I've always been a little puzzled by how analog horizontal resolution worked, and reading the wikipedia entry on the resolution of different things, it appears that old 480i SD broadcast television and Beta SP had 330 "lines" of horizontal resolution, which on the page is estimated to be the equivalent to around 440 pixels. I guess since it's analog, it doesn't mathematically need to be a 4:3 ratio in order to work on a 4:3 display?
So I'm wondering - since 4:3 DVDs are mathematically 4:3, does this mean the video has to be scaled/interpolated horizontally when it's transferred from videotape, thereby softening the image? I have noticed that when I play tape-based DVDs on my imac, they actually look sharper when I downscale the player than they do at the default size, although at the expense of a little bit of fine detail.
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Tape is analog so it doesn't come in discrete units along the horizontal axis, it's a continuous waveform. When digitizing it you can use as few or as many samples as you want. The bandwidth of that analog waveform on VHS tape is such that it can only resolve about 350 alternating black and white vertical lines (color resolution is far less, about 40 lines). It's customary to sample standard definition analog video with ~704 samples, usually with 8 pixels of padding at the left and right edges -- 720 pixels total. That's enough to capture the resolution of studio video tape.
NTSC DVDs are almost always 720x480. That's a 3:2 aspect ratio. But the encoded picture is either 4:3 or 16:9 when displayed. The player or TV adjusts for the display aspect ratio. Any time you enlarge a small image you get a fuzzy big image. Any time you reduce a large image to a small image you get an apparent sharpening.
Last edited by jagabo; 19th Jun 2014 at 10:25.