## 2 Materials and Methods  
### Hardware Composition  
The sweet pepper greenhouse maintained a temperature between 20 and 30 \({}^{\circ}\)C and a relative humidity between 60 and 80% [28]. A Blackfly BFLY-U3-13S2C-C color camera (Teledyne FLIR LLC, Wilsonville, OR, USA) was selected to obtain images in the sweet pepper greenhouse (Table 1). The operating temperature range of the selected camera was 0-45 \({}^{\circ}\)C. The humidity was 20-80%. Most images were in the 400-950 nm range to analyze the NDVI. The image sensor used in this study acquired images from 400 to 950 nm (Figure 1).  
The standard size of the passage width of the sweet pepper greenhouse was 1.6 m. The width between crops not interrupted by sweet pepper crops when moving from one passage to another was 1.0 m [29]. The planting density ranged from 3.3 to 3.5 stems/m\({}^{2}\)[30]. The  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Model** & **Imaging Sensor** & **Resolution** & \
\begin{tabular}{c} **Operating** \\ **Temperature** \\ \end{tabular} &
\begin{tabular}{c} **Operating** \\ **Humidity** \\ \end{tabular} \\ \hline Blackfly BFLY- & Sony ICX445, & 1288 \(\times\) 964 & 0–45 \({}^{\circ}\)C & 20–80\% \\ U3-13S2C-CS & 1/3”, 3.75 μm & (30 FPS) & 0–45 \({}^{\circ}\)C & 20–80\% \\ \hline \hline \end{tabular}
\end{table}
Table 1: Specifications of the Blackfly BFLY-U3-13S2C-CS color camera.  
Figure 1: Spectral sensitivity of the imaging sensor, Sony ICX445.  
spacing of sweet pepper nutrient solution beds based on the planting density was within 0.3 m. An 8 mm lens was selected to acquire images of the sweet peppers planted at intervals of 0.3 (the minimum) to 1.0 m (the maximum). The size of the Sony ICX445 image sensor on the selected camera was \(1/3^{\prime\prime}\). The field of view (FOV) according to the working distance using an 8 mm lens is shown in Figure 2. The distance between the pupils of human eyes ranges from about 60 to 75 mm [31]. Thus, the distance between cameras was set to 70 mm to acquire sweet pepper images (Figure 3). According to Figure 2, the area of the imaging system in this study overlapped from a maximum of 530 to a minimum of 230 mm. The average length of sweet pepper leaves was 223 mm. The average leaf width was 121 mm [32] and the average diameter of sweet pepper fruit was 80.92 mm, suitable for obtaining overlapping images of each sweet pepper part at the corresponding distance.  
The device for obtaining images of the sweet peppers was designed as shown in Figure 3a. Figure 3b shows image acquisition. The sweet pepper was planted in nutrient solution beds. The minimum height of the nutrient solution beds was 0.1 m and the camera's FOV at 1 m was 0.6 m. Thus, the height of the camera from the ground was set at 0.7 m. In addition, halogen lamps were selected as image light sources. Three lamps each  
Figure 3: A structure for image acquisition (**a**) and image acquisition in the greenhouse (**b**).  
Figure 2: FOV of 8 mm lens and overlapping area of vision system.  
were installed on the upper side and the lower side for lighting. A halogen lamp 44870 WFL (Osram, Munich, Bavaria, Germany) was selected as an image light source to assist image acquisition in order to obtain an image from the 435-950 nm region. The selected lamp had a brightness of 680 lm of 50 W and a color temperature of 3000 K. Halogen lamps have a broad spectrum from visible light to infrared regions [33]. For image analysis using the NDVI, a band-pass filter from the 435 to 950 nm region of BP-Series (Midwest Optical Systems, Palatine, Illinois, USA) was used. Specifications of the band-pass filter used are shown in Table 2.