Chroma Key tricks - removing a region by masking?

Christian de Godzinsky wrote on 8/20/2010, 6:46 AM

Hi,

I have used the Vegas Chroma Key filter just for some basic things. Now I have the following dilemma to solve, and I'm looking for a simple and elegant solution:

Normal green screen, the object to be at the foreground has one unwanted small part that is also green. I would like to mask this area so that the Chroma Key ignores this area and keeps the foreground.

How to do this - in a simple way ???

I can add a mask to the chroma key filter that is applied onto the foreground track, but the mask just does not work that way! I can mask in such a way that only the inner part of the masked area is chroma keyed, or that the outer part is chromakeyed - the inner always being transparent...

Do I have to layer another track on top of the original foreground track to do this trick? I assume this is often a problem with chromakeying, the foreground object has a small part that goes transparent (due to similar color as the background) - but you would like to mask it out - to keep it...

Gratefu l for any guidance about how to do this properly...

Christian

Comments

Ethan Winer wrote on 8/20/2010, 7:18 AM

> I would like to mask this area so that the Chroma Key ignores this area and keeps the foreground.

I'm not an expert, but I'd do this by duplicating the same clip on the track above the main track. Then set the mask on the upper track so just the green portion you want to keep shows through. Being on an upper track will override the Chroma Key on the main track.

--Ethan

farss wrote on 8/20/2010, 7:47 AM

To do what Christian wants to do then duplicating the event to an upper or lower track and masking it is the only way I can think of. I cannot think of any practical reason to put it on an upper or lower track both would give the same outcome, you've still got to add a mask.

Bob.

Christian de Godzinsky wrote on 8/20/2010, 11:38 AM

Thanx Ethan & Bob,

So it is - as I assumed - adding a copy of the track above and masking it there does the trick...

Somehow, this seem like a little archaic. Isn't this a typical situation where you can see through an object and need to just remove that part from the chromakey processing?

One would assume you could acheve this kind of masking - within the same track... but that is not the case...

The problem is that my track is very complicated and constantly edited. If I want to see the result, I then have to repeatedly copy the lower track contens to the upper track, every time I need to edit the original track and want to see the results. I was wondering if there is a more elegant way of doing this...

Cheers,

Christian

farss wrote on 8/20/2010, 3:35 PM

"Somehow, this seem like a little archaic. Isn't this a typical situation where you can see through an object and need to just remove that part from the chromakey processing?"

"Seeing through" an object because it has a physical hole in it would not hamper the CK process. Having the CK create a hole because of a reflection means you stuffed up when you shot it. I've yet to find any 'fix it in post' processes to be elegant.

" I was wondering if there is a more elegant way of doing this..."

You could go through all the footage, get it keyed correctly and render it out to uncompressed with alpa. The amount of disk space used may scare you off doing this.

You could create a Vegas project just to do the keying and nest that project into your main project.

Either way my mental approach is to 'just do it', ignoring any creative decisions. Then when I've fixed all the technical stuff ups get creative. Mixing the two in the one thought process doesn't work for me.

Bob.