Talk:Anamorphic widescreen

Widescreen DVD

This sentence seems to have a problem:

Widescreen pictures on DVD are stored in a horizontally squeezed format, in order to maximize the available storage space, and not waste as much on storing the black letterboxing bars.

My understanding of the MPEG is that, being a compressed format, there would be no overhead for "storing the black letterboxing bars." Large black areas that never change wouldn't require much, if any, space to express. I can imagine that it might have an effect on processing time, depending on how the codec is implemented. Is there an MPEG subject-matter expert on hand to weigh in on this? Cleduc 3 July 2005 01:44 (UTC)

I don't remember whether I wrote the above sentence, but it's mainly pixels that would be wasted, rather than bytes of encoded video. If you letterbox a 16:9 video to 4:3, only about 75% of the vertical resolution actually contains picture. Encoding such a video to DVD, you'd be wasting 25% of your pixels on blackness, when they could be used for enhanced picture resolution. It's analogous to the first illustration, when 25% of the film surface is "wasted". I'll fix the sentence. -- Wapcaplet 3 July 2005 02:50 (UTC)

This discussion is probably beyond the scope of this article as we cannot influence the way commercial DVDs are being produced. To my understanding pixels would only be wasted if the target display has a higher resolution than PAL/NTSC and will upsample the picture. If the display is only capable of 720 px horizontal resolution then the picture simply has to be vertically downsampled again. And since the whole space of the data medium is being used anyways (as Cleduc noted) the 25% of "extra pixels" will take away bits from the rest of the stream decreasing its quality.
I see anamorphic MPEG-2 DVDs heavily influenced by the technology of analogue storage and transmission of the past, similar to the still used interlaced frame format. I mean why would there be any need to decode and resample the picture afterwards if a stream of the right resolution can be created in the first place without any need to do resizing? The specification of DVD might have been kept simple by allowing only a fixed number of resolutions (PAL/NTSC and fractions of them) but this is not a physical limitation of video adapters or the data medium. But where's simplicity there if a post-decoding process is required?

Anamorphic widescreen DVDs store a stretched picture

It's worth to note that no quality will be gained if this stretching is digital from a 720*405 source. The footage must originally have 576 or more pixels of vertical resolution. (for PAL)

 -- J7n 04:57, 5 July 2006 (UTC)

aggreed, let's change it! Clemonsjw 21:46, 6 September 2007 (UTC)

Pixels and lines

"Anamorphic widescreen DVDs store a stretched picture, to make optimal use of vertical resolution, and to avoid wasting pixels on the black letterboxing bars."

This is incorrect as pixels are not used on NTSC signal, but lines of resolution. I have changed the sentence to reflect this:

Anamorphic widescreen DVDs store a stretched picture, to make optimal use of vertical resolution, and to avoid wasting lines of resolution on the black letterboxing bars.

Kether83 20:22, 28 December 2005 (UTC)

The section is about the DVD, not the NTSC standard. DVD is digital and its 720x480/576 resolution consists of pixels, so the statement was not incorrect. Shawnc 07:42, 30 December 2005 (UTC)

The use of "horizontal" and "vertical" causes confusion.

In the second paragraph of the article appears:

"To make full use of the available film, an anamorphic lens is used during recording; this lens effectively squeezes the picture horizontally so that (in the case of the common 2x anamorphosis lens) a frame twice as wide fills the available film area (Figure 2)."

