## 3 Result and Discussion
### Identification of Fungal Growth Days by Explanatory Principle Component Analysis (PCA)  
PCA on full wavelength images was performed using ENVI software. The same set of replicates of _A. flavus_ and _A. parasiticus_ was then used to analyze the feasibility of the identification of fungal growth days by PCA. The image of each fungal type was analyzed individually. Since PC\({}_{1}\) mainly represents the average that is the common grey value information of the fungi surface, the PC\({}_{1}\) score image was ignored directly in this work. The PC score images (PC\({}_{2}\) to PC\({}_{6}\)) obtained from the PCA of the hyperspectral reflectance image of _A. flavus_ were shown in Figure 5. In PC\({}_{2}\) image, fungi on day 1 showed distinctly lower response than others, as after day 2 mycelia started to grow, and the surface, as well as superficial layer texture of the whole media, was changed, while PC\({}_{3}\) and PC\({}_{4}\) offered the best contrast to fungi on day 5, day 6, and others, individually. It can be inferred that PC\({}_{3}\) and PC\({}_{4}\) may highlight the change caused by conidia emerging. It is thus likely that those PCs can explain variation due to physical differences. In PC\({}_{5}\) score image, fungi on day 2 showed obvious responses. In PC6 score image, fungi on day 3 and day 4 were different to others. Similarly, _A. parasiticus_ incubated for different day also can be identified by PC\({}_{2}\) to PC\({}_{6}\) 2-6 score images. Figure 4: Image of _A. parasiticus_ at 520 nm. Figure 5: The second to sixth principal components (PC\({}_{2}\) to PC\({}_{6}\)) images of _A. flavus_. As individual score images of PC\({}_{2}\) to PC\({}_{6}\) can convey the differences between fungi with different incubation times, the score plot of these 5 PCs was further used to visually display fungi with different incubation times. When plotting PC\({}_{2}\) to PC\({}_{6}\) using the 5-dimensional visualization method and rotating the scatter plot in 5-dimensional PC score space, five distinct clusters of pixels apparently scattered in the score plot (Figure 6a,b). Classification plots were created by assigning each cluster to a class in the score plot and projecting it onto the image to form corresponding classification images (Figure 6c,d). The score plot and classification images of _A. flavus_ were shown in Figure 6a,c. The blue cluster in the plot is associated with fungi on day 1 in the classification image, the cyan cluster is associated with day 2, the mustard cluster is associated with day 3 and day 4, the pink orange cluster is associated with day 5, while the red cluster is associated with day 6. Apart from the difference that was apparent in mycelia density, there were no significant changes between _A. flavus_ on day 3 and day 4. This may cause the unclear distinguishment of _A. flavus_ on day 3 and day 4. _A. parasiticus_ was analyzed in the same way. The score plot and its classification image were shown in Figure 6b,d. The blue cluster in the classification plot is associated with fungi on day 1, the cyan cluster is associated with day 2 and day 3, the mustard cluster is associated with day 4, the pink orange cluster is associated with day 5, while the red cluster is associated with day 6. Because mycelia grew rapidly from day 2 to day 3, _A. parasiticus_ on day 2 and day 3 were misclassified into the same group in the class result image. Similar classification result by PCA score plot was found in the previous study of [PERSON] et al. [24]. The authors used PCA to group the kernels inoculated with fungi for different time intervals (0; 17; 20; 23; 26; 43; 69; 90 h). The maize kernels inoculated and incubated for 20-90 h were considered as one group, since the differences within maize kernels inoculated with fungi for 20-90 h were smaller than differences between groups of inoculated kernels for 20-90 h, uninoculated kernels, and inoculated kernels for 0-17 h.  
A new set of replicates of _A. flavus_ and _A.