Predictable sample error detector and a planar prediction corrector for removal of isolated transmission errors in Walsh--Hadamard transformed pictures

An error detection and correction system is described which will correctly detect the amplitude of a sequency error in a transmitted Walsh--Hadamard-transformed picture, provided no more than one error per block occurs. For a head-and-shoulder picture, a planar prediction corrector will then remove any sequency error whose magnitude is ⩾ (10/256) Δ, where Δ is the quantisation step size.