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Picture formats on DVDs  

post #1 of 9
Thread Starter 
Hi!
I don't know if you should say hello, or introduce yourself the first time you write on a Bulletin Bord. Seems a bit inpolite not to do so, so let me just briefly say my name is Joakim Quensel (but people call me "JQ"), and I am a 32 year old Swede (please excuse my English, and I am too lazy to run a spellcheck on what I write), living in Swizerland, who is very glad to have found this forum which seems to be really good!

Anyways, I have a question regarding DVD formats. I'm a bit confused about how the different formats, anamorfic and non-anamorfic, is stored on the DVD. Are there actually two films on the DVD, "letterbox" and "Wide"? Or does the DVD skip every 4th line for the "Letterbox" format or how does it work?

Same question for "Pan&Scan" which gives me a 4:3 picture, that is cut at the edges. Is this format stored as a seperate track?

On most anamorfic DVDs,I can select only "Wide" or "Letterbox. On some I can select only Pan&Scan or both. Then I have this DVD (American History X, european version) where I can only get the anamorfic picture. Very irretating (I have a 4:3 proj TV). Does not all anamorfic DVDs support 4:3 viewing?

Would be really gald if anyone at this forum could give me some clarity int this mater. Good links about technical DVD-stuff would also be highly apreciated.

BR /
Joakim
post #2 of 9
Welcome aboard!

When I talk about resolution, I'm talking mainly about the NTSC format. PAL has a bit more resolution.

If you have an anamorphically enhanced (16x9 enhanced) DVD and you are watching the widescreen version of a film (if given a choice between pan and scan or widescreen versions on either side of the disc, or on a separate layer) then there is only one 1.78:1 image squeezed into a 4:3 video frame. A DVD player set to its 4:3 television mode will downconvert the image by throwing out lines or blending lines together to get a proper geometry, losing 30% of the full visible resolution of the DVD in the process. Then the player adds electronic black bars on the top and bottom to frame it as 1.78:1 (16x9). If a movie was photographed with an intended ratio wider than 1.78:1, then the telecine operator would have added thicker black bars within his 1.78:1 widescreen television monitor frame for correct composition.

No Region 1, 16x9 enhanced DVDs have ever taken advantage of the auto pan&scan mode (requires that the DVD be flagged and encoded for it) that's part of the DVD specs. Any studio that wishes to release a cropped version will have it as a separate transfer. However, on European PAL DVDs, it is used on a random basis.

Non-anamorphic DVDs are 4:3 video transfers to begin with (not done using HDTV widescreen equipment and HD video masters). All of the black comprising the matte bars on the top and bottom of the picture is part of the full 480 lines of resolution, so a smaller percentage of resolution makes up the picture in between the bars. On the other hand, a 16x9 enhanced DVD with a 1.78:1 ratio (shown on a widescreen TV) will use ALL 480 visible lines to make up the movie's picture. Giving you an increase of about 30% more resolution than before.


Of course, as this and other forums are about recreating the theatrical experience at home, we should respect the original theatrical composition of a filmmaker's work. If a movie was shot for a widescreen, that's the way it was usually intended to be seen.

No pan and scan for me, thank you.

Hope this helped to answer some of your questions.

Dan

[This message has been edited by Dan Hitchman (edited 08-21-2000).]

[This message has been edited by Dan Hitchman (edited 08-21-2000).]
post #3 of 9
Thread Starter 
Yes, I totaly agree thatn movies are better viewed in their original format. Unfortunately, my 4:3 rear projection TV does not support widescreen, so I'd have to live with the lower resolution (until I get a projector).

So, if I understand your answer right, "Pan&Scan" is stored as a seperate track, but "Letterbox" is downconverted by the DVD itself. Correct?

If I would have guessed, I would have thought it was the other way. Seems easier for a DVD to go from anamorfic to Pan&Scan, it would just have to skip the outer 33% of each line. Anamorf to letterbox seems to be much more complex.

OK, so if the anamorfic to letterbox conversion is made by the DVD, then it should work for every anamorfic DVD, right? As I mentioned, I have this mproblem with one of my DVDs that I can only view in stretched anamorfic.

One more question related to how the picutre is stored on the DVD:
Is the picutre stored interlaced, i.e. (480 lines NTSC assumed) line 1, 3, 5, ..., 477, 479, 2, 4, 6, ..., 478, 480?
Or is it stored progressive (line 1, 2, 3, ..., 479, 480) and the DVD makes up the interlaced picture?

For a lcd or DLP, how is a interlace picutre displayed? Is every pixel refreshed with 60 Hz, or doe only 50% of the pixel refresh every 1/60 of a second?
post #4 of 9
Let me begin by saying that I am by no means an expert, but rather an enthusiat who tries to stay well informed. I make every effort to not pass on false information, but if somebody notices something here that is incorrect, I would welcome the criticism and hope that you show me the error in my ways.