I am confused by the use of the words "horizontally" and the linked use of "wide". Take the first. To all English speakers everywhere the word "horizontal" means "in a left/right, or East/West" direction. As in "the surface of a liquid is always horizontal", or "lie down on the bed in a horizontal position". Yet, in Figures 1 and 2, the image is manifestly being squeezed in a vertical direction. That is, the "force" doing the squeezing acts in a vertical (up/down, North/South") direction, from the sky to the ground, as when you put a "Jack-in-the-box" toy back in his box by squeezing him vertically. The only explanation for this bizarre way of description is to consider the strip of film in the figures as having been turned round 90 degrees and thus shown vertically in the Figures (from your head and dangling on the floor), it being perhaps the normal practice in the film industry to view film laid out left to right, in which case a film-maker would consider Figure 1 as being squeezed horizontally. But that way of looking at it follows merely because of the way in which he was holding the film and totally without regard to the fact that the image (the landscape) as presented in Figures 1 & 2 has undoubtedly been squeezed vertically (sky to ground). There can be no doubt about that. To state that such squeezing of the image, as you present it in the article to viewers of Wiki, is horizontal is incredibly confusing for non-experts trying to grasp the way in which the word "anamorphic" is used. People like me shooting widescreen video for DVD and TV display have no need of historical terms protruding from the age of film. I urge you to revise the use of these words in this article to make it more intelligible.

The beginning of the later section DVD Video may need amendment in the same way. The present wording "the player will send an anamorphic (horizontally squeezed) signal to the TV, which will compress the scanlines of the displayed image vertically !!! As it stands, this sentence is internally inconsistent and very confusing.

Steve Kirkby, 03/12/2006

This is somewhat confusing, especially since a vertically stretched image and a horizontally squeezed image may appear to be the same thing without appropriate reference.

In filmmaking, an anamorphic lens horizontally squeezes the image. There is no doubt about that - the vertical dimension remains unaffected while the horizontal field of view is expanded by the power of 2. This will, however, cause images which are not de-anamorphozed to look very thin, which the eye can mis-perceive as vertical stretching. However, the vertical dimension maintains itself while the horizontal is squeezed and unsqueezed. In other words, a 40 mm 2x anamorphic lens will have the same vertical field of view as a 40 mm spherical lens, but the horizontal field of view will be equivalent to a 20 mm spherical lens.

In the case of DVD anamorphic compression - which is an entirely digital process involving pixels, not optics - the image is vertically stretched in order to maximize the frame resolution by not wasting vertical resolution on black bars. The picture is then digitally scaled back to its correct aspect ratio when it goes out to the TV. There is no change in the actual horizontal resolution - only the vertical has been recompressed. This should result in higher picture quality, because more vertical resolution is given to the frame image instead of the black bars.

The truth is that these are two totally different concepts which only share the property of anamorphism (image stretching), and it might be a good suggestion to split these into separate articles, as they do not really have anything to do with one another directly. Girolamo Savonarola 01:09, 3 December 2006 (UTC)

Thank you. It seems clear now. Splitting the article in two is an excellent idea. The confusion seems to flow from what the eye perceives, as you mention. Squeezing or stretching an image horizontally has the same perceived effect respectively as stretching or squeezing it vertically. The confusion seems to lie in the actual, practical, historical (I am thinking of celluloid film here) way in which these alterations are made. In the video world the terms often used include (my definitions) "anamorphic image or clip: an image or video clip that is designed to be displayed in widescreen format but which is by default displayed in the 4:3 format unless the displaying device is instructed otherwise." "anamorphic flag: an item of data attached to or embedded in a video file used to instruct a displaying device to stretch the file's images from its 4:3 format to widescreen format". I often think that formal definitions of terms are not helpful in promoting understanding, being of more use to those who already understand the subject and are looking for guidance on the exact, expert, use of the term or to settle disputes. To promote understanding (that is, for newcomers) additional descriptions are better, especially those which use more words* and give examples, and also those which look at the matter from more than one angle as in the "definition" of software: "anything that you can drop on your foot"! an enlightening, additional, way of describing it which instantly lights the recipient's lamp of understanding. *May the patron saint of students protect them from the elegant brevity of an expert's description. Wiki does not fall into that trap.

