WHAT IS 3D?

3D stands for 3 Dimensions or 3 Dimensional and refers to something with width, height, and depth (described using the axes X, Y, & Z). The term is generally applied when something that is traditionally flat (two dimensional) such as a picture has depth added. For example 3D television, 3D movies, or 3D images to distinguish them from their traditional flat versions.

2 EYES 3 DIMENSIONS

3D VISION or STEREOPSIS means solid viewing. It is the sense of depth or three-dimensionality that we achieve because we have two eyes trained on the same point. Our eyes are separated by six or seven centimeters (the average adult inter-pupillary distance) and so they each have slightly different viewpoints. The discrepancy in those views is used by the brain to extract depth information about the observed scene. Essentially, the closer an object is to the eyes, the greater will be the horizontal shift in its image between the eyes.

CREATING A 3D EFFECT

The ability of the brain to perceive depth when presented with slightly varied views makes it easy for us to mimic real three dimensional scenes by offering the eyes two such views (this is a bit like the good luck that we have with colour reproduction needing only red, green, and blue to mimic the whole spectrum). There are various techniques for mimicking or reproducing a sense of depth, many, but not all of which, rely on offering the eyes two linked views:

• Anaglyphs red green glasses (see how anaglyphs work and see some examples of anaglyphs)
• 3D movies (using circularly polarized glasses)
  • See an animation of a circularly polarized wave.
  • See a diagram of linear to circular polarization.
• Stereo image pairs (see some examples of image pairs)
• Autostereograms (see some examples of autostereograms)

VISION

Vision is a very complex process that builds an internal model of the world which is constantly updated by the eyes. The eyes scan in broad movements and also in very rapid small movements (saccades) focusing as they do so on different parts of the scene. We can only have a clear focus on a very small area and so our sensation of everything being in focus relies on our visual memory (persistence of vision).

DEPTH CUES

The difference in the images received by the eyes is only part of the information used in depth reconstruction:

• Perspective (things getting smaller the further away they are)
• Distance haze or blur (things tend to become more blue and hazy the nearer they are to the horizon because of atmospheric effects)
• Parallax: how things move relative to each other (close things move relatively more).