Converting a full color (CMYK) EPS file into a one-color or two-color image can be tricky in Photoshop, but there are a couple ways to do it right. We’ll also show how to lose a white background in order to create transparency.
Jared Young, a marketing writer in Bend, Oregon, writes,
I have a full-color company logo saved as an eps file. I would like to use the logo on merchandise that requires I use one or two colors. How can I turn my full color logo into a mono or duotone image (canâ€™t use gradients)? Also, is it possible to turn the white background into a transparent background on this image?
First of all, you should make absolutely sure this is a bitmap graphic and not a vector graphic. EPS files are often vector graphics created in Illustrator, especially logos like this one. Open your image in Illustrator and zoom in closely (see Figure 1). If the edges are sharp and clear like the detail on the left, then this is a vector image. If it’s pixellated, then it’s a bitmap image. A more accurate test is shown in Figure 2: open the file in Illustrator and choose Select â€“> All (Cmd/Ctrl-A). A vector image will show points along its edge (left detail), marking the vector path, while a bitmap image has no vector paths so selecting it in Illustrator will only show a box around the image (right detail).
Figure 1: The resolution test in Illustrator. Vector on the left, bitmap on the right.
Figure 2: The selection test in Illustrator. Vector on the left, bitmap on the right.
Quick tip: To select every shape with a specific fill or stroke, select one and then use Select â€“> Same â€“> … to select them all.
If your EPS file is made of vectors, then it’s a snap to bring it into Illustrator, select each colored area and make it a spot color. Quick tip: To select every shape with a specific fill or stroke, select one and then use Select â€“> Same â€“> … to select them all. Placing an EPS with spot colors in your page layout application will output spot color plates just fine. And unless there is a white shape below the graphic, there will be no background when the graphic is placed and printed so transparency is no concern. Jared, I’ll bet that if you tried Illustrator you will find your task a lot easier than if you used Photoshop.
BUT MAYBE NOT
What if your EPS file is a bitmap, not a vector? It can happen; there’s lots of designers who unknowingly rasterize EPS files because they don’t understand the difference, and not only does it convert spot colors to full color (CMYK, RGB or another color mode) but it also adds a white background that eliminates transparency. If that’s the case, you will need Photoshop or another bitmap graphics editor. Unfortunately Photoshop isn’t well-suited for spot color work; it’s designed to work with full color modes such as CMYK and RGB, which are additive and subtractive color models. Spot color, on the other hand, presents the color as it is and doesn’t mix colors to create its tonal range. There are three options that come to mind to convert process to spots in this situation:
Add spot channels to a grayscale image. This is the option that I recommend. Convert your image to grayscale, then select all the elements of a particular value range and move them to a new spot channel (created in the Channels palette). You can output this file as an EPS or PDF file and output the plates fine.
Convert to duotone. This option involves converting your image to grayscale with two or three distinct value ranges (black, dark gray and light gray, for example) then converting to duotone and using the Duotone Options dialog box to map spot colors to those three values. For more information on this technique, check out my recent tutorial on creating letterpress effects with duotones.
Add spot channels to a multichannel image. This technique is similar to adding spot channels to a grayscale image, except your color mode will be Multichannel (Image â€“> Mode â€“> Multichannel) and you can output this file in only five possible formats, the most notable one being DCS, a legacy (read: obsolete) format used in years past to bring spot color channels into QuarkXPress and other desktop publishing apps. Unless your workflow requires it, I’d recommend staying away from this one.
Because it’s often a pain to select precisely all the pixels you want to colorize (Color Range helps, but it’s still not perfect) I really recommend getting the file into Illustrator first and hoping it’s a vector graphic.
Transparency in bitmaps has come a long way in the past few years. InDesign has been working with transparent bitmap graphics for several years and QuarkXPress has finally decided to play catch-up. Layered Photoshop files (which can be natively imported into InDesign) are easily given a transparent background by removing its background layer. Transparency will be marked by a checkerboard pattern, which can be altered in color and size in Preferences â€“> Transparency & Gamut…. I prefer small and light cyan squares so they’re more subtle.
If your background layer has bitmap data you need to retain, or if your image is flattened (in Jared’s case this is almost certainly the case) you’ll need to perform some more selections to grab the white background and delete it, revealing the transparency underneath. If your image is flattened (look for the italicized Background layer name and the lock on the layer) double-click the background and convert it to a layer (the lock will disappear and your layer will be renamed “Layer 0″ and unitalicized). Again, it can be tough to grab all the white areas with your selection tools; in the case of Jared’s logo, it’s probably hard-edged so that makes it easier. If you have some white fringe pixels along the edge that you can’t select, consider using some matting options (under the Layer menu) to defringe or remove the white mat.
Jared, I hope this helps you out with your situation. If any readers have other problems that are stumping them, or just questions about some of Photoshop’s features, drop me a line below or e-mail me directly at firstname.lastname@example.org!