So how do you manage your projects so you get predictable results? Answer: manage the two different forms of digital assets (raster and vector) so that the color range of your print file fits within the range of your output device. This is sometimes called a CMYK neutral workflow.
Let’s talk a little bit about print files. The basic types of print file are the JPEG, TIFF, EPS (encapsulated postscript) and the PDF aka…Acrobat file. JPEG’s and TIFF’s are strictly for raster/image/photo file types. EPS and PDF/Acrobat files can contain raster and vector art. You may have heard of postscript (PS) files, but it’s used less and less these last few years. Postscript has essentially been replaced by encapsulated postscript (EPS). For the sake of a more compact post, let’s concentrate on the EPS and PDF file types.
There are several structural differences between the two file types. But, the main difference is ICC profile support. The EPS file does not support the inclusion of ICC profile data; Acrobat does. And this is why so many printers and large format service providers use EPS as their preferred print file. What your output provider wants to avoid is a conversion phenomenon akin to double-dipping. Most RIPs look for profile data. When they find it, they will (unless managed by the RIP operator) apply another instance of image compression to the print file to fit the color range of the specified ICC. In other words, your compressed photo gets re-compressed.
ICC’s are not really a perfect model for vector art. Think back to the diagram, InkjetVsSWOP.png in a previous post. If you strictly interpret the 3D lab image for offset printing, you would conclude that a perfect green (100% cyan and 100% yellow) can’t be achieved on an offset press. We’ve all read enough magazines to know you can get bright yellows, reds, greens and rich colors from offset printing. So, what’s going on here?
You’ve probably guessed it. At some point, your output provider is discarding the ICC profile information. And it sounds like heresy after all you’ve heard about the necessity of working with agreed upon profiles for color management. But don’t let your head explode just yet. Let’s get back to image management.
Image management is simply making sure all your elements (text and photos) conform to the range of your final output device. Pick the appropriate workflow and work with the end product in mind.
Here are a few tips for you budding graphic designers:
Consider color conversion a one-way street for your vector art. Your classic light blue (100% cyan) will appear similar when you switch your file to RGB. But, if you were to switch your file back to CMYK the values are transformed to roughly 70% cyan and 14% magenta. We always make my vector art in CMYK. That way, if we have to make an RGB graphic from it we don’t have to worry about missing a corrupted value for print. Also, our web graphics will more closely resemble my print files.
Do NOT convert vector art to an ICC profile. Occasionally, you’ll see this option when “Placing” (linking to an external file) or pasting other art into your current working document. The color values will shift in an unpredictable manner, just think back to what happens to 100% cyan when you change it to RGB and then change it back to CMYK.
Make sure all your scans, photos and Photoshop art share the same profile and color space before assembling your art. We know most applications have a “Convert to Profile” export option. This is not a reliable way to work. When you employ blind processing, you’re asking for an unpleasant surprise. You’re much better off doing the image work yourself.
Use TIFF’s instead of JPEG’s (and ZIP compression when exporting to PDF). Once upon a time, JPEG compression was the recommended way to save images for print due to limits on memory and processing power. One way JPEG compression controls file size is by consolidating color together within a certain range of values. You may have heard of JPEG’s as a lossy (or lousy, if you’re as picky as we are about image quality) form of compression. If you’ve ever wondered where those boxy looking squiggles or blocky halos around text came from in digital art, now you know. In addition, the default compression for saving as a PDF is JPEG. When you pile JPEG compression on top of JPEG compression you’re just asking for an unattractive result. We now have more memory, much more powerful CPU’s, graphics cards and RIP software.
If you want more information on JPEG compression, check out the Wikipedia page: http://en.wikipedia.org/wiki/JPEG
And finally, CYA! Conserve Your Assets! Always keep customer supplied originals, unaltered. The client may ask for them at some point. You may need to compare appearances or justify edits and output with your client standing over your shoulder. CONSERVE YOUR ASSETS; it bears repeating. 🙂
PS: You may have noticed the inclusion of the Light Jet and Durst Lambda under Large Format RGB. Conventional large format inkjet imaging has progressed to the point of photo quality output which can (IMHO) outperform the Durst and Light Jet machines. Also, new archival, acid-free papers and fade-resistant inks are eliminating the advantages of large-format photo output for lifespan.