The basic operation for a digital desk application is tracking some pointing device, such as a finger, a pencil or an eraser. The tracking problem can be expressed as: ``Given an observation of an object at time t, determine the most likely location of the same object at time ''. The pointing device can be modelled as a reference template. The reference template is a small neighbourhood, i.e., a window w(n, m) of a picture p(i, j) obtained at some prior time, t. The reference template is compared to the image by computing a sum of squared differences (SSD) at each pixel with a MxM search region :

A perfect match gives a value of 0. Implementing cross-correlation by SSD requires solving practical problems such as determining the sizes of the reference template and of the search region, triggering and breaking tracking, and updating the reference template.

Fri Jul 21 18:22:45 MET DST 1995