Aspect Ratio and the ITU-R Standard Strike Again

[Nicholi]

I'm just a little confused myself. I've checked the main G-knot version 0.28.7 as well as the newest beta 0.32.0. I'm not sure how something like this could be overlooked...or I'm just really mis-interpreting the labels of the things I'm selecting.

Why is it when you select 'NTSC anamorphic 16:9' for 'Input Pixel Aspect Ratio', it believes the Display Aspect Ratio is 1.823 ?

I usually manually select Display AR, and enter 1.778 to do my cropping/resizing calculations. However I decided to just click 'NTSC anamorphic 16:9' to see what it calculated and of course I got a wholly different answer because 1.78 is not the same number as 1.823.

Just a bit confused as I would think that the selection 'NTSC anamorphic 16:9' would calculate the cropping/resizing on an AR of 1.78 (aka 16:9).

Am I just confused as to the meanings of 'Input Pixel Aspect Ratio' ? Or is this really a grievous error ?

One of my associates believed perhaps that the selection for 'NTSC anamorphic 16:9' actually meant it was guessing at an AR level between 1.78 and 1.85 (as many DVD labels are incorrect when all they say is 16:9 Anamorphic Widescreen, when the AR is sometimes 1.85...which is not 16:9). Though I have no idea really what all this 1.823 business is still about thinking that.

[manono]

Hi-

Why is it when you select 'NTSC anamorphic 16:9' for 'Input Pixel Aspect Ratio', it believes the Display Aspect Ratio is 1.823 ?

If you go into the Options Tab and uncheck the ITU box, you'll get what you want. That doesn't make it right, but it may be what you're looking for.

One of my associates believed perhaps that the selection for 'NTSC anamorphic 16:9' actually meant it was guessing at an AR level between 1.78 and 1.85...

So, how do you explain 2.35:1 movies?

many DVD labels are incorrect when all they say is 16:9 Anamorphic Widescreen, when the AR is sometimes 1.85...which is not 16:9

You (and your associate) are confusing the movie AR with the DAR, or how the movie is resized by the player. Again, where does the very common 2.35:1 anamorphic 16:9 movie figure into your thinking? Here, read this:

http://www.doom9.org/aspectratios.htm

[Nicholi]

So, how do you explain 2.35:1 movies?

How is a 2.35:1 AR movie have anything to do with 16:9 ?
Or I've just totally misunderstood the concept of 16:9. 16/9 is 1.78 correct ? The option you select specifically says 16:9 ... I'm just trying to understand why a 16:9 movie (16/9 = 1.78) would have a AR of 1.823...when 16/9 is 1.78...not 1.823.

That is to say a movie (which IS a 1.78:1 anamorphic source) put into gknot would be told to use 640x352 (defaults, and no cropping, such as the remastered Akira movie, which needs no cropping). It would be displayed at an AR of 1.818 (640x352) if the option 'NTSC anamorphic (16:9)' is selected. When the movie is meant to be played back at a DAR of 1.78.

If I had a movie that was in fact 2.35:1 AR I would enter 2.35 into the 'Display AR' for the input. I have no idea how a movie can be called 'anamorphic 16:9' and '2.35:1 AR' at once though.

Please if anything explain to me what the proper meaning of 16:9 anamorphic is then. As that linked doom9 guide does not explain it. And I've seen many other sites of the same thing. I thought 16:9 specifically referred to the movies with an AR of 1:78:1. Other movies such as 1.85:1, and 2.35:1 were simply other widescreen movies but not 16:9.

For most things the AR and DAR are the same I would think, as the encode I'm making is itself not anamorphic but will be hard resized to the proper AR. So if a movie was 1.78:1 anamorphic (and you are not making an anamorphic encode, and also assuming no cropping) your Display Aspect Ratio should also be 1.78:1 ?

I think I'm in a world of hurt if everything I said was incorrect...

[Nicholi]

Mlach...

somehow completely missed the thread "Resolutions, Aspect Ratios And The ITU-R BT.601 Standard" directly above this one.

I'm betting the answer is there so I'll go read that...

[Nicholi]

I did not want to reply to that ITU Standard post as it seems quite old and likely reviving a dead topic I'm sure no one will reply to so...here are my newb questions.

Going to try to make my questions very clear, so I can understand whats going on here.

If a DVD is specifically called 1.78:1 Anamorphic Widescreen, why shouldn't its finalized encoded AR (the aspect ratio it is displayed at, DAR) be 1.78 AR?

As with my example of Remastered Akira (which I now see has 2 black pixels on the right side, but barring that is perfect). It is a 1.78:1 Anamorphic DVD. According to the ITU standard, it should be played back at 1.818 AR, res for example is 640x352. Why is this correct?

