To improve compressibility in the data compression of a color conversion table to be used for image processing to store it in a storage medium.

Concerning the respective axial directions of the inputting space of the color conversion table, the changing rate of table data is investigated and the table data is rearranged in the increasing order of the changing rate of an axis (S101). With this processing, the rearranged table data is given difference along the axis or in a straight line parallel with the axis in the increasing order of the changing rate of the axis (S105, S109 and S112) and data compression is given to the data given difference (S115). As the result of this, the run length of a neighboring value is extended and correlation between data can be improved more by giving difference to it, thereby compressibility in data compression is improved.