Question: Calculating NDVI - using PiNoIR camera and blue filter

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JLJ asked on April 09, 2018 19:31
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Hello,

I have been reading a lot recently about NDVI and am going to have a go at producing some images using a rpi NOiR camera with the blue filter to gather some NIR rich images. I am trying to look at plants (Lettuce) and how the NDVI changes over time as a potential quality parameter.

I have been searching through Public Lab's site and can't quite find the information I am seeking, so I thought I would ask the question. I know the calculation for NDVI -- (NIR - R) / (NIR + R).

My question is about how i would calculate this. My current thinking is that if I take a picture with and without the filter (as the filter will only allow blue light and NIR through) and RGB image would now be NGB? and then I could simply do the calculation from those images.

Using the code here -- https://publiclab.org/wiki/python-webcam-codes

I am working out of a University in the United Kingdom



ndvi nir raspberry-pi

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1 Comments

sjmanosalvas 4 days ago

Please your help, I bought the Blue and Red Filter (https://publiclab.myshopify.com/collections/diy-infrared-photography/products/infragram-diy-filter-pack?variant=1058088684) to raspberry pi NoIR camera, but i don't how to put this filters to the camera, I have this camera https://www.raspberrypi.org/products/pi-noir-camera-v2/, but I don't know if I have to remove the small lenses or what i have to do?

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2 Answers

It is possible to compute a facsimile of NDVI from a single photo taken with a Pi NoIR camera and blue filter. The blue channel in the photo will capture mostly blue light, and the red channel will capture mostly NIR. Instead of using red light for visible light, blue light is used. To use red light for visible light, a red filter can be used.
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The sensor in the Pi camera and all consumer cameras is not as sensitive to NIR as it is to visible light, so the relative values for NIR and visible light will not represent the actual difference between visible and NIR light reflected form foliage. Therefore the computed NDVI values will not be similar to legacy NDVI values. The photo from the Pi camera must be modified with a calibration process before it will produce meaningful NDVI.
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To produce an NDVI image from a photo, you can use the Photo monitoring plugin for Fiji: https://github.com/nedhorning/PhotoMonitoringPlugin.
, Your lettuce must be illuminated by sunlight or other source with a strong and consistent component of NIR. As the color or angle of the light source changes, the computed NDVI values will change, so to discern subtle changes in lettuce vigor, the light source for photos must be held constant.
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Chris


JLJ 11 days ago

Hello Chris, thank you for the swift and detailed response. Do you have any recommendations for a light source that I can buy?

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Incandescent or halogen lamps emit lots of NIR. Fluorescent, sodium, mercury, and LED lamps do not.
The image below is from here: http://perfecthealthdiet.com/wp/wp-content/uploads/2015/06/Valtsu-image-02.gif

incand_NIR.gif


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