The G-2 cluster (22 compounds) contained a saturated aliphatic hydrocarbon as its main chain and alkenes, alkyne groups, CN, and ketone groups as branches. In addition, inorganic compounds, such as BN and MgO, were included in this cluster because the signals of the aliphatic hydrocarbons used in the Nujol method were observed. A copper complex was also assigned; however, the CH stretching characteristic appeared at approximately 3000 cm -1 , which was derived from the ligand matching that of the G cluster. In addition, the amino and carboxyl groups were different from those of the other compounds; therefore, they were located on separate branches. The average TC was low (0.2179) because of the inclusion of inorganic compounds and metal complexes. Noise immunity. To assess the robustness of our method to noise, we performed hierarchical clustering on images with added white noise. The internal structure of each cluster remained stable even when noise with a σ (noise σ indicates the degree of noise variation; the higher the value, the greater the effect of noise and the greater the fluctuation in pixel values) of 20 was introduced (Figure ). However, although the bonds between clusters did not change at σ of 5 and 10, they were altered at σ of 20. This sensitivity at higher noise levels may be attributed to the intermediate nature of cluster F, which contains compounds with both aromatic and aliphatic features, making its association with other clusters more susceptible to noise-induced variations. Furthermore, we tested the method's resilience to extreme image degradation by changing the pixel values of the white parts (pixel value = 255) of the image to 1, making it appear completely black to the human eye. Despite this drastic alteration, the hierarchical clustering results remained unchanged (Figure ). These findings demonstrate the high resistance of our image-based method to degradation of image quality, suggesting its potential applicability even with noisy or low-quality spectral images.