Figures (7)  Tables (3)

    • Figure 1. 

      Sample spectra of apples.

    • Figure 2. 

      Boxplot and normal curve plots of firmness.

    • Figure 3. 

      Wavelength processing graph based on the seven different pre-processing algorithms and the raw wavelength graph. (a) Min Max Scaler, the spectrum of the MMS for dataset, (b) Standard Scaler, the spectrum of the SS for dataset, (c) Mean Centering, the spectrum of the CT for dataset, (d) Standard Normal Variate, the spectrum of the SNV for dataset, (e) Moving Average, the spectrum of the MA for dataset, (f) Savitzky Golay, the spectrum of the SG for dataset, (g) Multiplicative Scatter Correction, the spectrum of the MSC for dataset, (h) Raw Wavelength, the spectrum of the RW for dataset.

    • Figure 4. 

      Firmness feature extraction of CARS. Trend charts of (a) selecting the number of wavelengths and (b) RMSECV.

    • Figure 5. 

      Firmness feature extraction of RF.

    • Figure 6. 

      Matrix heatmap.

    • Figure 7. 

      Line plots of actual vs predicted firmness on the prediction set.

    • Method $ {R}_{c}^{2} $ RMSEC $ {R}_{p}^{2} $ RMSEP
      MMS 0.7247 0.8081 0.7130 0.8330
      SS 0.7795 0.6855 0.7690 0.7336
      CT 0.7758 0.6935 0.7780 0.7083
      SNV 0.7750 0.6993 0.7861 0.6770
      MA 0.7876 0.6481 0.6778 0.8902
      SG 0.7913 0.6434 0.6680 0.9013
      MSC 0.7862 0.6525 0.7925 0.6537
      RW 0.7942 0.6357 0.7891 0.6613

      Table 1. 

      Comparison of different processing methods in the calibration set and prediction set.

    • Model No. of wavelengths $ {R}_{c}^{2} $ RMSEC $ {R}_{p}^{2} $ RMSEP
      RW-PLS 462 0.7862 0.6505 0.7925 0.6537
      CARS-PLS 13 0.8484 0.5965 0.8325 0.6257
      RF-PLS 17 0.7666 0.6719 0.7480 0.7054

      Table 2. 

      Comparison of different feature wavelengths in the calibration set and prediction set.

    • Model Input $ {R}_{c}^{2} $ RMSEC $ {R}_{p}^{2} $ RMSEP
      PLS CARS 0.8484 0.5965 0.8325 0.6257
      MLR CARS 0.8843 0.4994 0.8718 0.5069
      HTL CARS 0.9344 0.4487 0.9254 0.4691
      BPNN CARS 0.9523 0.4184 0.9350 0.4654

      Table 3. 

      Parameter evaluation of models and CARS feature wavelengths for firmness prediction.