Here's the deal. Pan & Scan (also called Fullscreen) is a process done either in the film to video transfer stage, or from the video masters to convert a wide image (1.85:1, 2.35:1, etc..) to one that will fit on the vast majority of television screens, which are 4:3. An editor (sometimes with the help of the director) will position a 4:3 frame over the OAR (original aspect ratio) image. Sometimes the P&S frame will be in the middle of the OAR image, sometimes off to the side, and very often will move from left to right (or right to left) during a shot. This is not the same as your Zoom feature on either your DVD player or TV; that just enlarges the image and always shows the middle portion. Pan & Scan is a process that cannot be easily approximated by a player, and thus requires it's own, seperate track on a DVD. Setting your DVD player to send a 16:9 signal should have no effect, because the entire signal has an aspect ratio of 4:3.

Letterboxed images are also designed specifically for a 4:3 TV. The OAR image is encoded with black bars above and below the image; the black bars are part of a complete image with a 4:3 aspect ratio that is encoded on a disc. When shown on a widescreen TV (16:9 or, 1.78:1) the black bars above and below the film image will be visible, and there will also be space on either side of the image that must be filled in by the TV. It is a 4:3 image (with black bars at top and bottom) set in the middle of a 16:9 frame. When viewed with a regular 4:3 TV a letterboxed image will fill the screen side to side and have black bars top and bottom. (Note: the size of the black bars in both letterbox and anamorphic tranfers are dependant on the OAR of the film. A 2.35:1 movie will have larger bars than a 1.85:1 movie, or said in a different way, on the same TV a 2.35:1 image will be shorter than a 1.85:1 image.) Like Pan & Scan, or Fullscreen , setting your DVD player to output a 16:9 signal will have no effect, as there is no 16:9 signal present (letterbox is 4:3, remember?)

Anamorphic DVD's present a different challenge, though. Essentially these discs are optimized for people with projectors and widescreen TV's. The OAR image (let's pretend it's 1.85:1) is compressed side to side during the encoding process. When this now 16:9 bitstream is fed to a 4:3 TV the image looks tall and squeezed. This is because the 4:3 TV cannot apply the horizontal resolution properly (it's a 16:9 image, right?) but it can realize the full vertical resolution - so the image looks like it's squeezed from left to right and rather than being 1.85:1 it looks closer to 1.33:1, and thus, tall. When this bitstream is fed to a 16:9 TV (or projector) the horizontal resolution can be spread out over the full width of the screen - since you can now realize both the full horizontal and vertical resolution the OAR has been restored. A standard 4:3 TV can still be used for anamorphic discs, though. The DVD player must be set for 4:3, and then the player will downconvert the anamorphic image, essentially discarding some of the lines, in order to shorten the picture (top to bottom) and restore the OAR. Not all DVD players do this equally well, though. Most are pretty good.

Anamorphic discs are "future proof" in the sense that many people's next TV will be 16:9. Letterboxed discs, although they seem to produce the same picture as an anamorphic disc on a 4:3 set, are vastly inferior when viewed on a 16:9 set. As an aside you should note the aspect ratio of these 16:9 TV's is really 1.78:1, and few discs are actually produced with that ratio. Most discs tend to be 1.85:1 or 2.35:1, and both of these, even when viewed on a widescreen set, will produce some level of black bars.

As far as how the information is stored on the DVD, I'm pretty sure that it's stored as 480i. Progressive players can recreate the 480p picture internally, or your TV can do with a line doubler/scaler. There are a few ways, but the best is for the player to do it BEFORE converting the signal to analog. The best players can detect "flags" imbedded in the bitstream and use those to help them piece back together the 480p image, essentially reversing the 3-2 pulldown process that's used to go from film to video in the first place. I'm no expert though. If the process interests you, let me know and I'll see if I can dig up some links. Enjoy.
post #5 of 9
Thread Starter 
Thanks a lot for the info!

Still a few questions though

Is the Pan scan fromat a spererate track, or is it just a smaller number of bits that indicate what part of the anamorfic picture that shoulld be displayed?

If the "letterboox" format is produced by the DVD, what could the explaqnation be that for one of my discs, I only get the streched picture?

If the player/scaler/linedoubler manage to produce the "correct" progressive picture (i.e. 480p/24Hz), what is the output? 480p/60Hz where the frames are shown 2 times / 3 times / 2 times and so on?

Do progressiv players work on PAL films?

If the linedoubler does not reproduce the original film-frames, how is the progressive signal produced?
post #6 of 9
I'm going to try and answer each of your questions as best as I can:

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Is the Pan scan fromat a spererate track, or is it just a smaller number of bits that indicate what part of the anamorfic picture that shoulld be displayed?
************************

Pan & Scan is completely seperate track. In my experience, most discs with both a widescreen (letterbox or anamorphic) and P&S keep them on different sides. You have to actually turn the disc over to see the other track. There are some instances, like "Titanic", where the original film is actually shaped 4:3, and the director mattes the film with black strips (this is a really simplified explaination) to create the widescreen ratio of 1.85:1 (or 2.35, or whatever); he shoots the film knowing that he's going to matte it. When it's time to do the pan & scan, though, he can remove the mattes and reposition the frame that he wants to capture. So if we agree that a 1.85:1 frame will contain information on the sides that don't fit into a 4:3 frame, it is POSSIBLE (though not always) that a Pan & Scan version will contain information above and below the 1.85 frame; you might see some the top of a building that was cut off, or the wheels of a car or whatever. (Note: the ability to do this depends on the actual filming process. Not all films are able to "recapture" this information above the frame) The point is, it is a totally seperate track.

