Feature Film DVD Transfers

[Guest lonedog]

.................

Edited December 17, 2004 by lonedog

[Michael Most]

Why is there such a big discrepancy in the picture quality between one dvd and another? And i'm not just talking about the lower budgeted films verses the blockbusters, it seems to be across the board. Some are excellent (for DVD) and some are rotten.

 

That's a blanket statement that I find to be completely untrue. You need to cite some examples if you feel this is not the case.

[Filip Plesha]

I agree with you. There is a rather big difference between different DVD's.

It's milder on a TV set, but when you examine it on a computer, you can really see it. Some DVD's can't even be played fullscreen on a 17'' monitor because of the horrible compression. And yet some feel clean and sharp even on fullscreen.

 

It's because of all the different copression techniques used, and because of different amounts of compression in general.

 

I find that picture quality on DVD's has improved from the begining to now.

But there are exeptions.

 

And remember that the image quality of the movie depends not only

on the quality of the source video on the disc, but also on the techniques your

software/hardware uses to unstrech the image.

If you have some way of reaching the source video file, you will find that

the image is a lot sharper than the one you end up seeing, because

when it is resampled to normal aspect ratio, it has to pass through some sort of antialiasing filter. The source image is usually 1.25:1 in aspect ratio

and usually looks as your avarage JPEG image (normally sharp), but with

some compression artefacts of course. Yet when you pause the playback in the re-rendered mode you never get a good sharp image that looks like a still image file.

Edited December 13, 2004 by Filip Plesha

[Phil Rhodes]

Hi,

 

> you have some way of reaching the source video file, you will find that

> the image is a lot sharper than the one you end up seeing, because

> when it is resampled to normal aspect ratio, it has to pass through some sort of

> antialiasing filter. The source image is usually 1.25:1 in aspect ratio..

 

What? I think you're basically on the right track here, but the specifics are wrong. Video is stored on DVDs as either a 720x576 or 720x480 frame, representing either a 4:3 or 16:9 image. Most commonly you'll have a feature film transferred as 16:9 so your DVD player may well be (badly) resampling it to fit a 4:3 display.

 

Where'd you get the 1.25 number from?

 

Phil

[Filip Plesha]

The difference between 720x576 and 720x480 is not that one is used for 16:9 and other for 4:3, but it is the difference between NTSC and PAL DVD's.

Both 4:3 and 16:9 have the same number of pixels horisontal or vertical.

The only difference is in unsqueesing factors. The aspect ratio for PAL DVD's is

1.25:1 (why do you ask me where did I come up with the number? You posted the right numbers yourself, just divide them) no matter what the image is on the recording.

I'm guessing there is some additional data that commands software players to perform different unstreching factors.

 

This is exactly why most software players have a default resolution of 1K (1024)

when showing films. This is very close to the resolution of unstreched DVD image.

But I haven't seen yet any incorporated filters that correct for the softness due to

antialiasing.

Which is kind of frustrating because if you perform the unsquesing in photoshop manually, and add a little bit of unsharp mask, you get a nice sharpness similar to that on the source video data, and more detail than you get with the top software DVD players today. It's almost as good as a 1K image.

 

Now, I don't have a fancy hardware DVD player, just an entry level Sony (I usually watch movies on my computer so I don't use it often), so I don't know if the high end hardware players do the rerendering a bit more sharply.

[Mark Allen]

I agree that the quality varies a great deal. Studios will often outsource their movies for compression to different facilities and they don't all do it the same. In addition to having the cleanest source, the art of compression techniques really is a craft and not a button push. Some facilities understand that and some don't. A good compression house will customize the compression for the movie - making sure that scenes with a lot of pans have enough data rate while still ones can loosen it up.

 

You'll also find that the data rates are vastly different depending on the length and special features on the DVD. That's probably the largest difference right there. If your quality level is 3 vs. 6 - that's obviously a big difference and even studio movies will have to go down to 3 in order to fit the whole movie and all the features.

 

ABout still frame - some dvd players can recognize material that was telecined and will actually take out the pull down for the stills. Some will even remove the pulldown for the movie altogether. However, in order to get this to happen, you have to prepare the movie right.

[David Mullen ASC]

There are several factors that affect the quality of the DVD, starting with the source material for the transfer, the equipment used for the transfer, the skill of the people using the equipment, the tape format the transfer is stored on, the quality of any downconversions if the transfer was to HD, and the quality of the DVD authoring and pressing, compression rate, etc. Not to mention the quality of the playback and display device...

 

Pretty much what you'd think.

[Phil Rhodes]

Hi,

 

What is this about removing pulldown? For that matter, what's this entire deal about progressive scan DVD players? I understood that all NTSC DVDs containing 24p-originated material contained 24fps MPEG data which is 3:2'd by the playback deck.

 

Phil

[Filip Plesha]

Hi,

 

What is this about removing pulldown? For that matter, what's this entire deal about progressive scan DVD players? I understood that all NTSC DVDs containing 24p-originated material contained 24fps MPEG data which is 3:2'd by the playback deck.

 

Phil

<{POST_SNAPBACK}>

 

 

The video on the disc is interalced. Progressive players deinterlace the image, and send a progressive video signal to progressive displays.

The two basic techniques for this are Weave and Bob. Weaving means combinind two half-frames into one. And Bobing means doubling each half-frame (field) into full frame. Of course there are some techniques that use interpolation for Bobing to make a sharper frame.

