Abstract:
A method is disclosed. The method includes receiving a first data component of an image data stream at a cache within a control unit, appending a first signature value to the first data component to obtain a first modified image data and generating a second signature value based on the first modified image data.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates generally to the field of printing systems. More particularly, the invention relates to image processing in a printing system. 
       BACKGROUND 
       [0002]    Print systems include presentation architectures that are provided for representing documents in a data format that is independent of the methods that are utilized to capture or create those documents. One example of an exemplary presentation system, which will be described herein, is the (Advanced Function Presentation) AFP™ system developed by International Business Machines Corporation. According to the AFP system, documents may include combinations of text, image, graphics, and/or bar code objects in device and resolution independent formats. Documents may also include and/or reference fonts, overlays, and other resource objects, which are required at presentation time to present the data properly. 
         [0003]    Once the documents are received at a printer, processing is performed to convert a document into a printable format. However, processing high-resolution images in an incoming data stream into a printable format typically involves highly compute-intensive operations (e.g., scaling, rotation, decompression, color conversion, etc.). 
         [0004]    Further, it is common for a printer to frequently process repetitive images throughout a print job. For instance, a print job may include a full-page background image or a company logo that appears on every printed page. Thus, printers may cache images to avoid the need to render images that have previously been presented and rendered into sheet maps. Such caching of rendered image bitmaps improves the overall performance of a system provided that the system has a mechanism (such as a hash key or “digital signature” generator) to uniquely identify an image. That is, the printer must be able to accurately identify an image so as to avoid using the incorrect rendered bitmap from the image cache. 
         [0005]    In the image transform, a signature is created based on the entire contents of the image. However, this requires that the entire image reside in a memory buffer (or file system) at the point where the signature is created. For Image Object Content Architecture Format (IOCA) images, this is especially limiting given that the input can be processed in a serial manner (e.g., the input can be “streamed” to the image transform). Moreover, there is a need in some printers to uniquely identify an image without having the entire image resident in a memory buffer or file system. For example, in some printing environments, available memory to process images and related objects on each page is extremely limited. 
         [0006]    As a result, a mechanism to generate digital signatures for image identification where the image does not entirely exist is desired. 
       SUMMARY 
       [0007]    In one embodiment, a method is disclosed. The method includes receiving a first data component of an image data stream at a cache within a control unit, appending a first signature value to the first data component to obtain a first modified image data and generating a second signature value based on the first modified image data. 
         [0008]    In another embodiment, a printer includes a print engine; and a control unit. The control unit includes a cache to receive an image data stream; and an image transform to append a first signature value to a first data component received at the cache to obtain a first modified image data and generate a second signature value based on the first modified image data. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    A better understanding of the present invention can be obtained from the following detailed description in conjunction with the following drawings, in which: 
           [0010]      FIG. 1  illustrates one embodiment of a printing system; 
           [0011]      FIG. 2  illustrates one embodiment of a control unit; 
           [0012]      FIG. 3  illustrates one embodiment of a computer node; and 
           [0013]      FIG. 4  is a flow diagram illustrating one embodiment of the operation of a control unit. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    A mechanism to generate image transform signatures in a print system is described. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details. In other instances, well-known structures and devices are shown in block diagram form to avoid obscuring the underlying principles of the present invention. 
         [0015]    Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment. 
         [0016]      FIG. 1  illustrates one embodiment of a printing system  100 . Printing system  100  includes a print application  110 , a server  120 , a control unit  130  and a print engine  160 . Print application  110  makes a request for the printing of a document. In one embodiment, print application  110  provides a Mixed Object Document Content Architecture (MO:DCA) data stream to print server  120 . 
         [0017]    In other embodiments print application  110  may also provide PostScript (P/S) and PDF files for printing. P/S and PDF files are printed by first passing them through a pre-processor (not shown), which creates resource separation and page independence so that the P/S or PDF file can be transformed into an AFP MO:DCA data stream prior to being passed to print server  120 . 
         [0018]    Print server  120  processes pages of output that mix all of the elements normally found in presentation documents, e.g., text in typographic fonts, electronic forms, graphics, image, lines, boxes, and bar codes. The AFP MO:DCA data stream is composed of architected, structured fields that describe each of these elements. 
         [0019]    In one embodiment, print server  120  communicates with control unit  130  via an Intelligent Printer Data Stream (IPDS). The IPDS data stream is similar to the AFP data steam, but is built specific to the destination printer in order to integrate with each printer&#39;s specific capabilities and command set, and to facilitate the interactive dialog between the print server  120  and the printer. The IPDS data stream may be built dynamically at presentation time, e.g., on-the-fly in real time. Thus, the IPDS data stream is provided according to a device-dependent bi-directional command/data stream. 
