An image processing apparatus performs conversion and a first compression on upper bits in image data, thereby generating a first compressed data set, and performs a second compression on lower bits in the image data, thereby generating second compressed data. The image processing apparatus then performs a first decompression on the first compressed data set, thereby generating a first uncompressed data set, and performs a second decompression on the second compressed data, thereby generating second uncompressed data. Finally, the image processing apparatus interpolates the first uncompressed data set based on the second uncompressed data.