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Without FRC, 24Hz rendered film is normally displayed on progressive systems by duplicating frames in a 3,2,3,2,3,2... pattern (with the average repetition of 2.5 as expected). This output pattern itself has a repetition rate of the greatest common divisor ({mod}) of 60 and 24, i.e. {mod}(60,24) = 12Hz. Unfortunately, this frequency is visually annoying, particularly with fast camera pans. You may yourself have become aware of juddering motion while watching movies. The effect can be reduced by using a display that refreshes at 120 FPS (5:1), as then the motion repetition is {mod}(24,120) = 24Hz, not 12Hz. |
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