Abstract:
An image processing apparatus comprises: a reception unit adapted to receive image data transmitted from a host computer; first and second communication units adapted to communicate with a second image processing apparatus different from the image processing apparatus; a determination unit adapted to determine a type of image data; and a decision unit adapted to decide, on the basis of determination by the determination unit, whether to use the first communication unit or the second communication unit to transfer the image data.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an image processing system such as a network printer and, more particularly, to a system which forms an image on a paper medium in accordance with a PDL print job described in a page description language (PDL). 
     BACKGROUND OF THE INVENTION 
     Conventionally, an image processing system has been used, in which an image forming apparatus and image reading apparatus are connected to an image processing controller connected to a PDL controller through a command I/F and Video I/F. The PDL controller creates raster image data by rasterizing each page of a print job described in PDL into an image. The command I/F serves to exchange commands. The Video I/F serves to exchange video image data. 
     The PDL controller interprets a PDL job received from a host computer connected through a network or the like to form a raster image, and sends a command sequence generated on the basis of the analysis result to the image processing controller through the command I/F. The PDL controller then sends the image data to the image processing controller through the Video I/F. 
     The image processing controller starts the image forming apparatus to form an image on a paper medium on the basis of the received command sequence and image data, and then output the paper medium outside the apparatus (see, for example, Japanese Patent Laid-Open Nos. 8-272555, 10-171617, and 11-240211). 
     In this conventional image processing system, image data is transferred by using the Video I/F, which is an image transfer path, regardless of the type of job to be processed. This Video I/F is exclusively designed for the transfer of uncompressed raster image data. When the image forming apparatus is a color printer, the Video I/F is designed to transfer 8-bit CMYK (four colors) signals per pixel in synchronism with an image clock. The data transfer rate of the Video I/F can be sufficiently increased in accordance with the engine speed. This I/F, however, requires dedicated hardware and its control mechanism, and hence leads to an increase in cost. 
     In addition, the transfer of image data occupies the Video I/F regardless of the type of image. Therefore, the next job cannot be transferred unless the transfer of the previous job is completed, even if the job does not require high image quality or is designed to print a black-and-white image by using an image forming apparatus capable of color printing. That is, the dedicated hardware is not effectively used. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in consideration of the above situation, and has as its object to effectively use a Video I/F which is dedicated hardware and achieve a reduction in cost. 
     According to the present invention, the foregoing object is attained by providing an image processing apparatus comprising: a reception unit adapted to receive image data transmitted from a host computer; first and second communication units adapted to communicate with a second image processing apparatus different from the image processing apparatus; a determination unit adapted to determine a type of image data; and a decision unit adapted to decide, on the basis of determination by the determination unit, whether to use the first communication unit or the second communication unit to transfer the image data. 
     According to the present invention, the foregoing object is also attained by providing an image processing apparatus comprising: a reception unit adapted to receive image data transmitted from a host computer; a rasterization unit adapted to rasterize the image data; first and second communication units adapted to transmit the image data rasterized by the rasterization unit to a second image processing apparatus different from the image processing apparatus; a determination unit adapted to determine a type of image data; and a decision unit adapted to decide, on the basis of determination by the determination unit, whether to use the first communication unit or the second communication unit to transfer the rasterized image data. 
     According to the present invention, the foregoing object is also attained by providing a data transfer method in an image processing apparatus having first and second communication units adapted to communicate with a second image processing method different from the image processing apparatus comprising: receiving image data transmitted from a host computer; determining a type of image data; and deciding, on the basis of the determined type of image data, whether to use the first communication unit or the second communication unit to transfer the image data. 
     According to the present invention, the foregoing object is also attained by providing A data transfer method in an image processing apparatus having first and second communication units adapted to communicate with a second image processing method different from the image processing apparatus comprising: receiving image data transmitted from a host computer; rasterizing the image data; determining a type of image data; and deciding, on the basis of the determined type of image data, whether to use the first communication unit or the second communication unit to transfer the rasterized image data. 
     Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a block diagram showing an arrangement of an image processing system according to embodiments of the present invention; 
         FIG. 2  is a flowchart showing a basic flow of operation at the time of printing in the image processing system according to the embodiments of the present invention; 
         FIG. 3  is a flowchart showing an example of the processing of switching between compression and noncompression depending on image quality modes according to a first embodiment of the present invention; 
         FIG. 4  is a flowchart showing an example of the processing of switching the types of compression depending on color modes according to a second embodiment of the present invention; 
         FIG. 5  is a flowchart showing an example of the processing of binarizing a black-and-white image according to the second embodiment of the present invention; 
         FIG. 6  is a block diagram showing another arrangement of the image processing system according to the second embodiment of the present invention; 
         FIG. 7  is a flowchart showing an example of the processing to be performed when compression/noncompression switching processing and compression processing type switching processing are combined according to a third embodiment of the present invention; and 
         FIG. 8  is a flowchart showing an example of the processing of switching communication paths depending on whether or not a security mode is designated according to a fourth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described in detail in accordance with the accompanying drawings. 
     (Arrangement of Image Processing System) 
       FIG. 1  is a block diagram showing the arrangement of an image forming system according to the embodiments of the present invention. 
     The image forming system according to the embodiments is comprised of an image processing controller  10 , PDL controller  11 , image reading unit  12 , and image forming unit  13 . 
