Fig. 1. Original spectral data of corn leaves under different stress gradients
(a): Original spectral curve of corn leaves under different Cu²⁺ concentration stress; (b): Original spectral curve of corn leaves under different Pb²⁺ concentration stress

Fig. 2. Spectra processed by different spectral conversions

Fig. 3. Correlation between CLI and Cu-Pb element types of each order

Fig. 4. The distribution of two-dimensional copper-lead discriminant feature points and discriminant rule lines in the training set

Fig. 5. The distribution of two-dimensional copper-lead discriminant feature points and discriminant rule lines in the verification set

Fig. 6. The distribution of three-dimensional copper-lead discriminant feature points and discriminant rule plans in the training set

Fig. 7. The distribution of three-dimensional copper-lead discriminant feature points and discriminant rule plans in the verification set