Ghosting

jambutty · 14-09-2008, 17:32

I was playing around with my Sony DCR-SR32E camcorder the other day familiarising myself with it when I noticed something odd.

Unintentionally I had pointed it at my TV, which was on, and the picture in the view screen had a ghosted band across the picture. Sometimes near the top, sometimes near the bottom or part way between or not at all for a few seconds or just slowly moving up and down.

Pointing the camcorder at my computer monitor did not result in that ghosted band. I should add that my computer monitor is an LCD screen, whereas the TV is a CRT type.

I can take a photo of the picture on the TV screen with my digital still camera without that ghosted band appearing so what’s going on?

Is this something that the manufacturers of camcorders have done to prevent people from ‘recording’ films/programmes on TV? I can place my camcorder on a tripod and adjust it so that it films just the screen, so it could be done in theory.

K.S.H · 14-09-2008, 18:15

Read about this before and IIRC its all down to different refresh rates

Studio25 · 14-09-2008, 21:58

A CRT screen works on the basis of a line of electrons that scan down the screen. The bright band you see on digital images (on both stills cameras and video cameras) is the bit of the screen that is scanned while the shutter is open. The rest of the screen, if visible, is just the glowing remains of previously scanned phosphor.

If the band moves, it's just the result of a different in the time you take the picture. You'd expect it with stills, but with video, it's indicative of a TV and video camera that are not working exactly in synch.

An LCD screen will flicker as a whole, not in bands. It does have a screen refresh rate, like the CRT screen, but the whole screen refreshes simultaneously. The brightness if the image will be dependent on where the image is taken between one screen refresh and the next.

jambutty · 15-09-2008, 11:18

Quote:

Originally Posted by Studio25

A CRT screen works on the basis of a line of electrons that scan down the screen. The bright band you see on digital images (on both stills cameras and video cameras) is the bit of the screen that is scanned while the shutter is open. The rest of the screen, if visible, is just the glowing remains of previously scanned phosphor.

If the band moves, it's just the result of a different in the time you take the picture. You'd expect it with stills, but with video, it's indicative of a TV and video camera that are not working exactly in synch.

An LCD screen will flicker as a whole, not in bands. It does have a screen refresh rate, like the CRT screen, but the whole screen refreshes simultaneously. The brightness if the image will be dependent on where the image is taken between one screen refresh and the next.

Although you weren’t to know, I am aware of how a CRT TV works, at least the old style. Technology has moved on since my day.

But thanks anyway, the picture is much clearer now. Er! Pun intended, I think!