I understand that of course your final AR can sometimes NOT BE the initial DAR the movie is meant to be played back at, because of cropping black border issues. A movie which is 1.78 AR may be in fact have a final resolution of 640x368 (AR 1.739) to maintain a low Aspect Error Ratio, but because the Aspect Error Ratio is low you are assured the video is still correctly displayed even though the AR is not 1.78. However in the case of a movie that needs litte to NO cropping, I can't understand why 1.78:1 would not be the correct AR in the end?

Is the movie played back on a CORRECT player at 1.78:1 ? Or the initial value that gknot dislays as 1.823 (ITU standard checked)? So is there even such a thing as a movie that is 1.78:1 AR?

Edit: Just more of a direct question. For a movie that is 1.85:1 or even 2.35:1 AR anamorphic you would enter that in the 'Display AR' box of 'Input Pixel Aspect Ratio' for Gknot correct ? However a movie that is 1.78:1 you would simply select 'NTSC anamorphic (16:9)' which enters 1.823 into the grayed out 'Display AR' box ?? Thats just where the confusion really hits for me.

[manono]

If I had a movie that was in fact 2.35:1 AR I would enter 2.35 into the 'Display AR' for the input.

No you wouldn't. You'd enter either 16:9, or 4:3, depending on how it was encoded. There are only 2 DARs in common usage, 16:9 and 4:3. Again, you're confusing the movie AR (for widescreen, 1.66:1, 1.77:1, 1.85:1, 2.35:1 and many others) with the DAR (16:9 or 4:3). The DAR tells your player how to resize the movie, and has nothing to do with the movie's AR.

Take a look at the movie in DGIndex, or when you open the .d2v in GKnot. If NTSC, it's 720x480, or 1.5:1, and for an anamorphic 16:9 DVD it looks stretched vertically. After doing the cropping and resizing for low AR Error, hit View->Resize above the .d2v picture. Now it looks normal, right? That's what your DVD player will do, stretch it horizontally so that it looks normal. Balls and suns are round again.

Ordinarily, for .avi, we do this resizing before encoding, although it's possible to leave it alone, encode anamorphically, and then have your player resize it on playback.

How is a 2.35:1 AR movie have anything to do with 16:9 ?

It has everything to do with 16:9. It proves everything you said was incorrect.

I have no idea how a movie can be called 'anamorphic 16:9' and '2.35:1 AR' at once though.

At the risk of beating you to death with this, the next time you're at Wal-Mart or some place that sells DVDs, go find a DVD whose movie is 2.35:1. Try one of the LOTR movies (which are actually about 2.42:1). Look on the back, and you should see something like "Anamorphically Enhanced", or "16:9", or "Enhanced for 16:9 (or Wide Screen) Televisions".

And at the risk of repeating myself, if you don't like seeing 1.823 when you open a 16:9 movie in GKnot, go to the Options Tab, and uncheck the "Follow ITU-R BT.601 Standard" box. Then when you return to the Resolutions Tab, it'll say 1.778:1. Just for the record, I don't recommend that you do that, for the reasons outlined by TheWEF in the Sticky. I'm a firm believer in the ITU Standard. Plus, I watch my movies on a television. However, you should know that this issue is a bone of contention around here. The great man himself (Doom9) thinks the box should be unchecked. I think that len0x (the GKnot/AutoGK developer) is undecided at the moment.

For most things the AR and DAR are the same I would think...

Once more with feeling...WRONG.

[jggimi]

Let me try. Aspect Ratio is very confusing, and can be very complicated with PAR, DAR, and ITU standards. Here's how I simplify aspect ratio so that I can understand it: Display hardware (televisions and monitors) are made in two different shapes. 4:3, also known as "standard," and 16:9, also known as "widescreen." That's it.

A standard PC monitor is 4:3, and because the shape of the space for pixels is square, resolutions are in 4:3, such as 800x600 and 1024x768.

A widescreen monitor is 16:9, and because the shape of the space for pixels is square, resolutions are in 16:9, such as 1280x720.

DVDs do not have square pixels. DVDs have fixed resolutions: 720x480 NTSC, or 720x576 PAL. Neither of these is 4:3 or 16:9. The 4:3 or 16:9 DAR flags on the DVD describe the shape of the TV/Monitor that the video is designed to fit.

For content that is not exactly 4:3 or 16:9, the video stream will include letterboxing or pillarboxing. Most modern films are shot wider than 16:9, so there is usually letterboxing. This letterboxing in the video is cropped out when converting to AVI with GK/AGK.

There are plenty of widescreen movies authored with 4:3 DARs. These have more letterboxing, and consequently, less image, than if they'd had 16:9 DARs.

Consumers configure their set-top DVD players and tell them the shape of their TVs. One can usually pick from 4:3 Pan & Scan, 4:3 letterbox, or 16:9. When the DAR is 4:3, this setting is ignored and the player outputs standard 4:3 video.

