Subjective effects of d.p.c.m. errors and predictor leak on visual telephone pictures
J.A. Kitchen, Rozenn Nicol, J.M. Corbett · Proceedings of the Institution of Electrical Engineers · 1977
A technique for reducing the visibility of transmission errors in television signals which have been digitally encoded using differential pulse-code modulation(d.p.c.m.) is to weight the predicted value of the signal by a factor less than unity. This prediction ‘leak’ has the effect of reducing the extent of the propagation, and hence the visibility, of transmission errors, but it may also increase the quantising distortion. A closely controlled subjective investigation of this error visibility against quantising distortion trade-off is described. Details of both the equipment and procedure followed are given and a mathematical model is derived to allow the plotting of curves of constant impairment for varying leak factor and error rate. The investigation indicated that for moderate channel error rates, a leak factor of 15/16 is a good compromise between error visibility and quantisation distoration.