Abstract:
A printer server connectable to a plurality of printers includes a receiver for receiving print data from an external apparatus, a first discrimination unit for discriminating a representation by which the received print data is described, and a selection unit for selecting, from the plurality of printers, a printer to print an image corresponding to the received print data. A second discrimination unit of the printer server discriminates whether the selected printer is capable of processing print data in the discriminated representation. When the selected printer is not capable of processing print data in the discriminated representation, a controller of the printer sever converts the received print data into print data in another representation and transmits the print data in the other representation. The controller transmits print data in the discriminated representation when the selected printer is capable of processing print data in the discriminated representation. The apparatus also includes a status receiver for receiving, from the selected printer, status information indicating that transmitting print data has been printed normally. A status sending unit of the apparatus sends the status information to the external apparatus.

Description:
This application is a division of application Ser. No. 07/939,144, filed on Sep. 2, 1992. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a scanner printer server system constituted by connecting an integrated type scanner printer to a network. 
     2. Description of the Prior Art 
     Hitherto, a sole scanner or a printer has been used in such a manner that it has been directly connected to the host computer. On the other hand, an integrated type scanner printer has been usually used solely as a copying machine and the scanner or the printer of the above-described type has not been used as a scanner printer server while being connected to a network. 
     On the other hand, there has been used a structure in which a printer is commonly used while being connected to a printer server on a network. In the usual case, a printer server of the aforesaid type transfers data adaptable to the specifications of the printer from the host computer to the printer. 
     Recently, network systems have been widely used and a large scale network has been employed in which the LAN is arranged in the overall context of an intelligent building or the like for example. Furthermore, a nationwide network such as WAN (wide area network) in which the LAN is directly connected by public lines and an advanced information network such as ISDN have become available. 
     Therefore, it has been possible for a host computer on one floor in one building to be utilized from another floor of the building or from another building, or a host computer located in Osaka can be utilized from Tokyo. 
     Therefore, the printer server should become available for use in a very wide region as well as in a relatively narrow area, which has been so far achieved. 
     Furthermore, the scanner printer has been advanced in function and resolution, and color scanner printers have become available. Therefore, data can be read from various scanners so as to be transmitted to the printer. 
     The method of transferring an image has generally been set by a host computer directly connected to the scanner or the printer. 
     On the other hand, a system so arranged that the scanner and the printer are both connected to the network will enable a user to utilize a distant scanner and printer by using the host computer located on the network. 
     This is very effective because a plurality of users are then able to utilize the distant scanner and the printer from a plurality of host computers. 
     In order to perform communication between the host computer and the scanner printer server, each layer of the control/programming hierarchy must be aligned with its corresponding layer across the communication channel. The layers may be those as shown in FIG.  20 : 
     1) Page description language (PDL) such a PostScript or CaPSL 
     2) Image encoding method such as ADCT, MMR, MR, VQ (Vector Quantizing) 
     3) Format such as a dot sequential, line sequential, or plane sequential method (interleaving) 
     4) Color space such as RGB, Lab, or YIQ 
     5) Number of gradations expressed by 1, 2, . . . , 8 bits/Color 
     6) Size and position of the image (trimming) 
     7) Resolution expressed by 100 dpi, 200 dpi or 400 dpi, or the like 
     In a case of a scanner printer server to which a plurality of scanners and printers or an integrated scanner printer is connected, the process to be performed by the server before the transmission of data has varied due to the differences in the performance of their I/O devices. 
     In the usual case, priority is given to the fact that scanning or printing is performed in the form required by a user of the host computer. Therefore, the scanner printer side has a variety of conversion means to scan or print data in the form required by the user. 
     Hence, the parameters for the distant scanner or the printer for use at the time of the various conversions must be set from the host computer. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide a scanner printer server with which the labor required to perform various settings can be reduced. 
     Another object of the present invention is to provide a scanner printer server with which the labor required to perform various settings can be omitted. 
     Another object of the present invention is to provide a scanner printer server which can be adapted to data expressed by page description language or data which is not expressed by page description language. 
     In order to achieve the aforesaid objects, according to one aspect of the invention, there is provided a scanner printer server system composed of a host computer and a scanner printer server connected to a network, a scanner and a printer being connected to the scanner printer, the scanner printer server system being characterized in that the printer or the scanner printer server has at least one function selected from a page description language conversion and a decoding function, the printer has at least one function selected from a color space conversion, a resolution conversion, a gamma conversion, a masking conversion, a black generation, a base color removal and an N-value coding function, where data transmitted from the host computer is converted in accordance with an image parameter supplied from the host computer, and the converted data is printed. 
     These and further objects, features and advantages of the invention will be appear more fully from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a structural view which illustrates a system according to the present invention; 
     FIG. 2 is a structural view which illustrates a scanner printer server; 
     FIG. 3 is a structural view which illustrates a scanner; 
     FIG. 4 is a structural view which illustrates a printer; 
     FIG. 5 is a structural view which illustrates an image reading section  305 ; 
     FIG. 6 is a structural view which illustrates a printing section  405 ; 
     FIG. 7 illustrates the image scanning and printing operations; 
     FIG. 8 illustrates timing in detail; 
     FIG. 9 illustrates the operation of a dual port ram at the time of the scanning and the printing operations; 
     FIG. 10 illustrates the operation of the dual port ram at the time of the scanning operation; 
     FIG. 11 illustrates the operation of the dual port ram at the time of the scanning operation; 
     FIG. 12 illustrates the operation of the dual port ram at the time of the printing operation; 
     FIG. 13 illustrates the operation of the dual port ram at the time of the printing operation; 
     FIG. 14 illustrates the pre-scanning and scanning operations; 
     FIG. 15 illustrates the printing operation; 
     FIG. 16 illustrates a case where an error has taken place at the time of the printing operation; 
     FIG. 17 illustrates the operation to be performed when a plurality of sheets of one image are printed; 
     FIGS.  18 ( a-i ) illustrate packets; 
     FIGS.  19 ( a-h ) illustrate commands between the scanner printer server and the scanner printer; 
     FIG. 20 illustrates communication to be performed between the scanner, the printer and the scanner printer server; and 
     FIG. 21 illustrates the scanning operation and an operation of developing PDL data. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will now be described. 
     Referring to FIG. 1, reference numeral  101  represents a host computer,  102  represents a scanner printer server,  103   a  to  103   b  represent various scanners,  104   a  to  104   d  represent various printers, and  105  represents an ethernet. 
     Reference numeral  106  represents a client process,  107  represents a server process,  108  represents DATA (an image data signal),  109  represents a VSYNC (a vertical synchronizing signal),  110  represents a HSYNC (a horizontal synchronizing signal),  111  represents a CLOCK (a clock signal),  112  represents a S.COM (a scanner serial command signal), and  113  represents a P.COM (a printer serial command signal). 
     The DATA (the image data signal)  108 , the VSYNC (the vertical synchronizing signal)  109 , the HSYNC (the horizontal synchronizing signal)  110  and the CLOCK (the clock signal)  111  are collectively called a Video I/F (interface). 
     A variety of connections established between the interface and the scanner or the printer are illustrated in such a way that an SCSI interface is used to establish a connection with the scanner  103   b  and the printer  104   b , a Centronics I/F is used to connect the printer  104   c  and an RS232C interface is used to connect the printer  104   d.    
     In general, both the scanner and the printer are connected to the SCSI, and a printer is usually connected to the Centronics I/F or the RS232C. The scanners and the printers to be connected to the aforesaid I/Fs have variable functions therein. 
     Since the Video I/F is an interface for mainly transmitting/receiving raw image data, the scanners or the printers to be connected usually have neither the page description language developing function nor the compression/expansion function. 
     The scanners and the printers are collectively represented by reference numerals  103  and  104 , and the interface Video I/F is employed as an example. 
     The host computer  101  executes the client process  106  for controlling the various scanners  103   a  to  103   b  or the printers  104   a  to  104   d.    
     In the scanner printer server  102 , the server process  107  is executed under control performed by the client process  106  so as to control the scanner  103  (which represents the scanners  103   a  to  103   b ) and the printer  104  (which represents the printers  104   a  to  104   d ). 
     The client process  106  communicates with the server process  107  via the ethernet  105  so as to read an image transmitted from the scanner  103  and as well to cause the printer  104  to print the image. An independent copying operation between the scanner  103  and the printer  104  can be performed. 
