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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.