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VISIBLE LIGHT
How do machines see?
Many types of sensors are available to robots to enable them to 'see' what's going on around them. An infra red sensor or camera for example, would allow a robot to detect and image things that are radiating energy in the form of infra red radiation. Similarly, an ultraviolet sensor would enable a robot to 'see' objects emitting energy in the ultraviolet part of the spectrum.
But robots can also see the world in a similar way to humans. We have eyes, which are a bit like very sophisticated biological cameras whereas robots can use CCD video cameras which are sensitive to radiation in the visible light part of the electomagnetic spectrum. |
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 What's a CCD?
 CDD stands for Charge-Coupled Device. |  |
A CCD video camera uses a small rectangular piece of silicon rather than film to receive incoming light. The CCD silicon chip has an array of individual light-sensitive cells called 'photosites'. Each photosite is one element of the whole picture that is formed and this picture element is called a 'pixel'. The CCD detects light because the silicon releases an electron when a photon of light hits it. This is called the photoelectric effect. The current generated by the CCD is amplified and fed to a computer processor.
Pattern recognition
A machine sees the world in a very different way to humans. When we see a friend's face, we are able to instantly recognise that person but a computer doesn't see a face; its computer processor just 'sees' a shape through its video camera which it compares against a database of other shapes it has been programmed to recognise. Usually, CCD cameras have a lens to focus the incoming light onto the surface of the silicon chip. The lens improves the quality of the image and allows the computer processor to achieve better pattern recognition.
So, how do humans see?
The human eye has a light sensitive screen at the back called the retina. Specialised cells on the retina called rods and cones are sensitive to light. When light falls on these cells, they send the information along the optic nerve to the brain. Basically, the rest of the eye is built to protect the retina and to focus the light onto it.
Firstly, we need to control the amount of light entering the eye.
The amount of light entering the eye is controlled so that the retina doesn't get damaged. The round coloured part of our eye is the iris it acts like a shutter with a hole in the middle - the pupil. There are two sets of muscles; circular and radial muscles which control the size of the pupil. Radial muscles contract to make the pupils bigger and circular muscles contract to make the pupil smaller.
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How is the light focused onto the retina?
When light shines on something, say a flower, it is reflected from the flower in all directions. Some of this light enters the eye through the cornea and it goes through the lens which then focuses the image of the flower on the retina. |
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The lens in our eye is flexible and can change shape so we can see things near and far. When we look at a distant object, the muscles pulling on the lens get tighter which causes the lens to flatten.
If we then focus on a near object, the muscles relax allowing the lens to become fatter and more convex so it will focus on near objects. The ability of the eye to focus is called accommodation.
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SENSORS radio infra red light radiation
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