New trends in physics teaching, v.4; The ... - unesdoc - Unesco

New Trends in Physics Teaching IV
Figure lla. Object made up of transparent and opaque regions. b. Centre region of the diffraction pattern of a showing only
three repeats in the vertical direction; in the full pattern there are several more repeats above and below those shown. C. Central
unit of b. d. Recombination of c. [24.]
result wil be more meaningful; if, on the other hand, no additional information is incorporated,
then the filtering is merely cosmetic.
The second problem that we shall consider illustrates this difference very well. Noise is the
great enemy of communication and it may often happen when, for example, a space probe working
at extreme range, or with almost exhausted power supplies, that a visual signal is completely
obliterated by the ‘snowstorm’ effect. However if we are trying to transmit a picture that is
stationary for a given length of time, it may be possible to filter out the noise. The possibility
rests on the randomness of the noise signal and the relative constancy of the required visual
signal. There are many ways of using this information. One possibility would be to convert the
sequence of frames into digital form and then to integrate all the successive digits corresponding
to each point of the image in turn. If the integration is carried out over a large enough series of
frames the ‘noise’ wil average out and the required signal wil be enhanced.
Image processing generally is a most useful and valuable technique. But it can also be misleading
and it is very important that the user should know exactly what has been done to a particular
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