Robotics Reference
In-Depth Information
a preponderance of different shades of green, such as green with blue
and green with yellow, so the principal challenge for the IBM team was
to automatically draw a fine distinction between similar colours, and to
make such a system reliable.
While it is not difficult to distinguish the colours of various fruits
and vegetables under laboratory conditions, a supermarket environment
creates problems such as ambient lighting, which might confuse a colour
detection process. A scanning system was devised to reduce this problem.
The fruit or vegetable is placed on the glass surface of a scale that has been
built into the checkout counter. An inexpensive CCD camera is located
under the glass, pointing upwards at the produce, which is illuminated
from below by a fluorescent tube. Two images of the produce are taken,
one with the light on and the other with it off. The images of the produce
can be separated out from its background by analyzing the differences
between the two images.
Once the image of the produce is captured, its colour is analyzed into
hue,
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saturation
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and intensity,
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which together form a colour “signa-
ture”. By combining this colour information with data on the shape, size
and skin texture of the produce, Veggie Vision is able to recognize what
fruit or vegetable it is looking at and to price it accordingly.
Recognition in Three Dimensions
Because light takes a finite and measurable amount of time to travel be-
tween two points, if we know how long light takes to make a journey we
can calculate the distance it travels. The light illuminating each individ-
ual pixel in an electronic image sensor comes from the different features
in the scene being viewed. By determining the amount of time that light
takes to reach each pixel from a feature in the scene, it is possible to cal-
culate the exact distance from that feature to the pixel. This enables a
computer system to build up a three-dimensional relief map of the sur-
faces in the scene.
The Palo Alto company Canesta describes in a patent document sev-
eral of its inventions for timing how long light takes to travel from a scene
to the surface of the company's sensor chips. The basis of this technology
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A hue is a particular gradation of colour—a shade or tint.
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Saturation is vividness of hue; the degree of difference from a grey of the same lightness or
brightness. The less grey there is in a colour, the more saturated it is.
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Intensity is the strength of a colour, especially the degree to which it lacks its complementary
colour.