*****************************************
If the "letterboox" format is produced by the DVD, what could the explaqnation be that for one of my discs, I only get the streched picture?
*****************************************

Chances are that this is an anamorphic disc and you have got your DVD player set to send a 16:9 signal; it's not really a letterboxed disc. If you have a standard TV you should set your DVD player to send a 4:3 or Standard signal to the TV. If you have a widescreen TV (which I don't think you do) or a 4:3 TV that can do the vertical squeeze trick, you can use the 16:9 signal.

Don't assume that a picture that has black bars has to be letterbox. That term should only be used for widescreen movies that have been encoded WITH the black bars to make them fit a 4:3 monitor. Although an anamorphic DVD will look essentially the same on your 4:3 TV, there is a different process going on. Check the box of this "letterboxed" DVD. It probably says something like "enhanced for widescreen TV's" or "Anamorphic". Part of the problem is that not all studios use the same terms and it gets confusion.

**************************************
If the player/scaler/linedoubler manage to produce the "correct" progressive picture (i.e. 480p/24Hz), what is the output? 480p/60Hz where the frames are shown 2 times / 3 times / 2 times and so on?
***************************************

If the player is progressive and is creating the 480p signal, then the signal is 480p. If the TV (like mine) is doing the doubling/scaling, the DVD player sends a 480i signal which the TV converts to 480p. I don't know of any TV's that accept both a 480i and a 480p signal, but they probably do exist. Obviously not all TV's (in fact few) have internal line doublers, but more and more are hitting the market as we speak.

When I mentioned 3-2 Pulldown I had forgotten that you live in Sweden. If I'm not mistaken you use a PAL system which has 25 frames per second for video. Our NTSC system uses 30 frames. Film uses 24 frames. 3-2 Pulldown is a technique used to convert film (24 frames) to NTSC video (30 frames). I think to go to PAL one film frame is repeated per second, but I'm not sure.

Don't forget that for NTSC these 30 frames are broken down into 60 fields, with alterating lines. This is the 480i signal.

*********************************************
Do progressiv players work on PAL films?
*********************************************

I have no idea if there are PAL progressive players on the market yet, but I can't see any reason why they wouldn't be possible. Before doing any research, though, check to see if your TV is even compatible.

******************************************
If the linedoubler does not reproduce the original film-frames, how is the progressive signal produced?
*****************************************

You can't really recreate the film's frames because there are only 24 of them. What you can do it recreate the 30 frames (25 for PAL) that were created during the mastering process, and achieve a 480p signal. If you can create that 480p signal within the DVD player, before the 480i is converted to analog you will have the best possible 480p signal.

Enjoy.
post #7 of 9
Thread Starter 
Thanks again for the info!

The problem with the stretched picture on my "American History X" disc is only on this particular disc. Yes, the picture is anamorfic, but I have a lot of other anamorfic DVDs that work fine (I have selected "letterbox" on the initial setting on my DVD). If it is like you say that the letterbox format is produced by the DVD itself, and this is not a sperate track, then it should work for all anamorfic discs, shouldn't it?

I have several Region 1 DVDs, so the progressive NTSC players interest me as well when I am going to upgrade my HT with a projector and a maybe a new DVD or scaler. The "original" format on the DVD is actually 480p/24Hz (or PAL, 576p/25Hz). What I woulder is if a NTSC scaler/linedoubler/progressive player output 480p/60Hz or does it change the frequency to a multiple of 24? If it keeps 60Hz, then I guess the output is each original film frame repeated 2 times, 3 times, 2 times and so on. Does not seem to be optimal.
post #8 of 9
I found the article in the following thread very helpful in understanding the different formats: http://www.avsforum.com/ubb/Forum16/HTML/000035.html

Hope this helps you as well.
Regards,
Drew
post #9 of 9
Thread Starter 
The article says that the 4:3 conversion is done by the DVD and that soime DVDs do this conversion better than others.

I still have the problem with my American History X DVD though. If the 4:3 adaption is done by the DVD, there is no explanation why it would not work on this particular disc.

I would be very interested in some info on how exactly different progressive DVD players, linedoublers and scalers work, both for film material (3-2 pulldown and PAL) and real interlaced material.

When the picture is digitilized, is the value for each pixel an average for the pixel, or a sample from the center of the pixel (I guess this would have a large impact of the possibilities on up- and down scaling the picture).
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