Interpolation Scheme

To further improve the accuracy of the motion estimates, the next parameter we experimented with was the choice of interpolation scheme for the motion estimation. In addition to the standard tri-linear scheme, a windowed-sinc interpolation (using a Hanning window of size $7 \times 7 \times 7$) was tried. While considerably slower than trilinear interpolation, the sinc approach is able to further refine motion estimates after the initial trilinear stage has converged on a solution thus providing greater accuracy. The results in Figure 14 show the greater degree of accuracy achieved over using trilinear interpolation alone. Note that on the third data set (cropped to allow distinction between the other four sets), the improvement was consistently over a value of 2.0.

Figure 14: Median (over time) RMS (over space) error results for the MCFLIRT scheme applied to synthetic data exhibiting known motion of one of five designs and audiovisual activation at increasing intensities. A positive value indicates improved accuracy as a result of incorporating the final sinc interpolation stage. Cost function notation corresponds to Table 1 and demonstrates the improvement in accuracy achieved by using smoothed cost functions and additional sinc interpolation when compared to the basic trilinear scheme reported in Figure 13