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Old 3rd February 2006, 16:28   #21  |  Link
kotrtim
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Quote:
Good question. How would you know definitively? Are all NTSC Television sources 4:3? If so, why the padding bars?
A DVD can either have 4:3 or 16:9 , but sometimes movies are made with aspect different from the two above, something like 235:100, it does not fit 4:3 or 16:9 , therefore black bars are added to make it 4:3/16:9, besides that the original ratio of the film can be preserved

Last edited by kotrtim; 3rd February 2006 at 16:36.
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Old 3rd February 2006, 16:41   #22  |  Link
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Quote:
Originally Posted by kotrtim
A DVD can either have 4:3 or 16:9 , but sometimes movies are made with aspect different from the two above, something like 235:100, it does not fit 4:3 or 16:9 , therefore black bars are added to make it 4:3/16:9, besides that the original ratio of the film can be preserved
But 720x480 is not 4:3 or 16:9. Do you mean that DVD can only support 4:3 or 16:9 AR signalling?
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Old 3rd February 2006, 16:47   #23  |  Link
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Quote:
Originally Posted by kotrtim
A DVD can either have 4:3 or 16:9 , but sometimes movies are made with aspect different from the two above, something like 235:100, it does not fit 4:3 or 16:9
Ofcourse they do. This is what the subject of anamorphic images is all about.

As I mentioned before, a movie with an aspect ratio of 2.35:1 can be represented as a fraction of 47/20 (ie: 47 divided by 20 equals 2.35). Which can be worked into the formula I provided.


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Old 3rd February 2006, 16:52   #24  |  Link
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I get the impression that you guys are trying to "run" before you can "walk".

You really must do some reading up on what "uncorrected" anamorphic images look like...

What I mean be "Uncorrected" is, what the image looks like before any form of aspect ratio signalling has been applied, whether it be SAR, PAR or DAR!


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Old 3rd February 2006, 17:06   #25  |  Link
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I've never seen any DVD with 47/20, I've film with 2.35:1 which has added black bars to make it 4:3

Do you mean that that DVD-video standard can have any fraction of aspect ratio besides 4:3 and 16:9?

Does anamorphic means the pixels are displayed rectangularly instead of squares?
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Old 3rd February 2006, 17:24   #26  |  Link
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Quote:
Originally Posted by SeeMoreDigital
I get the impression that you guys are trying to "run" before you can "walk".

You really must do some reading up on what "uncorrected" anamorphic images look like...

What I mean be "Uncorrected" is, what the image looks like before any form of aspect ratio signalling has been applied, whether it be SAR, PAR or DAR!


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Well, I've just read http://www.doom9.org/index.html?/aspectratios.htm and its has plugged some of the gaps in my knowledge.

"Uncorrected" anamorphic images are 720x480 (for NTSC) with the aspect ratio of 1.5:1, right?

And the DAR can be set to signal stretching to either 4:3 or 16:9 (and two others). But, going back to my example case earlier, if the source was in fact 4:3 then the DAR would be set to that, and there should be no padding borders. So why are there borders? My only conclusion is that the original source is NOT 4:3 but rather 176:135, and the borders are there to correct the aspect ration from 4:3! So it seems to me that kotrtim has the right of it, and that I should use the uncropped size for SAR calculation.

Do you agree with my reasoning, SeeMore? Or ir there yet more that I don't correctly understand.

Edit: Correction.

Last edited by bkman; 3rd February 2006 at 17:37.
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Old 3rd February 2006, 18:25   #27  |  Link
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Quote:
Originally Posted by bkman
"Uncorrected" anamorphic images are 720x480 (for NTSC) with the aspect ratio of 1.5:1, right?
Yep that's correct!

Quote:
Originally Posted by bkman
And the DAR can be set to signal stretching to either 4:3 or 16:9 (and two others). But, going back to my example case earlier, if the source was in fact 4:3 then the DAR would be set to that, and there should be no padding borders. So why are there borders? My only conclusion is that the original source is NOT 4:3 but rather 176:135, and the borders are there to correct the aspect ration from 4:3! So it seems to me that kotrtim has the right of it, and that I should use the uncropped size for SAR calculation.
Yes the are two DAR levels for commercial 4:3 and 16:9 NTSC DVD's. There are also two DAR levels for commercial 4:3 and 16:9 PAL DVD's.

