Abstract:
A printing system having a print engine, the printing system includes a print engine capable of printing an image on a media; an input buffer adapted to store processed elements of pages for pages to be printed; an assembly means adapted to assemble ready to print pages from the elements of pages; an estimator adapted to estimate complexity of pages assembly according to the elements of pages in the estimated page; a transmission interface for transmitting the ready to print pages to the print engine and to transfer an image to the media; and a speed control element for controlling a speed of the print engine wherein the speed is set according to the estimated complexity of pages assembly.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Reference is made to commonly-assigned copending U.S. patent application Ser. No. ______ (Attorney Docket No. K000572USO1NAB), filed herewith, entitled PAGE COMPLEXITY ANALYZER, by Lax; the disclosure of which is incorporated herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to high speed variable data printing systems and, more particularly, to assuring the supply of sufficient data to the print engine of a high speed printing system so the engine can operate continuously and efficiently. 
       BACKGROUND OF THE INVENTION 
       [0003]    High speed printing systems must assure the supply of sufficient data to the print engine so that the engine can run without stopping since it is impractical to stop and start the printer in a short period of time. Typically, the system is designed to run at full rate for most documents. However, a certain document may have very complex pages that when processing them the system will not be capable of providing the data at full rate. The complexity of a page originates from ripping raster image processing (RIP) complexity which for page description languages (PDL) such as Postscript is highly data dependent and may consume considerable amount of time for page processing. Most printers buffer a small number of rasterized pages in memory to help smooth the data stream to the printer. This may ease short or erratic increases in page complexity, but cannot solve the problem for long sequences of complex pages. In this case the printer must be slowed down in order to accommodate for the increase in complexity. 
         [0004]    A solution to the problem is described in the U.S. Pat. No. 6,762,855 (Goldberg et al.), which suggests using a large image buffer memory for holding completely processed images (previously rasterized) in combination with an intelligent control system. The raster image processed pages can be stored in a compressed form to increase capacity of storage. This enables the system to accumulate slack time that is left over from raster image processing of non-complex pages, and allocate it to complex pages so speed of printing is optimized with average ripping time. This accommodates situations where, on average, the complexity of pages and the system bandwidth are comparable, but may be overtaxed for some periods. The printer controller uses information from the buffer manager to control the speed of the transport, so that the speed of consuming image buffers is matched to the speed of ripping the pages. The printer controller continually inspects the backlog of pages in the buffer memory. If the backlog of pages grows, the printer controller instructs the transport to increase the web speed. If the backlog of completed pages fills the memory buffers (or some other predefined amount of pages is reached), the speed is increased to maximum web speed. However, if the backlog of completed pages decreases, the controller assumes that the amount of processing is such that the printer cannot maintain the current web speed. Hence it will ramp the transport down to maintain the queue at a steady point. 
         [0005]    The invention described below uses a digital front end (DFE) architecture at which a job is ripped (rasterized) and stored in a ready to print (RTP) format on disk during the process stage. The processing can be done offline if desired. The RTP format is highly structured and therefore the complexity of an RTP format page can be predicted more precisely than a page which is described by a PDL language. 
       SUMMARY OF THE INVENTION 
       [0006]    Briefly, according to one aspect of the present invention a printing system having a print engine, the printing system includes a print engine capable of printing an image on a media; an input buffer adapted to store processed elements of pages for pages to be printed; an assembly means adapted to assemble ready to print pages from the elements of pages; an estimator adapted to estimate complexity of pages assembly according to the elements of pages in the estimated page; a transmission interface for transmitting the ready to print pages to the print engine and to transfer an image to the media; and a speed control element for controlling a speed of the print engine wherein the speed is set according to the estimated complexity of pages assembly. 
         [0007]    The invention and its objects and advantages will become more apparent in the detailed description of the preferred embodiment presented below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is schematic system architecture structure of print controller feeding data to print engine; 
           [0009]      FIG. 2  is a diagrammatic scheme of the processing print station; 
           [0010]      FIG. 3  is a diagrammatic scheme of the data merger; 
           [0011]      FIG. 4A  is a diagram of series of blocks with calculated block percent and selected speed for the block perfect; 
           [0012]      FIG. 4B  is a diagram of series of blocks with calculated block percent and selected speed for the block perfect; 
           [0013]      FIG. 5A  is a diagram of series of blocks in a partially populated input memory with calculated block percent and selected speed for the block perfect; and 
