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Rear vs. Front Projection

Immersive displays can utilise front or rear projection surfaces. Find out the difference.

The distinction seems simple: front projection screens reflect light while rear projection screens diffuse light through the material from behind the screen. But how do you go about choosing the right type of screen for your immersive VR room or simulation project and what are the factors to take into account?

Rear projection

One of the main advantages of rear projection is that there is no risk of casting shadows, either from the viewer’s body or other objects, no matter how close you stand to the screen’s surface.

Contrast and colour saturation are also better on rear projection screens in areas with high ambient light.

Choosing an appropriate substrate for a virtual reality display is important for this method to be effective.

For the surface, the flatter the better. This helps to retain as precise a geometry as possible.

Glass

Glass typically offers the best foundation but like all rigid substrates it does have limits to the sizes that can be manufactured and it is by far the most challenging material to transport, handle and install especially when you consider entering a continuous section of glass into the fabric of an existing building.

Rigid acrylics

Rigid acrylics are more cost effective than the glass alternatives but also challenge the installer for access and handling.

Glass or rigid acrylic is often preferred, and both require a unique optical coating to guarantee the best visual experience. Either substates mentioned require unique optical coatings to ensure the projected images produced are able to be used effectively for visual applications of this nature, attributes like supporting wide viewing angles and the colour critical angle are important for the best visual experience. The optical coatings are also key to reduce undesirable artefacts attributed to hot spotting, reflectivity, and ambient light sources.

Offering good contrast levels, supporting edge-blending and stereoscopic content are all key attributes that matter in the final selection of the optical coating to be utilised.

Semi-rigid acrylic

For clients with challenging room spaces where access is more prohibitive, semi-rigid acrylic materials can be used for the screen surfaces. They offer the ability to be rolled up and restrained temporarily, like a carpet during transport in order that they can be entered into the space and tensioned flat. With such screens, there are compromises, one of which is that the material is definitely not as flat as its rigid counterparts for its geometry.

Fabric screens

Fabric tensioned materials are often desired by customers for their cost effectiveness and ease of transportation. Whilst some of these more specialist surfaces offer attributes to support some of the characteristics outlined above the issues for using a fabric screen surface is one of stability of the image over time.

Fabric screens need constant tension and their characteristics can change if the thermal management of the room is subject to alter. Another observed behaviour that is undesirable can be the effect of air pressure changes within the room such as a nearby door opening causing a temporary disturbance to the screen surface which moves the visual for a few seconds before stabilising once more. Fabric screens however are able to be replaced more easily than their rigid counterparts, yet they are more susceptible to damage over time.

Polymer fabric screen

A unique innovation is to utilise a specialist polymer fabric screen that has a patented tensioning system. This dramatically minimises the air-pressure and tensioning issues whilst offering a screen that can be easily transported. This surface also brings a flatness that is arguably better than a rigid acrylic material, making it a definite flexible alternative.

Front projection

Front projection surfaces for immersive displays are by far the most cost effective to deploy compared to the rear projection alternatives.

Front projection can be addressed by using a folded lens optics or ultra-short throw approach for the light path, enabling an extreme angle for the light to fall onto the screen surface. This extreme angle of light enables the projector to be located closer to the “face” and reduces the chance of the user or an object intersecting the light path and creating a shadow.

However the possibility of creating a shadow remains and the interaction area possible without such an artefact is reduced by consequence.

Using front projection surfaces also creates some reflection issues where the multiple screens can be more likely to wash each other out to some degree due to their reflective nature, thus the contrast levels achievable for the image are reduced.

Front projection can be achieved upon different flexible and solid substrates coated in a suitable finish that is complimentary to gain the best attributes from the projected images upon them.

With all materials , whether for front or rear projection, one important factor is the mechanic design and frame works that knit the screen faces/facets together. With any immersive display of this nature the corner interfaces between the faces is key to providing the illusion of a continuous image. Special corner joins and mechanisms can be used to reduce this seam to a minimum and once viewing in a stereoscopic mode, this join may become almost invisible to the eye.

The sizes of the faces differ depending on what level of immersion clients desire and what types of content they need to see at a 1:1 scale in the virtual visuals. The size and footprint of the immersive space can be dictated by how much physical volume you may require to conduct your application within. For example, if you want to walk several metres naturally rather than to move your view through the virtual world using a motion model instructed by a wireless interaction device then the space required has to be calculated. The larger the displays visual surfaces become dictates how many projectors are needed to map the visual content onto those very surfaces, especially if a particular image quality or pixel size is to be retained.

In summary, projection surfaces come in all shapes, finishes and sizes and have varying attributes and price performances to consider. If you’d like to find out more about immersive displays and how it can benefit your business, please don’t hesitate to contact us. Here at Antycip, we offer a range of immersive environments and services that will help you enhance the way you work.

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