A flickering of fine horizontal edges caused by interlaced scanning.

A fine line appearing in only one field is presented below the flicker frequency; therefore, it flickers. Twitter is eliminated in line doubling schemes that change from interlaced to progressive scanning, as most of the IDTV schemes do. Interestingly, twitter was much less of a problem in the early days of NTSC, than it is today, because early cameras and displays didn’t have sufficient detail to confine an edge to one scanning line.