From the course: VFX Keying: Master Course

The classic Premultiply > Merge over - Nuke Tutorial

From the course: VFX Keying: Master Course

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The classic Premultiply > Merge over

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- [Steve] This chapter is about the many different ways you can combine your foreground layer with the background. This is about the compositing, not keying, spill suppression, or color correction, as these are covered in other chapters. This first video is about the classic premult, then merge over workflow. So we can see it right here, we're pushing it a bit. So starting with our green screen, we of course do the obligatory denoise. Now here is a core mat, that has already been prepared. And we use that with the spill suppression, just to dig out the spill suppression in the core. So this is our spill-suppressed image, and here is our key, which has already been created, because this is not about creating the key, this is about putting all the pieces together. So we take our key, and with the copy node, we put it behind our spill-suppressed images. So now, I have a four channel, not premultiplied image. We do the premult, which clears the outside area to black, and then we do the merge over with the merge over node. Now I got a little toggle switch tchotchke here, that I made for you, that I can just toggle between the test pattern, and a real comp. Of course, the actual background you use has a dramatic effect on the edge treatment. Well, that was easy, but lets take a closer look at our comp. I'm gonna push in over here. Hmm, I have this unpleasant, dark edge thing going on here. Um, if we look at his hair, I got some pretty good detail. Keep in mind, that this was an unusually nice green screen, okay? But if I compare the original green screen, with the comp, I've lost a little bit of that hair detail. Let's check over here with the lady. And, we can see we've lost again, a little bit of our hair detail in the comp. Okay? Now, some of the later videos in this chapter are going to address these issues. Well that was easy, but there were issues with the fine edge detail, and motion blur. The next video will show us how to get more control over the edges, by using the admix node for the composite.

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