A scan converter is a hardware device that converts a video signal into a format compatible with a specific type of display. The most common scan converter translates digital computer video signal s into a format suitable for viewing on a conventional analog television set. Devices also exist that can convert conventional TV signals into computer-display format.
Scan conversion is a sophisticated process, because the raster (set of horizontal lines) in a conventional TV video signal is interlaced, while the raster in a computer display is normally non-interlaced. In an interlaced display, the horizontal lines are scanned alternately in two interwoven rasters, so a complete frame requires two raster scans. In a non-interlaced display (also called progressive scan), the lines are scanned sequentially from the top to the bottom of the screen, so a complete frame requires only one raster scan.
Scan conversion can degrade the image resolution (detail) of a video display. This is not necessarily a problem with large-screen or projection-image TV sets when they are used for presentations, where the images rarely involve fine detail. But it can present a problem for the serious graphic artist, or for the user who must work with document files or complex Web pages containing large amounts of text in small point sizes.
Besides the typical TV-to-computer or computer-to-TV applications, specialized scan converters can be obtained for applications such as:
- Conversion of radar images to computer-display format.
- Conversion of images from a cathode-ray oscilloscope to computer-display format.
- Conversion of slow-scan television ( SSTV ) images to conventional TV or computer-display format.
- Viewing analog video tapes on computer displays.
- Use of computer imagery in teleconferencing.