A video projector takes a video signal from a computer or video player, and projects the image on a projector screen using a lamp and lens system. All video projectors use a very bright light to project the image, and most modern ones can correct most distortions, such as curves, blurriness, and other inconsistencies through manual control settings. Video projectors are widely used for conference room presentations, classroom training, and home theatre applications.
A video projector may also be built into a cabinet with a rear-projection screen (rear-projection TV, or RPTV) to form a single display device, now popular for "home theater" applications. Common display resolutions for a portable projector include SVGA (800×600 pixels), XGA (1024×768 pixels), 720p (1280×720 pixels), and 1080p (1920×1080 pixels). There are also very light weight video projectors perfect for a traveling executive.
The cost of a device is not only determined by its resolution, but also by its light output, acoustic noise output, contrast, and other characteristics. While most modern projectors provide sufficient light for a small screen, a projector with a higher light output (measured in lumens, abbreviated "lm") is required for a larger screen or a room with a higher amount of ambient light. A rating of 1000 to 1500 ANSI lumens or lower is suitable for smaller screens with controlled lighting. Between 1500 and 3000 lm is suitable for medium-sized screens in a typical setting. Over 3000 lm is great for very large screens in a large room with no lighting control (for example, a conference room). Projected image size is important; because the total amount of light does not change, as size increases, brightness decreases. Image sizes are typically measured in linear terms, diagonally, obscuring the fact that larger images require much more light (proportional to the image area, not just the length of a side). Increasing the diagonal measure of the image by 25 % reduces the image brightness by 35 per cent; an increase of 41 per cent reduces brightness by half.
DLP (Digital Light Processing) is a technology by Texas Instruments, used in projection TV and video projectors. One application of DLP is DLP projectors (small standalone projection units). DLP, along with LCD and LCoS are the current display technologies behind rear-projection television, having replaced the older CRT projectors. These rear-projection technologies compete against LCD and Plasma flat panel displays in the HDTV market. DLP is also one of the leading technologies used in digital cinema projection.
Leading manufacturers of projector, projector accessories, and lamps, include: Canon, Elite Screens, Epson, Hitachi, InFocus and Ricoh. A related product is the digital white board (or digital boards) and overhead projectors.