Current sketching software only recognises the geometry of a sketch - for example, that two lines meet at a specific angle - and cannot recognise context at all. The MIT software monitors the image as it is being drawn onto a computer screen and allocates probabilities to various interpretations of what it might represent. As the user adds more detail, the software adjusts these weightings. To do this, it uses a technique known as Bayesian analysis, which is normally used to compute the likelihood of specific causes, given certain effects.
"With our software, the 'causes' are what the user had in mind to draw, and the 'effects' are what was actually drawn," says Randall Davis, who has developed the code with Christine Alvarado at MIT's Artificial Intelligence Laboratory. Once the computer has settled on an interpretation, it applies the laws of physics such as gravity and friction to set the virtual world in motion. Cars roll down hills, pendulums swing, and objects bang into each other. The Bayesian part of the software is still at an early stage: it recognises only squares. Davis's next goal is to get it to recognise a much broader range of crudely drawn shapes. Part of the problem is thinking up all the possible ways someone might draw a shape, so as to be able to assign realistic probabilities to particular patterns on the screen.
Written by Celeste Biever
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New Scientist issue: 13th September 2003
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