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How to calculate aspect ratios?


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#1 Marcus Frakes

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Posted 21 November 2005 - 04:58 AM

Is calculating aspect ratios simply a matter of dividing the width by the height of a frame size? For example a film frame that was 15mm wide and 10mm high would produce an aspect ratio of 1.5?? Is there any other dimension to consider (ie during transfer, post, standardized cropping??)

Thanks
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#2 Phil Rhodes

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Posted 21 November 2005 - 05:24 AM

Hi,

> Is calculating aspect ratios simply a matter of dividing the width by the height of a frame size?

Yes.

> For example a film frame that was 15mm wide and 10mm high would produce an aspect ratio of 1.5??

It would usually be expressed as 1.5:1, but yes. As often, it would be expressed as the lowest integer factor, in that case 3:2.

On video you can really only have two aspect ratios on tape - 4:3 or 16:9, 16:9 being near as makes no difference to 1.85:1 flat 35mm film. You are of course free to put whatever aspect ratio you like inside that by creative use of black bars, which is what happens when you have a 2.39:1 scope film on a 16:9 DVD, or when 16:9 standard def is broadcast as 14:9 on analogue terrestrial TV in the UK.

On film most often it'd be either 1.85 or 2.39 (sometimes called 2.35 or 2.40) or, much less commonly, 1.66:1, which is derived from standard 16mm. Again you can matte anything you like inside it, but be aware that the edges of the picture which are defined by the screen masking (which is a piece of black fabric) will look sharper and blacker than matted bars, which you might find unacceptable. This is most often done for trailers for scope films, since trailers are usually shown in 1.85:1.

So really, you have 4:3, which is often considered ugly, 16:9 which is almost exactly 1.85, or 2.39, that is flat TV, widescreen TV/widescreen film, or scope. If you're shooting a feature film, you are liable to be required to supply a full frame panned and scanned 4:3 master as well as a 16:9 transfer showing the whole of whatever frame you originally shot it for, with black bars if it's scope or so-thin-it's-invisible black bars if it's 1.85. If you are shooting for TV, what you see is generally what you get, but some 16:9 standard def markets require protection for 14:9, that is don't allow anything critical to go outside of the 14:9 area.

Phil
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#3 Laurent Andrieux

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Posted 21 November 2005 - 02:50 PM

As often, it would be expressed as the lowest integer factor, in that case 3:2.


It'svfunny to se that, usually, in video ratios are given as integers, and in film in a :1 ratio, 4:3 in video is 1.33:1 in film (standard academy)... Anybody knows why ?
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#4 John Pytlak RIP

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Posted 21 November 2005 - 03:47 PM

The SMPTE standards specify aspect ratios, which are the ratio of image width divided by image height. If an anamorphic lens is used, factor in its magnification in as well.

For example, standard SMPTE 195 recognizes the following aspect ratios for 35mm prints: 2.39:1 (scope), 1.85:1, 1.66:1 and 1.37:1.
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#5 David Mullen ASC

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Posted 21 November 2005 - 06:38 PM

As to why video engineers prefer aspect ratios expressed using whole numbers, beats me.
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#6 Boone Hudgins

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Posted 22 November 2005 - 01:37 AM

Strangely enough WXGA monitors, 1280x768, are 16x10, or 1.66:1. I don't get that.
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#7 Adam Frisch FSF

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Posted 22 November 2005 - 02:38 AM

The PAL standard is 720X576, i.e. 1.25:1 (5:4). Yet the TV sets they're shown on are 1.33:1 or 4:3. Just goes to show you that a committee isn't very well suited for this kind of thing.

I also see a lot more aspect ratio problems today than one used to. In my hotel room now where I write this, I have a 16:9 flat TV. On every channel the image looks slightly squished. Mind you, this has nothing to do with the settings of 16:9 and such (I've checked), 'cause it's less squishing than that, it's just small anomalies here and there that add up. Go to any retailer that sells TV and count the flatscreen TV's that show the film perfectly right - there won't be many. I don't know where the problem lies, but I think it's combination of all these software aspect ratio converters built in to DVD's, TV's and every other gadget and they kind of seem to gang up on eachother.. :(
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#8 Phil Rhodes

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Posted 22 November 2005 - 02:23 PM

Hi,

While waiting for someone in a shopping centre a few days ago, I actually went into an electronics store and adjusted all the TVs to display correctly. Yesterday, they'd all been put back wrong.

