The vertical resolution of a system depends on the total number of active scanning lines, whereas the critical flicker frequency (CFF) is the lowest possible apparent picture repetition rate which may be used without visible flicker. If during one vertical scanning field alternate scanning (odd) lines are formed and during the second scanning field the remaining (even) lines are formed, at the end of the one frame period all the lines are formed. This process called interlaced scanning gives a vertical scanning frequency of twice the true picture-repetition, or frame frequency. The situation is illustrated in Fig. 30.10 and further elaborated in Fig. 30.11.



Fig. 30.10 One complete frame in interlaced scanning ...

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