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) ...

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rishabh326_info "An infrared camera (also known as a thermal imager) detects and measures the infrared energy of objects. The camera converts that infrared data int..." | Read more » over 1 year ago
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gadgets_africa "Points that help you with regards to buying the best Smartphones Nairobi There are many users who want to know the basic points that one should ch..." | Read more » almost 2 years ago
Ag8n "It looks like a single beam instrument was used for this work. With a double beam instrument, there is no need for phrases like "OD435/OD415". Th..." | Read more » almost 2 years ago
imvec " @imvec has marked @xose as a co-author. " | Read more » almost 2 years ago
warren "wow the blue color of your image looks quite good. It could be interesting to take a picture of some grass or some vegetation that's more consisten..." | Read more » almost 2 years ago
xose "You can use the pi-builder to embed it on a Raspberry pi. The software consists in a camera interface, the image sequencer and the infragram ;D ht..." | Read more » almost 2 years ago
Ag8n " Lichen1.docx Hopefully, this will attach. " | Read more » almost 2 years ago
Ag8n "In this area, lichens aren't common. Attached is a rough draft using lawn clippings to set up and test using various instruments. Don't know how ..." | Read more » almost 2 years ago
bhamster "Hi @jdetka, this question by @patalbright and the comments section might have some tips to try: How to find the sweet spot for manual white balance..." | Read more » almost 2 years ago
jdetka "Hello, Did you make any additional progress with this? I'm trying to do the same thing and maybe we can collaborate on a solution. " | Read more » almost 2 years ago
jdetka "Is there a way to run the infragram code locally on a PC? I'll be in a region that doesn't have internet but I still want to be able to analyze ima..." | Read more » almost 2 years ago
scottroger411 "thanks for sharing this information with me. " | Read more » almost 2 years ago
Ag8n "The tungsten lamp remarks only apply to the 660 nm red lines. " | Read more » about 2 years ago
Ag8n "Best bet- use an old fashioned tungsten lamp. Not a LED claiming to be a tungsten lamp. An LED has a narrow bandwidth. An old fashioned tungsten..." | Read more » about 2 years ago
Ag8n "Looking into the 660 nm lines. It's not that LEDs don't exist for 425 nm region. They do. But the ones in the catalogs seemed expensive. Going ..." | Read more » about 2 years ago
Ag8n "There are 3 in 1 flashlights ( blue, white, and red) that would be good for this application- as long as the color was more like purple instead of ..." | Read more » about 2 years ago
Ag8n "If you are using the public lab spectrometer, a light source for around 400 nm is needed. It looks like there are some blue or violet led bulbs/ f..." | Read more » about 2 years ago