Aspect Ratios - Put Simply

Aspect Ratios - Put Simply

Aspect Ratios - Put Simply

IVC DIGITAL FILM CENTER

Aspect Ratios

By Jim James

Chief Engineer IVC

The aspect ratio of an image is the relationship of its width to its height. Put simply, it describes the wideness of a film or TV image. (An aspect ratio of 2:1 means the image is twice as wide as it is high). In video there are only two common aspect ratios, 1.33:1 for conventional TV (4x3), and 1.78:1 for widescreen video (16x9). In film there are many different formats, but the four most common are 1.33:1, 1.66:1, 1.85:1, and 2.39:1. (The larger the number the wider the image.) The challenge is how to fit all those film ratios into the two formats of video.

For an old 1.33 movie to be shown on a 4x3 TV is simple. It just fits. For everything else life is more complicated. The producer is left with only two choices, crop the picture to fit the screen, loosing some of the image (Full Screen), or fit the entire picture into the screen and fill the leftover areas with black (Letterbox or Pillarbox). If the source aspect ratio is larger than the video aspect ratio the black bars are on the top and bottom and called "Letterbox". If it is smaller the bars are on the side and called "Pillarbox". How large the mask is depends on how big the difference is between the source, or inner aspect ratio, and the container, or outer aspect ratio.

How to Remove the Confusion

When defining a mixed aspect ratio project it is important to clearly specify what you mean. It is unclear whether "1.33 1.78" means letterbox in a 4x3 screen, or pillarbox in a 16x9 screen. Because there are only two video aspect ratios and they are more commonly defined as 4x3 or 16x9, it is a good idea to use that format to define the video, or outer, ratio, and the other format for the source or inner ratio. If you say "1.33 in 16x9" it is very clear that you mean pillarbox, or if you say "4x3 1.85" you mean letterbox.

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