The size of the reference template must be determined such that it includes a sufficiently large portion of the device to be tracked and a minimum of the background. If the template window is too large, correlation may be corrupted by the background. On the other extreme, if the template is composed only of the interior of the pointing device then the reference template will be relatively uniform, and a high correlation peak will be obtained with any uniform region of the image, including other parts of the pointing device. For a reasonable correlation peak, the reference template size should be just large enough to include the boundary of the pointing device, which contains the information used for detection and localisation.
Figure 2: Reference template for a finger.
In fingerpaint, our workspace is of size 40 cm by 32 cm. This surface is mapped onto an image of 192 x 144 pixels, giving pixel sizes of 2 mm by 2.2 mm. At this resolution, a finger gives a correlation template of size 8 by 8 pixels or 16mm by 18mm, as shown in figure 2.