     FIG. 2 is a structural view which illustrates the scanner printer server  102 . 
     Reference numeral  201  represents a CPU,  202  represents an ethernet controller,  203  represents a RAM,  204  represents a ROM,  205  and  206  represent dual port rams,  207  represents a serial interface,  208  represents a timing control circuit,  209  represent a main bus,  210  represents a data bus,  211  represents a disk interface,  212  represents a hard disk,  213  represents an encoding/decoding circuit and  214  represents an interpreter for developing the page description language. 
     When the scanner printer server  102  is started, the CPU  201  starts the program stored in the ROM  204  so as to execute the server process  107  while making the RAM  203  a temporal storage portion. At this time, communication with the client process  106  of the host computer  101  can be performed by establishing a connection with the ethernet  105  by means of the ethernet controller  202 . 
     The serial interface  207  communicates a command between the scanner printer server  102  and the scanner  103  and the printer  104  in a serial manner. 
     The dual port rams  205  and  206  are accessible from both of the main bus  209  and the data bus  210 . The aforesaid dual port rams  205  and  206  are controlled by the timing control circuit  208  so as to transfer data between the scanner  103  and the printer  104  by the dual buffer system. The transference at this time is performed by the synchronization system including the signals VSYNC (the vertical synchronizing signal)  109 , the HSYNC (horizontal synchronizing signal)  110  and the CLOCK (the clock signal)  111 . 
     The serial interface  207  communicates a command with the scanner  103  by means of the S.COM (the scanner serial command signal)  112  by serial transmission. Similarly, the serial interface  207  communicates a command with the printer  104  by means of the P.COM (the printer serial command signal)  113  by serial transmission. 
     As the aforesaid data to be transmitted, a prescan command, a scan command or the like is transmitted from the scanner printer server  102  to the scanner  103 . On the other hand, a copy command or status information denoting, for example, an operation abnormality is transmitted from the scanner  103 . Similarly, a print command or the like is transmitted from the scanner printer server  102  to the printer  104 . On the other hand, status information such as paper out or paper jam operation abnormality is transmitted from the printer  104 . 
     The disk interface  211  is an interface to establish a connection with the hard disk  212 . 
     The encoding/decoding circuit  213  encodes data read from the scanner  103 , and also decodes encoded image data transmitted from the ethernet  105 . The encoding operation is performed by an ADCT method for example. 
     The ADCT encoding method is an encoding method for color still images which is being subjected to a standardizing operation by JPEG (Joint Photographics Expert Group), which is the joined organization of CCITT SG VIII and ISO/TC97/SC2/WG8 to meet a formal counsel which will be made in 1991 (see Mar. 19, 1990 issue of Nikkei Electronics). 
     The interpreter  214  interprets PDL (Page Description Language) so as to develop the image by a bit map or a byte map in the dual port rams  205  and  206 . As a result, the printer  104  is caused to print the image. The PDL is exemplified by Post Script, or CaPSL (CAnon Printing System Language). 
     FIG. 3 is a structural view which illustrates the scanner  103 . 
     Reference numeral  301  represents a scanner serial interface,  302  represents a scanner CPU,  303  represents a scanner drive circuit,  304  represents a scanner timing control circuit,  305  represents an image reading section, and  306  represents an operation panel. 
     The operation to be performed in a case where an image is scanned will now be described with reference to FIG.  3 . 
     The scanner serial interface  301  receives the scan command from the scanner printer server  102  so as to transmit the scan command to the scanner CPU  302 . 
     Then, the scanner  302  sets the image size and the image scan start position in response to the scan command. 
     The scanner CPU  302  controls the scanner drive circuit  303  to cause the image reading portion  305  to read the image for each line as shown in FIG.  7 . 
     At this time, the scanner timing control circuit  304  transmits the HSYNC (the horizontal synchronizing signal)  110 , the VSYNC (the vertical synchronizing signal)  109 , the CLOCK (the clock signal)  111  and image data synchronized with it to the DATA (the image data signal)  108 . 
     The scanner printer server  102  reads the image data in synchronization with the HSYNC (the horizontal synchronizing signal)  110 , the VSYNC (the vertical synchronizing signal)  109  and the CLOCK (the clock signal)  111 . 
     FIG. 4 is a structural view which illustrates the printer  104 . 
     Reference numeral  401  represents a printer serial interface,  402  represents a printer CPU,  403  represents a printer drive circuit,  404  represents a printer timing control circuit, and  405  represents a printing section. 
     The operation to be performed when an image is printed will now be described with reference to FIG.  4 . 
     The host computer  101  has data available, the data being required to be printed. The data is exemplified by data formed into raw image data, compressed image data, and page description language. Then, a printer whereby printing is performed is instructed and information about this is transmitted to the scanner printer server  102  via the network  105 . If the client process  107  of the server  102  receives data formed into the page description language and the instructed printer does not have the function of bit-map developing the page description language, the client process  107  develops data in the server  102  and transmits the print command to the printer  104  via the interface to which the instructed printer is connected. If the connected printer does have the function of developing the page description language, the server  102  transmits data formed into the page description language to the printer  104 . 
     The server  102  subjects the transmitted data to a process to be performed therein in accordance with the relationship between the transmitted data and the functions included by the instructed printer. 
     In a case where a function included by the instructed printer is used, the server  102  acts only to transfer the data. Then, the description will be made about a case where the printer connected to the server  102  does not include such a function. The printer serial interface  401  receives the print command from the scanner printer server  102  and transmits it to the printer CPU  402 . 
     Then, the printer CPU  402  sets the size of the image and the position at which printing of the image is started in accordance with information transmitted together with the print data or with the instruction in the case of the page description language. 
     The printer CPU  402  controls the printer drive circuit  403  so as to read the image for each line as shown in FIG.  7 . 
     At this time, the scanner printer  102  transmits the HSYNC (the horizontal synchronizing signal)  110 , the VSYNC (the vertical synchronizing signal)  109 , the CLOCK (the clock signal)  111  and image data in synchronization with the aforesaid signals as shown in FIG.  8 . 
     The printer timing circuit  404  receives the image data in synchronization with the HSYNC (the horizontal synchronizing signal)  110 , the VSYNC (the vertical synchronizing signal)  109  and the CLOCK (the clock signal)  111  supplied from the scanner printer server  102  so as to cause the printer portion  405  to print it. 
     FIG. 5 is a structural view which illustrates the image reading section  305  having no compression function and arranged to transmit the raw image data. 
     Referring to FIG. 5, reference numeral  501  represents a level conversion section,  502  represents a scanner gamma conversion section,  503  represents a scanner color conversion section,  504  represents a resolution conversion section, and  505  represents a scan engine. 
     Referring to FIG. 5, the image reading section  305  is composed of the level conversion section  501 , the scanner gamma section  502 , the scanner color conversion section  503 , the resolution conversion section  504 , the scan conversion section  505  and the scan engine  505 , which are respectively connected to a bus (omitted from illustration), so that parameters from the scanner CPU  302  can be converted. 
     The scan engine  505  reads an RGB color image, performs a shading correction, and transmits image data. 
     The resolution conversion section  504  converts the resolution of reading the image, the resolution being able to be selected from a group consisting of 400 dpi (dot per inch), 200 dpi, 100 dpi and the like and instructed by the scanner CPU  302 . 
     The scanner color conversion section  503  converts the color of the image. If the required image data is RGB data of the standard color space data, a suitable correction is selected and performed so as to be transmitted. Furthermore, conversion of the RGB color data into, for example, a YCrCb color space data is performed in the scanner color conversion section  503 . In a case where white and black data is required, yellow data is used, which is the brightness data of the aforesaid YCrCb, or else green data, which is the intermediate wavelength data of the RGB color data, is used so as to perform the white and black conversion. The scanner color conversion is instructed by the scanner CPU  302 . 
     In the level conversion section  501 , the number of effective bits for one pixel is converted. For example, the lower bit of YCrCb composed of 8 bits for each color and subjected to the gamma conversion is omitted and the dynamic range is so converted that Y is made to be 6 bits and each of Cr and Cr is made to be 4 bits. The aforesaid level instruction is performed by the scanner CPU  302  in accordance with an instruction issued by the host computer  101 . 
     FIG. 6 is a structural view which illustrates the printing section  405 . 
     Reference numeral  601  represents a printer color conversion section,  602  represents a printer gamma conversion section,  603  represents a masking conversion section,  604  represents a black generating/base color removing section,  605  represents a binary coding section, and  606  represents a print engine. 
     The printer color conversion section  601  converts the image into RGB system. In a case where the image formed into, for example, a color space of YCrCB, has been supplied, it is converted into the RGB system. 
     The printer gamma conversion section gamma-converts the supplied image by a known function: 
     
