Nuke Keying Tutorial | Greenscreen Beginner Concepts

hey guys this is just a free preview from nuke 505 of my keying and color integration course um how to take footage and integrate it with the background but also do difficult uh extractions how to get those Alphas as well um and the all the steps that come with it so grain workflows um yeah semi-transparent edges difficult Keys is really what it's about so not TV level but more feature film uh level work is kind of what the course is but in this video it's just a few lectures from that class going over the high level Concepts sort of the underlying fundamentals you actually need to understand before you even go into nuke of just how to approach and problem solve a basic key but it does go more advanced and more intermediate than that so A few other clips from this course you can see the kind of level detail we get into combining multiple Keys together combining lots of Roto shapes and motion blur and all of those things the things that as a beginner it's easy to struggle on because you don't see how the the pieces connect together and oftentimes you know it can seem complex but actually it's just a few simple Concepts that need to be laid out first that if you understand them you'll see the full picture and it's actually not as hard as it seems so this is some other uh just quick time lapses from that course showing some of the integration and the color work that we can get into various workflows with that and yeah the artistic side as well so just uh those really really small details I can make an image feel more integrated and uh also I think it's the most fun side of compositing so that's also a big part of the class so um yeah in the next few minutes it'll just be some of the high level Concepts not node focused about keying in general so if you're really starting out really for beginners is who it's aimed at here you might find it useful example of a perfect ideal key so this is kind of so when you're kind of starting out and you're learning keying some of the information out there is just like using one of the nodes and then you're getting a key and that's just usually not how it works usually it's kind of combining multiple keyers and it's more of an advanced process so if we look at this video and I hit play here we have like a guy in a green screen we take our little Color Picker and we just basically select the color and voila we have like a perfect character cut out put over the background and your job's done you get home you get paid which is generally never how it works basically most of the time we have green screens that are not lit perfectly like this and you don't have this perfect scenario and usually takes a lot more work so we need to understand a little bit deeper so this is a more realistic green screen we have a unevenly lit screen here so we see it's it's been lit this is basically just a fake drawing but it's lit more on the right side here and it's darker here we also have some problems we have a microphone standing in the way on the left side and we also have some wrinkles on the bottom of the green screen so this is something that's very standard you have all these problems so unwanted objects bad overlap and then also our character has some spill so because of the this is all simulated but you know we'll look at real examples after this but uh we see that that green outline is around the character because the the bounce light or the light is bright enough to basically bounce off the surface and go on to the character which is going to cause US problems when we're trying to key it we could get semi-transparent edges we could also you know you might be able to pull a nice key still but you're still going to have that that contaminated color so we have to learn how to deal with all these problems and lastly we also have uh just you know by bad luck we have this character wearing a tie that has some green dots on it so those would those would be a problem as well that we would use a hold out we would have to Roto this so that it doesn't get keyed so that's kind of just the realistic scenario those are all the problems we see before we even start the shot we see the problems we also see that these legs are going over the wrinkles and some of these wrinkles might be black so we can't actually key them um so this is something that we'd have to deal with a different way we'd actually use some rotoscoping to combine it and of course we have the spill so that's the area I was talking about earlier and that's something to think about before you start a shot so requires a more complex approach if we were to just try one keyer this is what would happen we would go in here we would select the color but then you see all of this problem area is actually basically being added over the background you see it's darker here and it's brighter here so that Darkness isn't being keyed the same way is the area we selected so the area we select is good so maybe we select this this lighter green color and it's getting removed properly but the darker green is kind of still there a little bit and we're also having the wrinkles coming through and we still have the microphone so if we look at it also we have this green spill on the character which is not being handled very well either so if we go further and we just look at what the alpha of that thing looks like we see where all our problems are coming in the black is good because we've removed this area but all these area that's not supposed to be here that's not our main character that's a problem so obviously we have the tie so there's holes in the middle of our character we also have uh this left side here that needs to be transparent but it's not and then obviously the wrinkles and the object there so this is what we're looking for we're actually looking for an alpha that looks like this and that's not what we have so before you start your shot you want to identify all those problem areas you want to think about how you're going to go about solving them and we've already done that we've kind of identified them but we want to just you know think about it mentally how this puzzle is going to be solved so this is the way I would solve this shot and probably would have to be solved this way so we could separate it into two keys here so we could put basically one keyer selecting this color and another one selecting this color and we can actually blend them across each other with a key mix so that's what a key mixing is it's taking two different results and blending them together with a roto shape uh we could also