[softwarelist] Re: Layout sheet

On Tue, 23 Jan 2007 17:04:52 +0000, Ray Dawson wrote:

> Martin Wuerthner <public@xxxxxxxxxxxxxxx> wrote:
> 
> > Sorry, PDF does not have a concept called "layer", nor any specific
> > feature that resembles the idea of a layer.
> 
> You had better take that up with Adobe who advertise the concept of layers
> in Acrobat and their other graphics packages.

That doesn't mean that there's actually a layer representation in the PDF
format that's usable to anything other than these packages. Rather, it
seems that it's possible to support specific types of content with this
capability.

The PDF Refererence (fifth edition), describing PDF version 1.6 has this
to say about aspects of layering which might be what you're referring to:

    "4.10 Optional Content
     Optional content (PDF 1.5) refers to sections of content in a PDF
     document that can be selectively viewed or hidden by document authors or
     consumers. This capability is useful in items such as CAD drawings,
     layered artwork, maps, and multi-language documents."

> Applications which use layers can save them into PDF files where the layers
> can be accessed and manipulated in Acrobat.

Page 485 says:

    "Note: The concept of a transparency group is independent of existing
     notions of group or layer in applications such as Adobe Illustrator®.
     Those groupings reflect logical relationships among objects that are
     meaningful when editing those objects, but they are not part of the
     imaging model."

Page 776 (on page-piece dictionaries):

    "Applications can use this dictionary as a place to store private data in
     connection with that document, page, or form. Such private data can
     convey information meaningful to the application that produces it (such
     as information on object grouping for a graphics editor or the layer
     information used by Adobe Photoshop®) but is typically ignored by
     general-purpose PDF viewer applications."

So, we learn that the PDF specification is rather complex and supports lots
of different types of domain-specific things can be done that aren't widely
supported across different applications and platforms.

> Louie's printer is obviously familiar with the concept of layers in PDF
> files - as any publishing professional would be - and has advised her
> accordingly. 
> 
> It does, however, seem unlikely that a RISC OS graphics application was
> able to save as a layered PDF, and the problem is probably elsewhere - but
> just because a RISC app can't do it doesn't mean that it isn't a facility
> available.
> 
> I would refer you to the Adobe web site for further information about how
> PDF files work and what facilities are available - including layer
> manipulation. It's all there, if you bother to look.

The report of what the printer said sounded pretty vague to me, but I'm not
terribly interested in getting to the bottom of that problem. I only
responded because you used such a condescending tone with Martin.

I suggest you take a look at the PDF Reference and suggest a workaround for
the problem.

David

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