Hi Steve, If this is true then I ask to what extent it matters. Transparencies are rendered to pixels at one stage or another in all print workflows and there is no right or wrong appearance for spot color gradients except for closed-loop systems with arbitrary reference. As for the solids, even Pantone changes the CIElab values on occasion. I have encountered problems with all four formats. Using Photoshop as a RIP may render differently than a dedicated RIP sometimes but its equal opportunity for better or worse. We RIP 1000+ pages per day for offset printing and rendering errors are very rare (none, one or two a month that we are aware of). PDFs can process dynamically due to output intents, page boxes, xmp data and so forth which can make the requirements for a workflow or RIP configuration less clear. I find with problems files that the designer isn't even able to rasterize a page to their own liking; I call these bad files because they must be reworked to render correctly regardless of downstream workflow. My gripe with PDFs happens when viewing, or Ripping to screen. 1. Line widths that should be displayed less than 1 monitor pixel width are displayed no less than the size of a monitor pixel for obvious reasons. Acrobat has to decide to show or not show the object. Unfortunately 0.00 mm width lines are displayed too. 2. Page display preferences can (a) make outlined fonts look unrealistically chunky and (b) show white lines that will not exist in print. 3. The default rendering intent for cmyk to monitor RGB is relative colorimetric and it is not intuitive for clients to "simulate paper" to see dynamic range realistically. 4. Multi-page mixed stock/surface PDFs can only have one output intent rather than let this happen on a page level basis. 5. Overprint preview is not forced in non pdf/x files and even then can be over-ridden in preferences. These types of things will entitle customers to say something was or was not in the proof that was not matched in print. Toggling Page Display preferences is necessary to see some documents correctly. No single setting works for all PDFs. Considering this I still would not suggest against ripping PDFs to screen. Dedicated pixel formats can be misleading too. Matt Louis On 8/24/12 8:27 AM, "Steve Miller" <SLMiller@norwood.com> wrote:
I've been doing some research with PDF files and RIPs. We want to have a PDF only workflow and one RIP vender is saying we should not use PDF files. Instead, they recommend .eps, .tif or .jpg. Here's a reply from one RIP vender.
"The pdf print engine is implemented as a base feature in the" (enter any vender name here) " RIP programs. It has advanced handling of pdf and pdfx file formats. It was necessary for" (enter any vender name here) "to add this feature due to Adobe's constant alteration of the pdf encoding process and handling of transparencies, spot color handling in gradients, and compression methods. There is a basic flaw in the conversion of spot color in the pdf format to the rastered ink dots of an inkjet printer. This is a problem that all RIPs have.. It is a problem inherent in the pdf format being rendered into the inkjet dot format. The repeat printability of colors suffers in this format. While Adobe also alters the EPS format, color consistency from print to print is stable."
Is this a true statement?
-- Steve Miller Color Management Specialist