Stereoscopy In Projection Environments- Is It The Future Or The Past?

3D Stereoscopic Image Projection

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A quick timeline

1838 – Stereoscopes: the very first 3D viewer

In 1838, English inventor Charles Wheatstone made the groundbreaking discovery that would kickstart this entire branch of technology in the first place:

“The mind perceives an object of three dimensions by means of the two dissimilar pictures projected by it on the two retinae.”

In other words, each of our two eyes views the same object from a slightly different position and angle. Our brain, however, combines both signals into a singular picture, which is where our sense of depth perception stems from.

To demonstrate this, Wheatstone developed the preliminary stereoscope: a device consisting of a pair of mirrors positioned at 45 degrees to the user’s eyes. Each mirror reflected an identical drawing positioned off to the side and parallel from each other, creating an illusion of one singular image being displayed rather than two separate ones.

The user would find that the reflected image in the mirror had more depth and volume than the original drawing alone.

1849 – Lenticular stereoscope

It wasn’t too long before David Brewster, a scientist who specialised in optics, took note of Wheatstone’s observations and set out to improve upon the original 3D viewing device. He proposed what he termed the ‘lenticular stereoscope’ in 1849. Dubbed the world’s first portable 3D viewer, this model used two lenses in lieu of mirrors, and the user would look through the device as they would a pair of binoculars.

1853 – Anaglyph 3D (a.k.a the retro cinema glasses)

When you think of 3D glasses, the first ones that come to mind are those paper ones with the colourful lenses, aren’t they?

Anaglyphic photographs and films display both eyes’ views on the same image simultaneously: they are positioned slightly apart and encoded by colour (usually red and cyan). When the viewer puts on those retro glasses to view this funky film, each of the cellophane lenses filters out its own colour so the eye gets to view its own designated picture.

Super anaglyph

One of the biggest disadvantages of the anaglyph format is that the resulting image isn’t always faithful to the original. Because the coloured lenses filter out particular hues, an anaglyph photograph may not have the full range of colours found in the original. Some companies have acknowledged this flaw and built upon the anaglyph idea by developing more sophisticated methods for separating the left and right visual channels.

Dolby 3D uses what’s known as an interference filter system (a.k.a. “super anaglyph”); rather than separate the left and right eye images by one single colour, both images are in full colour albeit at slightly different wavelengths (not different enough for the naked eye to tell apart). The lenses in the special glasses separate the display into bands of colour (red, green and blue), only letting through the picture meant for the individual eye. That way, the Dolby 3D system gives viewers the best of both worlds: eye-popping pictures in eye-popping colour!

1890 – Polarisation: light angles are the new colours

First demonstrated in the 1890s, the idea of polarised 3D works very similarly to anaglyph 3D: the images for each eye are positioned on the same display, differentiated by a filter and viewed through special glasses. The key difference is that while an anaglyph display uses colour, a polarised 3D uses, you guessed it, polarisation.

But what exactly is polarisation?

Light travels in the form of electromagnetic waves. Most of the time, the waves that make up the light you see travel in all angles. When light is polarised, however, it means it’s filtered so that only waves travelling at a particular angle pass through.

Polarised 3D takes advantage of this to offer audiences the three-dimensional illusion without any impact on colour. The two eyes’ images are projected onto the same screen, albeit polarised in opposite directions. The viewer puts on glasses that contain polarised filters in the lenses; each lens lets in the light polarised in one direction and blocks out all light polarised in the other.

Because of its low cost and minimal impact on picture quality, this is nowadays the most common type of 3D system used in cinemas.

1922 – Active 3D

Active 3D is when the glasses or lenses used to view are ‘active’ in the sense of being powered, rather than just serve as mere panels to look through. Though in the world of electronic media it’s a relatively modern technique, the concept itself dates back to 1922.

Laurens Hammond, best known for inventing the Hammond organ, devised a then-novel lens for viewing cinema films in 3D: the Teleview. As two projectors showed each eye’s films with the shutters out of sync, the audience would look through a viewing device attached to their seat. This device would block out the appropriate eye, thanks to a rotary shutter operating in sync with the projectors. The experimental system was only used in one cinema viewing, because it was expensive to implement

Only one of both eye’s images are presented on the screen at once, and the glasses are constantly ‘winking’: the left eye’s view is blocked when the screen displays a picture for the left eye and vice versa. The winking is controlled via a timing signal synchronised with the screen’s refresh rate.

The frame rate of a film projected through an active 3D display has to be double that of a standard one. Another disadvantage of the active 3D system is that it doesn’t work with most modern monitors due to the extremely high refresh rate required to view the picture without any flickering.

1985 – Autostereoscopy: glasses not required

The term ‘autostereoscopy’ doesn’t just refer to a single method: it’s an umbrella term covering all stereoscopic display types that don’t require glasses or lenses to view.

Perhaps one of the most well-known examples of this form of stereoscopy is the Nintendo 3DS. The 3D effect in the top screen works via a parallax barrier, an array of strips placed over the LCD screen which project the display at just the right angles for giving the player a sense of depth perception. The parallax barriers can be disabled if the player wants to game without the 3D effect.

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