Remarks on the differential method for the estimation of movement in television images

In this paper a physical interpretation is given of a method for the estimation of movements in television images. The method, already presented by the author in other papers, is based on a linear regression of the image derivatives, both spatial and temporal. It is shown that a centered finite differences approximation of the image differentials is mandatory to obtain good performances. Experimental results are issued to support theoretical conclusions.     

Doppler centroid estimation for ScanSAR data

We introduce a novel accurate technique to estimate the Doppler centroid (DC) in ScanSAR missions. The technique starts from the ambiguous DC measures in the subswaths and uses a method alternative to standard unwrapping to undo the jumps in estimates induced by modulo pulse repetition frequency (PRF) measures. The proposed alternative is less error prone than the usual unwrapping techniques. Doppler Ambiguity is then solved by implementing a maximum-likelihood estimate that exploits the different PRFs used in different subswaths. An azimuth pointing of the antenna that does not change with subswaths, or that changes in a known way, is assumed. However, if the PRF diversity is strong enough, unknown small changes in azimuth pointing are tolerated and accurately estimated. This estimator is much simpler and more efficient, than those in the literature. Results achieved with both RADARSAT 1 and ENVISAT ScanSAR data are reported.     

Motion compensated image interpolation

Field skipping is a variable technique for reducing drastically the bit rate necessary to transmit a television signal. All fields have to be reconstructed at the receiver end, but nearest-neighbor or linear interpolations give poor performances when significant scene activity is present; therefore, some motion compensation scheme is mandatory. Although any of the algorithms proposed for motion estimation can be used for motion compensated interpolation, in this paper only the pel-recursive algorithm is considered. Past experience is briefly summarized and, based on criticism, improvements to the basic algorithm are proposed that seem to lead to an estimated motion field that is accurate enough. Multiple recursions and appropriate selection rules are proposed to counteract streaking effects of the recursive algorithm when it crosses image boundaries. The estimation of a forward and a backward motion field is used to identify image areas where occlusion effects are present. Experimental results are presented that seem to indicate that the proposed interpolation scheme has good performance     

Design of a computerized emission tomographic system

The design of a computerized tomographic system is considered. The algorithms for digital filtering and two-dimensional interpolation are analyzed. The disturbances introduced by the small number of projections, the finite impulse response of the filter, rounding and crude interpolation are discussed. Finally a recently developed algorithm for tissue absorption compensation is briefly summarized.     

Tracking moving objects in television images

The estimation of the velocity of objects imaged by television cameras is useful in different areas of image processing.The problem is solved by means of a linear estimation algorithm and the effects of noise superimposed to the signal are analyzed. The structure of a real-time estimator is then presented. Experimental results show that a very fine accuracy is obtained. They encourage its application to image coding for redundancy reduction using movement compensation.