Weaving is usually used for film material because half of the information of the same film frame is in one video half-frame and the other half is in the other half-frame. With PAL it's pretty straightforward. But with NTSC, if you introduce weave deinterlacing in it's simplest form, you get motion artefacts (two good frames, folowed by two messed up frames etc). Because not every

film frame is lucky enough to get a reservation for two video half-frames.

So in NTSC weaving the third field from those film frames that got 3 fields is skipped.

 

I am so glad to be in PAL region. More resolution, sharper images, less "issues"

[Alvin Pingol]

>>what's this entire deal about progressive scan DVD players? I understood that

>>all NTSC DVDs containing 24p-originated material contained 24fps MPEG data

>>which is 3:2'd by the playback deck.

 

I thought this as well. I've just always understood "Progressive Scan" DVD players to be nothing more than DVD players with component outputs that bypass the built-in telecine.

 

Most progressive scan displays, on the other hand, can detect pulldown pattern and remove it...

[Phil Rhodes]

Hi,

 

I'm sure I've read that too, although I have seen NTSC DVDs with 3:2 burned into the disc.

 

And strictly speaking, 3:2 pulldown isn't "interlaced". It's using the same technical mechanisms as an interlaced image, but it's not representative of the same temporal sampling. In the same way, the HDW-A500 HDCAM deck currently sitting three feet to my left says "24PsF" (actually 23.98PsF, but what's 0.02 of a frame between friends) which is no more "interlaced" than 3:2 is.

 

Phil

[Filip Plesha]

What do you mean that it's not interlaced?

 

Are you perhapse refering to a 2-3 pulldown from 24P to 30P?

That would be the same as deinterlaced 60i from a 24P source.

 

Or perhapse our terminology is not the same?

 

For me, the word interlaced means "split into fields, that carry only half of the image data"

[David Mullen ASC]

I think Phil is referring to interlaced origination versus simply storage of progressive or film frames as fields (which PsF does.)

[Filip Plesha]

oh, I see, then it makes sense.

But I was talking about image storage only. And since the discussion is about DVD's, I was talking about film images 24P, stored as interlaced images.

 

Even thought the two fields show the same frame I still call them interlaced, because that's how they are stored.

[Phil Rhodes]

Hi,

 

That's exactly the point; I was under the impression that a 24p-originated NTSC DVD is actually stored as 24p, not interlaced.

 

I'll happily stand corrected if anyone can clear this up.

 

Phil

[Filip Plesha]

Hi,

 

That's exactly the point; I was under the impression that a 24p-originated NTSC DVD is actually stored as 24p, not interlaced.

 

I'll happily stand corrected if anyone can clear this up.

 

Phil

<{POST_SNAPBACK}>

 

What is there to clear up? 24P material is stored in interlaced format on standard DVD video. For PAL it's just splitting frames as usuall and speeding it up (2:2 pulldown), and for NTSC there is a 2:3 pulldown. What is unclear?

Edited December 15, 2004 by Filip Plesha

[Guest Sean McVeigh]

What is there to clear up? 24P material is stored in interlaced format on standard DVD video. For PAL it's just splitting frames as usuall and speeding it up (2:2 pulldown), and for NTSC there is a 2:3 pulldown. What is unclear?

<{POST_SNAPBACK}>

 

Erm, I'm with Phil on this one.. I am quite certain the frames are stored progressively on a 23.98fps MPEG stream. I'm right now looking for proof somewhere, but I know when I master out at that rate in whatever software package I'm using, my choice of field dominance (even/odd) vanishes.

Of course, reading the specs should clear all of this up.

 

-Sean

[Filip Plesha]

Erm, I'm with Phil on this one.. I am quite certain the frames are stored progressively on a 23.98fps MPEG stream.  I'm right now looking for proof somewhere, but I know when I master out at that rate in whatever software package I'm using, my choice of field dominance (even/odd) vanishes.

Of course, reading the specs should clear all of this up.

 

-Sean

<{POST_SNAPBACK}>

 

Ok, then, perhapse I was wrong, we'll just wait for someone who can quote some official paper or something like that.

[Mike Donis]

You can get DVD players that'll remove the pulldown from telecined material, but most Hollywood DVDs are in fact stored as 23.98fps MPEG2 files on the disc itself.

 

It most definitely is possible for this to be done - even consumer programs such as Vegas or Premiere support 24P native rendering, and DVD programs can indeed burn 24P DVDs, that being the source file having a 23.98fpsMPEG, rather than a telecined master encoded in 60i.

 

I'm sorry that I can't find any "official" documents about it, I haven't the time right now, but check out www.DVXuser.com and find lots of information on how to make 24P DVDs yourself.

 

It is possible for consumers to take control of this higher-quality technology, and I can only give a personal guarantee that Hollywood does the same.

[Filip Plesha]

So, I guess I deserve a big "told you so" now...

[Mike Donis]

So, I guess I deserve a big "told you so" now...

<{POST_SNAPBACK}>

 

:rolleyes:

 

I won't worry about it if you won't :D B)

[Filip Plesha]

:rolleyes:

 

I won't worry about it if you won't  :D  B)

<{POST_SNAPBACK}>

 

 

Actually I was talking about Phil Rhodes... :)

[Phil Rhodes]

Mnh... uh... what?

 

Oh. Right. You are forgiven, my son.

 

Phil

[Mike Donis]

Actually I was talking about Phil Rhodes... :)

<{POST_SNAPBACK}>

 

:D I guess I got ahead of myself there...

[Filip Plesha]

And you are forgiven for calling me "my son" :)