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Posted by Steve Roberts on 10/09/06 11:39
On Thu, 5 Oct 2006 20:37:01 -0400, "Joshua Zyber"
<joshzyber@comcast.net> wrote:
>- A 4:3 image on DVD fills the entire 720x480 pixel grid and uses all of
>those pixels.
>- An anamorhic 16:9 image on DVD also fills the entire 720x480 pixel
>grid, using the exact same number of pixels.
Neither of those statements is actually true. Both are basd on the
analogue video standard. Both 4:3 and 16:9 occupy the middle 702
pixels (or 704 according to some specs) of the available 720. The
rest is analogue blanking. Most companies do in fact zoom in slightly
to fill the entire frame, resulting in an image which is actually
slightly wider than it ought to be - approx 1.37:1 instead of 1.33:1
This causes us headaches in the broadcast industry, as some
manufacturers get this right and some (notably even biggies like
Sony!) get it wrong. For example, a Sony HDCam recorder down-converts
1920 x 1080 HD to 720 x 480 (or 720 x 576 in the PAL world),
completely filling the standard definition frame. This is wrong - it
should convert the image to 702 x 480 and pad the picture out with 9
black pixels on either edge.
Although it's not a lot on the face of it, it's exactly the sort of
problem that is a royal pain in the arse when, for example, taking
motion tracking data from a system that does it one way and trying to
use it in a system that does it the other!
Steve
The Doctor Who Restoration Team Website
http://www.restoration-team.co.uk
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