     The image processing controller  10  performs control by using a CPU  101 , and includes an HDD  104 , a memory (not shown), and the like. The image processing controller  10  also includes a network I/F unit  102  for exchanging commands and statuses with the PDL controller  11  and a Video I/F unit  103  for receiving raster image data from the PDL controller  11 . The image processing controller  10  is connected to the PDL controller  11  through these I/Fs, and is also connected to the image reading unit (e.g., a scanner)  12  and image forming unit (e.g., a printer)  13  through I/Fs (not shown). In addition, the image processing controller  10  includes a user I/F unit (not shown) having keys and a liquid crystal display. 
     Note that, in the image processing controller  10 , dedicated I/Fs are used for the image forming unit  13  and image reading unit  12  and are comprised of control signals lines and Video data signal lines. A Video data signal line is a signal line for transmitting or receiving image data. A control signal line is a signal line for transmitting transmission/reception timing control signals for Video data and various kinds of control instructions to the image reading unit  12  or image forming unit  13 . 
     The image reading unit  12  includes a CCD. The image reading unit  12  can read an image on an original set on a platen, create digital data of a raster image, and send it to the image processing controller  10 . The image reading unit  12  may include an ADF (automatic document feeder) to continuously read a plurality of originals. 
     The image forming unit  13  includes a print engine based on an electrophotographic scheme, ink-jet scheme, or the like. The image forming unit  13  can form an image on a paper medium on the basis of the image data sent from the image processing controller  10 , and output the medium outside the apparatus. When the image forming unit  13  includes a plurality of paper feed cassettes, a plurality of different sizes and types of media can be selected and fed, and images can be formed on the selected media. The image forming unit  13  may further include a specific finishing apparatus. In such a case, a plurality of copies of documents can be sorted and saddle-stitched in the form of a booklet. 
     The image processing controller  10  can compress a received image, store the image in the HDD  104 , and perform processing such as rotating it in a desired direction and enlarging or reducing it to a desired size. The image processing controller  10  also performs color appearance adjustment such as smoothing or calibration. The image processing controller  10  also includes a memory (not shown) and uses it as a work area for these processes. The processes are mainly performed in a software manner by the programs stored in a ROM (not shown) or the HDD  104  operated by the CPU  101 . Obviously, however, in order to increase the processing speed, part of image processing may be implemented by hardware and performed by using the image processing unit in the form of hardware. 
     The PDL controller  11  is controlled by programs operating on a CPU  111 . The PDL controller  11  includes an external I/F (not shown) and receives a print job described in a page description language (PDL) from a host computer through the external I/F. The PDL controller  11  forms a print job sequence on the basis of the received PDL job, rasterizes an image, and starts the print job. In addition, upon receiving a command from the host computer or the like, the PDL controller  11  can execute a scan job of sending an original read command to the image processing controller  10  and sending the received image data to the host computer or the like. A network I/F unit  112  is an I/F for exchanging mainly commands and statuses with the image processing controller  10 . A Video I/F unit  113  is for transmitting an image to be printed to the image processing controller  10 . A memory  114  is used as a work area for the operation of programs and a frame buffer for temporarily storing the obtained raster image. An HDD (not shown) is also provided to store an OS, programs, job data, and raster images. 
     (Operation in Copy Mode) 
     The system including the image processing controller  10 , image reading unit  12 , and image forming unit  13  shown in  FIG. 1  can perform copy operation. When start of copy operation is instructed by the user through a user I/F unit (not shown), the image processing controller  10  generates a copy job sequence in accordance with a copy mode such as a preset finishing or color mode. 
     First of all, the image processing controller  10  outputs an image read command to the image reading unit  12  to read image data from an original set on the document table (not shown) of the image reading unit  12 , and temporarily stores the read image data in the HDD  104  or the frame buffer in the memory. 
     The image processing controller  10  then outputs a print start command to the image forming unit  13 , and sends out the image data stored in the HDD  104  or frame buffer in the order based on the copy job sequence in accordance with the image leading end signal sent from the image forming unit  13 . 
     If finishing operation has been designated through the user I/F (not shown), the CPU  101  designates the finishing operation mode at the time of instructing the print start. The image forming unit  13  starts operation in accordance with the mode designation, sequentially forms sent images on paper media, and outputs them to the finishing apparatus. The finishing apparatus executes finishing operation, such as stapling, bin feeding for each specific number of media, or the like. 
     If the image reading unit  12  includes a DF (not shown), images can be consecutively read from a plurality of originals set on the DF one by one. The intervals at which originals are read one by one can be designated by a program operating on the CPU  101  in accordance with the arrangement of the image processing controller  10 . If, for example, the image processing controller  10  has an HDD  104  or memory with a sufficient capacity, all the originals may be read first, and then the image data of the originals may be sent to the image forming unit  13  one by one in a desired order in accordance with the form of finishing or the like. If such a memory does not have a sufficient capacity or the time taken for the first copy to be output (FCOT) is to be shortened, the image forming unit  13  may be started in synchronism with the start of image read operation to output an image in accordance with the image leading timing of the image forming unit  13  every time one image is read. 
     In addition, in order to solve mismatches between the size and direction of a read image and those of a paper sheet on which the image is to be formed, a sequence may be generated such that each image is output to the image forming unit  13  after processing such as enlargement/reduction and rotation is performed. 
