Basically you can't unless you can set the monitor to the same frame-rate as your camera...

Another option, but much more complicated, is to replace the computer screen in post.

Question, if you had a repeating loop of chroma-key green on the screen would it still have the horiontal line?

RJSchwarz
San Diego, CA

I was thinking of tracking the corners of the screen and dropping in a complete replacement video, but green would probably work to chroma-key it with a bit of care.

If the camera shutter speed is set to an integer multiple of the frame-rate of the monitor (e.g. shooting 60 fps with 1/75 shutter and a 75 fps screen) then you'll get a line across the screen but it shouldn't be anywhere near as bad as shooting at a totally different frame-rate. The latter normally gives a dark patch that moves up and down the screen rather than just a thin line across it.

Painting the screen green (or blue) is another option if its a junky set. Makes for easier post-production overlays. Thrift store might have a cheap tv, shouldn't matter if it actually works or not.

RJSchwarz
San Diego, CA

quote:

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Question, if you had a repeating loop of chroma-key green on the screen would it still have the horiontal line?

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You'd still have the same problem as the black line it is generated by the difference between the frame rate of the television and that of the camera. It doesn't matter what's on screen.

It is sometimes possible to counter this effect with certain cameras where you can control the shutterspeed (i.e. Canon XL series). See the FAQ for more info on doing this, otherwise the other suggestions in this response are sound.

Ben C.

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Benjamin Craig
Editor-in-Chief, filmmaking.net

Your problem is with refresh rates. If you can, set the computer monitor's refresh rate to 60Hz. This will make your life easier. TV screens all use 60Hz refresh rates.

If you have adjustable shutter speed on your camera, set it to no faster than 1/60 of a second, and you should be fine. Note that when shooting a CRT screen, you should have your camera locked down on a tripod. If you move the camera at all, the image on the screen will appear to split in half.

You may still get a very small light or dark scanline moving up or down the screen, but it will be barely noticeable.

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Andrew Gingerich
Exploding Goldfish Films
Check out my vodcast on iTunes: http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewPodcast?id=96931870

the refresh rate depends on if you are shooting pal (50hz) or ntsc.

Also, I've never tried this first hand but I have read that if you shoot a laptop monitor, or the flat screen i mac sort, they process the picture in a different way and you don't have the same problems with refresh rates. Like I say, never tried it first hand, but its worth checking out.

If that is not an option you may be able to limit the effect of the bar (but probably not knock it out totally), by setting your camera onto a slow shutter speed. I know this works to some extent with stills photography.

P.

Yes, I know for a fact that LCD screens do not show scanlines, as I've shot them many times in the past (Plasma screens and DLPs may also work, I don't know).

I would avoid chroma-keying the screen, as it is so hard to do right (even in big-budget films, they just can't seem to get the picture to be sharp but still pixelated--it ends up looking quite tacky).

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Andrew Gingerich
Exploding Goldfish Films
Check out my vodcast on iTunes: http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewPodcast?id=96931870