Color correction only on part of the clip. Is it possible?

Condemor · Post by **Condemor** » Sat Nov 28, 2009 6:54 am

Hello everyone

I am using a green screen for the chroma key effect. The background video I am using has a kind of grey tone and I would like to adjust the brightness and contrast of the foreground clip (me) to match it. The problem is, when I do that, the green screen also changes color and when I apply chroma key, the green is not so uniform anymore and I have transparency problems.
Is it possible to apply color correction to only a part of the foreground video?. Basically, to everything that is not green.

Thanks

Post by **Ron P.** » Sat Nov 28, 2009 7:24 am

AFAIK, this is not possible with VS. Ulead did have a utility called Video Graphics Lab, that consisted of Video Paint and CG Infinity. The Video Paint program, is what's known as a Roto-scoping program. With it you could do such things as touching up video.

That said, you still needed their higher-end NLE, MSP to make effective use of Video Paint. MSP allowed creating and using various overlay Keys such as Chroma, Luma, and Gray. While VS does have a Chroma-Key, and since you are making use of it to key out green, you further need to be able to adjust the gray and luminance.

Condemor · Post by **Condemor** » Sat Nov 28, 2009 7:42 am

Thanks vidoman. I suppose I will have to try and get the brightness and contrast right while shooting the video then.

Post by **Ron P.** » Sat Nov 28, 2009 8:09 am

Have you tried applying the Brightness/Contrast video filter, or using the Brightness/Contrast adjustments in the Edit Tab? If the latter, have you tried adjusting the Saturation and/or Gamma? It seems that if you want to make your overlay appear more dull, you need to de-saturate it some.

Try applying the Color Balance Filter to see if that can help. You can mix several filters, up to 5 if I recall correctly, and so long as you uncheck the box to Replace Last Filter. You can also change the Layer/stacking of these filters, which will change how it effects the video.

Condemor · Post by **Condemor** » Sat Nov 28, 2009 8:14 am

Yes, that is what I was doing, but then the green background also becomes "greyish" and the chroma key is not very effective as it does not stand out as much from the person as it did before and Videostudio cannot identify the borders.

Post by **Ron P.** » Sat Nov 28, 2009 8:22 am

It does seem then, you need more control, such as the gray-key and also be able to use garbage mattes, to help clean up the border. Consumer NLEs just don't have that capability.

With the more pro-sumer NLEs you have a lot of control and latitude with these things. MSP, while was not nearly as costly as FCP, Adobe's and others, was very capable of these things. Too bad Corel only saw the garbage bin for this program. I still have it, still use it. However there is no support for it, it does not support the newer Hi-Def formats, but for my purposes, the old trusty DV format, it works wonders...

Just checked Corel's Store/Catalog and for a limited time, you can still pick up MSP 8, and they've cut $100 off the price..

sjj1805 · Post by **sjj1805** » Sat Nov 28, 2009 5:00 pm

What is possible and what is practicable are two different things.
It depends upon the duration of the affected piece of video because the longer it is then the more frames will be involved.

using PAL as an example:
25 frames per second = 1,500 frames per minute = 90,000 frames per hour.
With this in mind please view:
Video Sequence File