     (I/F between Image Forming Unit and Image Processing Controller) 
     The image forming unit  13  in the embodiments can receive color multilevel image signals and monochromatic (typically, black-and-white) binary image signals as input images. The image forming unit  13  can also receive a 1- or 2-bit TAG signal for each pixel, which represents a property of an area in an image. 
     In the case of color multilevel images, the image forming unit  13  receives a 32-bit signal (8 bits for each of C, M, Y and K signals) per pixel. In this case, a pixel clock is designed to form a 600-dpi image in accordance with the image forming speed. That is, in the case of color images, images are basically formed at 600 dpi. If, however, a TAG signal is attached to a specific pixel, an image can be formed with improved gradation characteristics by decreasing the resolution to 300 dpi by pairing two adjacent pixels to one unit. That is, a TAG signal is used as a signal indicating a photographic image area to discriminate it from a character area, thereby allowing good image formation in accordance with the characteristics of the respective areas. As hardware signal lines, four (CMYK) 8-bit signal lines and one 1-bit signal line (for TAG), i.e., a total of five signal lines, are provided. Obviously, in addition to them, control signal lines are provided. These signal lines may be parallel signal lines. However, a high-speed serial line may be used to virtually realize 5+α signal lines using drivers at the two ends of the line. 
     In contrast to this, in the case of black-and-white binary images, the image forming unit  13  receives a 1-bit signal per pixel. In this case, an image clock is designed to form an image at 1,200 dpi. This image is a black-and-white binary image, and hence has already undergone processing such as dither processing of making an image in a photographic area have gradation characteristics in the image processing controller  10  or PDL controller  11 . There is therefore no need to change the processing in accordance with a TAG bit. No independent line is required as a hardware signal line, and the same signal line used to transfer color multilevel images can be commonly used. For example, a 1-bit TAG signal line may be used as an image signal line in the black-and-white binary mode, and may be operated in accordance with a double-speed clock (quadruple-speed clock considering sub-scanning as well). Alternatively, the least significant one bit for each of C, M, Y and K signals, i.e., four bits, may be used with the clock equivalent to 600 dpi, and image information may be extracted as information corresponding to the clock equivalent to 1,200 dpi by using a driver. 
     Obviously, in addition to these operations, for example, 8 bits×1 color mode may be implemented for a black-and-white multilevel image. In this case, of the signal lines for C, M, Y and K signals, only the signal line for the K signal may be used in addition to the signal line for a TAG bit. 
     (I/F between PDL Controller and Image Processing Controller) 
     The first I/Fs between the PDL controller  11  and the image processing controller  10  are the network I/F units  112  and  102  using Ethernet. The two controllers mainly exchange, through these I/Fs, commands such as a print command and mode designation command and status which is information indicating whether or not the image forming unit  13  or image reading unit  12  is in an operative state or whether or not an error or the like has occurred. A general-purpose Ethernet I/F is a relatively low-speed I/F designed to send a relatively small amount of information at a time. However, this I/F uses a general-purpose protocol such as TCP/IP, and allows a multi-channel arrangement that exchanges a plurality of types of information at once by setting a plurality of addresses and ports. In the system according to the embodiments, each network I/F has purpose-specific ports such as a print port, management port, and event port, in parallel, as independent channels. Obviously, this system may have an arrangement using serial lines such as RS232C, USB, or IEEE1394 or parallel lines such as Centronics I/Fs instead of Ethernet. 
     The second I/Fs are the Video I/F units  113  and  103  used for transferring image data. These Video I/F units  113  and  103  are designed to parallelly (logically) send signals such as 8-bit C, M, Y, and K signals, a 1- or 2-bit TAG bit signal representing a property of an image area, a pixel clock representing a pixel unit of a signal, and a Line enable signal representing a delimiter for each line. Signal lines may be provided by a physically necessary number. This, however, results in a thick cable. For this reason, several high-speed serial lines are used to virtually realize a necessary number of signal lines by using drivers at the two ends. Unlike the general-purpose Ethernet I/Fs used as the network I/F units  112  and  102 , the Video I/F units  113  and  103  are designed exclusively in consideration of the performance of the system, and can transfer data at a sufficiently high rate. However, the Video I/F units  113  and  103  are of one channel capable of sending one image data at a time. 
     (Operation in Print Mode in PDL Controller) 
       FIG. 2  shows a flow of operation performed in the PDL controller  11  when printing is carried out. 
     First of all, the PDL controller  11  receives a print job from a host computer (not shown) through a network I/F or an external I/F (not shown) such as USB or IEEE1394 (step S 101 ). The print job is in the PDL job form which is described in a so-called page description language (PDL) such as PS, PCL, or LIPS, and is generated from an application program operating on the host computer or the like through a print driver. That is, the PDL job includes information (mode designation) required to form a job sequence, for example, the size of paper sheet required for each page, a medium, double-sided/single-sided designation, a color mode, and finishing, and image data of each page in the PDL format. 
     The PDL controller  11  extracts the mode designation from the received PDL job (step S 102 ), and interprets it to form a job sequence which indicates how many paper sheets are to be fed from which paper feed cassette, which discharge bin paper sheets are to be discharged, or a number of paper sheets after which paper feed cassettes are to be switched, in accordance with processing such as finishing and double-sided printing (step S 103 ). 