         [0020]    According to one embodiment, control unit  130  process and renders objects received from print server and provides sheet maps for printing to print engine  160 . In such an embodiment, control unit  130  includes a multitude (e.g., ten) of compute node machines, with each node having two or more parallel page output handlers (POH&#39;s). In one embodiment, each POH includes a separate transform that processes received objects. In such an embodiment, the transforms process image objects. However, in other embodiments, the transforms may process any type of data object received at control unit  130 . 
         [0021]      FIG. 2  illustrates one embodiment of a control unit  130  including compute nodes  200   a - 200   n.  As shown in  FIG. 2 , node  200   a  includes transform engines (transforms)  210   a   1 - 210   an,  while node  200   n  includes transforms  210   n   1 - 210   nn . In one embodiment, each transform  210  includes an associated memory database (or local cache)  220  that caches image objects that a corresponding transform  210  encounters more than once. 
         [0022]      FIG. 3  illustrates another embodiment of compute node  200  showing a single transform engine  210  and local cache  220 . According to one embodiment, each object received at control unit  130  is tagged with a unique identifier (UID). In one embodiment, the UID is a Message-Digest algorithm 5 (MD5) encryption based on processing parameters, data length and a data MD5 hash. In addition to the UID, each object includes control information and data. 
         [0023]    In one embodiment, the control information is relatively small (e.g., less than 200 bytes) and describes the object&#39;s dimensions and placement. Since the control information is relatively small, the control information and UID for an object is stored in the local cache  220  associated with the transform  210  that processed the object. Meanwhile, the object data is stored at a disk database  250  since the data is typically large. Disk database  250  is central to each of the transforms  210  at node  200 , and thus stores data for objects processed by all of the transforms  210 . 
         [0024]    As discussed above, available memory at control unit  130  to generate object UIDs may be limited. Particularly, memory resources may be insufficient to store the entire content of an image while generating a UID. According to one embodiment, transforms  210  generate UID signatures by recursively generating signatures created based on partial image content until the entire image has been received, at which point the last signature generated is the UID used to identify the image. 
         [0025]      FIG. 4  is a flow diagram illustrating the operation of a transform  210  for generating a UID upon an object being received. At processing block  410 , the signature is initialized to some initial value. At processing block  420 , bytes of data are read from the image input data stream into local cache  220 . According to one embodiment, transform  210  reads in an amount of data in bytes equivalent to the local cache  220  size minus the signature size (e.g., 100 bytes), or until the end of the image is reached. 
         [0026]    At processing block  430 , the current signature value is appended to the data read in processing block  420  (e.g., the initial signature value for the first read data) to create modified image data. At processing block  440 , a new signature is generated based on the modified image data in local cache  220 . At processing block  450 , the new signature value, which replaces the current signature (e.g., the initial signature value), is stored. 
         [0027]    In one embodiment, transform  210  may begin serially processing the image as the image is received. In such an embodiment, transform  210  is provided the originally received image data (e.g., not the modified image data). In a further embodiment, the output from transform  210  may be referenced by the signature created based on the modified image data. Alternatively, transform  210  may be provided the actual number of bytes read into cache  220  (e.g., data in cache  220  without the signature). 
         [0028]    At decision block  460 , it is determined whether there is additional bytes of data in the data stream that is to be processed. If so, control is returned to processing blocks  420 - 450 , where subsequent bytes of the image input data stream are read into cache  220 , the current signature value (e.g., value calculated in the previous iteration) is appended to the read data to create modified image data and a new signature is generated the current signature value is appended to the data read and stored. If the end of the data stream has been reached, the signature generated in processing block  440  is used as the UID to identify the image, processing block  470 . 
         [0029]    Embodiments of the invention may include various steps as set forth above. The steps may be embodied in machine-executable instructions. The instructions can be used to cause a general-purpose or special-purpose processor to perform certain steps. Alternatively, these steps may be performed by specific hardware components that contain hardwired logic for performing the steps, or by any combination of programmed computer components and custom hardware components. 
         [0030]    Elements of the present invention may also be provided as a machine-readable medium for storing the machine-executable instructions. The machine-readable medium may include, but is not limited to, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards, propagation media or other type of media/machine-readable medium suitable for storing electronic instructions. For example, the present invention may be downloaded as a computer program which may be transferred from a remote computer (e.g., a server) to a requesting computer (e.g., a client) by way of data signals embodied in a carrier wave or other propagation medium via a communication link (e.g., a modem or network connection). 
         [0031]    Throughout the foregoing description, for the purposes of explanation, numerous specific details were set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that the invention may be practiced without some of these specific details. Accordingly, the scope and spirit of the invention should be judged in terms of the claims which follow.