Looking at the TV screen, we see how to “finish” the picture, often not having the slightest idea about how it is formed. Well known users of the YouTube videoblogger Slow Mo Guys by using high-speed cameras filmed the process of forming the image on the TV screen.
If you clear the screen with a regular camera, you can easily see the formation of sweep, since the sweep frequency and the speed of the camera is not quite the same. However, using high-speed cameras can reduce the refresh rate even more and see how it does line by line.
The footage shows that the image is formed not only top down but also from left to right. Each pixel is updated literally by the piece and the result is a picture familiar to our eyes.
Source — The Slow Mo Guys