formats and resolution?

[draggoon01]

read the doom9 guide on ratios and resolution. but i got to wondering, why was dvd made with 720x480 ratio? if it's intended for 4:3 or 16:9, why not define it in a resolution corresponding to one of those resolutions?

is there any information on how high definition videos will be set at in the future (resolution and aspect ratio)? like hd-dvd or hdtv? will all future videos always use some 4:3 intermediate that will be stretched to 16:9?

lastly is 1080i the upper limit defined? will there never be 1080p? i ask because been reading that many people say 720p looks better than 1080i. seems like waste to even have a 1080i.

[Zarxrax]

720x480 is 4:3 on a TV set, because tvs do not use square pixels.

[draggoon01]

Originally posted by Zarxrax
720x480 is 4:3 on a TV set, because tvs do not use square pixels.

can you elaborate, i don't follow.

4:3 is 1.33
16:9 is 1.77

720x480 is 1.5

[RadicalEd]

the pixels on a TV aren't square, they're taller than they are wide by a ratio of 10:11. Since the pixels are sqashed like that, it takes 704 pixels to fill up the space that would only take 640 pixels on a square pixel device like a monitor, so 704x480 is 4:3 on a TV set.
You can see this mathematically by taking 704/480 = 1.4666
1.4666 * 10/11 = 1.333
Or
640 * 11/10 = 704

720 is used for DVD because the extra 16 pixels on the sides reduce the amount of actual picture data that is hidden by overscan. Those 16 pixels are inactive as far as picture data goes.