RGB vegetation indices explained: VARI, ExG and GLI vs NDVI.

The formulas

• VARI (Visible Atmospherically Resistant Index) = (G − R) / (G + R − B)
• ExG (Excess Green) = 2G − R − B, often on normalised bands
• GLI (Green Leaf Index) = (2G − R − B) / (2G + R + B)

Strengths and limits

These indices are free to compute and good at separating vegetation from soil. They are sensitive to lighting, shadows and camera colour processing, and they track greenness rather than the near-infrared response NDVI captures.

Learned RGB NDVI

Instead of a fixed formula, a model can learn the relationship between RGB pixels and NDVI from paired samples. Nabhya uses this approach to output a near-NDVI vigour field from ordinary drone frames. Read more on our NDVI from RGB page.