Hertz (symbol Hz) is the IS (International System) unit of measurement for frequency.
This unit of measurement can be applied to any periodic event. One hertz equals one pulse per second, so, for example, the ticking of a clock can be said to have a frequency of 1 Hz.
Hz [=] 1⁄s or Hz [=] s−1
The equivalent unit cycles per second (cps) can be found in older publications.
Frame rate is the capture or playback rate of the individual images (frames) that make up a video. The sequence of these images creates a video: a succession of images that generate the illusion of movement in human perception.
Heinrich Rudolf Hertz was the physicist who gave important scientific contributions in the field of electromagnetism. In fact, the unit of measurement of frequency takes its name (hertz, Hz). The tool used to measure the frame rate in Hz is the progressive scan monitor. However, it can also be expressed in terms of frames per second (fps). For the human eye, the number of FPS required for smooth playback, i.e. the ability to see a video without interruption, is approximately 30 frames per second, but this value can change depending on the type of video, format, video camera, etc.
In television and cinema, the standard video scan modes and related frequencies are:
- 24p (non-interlaced scanning system): Originally conceived for digital video editing but also widely used for aesthetic reasons. It is a digital video editing system which consists in acquiring images and sounds through digital rendering and subsequent processing via PC. It relies mainly on a computer, video editing software, viewing and listening devices, memory and tools for acquiring and delivering images. This montage is defined as non-linear as the process takes place parallel to the media, i.e. on digital copies of them, and not in linear verticality.
When converting to NTSC, the frame rate is slowed down to 23.976 fps, while when converting to PAL or SECAM, it is speeded up to 25 fps. The 24p mode was the cinema standard of the mid-1920s.
- 30p (non-interlaced scanning system) is a 30 fps standard. The system for displaying, storing or transmitting images in which all lines of each frame are displayed in sequence is called progressive scan. Its vertical resolution has a better yield than an interlaced signal, at the same number of fps, for this reason it is used for high definition contents. the 30p standard allows, in fact, a noise-free video playback of digital, analog or image signals. The use of this frame dates back to 1954-1956.
- 50i (interlaced scan systems). The 50 semi-frames per second correspond to 25 fps, it is a standard of the PAL and SECAM coding systems, commonly used by European analogical televisions.
- 60i (interlaced scanning system). The 60 or 59.94 semi-frames per second equals 29.97 fps). It is the standard interlaced scanning system for the NTSC analog encoding system (commonly used by US TVs). The standard was developed by Vladimir Zvorykin and Philo Farnsworth in 1934 and adopted by the NTSC system seven years later, in 1941. In 1953, following the introduction of color, the original frame rate was reduced by a factor of 1000/1001 to in order to avoid interference between the chroma subcarrier and the audio carrier of the signal.