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Anti-aliasing and Green Screen


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#1 Synnah

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Posted 13 February 2008 - 10:55 AM

As you might know, what anti-aliasing does is blend the pixels between two high-contrast areas with colours that are half-way between the two, so that jagged bits are less pronounced. However, when green-screening, this leaves you with a line of green pixels that aren't exactly the same colour as the background, around the object or person you want to use. There are two ways of getting rid of this outline:

- Decrease the sensitivity of the green-screen filter, so that it also filters out slightly less green pixels. This has a chance of filtering out other areas of your video, however, so if your characters are wearing green clothing, it's not ideal.

- Don't anti-alias in the first place. This will give your characters a slightly rough, jagged look, but you can apply a smoothing filter, or a very slight gaussian blur, using your video editing software, which should help.

If you weren't sure, anti-aliasing can be switched off in the Graphics tab of the Settings menu. Just adjust the slider to '1'.

It's probably worth mentioning that this is really only going to be an issue if you render out of Moviestorm in a lossless format (Something that's now possible using DirectShow rendering), as filtering out only the exact colour of the green screen in a compressed video is going to leave some artifacts behind anyway (As compression tends to average out colours). So if you only want to filter the exact greenscreen colour (00FF00, I assume), you'll want to turn anti-aliasing off and render in an uncompressed or lossless format.

Oh, also if you're green screening, do remember to turn the Moviestorm watermark off when rendering!
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#2 Spong3y

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Posted 13 February 2008 - 11:38 AM

A great tip, Synnah! Although users using Sony Vegas can always use the built in chroma blur on the chroma keyer, it's a feature that blends the greenscreened video to the background, giving it a more realistic look.

A very well written tutorial, it solved a lot of problems with greenscreening.
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#3 Synnah

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Posted 13 February 2008 - 12:08 PM

Oh! I should really do more research into video editors. We do need a copy of Sony Vegas here in the office. I don't think I can extend our budget to Premiere, though.
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#4 revdoug

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Posted 13 February 2008 - 01:04 PM

Bravo and thank you!

I had to abort one movie because of this very problem. I was trying to combine Moviestorm actors with a clip I made with Half Life 2. The halo was ruining it.

I'll be trying again soon with this new info.

revdoug


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