Services - 3D

The Event Projection Guilde to 3D.

You might have noticed 3D has made a bit of a comeback of late! After Avatar came out there's been a huge serge in 3D movies and technology to bring this to the consumer. Active 3D technology is still in its infancy but with more application such as video games and events it looks like this time round 3D might be here to stay.
Stereoscopic photography and film is nothing new and comes in all sorts of flavours, some more tasty than others. The illusion of depth that we see when viewing 3D content is achieved by offsetting two images, one for the left and one for the right eye. The images are then combined by the brain to give perception of depth. There are techniques where glasses are not required but we'll ignore this for now.

When it comes to projection there are two principal techniques used to display 3D content, active and passive, both of which utilise glasses to filter offset images from a single source separated to each eye are as follows;

Passive

Passive 3D glasses are any 3D glasses that don't require a power source to view 3D content. The two most common types of passive glasses are anaglyph and 3D polarised glasses. The major benefits of passive 3D glasses is cost since they do not require power. 

Anaglyph

This is the most basic and therefore the cheapest way to project 3D content. Potentially any projector can be used and there is no need for a special screen. Most people will be familiar with cheap cardboard glasses where the two lenses are different (usually chromatically opposite) colours, such as red and cyan. The content is made up of two colour layers, superimposed, but offset with respect to each other to produce a depth effect. The content is made up of two differently filtered coloured images, one for each eye. When viewed through coloured anaglyph glasses, they reveal the 3D image. Anaglyph images are relatively poor in terms of brightness and accurate colour rendering.

Polarised

There are two forms of Polarised 3D glasses; linear polarised and circular polarised.

Linear polarised glasses require the user to maintain a vertical head position, tilting your head left or right can break the 3D effect because the content relies on one eye seeing the vertically polarised image and the other seeing the horizontally polarised image. When the head is tilted the polarised lenses no longer line with the polarised double image on the screen.

Circular polarisation does away with this problem but it requires a special projector and filter. Two images are projected superimposed onto the screen through circular polarising filters of opposite handedness (left/right). The glasses contain another pair of circular polarisers mounted in reverse. Light that is left-circularly polarised is blocked by the right-handed filter, and vice-versa. The result is similar to viewing using linearly polarised glasses, except the viewer is free to tilt his or her head and still maintain correct left/right separation.

One critical draw back to either polarised 3D system is the requirement for a special screen. The light reflected from a standard white projection screen tends to lose some polarisation and the perceived 3D effect is distorted. This problem can be eliminated if a silver screen or aluminised screen is used.

We also have to take into account the light loss from viewing content through polarised glasses. Polarised glasses are a bit like sunglasses so a brighter projector is required for viewing 3D content than 2D content.

The second potentially expensive draw back to passive polarised 3D projection is that a pair of aligned DLP projectors must be used, one for each eye. This also leads to the requirement of polarising filters, and a source (computer or processor) with a dual-head graphics card that can output both images to each of the projectors.

Another benefit to passive 3D glasses is that since the viewer is being shown both images at once it does not half the frame rate of the content like active glasses do (see Active below).

Active

Active 3D glasses require a power source to power an inbuilt shutter mechanism which is synced to the display.
The glasses have an LCD layer in each lens which can be made to go dark (shut) alternately to show each eye a different image. They are powered by batteries and receive the sync signals via infrared, radio or Bluetooth transmitter that sends the timing signal in sync with the refresh rate of the screen which in turn displays alternately displays different perspectives for each eye. This alternate-frame sequencing technique achieves the desired effect of each eye seeing only the image intended for it.

The advantage of this system is that active 3D glasses allow full colour and picture information since both images are not being overlaid, and virtually eliminate the ghosting effect seen on passive polarised systems. 

The disadvantage to active 3D glasses is that the separate images for each eye are not delivered at the same time so flicker may be apparent. The content will alternate the images shown to each eye at whatever the frame rate of the content and refresh rate of the display offers. This means that for smooth playback the frame rate needs to be doubled. For example, with 60 frame per second content each eye is being shown only 30 images per second effectively halving the frame rate seen by the viewer. This means that high-end technology is required throughout the chain. This is most noticeable during slow camera pans or during fast motion. The higher the frame rate the smoother each of these actions will appear. For DLP projectors a refresh rate of 120Hz is required for smooth playback.
It is also important to remember that shutter glasses are shutting out light half of the time and they can be slightly dark even when open and letting light through, because they are polarised causing a darker picture perceived by the viewer. This means that a brighter projector is required to compensate. 

At Event Projection we can offer 3D projection, both Active and Passive and also Active 3D Plasma systems including the flagship 103" Plasma from Panasonic.

If you have an project that requires 3D and would like us to help explain the options, call today on 0207 232 1748 or email 3D@eventprojection.co.uk