Just what exactly is Anamorphic Widescreen? (1 Viewer)

[cafink]

A question for you, David¡¦
I understand exactly what you're saying. But a DVD, no matter the aspect ratio of the film contained on it, is going to be played in a DVD player. Isn't the output of that player going to be a "standard" 4:3 signal, no matter what? It's not outputting a "true" 16:9 signal, because even if you have your player set to 16:9, it's outputting a signal that is 100% compatible with every 4:3 television. Isn't that NOT the case with a 16:9 broadcast?
Similarly, if you have a 16:9 television, and you're recieving a 16:9 television broadcast, there's only one way to display it, right? It's going to fill up your television completely. But If you recieve a 4:3 broadcast, you have a few options: you can windowbox it, stretch it to fill the screen, or zoom in and crop off the top and bottom. Which of these two scenarios is more like having a DVD player hooked up to that same television? It's the 4:3 one.
I have only limited experience with 16:9 sets. If I'm mistaken about any of this, please point out my errors.

 

[Jonathan Burk]

DVD's intended for playback on NTSC equipment are encoded at 30fps, while DVD's intended for PAL playback are encoded at 25fps. But it's the player that actually outputs a 525 line, 60 field/sec NTSC signal, or a 625 line, 50 field/sec PAL signal.

 

[DaViD Boulet]

quote: Based on what I understood you to say, the data appears to be significantly the same on both regions...
Should I assume that the basic difference is an encoding so that the marketing people can keep folks in region X from seeing region Y discs? Is in fact that actual data carrying the film data the same?[/quote]
For the most part. Because our american NTSC TVs have @480 viewable (horizontal) lines, 480 was chosen as the resolution for SD-DTV and DVD. 720 is a good left-right matching resolution (not sure the significance of that exact number) so our R1 DVDs are a digital image with 480 x 720 pixels of resolution. DVDs that are oriented for countries with PAL TV systems actually have higher resoluton...576 x 720 (PAL TVs have @567 viewable scan-lines vs our 480).
There's no literal NTSC signal on the DVD. The analog NTSC (or PAL) signal is created by the player. In fact the Malta DVD player made in China can output a beautiful NTSC picture from "PAL" DVDs and v.v. It's all a matter of decoding.
Movies have 24 frames-per-second. NTSC TV has 60 (interlaced) fields per second (which would take up the same amount of space as 30 progressive frames per second). Because the less redundant video on the DVD the better as far as compression/playing time, most DVDs mastered from film actually store the 24 frames per second (which is less than 30 frames per sec)...and then instruct the DVD player to convert this to the 60 fields-per-second NTSC signal for the television.
PAL TV uses a slightly slower refresh rate...50 fields-per-second. You could also design a DVD player that could over-ride the instructions on the "NTSC" R1 disc and instead produce an analog PAL output (the Malta DVD player) as well as produce an analog NTSC output from a PAL disc. (since 24 fps movies works out pretty close to 24 frames/50 fields per second...PAL playback of movies doesn't do the 3-2 pulldown the same way we do for NTSC...instead, movies are sped-up slightly so you end up getting 25 frames per second on PAL TV of a movie that was filmed for only 24 in the theater).
Yep, you've got the basic idea. I've oversimplified, but that's the general deal...digital info that is then properly formatted for analog output for PAL or NTSC standards by the DVD player.
I guess it goes without saying you could also output the 480P signal for HDTVs and front-projectors...which is what progressive-scan DVD players do (that's definitely NOT an NTSC signal!).
quote: I understand exactly what you're saying. But a DVD, no matter the aspect ratio of the film contained on it, is going to be played in a DVD player. Isn't the output of that player going to be a "standard" 4:3 signal, no matter what? It's not outputting a "true" 16:9 signal, because even if you have your player set to 16:9, it's outputting a signal that is 100% compatible with every 4:3 television. Isn't that NOT the case with a 16:9 broadcast?[/quote]
The electronic signal doesn't have any real "shape" to it at all. The question is more "what's the aspect ratio that would create the proper gemoetry with this signal?"--in other words...make circles round and not oval.
Your DVD player just outputs an image. It's NTSC compatible because it's a 480I signal. If you output a native 16x9 image...it looks distorted on your 4x3 monitor. In that sense, you're seeing how the 16x9 image is "not compatible" with your television. If you had an adjustment to shrink the vertical raster to compress the scan-lines closer togther (like some TVs do)...you could watch that native 16x9 image without distortion.
Think about your computer screen. It's 4x3. Everything on it right now is probably the proper shape. Circles probably look round. Now take your horiztal or vertical sizing knob (or menu) and turn or click. You can easily change the horiztonal or vertical raster (scanning) of your monitor to change the shape...shrink the image...and distort the image.
Overscan is the name of this adjustment on your TV. Your TV comes properly calibrated to display the incoming images with an even spread of the scan-lines from top to bottom...left to right...so images appear 4x3 in shape...just like they should.
For those with 4x3 TVs with the special "16x9" mode...the TV does just what your computer does when you adjust the vertical raster...it compresses the scan-lines into a more narrow area so now the resulting image is 16x9 in shape.
Ok, so now you've got a 16x9 TV. It's calibrated so the scan-lines (raster) scan to properly display a 16x9 shape. (Actually, my 16x9 TV rendered circles with a slightly egg-shape when I got it so I went into the service menu and adjusted the overscan to create a true 16x9 image) Now you want to reveal a 4x3 image...your raster can simply shrink in from left to right to properly display a native 4x3 image (most RP 16x9 sets don't do this...they electronically add gray side-bars to the image and display the result using the full horizontal raster do avoid uneven CRT wear).
And think about a CRT front-projector. It's CRT tubes are round. I guess one could consider the ideal native-shaped image to be a square. Raster adjustment determines whether your CRT front-projector displays a 16x9 or a 4x3 ...or a 2.35:1 image using all available scan-lines.
Sound confusing. Just fiddle with the horizontal and vertical size adjustments on your computer monitor for a while unitil it makes sense that the incoming image isn't really a literal "shape" at all...it's all a matter of what shape it's supposed to look like to preserve geometry and how the display your using renders it.
-dave
[Edited last by DaViD Boulet on September 14, 2001 at 03:59 PM]
[Edited last by DaViD Boulet on September 14, 2001 at 04:03 PM]

 

[Graeme Clark]

Thanks, I think I got it now.
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[Jonathan Burk]

I think some confusion may come from the fact that there were anamporphic Laserdiscs, in which a 16x9 image was horizontally squeezed into into a standard NTSC image, and then a widesreen TV would un-squeeze the image to fill the screen. They were a promo tool used by Toshiba, and anyone who was familiar with these discs could assume that DVD is doing the same thing.

 

[cafink]

I think some confusion may come from the fact that there were anamporphic Laserdiscs, in which a 16x9 image was horizontally squeezed into into a standard NTSC image, and then a widesreen TV would un-squeeze the image to fill the screen. They were a promo tool used by Toshiba, and anyone who was familiar with these discs could assume that DVD is doing the same thing.

They ARE doing the same thing!