The padding (borders) which can often be seen to the left and right of DVD images is (arguably) there to help reduce "over-scan". Normally when playing DVD's via a stand-alone player and viewing them via a TV, you would not see this padding but on a PC you do.

But even if you crop away the left and right padding boarders, the "target" aspect ratio shape is still indended to be either 4:3 or 16:9.


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Old 3rd February 2006, 18:59   #28  |  Link
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Quote:
Originally Posted by SeeMoreDigital
The padding (borders) which can often be seen to the left and right of DVD images is (arguably) there to help reduce "over-scan". Normally when playing DVD's via a stand-alone player and viewing them via a TV, you would not see this padding but on a PC you do.
That would explain a lot, but as you say it is arguable and may not always be the case. So there is a choice when calculating the SAR in that respect, I think, where some might think it is more correct to do it one way, and others the other.

Thanks for your help with my questions, btw.
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Old 3rd February 2006, 20:05   #29  |  Link
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Quote:
Originally Posted by bkman
That would explain a lot, but as you say it is arguable and may not always be the case. So there is a choice when calculating the SAR in that respect, I think, where some might think it is more correct to do it one way, and others the other.

Thanks for your help with my questions, btw.
When you read my posts you will see I tend not to mention terms such as SAR, PAR and DAR. This is because people tend to pre-assume their values are always "fixed".... Which they are not!

The level of "Aspect Ratio Signalling" (ARS) you will require will change in relation to your source "Movie's Aspect Ratio" (MAR) and your "mod16" pixel frame size (after cropping and resizing).

Here's an "extreme" example of what I mean. If you had an MPEG-4 file with say, a resolution of 496x464 but you knew it should be displayed at 2.35:1 shape, you could use the following calculation: -
Code:
MAR    FAR                              ARS 
47     464     21808                    1363
--  x  ---  =  -----  lowest dominator  ----  Giving an ARS value of 1363:620
20     496      9920                    620
EDIT: I forgot to include the "Extreme Example" sample.


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Last edited by SeeMoreDigital; 3rd February 2006 at 22:33.
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Old 4th February 2006, 22:34   #30  |  Link
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Not being the best at math, is there any easy way to work out the lowest common denominator? Is it possible to enter in 1920:2112 as the SAR in MeGUI or must I absolutely break it down further?
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Old 4th February 2006, 22:45   #31  |  Link
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Quote:
Originally Posted by SeeMoreDigital
If you can guys, try and calculate "everything" as a fraction, because converting fractions to decimals and back to fractions again "can" produce conflicting Aspect Ratio Signalling (ARS) values.

If your NTSC movie has an aspect ratio of 1.33:1, then this can be represented as a fraction of 4/3. Meaning: -
Code:
4     480     1920                    8
-  x  ---  =  ----  lowest dominator  -  Giving an ARS value of 8:9
3     720     2160                    9
If your NTSC movie has an aspect ratio of 1.77:1, then this can be represented as a fraction of 16/9. Meaning: -
Code:
16     480     7680                    32
--  x  ---  =  ----  lowest dominator  --  Giving an ARS value of 32:27
 9     720     6480                    27
If your NTSC movie has an aspect ratio of 1.85:1, then this can be represented as a fraction of 37/20. Meaning: -
Code:
37     480     17760                    37
--  x  ---  =  -----  lowest dominator  --  Giving an ARS value of 37:30
20     720     14400                    30
If your NTSC movie has an aspect ratio of 2.35:1, then this can be represented as a fraction of 47/20. Meaning: -
Code:
47     480     22560                    47
--  x  ---  =  -----  lowest dominator  --  Giving an ARS value of 47:30
20     720     14400                    30
If your NTSC movie has an aspect ratio of 2.40:1, then this can be represented as a fraction of 12/5. Meaning: -
Code:
12     480     5760                    8
--  x  ---  =  ----  lowest dominator  -  Giving an ARS value of 8:5
 5     720     3600                    5
For working out the "Aspect Ratio Signalling" values of PAL sources, simply substitute 480/720 to 576/720 and recalculate.

