From the course: VFX Keying: Master Course

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Which math operation to use and when

Which math operation to use and when - Nuke Tutorial

From the course: VFX Keying: Master Course

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Which math operation to use and when

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- [Instructor] When merging keys together, you have to pay close attention to which math operation you use. Some will replace one key with another, others will add them on top of each other, while others can build up alpha channel values greater than one, which you never want to happen. So let's push in here and take a look at this plus operation setup here. I'm going to connect my viewer here and open up the sampler node so we can see what's going on. So here's my setup. I have these two ramps that go from zero to 1.0. Now the sampler node, set right over here, is simply sampling the entire scan line from left to right and plotting it up here. So this is saying on the left edge I've got zero and on the right edge I've got 1.0 and it's kind of a nice linear ramp. Here's my channel merge node where I'm going to plus them together. And this shuffle just brings them out of the alpha channel into the RGB so the sampler can see them. Sampler doesn't do the alpha channel. So let's hook up…

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