## 3 Results and Discussion
### Measurements Related to Morphological Characteristics of the Plants  
Figure 16 illustrates a detection and localization example of five lettuce plants over a four-week period. The identified plants, labeled as A to E, were consistently photographed every Thursday starting at 12:00 am, throughout the laboratory experiments. The colored cropped images, which were further analyzed and processed in the specific experiment, had dimensions of 888 \(\times\) 888 pixels. The red circle in the figures represents the minimum enclosing circle of each plant's contour, which is plotted in blue. Additionally, the small red circle and blue square in each figure indicate the center of the circle and the centroid, respectively. The plot clearly demonstrates the successful detection and localization of all five lettuce plants across different growth stages. In Figure 17, an enlarged depiction of plant A is provided, illustrating example results of the 4-week growth interval experiment. The experimental outcomes for this plant are presented in the first row of the figure, which aligns with the first column of Figure 16. The second row of Figure 17 displays the corresponding results of manually traced plant contours (represented by yellow squares) for the same images. Additionally, the centroid of each contour is overlaid as a small magenta circle, facilitating a direct visual comparison. Table 6 also displays, as an example, the results concerning the computed total projected leaf area as related to the manual traced outcomes for this 4-week experiment. The evaluation metrics IoU, Precision, Recall, and F1 score are utilized again to compare these outcomes with the corresponding plant features obtained through the manual tracing of the lettuces' contours. \begin{table}
\begin{tabular}{c c} \hline \hline
**Evaluation Metric** & **Result** \\ \hline IoU & 0.761 \(\pm\) 0.054 \\ Precision & 0.764 \(\pm\) 0.046 \\ Recall & 0.979 \(\pm\) 0.042 \\ F1 score & 0.857 \(\pm\) 0.042 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Evaluation metrics results for the 15 iterations experiment on 6 baby lettuces. Table 6 also depicts the Euclidean distance \(m_{dt}\) (in pixels) between the centroids of the polygonal shape contour, which is automatically computed experimentally for each plant, as related to the corresponding one calculated from the manual traced plant contours. In a similar fashion, the \(c_{dt}\) (in pixels) is reported for the Euclidean distance of the centers of the minimum enclosing circles for each plant. With the symbols \(D_{man}\) and \(D_{exp}\), the diameters (in pixels) are considered for these circles, which, at the same time, correspond to the maximal distance between two pixels belonging to the lettuce (by means of the longest distance between any two points on  
Figure 16: Plant identification and localization results of 5 lettuce plants, in 4-week growth-stage intervals (color figure online). Figure 17: The first row depicts a zoomed-in version for plant A’s experimental results from Figure 16, for the 4-week growth interval. In the second row, the respective results of the manually traced plant contours (in yellow squares) for the same photographs, along with the respective center of mass overlaid in each one as a small magenta circle, are presented for a direct visual comparison (colored figure online). its contour's perimeter outline). Other parameters frequently used for quantifying plant growth using image analysis, which are reported in Table 6 for the specific experiment, are the stockiness \(S_{man}\) and \(S_{exp}\), which is a measure of circularity, or in other words, the roundness, with a value in the range 0 to 1 and compactness \(C_{man}\) and \(C_{exp}\), which expresses the ratio between the area of the plant and the area enclosed by the convex hull (by means of the contour of the smallest convex polygon that surrounds the plant) [30; 56; 57; 58; 59; 60]. The stockiness involves the area (\(A\)) and the perimeter (\(P\)) calculations of the leaves and depicts the difference with a circle.