       
           R′=f ( R ) 
       
     
     
       
           G′=f ( G ) 
       
     
     
       
           B′=f ( B ) 
       
     
     The aforesaid conversion is performed by using an LUT (Look Up Table), the LUT being set by the printer CPU  402 . 
     The masking conversion section  603  converts masking for the supplied image. 
     The aforesaid masking conversion can be obtained by a known primary conversion arranged as follows:          (       R   ″     ,     G   ″     ,     B   ″       )     =       (         a11       a12       a13           a21       a22       a23           a31       a32       a33         )          (           R   ′               G   ′               B   ′           )                              
     or a known secondary conversion arranged as follows:          (       R   ″     ,     G   ″     ,     B   ″       )     =       (           a                 11           a                 12           a                 13           a                 14           a                 15           a                 16           a                 17               a                 21           a                 22           a                 23           a                 24           a                 25           a                 26           a                 27               a                 31           a                 32           a                 33           a                 34           a                 35           a                 36           a                 37           )          (           R   ′               G   ′               B   ′                 R   ′     *     R   ′                   G   ′     *     G   ′                   B   ′     *     B   ′               1         )                              
     The aforesaid conversion is performed by the LUT (Look Up Table) or a gate array. The parameter of the aforesaid LUT or the gate array is set by the printer CPU  402 . 
     In the black generating/base color removing section  604 , the black color generation and the base color removal are performed as follows: 
     
       
           C= 255 − R″   
       
     
     
       
           M= 255 − G″   
       
     
     
       
           Y= 255 − B″   
       
     
     
       
           Bk=a  (min ( C, M, Y )) 
       
     
     
       
         
           C′=C−Bk 
         
       
     
     
       
         
           M′=M−Bk 
         
       
     
     
       
         
           Y′=Y−Bk 
         
       
     
