Patent Publication Number: US-9411548-B2

Title: Print processing method and printing system

Description:
This application is a continuation of U.S. application Ser. No. 14/049,131, filed Oct. 8, 2013 (pending), which is a divisional of U.S. application Ser. No. 13/182,314, filed Jul. 13, 2011 (abandoned), the contents each of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a print processing method and a printing system. 
     2. Description of the Related Art 
     Conventionally, the printer driver of a host PC generates page description language (PDL) data and transfers it to a print processing apparatus, which in turn performs print processing of the PDL data. More specifically, the controller in the print processing apparatus generates a display list (DL), and renders the data into a bitmap using a hardware or software renderer. 
     There has also been proposed a technique of processing a page which is accompanied by complicated render commands output from an application and hence takes much time for print processing when rendering the data, by segmenting the PDL data for each band to concurrently generate DLs, and concurrently rendering the DLs segmented for each band. See, for example, Japanese Patent Laid-Open Nos. 2000-141811 and 2009-245436. Concurrently processing PDL/DL data segmented for each band speeds up the processing of a page which takes much time for processing. 
     In addition, as forms of performing various types of processes on the server side, techniques called a cloud computing system and SaaS (Software as a Service) have recently begun to be used. 
     In the conventional technique described above, however, since PDL and DL data are segmented into bands and concurrently processed, if render instructions are unevenly distributed in a page, the processing times for the respective bands vary. For this reason, one page is not generated until the processing of a band including the largest number of render instructions is complete. 
     Furthermore, the conventional technique described above gives no consideration to the engine speed of a device which outputs a sheet of paper when segmenting PDL and DL data in a page. For this reason, even if PDL and DL data are segmented, the device cannot fully exhibit its performance. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and system which can perform data segmentation in consideration of the engine speed of a device, by using an optical segmentation method when performing parallel processing. 
     According to one aspect of the present invention, there is provided a print processing method for a printing system in which a client which issues a print instruction, a server including a plurality of processors which process page description language data, and an output device which outputs print data generated from the page description language data are connected to each other via a network, wherein the server executes: a reception step of receiving a print instruction from the client; a decision step of deciding the number of layers into which a page is segmented, based on render instructions included in the page description language data, and deciding the number of processors which perform parallel processing for generation of print data from the page description language data, based on the decided number of layers; a generation step of generating the print data equal in number to the number of layers based on which the number of processors is decided in the decision step; and a transmission step of transmitting the print data generated in the generation step in accordance with a request from the output device, and wherein the output device executes: a requesting step of requesting the server to transmit the print data; and an output step of processing the print data upon receiving the print data from the server in the requesting step, and outputting the print data onto a sheet. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing a plurality of apparatuses constituting a printing system; 
         FIG. 2A  is a block diagram showing the internal arrangement of an image forming apparatus, and  FIG. 2B  is a block diagram showing an example of the internal arrangement of an information processing apparatus; 
         FIG. 3  is a block diagram showing the functions of each apparatus of the printing system; 
         FIG. 4A  is a view showing conventional PDL segmentation (band segmentation), and  FIG. 4B  is a view showing PDL segmentation (layer segmentation) in this embodiment; 
         FIG. 5  is a view showing an overall processing sequence in the printing system; 
         FIG. 6  is a flowchart showing an overall processing procedure; 
         FIG. 7  is a flowchart showing a processing procedure in a PDL segmentation server; 
         FIG. 8  is a flowchart showing the details of PDL segmentation in the PDL segmentation server; 
         FIG. 9  is a flowchart showing a processing procedure in a virtual processor group; 
         FIG. 10  is a flowchart showing a processing procedure in an output device; 
         FIG. 11  is a view for explaining weighting operation for PDL segmentation; 
         FIGS. 12A and 12B  are views for explaining processing speed estimation in layer segmentation; and 
         FIG. 13A  is a view showing a case in which the virtual processors generate no DL even after the lapse of a predetermined period of time, and  FIG. 13B  is a flowchart showing the processing of deciding the number of virtual processors in accordance with a charge system. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the present invention will be described in detail below in accordance with the accompanying drawings. 
     &lt;Arrangement of Printing System&gt; 
     A plurality of apparatuses constituting a printing system will be described first with reference to  FIG. 1 . As shown in  FIG. 1 , the respective apparatuses constituting the printing system are connected to each other via networks  100 . 
