Public Lab Wiki documentation



NDVI and NRG

6 Authors | 27 Revisions | Talk

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 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

5396083342_3b253ef5ca_o.png

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

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

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

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 - - 0 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 »
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 »
Mobius non-fish-eye lens conversion - - @patcoyle - - 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.


IMG_0511-split.png

infrared-combination.png


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

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

5396083368_40528d3da2_o.png

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

Questions

Title Author Updated Likes Comments
Can you modify a drone's camera for ndvi pictures? @Bronwen 18 days ago 2
Feasibility-check: NDVI analysis of moss @zomb23 new contributor 28 days ago 3
How to design a camera for calculating ENDVI. @nickyshen0306 3 months ago 5
Need help to reduce the Blue in mobius point and shoot camera @Muneeswaran 4 months ago 6
What is the working principle of Blue/Red filter @nickyshen0306 4 months ago 2
How do I take root and hypocotyl pictures for plant without light influence @Xing 4 months ago 2
As per my ndvi output like this How can we calculate endvi or ndvi image ? @it13 6 months ago 5
AWB_Gains for PiNoIRCamera V2 (Red Filter) @kauemv2 7 months ago 2
Is the Olympus CAMEDIA C-3040 good for NDVI? @texacoon 7 months ago 4
How to calibrate the white-balance for NDVI using the BLUE filter? @cagiva 11 months ago 4
I am getting very low NDVI values. @Anice 11 months ago 4
Infragram Point and shoot photos: white balance not working @Muneeswaran 12 months ago 0
Processing a picture from Rasperry Pi NoIR camera with blue filter and getting NDVI values. @Aezys about 1 year ago 1
How was the frequency response graph interpreted in @cfastie blogpost, and how the computation of the NDVI was derived? @manueldun about 1 year ago 1
Need insight on using this lens on modded camera for NDVI: OCN (Orange+Cyan+NIR) filter @alanw over 1 year ago 3
Can you detect pvc microplastics with a nvdi camera? @Ag8n over 1 year ago 5
Is it possible to calculate average NDVI in a picture using infragram's sand box? @Hala73 over 1 year ago 6
How can I can make a raspberry pi camera just with the filters process the crops and immediately produce the results to a computer or to other device, without having to use the website? @csteran almost 2 years ago 16
How to make this picture in an NDVI image @Davide_Ferrante almost 2 years ago 3
How to get NDVI image by image src instead of choosing image ? @Ankita almost 2 years ago 1
Visible Atmospherically Resistant Index (VARI) @rway almost 2 years ago 0
How can I have a value of NDVI starting from a IR picture? I want to find a numeric value of NDVI in pictures teken with a normal camera without IR filter. is it possible? @giuliooooo almost 2 years ago 1
I need a help I'm doing a research project on NVDI processes @camiloreyes over 2 years ago 1
How to verify generated NDVI Images? @ccpandhare over 2 years ago 10
"Test images" for multispectral image processing @warren over 2 years ago 6
What is the algorithm used in generating the fastie colormap from NDVI in Infragram? @Jtaw almost 3 years ago 6
Can I use any red filter for capturing NIR light? @sujayj almost 3 years ago 2
GoPro Hero HD first version- Making full spectrum( Removing IR filter) @suman almost 3 years ago 7
What is the ideal white balance for the Infragam Point and Shoot? @abdul about 3 years ago 1
NDVI validation @aldrin about 3 years ago 4
do the work exactly @bruno over 4 years ago 1
NDVI in realtime video @andresc4 almost 5 years ago 8
Spec Cam to Infragram w/the flip of filter? (Rosco "Fire" #19) @natalie over 5 years ago 18
Creating NDVI images? @rway over 5 years ago 3
Show more

Ask a question  or help answer future questions on this topic

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.


5416397210_5e3be40cf5_o.png

5412520298_93873f36d0_o.png