You just can't help some people.

Phil
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#9 Joshua Provost

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Posted 22 November 2005 - 02:58 PM

The PAL standard is 720X576, i.e. 1.25:1 (5:4). Yet the TV sets they're shown on are 1.33:1 or 4:3. Just goes to show you that a committee isn't very well suited for this kind of thing.


Actually, Adam, PAL is 1.33:1 (4:3). In the case of PAL on digital video, the pixels also have their own aspect ratio, pixel aspect ratio (PAR), in this case 1.066(:1). So, the pixels are not square, but slightly fatter, expanding it out from the 1.25:1 frame aspect ratio you figured to the 1.33:1 that is displayed.

Also, other PAR: 1.42 for widescreen PAL, 0.9 for NTSC 4:3 and 1.2 for NTSC widescreen.

So, yeh, it is convoluted, but there is a method to the madness.

Edited by Joshua Provost, 22 November 2005 - 02:59 PM.

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#10 Laurent Andrieux

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Posted 22 November 2005 - 03:33 PM

Hi,

While waiting for someone in a shopping centre a few days ago, I actually went into an electronics store and adjusted all the TVs to display correctly. Yesterday, they'd all been put back wrong.

You just can't help some people.

Phil


Did you save the settings ? otherwise, they might have just been reset to default when turned off !

I remember when I began to work as a cameraman at TF1 (the first french tv channel) I was astonished that the tv sets that were in the backround of the news studio, seen by millions of people, every day, three times a day, you know, a whole wall of them, were just not adjusted so the colors where going every and anywhere...

Edited by laurent.a, 22 November 2005 - 03:37 PM.

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#11 Dominic Case

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Posted 22 November 2005 - 05:20 PM

Hi,

While waiting for someone in a shopping centre a few days ago, I actually went into an electronics store and adjusted all the TVs to display correctly. Yesterday, they'd all been put back wrong.

You just can't help some people.

Phil

Phil! We agree on somethiing!

Widescreen TVs are good for DVD of movies. But shops can't show DVDs to the public unless they are authorised. Free-to-air TV is OK, but most program material is the wrong aspect ratio. And no-one can hope to sell a widescreen TV that has black bars down the edges of the screen that they are charging so much more for. So they leave them set on a stretch mode, regardless of content.

No-one seems to mind that the images are distorted - 33% too fat . (Perhaps it makes the average Hollywood starlet look about the same weight as the average TV viewer :D )

If you really want to kill time next time you are waiting in a store, Phil, try finding an assistant and asking them to explain why the people on that TV seem so fat, yet they seem OK on this older-style (4x3) TV over here.

Then try to explain it to them :blink:
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#12 Laurent Andrieux

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Posted 22 November 2005 - 05:32 PM

Right again !

And some consumers just leave the screen that way after they've set it at home !

At least 3 times did I explain this "stretch mode thing" and set properly some friend's set (I don't have friends in cinema and video only ;) )
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#13 Charles MacDonald

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Posted 22 November 2005 - 08:33 PM

Widescreen TVs are good for DVD of movies. ... And no-one can hope to sell a widescreen TV that has black bars down the edges of the screen that they are charging so much more for. So they leave them set on a stretch mode, regardless of content.


Back when I was a young whippersnaper, a TV set with black bars down the side meant that it needed a new 6BQ6GTB Horizontal output tube. :rolleyes:

The stores are probaly trying to pervent having to sell off the demonstrator TV set Cheep. Some of the early flat screen sets are quite prone to image burn-in and so If you leave them on for a month with "normal" TV, the sides of the screen will be lighter when you try to view someting in wide screen.

I have even seen one dealer include in their TV facts booklet that Conventional Displays. (Cathode ray tubes) are known to last longer than some flat screens.

Charles who is wrting this looking at a CRT monitor!
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