If a pixel of interest on a line of interest is located in an attribute region different from that in which a pixel immediately preceding the pixel of interest is located, the luminance value and color difference values of the pixel of interest are recorded in this order adjacent to data recorded in a data packet set for the line of interest (S811). If the pixel of interest is located in the same attribute region as that in which the preceding pixel is located, the luminance value of the pixel of interest is recorded adjacent to the data recorded in the data packet (S812). The data packet generated by executing the above recording process on each pixel forming the line is output.