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Discussion in 'Beginners, General Questions' started by jasm, Oct 16, 2004.
what is the difference?
oops! I meant non-anamorphic and anamorphic
From the Home Theater Glossary:
Anamorphic - Refers to the stretching or squeezing of an image so that it utilizes the entire area of a film frame with a different aspect ratio. The most common usage has a 1.85 to 1 or greater wide screen movie "squished" on film with 4:3 aspect ratio frames. A special lens is used on the projector to exactly reverse this distortion and produce the correctly proportioned picture on the screen. The same technique is used in video from time to time. On DVD's, the same 720 by 480 pixel frame may be used to represent either a 4:3 or 16:9 aspect ratio picture. The player has selectable means of proportioning the picture so it appears correct, although on a standard (4:3) TV, the 16:9 image will appear letterboxed. Better results are had for a 16:9 enhanced version of the movie if the full screen mode is selected on the player and the height control on the monitor manually adjusted downwards. "Anamorphic" in video is a misnomer. Video has no aspect ratio until it is displayed on the screen. The TV set or monitor determines the aspect ratio using settings specified by the viewer or sometimes automatically by taking some format data (not the picture data) from the video signal. So far the label "anamorphic" is used only for the DVD 16:9 enhanced wide screen programs or 16:9 high resolution programs.
this is also covered in the faq and primer as well as on the excellent digital bits guide (there is a link in the primer).
Where did you get that nifty definition SimiA?
Glossary of Home Theater Terms
(See first thread on this page.)
Chris, I found it here:
?? Can you point me to exactly where you got it? I don't see any glossary there?
The site has gone thru many changes lately b/c of problems they're having. I don't see it anymore either.
Here's another glossary I use:
There's no "squeezing" involved. So-called "anamorphic" widescreen DVDs simply are encoded to output at 16:9. They have the same native resolution as 4:3-encoded DVDs (though letterboxed-only widescreen DVDs have less active picture resolution than the same aspect-ratio film presented on a 16:9-encoded DVD).
Once again, there's no squeezing involved -- just a different aspect ratio that's better suited for the presentation of widescreen films on a widescreen display.
This is also not true. DVD video is 1.33:1 period. In order to use the entire vertical resolution of the format for aspect ratios larger than 1.33:1, the image is squeezed horizontally into the 4x3 frame. DVD players always output a 4x3 frame, it is the job of the display device to properly unsqueeze the image and display it properly.
This is very easy to prove. Simply place a widescreen set in "Normal" or "forced 4x3" mode and make sure the DVD player is still set to "16x9". Then play an anamorphic DVD. The image will look horizontally compressed within the 1.33:1 frame.
DVD players cannot output a 16x9 signal, only 4x3. Anamorphic enhancement means that the video is horizontally squeezed in order to utilize the entire vertical resolution of the format.
No video device can ascertain the aspect ratio that the video is supposed to be displayed at except by finding information such as flags encoded in the video or by examining the content in terms of pixels, and applying artificial intelligence.
It is just by convention that the terms "enhanced for 16:9" and "anamorphic" as it applies to DVD mean that the same 720 (approx) x 480 pixel video frame was captured or televised from a 16:9 shaped field of view (which may include some black area on top and bottom) and is meant to be stretched to a 16:9 shape on a screen.
The 16:9 mode on a DVD player has the (720 x 480) video being output as-is at all times and the viewer should adjust the TV to make it look correct. The 4:3 mode on the player has DVD's not encoded as "anamorphic" played as-is, and "anamorphic" DVD video digested (subject matter letterboxed or sides cropped*) so the video frames as output will look correctly proportioned when stretched to 4:3.
* Use of the "pan and scan" setting on the player gives unpredictable results unless the DVD is also encoded for pan and scan which encoding to date is rare.
Sorry, Rich, but you're wrong. The word "anamorphic" is misleading (even inaccurate) when it comes to DVD; the anamorphic process as it is employed in cinema is not at all the same. A 16:9-encoded DVD simply outputs its 480 lines of resolution in a 16:9 frame, whereas a 4:3-encoded DVD outputs the same 480 lines in a 4:3 frame.
Do not confuse in-player "downconversion" of 16:9-encoded DVDs for screening on a 4:3 display that does not have a 16:9 mode.
is incorrect. As I stated, a DVD player that outputs NTSC video is incapable of outputting a 16x9 signal. Only ATSC supports such an aspect ration natively. However, in order to support the entire vertical resolution of DVD, the video image is squeezed to fit within the 4x3 frame that is delivered from the DVD player to the display device.
Again, an NTSC DVD Player cannot output a "16:9 frame." What it can do however, is squeeze a 16:9 frame into a 1.33:1 frame and flag the video stream. The display device is then responsible for reading the flag and unsqueezing the 1.33:1 frame to the full width of 16:9
This is explained in great detail in Jim Taylor's book DVD Demystified.
On film you can see, and compare against the original scene, the squished image now at a different aspect ratio and is referred to as anamorphically shot.
For video, a "frame" is "4:3" or "16:9" only because somebody said so. The picture is never seen squished until it is displayed on a screen, and as soon as it is so displayed it can (within the limitations of the TV) be stretched to any shape desired.
No one's disputing that it appears this way. The mistake is to conclude that, just because the image appears squeezed in your example, it has been squeezed in the same way that an anamorphic lens optically squeezes an image.
To quote Jim Taylor (emphasis added): "For anamorphic video, the pixels are fatter. Different pixel aspect ratios (none of them square) are used for each aspect ratio and resolution." The image on a 16:9-enhanced disc has been encoded for those "fatter" pixels, and if you display it using the "thinner" pixels of a 4:3 display, it's going to appear squeezed. But the "squeeze" is as much a function of the display format as it is of the disc encoding.
Which I don't think anyone will dispute are incorrect statements.
To quote Jim Taylor from the same FAQ (emphasis added):
"DVD has a frame size designed for 1.33 display, so the video still has to be made to fit, but because it's only squeezed horizontally, 33% more pixels (25% of the total pixels in a video frame) are used to store active picture instead of black."
That's all I was trying to point out.
I don't have a problem with them. Most of this is semantics.
Yes, semantics. If the word "anamorphic" had never been used to describe the encoding of DVDs in 16:9 talk of "squeezing" never would have arisen.
OKey Doke. I'm willing to let it lie.