I have no idea how the sensors inside a camera work. I know I can take jpeg and separate the R, G and B channels but I have no idea whether these channels are the real red, blue and green in visible spectrum of light.
Why do I ask this:
Working with remote sensing data (i.e. Landsat 8 data) I can composite bands 2,3 and 4 (blue, green and red respectively) into a visible image. I can operate bands 4,5 into a NDVI index, I can do lots of combinations, image classifications, etc. I know there are many corrections to perform (DN to radiance, reflectance, atmospheric, etc.) but this is another topic.
So imagine I have one regular camera and one camera that captures only NIR (or some IR wavelength), could I separate the RGB values of the first camera and calculate the NDVI index (or others) with the NIR camera? Does this make any sense?