Working With EPS Files in QuarkXPress™ and Photoshop

Part One

I've received a few emails about EPS files and decided to publish this tutorial to clear up any confusion that may arise when using them in QuarkXPress or Photoshop. EPS files are PostScript® and the letters "EPS" stand for "encapsulated PostScript". There is some basic data about EPS files in the tutorial found here in the "Read Me First" section of the site. This tutorial details some of the aspects of using EPS files in QuarkXPress or Adobe® Illustrator®. Adobe Photoshop5.5 was used to create the example EPS files.

This tutorial covers two points of particular interest:

a.) Why EPS images sometimes appear jagged onscreen and when printing them out.
b.) An EPS file saved with a clipping path is supposed to make the background appear transparent (more on clipping paths here). This tutorial covers why after making an EPS image with a clipping path, the background sometimes appears white when placed in a page layout program.

1. For this tutorial we will need to make two simple EPS files. Start by opening an image in Photoshop, then create a path to knock out the background (more on creating paths in Photoshop here). The image used here is called "CD.psd" and is found in the Training:Tour folder on the Photoshop CD. Give the new path a name. The deafult name Photoshop assigns to the new path is "Path 1".

2. Next, assign "Path 1" to be the clipping path. First make sure the path is selected then click the small triangle in the upper right corner of the Paths palette to access the Paths palette menu. Choose "Clipping Path" from the menu.

3. In the "Clipping Path" dialog, click the drop-down menu and select "Path 1". Click "OK" when done.

4. Next, click File > Save a Copy. In the dialog choose "Photoshop EPS" from the Format drop-down. Give the file a name (in this case name the file "CD.eps") and click the "Save" button.

5. The next dialog gives you some choices. The only two things we're interested in here are the preview image and the encoding. A preview image is a low resolution bitmap image which is saved with the EPS data. It can be either TIFF or PICT format. This example is on a Macintosh® so we will choose "Macintosh (8 bits per pixel)" (although TIFF would work equally well on the Mac®). The "Macintosh" choices use the PICT image format. A preview image allows you to see the EPS file onscreen for programs that don't render onscreen graphics using PostScript. It also allows the printing of a low resolution proof of the EPS file to a non-PostScript printer.

Next choose "ASCII" for the encoding. In this exercise we will open the EPS file in a text editor. Choosing "Binary" makes a more compact file.

6. Repeat steps 4 and 5 and save another EPS file, this time choosing "None" for the preview. Name this one "CD no preview.eps".

Part Two 7. Next, open QuarkXPress and create a new document. Make a new picture box with the Rectangle Picture Box tool (more here on how to do this). Load the "CD.eps" image into the picture box by clicking File > Get Picture. You should see a low resolution preview of the EPS file in the document. Save this document as "cd.qxd".   Note: When you load an image into a picture box in a QuarkXPress document, Quark™ will create its own low resolution preview image from the preview image saved in the EPS file. It creates all it's image previews using the CMYK color model even though the original images use the RGB or Grayscale color models. More here on color models. If the image files are missing at output time, Quark will print using these internal preview images. You will get one plate each for Cyan, Magenta, Yellow and Black by default when printing out a color separated job even though you may be doing a one color or two color spot job. More here on process color vs. spot color. 8. Create another new QuarkXPress document and make a rectangular picture box as before only this time load the "CD no preview.eps" image into the picture box. Save this document as "cd no preview.qxd". Your screen should look something like the one below left. Notice that without the screen preview, Quark merely reports that this is a PostScript® picture. But also note the shape of the gray area. This indicates that Quark recognizes the clipping path. The reason you do not see the image is because QuarkXPress does not use PostScript to render images onscreen. Now if you were to load this same EPS file into an Adobe® product like Illustrator®, you can see the image (below right). This is because Adobe uses PostScript to render images onscreen and does not need a preview image for you to see it. 9. Now let's do something different. Open the CD.eps file into a text editor to view the PostScript code. This is why we saved the EPS file using ASCII encoding. You couldn't do this if it was saved as a binary file. The image below shows a close up of the code. 10. EPS files are PostScript. They can be encoded as straight ASCII as in this example or they can be encoded in a more compact form such as binary or JPEG. The important point to remember here is that where you save the EPS with a preview there are two separate images in the PostScript code. When you look at a jagged image onscreen or in print, you are most likely looking at the low resolution preview, not the actual high resolution image.

Part Three

11. When you print out the document, you must use a PostScript® printer for the image to output at full resolution. This is because EPS is PostScript and requires a PostScript printer.

12. If you don't use a PostScript printer then the preview image will be used instead. A non-PostScript printer will be able to interpret the preview PICT or TIFF image but will not be able to interpret the PostScript code of the high resolution image so the low resolution preview image gets substituted. This explains why images appear jagged when output on a non-PostScript printer.

13. If you were to print out the document with no preview using a non-PostScript printer, then all you'll get is a gray patch with a black stripe.

14. The current version of QuarkXPress automatically detects embedded clipping paths and will display EPS images with transparent backgrounds (more here). QuarkXPress version 3.x and earlier handled EPS files with clipping paths differently. In the Windows® version, EPS files use the TIFF format for the preview image. The TIFF format doesn't support transparency but the PICT format on the Macintosh® does. This explains why in earlier versions of QuarkXPress on the PC the background of an EPS file appears white.