30 Jan
2005
30 Jan
'05
10:22 p.m.
Eric Smith wrote:
I maintain that PDF should not be used merely as a container for existing
graphics files because there is normally no easy free way to extract the image
data and use it in another program. I know that it *can* do it, but the
majority of users who do this screw it up massively (I'm thinking 150 DPI JPGs
of scanned text).
I am familiar with the internals of PDF as well, which is why I wrote portable.
Portable does not imply complete. Perhaps I shouldn't have used the
"*is*"
emphasis...
That is one of
the MISuses of PDF. PDF should not be used as a container
for bitmap images.
Why? What better open-standard file format can store a lot of pages using
lossless bilevel compression? PDF can store the original bitmaps (well-
compresses) together with the OCR results, so that you can have
mostly-searchable files that still look like the original doument. (As
opposed to typical OCR files that are completely screwed up and lose
information.)
And PDF can support a mix of bilevel and greyscale or monochrome in
the same document, or even on the same page. In case it
wasn't obvious, PDF *is* Postscript! It's *portable*
postscript.
Speaking as someone who has written software to read and write both
Postscrpt and PDF, I can tell you in no uncertain terms that PDF is
NOT Postscript. PDF happens to use a subset of the Postscript
imaging model, and has superficially similar syntax in some areas,
but that's about as close as they get. Since PDF can do the same things, there seems to be
little advantage
to using DjVu instead.
DjVu has other advantages, such as local/window/viewport decoding of images
with ludicrously high dimensions/resolutions but I understand your point.
Where are the tools to create DjVu-like PDF files? The best Acrobat can do is
OCR text but still leave the source bitmap in place... If I scan in a page
with a background color image with B&W text foreground, where are the PDF tools
to properly handle layer seperation? (Not CMYK seperation, you know what I
mean :-)
--
Jim Leonard (trixter(a)oldskool.org) http://www.oldskool.org/
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