     The aforesaid conversion is performed by the LUT (Look Up Table) or a gate array. The parameter of the aforesaid LUT or the gate array is set by the printer CPU  402 . 
     In the binary coding section  605 , the image is binary-coded if the print engine  606  is a binary printer. In order to perform the binary coding operation, a simple binary coding method, a dither method and an error diffusion method are changed over. Incidentally, the binary coding section  605  can be omitted from the structure if the print engine  606  is a multi-value printer. The aforesaid conversion is performed by the gate array. The binary coding method and the threshold for the binary coding operation, and the like are performed by the printer CPU  402 . 
     FIG. 7 illustrates a scanning and printing operation, where reference numeral  701  represents an image to be scanned or printed. 
     Symbol VSYNC represents a vertical synchronizing signal and HSYNC represents a horizontal synchronizing signal. The image  701  to be scanned or printed is transmitted for each line thereof in synchronization with the vertical synchronizing signal and the horizontal synchronizing signal. 
     FIG. 8 illustrates the timing, where symbol VSYNC represents the vertical synchronizing signal, HSYNC represents the horizontal synchronizing signal, and CLOCK represents a standard clock. Image data is transmitted for each pixel in synchronization with the CLOCK. 
     Although the embodiment shown in FIG. 8 is adapted for the RGB color data, the scanner color conversion section  503  is able to convert the color into an arbitrary group of three primary colors. 
     FIG. 9 illustrates the operation of the dual port ram at the time of the pre-scanning operation or the printing operation. As shown in FIG. 9, the image for each line is read by the scanner  103  from the dual port ram or the same is written to the printer  104  from the dual port ram at the time of the scanning or the printing operation. 
     The numbers shown in FIG. 9 denote the accessing order performed by the dual port ram at this time. 
     FIGS. 10 and 11 illustrate the operation of the dual port ram at the time of the pre-scanning operation. 
     When an image is read by the scanner  103 , the scanner printer server  102  alternately writes image data to the dual port ram for each line as shown in FIGS. 10 and 11. That is, the first line is read by the scanner  103  so as to be written to the dual port ram  205  as shown in FIG.  10 . 
     Then, the second line is read by the scanner  103  as shown in FIG. 11 so as to be written to the dual port ram  206 . If the host computer  101  requires raw image data, data in the dual port ram is read as is so as to be transferred to the server process  107  via the ethernet  105 . If the host computer  101  requires data formed into compressed image data, the encoding circuit  213  included in the server device shown in FIG. 2 is utilized to read data in the dual port ram  205 , the data being then image-compressed so as to be transferred to the server process  107  via the ethernet  105 . 
     Then, the third line is read from the scanner  103  as shown in FIG. 10 so as to be written to the dual port ram  205 . Simultaneously, data about the second line stored in the dual port ram  206  is read so as to be transferred to the server process  107  via the ethernet  105  in the form of the raw image data or the compressed image data. 
     Then, the image is read for each line by utilizing the dual buffer. 
     Incidentally, the scan engine  505  reads the image by the RGB dot sequential method. If a user issues an instruction to read the image by another method such as the line sequential method or the plane sequential method, scan conversion must be performed, the scan conversion being performed at the time of reading the image from the dual port rams  205  and  206 . 
     Then, the scan conversion operation to be performed at the time of scanning data will now be described. 
     An assumption is made that dot sequential RGB data is converted into, for example, a YCrCb color space by the scanner color conversion section  503 , and it is alternately written to the dual port rams  205  and  206  by the dot sequential method. 
     In order to convert the dot sequential YCrCb image into the line sequential data before it is transferred, the image data is so read that it is shifted by a degree corresponding to three pixels. 
     That is, only Y, which is the first color, is read from the dot sequential YCrCb image, and Y is transferred. Then, only Cr, which is the second color, is read and transferred. Finally, only Cb, which is the third color, is read and transferred. As a result, scanning conversion from the dot sequential YCrCb to the line sequential YCrCb image is performed. 
     Then, an operation in which the dot sequential YCrCb image is converted to the plane sequential YCrCb so as to be transferred will now be described. 
     Similarly to the line sequential operation, the scanner color conversion section  503  converts the dot sequential RGB into, for example, a YCrCb color space so as to be alternately written to the dual port rams  205  and  206  by the dot sequential method. 
     Since the conversion from the dot sequential form the plane sequential form cannot be completed by a single scanning operation, scanning is performed three times by the scan engine  505 . 
     At the time of the first scanning operation, only the first color Y is read and transferred, only Cr is read at the second scanning operation, and only Cb is read at the third scanning operation so as to be transferred. As a result, the dot sequential YCrCb image can be converted into the plane sequential YCrCb image. 
     In a case of the dot sequential YCrCb image, the image can be encoded by the ADCT method. Also in this case, the image read by the scanner  103  is alternately written to the dual port ram, and the same is, by the encoding/decoding circuit  213 , encoded at the time of the reading operation, the encoded image data being then written to the RAM  203 . The encoded image data is then transferred to the server process  107  via the ethernet  105 . 
     As a result, the image to be transferred can be compressed and therefore the quantity to be communicated can be reduced. 
     FIGS. 12 and 13 illustrate the operation of the dual port ram at the time of the printing operation. 
     In a case where an image is printed by the printer  104 , the scanner printer server  102  transmits data from the dual port ram for each line to the printer  104  as shown in FIGS. 12 and 13. 
     That is, the first line is read from the ethernet  105  as shown in FIG. 12 so as to be written to the dual port ram  205 . 
     Then, the second line is, as shown in FIG. 13, read from the ethernet  105  so as to be written to the dual port ram  206 . Simultaneously, data in the dual port ram  205  is read so as to be transferred to the printer  104 . 
     Then, the third line is, as shown in FIG. 12, read from the ethernet  105  so as to be written to the dual port ram  205 . Simultaneously, data is read from the dual port ram  206  so as to be transferred to the printer  104 . 
     Then, the image is similarly transferred for each line by utilizing the dual buffer. 
     Incidentally, the printer engine  606  prints an image by the RGB dot sequential manner. Therefore, if the user inputs an instruction to print the image in another form, for example, the line sequential form or the plane sequential form, scan conversion must be performed. The aforesaid conversion is performed at the time of reading the image from the dual port rams  205  and  206 . 
     Then, the scan conversion to be performed at the time of the printing operation will now be described. 
     In a case where dot sequential YCrCb image data is transferred from the server process  107 , the scan conversion can be omitted. The dot sequential YCrCb image data is transferred to the printer  104 , and it is then converted into dot sequential RGB by the printer color conversion section  601  so as to be printed. 
     In a case where line sequential YCrCb image data is transferred, it is read for each image at the time of reading the image data. That is, the first color Y of the first pixel, the second color Cr of the first pixel, and the third color Cb of the first pixel are read in the aforesaid sequential order. Then, the first color Y of the second pixel, the second color Cr of the second pixel, and the third color Cb of the second pixel are read in the aforesaid sequential order. Then, colors are similarly read, so that the line sequential YCrCb image can be converted into the dot sequential YCrCb image. 
     The dot sequential YCrCb image data is transferred to the printer  104 , and it is converted into dot sequential RGB data by the printer color conversion section  601  so as to be printed. 
     Then, the scan conversion to be performed in a case where the plane sequential YCrCb image has been transferred will now be described. 
     Since conversion from the plane sequential YCrCb image to the dot sequential YCrCb image cannot be completed by one reading, image data is temporarily stored in the hard disk  212 . 
     Then, the film stored in the hard disk  212  is sought so as to be read in the dot sequential YCrCb manner before it is written to the dual port rams  205  and  206 . Thus, the scan conversion is performed. The dot sequential YCrCb image data is transferred to the printer  104  so as to be converted into dot sequential RGB data by the printer color conversion section  601  before it is printed. 
     In a case where a dot sequential YCrCb image encoded by the ADCT method has been transferred, it is decoded to a dot sequential YCrCb image by the encoding/decoding circuit  213 . The dot sequential YCrCb image is alternately written to the dual port rams  205  and  206  for each line before it is transferred to the printer  104 . 
     As a result, an image can be compressed when it is transferred, and therefore the quantity to be communicated can be reduced. 
