4.2.4. Computational Cost

An experiment addressing the computational cost of the proposed method and that of some of the comparison methods (SIFT, SAR-SIFT, PCSD, HOPC, RIFT, SRIFT) was undertaken. The average run times of the di fferent methods on the real datasets are shown in Table 4. The experiment is carried out on a computer with an Intel i7-6200U CPU @ 2.30GHz and 8 GB of RAM. All the methods were implemented in MATLAB.


**Table 4.** Computational cost comparisons (seconds).

According to Table 4, the SIFT algorithm has the highest computational e fficiency, followed by the SAR-SIFT algorithm, because neither algorithm performs phase congruency calculation. Among the four methods that adopt phase congruency (PCSD, HOPC, RIFT, and SRIFT), RIFT shows the highest computational e fficiency because it replaces phase congruency with maximum index graph. PCSD and HOPC are in the middle level, but the calculation time of the proposed method is relatively high. Due to the use of the multi-scale space, phase congruency, and RIC system to deal with the NRD, as well as the complex scale and rotation variation, the proposed method is relatively time-consuming. Algorithm optimization and e fficiency improvement will be carried out in the future.
