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Losing transparency/colours from Publishe

Printed From: www.exp-systems.com
Category: PDF reDirect
Forum Name: Using PDF reDirect
Forum Discription: Questions and Comments on using PDF reDirect Freeware and Pro
URL: http://www.exp-systems.com/Forum_exp/forum_posts.asp?TID=174
Printed Date: 13 May 24 at 6:12PM


Topic: Losing transparency/colours from Publishe
Posted By: shazels
Subject: Losing transparency/colours from Publishe
Date Posted: 21 Feb 06 at 9:21PM
When PDF redirecting from a Publisher file, objects coloured with semi-transparent or faded colours sometimes resort to block colours/the base colour of the faded colour - meaning text or images on top of that background are no longer legible. Using Publisher 2003, Windows XP Pro.  Any thoughts?


Replies:
Posted By: Michel_K17
Date Posted: 21 Feb 06 at 10:34PM
Hi there,

   You have hit one of the limitations of the Postscript format. PDF files are created by using a Postscript printer driver, much as if you were printing to a real "physical" printer. Once the Postscript file is created, it is converted to the PDF file format, which is very similar to the Postscript format, except it is much better at compressing the data.

   Because there is no need for transparency when printing to a physical printer, the postscript format does not support transparencies. The PDF format was the same way up to (stretching my memory here) v1.3 of the specification (Reader v4). It was finally introduced in spec v1.4. However, the Postscript format still does not support transparencies. The only way that I know of creating transparencies in a PDF file is manually, by editing the PDF using a PDF editor that supports transparencies. Alternatively, there might be "PDF Creators" out there that do not use Postscript, and possibly do better than PDF reDirect.

   Postscript does try to "simulate" transparencies by converting your objects into bitmaps, with "holes" in them that let the background material bleed through. Try zooming in on your transparent objects in the PDF to see what happens. You should also find that they print OK to a physical printer, that is, your objects will appear transparent. However, this is a poor simulation, and one that does not work well when viewed on the screen.

   Unfortunately, this problem does limit your options for transparencies because most PDF creators use the Postscript method I described, including Adobe's own Acrobat. Hopefully this limitation will disapear in the future, possibly once support for transparencies is added to the Postscript specification. Your only immediate alternative is to look for alternate "non-postscript" printer drivers that supports transparencies. You could try BlackIce (www.blackice.com) or PDFonline (www.pdfonline.com): neither of these two use Postscript but neither specifically mention transparency support either. I have not tried either products, so I cannot make a recommendation.

   Sorry for rambling on. I hope that helps explain what is going on.

Michel.

Posted By: shazels
Date Posted: 21 Feb 06 at 11:08PM

Thanks Michel, for your extensive explanation!

Strangely, this problem doesn't happen every time - only randomly.  Which is even more confusing. 

Will try your suggestions - thanks a lot.

Shaz :)


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