Thursday, October 25, 2012

A cardinality sensor

Recently I was talking to Takeo Kanade, and he mentioned an old paper of his with Vladimir Brajovic, where the image produced by the sensor is sorted according to radiance. If two pixels receive the same light energy, then they get the same rank. Now you might think this is uninteresting, since you could just take a regular image and sort it in software. But remember, I said sorted by radiance (which is continuous), not intensity measurement (which is usually 0 - 255). For a scene that is over-exposed, with a regular sensor, you'd get an image that is mostly 255s. With the cardinality sensor, you'd get an image with lots of information, since it would preserve the rank of each scene point (which depends on the number of other scene points that are darker or brighter). Essentially each pixel is in a race to be overexposed, and once the pixel reaches the value 255, it increases a counter variable by 1 and takes the counter variable's value (which is its rank). Ties get the same value, but increase the counter variable by the number of tied pixels.

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