Fig. 9

Leaf morphometric parameters for different levels of standardised artificial damage (0–5) inflicted on spinach leaves. Results shown are average values for negative (N = 25) images and each damage level for positive (N = 5) images. The morphometric parameters A leaf area, B number of lesions, C lesion area and D leaf damage (%) were compared. Area was measured in pixels (px) and leaf damage was calculated as \(Damage = \left( {\frac{lesion area}{leaf area}} \right) \times 100\). Dashed horizontal line represents the overall mean across damage levels. A nonparametric Kruskal–Wallis test was used, followed by Dunn′s post hoc test. Significant differences (p ≤ 0.05) identified in the post hoc test are indicated by different lower-case letters (a, b) (Additional file 7). E Results of linear regression analysis between number of lesions and lesion size