A method of creating a multispectral decorrelation model for use in determining a visible image from a multispectral image captured using a multispectral image sensor, the method comprising the steps of: generating, using a plurality of quantum efficiency curves for the multispectral image sensor and a plurality of synthetic light spectrum vectors, a grid of synthetic multispectral pixel values and a corresponding grid of synthetic visible pixel values, wherein each synthetic visible pixel value is substantially decorrelated from a non-visible component of a corresponding synthetic multispectral pixel value; and determining a multispectral decorrelation model using the grid of synthetic multispectral pixel values and the corresponding grid of synthetic visible pixel values, wherein the multispectral decorrelation model in use maps a multispectral pixel value of the multispectral image to a visible pixel value of the visible image.