[murphyv310]

Back in 1962-63 British Relay did experiments under Henry Chmiel's wing of interpolating 405 basically doubling up the picture, each line was sampled and fed into a store and then compared with the next transmitted line, the difference was then used as a supplementary line, back in those days the equipment was massive to say the least and very temperamental, but it worked very well and the result was excellent especially on 23 and 25 inch tubes.

Henry had some cine film of the results which he showed me in the early 70's