at an end portion on the opposite side of the conveying belt  18  with respect to the pair of aligning rollers  16 . The original document D whose image information has been read by the scanner section  11  is fed from the original document mount  13  by the conveying belt  18 . Then, the original document D passes through the inversion roller  20 , the flapper  22  and the discharge roller  23  and is discharged onto an original document discharge portion  24  at the upper surface of the ADF  17 . 
   When a back surface of the original document D is read, the original document D conveyed by the conveying belt  18  is inverted with the inversion roller  20  by switching the flapper  22 . Then, the inverted original document D is fed by the conveying belt  18  to a predetermined position on the original document mount  13 . 
   The ADF  17  has a sheet feeding motor for driving the pick-up roller  14 , the sheet feeding roller  15  and the pair of aligning rollers  16  and a conveyance motor for driving the conveying belt  18 , the inversion roller  20  and the discharge roller  23 . 
   The scanner section  11  disposed within the main body  10  has a light source  25  such as a fluorescent lamp for illuminating the original document D disposed on the original document mount  13  and a first mirror  26  which deflects light reflected from the original document D in a predetermined direction. The light source  25  and the first mirror  26  are mounted to a first carriage  27  disposed below the original document mount  13 . A size sensor  28  which detects the size of the original document disposed on the original document mount  13  is mounted above the first carriage  27 . The first carriage  27  is disposed so as to be movable parallel to the original document mount  13 . The first carriage  27  is reciprocally moved below the original document mount  13  by the driving motor via an unillustrated toothed belt or the like. 
   A second carriage  29  which can move in parallel to the original document mount  13  is disposed below the original document mount  13 . A second mirror  30  and a third mirror  31  for successively deflecting the reflected light from the original document D, deflected by the first mirror  26  are mounted to the second carriage  29  so as to make a right angle. The second carriage  29  is moved in accordance with the first carriage  27  by the toothed belt which drives the first carriage  27  and is moved in parallel along the original document mount  13  at half the speed of the first carriage. 
   An imaging lens  32  which converges the reflected light from the third mirror  31  disposed on the second carriage  29  and a CCD sensor  34  which receives the reflected light converged by the imaging lens and photoelectrically converts the light are disposed below the original document mount  13 . The imaging lens  32  is disposed within a plane including an optical axis of the light deflected by the third mirror  31  so as to be movable via a driving mechanism. The imaging lens  32  images the reflected light at a desired magnification by being moved. The CCD sensor  34  photoelectrically converts the reflected light entered therein and outputs an electric signal corresponding to the read original document D. 
   The color printer section  12  comprises a laser exposure device  40  serving as exposure means. The laser exposure device  40  comprises a semiconductor laser  41  serving as a light source, a polygon mirror  36  serving as a scanning member for successively deflecting laser light emitted from the semiconductor laser  41 , a polygon motor  37  serving as a scanning motor for rotatably driving the polygon mirror  36  at a predetermined speed to be described later, and an optical system  42  for deflecting the laser light from the polygon mirror  36  and directing the light to photosensitive drums  44   a  to  44   d  to be described later. The laser exposure device  40  with the above-described structure is fixed to and supported by a supporting frame (not shown) of the main body  10 . 
   The semiconductor laser  41  is on-off controlled depending on the image information of the original document D read by the scanner section  11 . The laser light is directed via the polygon mirror  36  and the optical system  42  to the photosensitive drums  44   a  to  44   d . Then, circumferential surfaces of the photosensitive drums  44   a  to  44   d  are scanned with the light to form electrostatic latent images on the circumferential surfaces of the photosensitive drums  44   a  to  44   d.    
   The image forming section  12  has the rotatable photosensitive drums  44   a  to  44   d  serving as image holding members disposed at a substantial center of the main body  10 . A desired electrostatic latent image exposed by the laser light from the laser exposure device  40  is formed on the circumference surface of each of the photosensitive drums  44   a  to  44   d.    
   Successively disposed around each of the photosensitive drums  44   a  to  44   d  are a charger  45  for charging the circumferential surface of each of the photosensitive drums  44   a  to  44   d  to a predetermined electric charge, a development device  46  for supplying toner serving as a developer to the circumferential surface of each of the photosensitive drums  44   a  to  44   d  to develop the latent image at a desired image density, a peeling charger  47  for separating a transferred member (recording medium) fed from each of the sheet feeding cassettes  52 ,  53 ,  54 ,  55  and  57 , i.e., a copy sheet P from each of the photosensitive drums  44   a  to  44   d , a transfer charger  48  for transferring a toner image formed on each of the photosensitive drums  44   a  to  44   d  to the sheet P, a peeling pawl (not shown) for peeling the copy sheet P from the circumferential surface of each of the photosensitive drums  44   a  to  44   d , a cleaning device  50  for cleaning the toner remaining on the circumferential surface of each of the photosensitive drums  44   a  to  44   d  and a static electricity remover  51  for removing static electricity on the circumferential surface of each of the photosensitive drums  44   a  to  44   d.    
