Monday, October 15, 2012

Understanding HD - Frame Rates


WHAT IS HD AFTERALL?


The most basic definition to begin with is: all digital formats with a resolution greater than standard definition (SD) video are considered HD. The definition gets more complicated as we consider HD as a set of digital video formats rather than just one.

When digital filmmakers talk about shooting in HD, they talk about following three subsets: 720, 1080 and digital cinema. Scanning lines, Frames always is a part of the discussion when we try to explain the three subsets as mentioned above, so let’s understand them first:

 FRAME

The Video track is actually made up of series of still images, and when they are played in sequence, they appear to be moving. Frames of video are similar to frames of a film, just that you can’t hold them in your hand and point towards a light and see them. It’s not cellulose after all, but it works in the same principle. Instead, you need a computer to decode the electronic information that constitutes each frame and display it on a monitor.

The number of still images, or frames per second is called as FRAME RATE. The standard frame rate before the advent of sound in film used to be 14 – 18 frames per second. In the mid- to late-1920s, the frame rate for silent films increased to about 20 to 26 FPS. (Wikipedia). This change happened because it needed to synched with sound. So, soon films were running at 24 frames per second (fps). So, when you watch any of the silent films now, they appear to run faster as more frames are running per second than what was originally shot. Watch this restored version of “Alice in the Wonderland (1903)” http://youtu.be/zeIXfdogJbA

When it comes to HD, there are different frame rates associated with it. It needed to be compatible with American Analog  broadcast video, European analog broadcast video, so, here the subsets of three potential sources of HD frame rates:

  1. 24p and 23.976p. Frame rates based on Film. You will probably shoot in 24p, if you eventually want your footage shot in Video to be transferred to Film eventually. To know more why or why not you should go for 24 frames per second, see this tutorial by Larry Jordan: http://youtu.be/FO2dD4Z4oYI
  2. 29.97p, 30p, 59.94i, 60i, 59.94p, and 60p. Frame rates based on American television
  3. 25p and 50i. Frame rates based on European television.


What is ‘p’ and ‘i’ means, we will explore in the next section on scan lines, in my next post. 

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