A New Foveated Space-variant Camera for Robotic Applications

APPLICATIONS J. A. Boluda1 F. Pardo1 T. Kayser2 J. J. P erez1 J. Pelechano1 1Institut de Rob otica. Universitat de Val encia, Val encia, Spain 2Fachhochschule Mannheim, Mannheim, Germany ABSTRACT A foveated camera has been designed and fabricated. The camera is implemented using a new foveated CMOS sensor which incorporates a log-polar transformation. This transformation has specially interesting properties for image processing including the information selective reduction and some invariances. The structure of this sensor permits an individual access to each pixel, exactly in the same way that the access to a RAM. This is a very interesting property that makes a big difference between a CCD based camera and a CMOS based camera. In the other hand, the CMOS nature of the sensor implies a very important xed pattern noise due to the mismatch of the cell transistors. A xed pattern noise correction circuitry has been included in the camera, in order to achieve a good image quality. The solutions adopted for achieving a low noise/signal ratio are also presented. Finally, some guidelines for including this camera in an autonomous navigation system are shown. The easy way for calculating the time-to-impact through this camera suggests the utilization of this sensor system for real-time applications. 1. THE LOG-POLAR TRANSFORMATION In the human visual system the receptors of the retina are distributed in space with increasing density toward the center of the visual eld (the fovea) and decreasing density from the fovea toward the periphery. The log-polar transformation is described as a conformal mapping of the points on the polar (retinal) plane onto a cartesian (log-polar) plane following the equations: = log r = (1) The resulting log-polar projection is invariant, under certain conditions, to linear scalings and rotations of the retinal image. These complex transformations are reduced to simple translations along the coordinate axes of the log-polar image. This property is valid if, the scene and/or the sensor moves along (scaling) or around (rotation) the optical axis. The same properties hold in the case of a simple polar mapping of the image, but a linear dilation around the fovea is transformed into a linear shift along the radial coordinate in the ( , ) y