interlaced scanning

Thread Starter


Joined Aug 19, 2011
Revered members,
could u please explain in detail about interlaced scanning employed in TV? Even if you give some links i can study that and come back to this forum to clear whatever doubts that arise. I googled this topic, but nothing is satisfactory. Your help will be greatly appreciated. Thanks in advance members


Joined Oct 2, 2009
TV analog signal transmission and reception uses interlaced scanning to reduce flicker in the display. In North America, the NTSC standard uses 525 horizontal lines at 30 frames per second while in the UK, the PAL standard uses 625 lines at 25 frames per second.

The signal and display are synchronized to AC line frequency to avoid interference in the displayed picture.

A picture displayed at 25 or 30 times per second would flicker owing to a visual/psychological effect called "persistence of vision". To overcome this, one half of the frame (called a field) is transmitted and displayed at twice the rate (50Hz or 60Hz). Each field transmitted covers the entire TV screen but skips every other line.
The second field is transmitted to fill in the skipped lines. Hence it is called "interlaced scanning".

Even at 25 frames per second with PAL, I can observe flicker since I have been accustomed to 30 frames per second on NTSC.