a processing block is processed by using an extension - interpolation method , wherein the processing block consisting of n × n pixels which are classified into object pixels and background pixels and the e - i method comprises the steps of : selecting l rows of the processing block , each having at least one object pixels ; for each selected row , determining m representing a number of object pixels included in said each selected row and providing a first vector representing the m object pixels ; for each first vector , selecting an extension matrix among a multiplicity of predetermined extension matrices based on the m and n values and multiplying the selected extension matrix to the first vector to provide an extended first vector ; providing a first extended processing block which includes l rows , each row representing each of the extended first vectors ; for each column of the first extended processing block , providing a corresponding l - dimensional second vector ; selecting an extension matrix among a multiplicity of the predetermined extension matrices based on the l and n values ; and multiplying the extension matrix selected at step to each of the second vectors , to provide n extended second vectors .