Clarification regarding ISONoise

[kanlions]

I need a some clarification regarding the function ISONoise. From the code I understood two input parameters color_shift and intensity shift are used to initialize poisson and normal distributions respectively. The pixel level modification is done in HLS space in OpenCV.

I want to know why this library uses a poisson distribution for modelling and what must be the maximum permissible values of the parameters.

I would appreciate any help in this regard.