Suppose you are displaying a widescreen movie on a standard 4:3 TV. Since the TV isn't widescreen, the only option that doesn't chop off any of the movie is to display it centered in the screen, with large black bars above and below it. "Letterboxed" movies on videotape are stored exactly like that -- black bars above and below the picture, with the image in the center, designed for display on standard non-widescreen TVs. The important point to note is that the black bars are actually part of the image data on the tape.
Non-anamorphic widescreen DVDs are written the same way. They are intended for 4:3 TVs, so to create a widescreen image, they encode large black bars on the top and bottom. Viewers with widescreen TVs can use the "zoom" feature to take this center region and blow it up to fill the entire screen, cutting off the top and bottom (which are just solid black).
The problem with this, though, is that by encoding the image with large black bars on the top and bottom, you are wasting much of the video stream's vertical resolution and producing a much lower-resolution image than you could. You are also forcing viewers to switch in and out of "Zoom" mode depending on what the user is watching.
An anamorphic DVD solves these problems. Rather than having the black bars encoded in the video stream, the DVD uses the full vertical resolution of the disc, and the DVD player takes care of adding the black bars for 4:3 TVs (you have to tell your DVD player whether you have a widescreen TV or not). 4:3 TVs see the same image for both anamorphic and non-anamorphic images, but widescreen TVs see significantly higher resolution for anamorphic and additionally do not have to switch in and out of "Zoom" mode (as long as you only play anamorphic discs).
As the only DVD aspect ratios are 4:3 and 16:9, movies which are wider aspect ratio (say 2.35:1) will still need to have black bars encoded in the video stream. They just won't be anywhere near as large as they would be on a non-anamorphic disc.
Non-anamorphic widescreen DVDs are written the same way. They are intended for 4:3 TVs, so to create a widescreen image, they encode large black bars on the top and bottom. Viewers with widescreen TVs can use the "zoom" feature to take this center region and blow it up to fill the entire screen, cutting off the top and bottom (which are just solid black).
The problem with this, though, is that by encoding the image with large black bars on the top and bottom, you are wasting much of the video stream's vertical resolution and producing a much lower-resolution image than you could. You are also forcing viewers to switch in and out of "Zoom" mode depending on what the user is watching.
An anamorphic DVD solves these problems. Rather than having the black bars encoded in the video stream, the DVD uses the full vertical resolution of the disc, and the DVD player takes care of adding the black bars for 4:3 TVs (you have to tell your DVD player whether you have a widescreen TV or not). 4:3 TVs see the same image for both anamorphic and non-anamorphic images, but widescreen TVs see significantly higher resolution for anamorphic and additionally do not have to switch in and out of "Zoom" mode (as long as you only play anamorphic discs).
As the only DVD aspect ratios are 4:3 and 16:9, movies which are wider aspect ratio (say 2.35:1) will still need to have black bars encoded in the video stream. They just won't be anywhere near as large as they would be on a non-anamorphic disc.
