Why “refrying” a PDF is evil!
I got into a discussion/argument today in an online forum about the process of conversion of PDF->PS->PDF to help “clean up” PDF files. This process, called refrying is one that used to be quite popular - but since Acrobat 5.0 has been frowned upon by Adobe and others.The reason for this process being avoided is due to the wide variety of PDF features that can NOT be represented in Postscript. Remember that the last update to Postscript (Level 3) was in 1997, while PDF has undergone 3 revisions (1.4, 1.5 & 1.6) since then - with 1.7 coming shortly with the release of Acrobat 8.
Here are a list of things that you might use in the content of a PDF that don’t translate well to PostScript
- Transparency
- ICC-based colors
- 16bit color
- JBIG2 compression
- JPEG2000 compression
- Layers (Optional Content Groups)
Also consider that any additional information added to PDFs during a PDF-based workflow (such as from Creo, Agfa, Quite, etc.) will be removed during the PDF->PS downgrading…
Of course, there is also the myriad of non-content elements that can be found in a PDF that don’t translate to Postscript/print, such as
- Hyperlinks
- Annotations, Commenting and Markup
- Forms
- Multimedia (movies, sounds, etc.)
- Bookmarks
- Metadata
- and more….
There are also concerns regarding fonts & text “searchability” that can be introduced into the refrying process DEPENDING on how the operation proceeds. Differenet PDF->PS conversion tools, different OS platforms and even simply ‘printing to PS’ will produce wildly different Postscript output for the same PDF - thus producing wildly different output PDFs.
So in conclusion…
May 10th, 2007 at 5:01 am
Surely the concept of ‘refrying’ a PDF is to eliminate those aspects of a PDF that are either troublesome or irrelevant in prepress - in other words to simplify it.
Given that notion, out of the 12 examples given above of what doesn’t translate to PS, none of them are absolutely necessary to constitute a press-ready PDF, in fact some of them are frowned upon.
Where transparency is concerned, the advent of the APPE means that transparency is not the sticking point it once was, but some would still prefer to flatten it first.
Personally I prefer not to refry a PDF but rather to ‘optimise’ it using tools that are built for the task but I don’t think refrying is as flawed as is stated here.
May 22nd, 2007 at 6:38 am
So what do you do, when you have a huge publishing company with an Ad Production dept. We have ads suppplied from the client as PDF’s, now to put these on pages you have to place the PDF ads into the page and guess what Re-PDF. Now this is what every publishing house is doing so basically in my eyes refrying is not an option, it the only way.
May 22nd, 2007 at 7:11 am
I never said that Re-PDFing was a problem…PROVIDED you use a program like Adobe InDesign that is able to do so w/o going through Postscript.
Again, the problem isn’t doing PDF->PDF conversions, it’s bringing a MUCH lower denominator into the picture - aka Postscript.
Leonard
May 22nd, 2007 at 7:14 am
Colin - we are in agreement that there are indeed times when you wish to simply a PDF…that’s the whole purpose of standards such as PDF/X.
However, it is the WAY IN WHICH you go about doing the simpliification. Using tools that operate on PDF natively - such as the Preflight feature of Adobe Acrobat - is an excellent choice, for example. It’s the DOWNGRADING of the PDF language through Postscript that is problematic.
June 29th, 2007 at 2:22 pm
Although I agree with non-refrying, the workflow designed by my superiors includes refrying. The colour profiles in additional metadata are dumped and that doesn’t help. When I try and import/view metadata post process, I can’t differentiate the colour from the black and white pages. I wonder if there is a workaround.
September 28th, 2008 at 6:06 pm
mirc indir