Fig. 1. Noise reduction processing of Raman spectral signal of xylene^[26]

Fig. 2. Signal decomposition method for noise reduction of soybean oil with low signal-to-noise ratio by Raman spectra^[28]

Fig. 3. Comparison of ALWT algorithm with S-G filter and dWT for spectral simulation denoising (offset for visualization)^[30]. (a) y1, noise 10%; (b) y2, noise 20%t; (c) y3, noise 30%

Fig. 4. DTDDW processing effect^[31]. (a) Removal of pulse spikes; (b) noise reduction

Fig. 5. Raman spectral noise reduction results of cutoff optimized IDAR and other algorithms^[37]. (a)(b) NaHCO₃ powder; (c)(d) Vitamin C tablets

Fig. 6. Linear programming polynomial fitting baseline correction for Raman spectra of mouse liver^[43]

Fig. 7. Adaptive B-spline baseline correction effect^[45]

Fig. 8. GACspline baseline correction effect^[48]

Fig. 9. Baseline correction for noise spectra by DSTAspline^[51]

Fig. 10. Baseline correction effect based on dWT^[54]. (a) Original spectrum; (b) wavelet noise reduction; (c) dWT low-frequency reconstruction spectrum and its first derivative; (d) Gaussian fitting reconstructed Raman peak

Fig. 11. AWFPSI correction effect on baseline^[56]. (a) 7% glycerin and water; (b) 28% glycerin and water; (c) alcohol; (d) carbon tetrachloride; (e) polytetrafluoroethylene; (f) methanol

Fig. 12. Automatic Raman spectrum extraction based on CWT (noise reduction and baseline correction)^[57]. (a) Raman spectrum of skin cancer tissue; (b) treatment effect

Fig. 13. Comparison of baseline correction effects of ALS, airPLS, and arPLS^[60]. (a) Simulated Raman spectra; (b) true Raman spectral signals for 2, 6-dinitrotolune

Fig. 14. Baseline fitting comparison results of SEALS method and six other methods on simulated data^[65]. (a) Convex strong fluorescent background; (b) exponential strong fluorescent background; (c) affected by noise and fluorescent background

Fig. 15. Improved piecewise linear fitting correction of 266 nm UV Raman spectral base^[69]

Fig. 16. CVDE cluster visualization (10 classes) on non-preprocessed and preprocessed soybean oil Raman spectra