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Public Lab Wiki documentation


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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)


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 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 = (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:


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.


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


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

Purpose Category Status Author Time Difficulty Replications
Low cost NDVI analysis using RaspberryPi and PiNoIR - - @petter_mansson1 - - 0 replications: Try it »
Video tutorial: Creating false-color NDVI with aerial wetlands imagery - - @warren - - 0 replications: Try it »
Conversion of 4k sport camera for NDVI analysis with UAVs - - @azaelb - - 1 replications: Try it »
Video tutorial: Creating infrared composites of aerial wetlands imagery - - @warren - - 0 replications: Try it »
Mobius IR conversion - - @cfastie - - 0 replications: Try it »
Mobius non-fish-eye lens conversion - - @patcoyle - - 0 replications: Try it »
Getting started with infrared photography on Infragram.org - - @warren - - 3 replications: Try it »
Prototype: filter map tiles in real-time in a browser with ImageSequencer (NDVI Landsat) - - @warren - - 0 replications: Try it »
Use Image Sequencer for NDVI plant analysis with a modified mini sport camera observe review-me @warren 15m easy 0 replications: Try it »

Add an activity  or request an activity guide you don't see listed

Activities should include a materials list, costs and a step-by-step guide to construction with photos. Learn what makes a good activity here.



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.


This diagram explains the swapping, which allows us to 'see' infrared as if it were a normal color:


In NRG images, the deeper and clearer the red color, the denser and healthier the vegetation (more or less).


Title Author Updated Likes Comments
Why the color of Infragram picture is different from what I take with my Raspberry Pi using Picamera API @iman 7 months ago 5
Counter-intuitive NDVI values in drought-stressed plants? (RPi NoIR v.2 with a red filter and artificial lighting) @tumakin 11 months ago 6
How to find the sweet spot for manual white balance settings using Pi NoIR and a blue filter with artificial (full spectrum) lighting @patalbright 12 months ago 14
NDVI with a 2 camera setup @karunv about 1 year ago 2
NDVI Image Captures Non-Plant Objects @velahs over 1 year ago 7
Does anyone know the upper spectrum range of the Pi NoIR Camera V2? @justin_bauer over 1 year ago 1
Is there a way to convert an infrared video footage to NDVI? @sam14 over 1 year ago 2
Can I use the infragram.org for my thesis? Thanks! @tooooopher05 over 1 year ago 4
How can I make IR photos derived from various cutoff useful for creating NDVI (normalized difference vegetation index) images? @lev29 over 1 year ago 9
Can you modify a drone's camera for ndvi pictures? @Bronwen almost 2 years ago 2
Feasibility-check: NDVI analysis of moss @zomb23 almost 2 years ago 3
How to design a camera for calculating ENDVI. @nickyshen0306 about 2 years ago 5
Need help to reduce the Blue in mobius point and shoot camera @Muneeswaran about 2 years ago 6
What is the working principle of Blue/Red filter @nickyshen0306 about 2 years ago 2
How do I take root and hypocotyl pictures for plant without light influence @Xing about 2 years ago 2
As per my ndvi output like this How can we calculate endvi or ndvi image ? @it13 over 2 years ago 5
AWB_Gains for PiNoIRCamera V2 (Red Filter) @kauemv2 over 2 years ago 2
Is the Olympus CAMEDIA C-3040 good for NDVI? @texacoon over 2 years ago 4
How to calibrate the white-balance for NDVI using the BLUE filter? @cagiva almost 3 years ago 4
I am getting very low NDVI values. @Anice almost 3 years ago 4
Infragram Point and shoot photos: white balance not working @Muneeswaran almost 3 years ago 0
Processing a picture from Rasperry Pi NoIR camera with blue filter and getting NDVI values. @Aezys about 3 years ago 1
How was the frequency response graph interpreted in @cfastie blogpost, and how the computation of the NDVI was derived? @manueldun about 3 years ago 1
Need insight on using this lens on modded camera for NDVI: OCN (Orange+Cyan+NIR) filter @alanw about 3 years ago 3
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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 series.