     In addition, the PDL controller  11  extracts the image data portion from the PDL job, and converts it into raster image data which is a bitmap image in the frame buffer area on the memory  114  (step S 104 ). The obtained raster image data is compressed and temporarily stored in the memory  114  or an HDD (not shown) (step S 105 ). This operation is performed for all the pages of the job. 
     The PDL controller  11  notifies the image processing controller  10  of the formed job sequence in the form of a command sequence which implements the job sequence through the print ports (step S 106 ). The image processing controller  10  prepares for image reception by the Video I/F unit  103  on the basis of the received job sequence. When the preparation is complete, the image processing controller  10  notifies the PDL controller  11  of the completion of the preparation for the reception of image data through the print ports. 
     Upon confirming the completion of the preparation of the reception of image data in the image processing controller  10  (YES in step S 107 ), the PDL controller  11  transfers image data to the image processing controller  10  through the Video I/F unit  113  in synchronism with a control signal such as an image clock or Line enable signal (step S 108 ). 
     Transfer processing is performed for each page, and transfer start and end commands are exchanged through the print ports on a page basis. If processing by the image processing controller  10  cannot keep up with the transfer rate for some reason, the image processing controller  10  notifies the PDL controller  11  of a reception failure, and requests re-transmission of the image data of the same page. The processing in steps S 107  and S 108  is continuously repeated until the transfer of the image data of all the pages is completed (i.e., while NO is obtained in step S 109 ). Upon confirming the completion of the transfer of the image data of all the pages (YES in step S 109 ), the print processing by the PDL controller  11  is terminated. 
     Note that the process shown in  FIG. 2  is merely an example, and when image rasterization and storage processing in steps S 104  and S 105  for one page or more are complete, the flow may advance to step S 106  to perform command sequence transmission processing so as to transmit the command sequence and concurrently perform image data reasterization (step S 104 ) and image data transfer (step S 108 ) during intervals between command transmissions. 
     The image data sent from the PDL controller  11  to the image processing controller  10  is temporarily stored in the HDD  104  or the memory (not shown). At this time, the image forming unit  13  is started after the reception of all pages or one page or more depending on the settings of finishing and other various modes in the job sequence. 
     In starting the image forming unit  13 , the image processing controller  10  designates a paper feed cassette and modes such as double-sided printing and finishing and arranges page information associated with image data in internal queues of the memory (not shown) in the page order required by the operation of the image forming unit  13  in accordance with the job sequence transmitted from the PDL controller. At this time, at least image data to be transmitted first is converted in the frame buffer in the memory, and the remaining image data stored in the HDD  104  are sequentially transferred from the HDD  104  to the memory as soon as the frame buffer becomes empty. 
     The image processing controller  10  then sends image data to the image forming unit  13  in the order of the page information set in the queues in synchronism with an image leading end signal from the image forming unit  13 . The image forming unit  13  forms images, sent on a page basis, on media fed from the designate paper feed cassette, performs the designated finishing operation, and delivers the resultant media outside the apparatus. 
     (Raster Image Data Created by PDL Controller) 
     The PDL controller  11  in the embodiments can create two types of raster image data including a color multilevel image and a black-and-white binary image. The type of image to be created depends on a designation from a driver on a host computer. If no type is designated, the type of image to be created complies with the default designated in advance in the PDL controller  11 . 
     If original PDL data to be rasterized is black-and-white multilevel data or color multilevel data which is designated to be converted into black-and-white data by the driver, the rasterized black-and-white multilevel image is converted into a black-and-white binary image. In this case, the multilevel image is converted into a binary image by using the dither method or the like. In the embodiments, black-and-white binary data is rasterized at 1,200 dpi, and hence the resolution of a character and/or graphic area is changed from 600 dpi to 1,200 dpi by smoothing processing, thereby smoothing edges and the like. 
     Rasterizing data on the basis of a description by the PDL language makes it possible to discriminate whether a specific area of the image is a character/graphic area or a bitmap image such as a photographic image. In rasterizing a given image, the image processing controller  10  also stores such information as area information. This makes it possible to use the information for smoothing processing as in the above case of black-and-white binary images and the generation of TAG signals for the image processing controller  10 . 
     (Compression Function) 
     The PDL controller  11  includes compression and decompression functions for the obtained raster images. The PDL controller  11  compresses black-and-white binary raster image data by a so-called JBIG scheme. The JBIG scheme is a lossless compression scheme, and hence its compression ratio is not so high. Color multilevel raster image data can be compressed by the JPEG scheme. The JPEG scheme is a lossy compression scheme, and hence its compression ratio is high but the image quality deteriorates more or less. 
     The PDL controller  11  temporarily compresses the raster image data and stores it in the HDD (not shown), and rasterizes the image data again on the frame buffer in the memory  114  when transferring it via the Video I/F unit  113 . This makes it possible to perform image rasterization within a processable range in advance even if transfer of the previous page is not complete. 
     (Image Transfer of Black-and-White Binary Data) 
     When the image to be sent from the PDL controller  11  to the image processing controller  10  is a color multilevel image, data corresponding to the number of pixels of (8 bits×4 colors (CMYK)+1 bit (TAG))×1 page is an image data amount per page. If the image is a black-and-white binary image, the image data corresponds to the number of pixels corresponding to 1 bit×1 page. In addition, in the embodiments, the resolution of a color image is 600 dpi, and the resolution of a black-and-white image is 1,200 dpi. Therefore, the data amount is reduced to about ⅛. 
