What program are you using to view the PDF?
Adobe Luddite wrote:
I really do fumble my way around the Adobe suite so please be basic (and patient :-) ) in your answer.
No worries: so far, you did everything perfectly right:
* compare the effect on different input file formats
* rule out the possibility the lines are actually in those images
* rule out intended or unintended markings in the InDesign file itself
* check whether it persists in print or is screen only
* check if it's related to the screen zoom percentage.
As Matlock likes to say, when you rule out all logical causes, only the illogical remain. Unfortunately this is one of them: The lines are an artefact of the way Acrobat displays PDF files.
All items in a PDF are drawn on screen using different optimized routines (e.g., a JPEG is drawn by an dedicated JPEG decompression routine, where a simple bitmap such as a GIF image gets copied as it is; the same goes for 'text' versus 'line drawing'). Also, every drawable item may be clipped (masked). On top of that comes a translation of the 'real world coordinates' in the PDF to your screen, in a certain resolution, at a certain position inside a window, at a specific zoom level.
Every single step in the entire process is subject to some mathematical rounding, and those errors slowly but surely add up. When translated "to screen", the error may round up to one pixel -- but not more than that. That is why you see no border or only a single pixel one, regardless of your zoom level. The exact same thing may actually happen when printing, but on a 600 dpi full color laser printer (a medium low end full color output device) a single pixel measures 1/600th of an inch, or less than 1/20th of a millimeter -- too thin to see.
Acrobat offers some "Advanced" screen settings in its Preferences dialog, and sometimes it helps to enable or disable items in the category "Page Display" under "Rendering" (e.g., "Smooth text / lines / images", "Enhance thin lines"). If that works for you: remember, these display settings are for your personal computer only, and will not be saved along with your PDF document, so other people may still see these screen artefacts.
I've tried Acrobat 8 Prof, X Pro and Reader X. All give the same result on 2 different computers.
Thankyou for your detailed reply Jongware. I appreciate you taking the time.
I've now tried on 2 computers with 3 different Acrobat versions and still get the same result.
I did export it as EPS but illustrator fails when I try to Export to PDF. Same with Photoshop.
Very annoying as I really wanted to email this to people rather than sending it snail mail. I'll carry on trying to import / Export into a few more pieces of software and see if I can't come across some combination that solves the issue. I'm currently using CS6 so I may get it back down into CS3 and see what happens then.
Don't use EPS anymore! From Illustrator save as AI and from Photoshop save as PSD or PDF.
Don't use GIF for InDesign. Use PDF, PSD or AI instead.
Don't use print for creating a PDF, only save as from Ai or Ps, and export from InDesign.