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From Jeremias Maerki <dev.jerem...@greenmail.ch>
Subject Re: JPEG images in Postscript
Date Fri, 04 Jul 2003 17:24:47 GMT
Moving to fop-dev because it gets technical...

After a lot of searching I think I know what's wrong. It's not the
ASCII-85 filter behaving wrong. Chris' JPEG images contain trailing
zero's after the FFD9 (EOI, end of image marker) which fill the images
up to 16384 bytes. Now, I guess the error happens because the DCTDecode
filter stops working after encountering the EOI marker. Because there is
still some data unprocessed and because of the way images are currently
written to PostScript this leads to an error.

I'm currently figuring out how best to solve this. I'm looking at the
code from jpeg2ps which doesn't seem to have a problem with these JPEG
files. The code in there is made to ignore any trailing bytes but
processes the whole stream twice if I interpret correctly. Maybe looking
for the EOI marker in our code and cutting off there is better
performance-wise. But jpeg2ps' code is on the safe side in any case.
Preferences anyone?

On 01.07.2003 17:59:52 Jeremias Maerki wrote:
> Correction: I've just dropped my current ASCII85OutputStream in the
> maintenance branch but the bug persists. There's must be another one.
> Will investigate.
> 
> On 01.07.2003 17:18:20 Jeremias Maerki wrote:
> > Almost suspected it....I believe it's a bug in the ASCII-85 encoder
> > which I've fixed in the redesign but haven't been able to upload, yet.
> > I'll be able to fix the bug for the maintenance branch later this week.


Jeremias Maerki


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