High Speed Page Matching

In a print production system, the ability to associate each page with its original electronic form enables a number of important automation services, such as alternate-source page insertion, page/sheet routing and aspects of JDF-compliance. This work demonstrates the efficacy of a method capable of matching a scanned version of an incoming page to an original RIP, and was tested with a library of a thousand sample commercial pages. Frequency domain analysis suggests that low-resolution representations of pages can be used for matching purposes. This notion is corroborated by experimental results; a 98% correct matching is achieved for pages reduced to a bit-depth of 1-bit at only 1 dpi using a simple XOR method, and a perfect matching rate was achieved using pages represented at 16 dpi at a variety of bit depths using a sum of squared errors measurement. The method is implemented without placing any extra ink on each page. Introduction This paper focuses on the following question: is there an efficient method to uniquely identify each page (or sheet) on a device in a print production system? This work is motivated by the fact that the ability to associate physical media with original electronic documents addresses both present-day as well as forward-looking problems. For instance, it can be used to implement aspects of JDF compliance. It also could have a key role in distributed printing factory environments, which require high speed page identification for routing. The XML-based Job Definition Format standard (JDF) is meant to simplify the life cycle of a print job by acting as a selfdirected electronic job jacket defining all steps in the workflow. The processing instructions associated with each job (a “ticket”), the signal to begin processing, and the signal indicating processing is complete are all specified by JDF and an associated messaging format. If a compliant device is multiplexing between dynamically assigned jobs, there must be some mechanism to determine when each of these jobs is complete in order to implement JDF compliance; the work in this paper provides such a mechanism. Lin [1] (at this conference) proposes the idea of modeling the flow of pages in a print production environment after that of the flow of packets in a network. Figure 1 shows an example of this distributed model. Finishers include mechanisms such as page coating devices, page trimmers and binding machines, and are connected via logical “Routers”, depicted in yellow in the figure. Such devices do not currently exist, yet have several well-defined specifications. In order to determine how to direct a page in an automated fashion, each one must be able to associate each physical document to a page in a specific job, and therefore must include some physical mechanism to sense each page. Once this connection is established, well-understood network optimization tools can help to complete each print job efficiently, such that device utilization across multiple parallel jobs is maximized. This paper is organized as follows. First, previous approaches to the matching problem are summarized. Next, frequency domain analysis is applied to data typical of that used to perform matching, to help determine how high speed solutions may be constructed. An algorithm is then presented based on these results. Experimental measurements and discussion conclude the paper. The Page Matching Problem A number of different methods are available to track physical documents. One approach popular in commerce is to include overt marks, such as bar codes, for identification. A drawback of this approach in print production is that the markings must be removed from the page. This issue can be addressed by placing the marks on the area to be trimmed and adding a cutting stage into the workflow. Along with the disadvantages of extra ink on the page and possible extra cutting, page tracking is disabled after the trim stage with this approach. The goal, however, is to use a method to identify pages based on the content of the pages themselves without adding any additional marks. The problem is thus one of matching a captured (scanned) version of the page against a rasterized version (RIP) of the source.