A Walsh corrector is described for Walsh-transformed pictures. It enables all sequency errors > 4% of the sequency range to be corrected, provided that no more than one sequency is in error per block of lengthN. The penalty for this correction is a bandwidth increase of 100/(N−1)%. When the Walsh corrector is applied to d.p.c.m. pictures, single sequency errors per block are usually removed while burst errors do not propagate, being confined to the block of length N.