When the DAR flag is set to 16:9, the player will output according to the consumers' setting. 4:3 Pan & Scan will zoom in and "fill" the screen -- similar to movies that are "formatted to fit your screen." This eliminates widescreen content, and may still have some letterboxing. In addition, it's not content-aware (such as a commercial "fullscreen" edition), so action on the left or right may be off screen. 4:3 Letterbox will add additional letterboxing to the image, in order to fit the entire content on screen.

AVI files are usually made with square pixels. This is how AGK works, and how GK is typically used. In order to get to square pixels, a resizing is performed based on the DAR.I recently acquired a 1280x720 HDTV/monitor, and managed to explain aspect ratio to my 8-year old daughter very simply:"If you don't set your standard TV shows to have pillarboxes on the widescreen TV, you'll end up watching Spongebob Rectanglepants."

[Nicholi]

Alright thank you both for the elaborate posts. I do see the error now in my thoughts of intermingling DAR and the AR of the movie so much. However as my good friend Socrates would do (stupid summer class in Philosophy) I must continue the questioning as I'm still a bit confused concerning different anamorphic 16:9 AR's. This is not to offend or be annoying, just to finally get a better grasp of all this resizing.

Ok so there are primarily only two DAR's, 4:3 and 16:9, I see this now. No matter what the source you usually refer to one of these. I myself have only come into 3 types of source actually. 4:3 nonanamorphic, 4:3 widescreen with letterboxing, and 16:9 anamorphic 1.78 AR. The first having a DAR of 4:3 obviously, and the second both 16:9 (the letterboxing after cropping).

Now please rip apart anything in that paragraph if it untrue so I can be sure I'm following things here....though I must go on.

My confusion is still involving the anamorphic 16:9 encodes. For example simply 1.85 and 2.35 AR. Both like 1.78 AR, are resized to a DAR of 16:9. Where does the true meaning of their AR's lie then? A 1.85 and 2.35 AR dvd would also simply contain a source of 720x480 correct. But they are all resized to the same DAR. Since I have never actually seen/used a 1.85 or 2.35 source I'm not sure of any particulars and have no knowledge of what is different about them, besides the fact that their Aspect Ratio is different but I lose all cohesion when they come from the same source res and are resized to the same DAR. So please if you would be so kind explain to me what makes them 1.85 AR and 2.35 AR when they are to be displayed at the same DAR ? To my guessing they are all resized to Gknot's default setting at mod32 height/width 640x352 for 16:9 anamorphic encodes. This would be correct ?

Please once again I do not mean to offend/annoy...but simply reach the truth of this subject as much as I can. Though I hope after the next explanation all will be revealed.

[manono]

Hi-

Thanks jggimi for the lucid explanation. I (we) digested this difficult material long ago, and have trouble sometimes explaining it clearly. But we get questions like this periodically, and it doesn't hurt to go over it from time to time.

OK, how is a 2.35 movie anamorphic? Take a 720x480 16:9 anamorphically encoded movie. When resized by your player it becomes 853x480 (480x1.777...=853.333). That's the resized appearance of all NTSC 16:9 DVDs. A true 1.78:1 movie (very rare, by the way) will fill the DVD with no black bars. A 1.85 movie will have very small black bars on the top and bottom, although sometimes they have some bars on all 4 sides to take into account the TV's overscan. On a widescreen TV set, both will normally fill the entire screen. The small set of black bars of the 1.85 movie will ordinarily be hidden by the TV's overscan. In the case of a 2.35:1 movie, the black bars will be larger on the top and bottom. Encode one sometime, and you'll see. When the black is cropped away, and the movie is resized, it'll be around 2.35:1. 640x272 is a common .avi size for such movies. So that's the difference-a 2.35:1 movie just has larger black bars on the DVD, so that the video portion is much narrower when compared to a 1.85:1 movie. And a 1.66:1 16:9 DVD will have black bars on the right and left sides (pillar bars), which may or may not show up when played on a widescreen TV set. On mine they show as very narrow bars on the right and left sides. But even 1.66:1 movies can benefit from anamorphic encoding.

The first having a DAR of 4:3 obviously, and the second both 16:9 (the letterboxing after cropping).

No, a widescreen letterboxed non-anamorphic DVD is as 4:3 as a fullscreen movie. However, this may just be a semantic distinction. In order not to confuse ourselves any more than necessary, please reserve "16:9" for the DAR, and use 1.78:1 or 1.85:1 for the movie AR. We in R1 NTSC land are still saddled with far too many widescreen 4:3 movies. They suffer from having low resolution. So they can't resolve fine horizontal lines, and all too often show aliasing/stairstepping. I'm wrestling with one at the moment. Horrible things, those.

