Simply about Aspect Ratio

What is aspect ratio

According to Wikipedia, aspect ratio of an image is the ratio of the width of the image to its height, expressed as two numbers separated by a colon, e.g. x:y (pronounced “x-to-y”) .

The most widely used aspect ratios

The most common video aspect ratios are 4:3 and 16:9.

• The 4:3 ratio for standard television has been in use since television’s origins and many computer monitors employ the same aspect ratio.
• 16:9 is the international standard format of HDTV, non-HD digital television and analog widescreen television.

These aspect ratios can be easily distinguished. 4:3 has more “square” form, while 16:9 is more “rectangular” (See Pic. 1).

It should be mentioned that 16:9 aspect ratio is considered to be more aesthetically pleasing and closer to human eyesight. This aspect ratio approximates to the so-called golden ratio.

Most common problems connected with aspect ratio

1. All objects look narrow and prolonged, faces are “long”. This can happen, for example, when you watch a widescreen video (16:9 aspect ratio) on a square TV set that has 4:3 aspect ratio, so that your video is stretched vertically to fit the screen of the TV set (see Pic. 2).
   
   Pic. 2: Video stretched to 4:3 compared to the original video (16:9)
2. All objects look flattened out. This can happen if you watch an old movie or TV show that was shot in 4:3 aspect ratio on a widescreen TV set, so that your video is stretched horizontally (see Pic. 3).
   
   Pic. 3: Video stretched to 16:9 compared to the original video (4:3)

How to solve aspect ratio problems

Many problems connected with aspect ratio can be solved hardwarily – by setting a DVD player or a TV set to the necessary aspect ratio.
If you want to convert your video, you should remember about aspect ratio. Here you can find some tips on converting video with a glance of aspect ratio.

Why aspect ratio and frame size shouldn’t be mistaken

Probably, you know that a pixel is the smallest unit of an image. In video files square pixels are primarily used. It is evident that the width and height of a square pixel are equal to each other. In this case, the ratio between video dimensions in pixels will correspond to the aspect ratio of the video file. For example, a video file which consists of square pixels has 640*480 resolution, and its aspect ratio is 4:3 (640:480 = 4:3).

However, DVD files often use non-square pixels (they have rectangular shape, and the pixel width slightly differs from its height). In this case, the ratio between video dimensions in pixels will differ from the aspect ratio of the video file. For example, a 4:3 DVD video can have 720*480 resolution (720:480 ≠ 4:3). This difference is conditioned by different dimensions of a non-square pixel.

This entry was posted on Thursday, November 11th, 2010 at 8:11 am and is filed under Informative. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.