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Normal Optical Flow Imager


Various motion properties of an image can be computed by using Normal Flow measurements. Notable among these are focus of expansion, time to contact, etc. VLSI systems have been developed which combine processing with imaging but almost always the imaging resolution suffers in such cases.


We designed a two-dimensional dense Normal Optical Flow measurement chip implemented in 0.5 micron CMOS process which combines imaging and processing on the same chip efficiently. The algorithm computes partial derivatives with respect to time and space and uses their ratio to compute normal flow velocity. 


The chip has a 92x52 array of APS pixels, occupies an area of 4.5 mm2 and consumes 2.6mW power. It has two CDS circuits to improve the noise characteristics of the present and previous frame image. We use V-to-I circuits to compute spatial and temporal gradients and ratio circuits to compute the velocities. We also have confidence measures available to remove unreliable results where the spatial derivatives are below a certain threshold, thus making the ratios singular.