In this section I will cover the techniques I know of display a stereo image that is "natural". By natural I mean that no special glasses are required, and you don't need to train you eyes to do weird things to see the image. This is the Holy Grail of stereo imaging. With a natural technique you can just look at the picture and instantly see a 3D image.
What Are Holograms?
Holograms were discovered in 1947 by Dr. Dennis Gabor. A hologram is like a regular photograph but instead of being a photo of the general mixed up ambient light reflecting from an object, it is a picture of the actual patterns light, their phase and amplitude, reflecting from an object. The resulting hologram will reflect the same patterns of light as the original object when light reflects off it.
Creating a hologram first requires a source of coherent light. Normal light would just mix together and the actual light patterns could not be photographed, a source of coherant light is required, and that means a laser. Laser is a word that stands for "Light Amplification through Stimulated Emission of Radiation". I am not going to go into detail on how lasers work, all you need to know is that the photons (light particles) in laser light are all travelling in an ordered way in the same direction. Some cheap laser pointers can even be used to generate a holographic image (clickhere to read more on the subject).
Light, although consisting of particles called photons, also travels as a wave. A hologram is made using two waves of laser light, but the waves must be in sync, and therefore come from the same laser. The laser beam is split in two using a piece of glass. Some of the beam goes through the glass, some of it reflects off it. Each laser beam is too fine and narrow to illuminate anything larger than a pin-head, so each is widened using a lens. The first wave of laser light, called the reference beam, goes straight from the laser onto a piece of high quality photographic plate. The second wave of laser light is directed at the object to be photographed, the laser light reflects off the object and onto the photographic plate. When both waves of laser light meet they create the pattern that produces the final hologram.
There are two types of hologram. If the reference beam hits the photographic plate at the same side as the object beam, then this creates a transmission hologram. If the reference beam hit the opposite side of the photographic plate then this create a reflection hologram.
Transmission holograms are the most common and best illuminated from behind. Normally this isn't practical, so a reflective piece of foil is attached behind it. Transmission holograms also give a rainbow effect to the color of the picture.
Reflection holograms are light from the front, and are the typically the more expensive and better looking kind that you see at novelty stores. Reflective holograms are normally just one color, but it is possible for a hologram of this kind to contain two or three colors. Still not a full color image though.
Places like Yoshikawa Labs at Nihon University are working on holographic video and computer generated holograms...
"The pixel numbers are 10,240 x 6,144 and the size of the final hologram is 35 mm x 21 mm. When observed about 1 m from the hologram, one can recognize binocular parallax."
That's a lot of pixels for an image little over one inch across! We may see real-time computer generated holographic displays in our lifetime but we may have a little while to wait yet.
Lenticular Displays
This is another example 3D imagery that has been distributed in cereal packets :). A lenticular picture consists of several pictures interweaved together. A piece of plastic that has a prism like structure to it is attached to the surface of the picture. The plastic refracts different lines of the image depending on what angle you view it from. Lenticular pictures were first used to display simply animation like this...
Later, as the technology improved, it started to be used for displaying 3D images. After all, the two eyes of the viewer are looking at the picture from slightly different angles anyway, so why not show a stereo pair of pictures.
Lenticular pictures can display a stereo 3D image and/or a few frames of animation. Lenticular images have been around since the 1940s and were first mass produced by a company called Variview. They are cheap and easy to produce, with a good enough printer and some lenticular sheet (which you can buyhere) you can even make your own. Lenticular images are also usually clearer and more defined than holograms. Nowadays you often see them on the cover of video tapes (Independence Day springs to mind)
One of the exciting things about lenticular displays is that real-time computer generated lenticular video is now possible. Instead of having a static picture behind the lenticular screen, we have a hi resolution liquid crystal display. Its fairly simple to alter a game or other piece of software to render the scene twice and interleave the two images together before displaying them on a screen. With any luck this technology will be noticed by the big industry giants and we will see lenticular displays being available to the average Joe within the next few years.
No comments:
Post a Comment