     In this case, the respective apparatuses include a virtual processor group  102 , a PDL segmentation server  103 , an image forming apparatus  104  as an output device, and a client computer (client PC)  105 . The networks  100  are communication lines for the exchange of information among the respective apparatuses. The Internet  101  is a communication line for the exchange of information among the respective apparatuses over firewalls. The Internet  101  allows the network  100  to which the virtual processor group  102  and the PDL segmentation server  103  belong to communicate with the network  100  to which the image forming apparatus  104  and the client PC  105  belong, over the firewalls. 
     The networks  100  and the Internet  101  are, for example, communication networks which support the TCP/IP protocol, and it does not matter whether they are wired or wireless.  FIG. 1  shows the virtual processor group  102  as a processor group. However, a plurality of processors may be prepared as servers, and the PDL segmentation server  103  may include them. 
     The internal arrangements of the respective apparatuses constituting the printing system shown in  FIG. 1  will be described in detail next. The internal arrangement of the image forming apparatus  104  will be described first with reference to the block diagram shown in  FIG. 2A . 
     The image forming apparatus  104  includes two units, namely an image processing unit  1041  and a printing unit  1042 . In this case, the image processing unit  1041  incorporates a CPU  1043 , a direct storage unit  1044 , an indirect storage unit  1045 , a RIP  1046 , a user interface  1047 , and an external interface  1048 . Note that RIP is an abbreviation for “Raster Image Processor”. 
     The CPU  1043  is a unit which issues instructions for various kinds of control of the image forming apparatus  104  by executing predetermined programs. The direct storage unit  1044  is a work memory to be used when the CPU  1043  executes various programs. A program to be executed by the CPU  1043  is loaded into the direct storage unit  1044 . The direct storage unit  1044  is implemented by a RAM. 
     The indirect storage unit  1045  stores various kinds of programs including application programs and a platform program. Various kinds of programs stored in the indirect storage unit  1045  are moved to the direct storage unit  1044  when the CPU  1043  executes the programs. The indirect storage unit  1045  is implemented by an SSD (Solid State Drive) or HDD (Hard Disc Drive). Note that the CPU  1043  may be multiprocessor. 
     A platform will be described in detail below. Implementing the platform can execute the new application developed by the user on the image forming apparatus  104 , and can also customize the image forming apparatus  104 . 
     A method of implementing the platform will be described next. The CPU  1043  moves the platform program stored in the indirect storage unit  1045  to the direct storage unit  1044 . When the program is completely moved, the CPU  1043  becomes ready to execute the platform program. 
     The operation of causing the CPU  1043  to execute the platform program will be referred to as “to activate the platform”. Note that the platform will operate on firmware in the image forming apparatus  104 . In addition, the platform program provides an environment for the execution of an application program. 
     A method of executing an application program on the platform will be described in detail next. Printing software which accepts a print request operates on the platform. This printing software transmits print data received from the client PC  105  to the RIP  1046  to make it start rendering processing of the print data (DL). For example, this software then transmits the print data (DL) to a device connected via the network  100  and the Internet  101  by using a communication protocol such as HTTP (Hyper Text Transfer Protocol). Executing the application program on the platform can implement control of the image forming apparatus  104 . 
     A method of executing an application program will be described next. The activated platform moves the application program stored in the indirect storage unit  1045  to the direct storage unit  1044 . Upon completion of the movement, the platform becomes ready to execute the application program. The platform then executes the application program. The function of the platform which can be provided by executing the application program in this manner will be referred to as a “platform application” in this embodiment. In addition, the platform can perform part of each of the processes based on the flowcharts disclosed in the embodiment. 
     The RIP  1046  is a unit which inputs PDL (Page Description Language) data (to be described later) and generates a bitmap. The RIP  1046  is implemented by hardware or software. The user interface  1047  is a unit necessary to accept a processing request from the user. For example, this unit accepts a signal corresponding to an instruction input by the user via a keyboard, mouse, or the like. The external interface  1048  can receive data from an external apparatus and transmit data to an external apparatus. For example, external apparatuses include external storage devices such as external HDDs and external USB memories and separate apparatuses such as separate host computers and image forming apparatuses which are connected via networks. Note that the image forming apparatus  104  can communicate with the client PC  105 , the virtual processor group  102 , and the like via the networks  100  and the Internet  101 . 
