I'm working with a mapir nir + red camera meaning that its blue band captures nir light and its red captures red normally. I understand that NDVI is calculated using reflectance values.

How do I convert 8 bit RGB into reflectance values so that I'm able to calculate each NDVI value? Also, does converting an image to grayscale mean its reflectance?

  • You are working with a photo camera with a normal sensor (I suppose), maybe without the ir filter. Reflectance is calculated with radiance from a spectral sensor, they are not the same
    – aldo_tapia
    Nov 14, 2018 at 10:46
  • 3
    You can calculate NDVI from DN values of any bit depth., it is not necessary to convert to radiance or reflectance. This is only considered necessary when using sensor data and comparing images through time. Jan 12, 2019 at 1:16

1 Answer 1


Please go through this page:


This clearly tells you how to convert a DN value to reflectance. The important point to consider are multiplicative and additive re-scaling factor. As you'll clearly see, either these values are known to you (through metadata) or need to be calculated through more esoteric methods. It seems maybe the values are with OEM. If not, then there is no immediate way to convert DN values to reflectance.

  • Please read the post carefuly and note that the OP asked for reflectance correction using a "mapir nir + red camera". Even that caveat aside, assuming OLI could very well be erroneous and each sensor has it own equations for deriving reflectance. Jan 9, 2020 at 23:38
  • @JeffreyEvans I thought I made it clear with my answer that rescaling factors will be unique for each sensor. But you are right in saying that the 'formula' for conversion will be unique for the sensor and not as simple as OLI.
    – OverArch
    Jun 24, 2020 at 7:58

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