Lossless compression requires that the reproduced reconstructed bit stream be an exact replica of the original bit stream. The useful algorithms recognise redundancy and inefficiencies in the encoding and are most effective when designed for the statistical properties of the bit stream. Lossless compression of image signal requires that the decoded images match the source images exactly. Because of differences in the statistical distributions in the bit streams, different techniques have thus been found effective for lossless compression of either arbitrary computer data, pictures, or sound.