[gs-devel] PDF-A

James H.Cloos Jr. cloos at jhcloos.com
Mon Nov 3 00:02:52 PST 2003


>>>>> "Leonard" == Leonard Rosenthol <leonardr at lazerware.com> writes:

Leonard> And I don't believe it's really a "consumer can't
Leonard> support", but a "a PDF/IS file shouldn't contain".  A
Leonard> consumer can support more than provided for in the spec (so
Leonard> that you could have a single PDF consumer that handles all
Leonard> variants) - UNLESS it is a validating consumer.

Now that is more like how I'd like to see it worded, but the wording
in the spec doesn't say that to me, in part because it specifies both
what a producer must, may, should, must not and should not do, as
well as the same for a consumer.  It makes it look like you have to
forget everything extra if the PDF/is dict is present.

Of course for the ippfax *protocol*, given that it is intended for
publicly available servers (al la pots fax machines), limiting what
is supported by consumers is a good thing for security reasons.  But
I think they should put those limitations in the ifx spec, rather
than the pdf/is spec.  

>> The current draft only supports CCITTFax, JBIG2, and DCT images.
>> Flate can be supported, but not for image data.

Leonard> That makes no sense!  What do they envision screen
Leonard> shots (for example) being encoding in???

I don't think the reasoning was ever posted on the mailing list, and
as I'm not an IEEE member I never tried to participate in ifx's
weekly teleconferences.  

It looks like DCT is the only choice for colour and grayscale images
based on what filters are supported.  OTOH the spec talks about
indexed colour profiles as an alternative to ICC sRGB....

Leonard> That [no grayscale] would blow up the size of the document if
Leonard> grayscale images had to be converted to sRGB (with
Leonard> appropriate profile, I suspect).

The icc profile might not need to be embeded except by name, but IIRC
compression is presumed to cover the size increase.

The spec originally included grayscale support, but then they decided
to add colour profiles and then the patent issues hit the radar.

Another silly issue is that the draft specifies that all pdf/is files
must have a dpi between 300 and 1200.  Ie one cannot convert a
standard or fine fax file into valid pdf/is w/o first scaling it up
to 300+ dpi and a 1:1 aspect ratio....

But enough rambling....

-JimC




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