Understanding the Frame Rates: Why Many Movies and Screens Still Use 30Hz

The relationship between frame rates and refresh rates in movies and screens can be a bit complex. However, this article will break it down for you in a simple and clear manner.

Film Frame Rate

Traditional film is shot at 24 frames per second (fps). This frame rate is widely used because it provides a good balance between motion smoothness and cost of film stock and processing. It has become a standard in the film industry, known for its rich and smooth visual quality, and has been used for decades in movies and television productions.

Refresh Rate of Screens

The refresh rate of a display, such as a television or computer monitor, refers to how many times per second the screen updates its image. Common refresh rates include 30Hz, 60Hz, and higher. This rate affects the fluidity and smoothness of the displayed content.

Why 30Hz?

Many screens refresh at 30Hz because this rate aligns well with video content, particularly for NTSC (National Television System Committee) broadcast standards, which operate at 29.97 frames per second. This rate allows for smooth playback of video content, making it a practical and widely adopted choice.

Conversion and Compatibility

When displaying 24 fps content on a 30Hz screen, the video can be converted using techniques such as 3:2 pulldown and frame blending:

3:2 Pulldown

This method alternates between showing one frame for three refreshes and the next frame for two refreshes, effectively converting 24 fps to a format compatible with 30Hz. This technique helps in maintaining a smooth and consistent visual experience for viewers.

Frame Blending

This technique blends frames together to create intermediate frames, making motion appear smoother and more fluid. This helps in reducing the noticeable "jerky" motion that can occur when displaying 24 fps content on a 30Hz screen.

Higher Refresh Rates

Modern displays often support higher refresh rates like 60Hz or 120Hz, which can provide even smoother motion, especially for fast-moving content like video games or action movies. However, these higher refresh rates come with increased costs, particularly when dealing with film content, where the higher resolution demands higher quality film stocks and increased post-production requirements.

The Importance of 24FPS

At 24 fps, we might not notice individual frames, but human eyes still perceive the difference in motion smoothness between 24, 30, 60, or 120 fps. Higher frame rates typically result in a better viewing experience. However, achieving a higher fps comes at a higher cost, especially when dealing with photographic film reels.

Some early 20th-century films used frame rates as low as 15 fps, and the motion in these movies does appear jerky. While 24 fps is often seen as a bare minimum for creating a smooth motion without causing headaches for the viewer, 30 fps provides an additional 25% improvement in motion smoothness over 24 fps.

Conclusion

In summary, while our eyes can perceive motion fluidly at around 24 fps, screens often refresh at 30Hz or higher to accommodate various video standards and provide compatibility for different types of content. The use of 30Hz in many screens, including television and monitors, is a practical approach to balance cost and visual quality.