1. An image predictive coding method comprising: sampling an image signal into a plurality of blocks; generating a quantized DC coefficient of a current block; adaptively selecting a predictive block from either a left block or an above block immediately adjacent to the current block; deriving a DC predictive value of a current block from a quantized DC coefficient of the predictive block; and coding a difference value between the quantized DC coefficient of the current block and the DC predictive value.