More reading for you. SeeMoreDigital is a frequent contributer to discussions like these. In fact I expect him to jump in as soon as he sees this thread. He prepared a nice page some time ago, some of which is relevant here:

http://seemoredigital.net/03_Video_Only_Info/What_is_an_anamorphic_encode.html

And here's about the best site for an explanation of anamorphic DVDs, and why they're so much better:

http://www.thedigitalbits.com/articles/anamorphic/

On page 2 they have a couple of links that will explain and illustrate the 1.85:1 and 2.35:1 differences nicely:

1.85:1 (http://www.thedigitalbits.com/articles/anamorphic/anamorphic185demo.html)
2.35:1 (http://www.thedigitalbits.com/articles/anamorphic/anamorphic235demo.html)

More (http://www.gregl.net/videophile/anamorphic.htm)

[ice_uk99]

off-topic, but here i go: is there any tool out there that can give me "proper" (ITU standard) vertical resolution for a 1024 horizontal one? gordian knot only allows up to 800x resolutions, and autogordianknot (which, actually, allows 1024x) does not allow me to select the mod (mod4, mod8, mod16).

sorry about the off-topic thing.

[manono]

Hi-

Pretty far off-topic, alright. For the AutoGK part, it selects the correct mod for you, so you don't screw up. But I think you can override the AutoGK decisions with one of the hidden options.

When using GKnot, I'd suggest halving the 1024 to 512 and setting up your resize that way. So, set the W-Modul to Mod16 and the H-Modul to Mod8, set the horizontal resize to 512, crop and resize, and then double the results. That should work, I'd guess, although I've never tried it.

[SeeMoreDigital]

Originally posted by manono
...More reading for you. SeeMoreDigital is a frequent contributer to discussions like these. In fact I expect him to jump in as soon as he sees this thread. He prepared a nice page some time ago, some of which is relevant here:

http://seemoredigital.net/03_Video_Only_Info/What_is_an_anamorphic_encode.html Thanks guy's, but this thread appears to be about wrapped up!

The whole situation regarding PAR and DAR can be a very confusing one. Both have their place and both work when set properly.

That said, when generating anamorphic Mpeg4 encodes I would recommend that you use PAR settings and not DAR.

This is because some stand-alone players (ie: most if not all ESS chip-set based players) can't spin Mpeg4 encodes with DAR signalling. But all, seem to be able to spin encodes with PAR sinalling... not that many of them can make use of the signal anyway!

Personally I don't use Gordian Knot, so I don't know all of it's nuances, but like manono says, uncheck the ITU box!

ITU standards are all well and good. But it would seem over the months and years, they've become "open to interpretation" - like most things in life!

When it comes to PAR, I use my own settings. Which you are welcome to try too..... Nero Recode2 (Ahead) seems to be using them ;)


Cheers

[SeeMoreDigital]

Originally posted by ice_uk99
off-topic, but here i go: is there any tool out there that can give me "proper" (ITU standard) vertical resolution for a 1024 horizontal one? gordian knot only allows up to 800x resolutions, and autogordianknot (which, actually, allows 1024x) does not allow me to select the mod (mod4, mod8, mod16).

sorry about the off-topic thing. I'm interested... What's your sources 'aspect ratio' (or SAR)?

If you are intending to encode using square pixels, within a 16:9 pixel frame. Then 1024 horizontal pixels would give you 576 vertical pixels!


Cheers

[len0x]

Originally posted by ice_uk99
gordian knot only allows up to 800x resolutions

version 0.32 allows up to 1920x...

[niamh]

maybe this thread (http://forum.doom9.org/showthread.php?s=&threadid=81089) would be of interest to nicholi, even though it's about captures, it sheds a lot of light on PAR and DAR.

[Nicholi]

Alright just so I can finally wrap this up. The player as well as the final Res calculation performed in Gknot will make the correct AR distinction solely on the fact that 1.78, 1.85, and 2.35 AR movies have very different amounts of black bars on the sides to be cropped? Or is there a secret tag in the stream somewhere that specifically relates the DAR to be displayed at (such as mkv). Thats mostly what I am confused about.

Last example. 1 anamorphic 16:9 movie at an AR of 1.78 that completely fills its 720x480 source res (no black bars). Another anamorphic 16:9 movie at an AR of 2.35:1 also with no black bars (or does this one not exist filling the entire 720x480, thus why I am confused). To me it would seem both would be resized to the same thing in Gknot's calculation, though since I have never had a 2.35:1 I'm not sure of how it would tell the distinction. Only that KNOWING the movie is not 1.78 AR by various online database's which have the listed AR and of course if the movie's cover is correctly labeled. But I'm guessing, a 2.35 AR movie simply relates that the movie is 2.35 AR, the player as well as Gknot instantly picks up on this, and I'm just a rambling bafoon for no reason...I'm pretty sure I answered what I needed to know now.

It all started with not knowing that 16:9 describes a DAR....ok Thank you all!

