I am new to image processing. I am applying NDVI index on an image of an agricultural farm taken by drone. But the formula (NIR-Red)/(NIR+Red) is giving me wrong output (here instead of NIR we are using the blue channel). Then I came to know that the image I am using is taken by camera with NIR sensors. Would the formula differ from normal formula of NDVI?
Ok some replies
here instead of NIR we are using the blue channel
How are you expecting that to work? NDVI only works with NIR information available, not with blue channel information.
the image I am using is taken by camera with NIR sensorsably
Then there should be a NIR channel available. In normal circumstances this imagery is 4 channel data, where the 4th channel has the NIR information.
but the formula (NIR-Red)/(NIR+Red) is giving me wrong output
My best guess, you are running into data range issues, simply dividing integer channel images. Show us your code so we can have a look at what is acually going wrong.
Asked: 2017-02-16 02:36:21 -0600
Seen: 782 times
Last updated: Feb 16 '17
@LBerger Ideally when we apply NDVI on imaage plant should colored light grey and ground should colored dark grey. But I am getting reverse.
Yes, because you can't just switch the infrared channel with the blue channel!
In the image of a plant, red and blue values are roughly equal (R~B=a). Then the formula will give you (a-a)/(a+a)=0. Hence the dark color of the plant on your image.
One more thing: RGB cameras with IR blocking filter removed (like the Raspberry Pi NoIR camera) won't give you good NDVI.