   An image forming unit  45   a  ( 45   b ,  45   c  or  45   d ) is formed of the photosensitive drum  44   a  ( 44   b ,  44   c  or  44   d ) and various devices disposed around the photosensitive drum  44   a  ( 44   b ,  44   c  or  44   d ). 
   In this embodiment of the present invention, a Y image, an M image, a C image and a BK image are superposed from the upstream side in a direction in which an arbitrary point on the conveying belt  67  is moved, i.e., a direction in which the copy sheet P is conveyed. Thus, the respective image forming units  45   a  to  45   d  are disposed in the order of Y, M, C and BK. 
   The sheet feeding cassettes  52 ,  53  and  54  which can be drawn from the main body  10  are disposed in a superposed manner at a lower portion within the main body  10 . Copy sheets with different sizes are loaded within the cassettes  52 ,  53  and  54 . The large capacity sheet feeding cassette  55  is provided at the side of the cassettes  52 ,  53  and  54 . About 3000 copy sheets of a frequently-used size, e.g., A4 size are stored in the large capacity sheet feeding cassette  55 . The sheet feeding cassette  57  which also serves as the manual feeding tray  56  is detachably mounted above the large capacity sheet feeding cassette  55 . 
   A conveyance path  58  which extends from the cassettes through transfer sections, each of which is disposed between each of the photosensitive drums  44   a  to  44   d  and the transfer charger  48 , is formed within the main body  10 . A fixing device  60  is disposed at an end of the conveyance path  58 . A discharge opening  61  is formed at a side wall of the main body  10  so as to oppose the fixing device  60 . The finisher  80  is attached to the discharge opening  61 . 
   A pick-up roller  63  for picking up sheets one by one from the cassettes is provided in the vicinity of each of the sheet feeding cassettes  52 ,  53 ,  54 ,  55  and  57 . A large number of pairs of sheet feeding rollers  64  for conveying a copy sheet P picked up by the pick-up roller  63  through the conveyance path  58  are provided at the conveyance path  58 . 
   A pair of registration rollers  65  is disposed on the upstream side of the photosensitive drums  44   a  to  44   d  in the conveyance path  58 . The pair of registration rollers  65  corrects a tilt of the picked up copy sheet P and conforms a distal end of a toner image on each of the photosensitive drums  44   a  to  44   d  to a distal end of the copy sheet P. Then, the pair of registration rollers  65  feeds the copy sheet P to the transfer section at the same speed as the speed at which the circumference surfaces of the photosensitive drums  44   a  to  44   d  move. An aligning sensor  66  for detecting reach of the copy sheet P is provided in front of the pair of registration rollers  65 , i.e., at the side of the sheet feeding roller  64 . 
   The copy sheet P picked up one by one from the cassettes by the pick-up roller  63  is fed to the pair of registration rollers  65  by a pair of sheet feeding rollers  64 . Then, the distal end of the copy sheet P is aligned by the pair of registration rollers  65 . Subsequently, the copy sheet P is fed to the transfer section by the conveying belt (transfer belt)  67 . 
   In the transfer section, developer images formed on the photosensitive drums  44   a  to  44   d , i.e., toner images are transferred to the copy sheet P by the transfer charger  48 . The copy sheet P with the toner images transferred thereto is peeled from the circumferential surface of each of the photosensitive drums  44   a  to  44   d  by the peeling charger  47  and the peeling pawl (not shown). Then, the copy sheet P is conveyed via the conveying belt  67  configuring a part of the conveyance path  58  to the fixing device  60 . The developer images are fused and fixed to the copy sheet P by the fixing device  60 . Thereafter, the copy sheet P is discharging via the discharge opening  61  to the discharge tray  81  of the finisher  80  by a pair of sheet feeding rollers  68  and a pair of discharge rollers  69 . 
   An automatic duplex device (ADD)  70  which inverts the copy sheet P which has passed through the fixing device  60  and feeds again the sheet to a pair of registration rollers  65  is provided below the conveyance path  58 . The automatic duplex device  70  includes a temporary storage portion  71  for temporarily storing copy sheets P, an inversion path  72  which branches off from the conveyance path  58  and inverts the copy sheet P passing through the fixing device  60  to guide to the temporary storage portion  71 , a pick-up roller  73  for picking up the copy sheets P stored in the temporary storage portion one by one, and a sheet feeding roller  75  for feeding the picked up sheet through the conveyance path  74  to the pair of registration rollers  65 . A portion where the inversion path  72  branches off from the conveyance path  58  is provided with a sorting gate  76  for selectively sorting the copy sheet P to either the discharge opening  61  or the inversion path  72 . 
