The above equation is used for calculate the ENDVI value. I am interesting how to modify the camera to capture NGB. I have asked the similar question before and someone suggested me try to use orange or yellow filter. Which can filter out the blue. The working principle of orange or yellow filter is shown as below: https://publiclab.org/notes/cfastie/01-16-2015/orange-is-the-new-red. Is it use the green ray to replace the blue in the above equation? Any other low cost (as I know a triple bandpass filter can also been used) methods can be used apart from the orange filter? Thanks for your helping hands.