Basic Cinematography

What is Frame Rate?

A brief explanation and overview of what frame rate is, how it came about, and its relationship with the electrical utility frequency and bandwidth.

A frame is a rectangular image.

The traditional 35mm filmmaking process involves shooting at and displaying images at a certain rate, called the frame rate.

Frame rate is the number of frames that pass a given point in one second.

The most common shooting frame rate is 24 frames per second (fps). There are literally 24 complete images per second of footage.

50 Hz, 60 Hz and Bandwidth

There was a time when SD television existed without electronic cameras. Everything, including news footage, was shot on film, and then converted into the existing television standard.

In those days, everything electrical had to be designed around the electrical frequency (the Utility frequency) of a region. Some places have the 50 Hertz (Hz) standard, while others have 60 Hz.

Syncing electrical devices to the electrical utility frequency helped to prevent power line hum and magnetic interference from causing visible beat frequencies in the displayed picture of analog receivers. In simple terms, it kept the image clean and the engineers sane.

The folks with 50 Hz decided to design their television standard at 50 fps, while the folks who lived on 60 Hz decided to adopt 60 fps.

Wait a minute! That’s clearly wrong, you say. Everyone knows TV is either 25fps or 30fps, right? Not really.

50 or 60 fps was preferred over 24 fps. Why?

Two reasons – sports and resolution.

Fast moving footage, mainly sports footage, is difficult to watch at 24 fps. At 50 or 60 fps it’s almost eye strain-free.

Secondly, increasing the frame rate has been scientifically shown to increase the perception of sharpness (even though there is no change in resolution). Not as much as cinema, mind you, but good enough for the small television sets in the early days of broadcast TV.

But there was a problem. A bottleneck, if you will. It was called bandwidth.

Without wasting too much time in technicalities, let’s assume bandwidth is a door, through which we need to stuff a 60fps elephant. If it cost $100 to push a 60fps elephant through a 60 fps door, then it only cost $50 to push a 30fps elephant through a 30fps door.

For good or for bad, broadcasters decided cost was more important than ultimate quality, and in typical corporate fashion, asked their engineers to figure out how to shove a 60fps elephant at 60fps through a 30fps door.

How did they solve this problem? Read it here.