## 3 Results and Discussion
### Optimal Waveband Selection Using ANOVA Analysis Results
#### 3.2.2 Development of the Two-Waveband Ratio Algorithm (TWRA)  
Residue Detection Algorithm for Honeydew  
A two-waveband ratio algorithm (TWRA) was developed to detect honeydew residue on the surface of 2B-finished SSS. The resultant optimal wavebands for the original juice up to the 1:100 dilution samples were in the 460-480 nm and 650-680 nm ranges (Figure S3). The TWRA calibration accuracies were 91.79%, 90.56%, 87.51%, 85.40%, 75.19%, and 74.84% with threshold values of 0.98, 0.40, 0.34, 0.18, 0.15, and 0.14, and validation accuracies of 92.44%, 91.63%, 88.67%, 84.36%, 78.23%, and 73.43%, respectively, for the original juice and the 1:5, 1:10, 1:20, 1:50, and 1:100 dilutions. For the TWRA developed to detect honeydew residue on the surface of #4-finished SSS, the optimal wavebands for the original juice were 612 nm and 676 nm (Figure S7). The TWRA calibration accuracy was 90.64% with a threshold value of 0.55 and validation accuracy of 90.61%. The optimal wavebands for the 1:5, 1:10, and 1:20 dilution samples were in the 460-480 nm and 610-640 nm ranges. The TWRA calibration accuracies were 90.43%, 90.53%, and 82.77% with threshold values of 1.27, 1.11, and 0.74, and validation accuracies of 88.28%, 87.74%, and 81.93%, respectively, for these samples. The optimal wavebands for the 1:50 and 1:100 dilution samples were in the 540-580 nm and 640-670 nm ranges. The TWRA calibration accuracies were 62.19% and 59.61% with threshold values of 0.50 and 0.33, and validation accuracies of 62.46% and 59.60%, respectively. Residue Detection Algorithm for Orange  
For the TWRA developed to detect orange residue on the surface of 2B-finished SSS, the optimal waveband for the original juice and dilution samples up to 1:100 were in the 460-480 nm and 640-660 nm ranges (Figure S4). The TWRA calibration accuracies were 92.30%, 90.96% 90.06%, 88.48%, 84.90%, and 74.37% with threshold values of 0.43, 0.63, 0.44, 0.28, 0.17, and 0.17, and validation accuracies of 92.36%, 91.84%, 90.36%, 88.62%, 85.79%, and 72.02%, respectively, for the original juice and the 1:5, 1:10, 1:20, 1:50, and 1:100 dilutions. Based on the TWRA developed to detect orange residue on the surface of #4 finished SSS, the optimal wavebands for original juice, and the 1:5, 1:10 and 1:20 dilution samples were in the 450-470 nm and 610-660 nm ranges (Figure S8). The TWRA calibration accuracies were 97.98%, 91.03%, 90.63%, and 89.03% with threshold values of 0.29, 2.06, 1.64, and 1.13, and validation accuracies of 97.86%, 91.94%, 89.28%, and 89.94%, for these samples. The optimal wavebands for the 1:50 and 1:100 dilution samples were in the 560-608 nm and 664-676 nm ranges. The TWRA calibration accuracies were 88.35% and 88.14% with threshold values of 0.22 and 0.50, and validation accuracies of 88.14% and 87.73%, respectively. Residue Detection Algorithm for Apple  
For the TWRA developed for detecting apple residue on the surface of 2B-finished SSS, the optimal wavebands for the original juice and dilution samples up to 1:100 were in the 460-490 nm and 640-660 nm ranges (Figure S5). The TWRA calibration accuracies were 93.12%, 89.07%, 88.22%, 87.63%, 83.95%, and 77.02% with threshold values of 0.21, 0.70, 0.20, 0.16, 0.19, and 0.11, and validation accuracies of 92.90%, 89.53%, 87.53%, 83.90%, 76.09% and 72.91%, respectively, for the original juice and the 1:5, 1:10, 1:20, 1:50, and 1:100 dilutions. For the TWRA developed for detecting apple residue on the surface of #4-finished SSS, the optimal wavebands for the original juice were 564 nm and 676 nm (Figure S9). The TWRA calibration accuracy was 84.12% with a threshold value of 0.14 and validation accuracy of 84.18%. The optimal wavebands for the 1:5 and 1:10 dilution samples were in the 456-472 nm and 548-564 nm ranges. The TWRA calibration accuracies were 74.19% and 74.03% with threshold values of 0.26 and 0.22, and validation accuracies of 74.37% and 73.93%, respectively. The optimal wavebands for the 1:20, 1:50, and 1:100 dilution samples were 488-505 nm and 612-656 nm.