Basic Technical Knowledge
It is widely known why a series of still pictures creates the impression of continuous motion in our brain. It is called the ‘Phi-phenomenon’ and was defined for the first time by Max Wertheimer in 1912. Persistence of vision is the reason the human eye cannot distinguish more than 14 to 16 frames per second.
A series of pictures at any higher frequency blends into one continuous motion. In the early days of cinema the frequency was a field of experimentation, but ever since sound films or talkies were introduced, at least 25 frames per second were established as an international standard. In different parts of the world regional frame rates were developed depending on the frequency of the electric current. Most cameras can be set to any of the current frame rates used in the world. But depending on which markets they are build for, the factory-preset is different. Framerates are always measured in frames per second / FPS.
In addition to that, images can be recorded in interlaced (i) or in progressive (p) format. For interlaced scan two fields captured one after the other make up one frame, in progressive scan a full frame is captured.
25i Interlace: 50 fields per second.
25p Progressive: 25 full frames per second