NDVI and NRG ndvi

NDVI stands for "Normalized Difference Vegetation Index". NRG stands for "Near-infrared / Red / Green". NDVI and NRG are both ways to visualize the amounts of infrared and other wavelengths of light reflected from vegetation. Because both these methods compare ratios of blue and red light absorbed versus green and IR light reflected, they can be used to evaluate the health of vegetation. It's a snapshot of how much photosynthesis is happening. This is helpful in assessing vegetative health or stress. (Read more here: https://www.agronomy.org/publications/jeq/articles/36/3/832) ## Do-It-Yourself These techniques for vegetation analysis were developed for satellite imagery, but at Public Lab, we've been working a lot on capturing infrared imagery using our DIY [near-infrared camera](/wiki/near-infrared-camera) setup, and combining it with visible bands to produce NDVI images such as the one above. ## What these images mean What exactly are these images we're trying to make? What do they tell us about vegetation, and why? These diagrams should help to understand what it is we're doing and why these are good ways to analyze plant life. ## The NDVI equation [![NDVI_is_eq.jpg](/i/44723)](/i/44723) **NDVI = (Near Infrared - Red)/(Near Infrared + Red)** NDVI is a ratio which tries to emphasize photosynthesis while filtering out sun glare. The above equation is run for every pixel, using source data from an infrared photo and a visible light photo, like this pair: [![5390895115_c9d4d38fec_o.jpg](https://publiclab.org/system/images/photos/000/021/771/large/5390895115_c9d4d38fec_o.jpg)](https://publiclab.org/system/images/photos/000/021/771/original/5390895115_c9d4d38fec_o.jpg) The result can be false-colored to make the high-photosynthesis areas more clear, and used to examine where plants are and how healthy they are. [![PetVISNDVIcomp.png](https://publiclab.org/system/images/photos/000/021/770/large/PetVISNDVIcomp.png)](https://publiclab.org/system/images/photos/000/021/770/original/PetVISNDVIcomp.png) _Figure above: Normal color photo (right) and normalized difference vegetation index (NDVI) image (left). NDVI image was derived from two color channels in a single photo taken with a camera modified with a special infrared filter. Note that tree trunks, brown grass, and rocks have very low NDVI values because they are not photosynthetic. Healthy plants typically have NDVI values between 0.1 and 0.9. -- @cfastie_ ### Activities Here are a range of activities you can do to produce and interpret your own NDVI imagery, whether downloaded from a satellite imagery provider or [collected yourself using a DIY technique](/wiki/multispectral-imaging) [activities:ndvi] **** ![IMG_0511-split.png](https://i.publiclab.org/system/images/photos/000/000/279/medium/IMG_0511-split.png) ![infrared-combination.png](https://i.publiclab.org/system/images/photos/000/000/278/medium/infrared-combination.png) Most DIY converted cameras today (those from Public Lab) use RGN instead of NRG, so the blue channel represents infrared instead of the red channel. That looks like this: [![rgn-split.png](/i/45468)](/i/45468?s=o) **** ## NRG imagery Some people are also interested in producing NRG imagery (like the below image), where Near-Infrared, Red, and Green are used to compose a picture instead of the usual Red, Green, and Blue. [![5415783775_502f79ac8c_o.png](/i/25064)](/i/25064) This diagram explains the swapping, which allows us to 'see' infrared as if it were a normal color: [![5396083368_40528d3da2_o.png](/i/25063)](/i/25063) **In NRG images, the deeper and clearer the red color, the denser and healthier the vegetation (more or less).** ### Questions [questions:ndvi] ### Other examples of DIY NDVI imaging From around the internet: Begin watching at 2 minutes to see the resulting imagery: *This topic is part of the [Grassroots Mapping Curriculum](/wiki/mapping-curriculum) series.* **** [![5416397210_5e3be40cf5_o.png](/i/25066)](/i/25066) [![5412520298_93873f36d0_o.png](/i/25065)](/i/25065) ...

asked by @bc512

asked by @rway

Spec Cam to Infragram w/the flip of filter? (Rosco "Fire" #19)
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Modified camera with 25A red filter - NDVI needs calibration- Any Ideas?
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NDVI in realtime video
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How can one Infragram photo produce different NDVI results?
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what are the requirements of a camera for Filter replacement and NDVI imaging?
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How to process images using a mobius with an IR lens?
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Difference Between Image Calibration and Camera Calibration?
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Could this 720nm IR filter from ebay be used for NDVI/infragram?
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I need a help I'm doing a research project on NVDI processes
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How big is the filter in the infragram DIY filter pack?
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How can I have a value of NDVI starting from a IR picture? I want to find a numeric value of NDVI in pictures teken with a normal camera without IR filter. is it possible?
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How to make this picture in an NDVI image
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How can I can make a raspberry pi camera just with the filters process the crops and immediately produce the results to a computer or to other device, without having to use the website?
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Mapir Survey3 RGN image processing pipeline
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Infragram Point and shoot photos: white balance not working
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Creating NDVI images with PI no ir V2
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Should I use two sheets of filter?
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AWB_Gains for PiNoIRCamera V2 (Red Filter)
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What is the working principle of Blue/Red filter
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How to design a camera for calculating ENDVI.
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Bad NDVI Results from Pi NOIR with Blue Filter
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Can you modify a drone's camera for ndvi pictures?
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How can I process the images taken from modified camera?
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How to do the white-balancing for the RED filter?
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Can I use the infragram.org for my thesis? Thanks!
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How should I modify Infragram NDVI settings for Raspberry Pi Noir orbital photos?
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Does anyone know the upper spectrum range of the Pi NoIR Camera V2?
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NDVI results from modified camera is inaccurate
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infragram and Pi NoIR camera - NDVI not working
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How to find the sweet spot for manual white balance settings using Pi NoIR and a blue filter with artificial (full spectrum) lighting
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Counter-intuitive NDVI values in drought-stressed plants? (RPi NoIR v.2 with a red filter and artificial lighting)
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NDVI image issues from GoPro 3+ Silver
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