# Characterization and Separation of Traditional and Bio-Plastics by Hyperspectral Devices
## 2 Materials and Methods
### Spectral Acquisition Procedure  
Hyperspectral images are acquired with a platform based on the use of two linear spectrometers. The system, composed of one VIS and one NIR Specim Imspector spectrometer, has a spectral range 400-1700 nm, but only the region of the Near InfraRed (NIR, 900-1700 nm region) allows the unambiguous characterization of materials through highlighting features related to their chemical structure. The facility employed for the experimental investigation of this study comprises: one NIR Specim Imspector spectrometer, centered in the near infrared region (900-1700 nm), mounted in front of an InGaAs Sensor Unlimited camera, 320 x 240 pixel resolution, 25 um x 25 um pixel pitch, 50 fps maximum frequency of acquisition; one high-speed DVR Express @CORE with two Camera Link inputs used to acquire and manage the data, containing 1-terabyte solid state disk array; one power supply; one processing computer for controlling the entire system and managing image acquisition and storage; one lighting system comprising of two 500 Watt halogen lamps to ensure a proper sample \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Name**} & **Description and** & \multirow{2}{*}{**Sample Origin**} & \multirow{2}{*}{**Color**} & **Measured Density** & **Characteristic Size** \\  & & & & **(g/cm\({}^{3}\))** & **(cm)** \\ \hline PET\_V & Virgin particle & Primary raw & & & \\  & granules & material & & & \\ PET\_O & Water bottle & & & & \\  & Original shape & & & & \\ PET\_P & Water bottle & & & & \\  & Pieces & & & & \\ PET\_F & Water bottle & & & & \\  & Flakes & & & & \\ PS\_V & Virgin particle & Primary raw & & & \\  & granules & material & & & \\ PS\_O & Disposable dish & & & & \\  & Original shape & & & & \\ PS\_P & Disposable dish & & & & \\  & Pieces & & & & \\ PS\_F & Disposable dish & & & & \\  & Flakes & & & & \\ PLA\_V & Virgin particle & Primary raw & & & \\  & granules & material & & & \\ PLA\_1\_O & Water bottle & & & & \\  & Original shape & & & & \\ PLA\_1\_P & Wireless & & & & \\  & Water bottle & & & & \\ PLA\_1\_F & Flakes & & & & \\ PLA\_2\_O & Disposable dish & & & & \\  & Original shape & & & & \\ PLA\_2\_P & Disposable dish & & & & \\  & Pieces & & & & \\ PLA\_2\_F & Flakes & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Origin, shape, color, density and mean particle size of the samples investigated. illumination; one Spectralon panel as white reference standard; one conveyor belt to allow the target displacement at a constant rate. Images were acquired at 50 fps and the spectral resolution was 3 nm. A linear spectrometer captures a line image of the target and disperses the light from each line image pixel into a spectrum. Each spectral image contains the spatial information along an axis and the spectral information along the other axis. Multiple images must be acquired to reconstruct a two-dimensional scene based on the combination of several lines. In our setup, the image rows contain the spatial information, whereas the image columns the spectral information. The geometric calibration procedure described in [10] has allowed the detection of the portion of the NIR sensor useful for the construction of the hyperspectral cube. It also made it possible to determine the correspondence wavelength-column index. The spectral information occupies 254 columns with a spectral resolution of 0.32 pixel/wavelength. The objects under investigation are placed on a conveyor belt moving at a constant speed in a known direction and the spectrometer slip was set orthogonal to that direction. The reconstruction of the scene at a certain wavelength \(\lambda_{\text{j}}\) was obtained by simply placing all j-th columns of the acquired image sequence side by side. The samples are also investigated by a spectroradiometric device, in order to verify the presence and the position of absorption and reflectance peaks detected with the spectrometer platform. Spectra are acquired using a FieldSpec 4 (A.S.D.