Table 3.
Methods of image pre-processing.
| Normalization | Smoothing Denoising | Wave Selection | Feature Dimensionality Reduction | Calibration | Remarks | |
|---|---|---|---|---|---|---|
| [43] | Normalized reflectance spectra | |||||
| [31] | Normalized reflectance spectra | |||||
| [33] | Normalized reflectance spectra | |||||
| [63] | Normalized reflectance spectra | Glare Removal | ||||
| [34] | Normalized reflectance spectra | Savitzky–Golay smoothing | Manual background segmentation, automatic region of interest (ROI) selection | |||
| [80] | PCA | |||||
| [35] | Savitzky–Golay smoothing | PCA | First-order derivation for spectral dimension preprocessing | |||
| [17] | PCA | |||||
| [36] | PCA | |||||
| [37] | SNV | |||||
| [81] | SNV | |||||
| [82] | Normalized reflectance spectra | PCA | ||||
| [38] | Normalized reflectance spectra | Fixed Reference t-Distributed Stochastic Neighbors Embedding | HySIME noise filtering and extreme noise band Removal and spectral averaging | |||
| [83] | Normalized reflectance spectra | PCA | ||||
| [39] | Normalized reflectance spectra | PCA | ||||
| [84] | Shannon entropy | |||||
| [40] | Machine learning pre-processing | |||||
| [85] | Normalized reflectance spectra | PCA | Singular Spectrum Analysis (SSA) | |||
| [41] | Normalized reflectance spectra | Smoothing filter noise processing | ||||
| [86] | PCA | |||||
| [31] | Normalized reflectance spectra | |||||
| [42] | Normalized reflectance spectra | |||||
| [87] | Normalized reflectance spectra | Smoothing filter noise processing | ||||
| [88] | ICA | K-means | ||||
| [43] | Normalized reflectance spectra | |||||
| [44] | Normalized reflectance spectra | |||||
| [45] | Normalized reflectance spectra | |||||
| [89] | Normalized reflectance spectra | |||||
| [90] | Normalized reflectance spectra | ACO | Band Selection for Ant Colony Optimization (ACO) | |||
| [91] | PCA | |||||
| [46] | Normalized reflectance spectra | PCA | ||||
| [47] | Ratio between original Image and reference image | |||||
| [48] | Normalized reflectance spectra | |||||
| [51] | Normalized reflectance spectra | PCA | ||||
| [52] | PCA | |||||
| [49] | Normalized reflectance spectra | Smoothing filter noise processing | ||||
| [53] | Normalized reflectance spectra | |||||
| [54] | PCA | |||||
| [55] | PCA | |||||
| [56] | Median Filter | |||||
| [57] | Normalized reflectance spectra | Savitzky–Golay smoothing, gaussian filtered spatial smoothing | PCA | Outlier removal, background recognition | ||
| [92] | Standard normalization transformation | Gaussian filtered spatial smoothing | ||||
| [59] | Normalized reflectance spectra | |||||
| [60] | Normalized reflectance spectra | 3-order median filter, curvature correction | GFP bands removal | Background removal | ||
| [61] | Normalized reflectance spectra | |||||
| [62] | Normalized reflectance spectra |