           [0014]      FIG. 5B  is a diagram of series of blocks in a partially populated input memory with calculated block percent and selected speed for the block perfect. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    The present invention will be directed in particular to elements forming part of, or in cooperation more directly with the apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. 
         [0016]      FIG. 1  shows the system architecture used by the disclosed invention in a schematic structure. Print controller  104  feeds data to print engine  108  for printing at a rated print engine speed. 
         [0017]    Print controller  104  includes a control station  112  configured to control data feeding sequence to print engine  108 , to be coordinated with press controller  140 . Processing print station  116  receives digital print job for processing. The processing of the print jobs is performed by RIP element  132 . The print jobs are ripped (rasterized) into an RTP format and stored on disk storage  120  during the processing stage. The processing can be done offline if desired. While printing, the RTP is read from storage  120  into dedicated hardware elements ( 124 ,  128 ,  136 ) which prepare and send the processed pages to print heads  144  to be printed using transport element  148 . 
         [0018]    The RTP format is a highly efficient format which contains both fixed and variable elements in a compressed format. The ripping of a fixed element is performed only once per job, thus saving processing time and a single copy is stored per job, thus saving storage space. This is a huge advantage in common VDP (variable data printing) jobs, where many pages share the same master background and the unique variable information is only a small part of the page. 
         [0019]      FIG. 2  shows a diagrammatic illustration of the processing print station  116 . During the processing frontend stage  204 , the incoming print jobs  240  are spooled into spool disk  228 . The input element  212  receives print jobs  240  from spool disk  228 . The print jobs  240  are further rasterized by the ripping stage  216 . Additional processing steps  220  are performed on the rasterized data typically for color processing and other algorithms to repair possible artifacts during printing. The final processed job is written by RTP writer  224  to storage  120 . 
         [0020]    During the backend processing stage  208 , the RTP data is read from storage  120  by the data feeder  232 . The RTP data and related elements are further provided to hardware elements  236 , to be assembled and delivered to the printer for printing. 
         [0021]    During the printing stage as is shown in  FIG. 3 , the compressed elements are loaded from storage  120  into input memory  304 , which is a large image buffer holding compressed data. The stored compressed data (in a form of RTP) may contain information representing several hundred of pages. The elements are decompressed by decompressor  308  and the page is assembled into the output memory  312  and is passed to a first in first out (FIFO) buffer  316  which can hold few dozens of fully assembled pages. The assembled pages are further delivered to the printer via the video interface  320 . 
         [0022]    Similarly to the cited prior art U.S. Pat. No. 6,762,855, input memory  304  is a large raster image buffer of processed elements that can be used to resolve the ripping time complexity which is inherently undetermined. Although this invention does not use complete raster image processed pages, by the available page layout a determination is made for each page whether all element required for page assembly are loaded into input memory  304 . Monitoring the amount of pages that are loaded into input memory  304  also resolves the issue of the time it takes to read elements from storage  120 . 
         [0023]    The accumulation of elements in the input memory  304  cannot simply be used to control the print speed as there are additional sources of complexity which arise from the fact that the pages are not fully assembled and these complexities are not resolved yet. Pages with many elements or with several very large elements may be complex pages since they have an ‘area coverage’ (i.e. total number of pixels) that is greater than what the system was designed for. Additionally, total compressed size of all elements may be very large, requiring more bandwidth than designed for. Hence, although merger  300  hardware is designed to handle complex pages, i.e. pages with high area coverage or with high bandwidth requirements (low compression ratio), there may always be a case which exceeds the design. In these extreme and rare cases a problem may still arise, which will require to ramp down the printer speed. The relatively small FIFO  316  does not enable to use its backlog information for controlling the printing speed there is not enough time to slow down the printer gradually. Moreover, it introduces an acute problem of ensuring that the small FIFO  316  does not empty out during printing due to a sequence of very complex pages. 
         [0024]    Fortunately, opposed to ripping time, the time required for decompression and page assembly can be estimated and an upper bound and can be determined from several simple parameters of the elements that make up a page. As stated above, the system was designed to handle a certain level of complexity. Pages that stand within the designed complexity will be set to complexity level of 1, and will be counted as one ready page. Pages that exceed the designed complexity will be set to complexity level greater than 1, and will be counted as less than a ready page. A detailed description of RTP page complexity calculation is given below. This information is used to control the press speed in a manner that will be described in the following sections, thus enabling the smooth printing of complex jobs and RTP pages. 
         [0025]    A fundamental assumption is that the merger is designed and tuned to handle must jobs at full printer speed. That is, cases of pages with complexity greater than 1 are uncommon and sporadic. The chance for a sequence of complex pages, i.e. pages with complexity greater than 1, is very low. Hence, the cases that requires the printer to slow down due to page assembly complexity are rare. This enables a stricter but simpler approach to be taken and handle the worst case situation as this does not happen often. For instance, although some pages may principally have a complexity that is less than 1, which could be theoretically used to compensate for pages with complexity greater than 1, a strict but simplified approach is taken and set the minimal complexity to 1. 
