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Choosing the Right Projection Screen Surface

Courtesy of Draper, Inc.

When selecting a front projection surface, you'll want to consider several key factors. Here's an explanation of each.

Gain—Gain is a relative measure of a screen's reflectivity. Gain is a measure of brightness as compared to a block of magnesium carbonate, which serves as a standard for gain of 1.0. Gain is the statistic most frequently cited and charted to compare projection screen surfaces. A gain chart can also help in judging uniformity. The flatter the curve in the area where viewers are seated, the more consistent the image they will perceive.

Contrast—Contrast is the surface's ability to accurately reproduce and differentiate light and dark characters and backgrounds, or light and dark areas of an image. A front-projected image is created by a pattern of light on a light-colored surface. Naturally, the white areas are generally very bright. The dark areas, on the other hand, are simply the absence of projected light on a light-colored background—not solid dark objects like the opaque inks we see on a printed page. A projection screen that preserves strong dark tones actually makes the light-colored areas look brighter by comparison.

Ambient light rejection properties—A projection screen that rejects ambient light will retain better dark areas when the lights are on in the audience area—hence it will have better contrast under those conditions. This quality is very important for situations where the audience members are active participants in the presentation, or where the speaker wishes to move through the audience area, and whenever notes are likely to be taken.

Resolution—Resolution is the clarity of the projected image. Resolution obviously depends primarily on the projector's output, but the smoother the projection surface, the less likely it is to create a distracting moiré pattern when a high-resolution video or data image is projected on it.

Uniformity—Uniformity refers to the consistency of the screen's performance when viewed from various points off the projection axis (both horizontally and vertically), and when the brightness of the center of the image is compared to the corners. Typically screens with low gain, or brightness, provide the most uniform images.

Projection Format—Projection format is arrived at by looking at the height and width of the projected image which determines the screen's size and shape (AV, NTSC, HDTV, WideScreen, CinemaScope, overhead, slide or motion pictures).

The quality of the image perceived by the human eye is primarily a function of gain, contrast, uniformity and resolution.