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Amiga Plus 1995 #5 & #6
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000507_owner-lightwave-l _Fri Mar 24 16:30:41 1995.msg
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Date: Thu, 23 Mar 1995 23:19:05 -0700 (MST)
From: Ernie Wright <ernie@gaspra.pd.com>
To: lightwave-l@netcom.com
Subject: Re: LW aspect ratio
In-Reply-To: <9503230938241085@tenforwd.bbs.net>
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Sean Cunningham wrote:
> After reading all the back and forth over the whole aspect ratio debate
> and modeling something to fit the camera I've got one question: where
> does this 1.346:1 aspect ratio come from? What is it based on in the
> "real world?"
Justin Barrett replied:
> The width-to-height ratio of a single pixel on the screen. ...
> The pixels are not square, they're a little wider than they are tall.
> 1.346 times wide as they are tall, to be specific.
Good grief.
A medium res NTSC LW image is 752 x 480, with a pixel aspect of 0.859,
when Pixel Aspect Ratio on the Camera panel is set to "D2 (NTSC)", the
Amiga default. The magic image aspect formula is
pixel aspect * width / height = image aspect
And 0.859 * 752 / 480 = 1.346. Translation: framestores are 752
pixels wide, but each pixel is only 0.859 wide (if we assume it's 1.0
tall), so the "actual" width is 0.859 * 752. Divide that by 480 and
you get what the image width is when you set the image height to 1.0.
So a rectangle that's supposed to have the same shape as a framestore
has to be 1.346 times as wide as it is high. In a simpler world, the
ratio would be 1.333:1, or 4:3, the shape of your TV screen, but that
would imply a framestore width of 745, which isn't a computer-friendly
multiple of 16.
Now that you know all this, forget it. You can read "1.346" directly
from the info box on the Camera panel (in LW 3.5, anyway). But does
anybody remember if this has any bearing on the question that started
it?
- Ernie