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
cfastie "Yes I have seen Valspar in the US for many years, and Rustoleum is a big brand here. Maybe there is some international brand of art supplies that m..." | Read more » almost 9 years ago
AFairbairn "Good points. I am checking if my University has a spectrometer, I do not think my department does, however our geology people may have one. Waiting..." | Read more » almost 9 years ago
cfastie "Any place that sells paint has paint color chips, but these are too small to be useful as targets. But fancy paint stores have huge color samples. ..." | Read more » almost 9 years ago
cfastie "That's a really relevant article. They scale the graphs relative to a standard, so 100% is actually 20% reflectance. That means 25% reflectance of ..." | Read more » almost 9 years ago
AFairbairn "Chris, You are probably correct about the foil being a poor material because of how shiny it is, had not really considered that. I came across thi..." | Read more » almost 9 years ago
cfastie "ISO 100, 1/320 shutter speed That is much better than I thought would be possible. I don't know how those skinny little bands provide enough light..." | Read more » almost 9 years ago
AFairbairn "Jut did a really crude test, the image displays as it should, green in the cracks, green algae or whatever it is on the fence. The small panel in f..." | Read more » almost 9 years ago
AFairbairn "Chris, Thank you again for all the great information. I would assume the filter you found on PeauProductions website is the one in the lens I purch..." | Read more » almost 9 years ago
nedhorning "Here are a couple links that should help you get started: https://publiclab.org/wiki/infragram https://publiclab.org/notes/mlamadrid/12-08-2015/pho..." | Read more » almost 9 years ago
ino "hello, I have a infrared-visible camera, how i get the NDVI image? " | Read more » almost 9 years ago
cfastie "Ned listed some resources of spectral reflectance data of common things in this note: https://publiclab.org/notes/nedhorning/11-01-2013/why-a-red-f..." | Read more » almost 9 years ago
cfastie "PeauProductions has this filter here: This must be a dichroic filter. The narrow bands could produce good results. We don't know how much cross ..." | Read more » almost 9 years ago
AFairbairn "Chris, Thank you for your comments. I realize I should have provided a bit more information. Unfortunately a multispectral imager was not in my bu..." | Read more » almost 9 years ago
cfastie "It would be good to know something about the camera and filter you are using. Do you have a spectral curve for the filter? How is the camera white ..." | Read more » almost 9 years ago
aldehyde "@cfastie If i have Mobius infragram cam with red filter, will i receive RGN image?. And after this (Photo Monitoring Plugin), will i recive NDVI i..." | almost 9 years ago
cfastie "I answered Mnzr's question here: https://groups.google.com/forum/#!topic/plots-infrared/HfowVn5ULFM " | Read more » almost 9 years ago
mnzr "@cfastie Hello I'm working on a project in which we see how a person's exposure to plants affects them. Currently we have a wearable sensor with th..." | Read more » almost 9 years ago
cfastie "The red filter in your Mobius is blocking most blue light but passing most of the NIR light in the scene. The blue channel receives little other vi..." | Read more » almost 9 years ago
aldehyde "@cfastie I use of Mobius infragam cam (red filter) in Grow Chamber. Light -CFL. Received of infrared image Fig 1 and Fig 2. - after processing in ..." | Read more » almost 9 years ago
cfastie "I am not sure what your question is. I assume the red LEDs emit some NIR, but maybe not very much. With only red and blue LEDs, the amount of NIR r..." | Read more » almost 9 years ago
JohnsonC "@cfastie Hi I just have one more quick question while designing my next experiment. If I substitute the IR LEDs with red LEDs in my chamber when I ..." | Read more » almost 9 years ago
JohnsonC "@cfastie I will reflect on what you have said for my next experiments, thanks for your help! " | Read more » almost 9 years ago
cfastie "Oh, that's great to be able to disable AWB. I don't really know what manual setting would be best for your use. If you are going to be swapping f..." | Read more » almost 9 years ago
JohnsonC "@cfastie - That is really interesting to hear and thanks for the link to Ned's note there. I actually have an installed GHI camera that currently a..." | Read more » almost 9 years ago