I created two (2) Illustrator files - one in color and one in black and white - sent it to our usual printer and upon viewing the online proof (presented in PDF format) saw that the b&w image appeared as a negative image. I'm not sure why this would be. It has never happened before. Is there something in their proof?, Or, is it something in my monitor that is causing the "switch"?
It seems as though transformations are occurring at rendering stage. To keep things simple, open your PDFs in Adobe Acrobat 8 Professional and execute the preflight function (Advanced / Preflight). I would use the 'Convert to PDF/X-1a:2001 Only' (and choose a profile) - this will cleanse the PDF as such and remove any device specific data such as transfer curves.
Let us know how you get on ...
All the best,
Jon
I've been using Acrobat since v1.0 and still get amazed by its power. An Acrobat ACE since 1999