     The internal arrangement of each of information processing apparatuses functioning as the virtual processor group  102 , the PDL segmentation server  103 , and the client PC  105  will be described with reference to  FIG. 2B .  FIG. 2B  is a block diagram showing an example of the internal arrangement of an information processing apparatus  106 . As shown in  FIG. 2B , the information processing apparatus  106  includes a user interface  1061 , a CPU  1062 , a direct storage unit  1063 , an indirect storage unit  1064 , and an external interface  1065 . 
     The user interface  1061  is a unit necessary to accept a processing request from the user. For example, this unit accepts a signal corresponding to an instruction input by the user via a keyboard, mouse, or the like. The CPU  1062  is a unit which issues instructions for various kinds of control of the information processing apparatus  106  by executing predetermined programs. The direct storage unit  1063  is a work memory to be used when the CPU  1062  executes a program. A program to be executed by the CPU  1062  is loaded into the direct storage unit  1063 . The direct storage unit  1063  is implemented by a RAM. 
     The indirect storage unit  1064  stores various kinds of programs including application programs and an OS (Operating System). Various kinds of programs stored in the indirect storage unit  1064  are moved to the direct storage unit  1063  when the CPU  1062  executes the programs. The indirect storage unit  1064  is implemented by a ROM and an HDD. The external interface  1065  is connected to the network  100  and can communicate with other apparatuses connected to the network  100 . 
     &lt;Functions of Each Apparatus in Printing System&gt; 
     The functions of each apparatus in the printing system according to this embodiment will be described next with reference to  FIG. 3 .  FIG. 3  is a block diagram showing the functions of each apparatus in the printing system. The functions of the virtual processor group  102  will be described first. The virtual processor group  102  includes the functions of a request reception unit  4011 , a back-end processing unit  4021 , a queue service  405 , and a storage  406 . 
     The request reception unit  4011  has a function of accepting a processing request transmitted from the client PC  105  or the image forming apparatus  104 . The back-end processing unit  4021  has a function of processing a processing request by using a processing program. More specifically, the back-end processing unit  4021  performs processing by loading a processing program into the memory of a processor which executes the back-end processing unit  4021 . The request reception unit  4011  and the back-end processing unit  4021  are implemented by loading the request reception program and back-end processing program stored in the indirect storage unit  1064  in  FIG. 2B  into the direct storage unit  1063  and making the CPU  1062  execute them. 
     The queue service  405  has a function for asynchronous data communication with the request reception unit  4011  and the back-end processing unit  4021 . The storage  406  has a function of storing various kinds of data including data as an execution result obtained by processing by the back-end processing unit  4021 . The storage  406  is implemented by the indirect storage unit  1064  in  FIG. 2B . The virtual processor group  102  is assumed to operate as a Worker Role in Windows Azure. The functions of the virtual processor group  102  have been described above, and will be described in further detail later. 
     The functions of the PDL segmentation server  103  will be described next. The PDL segmentation server  103  has a PDL segmentation function  301 . The PDL segmentation function  301  is implemented by the CPU  1062 , direct storage unit  1063 , and indirect storage unit  1064  in  FIG. 2B . 
     In this case, PDL is data generated by the user using a printer driver  304  on the client PC  105  (to be described later). The PDL segmentation server  103  is assumed to operate as a Web Role in Windows Azure. 
     The functions of the image forming apparatus  104  will be described in detail next. The image forming apparatus  104  has the functions of a RIP  302  and platform application  303 . The platform application  303  has a function of acquiring data stored in the virtual processor group  102  connected via the network  100 . The platform application  303  is implemented by loading the platform application program stored in the direct storage unit  1044  in  FIG. 2A  into the indirect storage unit  1045  and making the CPU  1043  execute it. 
     The RIP  302  has a function of providing a rendering service of interpreting print data (DL) and converting the data into a bitmap. In addition, this service checks for the request reception unit  4011  whether the generation of print data is complete. At this time, the service performs this check based on the ID generated by the PDL segmentation server  103 . 
     The functions of the client PC  105  will be described last in detail. The printer driver  304  is installed in the client PC  105 . The printer driver  304  has a function of generating PDL data from application data based on information stored in an output device (image forming apparatus  104 ) connected via the network  100 . This function is implemented by loading the printer driver software stored in the indirect storage unit  1064  in  FIG. 2B  into the direct storage unit  1063  and making the CPU  1062  execute it. The above description is about the functions of each apparatus in the printing system according to this embodiment. 
