Images
A single still video image, whether created by a drawing or paint program or scanned from a book or grabbed with a video camera, can be stored in any of a wide variety of file formats. The data will be stored in a raster or a vector file format. A raster image is one composed of a field of pixels, each characterized by a color, and is usually created in paint programs, by scanning a picture or by grabbing an image. A vector format is created almost always by a drawing/CAD program and consists not of pixels, but objects such as curves, shades, and characters.
Raster formats can be generally separated into two categories. Lossy formats lose resolution (sharpness) when converted to, while lossless formats preserve image information. For example, when converting from a GIF (lossless) to a JPEG (lossy), some information is lost. However, lossy formats tend to be much smaller than their lossless counterparts, and for most photographic images, there will be almost no subjective difference.
The following list of image file formats is not inclusive, but describes the formats that comprise the majority of files encountered on the Internet. All of the following formats are raster formats unless otherwise stated.
Different file formats work with different programs, although almost all drawing/paint programs will read and write JPEG, GIF, and TIFF formats. GIF and JPEG formats are popular for FTP and the WWW because they are much smaller than other formats, so more of them can be stored. GIF and JPEG formats are not compressible, so it is generally a waste of effort to run a compression program on them. However, other file formats often compress by large amounts. PICT and TIFF formats work best with wordprocessing and desktop publishing programs like Microsoft Word 6.0 and Adobe Pagemaker 6.0.
Movies
Movies, as they are labelled here, consist of a series of still images, sometimes with embedded audio information, united in such a way as to produce a single playable file. MPEG and QuickTime are the two most commonly encountered movie formats on the Internet.
Sound
Files containing data used to recreate audio on a computer are called audio files and are also available in many different formats. Similar to image formats, audio files can either store a digital sampling of the sound wave (sound files, like a raster image) or contain a digital encoding of the type, shape, and timing of all the notes used in the composition (music files, like vector images).
Music software packages such as MusicProse and Finale, can also be used to compose music, but they use their own proprietary music formats.
Multimedia on the Web
Once you have the appropriate software, you have to configure your WWW browser to automatically play/display any downloaded multimedia file. This procedure varies by both platform and software, but is somewhat similar.
Helper applications are programs which can stand on their own but are referred to from within a WWW browser to enhance its capability to play/display multimedia file formats. Normally, you must tell your browser which programs to use for which file format encountered. Since Netscape Navigator is the most popular WWW browser for most computer platforms, its method of setting and using helper applications is be described below.
Netscape for Macintosh or IBM-compatible computers can be customized to automatically respond to almost any file format encountered. To do this:
- Pull down the Options menu and select Preferences.
- From the selection box at the top of the window that opens, choose Helper Applications.
- Now, find the row corresponding to the multimedia file format you wish to automate with a helper application, and select the radio button corresponding to the action you wish Netscape to take: save, launch helper application, or use Netscape's built-in viewer.
- If you want Netscape to open a helper application, you must click once on Browse and select an appropriate program.