1. An image generating system for generating a virtual image from at least first and second images of a scene generated from different respective first and second sensors each being sensitive to a different optical characteristic, the system comprising: a pixel transformation module configured to process respective groups of pixels in corresponding locations in the first and second images for determining a transformation between values of a group of pixels the first image and values of a corresponding group of pixels the second image; and a virtual image module for generating a pixel value in said virtual image from the first image by applying said transformation to a pixel value in the first image so that the pixel values in said virtual image appear as though they were generated from a sensor of similar optical characteristic to the second sensor.