     &lt;Conventional Page Segmentation and Page Segmentation in this Embodiment&gt; 
     The differences between the conventional PDL segmentation function and the PDL segmentation function in the printing system according to this embodiment will be described in detail next with reference to  FIGS. 4A and 4B .  FIG. 4A  shows a case of conventional PDL segmentation (band segmentation). In this case, the system renders, on the entire page, a triangle, circle, and rectangle sequentially arranged from the deepest side, from the render instructions included in PDL data (page description language data), so as to superimpose them. In this case, the apparatus segments the page into three bands, namely upper, intermediate, and lower bands, and concurrently processes them using three virtual processors. 
     As a consequence, the respective segmented PDL data include render instructions in the following manner. The first segmented PDL data includes render instructions corresponding to the upper portions of the triangle and circle. The second segmented PDL data includes render instructions corresponding to the intermediate portion of the triangle, the lower portion of the circle, and the entire rectangle such that they overlap each other. The third segmented PDL data includes the lower portion of the triangle. 
     When the loads of the respective rendering processes are calculated from the render instructions, the processing load of the first segmented PDL data is small, the processing load of the second segmented PDL data is large, and the processing load of the third segmented PDL data is small. 
       FIG. 4B  shows a case of PDL segmentation (layer segmentation) according to this embodiment. In this case, the system renders, on the entire page, a triangle, circle, and rectangle sequentially arranged from the deepest side, from the render instructions included in PDL data, so as to superimpose them. The system segments this page into three layers, with the background, intermediate, and uppermost layers respectively including the triangle, circle, and rectangle, and concurrently processes them using three virtual processors. 
     As a consequence, the respective segmented PDL data include render instructions in the following manner. The first segmented PDL data includes render instructions corresponding to the entire triangle. The second segmented PDL data includes render instructions corresponding to the entire circle. The third segmented PDL data includes render instructions corresponding to the entire rectangle. 
     When the loads of the respective rendering processes are calculated from the render instructions, the processing loads of the first to third segmented PDL data are all intermediate. 
     In parallel processing, the longest processing time among the segmented processes is regarded as the final processing time. For this reason, conventional band segmentation produces segmented PDL data with a light processing load and segmented PDL data with a heavy processing load depending on the uneven distribution of commands rendered in a page. This segmentation technique cannot always provide optimal segmentation. In contrast, segmentation for each layer as in this embodiment facilitates making adjustment so as to make the respective segmented PDL data have intended processing loads. 
     &lt;Weighting in Page Segmentation&gt; 
     Weighting in PDL segmentation in the printing system according to this embodiment will be described next in detail with reference to  FIG. 11 . In this case, the system renders, on the entire page, a triangle at the first level, a circle at the second level, and a rectangle at the third level, sequentially from the deepest side, based on the render instructions included in input PDL data, so as to superimpose them, and renders a rectangle at the 150th level on the uppermost surface. 
     As shown in  FIG. 11 , the processing of generating a DL from PDL data is characterized in that the larger the number of levels included in each PDL data, the longer the time it takes to process the PDL data, and vice versa. When finally printing the segmented PDL data, it is necessary to perform superimposition processing at the time of rendering. This processing must always be sequentially performed starting from the layer closest to the background surface. 
     When, therefore, segmenting PDL data, it is necessary to segment the PDL data so as to make PDL data on layers closer to the background surface include smaller numbers of levels and take shorter processing times, in consideration of the above characteristic, instead of evenly segmenting the PDL data in accordance with the number of virtual processors which can be used. This operation is called weighting. 
       FIG. 11  shows an example of how PDL data is segmented with weighting operation. In this case, when there are five virtual processors and input PDL data includes 150 levels, the number of levels included in segmented PDL data  1  in the deepest layer is 10, and the number of levels included in segmented PDL data  2  on segmented PDL data  1  is 20. The number of levels includes in segmented PDL data  3  on segmented PDL data  2  is 30. The number of levels included in segmented PDL data  4  on segmented PDL data  3  is 40. The number of levels included in segmented PDL data  5  on segmented PDL data  4  is 50. 
