1. A method for adjusting image data defining an image, the method comprising: generating a saliency map for the image; establishing a global transformation based on the image data wherein establishing the global transformation comprises ignoring parts of the image data corresponding to image areas indicated by the saliency map as having low saliency or weighing parts of the image data corresponding to image areas indicated by the saliency map as having low saliency less heavily than other parts of the image data corresponding to image areas indicated by the saliency map as having higher saliency; the method comprises one or more of: applying the global transformation to the image data to yield altered image data and either or both displaying the altered image data on a display or storing the altered image data on a non-transitory medium; and storing a definition of the global transformation on a non-transitory medium; and wherein generating the saliency map comprises: measuring the local contrast of the image at each of a plurality of spatial frequency scales and computing a weighted combination of the local contrast of the image at each of the plurality of spatial frequency scales.