Projection Concepts

Front projection is when an image is projected on the front or viewers side of the projection surface. The image is then reflected back to the viewer. This is generally the classic style of projection that most people are familiar with, having seen it in schools and movie theaters. One of the biggest benefits for front projection, particularly on stage, is that it efficiently uses space, with no space required behind the screen. Usually, for front projection, the projector is placed above either the audience or the stage to avoid shadows of people and objects in front of the screen, but many times the shadows are unavoidable. Front projection screens are typically lighter in color since they need to reflect light, darker colors are possible which allow for deeper blacks and more saturated images but usually need a more powerful projector. Click here to see which projections screens are best for front projection.

Rear projection is when the projector is projecting onto the rear of the screen with the image going through the screen toward the viewer on the front side of the screen. Sometimes called RP screens, these screens can have wildly different characteristics since the screen controls how the image is transmitted. Some screens have tight viewing cones, with bright and crisp images while others have a softer image with wider viewing cone. This technique is often used in situations where objects or people in front of the screen would cause shadows if front projection was used, or when there is high ambient light since RP screens natural colors tend to be darker and fade into the background when not in use. The one draw back is that ample space is required for the projector to be positioned behind the screen. Usually taking up a significant amount of space that cannot be used for anything else. Take a look at our options for rear projection screens here.

Front and Rear projections screens are duel-purpose screens, they can be used for both front and rear projection, depending on what is needed. These multi-purpose screens are used flexibility and longevity are key. These screens usually take on the role of a dependable cyclorama for a theatre or an event company's go-to rental screen. Because of their duel-roles, most of these screens are not as bright as dedicated front or rear projection screens, but this actually makes many of them quite good for soft edge blending and resistant to hot-spotting. These characteristics also make these screens quite good at diffusing light, so many end up being used for lighting effects, such as sunsets or color walls. Click here to see what Front and Rear Projection Screen options are available.

Full frame projection is the type of projection that most people are familiar with. It means you have one projector that is used to project on to the entire viewing area. This was really been the only way to project, whether it was front or rear projection, until recently and required large expensive projectors to be able to project on to a large surface area.

Soft Edge Blending is a style of projection that uses multiple projectors, blended together using special software to create one larger image. This allows for extremely large projected images to be achieved with multiple projectors. The software corrects for the overlap between each projected image however, it can only control the projectors and ignores which projection screen is projected upon. For soft edge blended projections, it is therefore essential to choose projection screens with the best possible luminance distribution. For front projection, our OPERA WHITE, GAMMALUX, SCENE, EVEN, or OPTIBLACK screens work well for edge blending and for rear projection OPTIBLACK, OPERA® CREAMY WHITE, OPERA® GREY BLUE and EVEN work perfectly for it.

Perforation or microperforation is typically used to help alleviate acoustic pressure through a projection screen, particularly middle to high range frequencies. Standard perforation is 57,000 holes/m² (37 holes/in²) with an open area of approximately 7%; microperforation is 300,000 holes/m² (195 holes/in²) with an open area of approximately 6%. For a relatively close viewing distance, a microperforated screen such as GAMMALUX® MICRO is recommended. For farther viewing distances, a standard perforated screen such as OPERA® WHITE Perforated is recommended. Under proper viewing distances and conditions, perforations are not visible.

Contrast is simply the ratio between black and white. Picture contrast is considered good when black areas are perceived as highly distinct from white areas. To determine the contrast ratio of a projection screen, we use a checkerboard grid of eight black and eight white squares and an NIT meter that calculates the average values of the black and white squares. For projection under normal conference room conditions, the following is a contrast guideline: a ratio from 6:1 to 10:1 is considered bad; 20:1 and up is considered good.

The black level is the intensity of the color black when projected onto a projection surface. The black level is influenced by the projection source and the projection screen. The optimal black level would assume a theoretical 0% reflection and transmission of the incident light in the black image areas.

1 Text projection of scattered light on a white projection screen.

2 Text projection of scattered light on a GREYSCREEN projection screen.

The luminance factor, also called gain, describes the efficiency of the screen and its ability to gather light. The criteria for establishing the gain of a projection screen as compared to a white chalk tile, made from barium sulphate, that has a standard gain of 1.0. When a measurement has a gain greater than 1.0, it reflects (front projection) or transmits (rear projection) more light than the white chalk tile. Gain is measured at different angles and is greatest at a 0° axis, when both the projected light and the viewer are parallel to the viewing surface. Gain decreases as the viewing angle becomes wider.

The luminance chart shows the luminance factor (gain) at different viewing angles. A flat curve indicates a uniform luminance distribution on the screen. A high rising curve indicates that the screen may have a tendency to hot-spot and may not be suitable for certain applications such as soft-edge blending projections. This may be referred to as light "fall-off".