     The details of this processing will be described in associated with &lt;Processing of Deciding Numbers of Levels in PDL segmentation&gt;, and the effects of weighting operation will be described in association with &lt;Processing Speed Estimation in Layer Segmentation&gt;. 
     &lt;Overall Processing Sequence&gt; 
     An overall processing sequence in the printing system according to this embodiment will be described next with reference to  FIG. 5 . First of all, the user issues a print instruction from the printer driver  304  of the client PC  105  to the PDL segmentation server  103  in step S 501 . Upon receiving the print instruction, the PDL segmentation server  103  returns a document ID and a server ID to the printer driver  304  in step S 502 . In step S 503 , the printer driver  304  sends the document ID and the server ID to the output device  104  which outputs a sheet of paper. 
     In step S 504 , the output device  104  sends the document ID to the PDL segmentation server  103  to perform polling to acquire PDL segmentation information. In step S 505 , the PDL segmentation server  103  also performs PDL segmentation processing based on the print instruction received in step S 501 . 
     The PDL segmentation server  103  transmits each segmented PDL data to the virtual processor group  102  in step S 506 , and receives the segmented PDL data IDs and the virtual processor IDs from the virtual processor group  102  in step S 507 . Upon completion of the segmentation of all the pages and transmission to the virtual processor group  102 , the PDL segmentation server  103  transmits the respective segmented PDL data IDs and the virtual processor IDs of the virtual processors which are processing the PDL data to the output device  104  in step S 508 . 
     In step S 509 , the virtual processor group  102  converts the respective segmented PDL data received in step S 506  into DLs. In step S 510 , the output device  104  performs polling to check, based on the segmented PDL data IDs and virtual processor IDs received in step S 508 , whether the generation of DLs from the deepest layer is complete. If this processing is complete, the output device  104  acquires the segmented DLs in step S 511 . In step S 512 , the output device  104  then renders the acquired DL and performs superimposition processing as needed. The output device  104  repeats the above processing for all the DLs. Upon completion of this processing, the output device  104  notifies the printer driver  304  of the end of printing in step S 513 . 
     &lt;Overall Processing Procedure&gt; 
     The operation of the printer driver, PDL segmentation server, virtual processor group, and output device will be described next with reference to  FIGS. 6 to 10 .  FIG. 6  shows an overall processing procedure in this embodiment.  FIG. 7  shows a processing procedure in the PDL segmentation server  103 .  FIG. 8  shows a detailed procedure for PDL segmentation in the PDL segmentation server  103 .  FIG. 9  shows a processing procedure in the virtual processor group  102 .  FIG. 10  shows a processing procedure in the output device  104 . 
     The overall processing procedure will be described first with reference to  FIG. 6 . In step S 601 , the printer driver  304  of the client PC  105  generates PDL data from print target data designated by a printing application in step S 601 . The printer driver  304  then determines in step S 602  whether a cloud environment can be used. If NO in step S 602 , the printer driver  304  causes the output device  104  to execute print processing under a conventional local environment in step S 603 , and terminates this processing. 
     If the printer driver  304  determines in step S 602  that a cloud environment can be used, as shown in  FIG. 1 , the printer driver  304  transfers the PDL data to the PDL segmentation server  103  on the cloud in step S 604 . With this operation, the PDL segmentation server  103  segments the PDL data received in step S 605 . The details of segmentation processing in the PDL segmentation server  103  will be described later in association with &lt;PDL Segmentation Processing (Web Role)&gt; 
     The PDL segmentation server  103  then transmits the segmented PDL data obtained by segmentation in step S 605  to the virtual processor group  102 . In step S 606 , the virtual processor group  102  concurrently generates the DLs of the segmented PDL data. The details of the processing in the virtual processor group  102  will be described later in association with &lt;Segmented PDL Data DL Generation Processing (Worker Role)&gt; 
     The generated DLs are transmitted to the output device  104 . In step S 607 , the output device  104  renders the respective DLs to generate a bitmap, and performs superimposition processing as needed, thereby generating a one-page image. The details of this processing in the output device  104  will be described in association with &lt;Rendering Processing in Device&gt;. 
     &lt;PDL Segmentation (Web Role)&gt; 
     Web Role processing as PDL segmentation processing in this embodiment will be described next with reference to  FIG. 7 . In step S 701 , the PDL segmentation server  103  receives PDL data as a processing target via the Internet  101 . In step S 702 , the PDL segmentation server  103  checks the engine speed of the output device  104 . In step S 703 , the PDL segmentation server  103  checks the number and throughputs of virtual processors of the virtual processor group  102 . 
