Gain is a measure of reflectivity of light coming off a screen when the measurement is of light targeted and reflected perpendicular to the screen and the screen is coated with magnesium carbonate or titanium dioxide, which is a bright white colour .
But greater gains can be accomplished with materials that reflect more of the light parallel to projection axis and less off-axis. A gain of 1.5 means that the screen reflects 50% more light than the screen standard. You can therefore use “high gain” screens to save money on the projector (use the additional gain on the screen to compensate the lost on the brightness of a projector) or increase the brightness of an existing projector image.
Where there is a limitation on the projector selection, the screen can be used as a method to produce extra brightness (gain). The screen will be made with additional coating to reflect as much light as possible to produce a bright image in a specific type of environment. The shortfall for this type of screen is it will narrow the viewing angle.Viewing angle is a measure of the distance from the centre of the screen at which you can still see the same quality image as from the viewing axis. Some projection screens are made with material which reflect more light perpendicular to the screen and less light to the sides, making the image appear darker if the viewer is not in the centre of the screen.
Higher contrast from the screen will be regarded as an important factor where the main aspect of the screen is to show films and pictures. The high contrast screen (normally grey) will give you the additional contrast to enhance display of these type of images.