A lot of people are confused by the different formats in which a document can be saved. Many think that saving a file in the eps format will prevent pixelation (aka, the "jaggies") when it is re-sized. Wanting to be on the safe side they save everything in this format, which can be very efficient for certain types of files and extremely wasteful in all others. Here's the low-down in a quick minute.

A drawing program like Freehand or Illustrator, uses mathematical formulae to describe the shapes you make. These are called vectors. Saving or exporting an eps file from these programs is very efficient because only the numbers are saved. Not until you import the picture and send it to a printer do the mathematics kick in and create all the little dots that are needed to make a picture at high resolution. Even better, if you import one of these pictures and stretch it bigger, the mathematics will include the new dimensions and you will not get the jaggies.

Other programs for painting and photography actually store all the little pieces of color exactly as they will print. These are called rasterized images. The number of the little bits stored is determined by you when you set the resolution for the image. Saving an image like this as an eps will not do anything special but it will make a very big file. That file will use more disk space to store it and more RAM as you work with it. The larger file size will also take longer to print and to transfer to disk. If you import a raster image and stretch it, it will get jaggies whether you save it as an eps file or not.

The reason that Photoshop has an eps saving option is for two special cases: duotone images and images with a clipping path. In the first case, the eps option stores special information about the duotone plates so that they can output correctly. In the case of a path, Photoshop stores the image as it normally does and saves only the path as vector information. Unless you need a duotone or a clipping path, an eps file slows you down and wastes space.

When you save an image from Photoshop, a good universal format to use is the tif option. If you want, it will let you save your channel masks as well. It also has an excellent compression option made specifically for tif files called LZW compression. This will not destroy any information in your file the way that jpg compression does. Even without the compression, the tif file takes up less room on your hard drive than if it were in the eps format.

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