Bit Literacy - Mark Hurst [40]
Image file formats
One of the most popular image formats is JPG, also known as JPEG, with the file extension .jpg and pronounced “jay-peg.” JPG was designed to work with images with many different colors and gradations of color. To minimize the amount of storage space an image requires, JPG compresses information wherever there is a gradual change in color. This makes JPG the best format for photographic images. Indeed, most digital cameras use the JPG format by default, so many users create JPG images without knowing it.
JPG is not a good choice, however, for images that need clear, distinct lines or color differences. Logos, line art, and icons tend to look blurry in JPG due to its compression, but they look much better in the other two common image formats: PNG and GIF.21 PNG is pronounced “ping” or “p-n-g,” and GIF is pronounced like “gift” without the “t”, though some people say “jif.” Unless you’re a Web designer or other creative professional, you’re unlikely to create PNG or GIF images; doing so usually requires an image-editing program. (One exception is the built-in screenshot function on Macintosh computers, which creates PNG images.) What’s important to know is that PNG and GIF create smaller files than JPG for images with clean lines, while JPG creates smaller files than PNG and GIF for photographic images.
The key difference between image formats is file size: the smaller an image file is in a given format, the better, because it takes up less memory and downloads faster for recipients. (Note that this is different from simply resizing an image to different dimensions, akin to framing a smaller version of an original painting. Resizing photos is covered in the “other essentials” chapter.) Stated another way, users should choose the format that requires the fewest bits to communicate the message. Elegance, brevity, simplicity: these are the qualities of a good file format.
Audio file formats
File size is also the key difference in audio. The most popular audio format is MP3 (pronounced “m-p-three”), with the file extension .mp3. An MP3 file is a compressed version of the original audio recording, so its sound isn’t quite as good as a store-bought CD, but the worldwide popularity of MP3 indicates that the quality is good enough for most users. Users choose MP3 because the quality is acceptable and the files download quickly. (Like JPG, in fact, many people use MP3 without knowing it. Most tools for “ripping” and “burning,” for transferring songs from CD to computer and back, use MP3 by default.)
Professionals who need to work with original audio, like composers and editors, often work in other audio formats. Two of these are WAV (.wav), pronounced “wave,” and AIFF (.aiff), pronounced “a-i-f-f”—full-sized, uncompressed file formats for audio. They have better sound quality than MP3—in fact, they can match the quality of a store-bought CD—but they are much bigger, so they’re less practical to share. A three-minute song in AIFF format could take up ten times the space (and hence download time) of an MP3 file containing the same song.
Thus the key criteria of file formats for audio and images are quality and size. Whichever format contains the message, at acceptable quality, in the fewest bits, is the best choice.
There’s one aspect to audio formats, however, that doesn’t exist in image formats: corporate ownership. The music industry, concerned about the easy shareability of MP3 files, has created audio file formats that use “digital rights management,” or DRM, to make duplication difficult.
One example of an audio format with DRM is AAC, with the extension of .m4p, best known as Apple’s format for songs on its online iTunes music store. AAC is a compressed music format, much like MP3, but