1. An image processing apparatus comprising a normalisation module operatively connected across a bus to a memory storing an image in which a region of interest (ROI) has been identified within the image, the ROI being bound by a rectangle having a non-orthogonal orientation within the image, the normalisation module being arranged to: divide said ROI into one or more slices, each slice comprising a plurality of adjacent rectangular tiles; for each slice, successively read ROI information for each tile from said memory including: reading a portion of said image extending across at least a width of said slice line-by-line along an extent of a slice; for each tile, downsample said ROI information to a buffer to within a scale S D <2 of a required scale for a normalised version of said ROI; and fractionally downsample and rotate downsampled information for a tile within said buffer to produce a respective normalised portion of the ROI at the required scale for the normalised ROI; and accumulate downsampled and rotated information for each tile within a normalised ROI buffer for subsequent processing by said image processing apparatus.