“…Several preprocessing schemes are selected for evaluation based on the summary in Table 1: - Single preprocessing schemes: None, SG, SG1D, SG2D, MC, AS, SNV, MMN, RNV25, RNV50, RNV75, AN, VN, MSC, OSC, NAS, and ALS; these count as 17 methods.
- SGxD followed by MC, AS, SNV, MMN, RNV25, RNV50, RNV75, AN, VN, MSC, OSC, NAS, or ALS; these count as 39 methods.
- MC, AS, SNV, MMN, AN, VN, MSC, OSC, NAS, or ALS followed by SGxD; these count as 30 methods. The methods contained in the second group and the third group can be frequently found in the literature.
- OSC + normalization 56 : OSC + MC, OSC + AS, OSC + SNV, OSC + VN, OSC + AN, OSC + MMN; these count as six methods.
- The two‐method permutations composed of VN, MC, SNV 32,50,52,54,55 count as 6 methods.
- Other methods include AN + SGxD + MC, 59 SGxD + AN + MC, 58 MSC + SGxD + MC, 25 and ALS + SNV 49 ; these count as 10 methods.
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