     Obviously, this data may be transmitted to the image processing controller  10  through the Video I/F unit  113 . When, however, the data amount is reduced to such an extent, the data can be compressed and incorporated in a command sequence to the print port upon compression. That is, the image data can be transmitted during the transmission of the job sequence through the network I/F unit  112 . The image processing controller  10  receives the image data concurrently with the job sequence, and hence need not establish synchronization with the Video I/F unit  113 . This reduces the processing load on the CPU  101 . 
     (Other Features) 
     The PDL controller  11  in the embodiments can process PostScript (PS) as a PDL language. Obviously, the PDL controller  11  can be designed to process a plurality of PDL data such as PCL, PDF, and LIPS data. 
     The user can designate the quality of a desired image by the driver (PPD). In accordance with this designation, the PDL controller  11  can adjust the degree of image quality deterioration by adjusting the compression ratio of the image to be temporarily stored in the HDD. 
     In addition, the user can designate color printing or black-and-white printing through the driver. 
     First Embodiment 
       FIG. 3  is a flowchart showing processing in a PDL controller  11  according to the first embodiment of the present invention. This processing exemplifies a case wherein a high image quality mode and low image quality mode are switched in accordance with the image quality designation in a PDL job which is designated through a user I/F such as a print driver. The processing in the flowchart of  FIG. 3  will be described in detail below. 
     Upon reception of a PDL job from a host computer (not shown), the PDL controller  11  interprets the received PDL job in step S 201 . The PDL controller  11  then generates a command sequence for this PDL job by extracting a mode designation for the job, e.g., the size of each page and medium designation. This PDL job includes the image quality mode designation designated by the print driver. 
     In step S 202 , an image quality mode is determined. If this PDL job corresponds to the high image quality mode designation, the flow advances to step S 203 . If the PDL job corresponds to the low image quality mode, the flow advances to step S 207 . 
     In the high image quality mode, the page description of the PDL job is interpreted in step S 203  to rasterize the data of each page into raster image data (bitmap image data) on the frame buffer of a memory  114 . 
     The raster image data created in step S 204  is then queued in the image buffer memory (not shown) for transmission in the memory  114 . At this time, if the buffer memory has a sufficient free space, the image data themselves may be queued in the order of pages to be transmitted. In general, however, it is difficult in terms of cost to mount a memory having such a large capacity. Therefore, labels corresponding to the raster image data of the respective pages are queued, and the raster image data themselves are compressed and stored in the HDD (not shown) in the PDL controller  11  in association with the labels. Note that each page number is uniquely defined in a job, and hence assigning a unique job ID to a generated print job can set “job ID+page ID” as a label for raster image data. In this case, a lossless compression algorithm is used, if possible. If only a lossy compression algorithm such as JPEG is allowed to be used in consideration of the HDD capacity, circuit arrangement, and the like, compression is performed by using a high image quality designation parameter with a compression ratio low enough to correspond to the high image quality mode. If this image is to be transferred through a Video I/F unit  113 , since the image must be rasterized, it is important to use a compression scheme that allows high-speed rasterization. 
     When the rasterization of the image is complete, a command sequence is transmitted in step S 205 . Upon reception of the command sequence, an image processing controller  10  starts preparing for the reception of the image. When the preparation for reception is complete, the image processing controller  10  notifies the PDL controller  11  of the corresponding information. 
     When the notification of the completion of the preparation for reception is received from the image processing controller  10 , the flow advances to step S 206  to transfer raster image data as Video data page by page through the Video I/F unit  113 . As described above with reference to the processing in step S 204 , since the image data queued in the HDD is compressed, the data must be decompressed before Video transfer. This decompression processing may be implemented by software as long as the processing can be done at a sufficiently high speed in accordance with the Video transfer rate. In general, hardware dedicated to decoding is mounted to perform the processing in real time using the hardware. In addition, in this Video transfer, timing commands indicating a start and end for each page are independently sent through the print port. 
     Note that since a job is often comprised of a plurality of pages, the rasterization processing and queuing processing in steps S 203  and S 204  are repeated page by page throughout all the pages, and a command sequence is then transmitted in step S 205 . Obviously, another port for transmitting commands indicating the start and end of image transfer may be prepared. In this case, after a command sequence is generated in step S 201 , the command sequence is quickly transmitted to the image processing controller  10 . After the transmission, Video data may be sent to the image processing controller  10  on a page basis while raster image is created. This allows the image processing controller  10  to know in advance which type of image is to be sent, and hence can quickly prepare for the reception of the Video data. 
     If it is determined in image quality mode determination in step S 202  that the low image quality mode is designated, raster image data is created in step S 207 . In this case, rasterizing image data is the same processing as that performed in step S 203 . 
     The created raster image data is then JPEG-compressed in step S 208 . In the first embodiment, in the low image quality mode, since image data is transferred by using a relatively low-speed command communication path, the data is JPEG-compressed in accordance with a lossy high compression ratio designation with a higher importance being placed on the amount of data than image quality. Using a general compression method like JPEG compression allows the image processing controller  10  formed as a different hardware to use a general decompression method. 