[manono]

Hi-

The player as well as the final Res calculation performed in Gknot will make the correct AR distinction solely on the fact that 1.78, 1.85, and 2.35 AR movies have very different amounts of black bars on the sides to be cropped? Or is there a secret tag in the stream somewhere that specifically relates the DAR to be displayed at

Both. It's in the stream. You can get the information (16:9 or 4:3) from both the Stream Information file that DVD Decrypter gives you, and from DGIndex when creating the .d2v file. And if you've selected 16:9 or 4:3 correctly in GKnot, then cropping away all the black bars and then resizing to low AR Error means that you can't go wrong. I've seen 2.0:1, 2.1:1, 2.2:1, 2.44:1, 2.55:1, all kinds. But you can't go wrong, following the simple procedures.

...or does this one not exist filling the entire 720x480

It doesn't exist. If it fills the .d2v screen, then by definition it's not 2.35:1. If you're ever in doubt about what the AR is, or you don't trust the results you see, then a visit to IMDB, or Amazon.com (or the back of the DVD box) will likely confirm what you see. They've all been known be wrong from time to time, though. Heck, even DGIndex or the Stream Info file have been known to be wrong, but very rarely.

[Nicholi]

Yes thank you very much again manono. I'm pretty sure I have a firm grasp of all this anamorphic'ness now. And of the knowledge of the ITU standard, which I shall not waiver from unless I somehow purposely see the DVD has been mastered incorrectly.

The only way I see to find this for sure would be to find a large square or circle (as with smaller ones the aspect ratio error may not be large enough to affect such a small diameter of pixels) and count the pixels horizontal and vertical. Though of course for the square it would have to be completely parallel to horizon of the vid. And for a circle/sphere, it would have to be sure as close to a perfect circle and from the correct angle.

But as far as I can tell, a friend and I continued through a few other movies, simply calc'ing resolutions and noting the DAR's. And even though different DARs were resulted from the ITU standard calculations, they actually seemed more correct (i went through a few blind tests as my friend resized some images of the ITU standard calc and an "exact" AR calc of 1.78, 1.85, and 2.35 whatever the movie was).

We did notice a few things, of course you yourself already know I'm sure. You will get a perfect 640x360 (1.78 DAR) from anamorphic 16:9 source only if you crop(8,0,-8,0), same for 4:3 movies to reach 640x480. I would assume those are "perfectly" mastered video's eh ? As we saw quite a few anamorphic 1.78 AR's that did not have 8 pixels worth of black bars on left right. Thus a res of 640x352, or 356 would come up, reducing the h-mod to as low as 4 to reach a nice aspect error.

Anyways, thank you again manono and everyone for your helpful posts.

[SeeMoreDigital]

Hi Nicholi,

If you are indending to convert you anamorphic Mpeg2/DVD's to anamorphic Mpeg4, then you may be interested in knowing these pixel frame size calculations (http://www.SeeMoreDigital.net/03_Video_Only_Info/Pixel_Frame_Size_Totals.html).


Cheers

[Nicholi]

Yes, I did run into your guide SeeMoreDigital. But I was a bit confused, as you don't present PAR's, but this nifty table which I know has some hidden knowledge in it somewhere... Just no idea how to extract it. What does that table show ? If anything just explain the 'NTSC 4:3 TV/PC Monitors', which is the only thing I'll be using if I'm reading the table correctly.

I am of course noting that the res in the 'To Nearest Full Pixel' seems to be the "exact" res per the given AR. And the mod16 res to the left of that. But aren't both of those quite useless in the eyes of following the ITU-R BT.601 standard per resizing the image ?

The 'Image Pixel Quantity(?)' is showing the total amount of square pixels in the image. Ok and the 'Matte Pixel Qty' is showing the amount of black square pixels that will be on the screen if it is lower than 4:3, and the 'Matte % Of Frame' of course the percent of the total black square pixels in the frame.

But I'm confused as to those resolutions ? As I know understand a 1.78 AR movie should not neccesarily end up at a DAR of 1.78.

[SeeMoreDigital]

Okay, take this little lot: -
PAL DVD Players, DV Camcorders and DVB Satellite Broadcasts
Frame Aspect Ratio = 1.25:1 = 'Anamorphic 1.25:1 Frame'
Picture To Nearest To Nearest Matte Image Matte %
AR 16th Pixel Full Pixel Pixel Qty Pixel Qty Of Frame
1.33:1 720 x 576 720 x 576 000,000 414,720 00.00
1.77:1 720 x 576 720 x 576 000,000 414,720 00.00
1.85:1 720 x 560 720 x 554 15,840 398,880 4.04
2.35:1 720 x 432 720 x 436 100,800 313,920 32.17
2.40:1 720 x 432 720 x 427 107,280 307,440 34.98
They provide the pixel quantities of 'anamorphic' DVD frames (plus other sources).

