Video Projection Terminology

Terms and Definitions Relating to Video Projectors

ANSI Lumens

Developed by the American National Standards Institute, ANSI lumens is considered to be the most accurate measure of the overall light output of a projector. Projected light intensity (Lux) varies, being brightest at the center of the beam and dropping off towards the edges. ANSI lumens average these different brightnesses to create an overall lumen value.

Aspect Ratio

The ratio of image width to image height of a projected picture. See Resolution.

Closed Caption

A video technology primarily used to provide an audio transcript of a program for hard of hearing viewers by superimposing synchronized text over the image.

Contrast Ratio

The ratio between the white and black values of an image. The higher the contrast ratio, the more details can be distinguished by the viewer.

Dichroic Mirror

A mirror typically used in DLP video projectors that separates the white lamp light into its red, green, and blue components by reflecting or refracting selective wavelengths of light.

DLP

Digital Light Processing - A display technology developed by Texas Instruments that utilizes an array of hundres of thousands of tiny mirrors shining through a color wheel. The angle of each mirror is varied to determine how much light for that color is displayed at that pixel of the image.

Focus

The minimum and maximum projection distances that result in a sharp picture.

Keystoning

The effect caused when the projector is not perpendicular to the screen, resulting in an image that is distorted from  rectangular. Many video projectors have built in Keystone Correction to compensate for this effect.

LCD

Liquid Crystal Display - A display technology that uses a matrix of red, green and blue crystals to create a picture. Each set of red green and blue sub-elements represents one picture pixel. The voltage to each sub-element is varied to create lighter and darker areas for each color, as required by the image to be projected. Light from the projector bulb is separated into the three colors with a dichroic mirror, passed throught the separate sub-elements and recombined to form the full picture. Older technology embedded all three color sub-elements on a single chip (single chip LCD). Newer technolgy uses a separate chip for each color (three chip or triple chip LCD).

Lumen

A measurement of the amount of light given off from a light source. The more lumens, the brighter the light. See ANSI Lumens.

Lux

A measure of light intensity equal to one lumen per square meter.

Native Aspect Ratio

The designed aspect ratio of a projector. The projector is optimized to display the best resolution and brightness at its native aspect ratio. Images displayed at other aspect ratios will have less resolution and brightness, resulting in a lower overall quality of picture.

NTSC

National Television Standards Committee - Video transmission system used in most of the Americas, Japan and Korea. Preceeding digital, it consists of a 30 frame per second signal with 525 scan lines.

PAL

Phase Alternating Line - Video transmission system used in Europe, most of Asia, Australia, and parts of South America. Preceeding digital, it consists of 25 frames per second with 625 scan lines.

Pixel

Picture Element - the basic element of a displayed picture. When expressed as horizontal pixels by vertical pixels, they define the resolution of an image.

Resolution

A measure of the number of pixels (dots) making up an image, expressed as horizontal pixels by vertical pixels. More pixels result in a higher quality image. The ratio of horizontal pixels to vertical pixels defines the aspect ratio. Common video resolutions include:
   EGA - 640 pixels x 350 pixels; 1.83:1 aspect ratio
   VGA - 640 pixels x 480 pixels; 4:3 aspect ratio
   SVGA - 800 pixels x 600 pixels; 4:3 aspect ratio
   XGA - 1024 pixels x 768 pixels; 4:3 aspect ratio
   HD - 1280 pixels x 720 pixels; 16:9 aspect ratio
   WXGA - 1280 pixels x 800 pixels; 16:10 aspect ratio
   SXGA - 1280 x 1024; 5:4 aspect ratio
   UXGA - 1600 pixels x 1200 pixels; 4:3 aspect ratio
   WUXGA - 1920 pixels x 1200 pixels; 16:10 aspect ratio
   FHD (1080p) - 1920 pixels x 1080 pixels; 16:9 aspect ratio
   QXGA - 2048 pixels x 1536 pixels; 4: x 3 aspect ratio

Throw Ratio

A ratio representing the relation between the throw and the width of the projected image, that defines how far the projector must be from the screen to fill the entire width of the screen. The throw is the distance between the projector lens and the screen. For example, if your projector has a throw ratio of 1.8:1 and your screen is 10 feet wide, the projector will need to sit 18 feet from the screen to fit the entire width.