     In step S 209 , the image data of the respective pages which are JPEG-compressed as page data are merged in the command sequence generated in step S 201 . Since a command sequence must be generated on a job basis instead of a page basis, the processing from the creation of raster image data in step S 207  to merging of compressed image data in step S 209  needs to be performed throughout all the pages of the job. 
     When a command sequence is generated by merging the image data of all the pages, the command sequence is transmitted to the image processing controller  10  in step S 210 . The image processing controller  10  can sequentially rasterize images oh a page basis while receiving the command sequence without waiting for data from the Video I/F unit  113 . 
     With the above processing, the data of a multilevel image for which high image quality is designated is transmitted through the Video I/F, whereas a multilevel image for which low image quality is designated is JPEG-compressed and transmitted as data attached to a command through the network I/F. In this manner, compression/noncompression of image data and data transfer paths can be selectively used. 
     In general office use or the like in which very high image quality printing is not required, an image is transferred through a command communication path unless high image quality is designated. Therefore, the Video I/F, which is low in frequency of use, need not be very fast, and hence can take a cost-saving arrangement. 
     In addition, assume that a port different from a port for the transmission of a print sequence is provided on a command communication path to transmit commands indicating VideoStart/End. In this case, as described above, in the case of a job for which the high image quality mode is designated, since Video Data transfer is started after a command sequence is sent, even if the Video I/F is occupied during the Video data transfer, the next job can be concurrently sent, together with image data, as long as a low image quality mode sufficient for general use is designated for the job. 
     The order in which image data are printed by the image processing controller  10  can be freely scheduled. If, therefore, an image forming unit  13  is activated in the order in which transfer of image data is completed, instead of the order in which command sequences are sent, regardless of the high image quality mode and low image quality mode, the image forming unit  13  can be effectively operated without unnecessary pauses. 
     As described above, in the case of a job for which high image quality is not required, image transfer of the job can be done through a command communication path in a compressed state, and hence can be sent without occupying the Video I/F. This makes it possible to effectively use the Video I/F which is dedicated hardware. In addition, decreasing the operating ratio of the Video I/F allows the use of low-speed hardware, and hence can achieve a reduction in cost. 
     Second Embodiment 
     The second embodiment of the present invention will be described next. In the second embodiment, compression methods are switched for color and black-and-white jobs. This processing will be described with reference to the flowchart of  FIG. 4 . 
     In step S 302 , a PDL controller  11  interprets the PDL job received from a host computer (not shown), and generates a command sequence. This PDL job includes a color job in which all pages are formed from color objects, and a black-and-white job in which all pages are formed from black-and-white object data. The PDL job may also include a black-and-white job designation for printing all pages comprised of color objects in black-and-white. 
     In step S 303 , it is checked whether the received PDL job is a color or black-and-white job. If the job is a color job, the flow advances to step S 304 . If the job is a black-and-white job, the flow advances to step S 306 . 
     In the case of a color job, the data of each page is rasterized in step S 304 . In step S 305 , the data are JPEG-compressed. This processing is the same as that described with reference to step S 208 . 
     In the case of a black-and-white job, raster image data is created in step S 306 . This raster image data may be binary data with each pixel consisting of one bit or multilevel data with each pixel consisting of eight bits, based on the original description in PDL. In the case of a black-and-white job which is based on a color multilevel image as the original PDL image and in which black-and-white job designation is made, the data is rasterized as multilevel black-and-white image data with each pixel consisting of eight bits. 
     In step S 307 , binarization processing is performed for the obtained raster image data. The steps in the binarization processing in step S 307  will be described in detail with reference to  FIG. 5 . 
     First of all, in step S 402 , the raster image data obtained in step S 306  is interpreted. In step S 403 , it is checked whether the data is multilevel image data or binary image data. 
     In the case of multilevel image data, image area segmentation processing is performed in step S 404 . In the image area segmentation processing performed in step S 404 , TAG bit information indicating each area information which has been stored upon PDL data rasterization is used, and a bitmap area is segmented into character areas and photographic areas in accordance with gradation change patterns. 
     In step S 405 , smoothing processing is performed for a character area. In this processing, for example, an 8×8 pixel area is enlarged into a 16×16 pixel area by pattern matching to smooth edge portions. That is, a 600-dpi raster image is enlarged into a 1,200-dpi image. Obviously, a halftone character which is not in black but is in gray is smoothed without any change in gray level. 
     In step S 406 , an area determined as a photographic area is increased in the number of pixels. In this processing, one pixel is simply enlarged into four pixels without any change in gray level. With the above processing, multilevel data are converted into 1,200-dpi data throughout the entire image area. 
     Thereafter, in step S 407 , the multilevel image is converted into a binary image by the dither method or the like. At this time, when a photographic area is binarized, high-frequency components are removed, and the gradation characteristics slightly deteriorate. Therefore, jaggies caused by conversion from one pixel into four pixels are absorbed and become less noticeable. That is, better gradation characteristics can be obtained by expressing gradation with 1,200-dpi binary data than by 600-dpi binary data. 
     If it is determined in step S 403  that the obtained image is originally a 600-dpi binary image, the flow advances to step S 408 . Image area segmentation processing in step S 408  can be done by using only the TAG bit information described above. 
