The NDREI operator algorithm computes the Normalized Difference Red Edge Index from a given product.

The NDREI results from the following equation:

NDREI = (N - RE1) / (N + RE1)

, where:

The bands are:

- RE1 is the Red Edge 1 band
- R is the Red band
- N is the NIR band

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

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