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) ...


Author Comment Last activity Moderation
eve-lyn0 "Very impressive results " | Read more » almost 3 years ago
achita_ea "Hi @petter_mansson1 I can not use Cloud Upload in MainNDVI Thise error missing 2 required positional arguments : 'preNDVIFilepath' and 'timestamp' ..." | Read more » about 3 years 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 » about 3 years 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 » about 3 years ago
liz "Thank you @cfastie! " | Read more » about 3 years ago
cfastie "I don't know what your camera's settings were and I don't know how your camera has been modified (does it have a red filter?). I don't know what th..." | Read more » about 3 years ago
liz "@cfastie , wondering if you might be around and able to drop some knowledge on this question? " | Read more » about 3 years ago
sirromrobert42 "I just want you to know that I am deeply grateful for your amazing post! Thanks for the kindness in sharing your expertise with us...Regards office..." | Read more » about 3 years ago
thongtinsaocom10 "Thedolive là một trong những trang website phát sóng trực tiếp bóng đá tốt nhất, tại đây bạn có thể xem các trận đấu bóng đá trực tiếp tốc độ cao, ..." | Read more » about 3 years ago
juancitro "Hi @velahs, The improvements you have obtained are really good. I would like to know, what is the process that you have followed to improve your ..." | Read more » about 3 years ago
boulax "hello I'm also interested in exploring ESP32-Cams " | Read more » about 3 years ago
neenasharma4808 "I visited your site and assumption I got some incredible information from your site, continue sharing such posts extensively further. Our http://ww..." | Read more » about 3 years ago
harry416788 "endocrinology medical billing " | Read more » about 3 years ago
vosshop2 "Seiko Prospex Mini Turtle SRPC39J1 Automatic Diver's 200M Men's Watch. Release new Seiko mini turte. " | Read more » over 3 years ago
theuntoldrecipe "Gud Ur Post Always Important all of us " | Read more » over 3 years ago
mp3download "Kylie Minogue comes through with yet another new song titled “Miss a Thing” and is right here for your fast download. https://walkingdeads6.online..." | Read more » over 3 years ago
warren "Very impressive - and yeah, what a great cheap camera... that filter switcher is amazing! " | Read more » over 3 years ago
amocorro "@DS501st What a great way to combine your interests! Thanks for documenting your process and sharing for the Public Lab community to replicate :hea..." | Read more » over 3 years ago
WendyJospeh "Is is good one. " | Read more » over 3 years ago
EllenHarri "Nice Post " | Read more » over 3 years ago
asadrazaq "Do you know whats the meaning of agriculture.. ? Agri means Agreed.. and culture is known to all some. So agriculture means agreeing with culture. ..." | Read more » over 3 years ago
MdSohanAli "Good Article Thanks For Sharing " | Read more » over 3 years ago
tumakin ""Otherwise it would be a classic case of P-hacking." - I was thinking something along these lines as well. This is something I definitely wish to a..." | Read more » over 3 years ago
shilpashetty "I like your blog so much it is so Call Girls in Mumbai good it is very informative and good thank you. " | Read more » over 3 years ago