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Glossary 59
2
ANSI
— measures 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.
Full On/Off contrast is always a larger number than ANSI contrast for the same
projector.
dB — decibel — A unit used to express relative difference in power or intensity,
usually between two acoustic or electric signals, equal to ten times the common
logarithm of the ratio of the two levels.
Diagonal Screen — A method of measuring the size of a screen or a projected
image. It measures from one corner to the opposite corner. A 9FT high, 12FT
wide, screen has a diagonal of 15FT. This document assumes that the diagonal
dimensions are for the traditional 4:3 ratio of a computer image as per the example
above.
DLP
®
— Digital Light Processing™ — Reflective display technology developed by
Texas Instruments, using small manipulated mirrors. Light passes through a color
filter is sent to the DLP mirrors which arrange the RGB colors into a picture
projected onto screen, also known as DMD.
DMD — Digital Micro-Mirror Device — Each DMD consists of thousands of
tilting, microscopic aluminum alloy mirrors mounted on a hidden yoke.
Focal Length — The distance from the surface of a lens to its focal point.
Frequency — It is the rate of repetition in cycles per seconds of electrical signals.
Measured in Hz (Hertz).
Hz (Hertz) — Unit of frequency.
Keystone Correction — Device that will correct an image of the distortion
(usually a wide-top narrow-bottom effect) of a projected image caused by
improper projector to screen angle.
Maximum Distance — The distance from a screen the projector can be to cast an
image that is usable (bright enough) in a fully darkened room.
Maximum Image Size — The largest image a projector can throw in a darkened
room. This is usually limited by focal range of the optics.
Minimum Distance — The closest position that a projector can focus an image
onto a screen.
NTSC — National Television Standards Committee. North American standard for
video and broadcasting, with a video format of 525 lines at 30 frames per second.
PAL — Phase Alternating Line. A European broadcast standard for video and
broadcasting, with a video format of 625 lines at 25 frames per second.
Reverse Image — Feature that allows you to flip the image horizontally. When