Interlaced and Progressive Scan SignalsStandard 480-line NTSC TV broadcasts (incl. cable television), VCR, DVD and laserdisc signals are sent in an "Interlaced Scan" format. A TV screen first draws the image's odd lines, one at a time sequentially from top to bottom (which takes 1/60 of a second), and then fills in the even lines (taking another 1/60 of a second). That is, the full picture (top to bottom) is first drawn with half its information hollowed out, and then the other half is filled in -- the entire process taking 1/30 of a second.
A newer and superior scanning method called "Progressive" permits the entire picture to be drawn sequentially from top to bottom without the odd/even interlacing. Some newer DVD players now have outputs for both an interlaced and progressive scan image. And HDTV signals are now being broadcast in both progressive and interlaced formats: 720p (720 lines of resolution in progressive scan format) and 1080i (interlaced).
Improving Picture Quality with Line Doublers and Scalars
Unlike TV picture tubes and
computer monitors, projectors don't actually "draw" the picture. Rather, at any
given split-second in time they are either projecting image or not (i.e., the
pixels are either "on" or "off"). Thus, an attempt to project an "interlaced"
signal would result in every other line (the "odd" lines) being projected by
themselves for 1/60 of a second, followed by just the even lines, resulting in a
picture worse than any big screen TV.
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