Home Theatre Glossary

Projectors : Glossary of Terms

The glossary is a reference guide to the technical terms used on this site to describe LCD projectors, other digital projectors, and projector accessories.

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a-Si: "Amorphous Silicon"
Active Matrix: Term used to describe LCD Displays which have micro-transistors that "open" and "close" each pixel.
Active Matrix TFT: A common type of LCD used in laptops, cameras, and LCD projection panels that were produced in the late 1980s to early 1990s. A typical active matrix TFT display is a single panel of LCD glass that controls all three primary colors. TFT displays are noted for their quick response time and their ability to display full motion video and animations without image ghosting.
Anamorphic Lens: An anamorphic lens is a lens that has different optical magnification along mutually perpendicular radii. This provides the ability to project a source image of one aspect ratio, such as 4:3, into a different aspect ratio, such as 16:9, by using different magnifications for the horizontal and the vertical dimensions of the projected image.
ANSI Contrast: Contrast is the ratio between white and black. The larger the contrast ratio the greater the ability of a projector to show subtle color details and tolerate extraneous room light. There are two methods used by the projection industry: 1) Full On/Off contrast measures the ratio of the light output of an all white image (full on) and the light output of an all black (full off) image. 2) ANSI contrast is measured with a pattern of 16 alternating black and white rectangles. The average light output from the white rectangles is divided by the average light output of the black rectangles to determine the ANSI contrast ratio. When comparing the contrast ratio of projectors make sure you are comparing the same type of contrast. Full On/Off contrast will always be a larger number than ANSI contrast for the same projector.
ANSI Lumens: 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 the most accurate representation of the image brightness. ANSI lumens are calculated by dividing a square meter image into 9 equal rectangles, measuring the lux (or brightness) reading at the center of each rectangle, and averaging these nine points.
Aperture: In television optics, it is the effective diameter of the lens that controls the amount of light reaching the photoconductive or photo emitting image pickup sensor.
Aperture Correction : Compensation for the loss in sharpness of detail because of the finite dimensions of the image elements or the dot-pitch of the monitor.
Aspect Ratio:

Aspect ratio is the ratio of the width of an image to its height. For example, a projector with a 16:9 aspect ratio will produce an image that is 16 units wide for every 9 units high. This is also referred to as 1.78:1 meaning the width is 1.78 times the height. For example, if you want an image 40 inches high then you need a screen that is at least 40 * 1.78 inches wide or 71 inches. Other common aspect ratios are 3:2, 4:3 and 5:4.

Native aspect ratio refers to the aspect ratio of the physical displays built into the projector. For example, a 1280 x 720 pixel display has a 16:9 native aspect ratio. A display that is 640 x 360 pixels is also a 16:9 aspect ratio, but with a fourth of the resolution of the other display.

Nearly every projector today will support multiple aspect ratios; however each manufacturer must decide who their intended audience is and optimize the projector for that audience. This means each projector has a native aspect ratio that is optimized for specific viewing material. Images shown in native aspect ratio will utilize the entire resolution of the display and achieve maximum brightness. Images shown in other than native aspect ratio will always have less resolution and less brightness than images shown in native aspect ratio.

Auto Balance : A system for detecting errors in color balance in white and black areas of the picture and automatically adjusting the white and black levels of both the red and blue signals as needed for correction.

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In April 1990 unanimous worldwide agreement on a calibrated non-linear RGB space for HDTV production and program exchange in ITU-R BT.709-2 was obtained. It specifies the encoding of real world scene tristimulus values into a reference display RGB colour space assuming a dark viewing condition.

The ITU specification is rather vague on defining the reference display. The sRGB standard provides a clear and well-defined reference display for ITU-R BT.709-2 for a dim viewing environment. [More] < PDF

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