There are so many different file types out there it can be confusing when you have to choose how to export your images! This is a quick primer on four (well, five) different file formats: three for the web – JPG, GIF and PNG – and two for print – TIFF and EPS.
JPG vs. GIF – For the Web
JPG is an abbreviation for Joint Photographic Experts Group, the committee that created this file type. It is best used for photographs or images that have gradients. JPGs do not support transparency and cannot be animated.
GIF is a proprietary file format from CompuServe. It is used in web graphics and is best for images that are made of solid colors, like logos. The GIF format only supports 256 colors in a single image, so while it is considered a lossless format (meaning they do not suffer compression artifacts), they do not look good for photographs.
GIFs support transparency (however, pixels are either transparent or opaque, nothing in between) and they can be animated. I didn’t animate the one to the right because it is distracting. Animated GIFs are quite effective to show before and after pictures, so long as they are relatively small.
Oh yeah, and we can’t forget PNG (PNG-24). Portable Network Graphics are the ideal web graphic file types. They are completely lossless and they support alpha transparency (a pixel can have a percentage of opacity, unlike GIF transparency). PNG-8, however, is essentially a GIF. PNG files tend to be larger than JPG and GIF and they are not willingly supported by Internet Explorer 6, but I believe 7 does support it.
Edit: Teppo so kindly pointed out my rather important omission of the fact that it is alpha transparency that IE6 does not support, not the PNG file itself. Thanks Teppo!
TIFF vs. EPS – For Print
TIFF and EPS files are used for print. Unfortunately in this web-based environment, I can’t truly show you a TIFF or an EPS.
TIFF is Tagged Image File Format and it is used for bitmapped images. Bitmap images are also known as raster images; they are pixel-based as opposed to vector (we’ll get into vector below).
When you export files from Photoshop for inclusion in a layout done in a program like InDesign or Quark, you’ll want to use a TIFF because it is lossless, though there are options to compress it. TIFF supports varying degrees of transparency; pixels do not have to be merely on or off. TIFF files can also have layers.
EPS is a file format used for vector images and it stands for Encapsulated PostScript (not to be confused with ESP: Extra Sensory Perception). Vector files store their data as a series of points on a grid with instructions on how the area between those points is filled in. That is why they are so small and why they are infinitely resizable (Yes, you can even make them larger!).
EPS is a common file format for exporting Illustrator files. It contains a bitmap preview of the image as well as instructions written in the PostScript language (printer speak) that describe how the object is to be printed.
Since TIFF and EPS do not compress their image data, there is no need to discuss which is better. If you are exporting a photo, use TIFF. If you are saving a vector file, use EPS.
Are there image file formats you prefer over these ones I listed? Which ones and, more importantly, why do you like them better?