TABLE 5.
Wilting accuracy matrix with the number of manually taken wilting scores (2018) on visual scale at the left and outside the table and the count of image-derived wilting scores in the table.
| Image-derived wilting score (0–5 scale) Proximal images | |||||||
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| Visual wilting score | Number of manually taken wilting scores | 0 | 1 | 2 | 3 | 4 | 5 |
| 0 | 4 | 0 | 4 | 0 | 0 | • | • |
| 1 | 72 | 0 | 52 | 20 | 0 | • | • |
| 2 | 65 | 0 | 20 | 41 | 4 | • | • |
| 3 | 26 | 0 | 0 | 20 | 6 | • | • |
| 4 | 0 | • | • | • | • | • | • |
| 5 | 0 | • | • | • | • | • | • |
| Total | 167 | ||||||
| Accuracy | 59% | 0 | 72% | 63% | 23% | • | • |
| Accuracy (second probability method) | 91% | ||||||
| Accuracy (nearest score method) | 99% | ||||||
| Aerial images | |||||||
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| Visual wilting score | Number of manually taken wilting scores | 0 | 1 | 2 | 3 | 4 | 5 |
| 0 | 87 | 85 | 0 | 2 | 0 | 0 | 0 |
| 1 | 13 | 0 | 3 | 8 | 1 | 1 | 0 |
| 2 | 27 | 0 | 2 | 13 | 6 | 2 | 0 |
| 3 | 20 | 0 | 0 | 7 | 6 | 6 | 0 |
| 4 | 16 | 0 | 0 | 5 | 3 | 8 | 0 |
| 5 | 5 | 0 | 0 | 1 | 1 | 2 | 1 |
| Total | 168 | ||||||
| Accuracy | 69% | 98% | 23% | 48% | 31% | 50% | 20% |
| Accuracy (second probability method) | 81% | ||||||
| Accuracy (nearest score method) | 90% | ||||||
Wilting was on a scale of 0 to 5†. The percentage represents the fraction of wilting values that were estimated correctly using RGB color indices‡ derived from RGB images. Indices were used to estimate leaf wilting using ordinal logistic regression*. The proximal images were taken 11 and 13 weeks after planting (WAP), whereas the aerial images were taken 15 WAP.
†A score of 0 represents potentially healthy plant with no wilting or leaf drooping symptoms; 1 represents some terminal and newer leaves fold up but overall the plant looks healthy; 2 represents an almost all leaves fold up and show signs of wilting, lower and older leaves start to fold; 3 represents wilting and drooping shows up on all leaves of the plant, low-moisture effect on older leaves is more prominent, bare ground starts to show up under the plant as leaves wilt; 4 represents all leaves are wilted and some leaves start to change color due to chlorophyll degradation, bare ground is prominently visible, some leaves have dried and crisped up; 5 represents all leaves have severely wilted and color of all leaves is light green to yellow, bare ground is fully visible, more than 50% of leaves are crisp and dry, the plant is almost physiologically dead.
‡RGB color indices – Intensity, Hue, Saturation, Lightness, a*, b*, u*, v*, green area (GA), greener area (GGA), crop senescence index (CSI).