Question about PDF manipulation

Jules Richardson julesrichardsonuk at yahoo.co.uk
Thu Jun 2 17:20:46 CDT 2005


On Thu, 2005-06-02 at 17:46 -0400, Paul Koning wrote:
> >>>>> "Jules" == Jules Richardson <julesrichardsonuk at yahoo.co.uk> writes:
> 
>  Jules> Looking at the PDF file, I'm not convinced there's any TIFF
>  Jules> data in there to be honest. It looks more like the image is
>  Jules> re-encoded from the input TIFF to PDFs own way of storing
>  Jules> bitmap data - in other words it's not simply a wrapper for a
>  Jules> bunch of TIFF images, but merely a wrapper for bitmap data in
>  Jules> PDF's own format. That's something of a disappointment; I
>  Jules> always thought PDF just encapsulated the input images rather
>  Jules> than re-encoding in any way...
> 
> Makes sense.
> 
> The purpose of PDF is to distribute final form documents, for viewing
> and for printing, including commercial printing. 

Yep - I've just only heard PDF files (in the context of preserving image
scans) described as being a wrapper - which tends to imply that they
preserve the original content, when in fact they're a complete storage
format in their own right.

> The encoding will be lossless, though (at least normally -- I think
> you can tell Distiller to use JPG style compression but sensible
> people know better than that).

Most likely... even TIFF images support lossy JPEG compression these
days, but I've only ever come across one or two files using it.

> For purposes of scanned document archives, that is what you need,
> which is why PDF is fine there.

I don't know though, sometimes it's nice to have a record of what
produced the images making up a collection of scans, which is the sort
of thing often embedded automatically by anything creating a TIFF file
(of course it's useful to know the process applied too in terms of any
colour correction etc.).

I suppose it's akin to a lot of programs that hangle JPEG images from
digital cameras throwing any EXIF data away - it's annoying losing the
info describing when / how an image was created.

Maybe there's an option to turn image recoding off when creating a PDF?
If it can supported embedded movies and the like (I doubt it encodes
those into its own internal format) then I'm surprised it can't embed
image content without manipulating it.

cheers

Jules




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