The Math of aspect ratio

What does the numbers represent when you talk of aspect ratios.
Like if i say hd at 4:3 is that a contradiction? Is it that hd automatically gets 16:9?
Is 720p 16:9 or is it smaller?

NTSC can be 4:3 or 3:2. what is the 4 and what is the 3? It appears that 16 in 16:9 is 4x the 4 in 4:3 and the 9 is 3x the 3 in 4:3.

Is there a math to this? Why cant say 1080i be 3:2.
Does the 4 in 4:3 some how reflect 720 and the 3 reflect 480?

3 years ago i asked a similar question but didn't have the tech know to ask correctly or more specifically?

""" What you do with what you have, is more important than what you could do, with what you don't have."

> > > Knowledge + Action = Wisdom - J. Corbett 1992 """"

Width:height
In PAL, 720 x 576 is 4 : 3.2, not exactly 4:3. HD is usually at 16:9 (rectangular), and SD usually at 4:3 (almost square). Then there is 16:9 full height anamorphic which distorts the 4:3 pixels to create a 16:9 image.

Pixel dimensions play a part (and this part i find fairly confusing- do all codecs display the same rectangular pixel ratios or are they different?). Otherwise, PAL/NTSC pixels aren't square- they are in fact, slightly longer than wide (slightly rectangular). When doing for web, make sure that they are corrected to display properly in square pixels, because computers traditionally display in square pixels.

...so you are saying that 3 years later you still don't know what Aspect Ratio is?

[en.wikipedia.org]

When life gives you dilemmas...make dilemmanade.

[en.wikipedia.org]

This is cool too...

The question to ask is what aspect ratio.

So from the visual (analog) output both PAL and NTSC SD are 4:3 aspect, but the actual pixel ratio and number of h/v pixel is different.
With PAL you got 5:4 in a digital world (720x576) with NTSC D1 it should be 20:9 (720x486), with NTSC SD DV it's 3:2 (720x480).
With SD the actual "digital" aspect doesn't change when it comes to "wide screen" i.e. 16:9. This means the visual (analog) output for both standards are 16:9 (square pixel PAL 1024x576, NTSC 720x400) but they have a different source aspect which is the same as the SD ratio.

Same with the new HDTV formats - they are all 16:9 analog. But they use use different kinds of pixel aspect ratio and therefore a different amount of pixels to fill width and height.
A 1440x1080 file format is considered in this video world! as 16:9 as it normally will be broadcasted at 1920x1080. In computer world it's just a 4:3 - though if the source is video it will look squeezed. And so on ?

Andreas

P.S. for some help of imagination the "major" aspect ratios should always use full numbers.

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with NTSC D1 it should be 20:9 (720x486)

Yeah I spotted that right away that wiki is wack...

NTSC DV & D1 are not the same pixel ratio unlike PAL D1/DV which are.

Also who ever heard of NTSC 480i having 1000 lines of resolution?

Interlaced NTSC D1 has an effective res of about 410 lines and interlaced PAL about 480 lines vertical resolution.

On an LCD though I believe you get effectively higher vertical resolution more like 460 for NTSC D1 due to the fixed nature of the display.

Read up on the Kell factor if you want to know why... [en.wikipedia.org]



For instant answers to more than one hundred common FCP questions, check out the LAFCPUG FAQ Wiki here : [www.lafcpug.org]

What is missing here is the effect the shape of the pixel has on the shape of the full image.

D1 PAL is 720 : 576 rectangular pixels = 768 : 576 square pixels = 4:3 = 12:9

D1 NTSC is 720 : 486 rectangular pixels = 640 : 486 square pixels = 4:3 = 12:9

SD (full height anamorphic) widescreen is the 16:9 frame squeezed into a 12:9 (=4:3) frame, viewed on conventional 4:3 equipment everything will be tall and thin.

Assuming this image is unaltered from camera to TV at home, this picture is then either stretched by the (16:9) TV to fit (thus everything is back to the correct shape) or on a 4:3 TV it is scaled vertically (* 0.75) to fit a 16:9 letterbox within a 4:3 frame or scaled horizontally (* 1.333) to cut out the 4:3 (12:9) centre of the original frame.

woah
OOOOOOK, so dv and d1 in an ntsc environment is 640x486 or an equivalent of 4:3 which is 12:9.

From this info i am thinking that 12:9 is the standard aspect for both pal and ntsc. The only difference is the amount of pixel (resolution).

In ntsc the 12:9 is handled as 4:3, 3:2, or 16:9 depending on the viewing mode.

out fcp at dv ntsc 3:2 , 4:3, or 16:9 TL, the 12:9 is altered changing the pixels as need for output. The 12:9 stays but the shift is in the pixel shape to create the stretch or squeeze need to fit.

yay or nay?

""" What you do with what you have, is more important than what you could do, with what you don't have."

> > > Knowledge + Action = Wisdom - J. Corbett 1992 """"

dv and d1 in ntsc is not the same size. Would have been a lot simpler if it were... I believe ntsc dv is 3:2, while d1 is 4:3. Personally i thought it was a bad move, that causes more confusion...

Then you have SD FHA which is 4:3 but stretched to create 16:9 by the player/tv. Basically, the pixels stretch, nothing else is changed.

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strypes
dv and d1 in ntsc is not the same size. Would have been a lot simpler if it were... I believe ntsc dv is 3:2, while d1 is 4:3.

Not exactly NTSC DV is 720:480 = aspect 3:2, NTSC D1 CCIR 601 = 720:486 aspect is 40:27 (shame on me I made an error on that computation before - but forgive a PAL man *), NTSC anolog is 640:480 and has a 4:3 aspect ?

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strypes
? that causes more confusion.

I agree.

Regards
Andreas


*)
720 =2*2*2*2*3*3*5
486 =2*3*3*3*3*3
what both have in common is 2*3*3, removing that -> 2*2*2*5:3*3*3 -> 40:27

Haha. I'm a PAL guy too... geez! 40:27? Wat a mess!

Oh yea, one more point, i believe, is that NTSC and PAL have different pixel aspect ratios? Man! i hate math!

could it be said that hd works in the same principle but has more pixels?

would hd be true square pixels?

""" What you do with what you have, is more important than what you could do, with what you don't have."

> > > Knowledge + Action = Wisdom - J. Corbett 1992 """"

Quote
J.Corbett
could it be said that hd works in the same principle but has more pixels?

It could.

Quote
J.Corbett
would hd be true square pixels?

No. It could be.

Have look at all this HD settings in FCP.

Regards
Andreas

Well, in hd does the 12:9 still exists?

and am i completely wrong to believe that the are more pixels in it?

""" What you do with what you have, is more important than what you could do, with what you don't have."

> > > Knowledge + Action = Wisdom - J. Corbett 1992 """"

J.Corbett Wrote:
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> Well, in hd does the 12:9 still exists?
>

Not in practice. Just like standard definition is fixed at 720 x 576 PAL pixels (sorry, ntsc guys )... HD is fixed at something x 720 or something x 1080. (haven't worked that much in HD), but they're all 16:9 frames.

HD IS about having more pixels, as well as having a digital signal/interface. It results in more clarity, especially on bigger screens.