         [0026]    The goal is to ensure that the FIFO buffer  316  never empties out. The basic idea is to look ahead and analyze the complexity of a block of pages, rather than a single page, and adjust the printer&#39;s speed so that it prints the block at a speed that is appropriate to the block&#39;s complexity. For example, a block that has a calculated complexity that is twice the normal complexity will be printed at a printer speed that is half the full speed, as the overall maximum time required to prepare and assemble the pages may be up to twice the time required for a normal page. This guarantees that the backlog of pages in the FIFO  316  does not decrease while printing the block of pages. Assuming the FIFO buffer  316  was full before the print started, it should remain full at the end of printing each block regardless of its complexity. 
         [0027]    The block size is chosen as a fraction of the FIFO buffer  316  capacity, typically around half the size (5-10 pages). On one hand, this gives a high enough resolution of the complexity to manage the printer&#39;s speed, and on the other hand it is a large enough block to relax the influence of sporadic complex pages. 
         [0028]    For each block a block percent is calculated. The calculated block percent represents an average of the page percent of the pages in the block. The page percent is the reciprocal of the page complexity as defined in page complexity explanation below. For example a block percent  100  indicates that the pages in the block can be printed at machine maximal speed, whereas block percent  50  indicates that the pages in the block are more complicated and therefore may require lowering the speed of the printer for effective printing. 
         [0029]    The block percent gives the maximal percent of the full speed at which the block can be printed. Furthermore, a linked list of block percents for all pages that are loaded into the input memory  304 , is constructed. By analyzing the list of block percents, the printer controller can determine the actual printing speed per block that does not exceed the maximal printing speed calculated by the page complexity on one side and on the other side stands with in the transports acceleration capabilities with smooth changes. 
         [0030]      FIGS. 4A ,  4 B,  5 A and  5 B show the resulted block percent and its impact of printer speed. Block percent versus speed  400 ,  404 ,  500  and  504  are shown in these figures. Each pair represents a block percent for the block and the desired printer speed required to print each block. 
         [0031]    In  FIG. 4A , the pairs indicated by numeral  408  show blocks that will be printed at full machine speed. Pairs  412  although can be printed at full rated speed will be printed at a reduced speed because the blocks that will follow them  420  are found to be complicated, hence require printing speed reduction. In order to reach the required speed for blocks  420  the printing speed for blocks at  412  should be gradually reduced to comply with printer&#39;s characteristics for speed change. Also the blocks in  416  although can be printed at full speed will gain speed gradually following printing the complicated blocks  420 . 
         [0032]      FIG. 4B  shows a similar situation to the one shown in  FIG. 4A . It shows few successive blocks  424  with reduced speed capability, found in input memory  304 . 
         [0033]    By setting a minimal amount of ready blocks required for full printing speed (e.g. 10 blocks), the printer controller will ramp down the speed when the list of ready block drops below this threshold. The printer controller will set the printing speed to the minimum between the speed dictated by the complexity and the speed that matches the rate of the emptying out page buffer as is shown in  FIGS. 5A and 5B .  FIG. 5A  shows input memory  304  with three different blocks. Starting with full speed capable blocks  408 , speed is reduced to comply with a slow block  420  following  408 . Blocks  508  are the last in the input memory  304  in this example. Although blocks  508  are capable to be printed at full speed, the speed is highly reduced to comply with gradual speed change in the printing device as well as with the accelerated data depletion from input memory  304 .  FIG. 5B  shows a similar example to the one shown in  FIG. 5A . Here two block series are shown, starting with  512 , comprising from low block percent, thus mandating speed reduction. Blocks  512  are followed with blocks  516 . Again, blocks  516  are capable for full speed printing, require high speed reduction to both comply with the gradual speed reduction of the printer and the accelerated data depletion from input memory  304 . 
         [0034]    The page complexity calculation is explained below. The system is designed to handle a certain level of “complexity”, generally overall 8:1 compression ratio (CR D =8) and 300% coverage (CV D =300). Hence, pages that are within this complexity are processed in real-time and do not require the slowing down of the print engine. Pages that are more complex will require more processing time and may require the slowing down of the print engine. 
         [0035]    Pages that stand within the designed complexity will have a complexity of 1, and will be counted as one page. Pages that exceed the designed complexity will have a complexity greater than 1, and will counted as less than a page. The functions for calculating the complexity of a page and for deriving the percent of a page that is done are given below. 
         [0036]    For each page a total compressed size (CS T ) is defined as the total size in bytes of all compressed elements that are going to be decompressed for the page. 
         [0000]    
       