   In a case of duplex copying, the copy sheet P which has passed through the fixing device  60  is guided by the sorting gate  76  to the inversion path  72 , inverted and temporarily stored in the temporary storage portion  71 . Then, the copy sheet P is fed by the pick-up roller  73  and a pair of sheet feeding rollers  75  to the pair of registration rollers  65  through the conveyance path  74 . The copy sheet P is aligned by the pair of registration rollers  65  and fed again to the transfer section. At the transfer section, toner images are transferred to a back surface of the copy sheet P. Thereafter, the copy sheet P is discharged via the conveyance path  58 , the fixing device  60  and the discharge roller  69  to the discharge tray  81  of the finisher  80 . 
   The copy sheet can be discharged by the automatic duplex device  70  with its printed surface facing downward. That is, firstly, an image is transferred to the surface of the sheet and fixed thereto. Then, the sheet is temporarily stored in the temporary storage portion  71 . The sheet is conveyed by pick-up roller  73  and the pair of sheet feeding rollers  75  and the pair of rollers  77  and passed through the conveyance path  74 . Thereafter, the sheet is aligned by the pair of registration rollers  65 . The sheet is passed through the conveyance path  58 , the fixing device  60  and the discharge roller  69 , and is discharged to the discharge tray  81  of the finisher  80 . 
   An operational panel (which will be described later)  91  for instructing various copy conditions including a copy magnification and the like and a start of copying (start key) is provided at an upper front portion of the main body  10 . 
   As shown in  FIG. 3 , the operational panel  91  is provided with a touch key-built liquid crystal display portion (LCD)  86  which performs operational guidance and various instructions. 
   As shown in  FIG. 3 , the liquid crystal display portion  86  is configured by an operation guidance display portion  86   a  on which an operational guide such as “READY” is displayed and a setting display portion  86   b  on which the contents of various settings are switched and displayed. As shown in  FIG. 3 , at the setting display portion  86   b , an initial screen is a screen for setting basic functions (BASIC) and a selected state in LCF 52  is displayed. A setting state in which a zoom magnification is 100%, a size of an original document is A4, “HIGH IMAGE QUALITY”, “NORMAL IMAGE QUALITY”, non-sort and non-staple are selected, a ratio of original document to copy sheet of 1:1 is displayed. Icons for instructing edit, program, setting changes and the like are displayed. 
   The setting display portion  86   b  includes setting screens EDIT, PROGRAM and SETTINGS. For example, with the setting screen PROGRAM or SETTINGS, setting of priority, canceling of job, display of job list, changing or adding setting of priority can be performed. 
   The above-described digital copying machine  1  may be used alone or may be used as a network printer. 
   In a case of using the digital copying machine  1  as a network printer, the digital copying machine  1  is configured to be connected via a local network (LAN) (not shown) to personal computers (PCs) (not shown) and a server (not shown). 
   An internal structure of a control circuit of the above-described digital copying machine  1  will be described with reference to  FIG. 4 . 
   The digital copying machine  1  is provided with a main control section  90  which controls the whole machine  1 . The main control section  90  is configured by a CPU (central processing unit) (not shown) for governing control of its operation, a ROM (read only memory) (not shown) in which a software for operating the digital copying machine  1  is stored and a RAM (random access memory) (S-RAM)  90   a  in which image data and operational data are temporarily stored. 
   The main control section  90  is connected via a bus  95  to the ADF  17 , the scanner section  11 , the color printer section  12 , the finisher  80 , the operational panel  91 , an image processing section  92 , a page memory  93 , an HDD  94 , an image determination section  97  and an image compression/expansion section  98 . The image processing section  92 , the page memory  93 , the HDD  94 , the image determination section  97  and the image compression/expansion section  98  are connected together via an image bus  96 . 
   The image processing section  92  processes original image data read by the scanner section  11  and image data from the page memory  93 , the image compression/expansion section  98  and the HDD  94 . Further, the image processing section  92  outputs the processed image data to the page memory  93 , the image compression/expansion section  98 , the printer section  12  or the HDD  94 . 
   The image processing section  92  has a color conversion section  92   a . The color conversion section  92   a  converts red, green and blue image data read by the scanner section  11  into yellow, magenta, cyan and black image data. 
   The image determination section  97  determines whether or not an original image is a highly detailed image by bitmap data of a sheet of original document (one of red, green and blue) expanded in the page memory  93  and the amount of the data. For example, a highly detailed image is a photographic image or a detailed design drawing. A non-detailed image is, e.g., an image formed of character strings. Whether or not the original is a highly detailed image may be determined by the total number of pixels having a predetermined density value or greater in each scanning line read by the scanner section  11 . 