     The PDL segmentation server  103  then interprets the PDL data received in step S 704  to check in step S 705  whether each page of the PDL data is a heavy page that does not allow to achieve the engine speed unless the render commands included in the page are segmented with a threshold or more. If NO in step S 705 , the PDL segmentation server  103  transmits the unsegmented PDL data to the virtual processor group  102  in step S 706 . The process then advances to step S 710 . If YES in step S 705 , the PDL segmentation server  103  decides the number of levels included in each segmented PDL data in consideration of the number of levels in each page, the number of virtual processors, and superimposition in step S 707 . The details of this processing will be described in association with &lt;Processing of Deciding Numbers of Levels in PDL Segmentation&gt; 
     The PDL segmentation server  103  then segments the PDL data into layers (for each layer) based on the numbers of levels decided in step S 708 . It is easy to perform segmentation because objects to be rendered are described in the PDL data from the deepest layer. Each PDL data segmented in step S 709  is then transmitted to the virtual processor group  102 . In step S 710 , the PDL segmentation server  103  determines whether the processing of all the pages of the received PDL data is complete. If NO in step S 710 , the process returns to step S 704  to process the next page. If the PDL segmentation server  103  determines in step S 710  that the processing of all the pages is complete, the PDL segmentation server  103  terminates this processing. 
     &lt;Segmented PDL Data DL Generation Processing (Worker Role)&gt; 
     Worker Role processing as segmented PDL data DL generation processing in this embodiment will be described next with reference to  FIG. 8 . In step S 801 , the virtual processor group  102  receives segmented PDL data to be processed from the PDL segmentation server  103 . In step S 802 , the virtual processor group  102  generates a DL from each segmented PDL data received in step S 802 . In step S 803 , the virtual processor group  102  determines whether to perform processing up to rendering processing by determining whether the band between the output device  104  and the virtual processor group  102  is wider than a predetermined band. If YES in step S 803 , the virtual processor group  102  interprets the DL and renders it into a bitmap in step S 804 . 
     If NO in step S 803 , the process advances to step S 805 , in which the virtual processor group  102  determines whether there is any transmission request from the output device  104 . If the virtual processor group  102  determines that there is no transmission request, the process loops until the output device  104  issues a transmission request. If there is a transmission request from the output device  104 , the process advances to step S 806 , in which the virtual processor group  102  transfers the DL generated in step S 802  or the bitmap generated in step S 804  to the output device  104 , and terminates this processing. 
     &lt;Rendering Processing in Device&gt; 
     Rendering processing in the device according to this embodiment will be described next with reference to  FIG. 9 . In step S 901 , the output device  104  receives print information from the printer driver  304  or Web Role. In step S 902 , the output device  104  determines whether the received data is segmented data. If NO in step S 902 , the output device  104  determines in step S 903  whether the data is a DL. If NO in step S 903 , the output device  104  receives the bitmap from the virtual processor group  102  in step S 904 . The process then advances to step S 919 . If YES in step S 903 , the output device  104  receives the DL from the virtual processor group  102  in step S 905 . In step S 906 , the output device  104  renders the received DL into a bitmap. The process then advances to step S 919 . 
     If the output device  104  determines in step S 902  that the received data is segmented data, the output device  104  determines in step S 907  whether the data is DL data. If NO in step S 907 , the output device  104  waits in step S 908  until a bitmap to be received is generated. If a bitmap is generated, the output device  104  receives the generated bitmap from the virtual processor group  102  in step S 909 . In step S 910 , the output device  104  determines whether it is necessary to perform superimposition. If the output device  104  determines that there is no need to perform superimposition as in a case in which the bitmap corresponds to the background surface, the process advances to step S 912 . If it is necessary to perform superimposition, the output device  104  performs superimposition processing for the background and the currently processed bitmap in step S 911 . In step S 912 , the output device  104  determines whether the processing of all the data is complete. If the processing is not complete, the process advances to step S 908 . If the processing is complete, the process advances to step S 919 . 
