frame size, pixel aspect ratio, and bears, oh my!

a client sent me a short clip from her fcp project today of a push in on a still frame. she wamted me to replicate it. according to quicktime, the file she sent me was:
"720x480" in format, normal size, and actual size.

i was exporting quicktimes from AE using the DV compressor, and getting files that said under the format heading:
"DV, 720x480 (640x480)"

now i imagine that it isn't coincidental that 640 is .9 times 720, but what is going on with the quicktimne so that it is both 720x480 and 640x480 at the same time? am i explaining myself???

i'm confused....

thanks everyone!

640x480 is the size of a square pixel image that will look normal on a computer screen. That would be the QuickTime version. Circles will be round.

720x480 is the non-square pixel version. Television systems "know" what that is and intentionally distort the picture so circles again come out round. Television display programs (Final Cut, DVD Player, etc.) "know" what that is, too.

The problem comes when you try to cross the two. Export a still from a television frame and Photoshop will think everyone gained 20 pounds.

I'm on less firm ground here, but I believe the two numbers are QuickTime "knowing" how to distort the picture to make it look "right."

Koz

thanks, koz, for the response. i am still a little unclear on the whole thing...for some reason it is having trouble sinking in...but i'll look for more resources elsewhere. anyone have a tutorial they can recomend?
greg

Ken Stone has what is widely believed to be the best collection of explainations, and whereas I couldn't find anything specifically tackling pixel sizes, you never know.

[www.kenstone.net]

What part of this is fuzzy? Why are there non-square pixels to begin with? Because the video digitizing process was chosen so it's the same in PAL as NTSC. In analog, managing PAL *and* NTSC is a big deal. In digital, it's a key click and sometimes not even that. PAL has non-square pixels, too, but they're non square the other direction.

Koz