Note that an PAL 1.33:1 (aka 4:3) frame and a 1.77:1 (aka 16:9) frame uses the same quantity of pixels. All of them being "image" pixels and none of them being "black matte".

However, if you watched an wide-screen anamorphic DVD with say, an aspect ratio of 2.35:1 (the AR size is usually stated on the DVD's the rear cover) the DVD is still encoded using 720x576 pixels, but some are encoded in black (for the top and bottom "matte") and the remainder are encoded with the main "image".

To be exact: -
The top matte will be encoded using - 720x70 black pixels
The main video will be encoded using - 720x436 image pixels
The bottom matte will be encoded using - 720x70 black pixels

70 + 436 + 70 = 576 - which is the full pixel height of the frame.

When it comes to Mpeg4 encoding, some people crop/cut away the mattes, other people keep them in.

But the most important thing you have to understand is, what an "anamorphic" image really looks like... many people unfortunately don't. Many people also don't understand that professionally encoded movie DVD's are never encoded using anything less than 720x576 pixel for PAL. And 720x480 pixels for NTSC.

Personally I would not bother trying to understand the ITU regulations. Not unless you're intending to capture from analogue sources and converting to digital. You also don't need to read up about anamorphic camera lenses!

But that's just my opinion...


Cheers

[scharfis_brain]

perfect 4:3 PAL is 702x576
and a perfect 16:9 is 702x576, whichgets resized to 1024x576
but anamorphic 720x576 has to beresized to 1050x576
and 4:3 720x576 has to be 788x576..

[SeeMoreDigital]

Originally posted by scharfis_brain
perfect 4:3 PAL is 702x576
and a perfect 16:9 is 702x576, whichgets resized to 1024x576
but anamorphic 720x576 has to beresized to 1050x576
and 4:3 720x576 has to be 788x576.. Yes, but these calculations are based on viewing video on an analogue CRT screen. Things are slightly different when viewing digital video on a digital (plasma, LCD or projector) screen via an DVI or HDMI connection. As there's no overscan involved and therefore, it does not have to be included in the calculations.


Cheers

[scharfis_brain]

even on Digital-non-overscan-Displays, you have to preserve the pixel aspect ratio of PAL, which is 1:1.094.

you may zoom in the image a little bit to get rid of black overscan borders.

but under all circumstances you have to preserve the ITU-Aspect Ratio

[SeeMoreDigital]

All I'm saying is... At the end of the day all PAL Mpeg2 movie DVD's are encoded using 720x576 pixels and all NTSC Mpeg2 movie DVD's are encoded using 720x480 pixels. Whether the Mpeg2 stream has a DAR of 4:3 or a DAR of 16:9.

And technically there is no reason why an Mpeg2 stream cannot be backed up to Mpeg4 using exactly the same quantity of pixels and be made to behave in exactly the same way as the source DVD. What's more this can be done using either DAR or PAR!

It's entirely up to your good self whether you chose to believe this or not. But I've generated many tests using my custom calculations and they are pixel perfect :D


Cheers

[scharfis_brain]

Oh, I didn't mention it for the en- or recoding.

it is just the displaying correction...

[SeeMoreDigital]

I'm not sure what you mean s_b?


Cheers

[scharfis_brain]

if you backup DVD to an mpeg-4 format, a clever person wouldn't need to resize for his encode, if the container supports PARs different to 1:1 (like AVI is limited to), cause the resize or better said the
AR correction of 1:1.094 for 4:3
and 1:1.094*1.3333 for 16:9
is only needed at the moment of playback...

[SeeMoreDigital]

You can now set PAR or DAR when generating Mpeg4 .avi or .mp4 encodes.

XviD offers an PAR and DAR encoder and decoder for AVI
3ivx offers an PAR and DAR encoder and decoder for AVI and MP4
Ahead offers an PAR encoder and decoder for MP4

When the correct figures are entered. The correct encodes are generated... it's as simple as that!

Unfortunately and in my opinion, the default settings that XviD and 3ivx use for anamorphic encoding are incorrect because they are based on their assumption of the ITU standard.... Mine are not!

But I don't mind being in the minority... as usual.


Tell you what, if you upload a short anamorphic Mpeg2 clip. I'll re-encode it to anamorphic Mpeg4 and you will see what I mean!


Cheers

[Nicholi]

What exactly is

their assumption of the ITU standard

Obviously many people here are into following the ITU standard exactly. And others simply talk about the #'s and all the other madness, which is all well and good and I undertsand all that.

However, if i'm encoding a DVD (not analogue nothing else) thats NTSC 16:9 anamorphic with a 1.78 AR. I do not want to make an anamorphic file, because of size restraints and such I simply want a hard-resized image. Should I...

