Computer Projection Technical Definitions

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Explanations of the terms and technology used in computer/ video projection systems and videoconferencing.

LCD

An LCD is a liquid crystal display. LCDs are most often used for notebook computer screens and is used in electronic computer projection equipment.

Active and passive matrix LCD

Active matrix LCDs are more responsive and therefore appropriate for full motion video, computer animation, and fast mouse movement. Active matrix also provides a higher degree of color saturation.

PDP (Plasma Display Panel)

An emissive display, as compared to an LCD panel which is a transmissive display, using a process similar to that found in fluorescent lighting, but with thousands of pixels. Much brighter than the LCD technology and has a wider viewing angle.

Pixel

A measurement of light

Amorphous and polysilicon LCD.

Both amorphous and polysilicon are types of active matrix LCDs. Polysilicon LCDs are more transmissive (allowing more light through) mainly because they use dichroic optics.

Dichroic optics

Dichroic optics is a technology where white light is split up into its red, green, and blue components using dichroic mirrors. A dichroic mirror lets one color of light pass through (either red, green, or blue), and reflects all others. Each of the three colors has an LCD responsible for the amount of the particular color. The light is then combined to form the image on the screen. Projectors with dichroic optics can display a much wider and more dynamic color spectrum than projectors with dye filter optics. Dichroic optics are used mostly in projectors with polysilicon LCDs.

ANSI lumens, and how are they measured

ANSI lumens is a measurement of the overall brightness of a projector. Because the center of a projected image is brighter than the corners, ANSI lumens is a more accurate representation of the image brightness than lux (one point on the screen). ANSI lumens are normally measured by dividing a square meter image into 9 equal rectangles, and taking a lux (or brightness) reading at the center of each rectangle. Taking the average of these nine points gives the ANSI lumens of the projector.

Contrast ratio

Contrast ratio is an average measurement of a totally white image vs. a totally black image at the 9 points described in lumens measurements. Because there is always a light source (either in the projector itself or in the overhead projector when using a panel), even a totally black image from a computer or video source will produce some white light. The higher the contrast ratio, the more vibrant the colors will be.

DLP

Digital Light Processing (DLP™) is a revolutionary new way to project and display information based on the Digital Micromirror Device (DMD™) developed by Texas Instruments. DLP technology is provided as a subsystem or "engine" to market leaders in home, business, and large screen/entertainment segments of the projection display industry. In the same way the compact disc revolutionized the audio industry, DLP is revolutionizing video projection.

Digital Micromirror Device (DMD)

The DMD is based on a Complementary Metal Oxide Semiconductor (CMOS) Static Random Access Memory (SRAM) with a superstructure array of aluminum micro-mirrors functionally located over each memory cell. The DMD digital light switch moves between its two states ("on" and "off") to create and reflect digital gray scale images from its surface when light is applied. The digitally created images are transferred through the appropriate optics and filters to create compelling projected or, in the future, digitally printed images.

Each mirror is 16 microns square (about 16/100 the size of a human hair) with a one micron space between mirrors on all sides. The number of mirrors in use on a single chip can range from 307,200 to 1.3+ million (with 1 mirror per pixel).

ITU

International Telecommunications Union (ITU), an agency of the United Nations. Products that adhere to ITU standards allow one caller to connect with any other caller. Standards developed by the ITU's Telecommunications Standardization Sector (ITU-TSS, formerly CCITT) do for desktop conferencing what their "V.dot" and "Group-III" standards did for data modems and fax machines: they ensure worldwide compatibility between devices from a variety of manufacturers.

T.120

T.120 is the data conferencing standard

Specifies standards for file transfer and white boards
Application sharing has been submitted to the ITU for ratification as part of the T.120 standard.

H.320

H.320 is the ITU standard for the public circuit switched network

This umbrella standard allows audio and video to be shared among conferencing systems from various vendors over ISDN
Includes the H.261 video standard, G.711, G.722, and G.728 audio standards, and the T.120 data conferencing standard.

Downward compatible

This means the product is compatible with the given resolution and all resolutions less than the given resolution. So an SVGA (800 x 600) projector would work with a SVGA (800 x 600) computer and also a VGA (640 x 480) computer.

Keystone Correction

Keystone is a term used to describe the projected image when it is not a perfect rectangle. Usually it is smaller at the bottom of the image and widens at the top. Keystone correction is an adjustment in the equipment to make the image a perfect rectangle.

D-ILA(tm) Technology

D-ILA or Direct-Drive Image Light Amplifier is a reflective technology that results in higher brightness and better contrast ratio.

Distribution Amplifier

Make it possible to send a single video signal (RGB, composite video or S-VHS) to multiple projectors or monitors.

Switchers

Make it possible to send multiple video signals (RGB, composite or S-video) to one projector or monitor.

Matrix Switchers

Make it possible to send multiple video signals (any format) to multiple projectors or monitors.

Component Video

Output from Betacam, W-VHS or DVD players.

S-Video

Output from laserdisc, VCR or DVD players.

Composite Video

Output from VCR's and all consurmer equipment.