Steve Kirkby 03/12/2006

Well, for simplicity's sake, you can think of it from the perspective of which dimension is considered more flexible: in film projection, all films tend to be projected at a constant height - the variation in aspect ratio is created purely by the width of the image displayed. So you'd compress the image along the horizontal axis. In video, however, the immobility of the screen edges means that the image width is kept constant and the aspect ratio is created by the height of the image (hence letterboxing). Therefore you'd compress along the vertical axis. This is all assuming that you're trying to keep the original aspect ratio and resolution, so things like pan and scan or zooming the image on a widescreen TV don't count, since they lose information - which is what anamorphic DVDs try to avoid. Girolamo Savonarola 16:36, 3 December 2006 (UTC)

Thank you. Steve Kirkby 03/12/2006

home theatre lens manufacturers?

Is it really useful to be listing these at all? jhawkinson 18:17, 13 March 2007 (UTC)

Don't know if I'm writing this in the correct place, but I figured a paragraph or two about additional anamorphic lenses used in home theatres for constant image height systems would fit in this article. —Preceding unsigned comment added by 195.27.17.6 (talk) 09:49, 14 April 2010 (UTC)

changes in brightness

All paragraphs within the Anamorphic lens enhancement heading are ambiguous and use language that is far too technical(which is fine, but the problem is that it fails to clarify and explain what they mean), especially when discussing changes in brightness. I suggest someone improve it.

Dr. Lucifer 23 June 2007 (UTC)

SCART

In the television section of the article it is stated that Sky digiboxes and other digital STBs use SCART to indicate whether the image is in 16:9 format. This is in fact incorrect. The widescreen marker is sent encoded as a digital signal in the analogue video feed. As susch the type of connection to the TV (SCART, composite, component or even RF) is not relevant. Wikipedia has an article on this: Widescreen signaling. Simon. —Preceding unsigned comment added by 80.177.14.78 (talk) 15:37, 9 February 2008 (UTC)

Not correct. The signal that flags the video as 16:9 format is carried on a specific pin of the SCART connector - specifically pin 8 where a voltage of 9-12 volts indicates 4:3 and a voltage of 5-8 volts indicates 16:9. It so happens that the 16:9 format is also flagged by a series of pulses on the last blank line before the first active video line of the analogue video signal. However, this latter arrangement only seems to be present on 625 line video (equivalent to 576i in the digital domain). NTSC video (480i) is allegedly designed to carry the same information, but the NTSC video standard fails to mention it and no DVD player that I am aware of includes it when outputting NTSC (even though it does so with PAL). This probably explains why 'PAL' DVDs correctly switch a TV to 16:9 mode and NTSC DVDs do not (when used with a connection other than SCART or HDMI). 109.153.242.10 (talk) 16:30, 13 January 2012 (UTC)

Graphics needed

The introduction needs a picture showing the difference between "normal" square pixels and rectangular pixels. Ben (talk) 01:07, 27 February 2009 (UTC)

Languages

I'm afraid, this article doesn't corresponds to articles in German, France, Japanese and Norway languages, which have hyperlinks from here. That articles corresponds to 'Anamorphic format' article. Runner1616 (talk) 05:29, 31 January 2012 (UTC)

Concave or convex?

As clarified in the above section about horizontal and vertical, "the vertical dimension maintains itself while the horizontal is squeezed and unsqueezed."

In the camera, light travels from subject to film and the image gets squeezed.

In the projector, light travels in the opposite direction, i.e. from film to screen, thus reversing the process and unsqueezing the image.

It follows that the camera and the projector could use identical lenses. Such a lens would be described as spherically convex and cylindrically concave.

The second paragraph of the article implies that the squeezing and unsqueezing is achieved by using a concave lens on the camera and a CONVEX lens on the projector. This is misleading. — Preceding unsigned comment added by Mark Eliassen (talk • contribs) 02:52, 5 August 2014 (UTC)

vertically expanded or horizontally compressed

The first sentence of the lede says 'Anamorphic widescreen is a process by which a comparatively wide widescreen image is vertically expanded to fit into a storage medium' An IP editor asserts that it should say 'horizontally compressed', while I assert that the current definition, as also previously discussed on the talk page, is correct. Also, while this is about the process of electronically storing information on differently aspected pixels, and not on a direct medium like film, I think that while we are at it, where the lede sentence says '(photographic film, for example)' it should be changed to '(DVD, for example)', to further differentiate from the article Anamorphic format. I would appreciate any suggestions, comments, improvements. Thank-you David.moreno72 03:23, 22 August 2016 (UTC)

