Table 2.
Reliability of the Threshold Methodologies
| 95% CI | |||||
|---|---|---|---|---|---|
| Threshold Methodologies | Mean Gray Value VD (%) | ±SD Gray Value VD (%) | ICC | Lower Bound | Upper Bound |
| 1-Step Threshold Methods | |||||
| Manual Threshold | 29.1 | ±4.9 | 0.525 | −0.090 | 0.839 |
| Mean Global Threshold | 40.3 | ±2.7 | 0.245 | −0.117 | 0.636 |
| Otsu Global Threshold | 29.7 | ±4.7 | 0.463 | −0.056 | 0.791 |
| Mean Local Threshold | 34.3 | ±5.0 | 0.836 | 0.567 | 0.944 |
| Otsu Local Threshold | 28.8 | ±5.2 | 0.516 | −0.099 | 0.836 |
| Phansalkar Local Threshold | 34.0 | ±6.1 | 0.831 | 0.547 | 0.943 |
| 2-Step Threshold Methods | |||||
| Close Morphology (1pxl) + Mean Local Threshold | 34.1 | ±4.9 | 0.838 | 0.567 | 0.945 |
| Close Morphology (1pxl) + Phansalkar Local Threshold | 34.6 | ±6.2 | 0.822 | 0.541 | 0.939 |
| Close Morphology (2pxl) + Mean Local Threshold | 34.2 | ±4.8 | 0.841 | 0.574 | 0.946 |
| Close Morphology (2pxl) + Phansalkar Local Threshold | 36.3 | ±6.6 | 0.763 | 0.352 | 0.920 |
| Bandpass Filter + Mean Local Threshold | 34.7 | ±5.0 | 0.835 | 0.574 | 0.943 |
| Bandpass Filter + Phansalkar Local Threshold | 37.9 | ±6.0 | 0.832 | 0.556 | 0.943 |
| Frangi Filter + Mean Local Threshold | 49.1 | ±7.2 | 0.679 | 0.253 | 0.884 |
| 3-Step Threshold Methods | |||||
| Top hat Filter + Mean Local Threshold | 29.7 | ±4.2 | 0.604 | −0.086 | 0.882 |
| Bandpass Filter + Gaussian Blur + Otsu Local Threshold | 36.5 | ±4.9 | 0.762 | 0.213 | 0.927 |
| Cornea Filter + Close Morphology + Mean Local Threshold | 24.7 | ±5.3 | 0.316 | −0.074 | 0.727 |
| Gold Standard Images | 33.9 | ±5.7 | — | — | — |
SD, standard deviation; pxl, pixel.
Methodologies with good reliability, ICC ≥0.750 (bold), that were selected for pxl location accuracy assessment.