Stereogram
A
stereogram is a type of hologram which is an optical illusion of depth that
is created from flat, two-dimensional image or images. Infact stereograms
are considered to be hybrids of holography and photography. These holograms
have the qualities of both media, but each add something of their own. These
stereograms are a series of holograms consisting of strips of hundreds of
the same images, which are multiplexed into a single hologram. This unique
and pioneering type of hologram is a breakthrough, as it allows reproduction
of living subjects, computer graphics, and virtually anything that can be
photographed to become a 3-D hologram with motion. In other words, this type
of hologram is created from hundreds of horizontal images which are taken of
the original object in motion. When light falls on the hologram, it is
reflected and scattered. This creates a 3-D image of the original object.
The final stereogram is created using laser light and high technology
optics.|
Process of Making Holographic Stereogram |
A stereogram is formed if we take several photographs of an image from different angles. Each of the pictures taken are then to be exposed onto a little area of the holographic filmplate.
The figure above shows us the principle of a stereogram with 3 pictures. These three pictures are multiplexed into one hologram. However, the stereogram formed is of low resolution because the number of pictures is less. Therefore it is important to use a large number of pictures to obtain a good resolution in the hologram. The more the number of pictures, the greater is the resolution. It is advisable to expose about 1 to 2 mm of the holographic film plate for each picture of the object.
Source:
http://www.fou.uib.no/fd/
1996/h/404001/kap10.htm
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Types of Stereogram |
- Stereoscopic imaging: It uses stereoscope to present a
slightly different image to each eye. If the images are narrow and
placed side by side, the stereo pair can be viewed with the naked eye.
- Anaglyph images: They combine two stereo images from slightly
different viewpoints into a single image and are recognized as "red/green"
or "magenta/cyan" images. The images viewed using "anaglyph
glasses", which use color filters to moderate the light reaching
each eye. This in turn creates the illusion of a three dimensional
image.
- Random dot stereograms: These employ either one anaglyph or
two stereoscopic images. The input image (or images) consist of random
dots with no discernible shapes. A hidden 3D scene emerges from these
random dots when the proper viewing device is used.
- Autostereograms: Using only a single image, they produce an
illusion of depth. By repeating a narrow pattern from left to right, the
image is usually generated by computer.
- Single Image Random Dot Stereogram (SIRDS): They are a form of autostereogram where each repeated pattern is altered slightly. This in turn creates a hidden image which is not discernible unless the right viewing method is used.
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Levels of Reality |
A holographic stereogram has two levels of reality:
- There is the surface level. This level appears chaotic and often
disorganized with its variety of colors and patterns.
- There is also the deeper and hidden level of reality. This is the hidden image, which actually contains the real meaning of the stereogram. Infact, the hidden image is the real reality image.
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How to view a stereogram ? |
The steps involved are as follows:
- Put your face near to the screen. You pretend that you are looking through the monitor.
- Next, move away very slowly from the screen.
- After making several attempts, as you move back the image will come into view.
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Applications of Stereograms |
Stereograms are widely used in variety of applications such as:
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