1. An image processing method for a head mounted display device, operable in respect of an image generated for display by the head mountable display device according to one or both of an initial position or an initial orientation of a viewpoint, the method comprising: detecting, by a sensor device, one or both of a current position or a current orientation of the head mountable display device depending upon a display time at which the image is to be displayed; and processing, by a processing device, the image using pixel position mappings in which at least a subset of pixels of the image are displaced by respective pixel displacements dependent upon a difference between at least one of the initial position and the detected current position or the initial orientation and the detected current orientation at the display time at which the image is to be displayed; the processing step comprising applying a lateral pixel displacement to at least a subset of rows of pixels, the lateral pixel displacement depending on a difference in lateral rotation between the initial orientation and the detected current orientation of the head mountable display device; wherein the lateral displacement is different for two or more subsets of rows of pixels, and the lateral displacement is greater for a subset of pixel rows towards a vertical centre of the image than for another subset of pixel rows towards a top or bottom of the image.