Whats the difference between interlaced and progressive video?
A. Progressive video presents a complete frame at a time. Interlaced video, on the other hand, builds each frame out of two fields — one comprising the odd-numbered pixel rows, or scan lines, the other the even-numbered pixel rows — which are presented alternately. Whereas the frame rate for 720p (progressive) HDTV is 60 per second (60 fps), the frame rate for 1080i (interlaced) is just 30 per second, but with a field rate of 60 per second. If you’re thinking, “Well, that seems like a bit of a cheat,” you’re right. It’s a pretty effective one most of the time, however, which is why interlacing was adopted for the analog television systems of the twentieth century. It allowed greater effective picture resolution within the transmission bandwidth allotted for TV channels, yet the screen was refreshed frequently enough to avoid obvious flicker on the cathode-ray tube (CRT) displays of the era. Its advantages outweighed its drawbacks.
