GB1329950A - Method of suppressing the effect of irregularities in scanning tube emission - Google Patents

Abstract

1329950 Television FERNSEH GmbH 8 Feb 1972 [9 Feb 1971] 5867/72 Heading H4F To compensate for variations in the light emissivity of a flying spot scanner tube 1, Fig. 1, direct light from the tube is directed by mirror 9 to a photo-cell W, to give an output # (1 Π#), # representing the correct constant luminosity value, and Π## the actual variations therefrom. The signal #(1 Π8) is fed to a clamping stage 13, controlled by the output of a circuit 12, receiving a short blanking signal H K as used in the tube 1 and a longer lasting blanking signal A, as used by the rest of the processing equipment, the amount of extension of signal A being shown by dotted lines. Circuit A thus gives a clamping pulse for said extension period thereby coinciding with the first part of the video signal. Said first part of the video signal is thereby clamped to zero such that the output of stage 13 is Π##. This is inverted in stage 30 to become # ##, and in mixers M (one for each of the red, blue, green colour channels) is added to a constant k = # to give (# # ##) before being multiplied with the colour signal T#,(1 Π#) to give T #<SP>2</SP>(1-#<SP>2</SP>) in which the term #<SP>2</SP> is so small as to be ignored.