# NDVI and NRG question: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) ...

Author Comment Last activity Moderation
12A "https://apkashub.net/ " | Read more » 13 days 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 » 3 months 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 » 3 months ago
tats_daniel "Hi Chris, I am experiencing the same problem with my NDVI values. Can you help on how you manipulated the red channel to resolve the issue. Thanks " | Read more » 5 months ago
warren "Also noting this page with good notes on blue filters: https://publiclab.org/questions/patalbright/10-20-2020/how-to-find-the-sweet-spot-for-manual..." | Read more » 7 months ago
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warren "If you open "camera settings" on the camera page you can adjust the white balance as described here: https://publiclab.org/notes/kauemv2/05-27-201..." | Read more » 10 months ago
shahdharam7 "Hi warren, Thank you for your response. I have used PI camera as mentioned in the link below. https://store.publiclab.org/collections/diy-infrare..." | Read more » 10 months ago
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 » 10 months 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 » 10 months 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 » 10 months 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 » 10 months 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 » 10 months 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 » 10 months 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 » 10 months 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 » 10 months 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 » 10 months 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 » 10 months 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 » 10 months 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 » 10 months ago
brindamcolinasverde "Also we need to understand that the pixels of your camera can be in different format. When you take a picture and put it in a webpage, like i menti..." | Read more » over 1 year ago
iman "Thanks @cfastie . The problem was with the Auto white balance and changing the awb from "auto" to "greyworld" solved the issue. " | Read more » over 1 year ago