A method of generating a target image based on a source image, the target image comprising target pixels and the source image comprising source pixels, the method comprising: generating a pixel value for each target pixel based upon a pixel value of a source pixel associated with a corresponding source location in the source image or based upon pixel values of a group of adjacent source pixels which form a region of the source image in which that source location lies, wherein: the source locations are organised into an order and linked in that order one to the next by a pattern of offset vectors, each offset vector indicating a respective source location relative to an adjacent source location in the pattern; each said offset vector is defined by a combination of a derivable vector and a correction vector; and the method comprises: calculating the source locations in said order and based on said pattern of offset vectors; when calculating at least a particular one of said source locations, obtaining the offset vector linking that particular source location to the source location immediately earlier in the order by deriving its derivable vector and combining that derivable vector with its correction vector, that derivable vector being the same as or calculated from the offset vector linking two source locations earlier in the order; and obtaining one of said source locations as a reference source location and calculating at least a candidate one of the other source locations in said pattern based on the reference source location and the or each offset vector linking the reference source location to the candidate source location in said pattern. generating a pixel value for each target pixel based upon a pixel value of a source pixel associated with a corresponding source location in the source image or based upon pixel values of a group of adjacent source pixels which form a region of the source image in which that source location lies, wherein: the source locations are organised into an order and linked in that order one to the next by a pattern of offset vectors, each offset vector indicating a respective source location relative to an adjacent source location in the pattern; each said offset vector is defined by a combination of a derivable vector and a correction vector; and the method comprises: calculating the source locations in said order and based on said pattern of offset vectors; when calculating at least a particular one of said source locations, obtaining the offset vector linking that particular source location to the source location immediately earlier in the order by deriving its derivable vector and combining that derivable vector with its correction vector, that derivable vector being the same as or calculated from the offset vector linking two source locations earlier in the order; and obtaining one of said source locations as a reference source location and calculating at least a candidate one of the other source locations in said pattern based on the reference source location and the or each offset vector linking the reference source location to the candidate source location in said pattern. the source locations are organised into an order and linked in that order one to the next by a pattern of offset vectors, each offset vector indicating a respective source location relative to an adjacent source location in the pattern; each said offset vector is defined by a combination of a derivable vector and a correction vector; and the method comprises: calculating the source locations in said order and based on said pattern of offset vectors; when calculating at least a particular one of said source locations, obtaining the offset vector linking that particular source location to the source location immediately earlier in the order by deriving its derivable vector and combining that derivable vector with its correction vector, that derivable vector being the same as or calculated from the offset vector linking two source locations earlier in the order; and obtaining one of said source locations as a reference source location and calculating at least a candidate one of the other source locations in said pattern based on the reference source location and the or each offset vector linking the reference source location to the candidate source location in said pattern. calculating the source locations in said order and based on said pattern of offset vectors; when calculating at least a particular one of said source locations, obtaining the offset vector linking that particular source location to the source location immediately earlier in the order by deriving its derivable vector and combining that derivable vector with its correction vector, that derivable vector being the same as or calculated from the offset vector linking two source locations earlier in the order; and obtaining one of said source locations as a reference source location and calculating at least a candidate one of the other source locations in said pattern based on the reference source location and the or each offset vector linking the reference source location to the candidate source location in said pattern.