a quick & simple guide to file formats

why should I care about file formats? If you've ever worked on an image for your website, blog, or printed materials, you've probably found yourself confronted with multiple acronyms when it came time to save the file. Staring at the options, you may have wondered if it really makes a difference whether the file is saved as a JPEG, a TIFF, an EPS, or other format, as long as it looks good on screen. There seems to be a lot of talk about file formats. Many different kinds of formats are available and we use them to the extent that confuses and bewilders even computer analysts. There are lots of them out there. But what do they mean? What are they used for? When to use what format? Why should you care what format your files are in?

What is a file format? A file format is the layout of a file in terms of how the data within the file is organised. Different file types are best suited to different uses. And just because a certain format works well for online graphics doesn't always mean it is ideal for print jobs - several interdependent technical considerations have to be looked at, including quality; flexibility; efficiency of computation, storage, or transmission; and support by existing programs. Functionality is key to any file/data format.

How do you identify a file format? The way to identify the file type is by looking at its extension, typically expressed as a dot followed by 2 to 4 letters. Most files will be either text, graphic, photo, audio or video files. In order to save space, most files on the net are compressed in one way or another. The most common compressed files are those with extensions like .ZIP, .SIT and .TAR. These extensions represent popular compression formats for the PC, Macintosh, and UNIX respectively.

Web pages require JPG or GIF or PNG image types, because that is all that browsers can show. On the web, JPG is the best choice (smallest file) for photo images, and GIF is most common for graphic images. JPG files are very small files for continuous tone photo images, but JPG is poor for graphics. JPG requires 24 bit color (graphics are normally not 24 bit color), and the JPG artifacts are most noticeable in the hard edges of graphics or text. GIF files (and other indexed color files) are good for graphics, but are poor for photos (too few colors possible). Both these graphics formats are platform-independent, which means you can view them on a PC, Mac or UNIX computer provided you have a viewer for them. Formats like TIF and PNG can be either way, 24 bit or indexed color - these file types have different internal modes to accommodate either type optimally.

Graphic images are normally not continuous tone (gradients are possible in graphics, but are not seen very often). Graphics are drawings, not photos, and they use relatively few colors, perhaps less than 16 colors in the entire image. In a color graphic cartoon, the entire sky will be only one shade of blue where a photo might have dozens of shades.

Photo images have continuous tones, meaning that adjacent pixels often have very similar colors, for example, a blue sky might have many shades of blue in it. Normally this is 24 bit RGB color, or 8 bit grayscale, and a typical color photo may contain perhaps 100,000 colors, out of the possible set of 16 million colors in 24 bit RGB color.

For video, popular extensions are .AVI and .RAM for the PC, .MPG (short for MPEG), which is platform-independent, but requires its own media player, and .MOV and .QT for QuickTime movies. QuickTime was initially developed by Apple just for the Macintosh, but now plays on Windows and UNIX, too.

Popular audio file formats include .MP3 for both Mac and PC and .WMA for the PC. Other file formats include .AIFF for Mac; .AU for Mac and UNIX; .WAV for the PC; and .RA for Real Audio, a proprietary system for delivering and playing streaming audio on the Web.

Here is a quick overview of the most common file formats, what they are typically used for and which applications you will need to open or edit them.

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