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Anamorphic DVDs - question


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27 replies to this topic

#1 of 28 Kramer Lowry

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Posted February 05 2005 - 05:45 PM

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#2 of 28 JeremyErwin

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Posted February 05 2005 - 06:54 PM

DVDs store their picture data in 480 interlaced rows. (Thus 480i). The number of columns varies, but it's more or less a 4:3 ratio, akin to that of a conventional TV set.
Most films of today are produced for the widesscreen. 1.85 is the most common standard, today, so in order to show the films on a 4:3 set, letterboxing must be used. If you just hard code in the matte, the end result will be that about 65 rows on the top and 65 rows on the bottom will be devoted to the "black bars" leaving 370 rows for the image.

Anamorphic DVDs store everything with a certain amount of horizontal compression, so that a widescreen monitor can "stretch" the image out to it's correct proportions. 480 rows can be devoted to the image, and the end result is somewhat more suited for large displays.

The letterboxed and anamorphic dvds store the same number of pixels for each frame, it's just that the anamorphic dvds don't devote nearly as many pixels to storing black mattes.


#3 of 28 ChrisWiggles

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Posted February 06 2005 - 06:15 AM

yes, just like anamorphic filming, the image is actually "distorted" to utilize as much space for the image as possible, and not waste data drawing in black bars.

I think this has been covered in depth in the primer, and if you google it, you'll get lots of informative explanations.

#4 of 28 Jack Briggs

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Posted February 07 2005 - 04:19 AM

Not really like anamorphic film at all. A so-called "anamorphic" widescreen disc simply encodes its 480 lines into a 16:9 window as opposed to a 4:3 window. And the best way to view such a disc is with a 16:9 display (or a 4:3 display with a 16:9 compression function). That's all.

#5 of 28 JeremyErwin

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Posted February 07 2005 - 08:58 AM

The original DVD frame is still 720x480 (in NTSC). It's stretched out to fill a 16:9 window (853x480) using bilinear or trilinear filtering.

HDTV frames, however, are not anamorphic.

#6 of 28 ChrisWiggles

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Posted February 07 2005 - 01:06 PM

Not really like anamorphic film at all.


???

It's exactly like anamorphic film, that's the whole point. You don't waste resolving space for black bars. If you view a frame of 16:9 video that's anamorphic, there aren't black bars in the frame, and it's squished. You can then view that directly on a 16:9 that gets stretched out sideways to compensate, or on a 4:3 with raster squeeze, for the best viewing. Same idea with not wasting film resolving power by using anamorphic lenses to utilize the entire 4:3 frame rather than using mattes and wasting resolution to black bars written onto the film.

#7 of 28 Allan Jayne

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Posted February 08 2005 - 01:31 AM

"Anamorphic" for film is a concept. Special lenses (anamorphic lenses) are used. Committing the material to video may or may not use such lenses, scanning the desired aspect ratio can be done electronically instead. One can get away scanning a 1.85:1 anamorphic film to produce an anamorphic DVD (16:9 equals 1.78:1), using a straight 4:3 scanner (telecine).

"Anamorphic" for DVD is a definition. It simply means that the subject matter for the same 720 x 480 pixel frame was captured from a 16:9 shaped subject view and the subject matter is intended to be displayed in a 16:9 shaped area on a screen.

"Anamorphic" for DVD is relative. For DVD the term was invented to distinguish from video material also on DVD and intended for display in a 4:3 shaped area. For U.S. HDTV 16:9 was defined as the standard so the word "anamorphic" is not used.

When the 720 x 480 pixel video frame is displayed as 16:9 it may or may not be upconverted to 853 pixels wide, depending on the TV. Particularly for analog and CRT based sets, more likely the individual pixels are just stretched a little.

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#8 of 28 Jonny_L

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Posted February 08 2005 - 02:07 AM

Quote:
Is there any difference between anamorphic and non-anamorphic DVDs? I am talking about the resolution/image quality, for 4:3 and 16:9 TVs.


On a regular 4:3 tv, anamorphic and non-anamorphic look approximately the same. Unless you have a 16:9 enhancement feature, then anamorphic looks significantly better. Like night and day actually.

On a 16:9 tv, a non-anamorphic DVD will appear letterboxed in a 4:3 frame in the middle of the tv. To see the image in the full tv screen zooming must be used, and significantly decreases the quality of the image. An anamorphic dvd will fill the entire screen naturally with a detailed image to usually spectacular results.

For more info see Jim Taylor's outstanding guide to DVD.

