I understand I can get a color from wavelength but it's not true for the opposite direction.
In case this picture would help.

![enter image description here][1]

To make this question simple, let's lighting and calibration aside to an optimized condition. 

I wonder if there is any way to get intensity value of a certain spectral wavelength for given pixel of a common image. That is, Wavelength and rgb of a pixel are both known. Based on that, I want to compute intensity of the wavelength for the pixel.


  [1]: https://i.sstatic.net/A4SoP.gif