An exploration of the intricacies of different image types and output options.
By Jared Smith
The most common vector graphic file types include EPS (Encapsulated PostScript, .eps), PDF, Adobe Illustrator (.ai), and CorelDraw (.cdr) files. These files work incredibly different than raster files. With vector files, information on each pixel is not stored; rather it contains the “instructions” needed to draw an image, such as points with x and y coordinates, the paths between those points, and the color of all pixels contained by the perimeter of a shape. Since the file contains the original instructions needed to redraw the image, it can be redrawn at any size as brand new with zero resolution loss. Not only is the image perfect each time it is redrawn, the information needed to rebuild this image at any size is considerably smaller than most raster files at the same scale.
There are literally hundreds of image-file types. Luckily, knowing the entire list of file types is not required to get good looking prints out of your presses.
EPS errors, live fonts, and color spaces
Now that we’ve discussed the difference between raster and vector, it’s important to look at how those differences can determine your final output.
Vector images can be affected in a few common ways. An issue that we see at our company from time to time is something we have nicknamed “an EPS error.” This basically refers to image output that has mysteriously omitted a point, a path, or an entire element, such as a shape or even a letter of a word. It would appear that a piece of the instructions has somehow been lost or corrupted when saving, transferring, or RIP’ing the file. Although it only happens to us a few times a year, we’ve noted that it seems to occur more often when a proprietary file type has been converted to another proprietary file type (such as .cdr to .ai), or when the file has an excessive number of points and paths, such as crazy patterns of multiple overlays. We also have seen this occur where a gradient and a transparency effect overlap.
Making sure our RIP software is updated to the latest version has helped keep EPS errors to a minimum.