     FIG. 14 illustrates the operation to be performed at the time of the pre-scanning and the scanning operations. Then, the operation of communicating data between the host computer  101  and the scanner printer server  102  and the scanner  103  to be performed at the time of the pre-scanning operation and the scanning operation will now be described with reference to the drawings. 
     In a case where an image is read from the scanner  103 , it is necessary to instruct the size of the image, the position of the image, the resolution, the format (dot sequential, line sequential, or plane sequential), the edge emphasis, the color space (RGB and YCrCb), the color (the color to be transferred, for example, only G is transferred), the level (the number of gradations of the color), the encoding method (the ADCT method, encoding is omitted or the like), the bit rate (the bit rate at the time of the encoding operation), the thinning rate at the time of the pre-scanning operation, the file to which data is read and the like. 
     Therefore, the client process  106  instructs the user to instruct the aforesaid parameters. The user then instructs the parameters and executes the pre-scanning operation. 
     Then, the client process communicates with the server process  107  in accordance with a sequence shown in FIG.  14 . 
     Referring to FIG. 14, the client process  106  transmits a PRESCAN packet to the server process  107 , the PRESCAN packet being composed of the XSIZE, YSIZE, XSTART, YSTART, XSTEP, and YSTEP, and the like. 
     In the server process  107 , the image is encoded and thinning is performed at the time of the pre-scanning operation, and the encoding method, the bit rate at the time of the encoding operation and the thinning rate are set after it has received the PRESCAN packet. The other information is, as the prescan command, transferred from the serial interface  207  to the scanner  103 . 
     The scanner  103  sets the parameters to the image reading section  305  in accordance with information about the pre-scan command. If the aforesaid parameters are correctly set, OK is returned to the server process  107 . 
     When the server process  107  has received OK from the scanner  103 , it returns an OK packet to the client process  106 . If it has not been set correctly, status information is returned to the server process  107 . 
     When the scanner  103  has received the pre-scan command, it reads an image from the Video I/F for each line. 
     At the time of the pre-scanning operation, the timing control circuit  208  of the scanner printer server  102  makes the HSYNC (the horizontal synchronizing signal)  110 , the VSYNC (the vertical synchronizing signal)  109 , the CLOCK (the clock signal)  111 , and the DATA (the image data signal)  108  to be high impedance. Furthermore, it reads data from the DATA (the image data signal)  108  in synchronization with the HSYNC (the horizontal synchronizing signal)  110 , the VSYNC (the vertical synchronizing signal)  109  and the CLOCK (the clock signal)  111  so as to write the data to the dual port rams  205  and  206 . 
     The server process  107  reads the image data, which has been read from the Video I/F for each line, from the dual port rams  205  and  206  so as to write the image data to the hard disk  212 . 
     At this time, the image is thinned in accordance with the thinning ratio of the XSTEP and YSTEP instructed with thee PRESCAN packet. The data about this is divided into sections each having a suitable size or combined with each other so that a plurality of DATA packets are formed, each of which is composed of a DATA tag, the number of bytes of the packet and image data, the DATA packets being then transferred to the client process  106  of the host computer  101 . 
     In the client process  106  of the host computer  101 , the thinned image data is picked up from the image packet supplied from the server process  107  so as to be displayed on a CRT. 
     When the scanner  103  has correctly transmitted all of the images, it transmits OK through the scanner serial interface  301  to the server process  107 . When the server process  107  has received OK from the scanner  103 , it transmits an OK packet to the client process  106 . 
     When the server process  107  has transmitted the OK packet to the client process  106 , it waits for the next command packet to be supplied from the client process  106 . 
     The client process  106  receives all of the thinned images, displays them on the CRT, and inquires of the user which region of the image is to be actually scanned. The user uses a pointing device such as a mouse to instruct the region to be actually scanned. Furthermore, it instructs the scan start to the client process  106 . 
     Then, the client process  106  transmits a SCAN packet composed of the XSIZE, YSIZE, XSTART and YSTART of the image to the server process  107 . 
     When the server process  107  receives the SCAN packet, it transmits OK to the client process  106  if information about this has been correctly set. 
     The server process  107  reads image data, which has been read to the hard disk  212  at the time of the pre-scanning operation, in accordance with the parameters instructed with the SCAN packet. The data about this is divided into sections each having a suitable size or combined with each other so that a plurality of DATA packets are formed, each of which is composed of a DATA tag, the number of bytes of the packet and image data, the DATA packets being then transferred to the client process  106  of the host computer  101 . 
     In the client process  106  of the host computer  101 , the image data supplied from the server process  107  is fetched so as to be sequentially written to the disk. 
     When the server process  107  has correctly transmitted all of the images, it transmits an OK packet to the client process  106 . 
     When the server process  107  has transmitted the OK packet to the client process  106 , it waits for the next command packet to be supplied from the client. 
     When the client process  106  has received the OK packet from the server process  107 , it waits for a next command issued by the user. 
     FIG. 15 illustrates the operation to be performed at the time of the printing operation. Then, the data communication between the client process  106  of the host computer  101 , the scanner printer server  102  and the printer  104  to be performed at the time of the printing operation will now be described with reference to the drawings. 
     When a user wishes to process documents or pictures by utilizing desk top publishing software (hereinafter called “DTP software”) with the host computer  101 , to process data in the page description language form which is the output data form of the DTP software and print the data, or when the user wishes to print image data in the raw image data form or the compressed image form, an instruction is made to print image data in the page description language form or the image data form. Furthermore, if the image data is printed in the form of the image data form, the size of the image, the position of the image to be printed, and the file name for holding the image to be printed on the host computer  101  are instructed. 
     In the server process  107 , the data form is discriminated and also the fact that a function in the instructed printer is used or a function in the scanner printer server  102  is used is discriminated. 
     Although default values for the parameters such as the gamma conversion, the masking conversion, and the like at the time of the printing operation are set, they may be changed. 
     In this case, the client process  106  shown in FIG. 15 transmits a GAMMA packet with the gamma table at the time of printing the image to the server process  107 . If the gamma table has been set, the necessity of transmitting it can be omitted. 
     When the server process  107  receives the GAMMA packet, it transmits a gamma setting command to the printer  104  if the second byte of the GAMMA packet shows the printer. If the same shows the scanner, the server process transmits the gamma setting command to the scanner  103 . 
     The printer  104  sets the LUT of the printer gamma conversion section  602  in accordance with the gamma setting command parameter. If it can be normally set, the printer  104  returns OK to the server process  107 . 
     When the server process  107  has received the scanner OK, it returns an OK packet to the client process  106 . 
     Then, the client process  106  transmits a MASKING packet with the masking table at the time of printing an image to the server process  107 . If the masking table has been set, the necessity of transmitting it can be omitted. 
     When the server process  107  has received the MASKING packet, it transmits a masking setting command to the printer  104 . 
     The printer  104  sets the parameter for the masking conversion section  603  in accordance with the masking setting command parameter. If it can be normally set, it returns OK to the server process  107 . 
     When the server process  107  has received OK from the printer  104 , it returns an OK packet to the client process  106 . 
     When the parameters for the gamma conversion and the masking conversion have been set, the client process transmits to the server process  107  a PRINT packet including an instruction of print data in the page description language, the raw image form or the compressed image form, an instruction to a printer for use, and XSIZE, YSIZE, XSTART, YSTART and PAGE of the image. 
     When the server process  107  has received the PRINT packet, it starts establishing a connection to the instructed printer. If the printer does not have the page description language intepreting function and if data in the form of the page description language form has been received, processing is performed in the scanner printer server  102 . If the same is the compressed data, a similar operation is performed. 
