Full resolution with anamorph movies ?

[Ogig]

Hi there,

when using target quality 100% and transcoding anamorph movies I was surprised to see that my movies have a width of 720 pixels.

I always thought that the correct aspect ratio of anamorph movies is achieved by keeping the number of lines and increasing the width. WinDVD and other DVD players support that as they show a picture of 1024x576 (PAL).

So, is AutoGK throwing away prescious resolution although 100% quality is desired ? :confused: Some advice please...

[unskinnyboy]

The PAL DVD resolution is 720x576 with letterboxing. When making an avi, by going above 720 to say 1024, you won't recreate any more details but will waste precious bitrate for sure. Try it! Set fixed width to 1024 or whatever else you want and try encoding. It should look worse than 720x??? resized to 1024x??? during playback.

(I hope I understood your issue correctly..)

Also please :search:. This has been discussed before. Many times!

[Ogig]

No, I'm not talking about letterboxing, which is an inferior method of storing widescreen content in a 4:3 standard resolution such as PAL or NTSC (black bars are part of the picture).

However, virtually all DVDs and most high quality digital TV content is encoded in anamorph format as it preserves more detail. It is achieved by squeezing the movie in width before encoding such that it has 4:3 format and is standard conform, and then resizing during decoding to the original picture aspect ratio. That's how I understood it, any way.

That implies that we loose resolution if we transcode to widths smaller than 1024 (that is if we don't use anamorph encoding in the target format as well).

Yes, I have used the search before posting (although I do post seldomly I'm a frequent reader), but nothing useful has come up. If you can provide any links to threads I'll gladly let this thread rest in peace.

Edit:
Just found the answer in an old c't article: the correct resolution is indeed 1024x576.

So AutoGK is not implementing target quality of 100% correctly. len0x, if you are reading this, is there any way you can fix this although you are still retired ? ;-)

[Wilbert]

That implies that we loose resolution if we transcode to widths smaller than 1024 (that is if we don't use anamorph encoding in the target format as well).
For clarity. You don't loose resolution because your width will be smaller than 1024 (namely 720), but you loose resolution because your height will be 405 (or smaller if you crop away the black borders). (Assuming you encode at 720x405.) I'm pretty sure this is what you mean though :)

[Ogig]

For clarity. You don't loose resolution because your width will be smaller than 1024 (namely 720), but you loose resolution because your height will be 405 (or smaller if you crop away the black borders). (Assuming you encode at 720x405.) I'm pretty sure this is what you mean though :)

Hmm, I'm not so sure about that. The whole idea about anamorph encoding is to have a fixed transition from 4:3 to 16:9, by that I mean from PAR 1.33 to PAR 1.78. Other target PARs are NOT supported. It follows from that, if a movie has PAR 1.78 there are no black borders at all, neither before nor after resizing, because the movies is squeezed in width, nothing else! The full number of lines is encoded!

However, cropping is an issue with movies that exceed PAR 1.78, e.g. cinemascope movies with PAR 2.35 where black borders are indeed part of the picture. But even those movies are resized to 1024x576 and afterwards cropped at the top and the bottom.

I've yet to see a reason why 720 px width would conserve full resolution. ;)

[Wilbert]

Hmm, I'm not so sure about that. The whole idea about anamorph encoding is to have a fixed transition from 4:3 to 16:9, by that I mean from PAR 1.33 to PAR 1.78.
Anamorphic says nothing about the PAR or the real aspect ratio of your movie. It only says that the DAR (display aspect ratio) is 16x9. This means that the size of your movie 720x576 (for PAL) is resized to 1024x576 during playback.

As an illustration there are movies with a real aspect ratio of 2.35 which are either letterboxed widescreen (4x3) or anamorphic widescreen (16x9).

Indeed, if the real aspect ratio of your anamorphic movie is 1.78 it doesn't have black borders, but not so for movies with a DAR of 4x3. The playback size is 720 x 720/1.78 = 720x404. Assuming the DAR is:

1) 4x3: playback at 768x576 = 720x540 => black borders: 540-404=136.
2) 16x9: playback at 1024x576 = 720x405 => no black borders.

I hope it's clear now.

nb, those numbers 1.78 and 2.35 are not PARs (pixel aspect ratio).

[Ogig]

With PAR I meant picture aspect ratio, sorry for the confusion. As I said the problem persists with sources that have a DAR of 16:9.


Indeed, if the real aspect ratio of your anamorphic movie is 1.78 it doesn't have black borders, but not so for movies with a DAR of 4x3. The playback size is 720 x 720/1.78 = 720x404. Assuming the DAR is:

1) 4x3: playback at 768x576 = 720x540 => black borders: 540-404=136.
2) 16x9: playback at 1024x576 = 720x405 => no black borders.

I hope it's clear now.


I had a hard time to understand your calculations, but I'm pretty sure it doesn't work that way. I've read several sources now, including Wikipedia (http://en.wikipedia.org/wiki/Anamorphic_widescreen#DVD_video) and The Ultimate Guide to Anamorphic Widescreen (http://www.thedigitalbits.com/articles/anamorphic/), the whole point in anamorphic encoding is to be able to keep the full number of lines. For correct display the picture is thus _stretched_ horizontally.

Your calculations imply that after stretching the picture is resized from width 1024 to 720 (to get a PAL conform width ??), but then we would end up with fewer lines and therefore get exactly the same quality as letterboxed movies, which obviously cannot be true. As I said in my very first post, software DVD players, e.g. Media Player Classisc or WindDVD, show a picture with width of 1024.

I'm getting weary...

[Wilbert]

I had a hard time to understand your calculations, but I'm pretty sure it doesn't work that way. I've read several sources now, including Wikipedia and The Ultimate Guide to Anamorphic Widescreen, the whole point in anamorphic encoding is to be able to keep the full number of lines. For correct display the picture is thus _stretched_ horizontally.
Yes, i agree. Sorry, if i implied otherwise. 720x576 (DAR 16x9) is played back at 1024x576.

I'm not sure what your actual question is. Let me first ask you what your definition of "Pixel Aspect Ratio". It's the playback size after cropping away black borders right?

I think your question is:
However, virtually all DVDs and most high quality digital TV content is encoded in anamorph format as it preserves more detail. It is achieved by squeezing the movie in width before encoding such that it has 4:3 format and is standard conform, and then resizing during decoding to the original picture aspect ratio. That's how I understood it, any way.
If you mean that anamorphic dvd streams have a pixel aspect ratio of 4:3, then this is not true. pixel aspect ratio can be 2.35, 1.78, etc ... as you say in previous posts. If you mean that the size of the stream is 4:3, this is also not true, since they are encoded at 720x576 (or 704x576).

Btw, streams with a DAR of 4x3 are also stretched (horizontally) during playback.

[Ogig]

I don't want to get into definitions as the procedure of anamorph encoding is pretty straightforward and has been explained more than once in this thread.

The original question was whether encoding such movies at less than 1024 pixel width means losing resolution. If you can agree with me on that and noone objects the topic should be settled...a pitty len0x is not around anymore to fix this in AutoGK.

[Wilbert]

I don't want to get into definitions as the procedure of anamorph encoding is pretty straightforward and has been explained more than once in this thread.
Whatever ...

The original question was whether encoding such movies at less than 1024 pixel width means losing resolution. If you can agree with me on
I already told you in my first response i agree with this.