When working on a video project, it's important to understand how frame rates influence the final look of your visuals. Most of us know that video clips are just a sequence of still images (or frames) played one after another, which is where the term "frame rate" comes in. Also known as frame frequency, frame rate is the number of times that a camera captures an image to create a video. This measurement is also used for computer graphics and video games. Typically, frame rate is defined as "frames per second" (or FPS).
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How Do Our Eyes Perceive Frames?
Every individual's vision is different, but the average person can process about 150 frames per second. There's also a "refresh rate", which tells you how fast the frames will flicker. This is measured in hertz (Hz), and the faster an image flickers on screen, the more realistic it looks to the naked eye.
The refresh rate concept originated in the old movie houses, where projectionists would flash each frame multiple times to help reduce motion jitter. So when we talk about frame rate (i.e. 24 FPS), we're referring to the number of unique images that play each second. Likewise, if the refresh rate is 72 Hz, that means each frame is being played (or "refreshed") three times.
Early Frame Rate Standards
So, how did the pioneers of filmmaking decide on an FPS standard? The earliest silent films had a variety of frame rates, which could span between 16 and 24 FPS, and this could even change in real time to fit the feeling of a particular scene. This is because the cameras were cranked by hand, so the camera operator had total control over the frame rate. Debates continued about an ideal frame rate, and during these early days, Thomas Edison was quoted saying that 46 FPS was the slowest acceptable frame rate that wouldn't cause eye strain.
By the late 1920s, silent films had increased their frame rates between 22 and 26 FPS. When sound was finally introduced in 1926, filmmakers and theaters had to decide on a definitive frame rate, in order to avoid fluctuations in audio speed. This is when 24 FPS became the standard. Edison's prediction also proved to be right, with projectors using a minimum refresh rate of 48 Hz (i.e. each frame flashing twice).
Frame Rate in Today's Film World
In the modern movie industry, 24 FPS has become the standard for 35mm films, although some directors and cinematographers have been experimenting with new frame rates to achieve distinct visual styles.
For example, Peter Jackson (director of the Lord of the Rings series) famously shot The Hobbit at 48 FPS, which resulted in much more detailed and lifelike visuals. However, it also lacks the dreamlike quality that people associate with the movies. Instead, it looks more like an HD nature video that you see in a television showroom, so it requires more elaborate special effects and makeup to still feel believable.