Why is TV 29.97 frames per second?

Recent questions

• Why do North American televisions run at 29.97 frames per second?

  North American televisions run at 29.97 frames per second due to historical technical constraints related to CRT screens. These screens work by sending a beam of electrons forward, lighting up the screen where it hits, allowing for image production through rapid scanning. The frame rate of 30 frames per second was influenced by the 60 Hz alternating current in the electrical supply, with the final rate of 29.97 chosen to ensure compatibility with the available frequency window for data transmission.

• How does interlaced video work in North American TV broadcasting?

  Interlaced video in North American TV broadcasting involves scanning 525 horizontal rows in two passes to create a complete frame. This method was used to optimize image quality and transmission efficiency. Line-by-line phase reversal was implemented to prevent interference between color signals and existing picture and sound signals, ensuring a smooth viewing experience for audiences.

• What is the difference between PAL and NTSC television systems?

  PAL television in Europe operates at 25 frames per second with 625 horizontal lines, offering better resolution than NTSC. PAL was deliberately designed with a frame rate and horizontal lines that aligned perfectly within the available frequency window for data transmission. In contrast, NTSC systems in North America run at 29.97 frames per second with 525 horizontal lines, chosen to ensure compatibility with existing infrastructure and backward compatibility.

• How did the introduction of color TV in 1953 impact North American broadcasts?

  The introduction of color TV in 1953 posed challenges for North American broadcasts due to the limited frequency window available for data transmission. To address this, adjustments were made to the frame rate and implementation of line-by-line phase reversal to prevent interference between color signals and existing picture and sound signals. These changes were crucial to maintaining broadcast quality and viewer experience.

• Why was the frame rate adjusted in North America instead of changing the number of horizontal lines?

  The decision to adjust the frame rate in North America instead of changing the number of horizontal lines was made to ensure a smooth transition and backward compatibility with existing systems. By keeping the frame rate at 29.97 frames per second and implementing line-by-line phase reversal, broadcasters were able to maintain signal integrity and prevent interference between color and existing signals. This strategic decision helped to ensure a seamless transition to color TV while preserving the quality of broadcasts.