intermediate photograph (or photographic record) that contains information for
reproducing a three-dimensional image by holography (www.hyperdictionary.com)
Holography: the branch of optics that deals with the use of coherent light from a laser in order to make a hologram that can then be used to create a three-dimensional image (www.hyperdictionary.com)
In simpler words: The hologram is the photo of a 3-dimensional object (or scenery) recorded on a film. The film itself does not show the image, just a wave pattern - but if hit by a beam of special light, a projection is created in space which looks 3-dimensional again. So, holography records 3 dimensions on a 2-dimensional (flat) medium. Quite a trick!
diagram shows how a hologram is made.
There is an important difference between a photograph and a hologram: a photograph consists of pixels which, combined, show the original image - a hologram consists of wave interference patterns which describe or "encode" the original object. It requires an additional step of creating the projection to make the object visible again.
As a consequence, if you cut a photograph in half, then half of its pixels will be missing. But if you cut a hologram in half, you can still use each of the pieces to project the whole 3-dimensional object that was recorded!
Although there are no actual dots in a hologram, it could be said that each of a hologram's "dots" contains the whole image. To visualize this better, look at the comparison below (note that on an actual hologram recording, you wouldn't see the cat's face - we are only talking about the information principle here):
|This is how a photographic image would appear if you look at it with magnifying glasses of increasing strength. If you were to cut away the pieces of the picture that are outside the frame shown, the pixels containing the information would be lost and the image could not be reconstructed.|
|This is the principle of information storage in the hologram. As mentioned before, the actual image would not be visible on the film, but the smaller sections of the film still contain the information about the complete object. If you cut it in half or even smaller pieces, you can still use each of the pieces to create a projection of the whole kitten (probably even with its ears intact - they have not been on the original photo used for the demonstration, so we will never know how they looked...)|