And

Bill Hunt's equally excellent guide to anamorphic widescreen over at thedigitalbits.com
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#9 of 28 Allan Jayne

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Posted February 08 2005 - 02:32 AM

Once you get everything set up right, an anamorphic DVD will give a much sharper picture compared with a non-anamorphic DVD of the same movie presented in the same aspect ratio but...

The exception is if the TV is 4:3 with no 16:9 enhancement, you need to use the player's 4:3 mode, in which case both will look about the same.
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#10 of 28 Jack Briggs

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Posted February 08 2005 - 03:33 AM

Chris, it is not "exactly like" anamorphic film -- at all. Please read the other posts here.

#11 of 28 ChrisWiggles

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Posted February 08 2005 - 05:35 AM

The concept is the same, the anamorphic "squeezing" of the picture to maximize the resolving capabilities of the medium on active picture rather than on black bars. In this sense the idea is very much similar.

Quote:
widescreen disc simply encodes its 480 lines into a 16:9 window as opposed to a 4:3 window.

The 480 lines are used for active picture material, instead of bars as well, the AR of the DVD in concept stays 4:3, but the *image* is a representation of 16:9 that if displayed on a widescreen TV or with a 4:3->16:9 raster squeeze, will then appear correct. If you're just feeding it to a 4:3 TV that can't do raster squeeze, you lose the benefit of an anamorphic DVD.

#12 of 28 Jack Briggs

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Posted February 08 2005 - 07:56 AM

Chris, no "squeezing" is going on. In a 16:9-encoded (i.e., "anamorphic") DVD, the 480 lines are presented in a 16:9 window. A 4:3-encoded DVD has the same goods in a 4:3 window.

However, if it's a 4:3 letterboxed DVD -- i.e., a widescreen film presented at the correct aspect ratio but in a 4:3 window -- then, yes, the letterbox bars are composed from the lines that would otherwise be available for the image itself in a 16:9-encoded DVD.

#13 of 28 ChrisWiggles

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Posted February 08 2005 - 08:40 AM

Not sure if this is just semantics, but if you have a 16:9 film encoded anamorphically, then there are no bars written on the DVD, the entire 4:3 DVD frame, conceptually, is used to write the 16:9 film. which means if you view the raw form, unaltered, from a DVD player set to 16:9 output mode, but on a 4:3 display, then things will be distorted(stretched). This is what's going on similar in concept to what is done with film.

By viewing on a 16:9 display, or a 4:3CRT with raster squeeze down to 16:9, you inverse the stretch that's on the DVD, essentially, so that the geometry is correct.

pretty straightforward.

http://www.thedigita....ic185demo.html

#14 of 28 ChrisWiggles

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Posted February 08 2005 - 08:43 AM

Quote:
the 480 lines are presented in a 16:9 window. A 4:3-encoded DVD has the same goods in a 4:3 window.

The "window" remains 4:3, the 16:9 portion is encoded using the full 4:3 frame with a vertical stretch. You wouldn't encode 4:3 material anamorphically, because that's silly. Then you'd be wasting space encoding pillarbox bars!

#15 of 28 Kramer Lowry

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Posted February 08 2005 - 08:48 AM

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#16 of 28 Michael Reuben

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Posted February 08 2005 - 08:53 AM

Quote:
Not sure if this is just semantics
It's not just semantics. It's a matter of understanding the two processes.

In anamorphic photography such as Cinemascope of Panavision, a lens actually squeezes a 2.35:1 image to fit on a 1:33:1 film frame (the dimensions are approximate but close enough for this purpose).

With a so-called "anamorphic" DVD, the picture is encoded for a 16:9 frame. Now, because this is still NTSC video, that frame uses the same number of pixels as a 4:3 standard TV frame, but the pixels are differently shaped (roughly speaking: they're rectangles instead of squares). Nothing is being squeezed, but if the resulting DVD is played back on a device with square pixels, the image will look as if it's been squeezed. That's how the term "anamorphic" came to be used in this context, even though it's really a misnomer.

Quote:
the 16:9 portion is encoded using the full 4:3 frame with a vertical stretch

Just as there's no "squeezing", there's no stretching either. That's what it may look like when there's a mismatch between the playback device and the monitor, but it's not the same process as projecting a Cinemascope film, where the projector lens literally "stretches" the image back to its original proportions.

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#17 of 28 JeremyErwin

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Posted February 08 2005 - 11:27 AM

bah. There's a little flag in the mpeg-2 stream that tells the decoder to present the image with squarish or wide pixels. It's up to the decoder and display to deal with this properly.