The same formula can be used to work out the "Aspect Ratio Signalling" values of cropped and re-sized encodes too by entering the relevant resolutions.


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Just to be clear so I would enter in the ARS values indicated above as the SAR in MeGUI?
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Old 4th February 2006, 22:50   #32  |  Link
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So for my 2.35 NTSC DVD
after cropping
47 368 17296
-- x --- = ----- which breaks down to ? This us entered as SAR in MeGUI
20 704 14080

Is this correct?
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Old 5th February 2006, 00:50   #33  |  Link
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Quote:
Originally Posted by DigitalDivide
So for my 2.35 NTSC DVD
after cropping
47 368 17296
-- x --- = ----- which breaks down to? This us entered as SAR in MeGUI
20 704 14080

Is this correct?
Yes... Initially this would provide an ARS of 1081:880.

However, this could be further converted to say: -
Code:
1080                             27
---- which, in turn decimates to --
 880                             22
That said, 199:162 would be more exact


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Last edited by SeeMoreDigital; 5th February 2006 at 01:05.
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Old 5th February 2006, 18:00   #34  |  Link
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Quote:
Originally Posted by SeeMoreDigital
Yes... Initially this would provide an ARS of 1081:880.

However, this could be further converted to say: -
Code:
1080                             27
---- which, in turn decimates to --
 880                             22
That said, 199:162 would be more exact


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SMD,

Is there a formula as to how to work out the lowest common den? Is it just guess work with a calculator? Give me something to go on..lol
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Old 5th February 2006, 18:17   #35  |  Link
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Quote:
Originally Posted by DigitalDivide
SMD,

Is there a formula as to how to work out the lowest common den? Is it just guess work with a calculator? Give me something to go on..lol
I use a Sharp EL-530V calculator to work out and simplify all these fractions.... But I'm thinking about developing a little "ARS Calculator" tool... Something like this: -




EDIT: Here's a 2.35:1 video sample, with a pixel frame size of 704x368 and aspect ratio sigalling at 199:162.


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Last edited by SeeMoreDigital; 5th February 2006 at 22:33.
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Old 5th February 2006, 18:53   #36  |  Link
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You should definitely create that ARS calculator. It would definitely help a lot and I'm sure everyone would appreciate it.
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Old 6th February 2006, 02:37   #37  |  Link
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i second that
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Old 6th February 2006, 08:03   #38  |  Link
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Quote:
Originally Posted by DigitalDivide
Just to be clear so I would enter in the ARS values indicated above as the SAR in MeGUI?
Nu-uh! MeGUI now uses what what SMD refers to as Movie Aspect Ratio everywhere. So the only values you will ever really need to know are 4:3, 1:1, 16:9, 47:20 (2.35) and 37:20 (1.85). MeGUI just does all the calculations that SMD described, but behind your back so that you don't have to see them.

Quote:
Originally Posted by DigitalDivide
You should definitely create that ARS calculator. It would definitely help a lot and I'm sure everyone would appreciate it.
Maybe you could try MeGUI's new system first? It should do all the calculations that SMD's does.
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Old 6th February 2006, 10:43   #39  |  Link
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SMD likes to stick to non-standard terminology. I think his MAR is the playback AR (after cropping away the black borders). If that's the case, than in many cases you don't know the MAR in advance, unless it is specified on the box of the dvd.
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Old 6th February 2006, 10:46   #40  |  Link
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Quote:
Originally Posted by DigitalDivide
You should definitely create that ARS calculator. It would definitely help a lot and I'm sure everyone would appreciate it.
yep ... such kinda 'calculators' are still released. one of the most known is called Gordian Knot. just give it a try ! well fitted to your dvd resizing problems.

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