Table 2.

A comparison of different methods and ablation study on the three datasets. Values in the table are average SSIM with frame distance from 1 to 5. Note that the ablation study of loop closure is tested using the first three sequences of the fetoscopy dataset as there are long loop closures in these sequences.

Dataset	Seq.	SIFT	Direct reg.	Optical flow	Average fusion	Fusion w/o LC	Fusion (proposed)
SCARED	1	0.822	0.607	0.741	0.631	N/A	0.841
	2	0.804	0.526	0.674	0.540	N/A	0.807
	3	0.709	0.597	0.620	0.633	N/A	0.718
	4	0.677	0.549	0.628	0.527	N/A	0.680
	5	0.770	0.712	0.756	0.690	N/A	0.780
Fetoscopy	1	0.697	0.746	0.834	0.691	0.856	0.857
	2	0.850	0.820	0.852	0.845	0.862	0.873
	3	0.872	0.888	0.896	0.891	0.894	0.901
	4	0.907	0.905	0.924	0.914	N/A	0.924
	5	0.915	0.915	0.960	0.912	N/A	0.960
	6	0.917	0.912	0.917	0.917	N/A	0.926
Hum. cad.	1	0.641	0.659	0.662	0.645	N/A	0.730
	2	0.537	0.594	0.656	0.521	N/A	0.681
	3	0.501	0.501	0.638	0.534	N/A	0.641
	4	0.407	0.416	0.520	0.453	N/A	0.520
	5	0.596	0.577	0.641	0.638	N/A	0.645