1. A method of deriving a representation of an image by processing signals corresponding to the image, the method comprising: deriving a two dimensional function of at least part of the image; processing the two dimensional function to obtain an intermediate representation of at least part of the image, and deriving the representation of the image from the intermediate representation; wherein the intermediate representation is obtained using a selected part of the image or a selected part of a two dimensional function of at least part of the image.