1. A method, for use in an image signal decoding system, for concealing class errors in an image signal transmitted in a compressed form by using a classified vector quantization method, wherein the image signal is divided into a multiplicity of blocks, each of said blocks being classified into one of a plurality of classes based on an edge pattern of said each block and said classes including a non-edge class which corresponds to a block having no edge pattern therein and a texture class which corresponds to a block having more than one edge patterns therein, said method comprising the steps of: detecting a block containing a class error; detecting boundary edges at each of four groups of neighboring pixels to the class error containing block, wherein each group of the neighboring pixels is located at a boundary of the class error containing block and included in one of four contiguous blocks to the class error containing block, pixel values of the neighboring pixels being considered to be correct; determining the non-edge class as a class of the class error containing block is less than two boundary edges are detected and the texture class, if more than two boundary edges are detected; obtaining an edge pattern in the class error containing block by connecting the detected boundary edges if two boundary edges are detected; determining the class for the class error containing block by selecting the most similar edge pattern to the obtained edge one, wherein said class is one of said plurality of classes; and repeating the above steps until classes all the blocks containing class errors are determined.