     In step S 409 , smoothing processing is performed for a character area as in step S 405 . 
     In step S 410 , the graininess of a photographic area is reduced by enlarging a 600-dpi binary dither image into 1,200 dpi image. In this processing, the average density of a relatively narrow range of the original image (e.g., a 5×5 pixel area) is calculated, and the density (multilevel value) of the central pixel is set to the average density. The resultant image is slightly blurred. Therefore, filtering may be performed for edge enhancement, and the number of pixels is then increased as in step S 406  or S 407  to obtain a 1,200-dpi binary image by the dither method or the like. 
     As described above, when the rasterized data is originally binary data with each pixel consisting of one bit, only smoothing processing is performed. 
     With the above processing, a good 1,200-dpi binary black-and-white raster image can be obtained from either black-and-white 600-dpi multilevel or binary data. 
     When the above binarization processing in step S 307  is complete, the binarized image is JBIG-compressed in step S 308 . The JBIG compression algorithm is a lossless compression algorithm, and allows the original image to be completely reconstructed by decompression. Therefore, no deterioration in image quality is caused by this algorithm. 
     In step S 309 , the image data compressed in step S 305  or S 308  is merged in a command. In this operation, image data is incorporated in the command sequence generated in step S 302  in addition to a portion where information such as a medium and size of each page is described. The command sequence finally generated in this manner internally holds JPEG- or JBIG-compressed image of each page. 
     In step S 310 , the generated command sequence is transmitted. The image processing controller  10  extracts image data from the received command sequence, JPEG- or JBIG-decompresses the data, and can immediately perform print processing or storing in the HDD of the data. 
     According to the flowchart of  FIG. 4 , after it is discriminated whether a received PDL job is a color or black-and-white job, the data is rasterized. However, color job/black-and-white job determination may be done after rasterization depending on the structure of a PDL language. 
     The second embodiment has exemplified the job in which all the pages are black-and-white or color. However, by performing the processing shown in  FIG. 4  on a page basis, the present invention can be applied to a job in which color pages and black-and-white pages are included on a page basis. 
     In addition, processing for a black-and-white job can be applied to a monochrome job comprised of monochrome objects as well as a black-and-white job. 
     According to the second embodiment, switching compression methods for a color job and black-and-white job enables to transfer image data by using a command communication path in each case. In this case, as shown in  FIG. 6 , a system can be constructed with an arrangement equivalent to the arrangement shown in  FIG. 1  from which the Video I/F units  103  and  113  are omitted, thereby expecting a great reduction in cost. 
     In addition, in printing a black-and-white job which is high in frequency of use in offices, in particular, 1,200-dpi binary losslessly compressed image data is used, and hence a system which can obtain a good print result with respect to a drawing constituted by characters, line drawings, and the like which is especially required in offices, and can properly cope with color printing which is low in frequency of use can be built at a low cost. 
     As described above, according to the second embodiment, performing image transfer of a black-and-white job by using a command communication path in a compressed state makes it possible to send the job without occupying the Video I/F. Therefore, the Video I/F which is dedicated hardware can be effectively used. In addition, decreasing the operation ratio of the Video I/F allows the use of low-speed hardware, and hence can achieve a reduction in cost. 
     By performing image transfer of even a color job by using a command communication path in a compressed state upon increasing the compression ratio using a lossy compression scheme, the Video I/F can be omitted from the system, thus achieving a reduction in cost. 
     Third Embodiment 
     The third embodiment of the present invention will be described next. 
     In the third embodiment, an example of a combination of the first and second embodiments will be described with reference to  FIG. 7 . 
     Upon reception of a PDL job from a host computer (not shown), a PDL controller  11  interprets the received PDL job in step S 702 . Note that the received PDL job includes a designation indicating a color job or black-and-white job in addition to an image quality mode. 
     In step S 703 , it is discriminated whether the received PDL job is a color job or black-and-white job. If the job is a color job, the flow advances to step S 704 . If the job is a black-and-white job, the flow advances to step S 306 . 
     In the case of a color job, an image quality mode is determined in step S 704 . If a high image quality mode is designated for the PDL job (i.e., a job determined as a color/high image quality mode job), the flow advances to step S 203 . If the job is a low image quality mode job (i.e., a job determined as a color/low image quality mode job), the flow advances to step S 304 . 
     In steps S 203  to S 206 , the same processing as that performed in steps S 203  to S 206  in  FIG. 3  is performed. A redundant description of this processing is omitted. 
     In steps S 304  and S 305 , the same processing as that performed in steps S 304  and S 305  in  FIG. 4  is performed. A redundant description of this processing is omitted. 
     If it is determined in step S 703  that the job is a black-and-white job, the processing in steps S 306  to S 308  is performed. The processing in steps S 306  to S 308  is the same as that shown in  FIG. 4 . In addition, the binarization processing in step S 307  is the same processing as that described with reference to  FIG. 5  in the second embodiment, and hence a redundant description thereof is omitted. 
     In step S 309 , the image data compressed in step S 305  or S 308  is merged in a command. In step S 310 , the generated command sequence is transmitted. These processes are also the same as those described in the second embodiment. 
     In the third embodiment, a black-and-white job uses an engine for outputting 1,200-dpi binary image data. For this reason, only color jobs are selectively processed in the high image quality and low image quality mode. However, black-and-white jobs may also be selectively processed in the high image quality mode and low image quality mode depending on the embodiment of an engine. 
