Do you know what the aspect ratio of your TV or Projector Screen is? If you do, then chances are you are pretty up to date with the variety of options available. If you don’t, then we’d like to bring you up to speed on what aspect ratio is as well as the history behind it. Aspect Ratio is simply a numerical way to describe the width to height ratio of a rectangular image.

The Aspect Ratio is generally represented by 2 numbers separated by a colon, with the first number depicting the width of the image and the second representing the height, in any given measurement (eg: cm, inches, feet).

Take the aspect ratio of 4:3. The 4 represents the width of the image while the 3 signifies the height of the image in any given unit of measurement. So, for every four inches the image is wide, it is 3 inches high. The unit is irrelevant; it is just the ratio that matters.

Until the introduction of HDTV, 4:3 was the most common aspect ratio for television and movies. Now, 4:3 and 16:9 (also known as widescreen), are the most common aspect ratios. These are also known as the “native” aspect ratios used in display devices, such as projectors and televisions. As there is not currently an industry standard with aspect ratio for television channels to broadcast in, some channels have adopted the High Definition 16:9 format, while others are still using the standard definition 4:3.

Most of the time, this isn’t a major issue. It just causes a little black band on the top and bottom or left and right of your picture. However, getting it right will ensure you see the image exactly as it was envisioned by the film maker. If you are viewing a movie or television show which has been made in an aspect ratio other than what you screen is, you are still able to watch it without distortion. The 2 ways of converting the irregular sized image to suit the projection device are zooming and cropping, or letter boxing / pillar-boxing.

As you can see in the images below, the image can be stretched to suit a 16:9 screen, although this causes pixelation and an unclear image. The alternative is to pillar box the image, so it is kept in the native ratio, with the remainder of the screen blanked out with black bands on the left and right sides.

Likewise, a widescreen image can be cropped to suit a smaller ratio screen, however, this causes the sides of the image to be cut off, potentially losing vital information from the image. The alternative is to “letter box” the image, which will keep the image in the intended width to height ratio, causing the black bands on the top and bottom of the screen.

The concept of "letter boxing" was created when renowned film maker Woody Allen refused to allow his 1979 release "Manhattan" to be cropped for release in cinemas.

Most projectors and TVs nowadays automatically adjust the image to fit on the desired screen size, so you won’t need to worry about getting it right. But hopefully now, the next time you watch a film with the black bands on the sides, you will understand why.