Image Processing Reference
In-Depth Information
Fig. 2.2 A large part of the electromagnetic spectrum showing the energy of one photon, the
frequency, wavelength and typical applications of the different areas of the spectrum
Fig. 2.3 The effect of illuminating a face from four different directions
If you are processing images captured by others there is nothing much to do
about the illumination (although a few methods will be presented in later chapters)
which was probably the sun and/or some artificial lighting. When you, however, are
in charge of the capturing process yourselves, it is of great importance to carefully
think about how the scene should be lit. In fact, for the field of Machine Vision it
is a rule-of-thumb that illumination is 2 / 3 of the entire system design and software
only 1 / 3. To stress this point have a look at Fig. 2.3 . The figure shows four images
of the same person facing the camera. The only difference between the four images
is the direction of the light source (a lamp) when the images were captured!
Another issue regarding the direction of the illumination is that care must be
taken when pointing the illumination directly toward the camera. The reason be-
ing that this might result in too bright an image or a nonuniform illumination, e.g.,
a bright circle in the image. If, however, the outline of the object is the only infor-
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