Table 2.

SNR values for each processing techniques and flat-bottomed holes.

Defect ID.	SNR
	Raw Image	TSR	PPT	PCA
A1	33.26	40.46	45.24	47.78
A2	-	32.39	42.15	44.56
A3	-	39.18	43.92	47.15
A4	28.17	39.47	44.56	47.72
B1	19.18	31.18	46.28	41.60
B2	-	26.15	-	-
B3	-	31.75	33.65	31.90
B4	12.19	28.78	40.76	38.85
C1	32.14	38.98	46.55	46.58
C2	-	32.29	36.52	34.91
C3	-	39.47	45.41	45.58
C4	28.39	38.28	45.90	46.76
D1	23.96	28.78	47.12	44.52
D2	-	15.62	-	-
D3	-	27.82	45.91	40.26
D4	21.44	27.64	47.10	44.16

Note: The symbol ‘-’ is the representation of non-detected defects.