A Guide to Understanding Aspect Ratio: Pan and Scan Vs. Letterbox

Understanding Aspect Ratio: Pan and Scan Vs. Letterbox
Aspect ratio is the ratio of the width of the image to its height. While viewing an image on the television screen, this ratio decides whether part of the image will be displayed, or the whole image will be modified to fit the screen. Let us take a look at the two most common ratios used to display CinemaScope pictures on a normal TV screen.
Academy Ratio
In 1931, the aspect ratio of 1.33:1 (4:3) was standardized by the Academy of Motion Picture Arts and Sciences as a standard film aspect ratio, and came to be known as the Academy ratio.
Standard NTSC and PAL film formats have an aspect ratio of 1.33:1, while CinemaScope formats have an aspect ratio of 2.35:1. Standard television sets can easily accommodate NTSC formats, but for CinemaScope formats, a few modifications need to be done. Pan and Scan and Letterbox are the two most common methods used to adjust widescreen images. Let us take at a look at how widescreen images are displayed using both these ratios.
Pan and Scan Vs. Letterbox
The original image is horizontal.
Pan and Scan Method
The Pan and Scan Method crops the image.
letterbox method
The Letterbox Method adds black bars to the image.
Pan and Scan
Widescreen images, as mentioned above, are difficult to display on a standard television set, which has an aspect ratio of 4:3. Thus, there is a need to play around with the image in order to make it fit. The Pan and Scan method does exactly the same by cropping the image. Generally, the sides of the image are cut off, so as to maintain the focus on the middle portion of the image. This cropping is done to highlight the central (most important) portion of the image.

The technician working on the Pan and Scan technique needs to decide which part of the image is important, and display the same so as to fill the TV screen completely. The problem with this technique is that the image loses its minute details. Almost 30% of the image is lost due to cropping. The image is further lost at its edges (all four of them) due to overscanning at the home television end. Overscanning is a method of adding additional area on all the four edges of the image, to make it fit the screen.

One notable example of the image being lost is the chariot race sequence in the movie Ben-Hur. The actual widescreen image has Beh-Hur driving four horses, but in the Pan and Scan version, only two horses were seen. In many movies, you will see one character talking with the others that aren't seen on the screen. You need to assume whom they are talking to! The worst-affected scenes are those which have panoramic shots. The entire shot is never visible.

Movies which were shot before 1951 were shot in the 4:3 or 1.33:1 aspect ratio, and thus, these images are never cropped. The actual image that was shot during filming is the one that is visible on TV screens.

Thus, the Pan and Scan version only gives a gist of the original image. The actual widescreen image which the director shot is never seen in this version.
The Letterbox technique reduces the image distortion that is introduced in the Pan and Scan method. In this method, black bars are added to the top and bottom of the image, but the image is not cropped. These bars are added to the image to maintain the 16:9 aspect ratio.

Most people have the notion that a Letterbox image is actually a distorted version of the original, but this is not true. The black bars make it possible to view the entire horizontal image. In this method, the original image is reduced in size so that its left and right edges fit the screen. The reduction in the size leaves unused space to the top and bottom of the screen. This space is filled by black bands.

Thus, the black bars on your television screens aren't an indication of image being lost, but an indication of displaying the entire image. DVDs are Letterboxed, while even a few cable channels are aired in this format. Almost all movies that are made today also release their Letterboxed versions in form of DVDs.
Movies that were made before 1951 will appear without any cropping or cutting of the image. However, movies after 1951 have distortions due to Pan and Scan versions (VHS). So, the next time you watch a movie with black bars, remember you are actually viewing the entire image.
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