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) ...

Author Comment Last activity Moderation
shahdharam7 "Hi Warren, Thank you for your reply. Image (2) and (4) are taken using infragram pi camera. The detailed description of the camera is mentioned i..." | Read more » over 2 years ago
warren "Sometimes different cameras use only one channel to focus, in order to work faster (less time combining channels before calculating). If they use t..." | Read more » over 2 years ago
warren "Hi, good questions! You may want to try doing a better white balance to try to get better signal from your images: https://publiclab.org/tag/white..." | Read more » over 2 years ago
jeffa_plain "Yeah, I plan to use a point-and-shoot camera next (preferably one with optical zoom) so I can get proper NDVI imaging done. other than that, thank ..." | Read more » over 2 years ago
warren "Yes, i agree there is some infrared data showing in the trees, and I do think it's possible to get useful info out. Just be aware that the dynamic ..." | Read more » over 2 years ago
jeffa_plain "I did indeed remove the IR lens from this! Thats why I bought the GoPro 3+ Silver because that's the only GoPro 3 that has an easily removable lens..." | Read more » over 2 years ago
warren "I think if you got closer in white balance in pre-configuring the GoPros, you can probably un-boost the blue channel some more and get better disti..." | Read more » over 2 years ago
jeffa_plain "I was kinda hoping that this would be as simple as inverting the color scale at the bottom but nothing that simple with stuff like this haha. From ..." | Read more » over 2 years ago
warren "Hi, I think you're right that you need to adjust the white balance, and you can learn more about how that works here: https://publiclab.org/notes/w..." | Read more » over 2 years ago
allifemats "Thump provide mobile grow rack,grow tent system,pollen trim tray and square pots for cannabis grow system. " | Read more » over 2 years ago
jeffa_plain "I'm not sure where I would use the (1-R), I just tried it and I didn't get anything that was useable. all that needs to happen it seems is the resu..." | Read more » over 2 years ago
jeffa_plain "From the research ive done since making this post, I think it may be because I cannot adjust the white balance on a GoPro, both of the images are r..." | Read more » over 2 years ago
warren "Hmm, interesting, can you share your original images? I think we might just be able to do (1-R) instead of (R) or something, for some of the values. " | Read more » over 2 years ago
warren "Hi @Rick88 your image looks OK - but your infrared image may benefit from being white balanced - there are some good resources here at #white-balan..." | Read more » over 2 years ago
Rick88 "Hi Warren, I followed through your tutorial. Here is the VIS and NIR images that I captured VIS Image NIR Image This the output generated wi..." | Read more » over 2 years ago
JWallace "Hi @boulax @mfb @mimiss I know this thread is a little old, but I've done a little experimenting with the esp32-cam in relation to ndvi processing...." | Read more » over 2 years ago
shahdharam7 "@peter_mansson1 Nice work. The final goal here is to analyze the nutrient effect. Right? The normal camera (Raspberry pi camera) can also get th..." | Read more » over 2 years ago
bhamster "@cfastie Aha, thanks so much for the modified image! And for the context. " | Read more » over 2 years ago
bhamster "This is a really clear and helpful explanation, thanks @nedhorning. And thank you for pointing out the other issue! Does this other image on the p..." | Read more » over 2 years ago
cfastie "If you want to replace the image with the questionable text "Red, Green, Blue" with one modified to include only "Red," you can find it here. I mod..." | Read more » over 2 years ago
nedhorning "NDVI uses an NIR and a Red band. Some documents have noted that instead of red you can any visible band but from my point of view that is not corre..." | Read more » over 2 years ago
bhamster "Hi @dlebauer, good catch, thanks for pointing this out. @cfastie, @nedhorning, @ektopyrotic, if you have any insights on why the NDVI equation in ..." | Read more » over 2 years ago
nguyenhamy190200 "https://ionia.com.vn/6-cach-lua-chon-may-loc-nuoc-ion-kiem-tot-nhat ade " | Read more » over 2 years ago
dlebauer "Great article - I noticed that the first image shows an equation (NIR-R|G|B)/(NIR+R|G|B). The way the R,G,B are shown, the mathematical operations ..." | Read more » over 2 years ago