In general, two types of video display are used: the projection system, comprising a projector and a projection surface, and direct-view screens (TV, computer screen, showcase or LED video wall, etc. ) While projectors are used to display a video stream on very large surfaces, while allowing the format to be changed, they are ideal for representing subjects in real size and for projections in front of an audience. On the other hand, the visibility of their projection is more affected by ambient light than a screen with direct vision. Direct vision screens, due to their more or less restricted dimensions, adapt and move quite easily within a space. Their image visibility is less affected by ambient light. They can also be used as an auxiliary video display for participants.
Projection systems generally require more time and preparation to be installed properly. Here are some points to consider:
¶ Nature and size of the projection surface
A projection surface can be very variable in nature and size. While the use of white walls or removable screens is quite widespread, there are other types of surfaces – with different degrees of opacity, shapes and textures – that can meet specific artistic needs: rigid panels removable, tulle, glass, plastic film, elastane, etc.
¶ Display from the ground
In a telepresence context, it is sometimes desirable to promote a link of gaze between local and distant subjects by placing a camera at face level, placed either in front of the projection surface or behind a screen with a sufficient opening to allow the objective of said camera to pass – for example, a vertical rigid panel with a hole at the height of approximately 1.5 m from the ground.
¶ Large size display
On the other hand, the size of a projection surface – or the use of a video monitor – will depend mainly on the space available, its location and the visual quality required. The larger the projection surface and the more the space in which it is located is illuminated, the more the projector must emit a sufficiently powerful luminous flux (in lumens) so that the image remains well defined. It is therefore necessary to find the right balance between the lighting required for video capture and a quality video projection.
¶ Surfaces in rear projection
Using a surface that allows rear projection – that is, projecting from the back of the screen (BOH) rather than the front (FOH) – helps avoid shading that would otherwise be caused by objects or subjects in front of the screen. The projected image should then be inverted accordingly. However, projecting video directly onto the subjects body may also be an effect desired by the art team. It is therefore necessary first to ensure that this type of projection does not thwart the artistic intentions.
¶ Semi-reflective surfaces
The optical illusion technique known as Pepper’s ghost, for example, employs a semi-reflective surface, such as plastic film or metallized glass, in combination with special lighting, in order to make certain objects or subjects appear, disappear, show through or transform them into something else.
¶ Location, orientation and range of spotlights
This consideration is in line with those of spatial layout and scenography, in particular with regard to the number of projections, depending on whether a projector is located at the front (FOH) or at the rear (BOH) of the projection surface, whether it is inclined at a non-perpendicular angle, or else, placed at a close or distant distance from said surface.
In the case of a rear projection, for example, a certain distance is required between the projector and the screen so that the visual rendering sufficiently covers the projection surface. It is therefore necessary to take into account the minimum space required behind said surface so that the projector is placed at a sufficient distance for the video display to be of suitable size.
In addition, there are different types of projectors depending on their throw, ranging from long throw (standard) to very short throw (ultra-short throw, or UST):
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In general, long throw projectors* can be placed at a distance ranging from 2 to 10 m from the projection surface, depending on the size of the display desired. But, for high-end projectors, intended to be permanently fixed in auditoriums, cinemas or large amphitheatres, it is possible to replace their lens in order to achieve much greater projection distances. Some also support aggregate layering of two or more projectors to increase the brightness of the visual output beyond what a single projector would be able to produce. Alternatively, it is also possible to perform edge blending, in order to increase the total resolution of the display or to obtain custom aspect ratios;
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Short throw projectors*, on the other hand, are usually installed at a distance of more or less 1 m from the projection surface;
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Finally, ultra-short throw projectors* must be installed less than half a meter away. A very short throw considerably reduces the distance between the projector and the projection surface, thus facilitating rear projection, in particular.
Projector type Long Range (LT) Short Range (ST) Very Short Range (UST) Distance (m) 2 to 10m ±2.5m <0.5m If the projection is for a human-scale display, showing one or more subjects full-size – such as a video stream from a camera tilted 90 degrees to the side, for example – it would be preferable orient the projector and the projection surface in the same way, i.e. vertically, using a suitable support. But beware, not all projectors are necessarily designed for a vertical position! It must first be ensured that said projector will not be damaged, in particular by overheating problems, as is often the case with laser projectors, if it is oriented differently.
Finally, in addition to the usual zoom and focus adjustments, it must be ensured that the projector allows sufficient trapezoidal (keystone) correction, in cases where the projector is placed at an angle to the projection surface.
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