IFX Mail Archive: IFX> PDF/is structuring - for 3/21 confere

IFX Mail Archive: IFX> PDF/is structuring - for 3/21 confere

IFX> PDF/is structuring - for 3/21 conference call

From: Buckley, Robert R (RBuckley@crt.xerox.com)
Date: Fri Mar 21 2003 - 12:12:15 EST

  • Next message: Rick Seeler: "RE: IFX> PDF/is structuring - for 3/21 conference call"

     
    What I am wondering is how religious we have to be about the ordering of the
    objects needed to image a page. Right now, PDF/is Ver. 0.5 proposes the
    following layout for page objects:
     
    Page Object
    Content Stream, Image Mask, Image Object %repeated as many times as
    necessary
                                                                            %one
    content stream per image or image-mask pair
    Resource Dictionary
     
    If the number of images or image-mask pairs on the page is not known in
    advance, then the Page Object cannot be definitively written until the page
    is completely processed since the number of content streams is not known at
    the time the writer encounters the Page Object. If there is only one content
    stream for the entire page, then the Page Object is known before any page
    processing has occurred, but the single content stream is not known until
    the page is completely processed. So place the content stream in the file
    after the all the images and image-mask pairs.
     
    Page Object
    Image Mask, Image Object %repeated as many times as necessary
    Content Stream
    Resource Dictionary
     
    A writer could assemble all this in memory before writing out the objects
    for the page-in that case, any ordering of objects is possible. The only
    certain constraint is that all the objects needed to image a page come
    together in the file. Even then there is no requirement that the Page Object
    be first. So the following is also plausible.
     
    Content Stream
    Image Mask, Image Object %repeated as many times as necessary
    Resource Dictionary
    Page Object
     
    I know Ver. 0.5 has conformance rules, but I believe it is based on
    assumptions about the writer and reader (and the supporting libraries) that
    need to be made more explicit. For example, a reader could accumulate all
    the objects in the file and then image the page when it encountered a Page
    Object. Or it could be set up to image the objects in the order they are
    encountered, but there is no guarantee that the image objects can even be in
    that order so that a page buffer is required.
                                                               
    Somewhere in here also is how the association is made between the content
    stream elements and the objects to which they apply. For example, when the
    content stream says "/Obj1 Do" how does it know which is Obj1? Is there a
    Name entry in the image object, or is it via the Resource Dictionary?
     
    There has been e-mail on some of these points before, but I would like to
    collect all the points in a single discussion at today's meeting.
     
    Rob

     
     
     
     



    This archive was generated by hypermail 2b29 : Fri Mar 21 2003 - 12:12:27 EST