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The prototype of
the CCD sensor has the following structure: the pixels are arranged on 30 concentric
circles each with 64 photosensitive sites. The pixel size increases from 30micron x
30micron for the inner circle to 412micron x 412micron for the outer circle. The total
chip area is 11mm x 11mm. The video acquisition rate is 50 frames per second. The total
amount of information is stored with less than 2Kbyte per frame. Thus, the chip realizes a
good compromise between image resolution, amplitude of the visual field and size of the
stored data. Computation of optical flow has been performed at a rate of about 4 Hz, using
a common 386 PC 33MHz. This has allowed to perform some very simple, but not trivial,
tasks such as computation of the time-to-impact of a target approaching a camera with the
retinal sensor mounted in, and the control of the approaching velocity to avoid the
collision.
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