An intra-frame decoder comprising: an extracting module operable to extract vector information from a data stream, wherein the vector information indicates a pixel position of each pixel of a prediction block, based on the size and direction of a vector provided by the vector information; a judging module operable to judge whether the pixel position indicated by the vector provided by the vector information is located in an already-decoded area or a not-yet-decoded area, for each pixel of the prediction block; a pixel-position-calculating module operable to calculate a further pixel position for each pixel position judged to be located in the not-yet-decoded area, wherein the further pixel position is: located in the direction of the vector provided by the vector information and at a distance of an integer multiple of the size of the vector provided by the vector information from the pixel position judged to be located in the not-yet-decoded area, and located in the already-decoded area; a prediction-signal-generating module operable to generate prediction image data for each pixel of the prediction block, based on pixel data of the further pixel positions calculated by the pixel-position-calculating module, and pixel data of the pixel positions judged to be located in the already-decoded area; and an image-reproducing module operable to add difference image data taken from the data stream to the prediction image data, thereby to create reproduction image data. an extracting module operable to extract vector information from a data stream, wherein the vector information indicates a pixel position of each pixel of a prediction block, based on the size and direction of a vector provided by the vector information; a judging module operable to judge whether the pixel position indicated by the vector provided by the vector information is located in an already-decoded area or a not-yet-decoded area, for each pixel of the prediction block; a pixel-position-calculating module operable to calculate a further pixel position for each pixel position judged to be located in the not-yet-decoded area, wherein the further pixel position is: located in the direction of the vector provided by the vector information and at a distance of an integer multiple of the size of the vector provided by the vector information from the pixel position judged to be located in the not-yet-decoded area, and located in the already-decoded area; located in the direction of the vector provided by the vector information and at a distance of an integer multiple of the size of the vector provided by the vector information from the pixel position judged to be located in the not-yet-decoded area, and located in the already-decoded area; a prediction-signal-generating module operable to generate prediction image data for each pixel of the prediction block, based on pixel data of the further pixel positions calculated by the pixel-position-calculating module, and pixel data of the pixel positions judged to be located in the already-decoded area; and an image-reproducing module operable to add difference image data taken from the data stream to the prediction image data, thereby to create reproduction image data.