Good day! I am new to the concept of NDVI and got interested in it since it allows for easier monitoring of the health of a crop with a use of a camera only. I have at hand the infragram kit and successfully modified a Canon camera (CHDK enabled) using red filter.
I would like to inquire regarding the post-processing of acquired images. I have learned that the red filter allows Red + NIR to pass. How can Red and NIR values be separated in the red channel? I have read in some comments that(a) 80% of the NIR in the blue channel is subtracted from the values in the red, and (b) 40% of the NIR is subtracted. What are the basis for these percentage? What factors/settings may affect this percentage?