Lenticular Holograms
Three dimensional pictures
Humans, along with many animals, have the ability to see three-dimensional images through the use of stereoscopic vision. Stereoscopic vision involves the use of both eyes.
Three-dimensional movies and pictures work by supplying each of your eyes with a different image. These two "flat" images can look three-dimensional.
When you focus on an object each eye has a slightly different view of it. Your left eye tends to see a little of the left side of the object, while your right eye sees a little more of the right side. Your brain automatically uses this information, plus the angle your eyes have to turn to focus on the object, to supply you with an estimate of the distance of the object.
The most basic method is to get each of the eyes to focus on different images. The two images are placed side by side. The viewer, by crossing their eyes, can interpose one on top of the other to generate the 3D picture. The advantage of this method is that the image has full colour. The disadvantage is that it takes some practice to get the necessary co ordination to do it unless you have a device called a stereoscope. This is the basis for traditional stereoscopic photography.
In recent times, the use of computers have taken an idea originally proposed in the 1960's and created elaborate stereo pairs and integrated them into a single image. There are many names for these auto stereo pairs, such as Magic Eye and 3D Eye. At the time of writing this technique is currently out of vogue, but achieved large coverage during the early 1990's. Two more traditional methods of seeing in stereo are anaglyph pictures and polarised light.
Lenticular photography
Lenticular photographs, and their animated counter parts, sometimes called Virtual Video, work by splicing images together either using a computer or photographic op- tics.
Splicing in this case means taking a thin strip from the first image and pasting it beside a strip of the second image. The next strip of the first image is then pasted next to this and so on.
A lens array, usually a plastic sheet known as a lenticular screen, is placed over the spliced images. The lens array causes one eye to see all the strips from the first image with one eye and all the strips of the second image with the other eye. This creates a dimensional picture. If several images are combined in this fashion, each being the frames from a movie, a moving image can be created.
Because our eyes are positioned horizontally, the three dimensional lenticular photo- graphs have the screen running vertically, relative to the viewer. This allows the lenses to direct the correct images to the left and right eye. If a sequence with fast motion were used, there would be a great disparity between the left and right eye view. For animated lenticular images, the screen is placed horizontally and movement is seen by tilting the image up and down. This way, there is no stereo cross over and the pictures (although two-dimensional) appear to move.
The field of lenticular photography has developed rapidly over the past few years, enabling more pictures and finer screens to be used. The modern lenticular is very different from the simple "flip images" found in cereal packets of the 1970's.
