While recording video or capture the screen through camera, we often see the scrolling, flickering screen or a black rolling lines or, instead of the stable image like our eyes saw. Do you know why and what is the reason behind it? Well to know the why TV gets flicker, let’s go through this article.
Well, there are two reason behind the annoying flickering screen:
- The Camera’s Eye – A difference in the scanning frequency between the TV and the camera
- Persistence of Vision – A difference in the way the phosphor dots are perceived between the human eye and the camera’s image sensor
The Camera’s Eye
Monitor or TV’s usually have their own refresh rate and 50Hz, 60Hz very common. It means that you screen refreshes 50 or 60 times in a second. Looking through human eyes, it is very smooth and fast as well as unnoticeable.
But the camera doesn’t work like our eyes, they have different mechanism of working. If the frame rate of camera match with redrawn screen of monitor or display, it will look fine. Usually it doesn’t happen. In camera, it captures certain part in one frame and the next parts in other frame and so on.
Your screen and camera that records the clips had different scanning frequencies. Since they aren’t synchronized, camera sees the line in different place each time it records an image.
And as result, we see flickering screen while recording through camera.
Persistence of Vision
The primary concern, here is the way that human eyes see pictures on a monitor or screen different in compare to camera. A picture on a screen is made by an electron beam which scans the picture tube, illuminating phosphor pixels arrayed in lines across the screen. For instance that electron beam makes 30 scans each second. However, an individual phosphor dot doesn’t really remain lit for the full 1/30th of a second that it takes for the electron beam to strike, complete a total scan, and after that strike once more. When the bar comes back to a line, the phosphor pixels have faded to black.
In any case, your eye doesn’t enroll that split second of darkness. The way human vision works, those spots seem to remain lit the whole 1/30th of a second. This visual wonder is called “persistence.” Our mind then takes there series of still pictures made by the shining phosphor dots and reassembles them into a steady picture that reproduces what we see in the normal world with a lot of accuracy.