NDI45

The Normalized Difference Index algorithm is more linear, with less saturation at higher values than the NDVI.

Some algorithms have already been presented in work by Delegido et al. (2011b) which specifically investigated the optimal bands to use in the NDVI formula with synthesised Sentinel-2 data.
Research found that bands 4 and 5 were the optimal combination.

The NDI45 results from the following (Sensor-dependent) equation:

NDI45 = (IR_factor * near_IR - red_factor * red) / (IR_factor * near_IR + red_factor * red)

For Sentinel-2 the formula is:

(B5 - B4) / (B5 + B4), where (Central wavelength/Bandwidth): B5 = 705 nm (15 nm), B4 = 665 nm (30 nm)

NDI45-Flags

Also the processor computes an additional flags band called 'ndi45_flags' with the following bit coding:

Bit Position	Description
Bit 0	The computed value for NDI45 is NAN or is Infinite
Bit 1	The computed value for NDI45 is less than -1 (minus one)
Bit 2	The computed value for NDI45 is greater than 1 (one)