A. Resize via ITU standard res's which are not perfect DAR's (DAR of encoded movie likely will not be 1.78, 1.85, 2.35, so forth).

B. Calculate my resolution and aspect error to an exact AR of 1.78, 1.85, 2.35.

The movie will be played back on a computer, not anywhere else. As sometimes it's seeming these res's come out to be very different. And although I want to believe in the magic of the ITU standard sometimes its frightening me. To resize to 704x384 (both mod32, and calculated from an exact AR of 1.78, with only an aspect error of 0.6%, via option B) or to resize to 704x372 (h-mod 4, a DAR of 1.892, with an aspect error of 0.1%, via option A).

You see there is of course only one correct option. Do I know if the DVD follows ITU standards? No, of course not...is there any DEFINITE test? It doesn't seem so.... So what is a guy to do. Blindly follow the standard or obey the math of exact DAR's.

Edit: Crop is (2,8,-2,-12) for those interested.

[piscator]

Personally, I always use option A (itu resizing). I also like a hard-resized image, since I'm not going to view something out of aspect anyway. And resizing on the fly at playback-time probably results in worse quality, because the filter is not so good as the Lanczos before encoding. Besides, the non-resized image would require more space for the encode. Oh, and I wouldn't worry about a few percent off to a perfect AR. It's not that you are really seeing so little difference in AR.

Anyway, if anyone is interested in the exact maths between AR/DAR. Here's an AVISynth script function I use to calculate just that (i use these scripts in batch scripting Compressability Checks in combination with r4rip).

function DVDAspectResizeHeight(clip c, int newWidth, int heightMultOf, float ar, float ituScale)
{
dar = ar * ituScale
newHeight = c.height * (newWidth/float(c.width)) * (720.0/576.0) / dar
newHeightMultOf = floor(newHeight/heightMultOf + 0.5) * heightMultOf
return newHeightMultOf
}

For PAL, ituScale is: 40.0/39.0
For NTSC, ituScale is: 81.0/79.0

Example of function:
LanczosResize(640,DVDAspectResizeHeight(640,16,4.0/3.0,40.0/39.0))

greetz,
Piscator

[Nicholi]

*Tallies one vote for ITU*

I'm wondering of SeeMoreDigital's point of view on the matter however, though he mostly seems to be all for anamorphic playback and not "hard-resizing" the video :) .

It's just so quite confusing. As if I understand all this madness correctly, your 720x480 1.78 AR anamorphic 16:9 source is resized to "853.3x480" upon playback, why isn't it also an exact 1.78 DAR upon lower resolutions?

As my previous example of whether to choose 704x384 or 704x372. Just trying to figure "what is more correct" (though i suppose that isn't what it should be called) if I choose 704x384 (and perhaps the ITU resizing IS the correct choice) I've made an aspect resize error of 3.2%. If I did it the other way, calculating the res upon an exact AR of 1.78 getting 704x372 there would be an error of 2.52% (if my calculations are correct).

I'm sorry again for bringing this all up again, but after seeing SeeMoreDigital's posts about XviD having their own interpretation of the different PAR's and such I got confused, along with the massive difference I saw in the 2 choices I had to resize by.

Just wondering about XviD's PARs as well. How can they be "incorrect"?

[SeeMoreDigital]

Nicholi,

Do you understand 'exactly' what an anamorphic encode is and what it looks like without DAR (or PAR) correction. If not it's very easy for you to become confused!

When I said the ITU standards are "open to interpretation" I base this on the information that both XviD and 3ivX use the following 'presets' to calculate an anamorphic frame: -

Default Codec Player Info
PAR Setting Calculation Video Size

4:3 PAL 12:11 625lines 15:11
4:3 NTSC 10:11 525lines 15:11
16:9 PAL 16:11 625lines 20:11
16:9 NTSC 40:33 525lines 20:11If you generated an anamorphic encode with their settings, your software player would not reveal the correct AR or pixel information under the players 'properties'.


With my settings: -

Required Custom Player Info
PAR Setting PAR Setting Video Size

4:3 PAL 64:60 (or 16:15) 4:3 or 768x576
4:3 NTSC 64:72 (or 16:18) 4:3 or 640x480
16:9 PAL 64:45 16:9 or 1024x576
16:9 NTSC 64:54 16:9 or 853x480
They do!


Cheers

[piscator]

My biggest objection against anamorphic encodes is that it doesn't go well with the AVI container format: you cannot store the DAR in it and you have to tell your player manually to playback resized. I know you can use matroska as a container and it can store the DAR. But matroska and its tools are still a bit buggy, a lot of players have problems with playback (even MPC) and I personally doubt it'll go far in the future if the big industries are not taking it on (with all on-going discussions on MP4 container formats).

