Band ratio image ($L_1/L_2$)

An image formed by dividing corresponding calibrated pixels in two spectral bands. If their signals have a common multiplicative factor, $L_1=k{\rho }_1$ and $L_2=k{\rho }_2$, their ratio is ${\rho }_1/{\rho }_2$ and does not depend on $k$. This explains suppression of some common illumination effects and enhancement of spectral contrasts. Additive atmospheric radiance and small denominators prevent exact cancellation and can amplify errors. Normalized difference vegetation index is a related normalized spectral contrast.