     If the output device  104  determines in step S 907  that the data is DL data, the output device  104  waits in step S 913  until a DL to be received is generated. When DL data is generated, the output device  104  receives the DL data from the virtual processor group  102  in step S 914 . In step S 915 , the output device  104  determines whether it is necessary to perform superimposition. If the output device  104  determines in step S 917  that there is no need to perform superimposition as in a case in which the DL data corresponds to the background surface, the output device  104  renders the DL data into a bitmap. The process then advances to step S 918 . If it is necessary to perform superimposition in step S 916 , the output device  104  generates a bitmap from the DL under processing which is to be superimposed while performing superimposition processing for the bitmap on the background. In step S 918 , the output device  104  determines whether the processing of all the data is complete. If NO in step S 918 , the process returns to step S 913  to start processing the next layer. If YES in step S 918 , the output device  104  outputs the generated bitmap onto a sheet in step S 919 , and terminates this processing. 
     &lt;Processing of Deciding Numbers of Levels in PDL Segmentation&gt; 
     The processing of deciding the numbers of levels in PDL segmentation in this embodiment will be described next with reference to  FIG. 10 . First of all, in step S 1001 , the PDL segmentation server  103  inputs three conditions including a number LSN of levels included in PDL data to be processed, an engine speed ES of the output device  104 , and a throughput PS of the virtual processor group  102 . The PDL segmentation server  103  then calculates a number LNP of levels that can be processed by the virtual processor group  102  within the engine speed ES from the throughput PS and the engine speed ES. 
     In step S 1002 , the PDL segmentation server  103  calculates a number PN of virtual processors for processing the PDL data at the engine speed by dividing the number LSN of levels included in the PDL data by the throughput of the virtual processor group  102 . In step S 1003 , the PDL segmentation server  103  determines whether the calculated number PN is larger than one. If NO in step S 1003 , the PDL segmentation server  103  assigns one-page PDL data to one virtual processor without segmenting the PDL data in step S 1004 . 
     If the PDL segmentation server  103  determines in step S 1003  that the calculated number PN is larger than one, the PDL segmentation server  103  calculates a median value ML of the number of levels in the PDL data by dividing the number of levels included in the PDL data by the number of virtual processors required in step S 1005 . In step S 1006 , the PDL segmentation server  103  calculates a weight LW for the number of levels for each virtual processor by dividing the median value ML of levels by the value obtained dividing the number LSN of levels included in the PDL data by two. In step S 1007 , the PDL segmentation server  103  decides the number of levels by adding or deleting the number of levels corresponding to the weight for each virtual processor with reference to the median value ML as the center. 
     In step S 1008 , the PDL segmentation server  103  determines whether the determined number of levels is too large or small. If NO in step S 1008 , the PDL segmentation server  103  terminates this processing. If YES in step S 1008 , the PDL segmentation server  103  adjusts the numbers of levels by adding or deleting the number of levels corresponding to the excess or deficiency to or from the number of levels on the foreground layer in step S 1009 . The PDL segmentation server  103  then terminates this processing. 
     &lt;Processing Speed Estimation in Layer Segmentation&gt; 
     Processing speed estimation in layer segmentation in this embodiment will be described next with reference to  FIGS. 12A and 12B .  FIG. 12A  shows various kinds of conditions  1201  assumed in this estimation. First of all, data processed is PDL data having complicated render commands which do not allow to achieve an engine speed of 50 ppm, if the current PDL data is not segmented. In this case, assume the following. When the levels are uniformly distributed, the time taken to generate the DL of one layer is 0.3 sec. The time taken for the RIP (Hard) on the device to render is 0.1 sec. The time taken for the RIP (Soft) on virtual processors is 0.3 sec. The time taken to perform superimposition at the time of rendering is 0.1 sec. The time taken to transfer the DL to the device is 0.1 sec. The time taken to transmit a bitmap to the device is 0.3 sec. Assume also that the number of DLs that can achieve the engine speed is estimated to be five. 
     Under these premises, as shown in  FIG. 12B , a timing chart  1202  indicates a case in which all the processes are performed within the device without using the existing cloud. In this case, since one CPU generates DLs, it is possible to process the DLs concurrently with RIP. This processing takes a total of 1.8 sec. Obviously, 50 ppm cannot be achieved. 