     The description will be made hereinafter about a case in which a printer which does not have the aforesaid function and which uses the Video I/F is used. 
     When the server process  107  has received the PRINT packet, it transmits the print command to the printer  104  through the serial interface  207 . 
     If the print command has been correctly set, the printer  104  returns OK to the server process  107 . 
     When the server process has received OK from the printer, it returns an OK packet to the client process  106 . 
     When the client process  106  has received the OK packet, it reads image data (the page description language form, the raw image data form, and the compressed image data form and the like included) from an instructed file. The client process  106  divides the read image data into sections each having a suitable size or combined with each other so that a plurality of DATA packets are formed, each of which is composed of a DATA tag, the number of bytes of the packet and image data, the DATA packets being then transferred to the server process  107 . 
     In the server process  107 , image data is fetched from the image packet received from the client process  106  of the host computer  101 . In a case where the image data is the page description language form, the page description language interpreter is started so as to perform the bit map development. In a case where the image data is in the compressed image data form, an extension process having an extension circuit is started so that the bit map development is performed. The data or raw image data, which has been developed in the bit map manner, is sequentially transferred to the printer  104  through the Video I/F so as to be printed. 
     At the time of the printing operation, the timing control circuit  208  of the scanner printer server  102  transmits HSYNC (the horizontal synchronizing signal)  110 , the VSYNC (the vertical synchronizing signal)  19 , the CLOCK (the clock signal)  111  and image data which synchronizes with it to the DATA (the image data signal)  108 . The printer  104  reads data to be printed from the DATA (the image data signal)  108  in synchronization with it so as to print it. 
     When the printer  104  has normally printed all of the images, it transmits OK to the server process  107  from the print serial interface  401 . When the server process  107  has received OK from the printer  104 , it transmits an OK packet to the client process  106 . 
     When the server process  107  has transmitted the OK packet to the client process  106 , it waits for the next command packet supplied from the client. The client process  106  waits for the next command issued from the user when it has received the OK packet from the server process  107 . 
     FIG. 16 illustrates a case where an error has taken place at the time of the printing operation. Then, communication of data between the host computer  101  and the scanner printer server  102  and the printer  104  at the time of the printing operation will now be described with reference to the drawings. 
     Similarly to the aforesaid printing operation, the client process  106  sets a gamma table and a masking table for use in the image printing operation. 
     Then, the client process  106  transmits to the server process  107  a PRINT packet including an instruction to print data in the page description language, the raw image form or the compressed image form, an instruction of a printer for use, and XSIZE, YSIZE, XSTART, YSTART and PAGE of the image. 
     When the server process  107  has received the PRINT packet, it starts establishing a connection to the instructed printer. If the printer does not have the page description language intepreting function and if data in the form of the page description language form has been received, processing is performed in the scanner printer server  102 . If the same is the compressed data, a similar operation is performed. 
     The description will be made hereinafter about a case in which a printer which does not have the aforesaid function and which uses the Video I/F is similarly used. 
     When the server process  107  has received the PRINT packet, it transmits the print command to the printer  104  through the serial interface  207 . 
     If the value of the parameter of the print command is incorrect, or if a defect such that the value cannot be set has been taken place, or if an error such as paper out has been taken place, the printer  104  returns status information denoting the error status to the server process  107 . 
     When the server process  107  has received the status information from the scanner, it converts the status information into a STATUS packet so as to return it to the client process  106 . 
     When the client process  106  has received the STATUS packet, it transmits an adequate message to the user in accordance with the status so as to indicate that an error has taken place. 
     If an error such as paper jam has been taken place during the printing operation, the printer CPU  402  immediately interrupts the printing operation and transmits the error status information to the server process  107  through the printer serial interface  401 . 
     When the server process  107  has received the status information from the printer  104 , it transmits the aforesaid status information as a STATUS packet to the client process  106  and waits or the next command. 
     When the client process  106  has received the STATUS packet, it transmits an adequate message to the user in accordance with the status so as to indicate the occurrence of the error. 
     FIG. 17 illustrates the operation to be performed in a case where a plurality of prints are made from the same image. Then, communication of data between the host computer  101 , the scanner printer server  102  and the printer  104  to be performed at the time of the printing operation will now be described with reference to the drawing. 
     The user uses the host computer  101  to instruct the file name if the image to be printed is formed into the page description language. If the image is formed into the raw image data form or the compressed image data form, the user instructs the size, the position of the image to be printed, and the file name on the host computer  101  which stores the image to be printed. An assumption is made here that the gamma conversion parameter and the masking conversion parameter for use at the time of the printing operation have been set. 
     Referring to FIG. 17, the client process  106  transmits a PRINT packet including an instruction to print data in the page description language, the raw image form or the compressed image form, an instruction to a printer for use, XSIZE, YSIZE, XSTART, YSTART and PAGE of the image, and PAGE which denotes the number of prints to be made to the server process  107 . 
     When the server process  107  has received the PRINT packet, it starts establishing a connection to the instructed printer. If the printer does not have the page description language intepreting function and if data in the form of the page description language form has been received, the processing of developing the data to the page description language is performed in the scanner printer server  102 . If the same is the compressed data, a similar operation is performed. 
     The description will be made hereinafter about a case in which a printer which does not have the aforesaid function and which uses the Video I/F is similarly used. 
     When the server process  107  has received the PRINT packet, it transmits the print command to the printer  104  through the serial interface  207 . 
     If information about the print command has been set correctly, the printer  104  returns OK to the server process  107 . 
     When the server process  107  has received OK from the scanner, it returns an OK packet to the client process  106 . 
     When the client process  106  has received the OK packet, it reads the image from the instructed file. The client process  106  divides the read image data into sections each having a suitable size or combined with each other so that a plurality of DATA packets are formed, each of which is composed of a DATA tag, the number of bytes of the packet and image data, the DATA packets being then transferred to the server process  107 . 
     In the server process  107 , image data is fetched from the image packet received from the client process  106  of the host computer  101 . In a case where the image data is in the page description language form, the page description language interpreter is started so as to perform the bit map development. In a case where the image data is in the compressed image data form, an extension process having an extension circuit is started so that the bit map development is performed. The data or raw image data, which has been developed in the bit map manner, is sequentially transferred to the printer  104  through the Video I/F so as to be printed. Simultaneously, the image data is stored in the hard disk  212 . 
     When the printer has normally printed the first image, it transmits OK to the server process  107  through the printer serial interface  401 . 
     When the server process  107  has received OK from the printer  104 , it reads an image for the second and ensuing images, which have been written, from the hard disk  212 , so that the images are sequentially printed by the printer  104  via the Video I/F. 
     When the number of pages instructed with the PRINT packet has been printed, the server process  107  transmits an OK packet to the client process  106  so as to indicate the fact that the printing operation has been performed normally. Furthermore, the stored image is deleted. 
     When the server process  107  has transmitted the OK packet to the client process  106 , it waits for the next command packet to be supplied from the client. 
     When the client process  106  has transmitted all of the images and has received the OK packet from the server process  107 , it waits for the command to be issued from the user. 
