![\"\"](\"https:\/\/darlotech.co.uk\/wp-content\/uploads\/2021\/12\/cues-1024x349.png\")
Maybe it’s thought that you need to have two eyes to see depth, but there are other cues which enable depth perception for a single eye, e.g. Occlusion, Linear perspective etc.<\/p>\n\n\n\n
When you try to recreate a real 3D view, then you must attempt to satisfy all these cues.<\/p>\n\n\n\n
In the following parts we’ll look at 3D on a 2D screen, holograms, light field displays and volumetric displays. It should be noted that these terms are often interchanges and definitions of each are not strictly adhered to. <\/p>\n\n\n\n
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3D image on a 2D display<\/h2>\n\n\n\n
Think 3D films at the cinema. The film is projected onto a 2D screen but we ‘see’ 3D. But here what we see is a depth component. <\/p>\n\n\n\n
These systems work on the principal that the projected image actually contains two viewpoints of the filmed scene, each representing the view from each eye if we were actually in the scene. <\/p>\n\n\n\n
In early films, each image of the scene as captured by two cameras, separated by a distance equal to the distance between our left and right eye (an average). passes through a filter, red and cyan. <\/p>\n\n\n\n
![\"\"](\"https:\/\/darlotech.co.uk\/wp-content\/uploads\/2021\/12\/anaglaphA-1024x503.png\")
The images are combined into what is called an anaglyph image and recorded. When viewing, the trick is then to separate the screen images out so only one of the two goes into each eye. This is achieved through wearing special glasses.<\/p>\n\n\n\n
More recently, other techniques have been used to separate out both images, including polarized lenses.<\/p>\n\n\n\n
![\"\"](\"https:\/\/darlotech.co.uk\/wp-content\/uploads\/2021\/12\/PolarizationA-1024x563.png\")
Light is a wave and has certain properties in including polarization. <\/p>\n\n\n\n
Light is an electromagnetic wave consisting of oscillating electric and magnetic fields which are always perpendicular to each other. When polarizations are discussed it generally refers to the electric wave. Light has an equal mixture of polarizations but we can restrict to one by passing through a filter as in the diagram above.<\/p>\n\n\n\n
An advantage over the red\/cyan scheme is that the colour of the polarized 3D is unaffected.<\/p>\n\n\n\n
This is not however true 3D. Take the cinema example. Everyone in the cinema will see the same scene with depth, those at the end of the rows at the sides will not see to the side of any object any more than those seated in the middle. For that we need light field or volumetric displays.<\/p>\n\n\n\n
Another possibility is to generate an image on a 2D display, detect where the viewers eyes are, and adapt the displayed image according to the orientation. In this scheme only one person see the effect at any one time.<\/p>\n\n\n\n
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2D Image on a 2D Display<\/h2>\n\n\n\n
This may sound a curious addition to this article, but 2D images on a 2D display are often described as 3D by those selling such technologies.<\/p>\n\n\n\n
A simple example is a Fan Clock. Here a rotating strip of LEDs on the fan blade illuminate in a certain way, synchronized to the rotating blade. If the LED flashes once every blade revolution, then is will look like a stationary point. Many LEDs on the blade then can cover a full circle and if illuminated correctly then can produce an image. So why is this declared 3D ? well it can actually look 3D. A more elaborate system uses a higher density of LEDs and not just one blade but up to 6 are used. (not necessarily a fan either). The reason you get some sort of 3D effect is that apart from the object you see through the display and see whatever is behind it, often at a further distance you that gives you a sense of depth. Secondly, these system often rotate the displayed object, so the viewer doesn’t move, the object does. <\/p>\n\n\n\n