Frame

What Is Frame

Many of us had this experience as children - we drew a matchstick man in the same place on every book page, and each matchstick man is changed a little with continuity. When we were done, we flipped the book quickly and the little man started moving.

This is the most primitive visual animation effect and explains that the video or animation is composed of countless static images in a row. Frame, therefore, is each image in a video or animation. In our example, each page of the book with the matchstick man on it is a frame.

Frames and Frame Rate

Frames and Frame rate are both concepts derived from Frame.

Frames is actually a short form of the number of frame generated. In a flip book, each page is a frame, and the total number of pages in the book is the frames.

Frame rate, on the other hand, is a process quantity that indicates the frames played in a second, often expressed as FPS. In other words, if an animation claims to be constant at 60FPS, it can update 60 static images in one second, which is 120 frames in two seconds.

Of course, if more frames are updated over a second, i.e. the higher the frame rate, the smoother and more realistic the animation one can see.

Persistence of Vision

The ability of frames to create visual animation effects relies mainly on the Persistence of Vision phenomenon of the human eye. The Chinese first discovered this phenomenon, and the trotting horse lamp is the earliest documented use of Persistence of Vision in history.

When the human eye looks at a fast-moving object, the object will be imaged on the retina, and the optic nerve will input the image into the human brain. When the image seen by the human eye suddenly disappears, the optic nerve's impression of the object still lasts for 0.1-0.4 seconds, which results in the human eye still retaining the image of the object during this period of time. This phenomenon is the Persistence of Vision.

Persistence of Vision is the basis for the production and dissemination of modern visual media such as film, television, animation, games, and so on. When we watch an animation, as long as the update interval of each frame is not more than 0.1-0.4 seconds, then this phenomenon will supplement the gap of the update interval, so that the visual effect of the animation has been kept smooth. On the contrary, when the frame rate of the image is lower than 10FPS, the Persistence of Vision will not work.