The above warning is an important one! If you have used a spot or PMS color in your InDesign, Quark or Illustrator layout and then applied some type of transparency effect — drop shadows, blending modes, feathering, etc — then this warning is telling you that your file will NOT print correctly. Ignoring it can derail your print project bound for offset or digital output. You can avoid this complication with a little understanding of color definitions and conversion.
With the release of InDesign 2.0 back in 2001, Adobe integrated transparency effects directly into its layout program. New tools allowed us to apply editable transparency effects to text, graphics, and images, the result being a greatly enhanced set of design tools. PDF 1.4 debuted in Acrobat 5 at this time as the first version of PDF that supported transparency. The only catch was that most printer’s RIPs at the time were not ready to handle the transparency effects. Havoc ensued. Times have changed since then and Postscript level 3 processors and pdf workflows effectively manage the flattening of transparent files at the correct time to produce accurate output. But the conflict between spot or PMS colors and transparency lives on.
If your InDesign or Illustrator color palette is using nothing but CMYK colors, you can use transparency with no problems. If you bring in, for example, your logo or a piece of art with a predefined PMS or spot color into your layout, then you have imported that color into your palette. In turn, if you apply that to color text or graphics and use a transparency effect on them, a high resolution output from offset or digital printing will result in the object printing as a blank or with an unintended color. To further confuse the matter, the job may print fine off a desktop printer or create a pdf file that appears fine on screen. However, if you ignore the warning (seen above) that Adobe gives you when you try to save the file, your print provider will most likely NOT be able to convert the spot color to process and retain the correct transparency effect. You must convert the spot color to process in your native file and re-export to pdf.
Before being “flattened”, transparency is considered “live” and exists as an optical effect onscreen and in video. It must be flattened in order to print. At this stage, the tranparent region is broken up into smaller non-transparent sections that can then be translated by the RIP (raster image processor) into a printable image. It is, however, a complex process and trouble spots arise from the use of spot colors as discussed above, where text or vector objects overlap pixel-based objects, and possibly with the overlapping of RGB and CMYK images. You can read Adobe’s Designers Guide for Transparency and Print at this link for further reference.
So How Do I Fix My Files?
We’ve updated this blogpost with some tips on best practices and how to avoid the cost, delay and disappointment of files that print in an unacceptable way. Read it here!
Rely on your printer for advice and direction with any questions you have when designing files that use transparency. They should be able to provide you with the time and money saving technical advice, and work with you on file preparation and submission. If they can’t, you have the wrong printer. The best advice, always, is to ASK YOUR PRINTER!