Why do you see black lines when you see a television recorded through a video camera?

Question

Why do you see black lines when you see a television recorded through a video camera?

Answer 1

A TV screen and the image on the camera image pickup are both scanned.  That means that a beam of is moving across the screen (in a conventional CRT) or a particular pixel is being sampled (in the case of a solid state device).  At any rate, the effect is the same, only a small dot is being updated at any one time.  You eye doesn't see this because it doesn't react that fast so you "see' a complete picture.

In the case of the camera, it is scanning (sampling pixels).  If the TV is scanning (painting the picture) in the same location the camera is looking, the camera sees that portion of the picture, if the camera is scanning where the TV isn't at that moment, the camera sees a blank screen.

I hope this helps.

Answer 2

That my friend is the tv's "lines of resolution" to give you the simple description.  Thats how the tv actually looks but the camera is not as sophisticated as our eyes so it picks it up.

Answer 3

A standard def TV 'paints' the odd lines, then the even lines.  This is done 30 times per second for the odd, and 30 times per second for the even.

A TV camera takes a picture 24 times per second.  Since 24 and 30 are so close together, the TV camera catches the painting of the same line .... 6 times per second which is visible.

The next second, a different line is caught which is why you see the black lines moving up the TV screen slowly.