Screen Glossary

TERM

DEFINITION

Aspect Ratio

Proportional relationship between width and height of an image.

Contrast Ratio

Defined as the luminance of the brightest color (white) to that of the darkest color (black).

Foot-lambert (fL , fl or ft-L)

Measure of luminance on the projection screen. The SMPTE (Society of Motion Picture and Television Engineers) recommend a minimum screen luminance of 16fL for commercial movie theatres.

Gain

Ratio of screen reflectivity when compared to a perfect matte white surface. Used to measure the amount of light reflected from a screen surface. Matte white or unity gain is 1.0.

Ghosting

Appearance of a faint double image resulting from low signal-to-noise ratio.

Half Gain Angle

Angle at which the screen reflects half the amount of light when compared to the gain measured at the center of the screen.

Hotspot

Screens having less brightness uniformity usually present a concentration of light in the middle of the surface; this is known as the hot spot. Often an effect of high gain/high reflectivity or when a surface has poor light diffusion properties.

Lumen

Unit of luminous flux. ANSI lumens, lumen measurement standardized by ANSI, is used to rate the brightness of a projector.

Luminance

The intensity of light emitted from a surface per unit area in a given direction, measured in foot lamberts.

Moiré

Visual effect caused by the interaction between the pixel grid and perforation pattern.

Peak gain

Gain measurement taken from the center of the screen, i.e. measure of brightness seen by viewer seated perpendicular to the center of the projection surface.

Projection Axis

Angle at which the projector is projecting light on the screen.

Rear view/Front view

Rear view screens are translucent and are used for projection from behind; light moves through the material. Front view screens are opaque; light is reflected off the material.

Screen Perforation

Used in conjunction with speakers behind the screen, rows of small holes made on the screen surface to let the sound go through. Micro-perforation is used to maximize acoustic transparency or if the audience is seated closer to the screen.

Signal-to-noise (SNR)

Ratio used to measure 3D contrast. It is the ratio between the signal (intended information) and noise (background, undesirable information). A high SNR means that the image can be clearly separated from the background, a low SNR means the signal and noise ratio are comparable and thus the image (signal) is harder to discern from the background(noise)

Speckling effect

Granular pattern that can be observed when alight beam is diffusely reflected on a surface with a rough structure such as a projection screen. Speckle patterns commonly occur in diffuse reflections of monochromatic light such as laser light.

Throw ratio

Distance between tip of projector lens and the screen divided by image width.

Viewing cone

Maximum angle at which a display can be viewed with acceptable visual performance. The limits of which are usually set when half-gain is reached.