Projection screens are installations consisting of blank surface and a support structure used for projecting an image for the view of an audience. Projection screens may be permanently installed as in a movie theater, painted on the wall[[1]], semi-permamanent or mobile, as in a conference room or other non-dedicated viewing space. Uniformly white or grey screens are used almost exclusively as to avoid any discoloration to the image, while the most desired brightness of the screen depends on a number of variables, such as the ambient light level and the luminous power of the image source. Flat or curved screens may be used depending on the optics used to project the image and the desired geometrical accuracy of the image production, flat screens being the more common of the two. Screens can be further designed for front or back projection, the more common front projection systems having the audience situated on the same side of the screen as the image source. This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... Google Image Search, one of the most comprehensive Image Searches on the net. ... A typical megaplex (AMC Ontario Mills 30 in Ontario, California). ... An office is a room or other area in which people work, but may also denote a position within an organisation with specific duties attached to it (see officer, office-holder, official); the latter is in fact an earlier usage, office as place originally referring to the location of one... See also list of optical topics. ...

Different markets exist for screens targeted for use with digital projectors, movie projectors and slide projectors, although the basic idea for each of them is very much the same: front projection screens work on diffusely reflecting the light projected on to them, whereas back projection screens work by diffusely transmitting the light through them. A Digital Projector is an electo-optical machine which converts image data from a computer or video source to a bright image which is then imaged on a distant wall or screen using a lens system. ... A movie projector is an opto-mechanical device for displaying moving pictures. ... A carousel slide projector, the most common form of projector A slide projector is an opto-mechanical device to view photographic slides. ... The reflection of sunlight on water Reflection is the abrupt change in direction of a wave front at an interface between two dissimilar media so that the wave front returns into the medium from which it originated. ...

Screens by installation type

Permanently installed screens can often be found in venues that are used for continuous visual presentations, such as movie theathres. These can be pre-assembled or assembled on the spot.

Pull-down screens are a often used in multipurpose spaces where permanently installed screen would require too much space. These commonly use painted fabric that is rolled in the screen case when not used, making them prone to damage when compared to rigid screens.

Rigid wall-mounted screens maintain their geometry perfectly, which makes them suitable for applications that demand exact reproduction of image geometry, and a good choice for presentation where aesthetics are important.

Mobile screens usually use a pull-down screen on a free stand. These can be used when it is impossible or unpractical to mount the screen to a wall or a ceiling, but the fabric of the screen can rarely stay immobile, giving imperfections to the projected image.

Home theater screens and gain

One of the most often quoted properties in a home theater screen is the gain. This is a measure of reflectivity of light compared to a screen coated with titanium dioxide, when the measurement is taken for light targeted and reflected perpendicular to the screen. Titanium oxide 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. Titanium dioxide, also known as titanium(IV) oxide or titania, is the naturally occurring oxide of titanium, chemical formula TiO2. ...

Frequently quoted gain levels of various materials range from 0.8 of light grey matte screens to 2.5 of the more highly reflective glass bead screens, some manufacturers claiming even higher numbers for their products. Very high gain levels could be attained simply by using a mirror surface, although the audience would then just see a reflection of the projector, defeating the purpose of using a screen. Screens with higher gain will exhibit more mirror-like properties, namely a bright "hot spot" in a place in the screen where the audience would see the projector, if screen would be replaced with a mirror. Opinions differ as to when this "hot spotting" begings to be distracting, but most viewers have trouble to notice as large as 30% difference in the image luminosity, unless presented with a test image and asked to look for variations in brightness.

Glass-bead screens exhibit a phenomenon of retro-reflection, where highest intensity of the light is reflected back to where it came from. This is intended for setups where the image source is placed in the same direction from the screen as the audience. Users frequantly report some hotspotting in such screens, although this type of screen is seen as desirable due to the high image intensity they can produce.

Screen geometry and optics

Square-shaped screens used for overhead projectors sometimes double as projection screens for digital projectors in meeting rooms, where space is scarce and multiple screens can seem redundant. These screens have an aspect_ratio(image) of 1:1 by definition. Other popular aspect ratios include 4:3 and a widescreen ratio of 16:9, which are often used as dedicated data projection and home cinema use, respectively. An overhead projector is a display system that is used to display images to an audience. ... The aspect ratio of a two-dimensional shape is the ratio of its longest dimension to its shortest dimension. ... A 32inch CRT widescreen television A widescreen image is a film image with a greater aspect ratio than the ordinary 35 millimeter frame. ...

Most image sources are designed to project a perfectly rectangular image on a flat screen. Optics designed for a curved screen will result in a pincushion effect when an image is projected on a flat screen.

Image brightness and contrast

Apparent contrast in a projected image - the range of brightness - is dependent on the ambient light conditions, luminous power of the projector and the size of the image being projected. In the presense of ambient light, a greater image will lead to less luminance (luminosity per unit area) and thus a smaller contrast. Some of the light in an image that is projected on the screen will also reflect back to the room, further increasing the amount of ambient light and thus decreasing the image contrast and the apparent image quality. Degration of image quality can be lessened by decorating the room with dark colours. This situation is different from the contrast ratios advertised by manufacturers, who record the light levels in an ideal room with projector on full black / full white, giving as high contrast ratios as possible. In visual perception, contrast is the difference in visual properties that makes an object (or its representation in an image) distinguishable from other objects and the background. ... Luminous flux is a measure of the energy emitted by a light source in all directions. ... The word luminance, a synonym for luminosity, means emitting or reflecting light. ...

Manufacturers of home theater screens have attemted to resolve the issue of ambient light by intruducing screen surfaces that direct more of the light back to the light source. The rationale behind this approach relies on having the image source placed near the audience, so that the audience will actually see the increased reflected light level on the screen. The level of omnidirectional light will be, in theory, unaffected by the reflective properties of the screen. Highly reflective screens tend to suffer from "hot spots", when part of the screen seems much more bright than the rest: this is a result of the high directionality (mirror-likeness) of such screens. Screens with high gain also have a narrower usable viewing angle, as the amount of reflected light rapidly decreases as the viewer moves away from front of such screen.

A relatively recent attempt in improving the percieved image quality is the introduction of grey screens, which are more capable of darker tones in the presense of ambient light than their white counterparts. It can be disputed whether such screens increase the actual contrast ratio possible in the image, as a grey surface will necessarily reflect less light from the projected image, as well. Grey screens are designed to rely on powerful image sources that are able to produce adequate levels of luminosity so that the white areas of the image still appear as white, taking advantage of the non-linear perception of brightness in the human eye.

One special screen worth of mentioning is Sony's black projector screen[[2]], which is designed to reflect the 3 narrow wavelengths of light that make up the light in digital projectors but absorb the rest. Sony Corporation (Japanese katakana: ソニー) (TYO: 6758), (NYSE: SNE) is a global consumer electronics corporation based in Tokyo, Japan. ... The wavelength is the distance between repeating units of a wave pattern. ...

More reading:

[3] - Projectorcentral.com - Screen gain, reflectiveness

[4] - Howstuffworks.com - How movie screens work

[5] - Hifishowroom - on different screen types by gain and viewing angle