Question: Best NDVI Filter

abrenner is asking a question about general: Follow this topic

abrenner asked on April 22, 2017 19:11
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Hello, I am new to NDVI but am trying to figure out what the difference is between an NGB and NRG filter. Which may be the better option, and why?



3 Comments

Are you interested in the difference between a blue filter and a red filter? A blue filter could be referred to as NGB (red is blocked and NIR replaces red in RGB). A red filter could be referred to as RGN (blue is blocked and NIR replaces blue in RGB). Ned has a note about why a red filter can be better for vegetation analysis: https://publiclab.org/notes/nedhorning/11-01-2013/why-a-red-filter-should-work-well-for-ndvi. Also, blue filters don't seem to work very well with small CMOS sensors which most webcams and small cameras have.

Chris

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There can be a lot of NIR contamination in the red channel when using RGN filters, especially in bright tropical sun at midday. To get higher NDVI contrast, I usually subtract the blue NIR channel from the red visual channel in Fiji/ImageJ before running the NDVI calculation.

This is on a cheap action camera, maybe compact and DSLR cameras have cleaner sensors.

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