Table. 1: Defect positioning error and measure length error of the test results and defects grayscale difference.

Project		1#	2#	3#	4#	5#	6#	7#	8#
Distance and error /centroid coordinate xD	Actual distance /mm	60	200	340	480	60	200	340	480
	Image displaying distance /mm	2×31	2×100.5	2×170	2×239.5	2×30	2×101	2×170.5	2×241
	Relative to the actual distance /mm	60	60	60	60	60	60	60	60
	Relative positioning error /%	3.33	1.67	0	1.67	0	3.33	1.67	3.33
Length and error	Actual length /mm	40	40	40	40	40	40	40	40
	Image displaying length /mm	2×15	2×19	2×20	2×21	2×20	2×20	2×21	2×22
	Relative error /%	25	5	0	5	0	0	5	10
Gray value and gray difference	Average gray value of the defect	106.13	94	52.52	22.36	142.33	157.43	222.86	231.30
	Average gray value of the weld	107.84	107.84	107.84	107.84	107.84	107.84	107.84	107.84
	Gray difference	-1.71	-13.84	-55.32	-85.48	34.49	49.59	115.02	123.46