   The image compression/expansion section  98  compresses each color image data from the page memory  93  with a compression rate and a compression method (an encoding method) set by the main control section  90 , and expands the image data from the HDD  94 . For example, data lengths before and after compression referred to as flanmeo are formed by a first compression for performing compression of data having a fixed length and a second compression for performing a reversible encoding. 
   The HDD  94  is an external storage device such as a hard disk for storing various data. 
   If the main control section  90  determines that a start key is pressed, the main control section  90  drive-controls the scanner section  11  so as to perform pre-scanning. 
   The main control section  90  compresses the image determined by the image determination section  97  with a compression rate and a compression method corresponding to an image quality set in advance. At that time, the main control section  90  determines whether or not printing can be performed with a sufficient image quality. 
   The main control section  90  has an input task and a print task, both of which are managed for each job. 
   Next, a description will be given of a print processing for color original document D in the above-described configuration with reference to a flowchart shown in  FIGS. 5A and 5B . 
   First, an operator selects “ORIGINAL IMAGE QUALITY” on a setting display portion  86   b  of the operational panel  91  and sets parameters including density and number of copies and the like (ST 1 ). Then, an operator presses the start key (ST 2 ). 
   The main control section  90  drive-controls the scanner section  11  and performs a pre-scanning for an original document D disposed on the original document mount  13  (ST 3 ). Thus, red image data read by the scanner section  11  is expanded in the page memory  93  (ST 4 ). The image determination section  97  determines whether or not the original image is a highly detailed image by bitmap data of a sheet of original (red) expanded in the page memory  93  and the amount of the data. The result of determination is outputted to the main control section  90  (ST 5 ). The main control section  90  determines whether or not printing can be performed with a sufficient image quality when compressing the image determined in the image determination section  97  with a compression rate and a compression method corresponding to the set image quality (ST 6 ). 
   As a result of the determination, when the main control section  90  determines that printing can be performed with a sufficient image quality, the image is printed in a normal manner (ST 18 ). If the determination by the main control section  90  is that the printing cannot be performed with a sufficient image quality, a processing is interrupted (ST 7 ). Then, a warning message such as “Would you like to copy in a high image quality mode to obtain a sufficient image quality?” is displayed on the operational guide display portion  86   a  of the operational path  91  (ST 8 ). 
   Then, when an operator selects the YES key (ST 9 ), the main control section  90  selects a low compression rate and an encoding method suitable for the low compression rate, and sets the compression rate and the encoding method in the image compression/expansion section  98  (ST 10 ). 
   The main control section  90  drive-controls the scanner section  11  to start scanning for reading a color original document (ST 1 ). Red, green and blue image data read by the scanner section  11  are color-converted into yellow, magenta, cyan and black image data by the color conversion section  92   a  of the image processing section  92 . Thereafter, the converted image data is respectively expanded in the page memory  93  (ST 12 ). Each color image data expanded in the page memory  93  is compressed by the image compression/expansion section  98  on the basis of the set compression rate and the encoding method, and the compressed data is registered in the HDD  94  (ST 13 ). At that time, the main control section  90  makes correspondence between an image number and the compression rate and the encoding method, and registers the compression rate and the encoding method in the RAM  90   a  as attribute information (ST 14 ). 
   The compressed image data registered in the HDD  94  is read out by control of the main control section  90 . The image data is expanded by the image compression/expansion section  98  on the basis of the compression rate and the encoding method. As a result, each of yellow, magenta, cyan and black image data is expanded in the page memory  93  (ST 15 ). Each piece of color image data expanded in the page memory  93  is outputted to the printer section  12  and printed at the printer section  12  (ST 16 ). 
   If an operator selects the NO key on the display in step  8  (ST 9 ), the main control section  90  determines that copying with a high compression rate continues (ST 17 ). Then, the process proceeds to step  11 . 
   If the main control section  90  determines that printing can be performed with sufficient image quality in the above step  6 , the process proceeds to step  11 . 
   The same processing is performed for the original documents D successively disposed on the original document mount  13  by the ADF  17 . When a plural number of copies are designated, print processing is performed for the second and subsequent copies by reading out the image data from the HDD  94 . 
   Then, the compression method is changed in accordance with the instruction and scanning is performed again, so that copying can be performed with a required image quality being maintained. 
   If copying is performed without changing the compression rate, the copy speed is fast but the image quality is decreased. 
   As described above, pre-scanning is performed at the time of copying and whether or not a sufficient image quality can be obtained with a compression rate set in advance by an operator is determined. Then, if necessary, a warning message is displayed in order for an operator to select continuing copying or copying with a decreased compression rate. Therefore, an image quality which satisfies the operator&#39;s needs can be provided. 
   Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.