Hello, I'm the IP editor.
I think it should say 'horizontally compressed' instead of 'vertically stretched/expanded' because, at least for digital videos, stretching a lower resolution material into an higher resolution requires "generating" the missing pixels via interpolation of (or better, extrapolation from) the existing ones, so the result will be quite blurry and of relatively low quality, even if the best algorithms are being used. Instead, compressing as in reducing the horizontal resolution from 1024 to 720 (in case of PAL 576i material, or 854 to 720 for NTSC 480i material) won't make the resulting video too blurry. A fun fact is that PAL video is always horizontally compressed: a full 4:3 frame would be 768x576 pixels, instead of 720x576 which is 5:4. 4:3 NTSC video instead would be 640x480, so it gets inevitably horizontally stretched to 720x480.
Digital horizontal compression is in fact used by today's SD digital television: the master feed is usually 1080i, and it is fed to the HD channel distribution more or less directly. Then the HD feed gets downscaled to 576i, but a 16:9 digital frame at 576i is 1024x576 pixels, so it also gets horizontally compressed into a 720x576 SD standards-compliant frame; and the relevant "widescreen" bits in the MPEG transport stream and/or codec extradata are set so that the set-top box will know how to render the image based on its settings. Then suppose that we have a set-top box connected to the TV via a classic PAL 576i analog video composite connection. For a 4:3 classic TV the STB will either further compress the image vertically (since the analog TV signal is also 720x576) so the image will be 720x404, and pad it with black bars (letterbox); or it will horizontally expand it to 1024x576 and then crop it to 720x576 (pan and scan). For a 16:9 TV the STB will just send the 16:9 picture as-is as 720x576 on the analog video link, and then the TV will expand the picture horizontally and then scale it to the native size of the LCD panel. (Actually analog video signals don't have an exact horizontal resolution expressed in pixels, but since the STB is digital then its video output will have a defined number of horizontal pixels before it gets converted to analog.)
For film instead, if I recall correctly 'horizontally compress' and 'vertically stretch' can be considered equivalent, as it is done using optical lens, which do not obviously have a defined number of sampled image pixels.
So, I think that always specifying 'horizontally compressed' is the best way. Or maybe what I said here could be somehow integrated in the article...
I hope this helps. --2001:470:7C50:48FF:0:0:DEAD:BEEF (talk) 05:53, 22 August 2016 (UTC)

That's entirely correct, anamorphic widescreen is horizontally compressed and not vertically expanded in order not to lose resolucion. By the way this technical explanation for digital anamorphic video is quite perfect I'd say! --2A00:1508:1:F010:3F9B:C251:D8AB:8C0D (talk) 20:59, 22 April 2018 (UTC)

Paragraph deleted from Blu-ray video section

This was in the middle of the section, and appears to have nothing to do with the BD format. It's hard to tell if it should go somewhere else, or if somebody was just "trying to help".

" An electrically coded video line (referred to as a field) is used in analog video transmission, recording and CRT displays, this can be sampled by a process called digitization which in professional SD video tape recorders is done at a rate of 720 pixels per field. This relates to the bandwidth used in digital serial connections and have come to be inaccurately called "rectangular" pixels. So called "square" pixels used to display 4:3 graphics and text on VGA CRTs are at 640×480 which excludes the sync pulses and blanking used in the field output. Therefore, to display a NTSC SD 4:3 capture of 720×480 you would have to crop the 8 pixels that are used for blanking off of each side and then "anamorphic-ally" scale the result to 640×480. Squeezing to create a 16:9 frame only does a good job of delivering widescreen with reasonable quality using standard 4:3 equipment when the compressed bit rate is high enough to avoid compression artifacts being noticed, as they are in a low rate MPEG-2 broadcast. "

Huw Powell (talk) 06:10, 14 January 2017 (UTC)