     A timing chart  1203  indicates a case in which virtual processors perform processing up to the generation of DLs without weighting operation described in association with &lt;Weighting in Page Segmentation&gt;. In this case, DLs are concurrently generated. However, it is not possible to start RIP until the processing associated with the background layer is complete. Therefore, the generation of DLs and RIP are not concurrently performed. As a consequence, this processing takes a total of 1.3 sec. 
     A timing chart  1204  indicates a case in which virtual processors performs processing up to the generation of DLs while performing weighting operation described in association with &lt;Weighting in Page Segmentation&gt;. In this case, since DLs are concurrently generated with weighting operation, the generation of the DL of the background layer is complete earlier than other layers, the DLs are generated concurrently with RIP. This processing takes a total of 1.1 sec. Obviously, an engine speed of 50 ppm can be achieved. 
     A timing chart  1205  indicates a case in which virtual processors perform processing up to the generation of bitmaps without performing weighting operation described in association with &lt;Weighting in Page Segmentation&gt;. In this case, although parallel processing is performed among the respective layers, the generation of DLs is not parallel with the generation of bitmaps. In addition, rendering to bitmaps increases the amount of information as compared with DLs, and hence it takes much time to transfer the information to the device. Obviously, this processing takes a total of 1.3 sec. 
     A timing chart  1206  indicates a case in which virtual processors perform processing up to the generation of bitmaps while performing weighting operation described in association with &lt;Weighting in Page Segmentation&gt;. In this case, although parallel processing is performed among the respective layers, the generation of DLs is not parallel with the generation of bitmaps. In addition, rendering to bitmaps increases the amount of information as compared with DLs, and hence it takes much time to transfer the information to the device. Obviously, this processing takes a total of 1.2 sec. 
     As described above, it is expected to speed up the processing by making virtual processors generate segmented DLs and to speed up the processing by implementing parallel processing in PDL segmentation by performing weighting operation. 
     &lt;When Virtual Processor Group Generate No DL Even after Lapse of Predetermined Period of Time&gt; 
     Processing to be performed when the virtual processor group generates no DL even after the lapse of a predetermined period of time will be described next with reference to  FIG. 13A . In step S 1301 , the virtual processor group  102  determines whether the PDL segmentation server  103  has generated DL data. This determination is the same as that in step S 909  or S 914 . If YES in step S 1301 , the virtual processor group  102  terminates this processing. If NO in step S 1301 , the virtual processor group  102  determines in step S 1302  whether the determination in step S 1301  has been performed for a time equal to or more than a time corresponding to a given threshold. If NO in step S 1302 , the process returns to step S 1301  to perform determination again. If YES in step S 1302 , the virtual processor group  102  transmits information instructing to reduce the segmentation unit to the PDL segmentation server  103  in step S 1303 , and then terminates this processing. 
     &lt;Decision of Number of Virtual Processors in Accordance with Charge System&gt; 
     The decision of the number of virtual processors in accordance with a charge system will be described next with reference to  FIG. 13B . In step S 1304 , the PDL segmentation server  103  determines whether the user is charged in accordance with the number of virtual processors to be used. If YES in step S 1304 , the PDL segmentation server  103  increases the segmentation unit for PDL data in step S 1306 , and terminates this processing. If NO in step S 1304 , the PDL segmentation server  103  decreases the segmentation unit to achieve the engine speed, and terminates this processing. 
     Note that in this embodiment, the PDL data generated by the client PC  105  is transmitted to the cloud. However, this system may be configured to generate PDL data on the cloud. 
     According to the present invention, it is possible to minimize the uneven distribution of the numbers of render instructions upon segmentation to perform optimal parallel processing. In addition, the embodiment is configured to segment data in consideration of the performance of the output device. This makes it possible for the output device to fully exert its performance even for data which includes many render instructions and does not allow the conventional output device to exert its performance. 
     OTHER EMBODIMENTS 
     Aspects of the present invention can also be realized by a computer of a system or apparatus (or devices such as a CPU or MPU) that reads out and executes a program recorded on a memory device to perform the functions of the above-described embodiment(s), and by a method, the steps of which are performed by a computer of a system or apparatus by, for example, reading out and executing a program recorded on a memory device to perform the functions of the above-described embodiment(s). For this purpose, the program is provided to the computer for example via a network or from a recording medium of various types serving as the memory device (for example, computer-readable medium). 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2010-189986, filed Aug. 26, 2010, which is hereby incorporated by reference herein in its entirety.