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Combining keylight matte (static) with white solid mask (parented). How can you do this?
I’m very tired so this will be short. I have a shot on the bus of a sign. I want to put text in the sign but a yellow pole is in the way. I could use the rotobrush but I want to practice alpha matting so I’m doing it that way.
I doubled my footage, garbage matted the sign, and successful keyed out the yellow pole. Now I need to somehow combine the matte from the keylight layer with a solid that’s masked in the shape of the sign, and parented to move with it as the bus shakes. The challenge is that one layer needs to stay still and the other is parented. As soon as I precompose to try to treat the combination as an alpha matte for the text, the parented thing can’t be parented anymore. If add a mask directly to the keylight layer and parent it, the keyed out area will move too.
any ideas?
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6 Replies
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[Jeff Rouric] ” The challenge is that one layer needs to stay still and the other is parented. As soon as I precompose to try to treat the combination as an alpha matte for the text, the parented thing can’t be parented anymore.”
Duplicate the thing that moves so you can put a copy for parenting in the precomp, too.
Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive | RenderBreak [blog] | Profile [LinkedIn] -
Thanks! This worked. I definitely overlooked that. But is this the “correct” way to do this or is it more like a workaround?
Also, now that I’ve precomped them together, I notice the black part doesn’t work as alpha. The inspector says 255 for alpha over the black part. How do I make that count? Would I have to use the set matte effect or is there something I’m missing?
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[Jeff Rouric] “But is this the “correct” way to do this or is it more like a workaround?”
Precomping is the only way to combine multiple elements to use as a track matte.
[Jeff Rouric] “Also, now that I’ve precomped them together, I notice the black part doesn’t work as alpha. The inspector says 255 for alpha over the black part. How do I make that count? Would I have to use the set matte effect or is there something I’m missing?”
Instead of an alpha track matte, you could use a luma track matte. Then the fill will be matted by the luma from the matte layer instead of its alpha. This makes it a lot easier to generate procedural mattes using traditional image manipulation tools.
Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive | RenderBreak [blog] | Profile [LinkedIn] -
Thanks, much better now! But I meant is duplicating the parent object into the precomp the best way, or is there a way…like I don’t know, converting child attributes to keyframes embedded in the layer or something…
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[Jeff Rouric] “I meant is duplicating the parent object into the precomp the best way, or is there a way…like I don’t know, converting child attributes to keyframes embedded in the layer or something…”
You could set up some expressions on position, anchor, scale and rotation, pointing back at the original layer, such that any changes in the main comp would automatically extend into the precomp — but it can get quite complicated if you start parenting the original or sliding it in time.
I don’t fully understand your layer stack from your original description, so it’s hard for me to say exactly how I’d approach it if I were starting from scratch.
Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive | RenderBreak [blog] | Profile [LinkedIn] -
Wait, yeah, expressions, that’s it! Ok so I figured out that if you use an expression to parent instead of just the pickwhip…
myParent = thisComp.layer(“Null 1”);
myProp = myParent.transform.position;
value + (myProp.value – myProp.valueAtTime(0))(got this from another thread here)
You can then convert that expression into keyframes. But I think I’ll just stick with the way you suggested. Thanks!
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