     According to the third embodiment, since the Video I/F is not used even for a color job as long as it is in the low image quality mode, the frequency of use of the Video I/F further decreases. This makes it possible to use a more inexpensive low-speed arrangement and to output images with a high image quality of 1,200 dpi in the case of black-and-white jobs. 
     As described above, according to the third embodiment, in the case of a job for which high image quality is not required or a black-and-white job, image transfer of the job can be done through a command communication path in a compressed state, and hence can be sent without occupying the Video I/F. This makes it possible to effectively use the Video I/F which is dedicated hardware. In addition, decreasing the operating ratio of the Video I/F allows the use of low-speed hardware, and hence can achieve a reduction in cost. 
     Obviously, this system can be designed to allow the user to designate an image quality mode or color mode through the print driver at the time of printing. Alternatively, the user may be allowed to set in advance usable modes through the PDL controller. 
     It is needless to say that monochrome data can be used in place of black-and-white data. 
     In addition, it is obvious that the image forming unit can be designed to process jobs without discriminating color jobs from black-and-white jobs. In such case, when an original mainly containing a photograph is to be processed, the high image quality mode using the Video I/F may be set. When an original mainly containing texts is to be processed, even if it is a color original, the original data may be binarized and losslessly compressed. Image transfer of the resultant data may be performed through a command communication path to print the data at 1,200 dpi. 
     Fourth Embodiment 
     The fourth embodiment of the present invention will be described next. 
     In the fourth embodiment, the PDL job transmitted from a host computer is processed by switching between data transfer through a Video I/F and data transfer through a network I/F depending on whether or not a security mode is designated. 
       FIG. 8  is a flowchart showing the flow of processing in the fourth embodiment. 
     The basic flow is the same as the flowchart of  FIG. 3  in the first embodiment. Referring to  FIG. 3 , in step S 202 , an image quality mode is determined to determine the high image quality mode or low image quality mode. In contrast to this, in the fourth embodiment, it is checked in step S 802  whether or not the security mode is designated. 
     In step S 801 , the PDL job received from the host computer is interpreted. If it is determined in step S 802  that the security mode is designated, the flow advances to step S 203  to transfer data through the Video I/F. If it is determined in step S 802  that the security mode is not designated, the flow advances to step S 207  to transfer data through the network I/F. 
     In steps S 203  to S 210 , the same processing as that performed in S 203  to S 210  in  FIG. 3  is performed. Therefore, a redundant description of this processing is omitted. 
     The fourth embodiment has been described above. This embodiment allows selective use of communication paths depending on whether or not the PDL job transmitted from the host computer designates the security mode. 
     The flowchart of  FIG. 8 , with reference to which the fourth embodiment is described, has exemplified the case wherein the Video I/F is used when the security mode is designated. However, when the security mode is designated, data may be transferred through the network I/F, whereas when the security mode is not designated, data may be transferred through the Video I/F. 
     In either case, if the security of a communication path used to transfer a job for which the security mode is designated is improved, the job for which the security mode is designated can be selectively transferred in safety. 
     Other Embodiments 
     Note that the present invention can be applied to an apparatus comprising a single device or to system constituted by a plurality of devices. 
     Furthermore, the invention can be implemented by supplying a software program, which implements the functions of the foregoing embodiments, directly or indirectly to a system or apparatus, reading the supplied program code with a computer of the system or apparatus, and then executing the program code. In this case, so long as the system or apparatus has the functions of the program, the mode of implementation need not rely upon a program. 
     Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the claims of the present invention also cover a computer program for the purpose of implementing the functions of the present invention. 
     In this case, so long as the system or apparatus has the functions of the program, the program may be executed in any form, such as an object code, a program executed by an interpreter, or scrip data supplied to an operating system. 
     Example of storage media that can be used for supplying the program are a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a CD-RW, a magnetic tape, a non-volatile type memory card, a ROM, and a DVD (DVD-ROM and a DVD-R). 
     As for the method of supplying the program, a client computer can be connected to a website on the Internet using a browser of the client computer, and the computer program of the present invention or an automatically-installable compressed file of the program can be downloaded to a recording medium such as a hard disk. Further, the program of the present invention can be supplied by dividing the program code constituting the program into a plurality of files and downloading the files from different websites. In other words, a WWW (World Wide Web) server that downloads, to multiple users, the program files that implement the functions of the present invention by computer is also covered by the claims of the present invention. 
     It is also possible to encrypt and store the program of the present invention on a storage medium such as a CD-ROM, distribute the storage medium to users, allow users who meet certain requirements to download decryption key information from a website via the Internet, and allow these users to decrypt the encrypted program by using the key information, whereby the program is installed in the user computer. 
     Besides the cases where the aforementioned functions according to the embodiments are implemented by executing the read program by computer, an operating system or the like running on the computer may perform all or a part of the actual processing so that the functions of the foregoing embodiments can be implemented by this processing. 
     Furthermore, after the program read from the storage medium is written to a function expansion board inserted into the computer or to a memory provided in a function expansion unit connected to the computer, a CPU or the like mounted on the function expansion board or function expansion unit performs all or a part of the actual processing so that the functions of the foregoing embodiments can be implemented by this processing. 
     As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.