Robotics Reference
In-Depth Information
ness. As Cohen's colouring rules became more complex, AARON became
more able and varied in its performance. Cohen devised a notion of
colour “chords”—ways of choosing colours that worked together in vari-
ous spatial relationships, and AARON was able to construct these colour
chords as a way of controlling the overall colour structure of the image.
Even so, the importance of brightness remained central to AARON's
ability to colour; while the structure of a colour chord demanded that all
its components, however selected, retain some required level of vivacity
as they became lighter or darker. Cohen also gave the program knowl-
edge about the range of colours from which it is sensible to choose when
painting people, and on the basis of this knowledge AARON makes its
own decisions as to which colours it uses.
When AARON became able to paint in colour Cohen decided to
link the program to a painting robot. He designed and built the robot
entirely by himself, even though he had no training in either electronics
or engineering but instead had to learn about these subjects from robotics
topics and magazines. The robot starts by filling its own palette of paint
pots, actually a row of bottles containing fabric dyes.
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The robot mixes
its own colours, selects the brush most suitable for the next area to be
painted, and keeps track of how many inches of brushstroke it has used
with each colour—this is how AARON knows when the robot is running
out of paint. AARON can cope with filling arbitrarily complex shapes in
a painting once it has located them, under the overall constraint that it
should attempt to keep the wet edge of a shape moving forwards, as far
as possible, and not leaving an edge to dry in one part of the shape while
it is working in another part.
The colouring and filling-in process requires some care on AARON's
part. When the program has to colour a potted plant, first it mentally
outlines every patch in the image, determines whether the boundary of
that patch is the edge of the leaf to which it belongs, and determines
whether that patch is part of a leaf or part of the background. Next
AARON assigns a number to each patch, in such a way that the same
number is assigned to every patch belonging to any single leaf. And
finally AARON employs a strategy, devised by Cohen, for ensuring that
it does not draw attention to the shape of a leaf as an isolated event, but
allows it to be seen as part of the whole object to which it belongs.
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Cohen would have preferred AARON to use oil paints but mixing and thinning the colours
would have been beyond the capabilities of his robot, not to mention the robot's inability to clean
the brushes adequately.
