In general, two types of video display are used: projection systems, which include a projector and a projection surface, and direct-view screens (television, computer screen, showcase, or LED video wall, etc.). Projectors are used to display a video stream on very large surfaces and allow the format to be modified; they are ideal for representing subjects at life size and for projections in front of an audience. However, the visibility of their projection is more affected by ambient light than a direct-view screen. Direct-view screens, due to their more or less limited dimensions, adapt and move quite easily within a space. The visibility of their image is less affected by ambient light. They can also serve as auxiliary video displays for participants.
Projection systems generally require more time and preparation to be properly installed. Here are some points to consider:
¶ Nature and Size of the Projection Surface
A projection surface can vary greatly in nature and size. While the use of white walls or removable screens is quite common, there are other types of surfaces—with different degrees of opacity, shapes, and textures—that can meet specific artistic needs: removable rigid panels, tulle, glass, plastic film, elastane, etc.
¶ Floor-Level Display
In a telepresence context, it is sometimes desirable to encourage eye contact between local and remote subjects by placing a camera at face height, either in front of the projection surface or behind a screen with a sufficiently large opening to allow the camera lens to pass through—for example, a vertical rigid panel with a hole about 1.5 m from the floor.
¶ Large-Scale Display
The size of a projection surface—or the use of a video monitor—will mainly depend on the available space, its location, and the required visual quality. The larger the projection surface and the brighter the space, the more powerful the projector’s light output (in lumens) must be to keep the image well defined. It is therefore necessary to find the right balance between the lighting required for video capture and quality video projection.
¶ Rear-Projection Surfaces
Using a surface that allows rear projection—that is, projecting from behind the screen (BOH) rather than in front (FOH)—avoids shadows that would otherwise be caused by objects or subjects in front of the screen. The projected image must then be reversed accordingly. However, direct video projection onto the bodies of subjects can also be an effect desired by the artistic team. It is therefore necessary to ensure that this type of projection does not conflict with artistic intentions.
¶ Semi-Reflective Surfaces
The optical illusion technique known as Pepper’s ghost, for example, involves using a semi-reflective surface, such as plastic film or metallized glass, combined with special lighting techniques to make certain objects or subjects appear, disappear, become transparent, or transform into something else.
¶ Placement, Orientation, and Range of Projectors
This consideration relates to spatial arrangement and scenography, particularly regarding the number of projections, whether a projector is placed in front (FOH) or behind (BOH) the projection surface, whether it is angled non-perpendicularly, or placed close to or far from the surface.
In the case of rear projection, for example, a certain distance is required between the projector and the screen for the visual rendering to sufficiently cover the projection surface. You must therefore consider the minimum space required behind the surface so the projector can be placed at a sufficient distance for the video display to be of suitable size.
There are also different types of projectors according to their range, from long throw (standard) to ultra-short throw (UST):
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In general, long throw projectors can be placed at a distance from 2 to 10 m from the projection surface, depending on the desired display size. For high-end projectors, intended to be permanently installed in auditoriums, cinemas, or large amphitheaters, it is possible to replace their lens to achieve much greater projection distances. Some also support stacking two or more projectors to increase the brightness of the visual rendering beyond what a single projector could produce. Alternatively, edge blending can be performed to increase the total display resolution or obtain custom height/width ratios;
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Short throw projectors are usually installed at a distance of about 1 m from the projection surface;
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Finally, ultra-short throw projectors must be installed less than half a meter away. Ultra-short throw allows the distance between the projector and the projection surface to be greatly reduced, facilitating rear projection in particular.
| Projector type | Long throw (LT) | Short throw (ST) | Ultra-short throw (UST) |
|---|---|---|---|
| Distance (m) | 2 to 10 m | ± 2.5 m | < 0.5 m |
If the projection is used for life-size display, presenting one or more subjects in their full height—such as a video stream from a camera tilted 90° to the side, for example—it is preferable to orient the projector and projection surface the same way, vertically, using a suitable stand. But beware, not all projectors are necessarily designed for vertical positioning! You must first ensure that the projector will not be damaged, especially by overheating issues, as is often the case with laser projectors, if it is oriented differently.
Finally, in addition to the usual zoom and focus adjustments, you must ensure that the projector allows sufficient keystone correction in cases where the projector is placed at an angle to the projection surface.