     Then, another embodiment of the present invention will now be described. 
     In the arrangement shown in FIG. 21, the client process  106  transmits a SCAN packet to the server process  107 , the SCAN packet being composed of XSIZE, YSIZE, XSTART, YSTART, XSTEP and YSTEP and the like. The server process  107  sets each parameter for the image process to be performed by the server in accordance with the instruction included in the SCAN packet. An instruction relating to the size of the image is transmitted to the scanner  103  through the serial interface  207 . 
     The scan  103  sets a parameter into the image reading section  305  in accordance with the information about the scan command. If the aforesaid parameters have been correctly set, the scan  103  returns OK to the server process  107 . 
     When the server process  107  has received OK from the scanner, it returns an OK packet to the client process  106 . 
     If it has not been set correctly, it returns status information to the server process  107 . 
     When the scanner  103  has received the scan command, it reads an image from the Video I/F for each line. 
     At the time of the scanning operation, the timing control circuit  208  of the scanner printer server  102  makes the HSYNC (the horizontal synchronizing signal)  110 , the VSYNC (the vertical synchronizing signal)  109 , the CLOCK (the clock signal)  111 , and the DATA (the image data signal)  108  to be high impedance. Furthermore, it reads data from the DATA (the image data signal)  108  in synchronization with the HSYNC (the horizontal synchronizing signal)  110 , the VSYNC (the vertical synchronizing signal)  109  and the CLOCK (the clock signal)  111  generated by the scanner  103  so as to read and write data to the dual port rams  205  and  206 . 
     The server process  107  reads the image data, which has read from the Video I/F for each line, from the dual port rams  205  and  206  so as to write the image data to the hard disk  212 . 
     If there is an instruction to transfer thinned data issued from the host computer, the image is thinned in accordance with the thinning ratio of XSTEP and YSTEP instructed with the SCAN packet simultaneously with the operation of writing data to the dual port rams  205  and  206 . The aforesaid data is divided into an adequate size or combined with each other so that a plurality of DATA packets are formed, each of which is composed of a DATA tag, the number of bytes of the packet and the image data are formed, the DATA packets being then transferred to the client process  106  of the host computer  101 . 
     The client process  106  of the host computer  101  fetches the thinned image data from the image packet supplied from the server process  107  so as to display it on the CRT. 
     When the scanner has normally transmitted all of the images, it transmits OK to the server process  107  through the scanner serial interface  301 . 
     When the server process  107  has received OK from the scanner, it transmits an OK packet to the client process  106 . 
     When the server process  107  has transmitted the OK packet to the client process  106 , it waits for the next command packet to be supplied from the client process  106 . The client process  106  receives all of the thinned images so as to display them on the CRT. Then, it inquires of the user the region of the image to be actually scanned. The user instructs the required region by using a pointing device such as a mouse. 
     Then, the instructed region is instructed to the client process  106 . Then, the client process  106  transmits a CUT packet composed of XSIZE, YSIZE, XSTART and YSTART, and the like to the server process  107 . 
     When the server process  107  has received the CUT packet, it returns OK to the client process  106  if information about it has been set correctly. 
     Then, the client process  106  transmits the page description language processed by another application program to the server process  107 . 
     The server process  107  develops the page description language by the interpreter  214  so that the character or the graphic bit map is processed. The image data read by the scanner and stored by the image storage means is read to a place instructed with the page description language from the region instructed with the CUT packet so as to be synthesized to the aforesaid bit map. The server process  107  transfers the synthesized image data to the printer so as to cause it to be printed. If there is an instruction to process the image with the page description language, the image data is read from the image storage means and simultaneously processed. 
     When the server process  107  has normally transmitted all of the images to the printer, it transmits an OK packet to the client process  106 . If an instruction is made by the client process  106  to perform continuous printing, the server process transfers the image data, which has been developed in the bit map manner, to the printer. 
     When the server process  107  has transmitted the OK packet to the client process  107 , it waits for the next command packet to be supplied from the client. 
     When the client process  106  has received the OK packet from the server process  107 , it waits for the next command issued from the user. 
     FIG. 18 illustrates the structure of the packet. 
     FIG. 18A illustrates the PRESCAN packet,  18 B illustrates the SCAN packet and  18 C illustrates the PRINT packet. 
     The first byte of each packet is a tag which indicates the type of the packet. For example, when the PRESCAN is 1, the fact that pre-scanning is performed is indicated. When the SCAN is 2, the fact that scanning is performed is indicated. 
     SCANNER NAME and PRINTER NAME are used to instruct the device name with which an image is inputted/outputted. 
     DATA TYPE is used to instruct the fact that the image data is in the page description language form, the compressed image form or the raw image data form. 
     XSIZE shows the X directional size of an image and formed by 2 bytes, while YSIZE shows the Y directional size of an image and is formed by 2 bytes. 
     XSTART shows the image scan or print start position in the direction X and is formed by 2 bytes, and YSTART shows the scan or print start position in the direction Y and is formed by 2 bytes. 
     XZOOM shows the scan or print resolution in the direction Z and is formed by 1 byte, while YZOOM shows the scan or print resolution in the direction Y and is formed by 1 byte. 
     FORMAT shows the method of scanning the image in such a manner that the dot sequential method is instructed with 1, the line sequential method is instructed with 2, and the plane sequential method is instructed with 3. 
     EDGE shows the degree of edge emphasis and the smoothing operation in such a manner that the edge emphasis is instructed with 16 to 1 and smoothing is instructed with −1 to −16. 
     COLOR TYPE shows the color space for the image in such a manner that RGB is instructed with 1 and YCrCb is instructed with 2. In a case of RGB, the first color is called R, the second color is called G and the third color is called B. In a case of YCrCb, the first color is called Y, the second color is called Cr, and the third color is called Cb. 
     COLOR shows the color of the image to be transmitted. In a case where only the first color is transmitted, the second bit is made to be 1, in a case where only the second color is transmitted, the first bit is made to be 1, and in a case where only the third color is transmitted, the 0-th bit is made to be 1. If all of RGB colors are transmitted in a case where COLOR TYPE is RGB, color becomes 7. If R and B are transmitted, it becomes 5 (the first color=4, and the third color=1). Similarly, in a case where COLOR TYPE is YCrCb and only Y is transmitted, it becomes 4. 
     LEVEL is formed by 2 bytes in which the first 4 bits show the number of gradations of the first color, the next 4 bits show the number of gradations of the second color, and the next 4 bits show the number of gradations of the third color. The final 4 bits are undefined. 
     The aforesaid number of gradations are instructed with two exponents in such a manner that 8 is used to instruct 256 gradations and 6 is used to instruct 64 gradations. CODE shows the encoding method in such a manner that 0 is used to instruct a case where encoding is not performed and 1 is used to instruct a case where encoding is performed in accordance with the ADCT. 
     UCR shows α at the time of generating black. 
     BI-LEVEL shows the binary coding method in such a manner that 0 shows the fact that the print engine  606  is a multi-value printer and therefore the binary coding operation is not performed, 1 shows a fattening pattern of a dither method, 2 shows a bayer pattern of the dither method, 3 shows a simple binary coding method, and 4 shows an error diffusion method. 
     THRESHOLD shows the binary coding threshold (0 to 255) of the simple binary coding method. 
     PAGE shows the number of pages to be printed. 
     FIG. 19D shows OK which is a kind of status information, OK being composed of only an OK tag formed by 1 byte. 
     FIG. 19E shows the GAMMA setting command having the second byte, the S/P of which shows the gamma table of the scanner  103  or that of the printer  104  to which setting is made. The ensuing portion is composed of 768 bytes for three colors each of which is assigned to 256 bytes. 
     FIG. 19F shows the MASKING setting command composed of a masking tag and a masking parameter composed of a fixed point formed by 2 bytes. 
     FIG. 19G shows the STATUS information composed of a status tag, the number of the statuses, and the statuses. 
     FIG. 19H shows the copy command composed of a copy tag formed by 1 byte. 
     Then, the copying operation by using the scanner  103  and the printer  104  will now be described. 