         
           
             
               CS 
               T 
             
             = 
             
               
                 ∑ 
                 
                   i 
                   = 
                   1 
                 
                 N 
               
                
               
                 CS 
                 i 
               
             
           
         
       
     
         [0000]    where N is the number of elements in a page and CS i  is the compressed size (in bytes) of element i. 
         [0037]    For each page an effective decompressed size (DS E ) is defined. Generally, the decompressed size is the number of pixels that are written to memory during decompression of the page. However, DS E  accounts also for some overhead that exists in the system and consumes time that could have been used for writing more pixels. This is achieved by adding to DS E  an amount of pixels that their time of writing to memory corresponds to the time lost on overheads. 
         [0000]    
       
         
           
             
               DS 
               E 
             
             = 
             
               
                 ∑ 
                 
                   i 
                   = 
                   1 
                 
                 N 
               
                
               
                 DS 
                 Ei 
               
             
           
         
       
     
         [0000]    Where N is the number of elements in a page and DS Ei  is the effective decompressed size of element i, and is given by the formula below: 
         [0000]      DS Ei =( x   Ei   *y   i )+ P   INIT    
         [0000]    In order to determine DS Ei  its components are to be defined:
       a. x Ei —effective width of element i
           x Ei =MAX{x i , BURST min }   where:   x i —width of element i   BURST min —minimum number of pixels that must be written to a memory line (typically 256)   
           y i —height of element i   b. P INITi —number of pixels that ‘can’ be written during initialization time of element i   P INIT T init ·Freq·Factor   where:   T init —initialization time of element   Freq—merger&#39;s clock frequency   Factor—number of pixels decoded per clock
 
A page size (PS) is defined as the number of pixels in a page, i.e. page width multiplied by page height. Now, the actual compression ratio is defined as follows:
       
 
         [0000]      CR A =PS/CS T , 
         [0000]    and the actual coverage as: 
         [0000]      CV A =DS E /PS·100.
 
         [0000]    The page complexity (PC) is defined as: 
         [0000]      PC=MAX{CR D /CR A ,CV A /CV D ,1}, 
         [0000]      PC&gt;=1 
         [0000]    and the page percent (PP) is given by: 
         [0000]      PP=1/PC*100 
         [0000]      0%&lt;PP&lt;=100% 
         [0050]    The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention. 
       PARTS LIST 
       [0000]    
       
         
           
               104  printer controller 
               108  print engine 
               112  control station 
               116  processing print station 
               120  storage 
               124  decompression page buffer 
               128  compression elements buffers 
               132  RIP 
               136  merger 
               140  press controller 
               144  print heads 
               148  transport element 
               204  frontend 
               208  backend 
               212  input 
               216  ripping 
               220  additional image processing steps 
               224  RTP writer 
               228  spool disk 
               232  data feeder 
               236  hardware elements 
               240  incoming print jobs 
               300  merger (assembly means) 
               304  input memory 
               308  decompressor 
               312  output memory 
               316  first in first out (FIFO) 
               320  video interface 
               400  block percent versus speed pairs diagram 
               404  block percent versus speed pairs diagram 
               408  full speed capable blocks 
               412  reduced speed for full speed capable blocks 
               416  elevated speed for full speed capable blocks 
               420  blocks with reduced speed capability 
               424  few blocks with reduced speed capability shown in succession 
               500  block percent versus speed pairs diagram 
               504  block percent versus speed pairs diagram 
               508  highly reduced speed for full speed capable blocks 
               512  blocks with reduced speed capability 
               516  highly reduced speed for full speed capable blocks