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Old September 25th, 2012, 03:21 PM   #1
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chroma key and dissolves - BIG problems

My bottom layers are showing through the key during dissolves in FCP. This sucks and I'm surprised that I couldn't find another discussion on this.

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I frequently do secondary color correction in FCP by duplicating the layer, keying out faces on the top layer and then cc'ing the bottom layer - usually to add brightness to dark faces.

Well, during a dissolve (any dissolve, I've tried them all), the key is weakened and their face shows dark again. This also happens if I just keyframe opacity. My guess is that the chroma keyer is calculating on the current luminance and values during the dissolve, which are different then when the video is at full opacity. This is crazy.

I've also tried nesting the two cc'ed layers, then adding a dissolve to the nest, but no luck - it still happens. I can manage to get around dip to black, by adding a black color matte, and dropping its opacity, but cross dissolves are still out of the question.

Any help?
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Old September 25th, 2012, 05:38 PM   #2
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Re: chroma key and dissolves - BIG problems

Export the CC'ed, layered shots to Prores then add the flat Prores shots back in.

Also, have you tried using the "Limit Effect" function in FCP's Color Corrector (single and 3 way)? It is a drop down tab at the bottom of the Viewer when you are in the "Visual" view mode. That may achieve the desired effect without the need of multiple layers.
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Old September 25th, 2012, 08:55 PM   #3
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Re: chroma key and dissolves - BIG problems

Do the key layers in a separate sequence and then drag that sequence as a clip into the main edit then the dissolves will work cleanly on all layers in the key. Or export the key sequence as a movie file and use that.
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Old September 26th, 2012, 09:58 AM   #4
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Re: chroma key and dissolves - BIG problems

William, what you described is nesting the layers, which I tried and didn't work. Oh well.

Perhaps I'm exposing bad workflow practices, because I know it's wrong, but basically I'm taking sequences that were edited a while ago, color grading them doing some audio sweetening, and then sending them to eventually be further edited by review. So I would like to do the best I can to allow them some wiggle room to make changes. This is wrong, I know.

Is there a way I can apply the grade to the full source clip, export that, then replace all instances of it in the timeline? This would give them all the flexibility they'd need to make further edits.
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Old September 26th, 2012, 10:21 AM   #5
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Re: chroma key and dissolves - BIG problems

Quote:
Originally Posted by Denez McAdoo View Post
Is there a way I can apply the grade to the full source clip, export that, then replace all instances of it in the timeline? This would give them all the flexibility they'd need to make further edits.
Have you tried my suggestion with the Color Corrector?

In regards replacing the whole clip, you could export the graded footage and then relink the clips in your FCP project to the newly graded one: Just right click on the clips and select "Reconnect Media" then select the graded version instead of the original.
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Old October 9th, 2012, 12:20 PM   #6
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Re: chroma key and dissolves - BIG problems

.... by the way, I'm noticing a similar effect when using a mask shape. I don't notice the feathered mask before the dissolve, and then I see the surrounding area go black faster then the area withing the mask during the dissolve.

I've tried nesting, and it doesn't work. Cross-dissolves seem fine, and I can always use the fade-up or fade-down on a black color matte trick to simulate a dissolve. But still.... what's up here?
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Old October 9th, 2012, 03:59 PM   #7
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Re: chroma key and dissolves - BIG problems

One more observation.

If you duplicate a layer, stack it on top of itself, and, say, color correct the bottom layer (this bottom layer will be hidden, as long as you don't do anything to the top layer), during a dissolve, the bottom layer will become visible.

This seems to suggest that the issue lies in the opacity drop of the dissolve, not in the calculations of the chroma keyer. Meaning that if you used, say, a green screen in FCP, then a dissolve or cross dissolve is useless, because your green will show during the dissolve? Crazy.
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