     In a case where the copying operation is performed, the user depresses a copy button of an operation panel  306  for the scanner  103 , so that the scanner control circuit transmits a copy command to the scanner printer server  102  through the scanner serial interface  301 . 
     When the scanner printer server  102  has received the copy command, it transmits a scan command to the scanner  103  and transmits a print command to the printer  104 . At this time, parameters for masking suitable for the copying operation are set. 
     When the scanner printer server  102  has received the copy command, it makes the HSYNC (the horizontal synchronizing signal)  110 , the VSYNC (the vertical synchronizing signal)  109 , the COLOR (the clock signal)  111  and the DATA (the image data signal)  108  signals to be high impedance. 
     When the scanner  103  has received the scan command, the scanner control circuit of the scan  103  reads the image in accordance with setting made through the operation panel  306  such as the print start position and the size of the image to be printed. Then, it transmits the HSYNC (the horizontal synchronizing signal)  110 , the VSYNC (the vertical synchronizing signal)  109 , the CLOCK (the clock signal)  111  and image data which synchronizes with it. 
     The printer timing control circuit  404  receives the image data in synchronization with the HSYNC (the horizontal synchronizing signal)  110 , the VSYNC (the vertical synchronizing signal)  109  and the CLOCK (the clock signal)  111  supplied from the scanner  103  so that copying is performed by carrying out printing. 
     At the time of the copying operation, the timing control circuit of the scanner printer server  102  makes the HSYNC (the horizontal synchronizing signal)  110 , the VSYNC (the vertical synchronizing signal)  109 , the CLOCK (the clock signal)  111  and the DATA (the image data signal)  108  to be high impedance. 
     Since scanning or printing of the image cannot be performed in a remote manner during the copying operation, the server process  107  transmits the STATUS packet denoting the fact that copying is being performed to the client process  106  when it has received the scan packet or the print packet so as to notify the user that scanning or printing cannot be performed. 
     In a case where image scanning or printing is being performed in the remote manner, copying cannot be performed. Therefore, the scanner CPU  302  displays on the operation panel  306  the fact that operation of the scanner or the printer is being performed so as to reject the copying operation. 
     Although this embodiment of the present invention is arranged to use the bus type ethernet  105  as the network, any network can be easily employed. 
     Although this embodiment of the present invention is arranged to use serial communication to communicate data such as commands, parameters and errors between the scanner printer server  102  and the scanner  103  or the printer  104 , an arbitrary communication interface may be used as an alternative to serial communication. 
     Although this embodiment of the present invention is arranged to use serial communication to communicate data such as commands, parameters and errors between the scanner printer server  102  and the scanner  103  or the printer  104  and the video interface is used to communicate image data, the present invention is not limited to the aforesaid communication interfaces. An interface such as the SCSI or GPIB which is able to communicate data in a bidirectional manner may be used to communicate information such as commands, the parameters and errors through the same communication passage for transmitting the image data. 
     Although this embodiment of the present invention is arranged to transmit the image by performing encoding by the ADCT encoding method in a case where the image is formed into the dot sequential YCrCb form, the present invention is not limited to the ADCT encoding method. Therefore, any encoding method may be employed. As a result, encoding of images except for the dot sequential YCrCb form can be performed and the image can be compressed before it is transmitted. 
     Although this embodiment of the present invention uses a dual port ram for one line, the present invention is not limited to this. A memory for a plurality of lines or for one frame can be provided so as to raise the processing speed. 
     Although this embodiment of the present invention is so arranged that the image is thinned before it is transmitted at the time of the pre-scan operation and the image is not thinned before it is transmitted at the time of the main scan, the image may be transmitted at the time of pre-scanning a color image by combining the following methods: 
     (1) Only the monocolor component is transmitted. 
     (2) The image is thinned before it is transmitted. 
     (3) The image is encoded before it is transmitted. 
     (4) The gradation of the image is lowered before it is transmitted. 
     (5) The resolution of the image is lowered before it is transmitted. 
     This embodiment of the present invention is arranged in such a manner that the image is read at the time of the pre-scanning operation, the image data is stored in the hard disk  212  and is thinned before it is transmitted. At the time of the main scanning operation, the image stored in the hard disk  212  is read so as to be transferred. However, the image is not stored in the hard disk at the time of the pre-scanning operation and it is directly transmitted by combining the following methods: 
     (1) Only the monocolor component is transmitted. 
     (2) The image is thinned before it is transmitted. 
     (3) The image is encoded before it is transmitted. 
     (4) The gradation of the image is lowered before it is transmitted. 
     (5) The resolution of the image is lowered before it is transmitted. 
     The image may be again scanned before it is transferred at the time of the main scanning operation. 
     This embodiment of the present invention is so arranged that the scan engine  505  performs scanning three times in a case where the image is read and it is scan-converted into the plane sequential form before it is transferred. However, an arrangement may be employed in which the image is read only one time, the image data is stored in the hard disk  212  and the image in the hard disk  212  is read three times. As a result, the number of the mechanical scanning operations can be decreased to one time and therefore the processing speed can be raised. 
     Another arrangement may be employed in which the image is stored in the hard disk  212 , simultaneously the scan conversion of the first color is performed, and the residual two times are read from the hard disk. 
     This embodiment of the present invention is arranged in such a manner that the image is binary-coded by the binary coding section  605  since the binary print engine is used. However, the present invention is not limited to the binary print engine and therefore an arrangement may be employed in which an N-value coding section is provided in a case where the N-value print engine is used, so that the present invention is able to be easily adapted to the engine of the aforesaid type. 
     As described above, a plurality of scanners and printers are connected to the scanner printer server while utilizing the functions of their devices. If the devices do not have the functions, the function of the server is utilized. As a result, various scanners and printers can be utilized in the same environment of the host computer. For example, in a case where the function of developing the page description language is provided for the printer, it is utilized as is. If the same is not provided, the function is included by the server and is utilized to perform the bit map development so that an output from an instructed printer is made. Furthermore, various parameters for the scanner or the printer can be instructed from the host computer on the network and therefore a complicated operation can be performed. 
     Furthermore, a storage means for storing the scanned image is provided for the scanner printer server, the image is temporarily stored in the aforesaid storage means at the time of the pre-scanning operation, and the stored image is read at the time of the main scanning operation. As a result, the required number of the scanning operations can be reduced from the two times to one time. Hence, the image can be read at high speed. 
     In a case where a plurality of prints are made, the image is stored in the storage means at the time of printing the first sheet and the image is read from the storage means for the two and ensuing sheets so as to be printed. Therefore, the image may be transferred only one time and hence the printing operation can be performed at high speed. 
     Furthermore, a color image is transmitted at the time of the prescanning operation by combining the following methods: 
     (1) Only the monocolor component is transmitted. 
     (2) The image is thinned before it is transmitted. 
     (3) The image is encoded before it is transmitted. 
     (4) The gradation of the image is lowered before it is transmitted. 
     (5) The resolution of the image is lowered before it is transmitted. 
     As a result, the image can be transmitted after it has been compressed and therefore an excellent effect can be obtained in that the quantity of communication can be reduced. 
     Furthermore, since a bidirectional communication passage is provided, the copying operation can be rejected in a period in which the scanner printer is being used from the network and the scanner printer cannot be used from the network at the time of the copying operation. 
     Although the invention has been described in its preferred form with particularity, it is understood that the present disclosure of the preferred form may be changed in the details of construction and the combination and arrangement of parts may be varied without departing from the spirit and the scope of the invention as hereinafter claimed.