use a garbage mat so a garbage mat again we went over quickly in the vocabulary I think but basically you just wrote out objects that aren't supposed to be there that aren't keyable so we can't remove that microphone with a key because it's not green so we just need to rotoscope around it and basically remove it from our Alpha so we do something like that just cut it off and say okay that's just garbage so that's what that is next thing we want to do is we actually have to garbage mat off the feet so if we have a scenario where there is ground and the character's feet are not over the green screen or there's really bad wrinkling this picture might not demonstrate it completely but if let's just say these wrinkles you can't key them out because there's too much black we don't want those wrinkles in our final image so what we do is we actually rotoscope the feet off of the character and then we use another rotoscope to bring back uh the just the bottom of the feet like this which and this is called a hold out so the red line is part of our garbage mat where we tell uh nuke or whatever software we're using to cut off that piece of the alpha and then after that we can do another Roto and just put it back in the pieces that we need uh also we'd want to do a hold out another one of these holdouts just protecting uh and solidifying that Alpha over the tie so we would say don't punch a hole in the green of these areas over the tie and that's basically uh how we would attack this so that's kind of combining multiple keyers and thinking about how we're going to do this and uh yeah so yeah that's pretty much a lot of times keying euroscoping they go together it's not just one or the other they're both trying to achieve the same result which is just getting a clean Alpha channel to Define uh what part of the image we're going to keep or remove so if we want to break down that idea a little bit further just to see it more visually uh even than what we saw um I'm just going to show you guys an example here of the idea we talked about with key mixing so if we want to look at on an uneven green screen and here we are using two keyers but sometimes we have multiple Keys you could have eight nine even ten keyers that solve different areas of your key this is an easier example we have two but we see uh key one on the right side here if we select that color with one of our keyers we see that it goes black and in solving it pretty well but it's not solving the rest of the image and we have key two over here where we use another key or node and we're going to get to the nuke nodes later so don't worry this is just the theory but we see Q2 we're selecting that color and it's punching a hole so we have the black which is good but neither one of them are solving the entire image so we need to use key mixing which means combining two or more Alphas together and remembering that black is transparent and white is solid so if we were to combine these two we use a roto shape we can actually do this in a node in Nuke so we would say we want to keep this area from Key one and keep this area from Key two and just combine those and now we have a key mix Alpha and that's solving this uneven green screen so we see that we still have the microphone and the wrinkles and the holes in the guy but we've at least solved the first part which is just getting that uneven green screen keyed out and we have a clean result behind our person so we want to solve the areas that the key here is not going to solve for us so we're going to use the garbage mats to remove areas that can't be removed by King and hold out mats to hold out or maintain the areas of the key that we need to keep so let me oops go back here and so here's our garbage mats we're going to garbage mat out the microphone so we're just a rotor shape will stencil it out and stencil it out from the ground here and then we'll have an alpha like this but now we've lost the feet of the character and we still have the holes in the center so we'd go back and we would actually rotoscope around the feet and we would need to animate the rotoscoping for as long as the shot Is So that obviously is a bit of manual work that we have to do but we restore it like this so that's our rotoscoping and then our final mat looks like this so we have it the character repaired uh and our final Alpha and finally we would combine it into the image so it's copying into the image um yeah so we'll we'll learn about that so if you guys don't know how do I copy an alpha into a picture what does that even mean um we'll go into that in Nuke and uh you know it's gonna go from the beginner to the complete advance of King so uh we'll go over that um one thing we'll do uh and the last thing we need to solve on this is we need to remove the Green from the edge of our character uh before we pre-multiply it so before we apply our cut out and merge it over the background we just want to do a color correction on just the edge of this character so because we've actually created this Alpha we can actually do in a road so we can shrink it Inward and we can actually create another Alpha that we're going to use just for color correction which is called an edge matte so if we go here we use that Alpha but we shrink it in just a little bit we can create uh basically an alpha that's just this white Edge that we see here and we can actually blur it just a little bit and you'll have an alpha that's if we're just looking at the white on this example we're going to use that to remove the Green from the edges so we see here the green is just on that edge so we've lined up our new Alpha that we've created this Edge matte and we're going to use it to counteract the green so here's our image we'll use that Alpha that we've just created and just remove the Green from our picture and you see that we not get a nicer result we darken it uh maybe we add the opposite color of green um whatever works and we'll look at different ways to do that which is called de-spilling so now we have a clean result we also have that Alpha stored in this picture if we go back this Alpha is still in there so we have a clean result of the guy and then we can pre-multiply so that would apply our cut out or apply the alpha that we created and we'll cut out our character and put him over the background like this

Channel: Compositing Academy

Views: 11,727

Keywords: keying, greenscreen, alpha, keying in nuke, nuke keying tutorials, nuke, compositing, digital compositing, hair keying, edge keying, bluescreen

Id: aeJTBwIudSs

Length: 13min 15sec (795 seconds)

Published: Tue May 16 2023