Besides this, it seems a bit a waste of space to just store all the additional verical lines if you're going to resize/downsize anyway during playback.

greetz,
Piscator

[SeeMoreDigital]

Originally posted by piscator
Besides this, it seems a bit a waste of space to just store all the additional verical lines if you're going to resize/downsize anyway during playback. Who does this?

The idea of backing up anamorphic DVD's to anamorphic Mpeg4 is so that you have a near perfect pixel-for-pixel (1:1) copy of the original.

If you playback your anamorphic Mpeg4 encodes on a 16:9 monitor, TV or projector, there's no down-sizing..... everything works in the same way an anamorphic Mpeg2/DVD works!


Cheers

[piscator]

Originally posted by SeeMoreDigital
Who does this?

The idea of backing up anamorphic DVD's to anamorphic Mpeg4 is so that you have a near perfect pixel-for-pixel (1:1) copy of the original.

If you playback your anamorphic Mpeg4 encodes on a 16:9 monitor, TV or projector, there's no down-sizing..... everything works in the same way an anamorphic Mpeg2/DVD works!
Cheers

Yes, everything works the same way as my anamorphic Mpeg2/DVD: downsizing only. A television set doesn't have a resolution higher than 720 by something, so the picture is downsized. And since I'm watching almost everything back through my TV set... Besides the resize filters during playback don't look as good as the Lanczos.
I also tried projectors for a while, but imo they are inpractical, noisy and far too expensive for the quality you get.

And as I mentioned, with AVI container you have to put the DAR info in the filename, so you remember to switch your player manually to proper playback AR (which is annoying if you have mixed anamorphic and non-anamorpic content).

greetz,
Piscator

[SeeMoreDigital]

Also, what people also have to understand is that most set-top Mpeg4/DVD stand-alone players do not offer automatic AR correction for Mpeg4 in AVI encodes. Even Mpeg4 streams that have been encoded with anamorphic signalling!

Embedding anamorphic AR signalling within Mpeg4 streams is a new innovation (started Dec03/Jan04 AFAIK) and currently, there are very few PC 'software players' (direct-show decoder filters) that support the feature, let alone 'stand-alones'!

People must not get confused... Just because their Mpeg4/DVD players can spin and auto AR anamorphic DVD's (ie: Mpeg2/VOB's), does not mean to say that the same player can auto AR anamorphic XviD or 3ivx encodes (ie: Mpeg4/avi)!


Cheers

[Nicholi]

Err...well as I already said the file I will be encoding is NOT going to be anamorphic. But I assume that means when forcing a res and AR you would of course choose the ITU resize'd calculations, SeeMoreDigital.

Interesting how XviD and such have the incorrect PARs, were I to do such an anamorphic encode I will of course be using your correctly calculated PARs SeeMoreDigital.

Well I think my questions seem to be leading nowhere, so much info on anamorphic subject.

[SeeMoreDigital]

Well Nicholi,

If you're not bothered about generating anamorphic encodes, that means you will be generating 'cropped and resized' encodes with square pixels... yes!

If this is the case, I can't see what your problem is!

.... but good luck to you all the same.


Cheers

[ZZZERO]

Everyone is probably sick of this subject already, but I do have one question that has been nagging for some time and this thread seems as good a place as any for it.

I'm wondering why the Gordion Knot resolution choices in the slider bar for 4:3 ratio are not exact 1.33 ratio. Instead of ratios like 640 X 464, which is a 1.379 ratio, why not the exact 640 X 480? What about other perfect ratios like like 576 X 432, 512 X 384, 448 X 336, and so on. Almost none of the ones offered are 1.33.

I'm sure there's some technical reason for this, but I had to ask because I really don't understand it.

[len0x]

Uncheck ITU resizing and you'll get your perfect 4:3 back...

[ZZZERO]

I unchecked ITU resizing. How do I get perfect 4:3 now? The slider bar still give the same resolution choices as before.

[manono]

It shouldn't. I'm looking at GKnot 30.0 at the moment. I have the W and H-Moduls set to their default 32 and 16. I have Crop disabled. I open a .d2v from an NTSC 4:3 non-anamorphic DVD, and I toggle back and forth between checking and unchecking the ITU Standard box, and check back in the Resolution Tab, and I go back and forth between 640x464 and 640x480. So should you.

I don't see what the big deal is with 640x480 .vs 640x464. Academy Ratio is 1.37:1 anyway, and more and more DVDs are being released with no black bars on the sides which, with the ITU box checked, and 2 pixels cropped from both the top and bottom (to lower the AR Error) will give you just that.

However, most full screen DVDs have some black bars on the right and left sides, and when you crop 8 pixels each from the right and left sides you'll get 640x480.

http://www.widescreen.org/aspect_ratios.shtml
http://www.ultimatedisney.com/oar.htm

[ZZZERO]

You're right. Every other resolution choice is now 1.33. I didn't look carefully enough and saw several non 1.33 ratios and thought nothing had changed.