Image encoding using object shape information

An image frame signal encoding method encodes a shape signal of an object in the digital image frame signal and decodes the encoded shape signal to provide a reconstructed shape signal and converts background pixel values in the digital image frame signal to extension values to thereby provide an extension image frame signal. And an image frame signal encoding method detects object blocks including one or more reconstructed object pixels therein and encodes a smallest process block having a dimension of L x L pixels and including all the reconstructed object pixels within each object block.