Modifying the NDVI Values Using Multispectral Images
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Thomas Taufan
il 1 Giu 2020
Commentato: Image Analyst
il 7 Giu 2020
Can I determine the minimum and maximum value of the NDVI variable? How do I make a threshold for example higher or equal to 0.3 are green and lower than that are red? Can I make bounding box for the specific pixels that has low values?(but in the plant area, not the road or things that are not vegetation)
Below is the code I used to compute :
R = imread('RED.TIF');
NIR = imread('NIR.TIF');
NDVI = (double(NIR) - double(R)) ./ (double(NIR) + double(R));
imshow(NDVI, []);
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Image Analyst
il 1 Giu 2020
Try this:
maxValue = max(NDVI(:))
minValue = min(NDVI(:))
binaryImage = NDVI > 0.3;
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Image Analyst
il 7 Giu 2020
The values from imread() are assumed to be the RGB values of the image. Like you said the R channel goes from 620 to 750 which seems a bit more IR than normal. But it's possible if you have a camera where they changed or got rid of the IR cutoff filter that is normally on top of the sensor. But a normal DSLR or machine vision camera would not have sensitivity out to 750 nm, only to about 700 or so. From 700 to 750 is near IR - very near. So near that it's actually missing most of the band that people would call near IR which is roughly 700 or 750 to about 1200-1400 nm. So band 3 which you extracted from Original_Picture is actually mostly red, unless you have a special camera to filter out the red and allow only wavelengths greater than 700 in. To get better IR you need to get a camera that is specifically made to record IR wavelengths. There are cameras like this available. I think you might even be able to get someone to alter your Nikon camera to remove the IR filter from the sensor or replace it with a sensor that doesn't have the filter on it.
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