1. A method of converting a first image of a first type to a derived image of a second type based on a second image and a third image, the second image being of the first type, the third image being of the second type, the second and third images being in registration with each other, the first image comprising a plurality of data points, each first image data point comprising first type data for the first image, the second image comprising a plurality of data points, each second image data point comprising first type data for the second image, the third image comprising a plurality of data points, each third image data point comprising second type data for the third image, the method comprising: performing a plurality of comparisons between a patch of the first image and a plurality of patches of the second image to generate a plurality of similarity indicators, the similarity indicators being indicative of similarities as between a first image data point and a plurality of second image data points; computing a plurality of weight factors based on the similarity indicators, the computed weight factors being associated with a plurality of third image data points; computing a derived image data point corresponding to the first image data point as a weighted combination of the third image data points that are associated with the computed weight factors, the weighted combination being in accordance with the computed weight factors; and repeating the comparisons performing step, the weight factors computing step, and the derived image data point computing step for a plurality of different first image data points to thereby generate the derived image from the plurality of computed derived image data points; and wherein the method steps are performed by a processor.