An image signal processing apparatus includes an adder to add an input data signal of a present frame to a cumulative data signal of a previous frame to output a cumulative data signal, an analyzing block to analyze a processing range of the cumulative data signal, a processing block to process the cumulative data signal based on the processing range to output a processed data signal, an encoding block to compress the processed data signal to output an encoded data signal, a memory to store the encoded data signal and the processing range, a decoding block to decode the encoded data signal read out from the memory to output a decoded data signal, and an inverse processing block to inversely process the decoded data signal based on the processing range to output an output data signal.