Like file compression, the goal of media compression is to reduce file size and save disk space. However, media compression algorithms are specific to certain types of media, such as image, audio, and video files.
Most popular image formats use some type of compression. Three of the most common include JPEG, GIF, and PNG. JPEG compression, which is commonly used for digital photos, incorporates a lossy compression algorithm that averages nearby colors and removes color variations that are imperceivable by the human eye. GIF compression reduces the color palette of an image to 256 colors or less, which provides an efficient way to represent each color within the image. PNG compression uses a lossless compression algorithm that filters the image data and predicts pixel colors based on other nearby pixels. While each of these algorithms work in different ways, they can all be used to significantly reduce the file size of an uncompressed image.
Several common audio file formats also use compression to save disk space. Popular audio formats, such as MP3 and M4A use compression algorithms that remove inaudible frequencies and reduce the dynamics of the sound. Since uncompressed audio files, such as AIFF and WAVE files, take up a lot of disk space, they are often compressed as MP3 or M4A files before they are distributed over the Internet. These files are typically around one tenth the size of the original audio files and have nearly identical sound quality.
Most video files are also compressed. Popular video formats, such as MPEG and DivX compress video using a specific codec. Each codec uses a custom algorithm that removes redundant information from the video. For example, if the background of a video doesn't change for awhile, a codec can reduce the file size by not redrawing the background every frame. A video codec may also incorporate audio compression to reduce the size of the audio track. Since encoded videos are decoded as they are played, the codec that was used to encode a video must also be available to decode the video. Therefore, in order to play a compressed video file on your computer, your video player software must have the appropriate codec installed.
Updated: April 8, 2011