Anamorphic DVD's Explained
In order to really understand this section, it is necessary to travel back in time.
Before the VCR emerged in the early 1980's, movies were broadcast to your television in a format know as "pan and scan."
Pan and scan is a technique where the wider film image is cropped off at the ends. Not surprisingly, cropping isn't the same for each frame of film. Instead, editors viewed each film frame and decided what to cut out to convert each frame to a 4:3 image. This technique was notorious for leaving out significant amounts information, and film buffs absolutely hated it.
When VCR movies emerged, film companies initially adopted this same cropping technique, but there was an incredible backlash from people who wanted to see movie images as they were originally filmed. So as an answer, film companies invented something called "letterbox" movies.
Letterboxed movies were VCR movies that kept the original aspect ratio of the movie by shrinking the entire image to fit into a 4:3 area. The result was a full widescreen movie, but at a much lower vertical resolution. Some people hated letterboxed movies because image details were difficult to see on smaller televisions.
(A 16:9 image as shown on a 4:3 standard definition television)
Things finally began to change with the advent of DVDs. Because DVDs offered an improved horizontal resolution, television companies started offering widescreen televisions for DVDs.
These first widescreen televisions were not high definition, but were 480i and 480p televisions with additional horizontal resolution. These televisions would take the letterboxed image and blow the whole image up to fit the screen. While this did work, it didn't solve the problem of lost resolution. At most, the original signal would still only contain 270 lines of vertical resolution. Blowing up the signal would create a larger image, but the results were fuzzy at best.
The solution came shortly after DVDs were introduced. New "anamorphic" DVDs were created to solve the loss of resolution.
An anamorphic DVD is recorded differently than older letterbox DVDs. Instead of recording the DVD with black bars at the top and bottom of the image, they use the entire 480 lines of vertical resolution - if showing a 16:9 image - and use up to 364 lines when showing 2.35:1 movies, which is a staggering 25% improvement over the older letterbox vertical resolution for a 2.35:1 movie.
How is this done? Anamorphic DVDs electronically, horizontally squeeze the 16:9 image to fit into a 4:3 area, instead of shrinking the overall image as done in letterboxing. This squeeze it a digital approximation of what would happen it you used a special lens to squeeze the image horizontally. Think of a carnival fun house mirror that squeezes your reflection to make you look thinner than you actually are. Below is an actual illustration of what an image actually looks like on the DVD, before and after your display device stretches the image back to its intended 16:9 shape.
It is important to understand is that the image recorded on to a DVD is actually distorted. You have to "tell" your DVD player what aspect ratio display device you're using to watch the movie correctly. If you tell your DVD player that you're using a widescreen television, when in fact you're using a 4:3 television, you will get an image that looks like the top image of the example shown above.
If you're using a 4:3 television, and you "tell" the DVD player to output to a 4:3 television, the DVD player then converts the recorded image into a letterboxed image. Because it must shrink the overall image to fit onto your television, you get the same loss of resolution that you would if watching a non-anamorphic letterboxed DVD. The lesson here is that anamorphic DVDs provide no additional benefits unless you have a widescreen television to take advantage of the higher vertical resolution.
If you do have a widescreen television, then the DVD player will output the distorted image to your television/monitor. It is then that the monitor/television electronically stretches the image horizontally into its intended correct aspect ratio of 16:9. If your television has settings for different aspect ratios, the television will have to be set to 16:9 to watch the DVD properly.
Remember that the television or monitor will stretch the image to a 16:9 aspect ratio regardless of what aspect ratio the movie is in. This means that if the movie is in a 1.85:1 or 2.35:1 aspect ratio, you will still have black bars displayed at the top and bottom of the image.
Most, if not all, newer DVDs that state "widescreen" are anamorphic DVDs. The back of the DVD usually will state what specific aspect ratio the movie is in, although some companies still refuse to put that valuable information on their DVDs.
Labels identifying anamorphic DVDs often appear as shown in the example below, however anamorphic DVDs are not always clearly marked as "anamorphic." You can assume a DVD is anamorphic if the DVD packaging reads "widescreen version" anywhere on the front or back covers.
Progressive scan DVD players
Newer DVD players have the ability to output signals as either interlaced or progressive scan images.
Generally, when film is converted to DVD, 3:2 pulldown is applied so that the DVD player can output an interlaced 480i signal. During the encoding of the DVD, the original two fields that make up a specific original film frame are flagged so that, if played on a progressive scan DVD player, the DVD player can easily convert the film into a progressive scan image. (See 3:2 Pulldown and Deinterlacing)
There are a few things to note about progressive scan DVD players:
- Once you output a progressive scan image, the signal is no longer an NTSC, or 480i signal. It becomes a 480p signal - p for progressive scan. If you don't have a television that can input a progressive scan image, you will not receive an image. (Note: Turning an interlaced image into a progressive scan changes the refresh rate from 60 fields per second to 60 frames per second, which is double the information per second. A television must be designed to handle that extra information.)
- A progressive scan DVD player will only output a progressive scan image via its component video, or digital video outputs. If you use the S-video or yellow composite type output, your television/monitor will only receive a 480i image. S-video and composite cables will not accommodate a high enough resolution to carry a progressive scan image.
- If you are watching a non-film based movie, the image may worsen if you output it as a progressive scan image.
- The built in deinterlacer of a progressive scan DVD player is very important to video quality. And, you get what you pay for. More expensive progressive scan DVD players will have higher-quality deinterlacers built in that can distinguish between film based-material and video. They adjust automatically for the best image quality possible. Also these higher quality deinterlacers will better handle video-based material without video artifacts common to low-cost deinterlacers.
- All HDTV monitors/televisions will be able to handle a 480p signal.