VARI: Estimating Green Cover From an Ordinary RGB Photo

Not every camera carries a near-infrared band — drones, phones and consumer cameras do not. VARI was built to squeeze a vegetation-fraction estimate out of the visible bands alone, which is why it has become a go-to index for low-cost aerial imagery.

How it works

VARI is a normalized combination of green, red and blue that mimics the vegetation contrast NIR would otherwise provide. It leans on the fact that green vegetation is relatively brighter in green and darker in red, while the blue term dampens atmospheric and illumination effects. It correlates surprisingly well with green canopy fraction despite using no infrared at all.

The math behind it

where Green is green reflectance, Red is red reflectance, Blue is blue reflectance.

How to interpret the output

The bands it needs

Real-world use

Its home turf is consumer-drone crop scouting, turf and lawn assessment, and any project where only RGB imagery exists — including squeezing vegetation maps out of archival aerial photography.

Watch out for

Without NIR, VARI is a fraction-of-green estimator, not a biomass or health index, and it is noticeably sensitive to shadow and changing light. Fly at consistent times of day and expect more scatter than an NIR-based index.