*2.2. Hyperspectral Image Acquisition System*

The Vis-SWNIR and LWNIR hyperspectral reflectance imaging system (Figure 1) built in the Intelligent Detection Laboratory of China Agricultural Intelligent Equipment Technology Center, was used to acquire the hyperspectral images of moldy maize samples in the wavelength range 327–1098 (nm) and 930–2548 (nm). The Vis-SWNIR hyperspectral imaging system consists of an imaging spectrometer (ImSpector V10EQE, Spectra Imaging Ltd, Oulu, Finland), an electron multi-plying charge-coupled device (EMCCD) camera (Andor Luca EMCCD DL-604 M, Andor Technology plc., Belfast, UK) with a resolution of 502 × 500 and a camera lens (OLE23-f/2.4, Spectral Imaging Ltd., Oulu, Finland), and a spectraCube data acquisition software (Isuzu Optics Corp., Xinzhu, Taiwan, China) controls the operation of mobile platform and acquisition of hyperspectral images. The LWNIR hyperspectral imaging system consists of an imaging spectrometer (ImSpector N25E, Spectral Imaging Ltd., Oulu, Finland), a charge-coupled device (CCD) camera (Xeva-2.5-320, Xenics Ltd., Leuven, Belgium) with a resolution of 320 × 256 and a camera lens (HSIA-OLE22, Spectral Imaging Ltd., Oulu, Finland), spectral acquisition software (Isuzu Optics Corp., Xinzhu, Taiwan, China). The two hyperspectral acquisition systems shared two 300 w halogen lampsadjusted at an angle of about 45 to provide a stable light source, a motorized displacement stage (EZHR17EN, AllMotion, Inc., Union City, CA, USA) for sample placement, and a computer (Dell, Intel (R) Core (TM) i5-2400 CPU @ 3.10 GHz) with two types of hyperspectral acquisition software.

**Figure 1.** Hyperspectral image acquisition system.

The moldy levels of maize varied with the culture time. In this study, to artificially cultivate the maize samples with different moldy grades, sixty samples were taken out from a constant temperature and humidity incubator on day 0, day 2, day 4, and day 6 as the moldy samples at healthy, mild, moderate, and severe levels, respectively. In order to collect the high-quality images without saturation and distortion, hyperspectral images of samples were acquired by line scanning method, and the distance between the lens to the moving platform, the exposure time and the mobile platform speed were set to 430 mm, 3 ms, 2.6 mm/s for Vis-SWNIR hyperspectral systems and 310 mm, 5 ms, 40 mm/s for LWNIR hyperspectral systems, respectively.
