The cross search algorithm (
CSA) also exhibited step behaviour and the number of matching criteria evaluations was largely independent of the sequence being coded. As a result of the step size being halved between stages (like the TDL, TSS and OSA) the steps were located at displacements that were integer powers of 2. This is clearly visible in the above graph.
As with the OSA, the quality of matches for blocks from the Garden sequence deteriorated as the maximum displacement increased. The MSE for the Football sequence fell to a minimum at ±6 pixels and then began to increase, but dipped at ±8 and ±10 pixels. As can be seen from Figure 4.15, the optimum displacement for the Tennis and Garden sequences were at ±4 pixels. The MSE for the Tennis sequence did not increase continuously as the maximum displacement increased but dropped slightly at ±6, ±8, ±10 and ±12 pixels. These additional minima for the Football and Tennis sequences suggest that the Cross Search Algorithm should be used only with even displacements. Further investigation would be required to confirm this hypothesis.
