1. An image predictive coding method comprising: sampling an image signal into a plurality of blocks; transforming the image signal of the blocks into a two-dimensional array of DCT coefficients having a DC coefficient and AC coefficients; quantizing the DCT coefficients into a quantized DCT value; and predicting a quantized DC coefficient of a current block from the DC coefficient of an immediately adjacent block adaptively selected from either a left block or an above block; wherein the DC coefficient of the selected block used for said predicting a quantized DC coefficient of the current block is scaled by a ratio of a quantization step-size of the current block and a quantization step-size of the selected block.