I have noticed a lot of confusion lately about what the different image file types are, and how they are used. This week, I’d like to use my blog posts to talk briefly about what you need to know when dealing with files.
An EPS will be a commonly requested file when a designer is dealing with your logo. An eps stands for “Encapsulated PostScript” and usually (though not always) is referring to something that is vector, and drawn in illustrator. An eps is important because vector files can be scaled infinitely without losing quality. They also can be isolated, with no background.
JPEG stands for Joint Photographic Expert Group. A JPEG (or JPG) is best used for full color, pixel-based imagery, like a photograph. Most JPEGs have a solid background and are not isolated.
GIF (controversially pronounces jif) stands for Graphics Interchange Format. GIFs are best used for images with solid color blocks (not photographs). GIFs are useful for online, as they can be compressed without losing quality.
PNG stands for Portable Network Graphics. PNGs have become a preferred format to a GIF for the web. PNG files can only be saved in an RGB color space. This means that they support screen color, but not the CMYK of print. PNGs should not be used in print documents.
AI, INDD, and PSD
Though they are file types and not image types, I feel compelled to include AI (Adobe Illustrator), INDD (Adobe In Design Document), and PSD (Photoshop Document) in the files list, in case you should ever run across them. These are files that open in the three Adobe programs. Though any PSD is compatible with any version of Photoshop, AI and INDD files are not backwards compatible. This means that if you have InDesign CS4, and someone sends you a file from CS6, you will not be able to open this. You can ask them to save the file backwards, however. In InDesign, you should ask for them to save it as an IDML file. In Illustrator, you can simply save back to the appropriate version via a menu.
I hope this helps clarify some of the basic file formats used in print and web design.