1. Send it to a display with wide (but fixed) pixels. This type of monitor doesn't seem like it would be very versatile with 4:3 material
2. Send it to a display with a built is scaler. Such displays might have a internal resolution of 480x853. The 480x720 MPEG frame is scaled to fill the wider resolution via trilinear scaling.
3. Scale the image in the dvd player before sending it on. Some DVD players can scale a 720x480 frame up to (say) 1920x1080. If it's a 4:3 image, a pillar box is added.
4. Send it to a CRT. A Cathode ray tube generally doesn't have a fixed resolution, and the timing of the electron guns can be adjusted to produce wider pixels.

I suppose that it might even be possible to use a special lens with an projection tv, but optical anamorphic technology is associated with its own set of problems.

Incidentally, Lars Von Trier and his cinematographers photographed "Dancer in the Dark" using anamorphic lenses coupled to standard 4:3 digital video cameras. It's all documented in the "100 cameras" segment.

#18 of 28 ChrisWiggles

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Posted February 08 2005 - 11:50 AM

Gosh, guys, you're chasing me in circles for no reason.

The concept is the same as with film. I'm not seeing why this is so contentious. You can put up an "anamorphic" image on a 4:3 projector, stick an anamorphic lense in front of it, and voila! There you go. It uses the same concept that is used in film, we're maximizing the usable picture area that can be encoded for the image.

Quote:
but it's not the same process as projecting a Cinemascope film, where the projector lens literally "stretches" the image back to its original proportions.

You can do *exactly* that!

We're all in agreement, so I'm not seeing the problem here, except that you seem to be objecting to the "squeezed" or "stretched" terminology. The concept is the same.

#19 of 28 Allan Jayne

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Posted February 08 2005 - 01:21 PM

Within the capabilities of the display device (TV, etc.) any video can be stretched or squeezed to any aspect ratio.

You can choose to (or be forced to) display the "anamorphic" DVD video as 4:3 from a projector and then may be able to put an anamorphic lens on the projector to get the video to be 16:9.

Someone else may be able to choose to display the same video as 16:9 on his projector or TV and not need an anamorphic lens.

Nowhere until it reaches a display device can video be seen to be distorted anamorphically or not. Whether the video is seen as distorted anamorphically is a function of the display device, not a characteristic of the video.

Anamorphically shot film always requires the matching anamorphic lens at projection time. The film can be inspected and seen to have the image distorted anamorphically.
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#20 of 28 adamKI

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Posted February 08 2005 - 03:16 PM

You guys are thrashing Chris unnecessarily. The two processes (anamorphic film vs. anamorphic video) are different but analogous, if you choose to make the correlation. Obviously, the people who invented widescreen enhanced DVD saw the similarities too ........... BECAUSE THEY CALLED IT ANAMORPHIC DVD!!!!! They didn't pull the term out of their collective asses.

All of your explanations fail to prove Chris' VISUALIZATION of the system wrong. Lets take a look at your rebuttals (well, just Allan's because I don't have all night) and form an analogy between film and DVD, shall we?

Quote:
You can choose to (or be forced to) display the "anamorphic" DVD video as 4:3 from a projector and then may be able to put an anamorphic lens on the projector to get the video to be 16:9.


You can also choose to show anamorphic film with a flat lens ... the reel won't burst into flames (although, I might!).

Quote:
Nowhere until it reaches a display device can video be seen to be distorted anamorphically or not. Whether the video is seen as distorted anamorphically is a function of the display device, not a characteristic of the video.

This is also true for film. If you hold a strip of film up to a light thereby "projecting" the film into your eye - that's a display device and you'd see a distorted picture in that case.

Quote:
Anamorphically shot film always requires the matching anamorphic lens at projection time. The film can be inspected and seen to have the image distorted anamorphically.


Anamorphically encoded DVDs always require a matching DVD player that can resolve the stream to the stream appropriately for your television.

And DVD streams can be inspected and seen to have the image "distored" because they are encoded anamorphically. Standerd NTSC pixels are essetnially square, film grain (film pixels, if you will) is essentially circular. Anamorphically displayed pixels are little 16x9 rectangles widened squares), anamorphically displayed film grains are little ovals (widened circles).

When anamorphic filming was invented they were taking an existing standard, academy ratio 35mm film, and adapting it for widescreen use. When anamorphic DVD was invented they were taking an existing standard, NTSC television (which was originally created for 4x3 televisions), and adapting it for widescreen use.

Enough of this ... either you will choose to see that these processes are DIFFERENT but ANALOGOUS or you won't. But it's pretty silly to pick on Chris because he chooses to visualize these concepts the same way the inventors of anamorphic DVD did.


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