Nuke 4 beginners - A Deeper Look l Nuke Alpha Channel

hey guys it's Shonda hunt here and for a quick second I want to talk about Alpha channels so we know we discussed earlier in one of our lessons we talked about all the channels that are available we most often work with the RGB channels as they are the channels that combine create the images that we see as we can see here we have the RGB and that stands for the red green and blue channels but what about the alpha Channel why is it okay for an image to have an alpha Channel sometimes and sometimes it doesn't the purpose of an alpha Channel is so that we can layer an image on top of another image so right now I just want to show you an example of this we have this image here and we can see that it does not have an alpha Channel because the only channels available here are displayed using these symbols these color boxes that are attached to the image the read note so we have red green and blue if I try to layer this image on top of this image which we see I get something that's transparent and that's because this read note needs a solid Alpha channel in order to layer properly on top of this image think of a channel as a container that contains image data so it's okay for some channels to be empty but when you want to layer things on top of each other you actually need a solid Alpha Channel there are several ways to create an alpha channel before we go over those though let me show you the opposite here we can see that this render actually has an alpha Channel because it has the RG and B red green and blue which represents the red green and blue Channel and then this white box here represents the alpha Channel now this image has an alpha Channel and if we go to our channels menu or if we hit a while our Mouse is in the viewer we can see that Alpha Channel if we view our other read note which doesn't have an alpha Channel we're still in the alpha Channel set and we don't see any Alpha here so if we try to layer this image on top of this image we see that that image layers over that image um the background office image solid it's not transparent like we have here and that's because for this channel I mean sorry for this read note and for this image we have an alpha Channel so when you want to layer things this Alpha your your operations are calling for this solid Alpha Channel um when it's deciding how to layer things on top of each other so you can see the images but when you in terms of starting to layer and work with these images um you will need that Alpha channel so I will show you here with the shuffle note I actually use the shuffle node and I'll just do this again so let's create a new Shuffle just to show you so I'm using this Shuffle note and I'm going to delete my Alpha Channel so if you hover over it you see it says it gives you an um a description so I've toggled off my Alpha and now when I try to view that same merge node we have the same thing that we have here where the image is transparent and that's because there's no solid Alpha there are operations that you can use where you might not need a solid Alpha but for merging things on top of each other you will need that solid Alpha so we can go ahead and turn this off and I'll show you ways to create that Alpha Channel if you don't have one now one of the reasons that we're commonly Keen green screen footage is because we're trying to extract that Alpha channel so that we can layer whatever was shot in our green screen on top of the background image that's also why we're used why we often use Roto mats we're usually using a roto to cut something out and as you can see your Roto is set to Alpha by default because usually when we're wrote on we want to cut something out and we want to layer that on top of something so if I just go ahead and roll this chair part of the chair let's say I want this part of my chair and then let's view our Alpha Channel through our Roto note we see now we have an alpha so we can use this Alpha channel that we created for different things we can use it for color Corrections we could use it to extract parts of the chair so if I go ahead and I say I want to cut that part of my chair out let's change this operation to mask so now we only have the chair and now let's say I want to merge that on top of this robot now we see we have that merged on top because we have that Alpha Channel coming in from our Roto no okay so let's look at ways to create an alpha channel so you can create an alpha Channel through a roto you can create the alpha Channel by extracting a matte basically which is you often use with the Roto or pulling a key you can also just add a roto to I mean add an alpha channel to your image right in the read note settings so if you double click on the read node the property settings will pop up for that read note and here we have the option to turn on an alpha channel for that layer and let's look at what happens down here once we turn on that Alpha Channel now we see we have the indicator that we have an alpha channel in this layer and if we click on that layer we now have an alpha channel so now if we try to merge that layer on top of our robot as we did before we see that it's solid so I'll just turn it off so you guys can see so now that layer is able to fully layer on top of our robot because we have that solid Alpha Channel with I'll show you another way to add an alpha Channel so we have our read note we can also I use the shuffle note to remove the alpha when I turned when I checked on the black box here now if I wanted to um bring in an alpha Channel I could use the same Shuffle note so let's take a look here we have our transparent image and that's because I turned off our Alpha for this layer and now if I turn on my shelf Shuffle note actually if I go to my Shuffle note I can now um create an alpha so if I select this we now have a solid Alpha again and you can see that image layered on top of the other and if I turn that off we see that it's gone so it's very important to have salad solid Alpha channels when you're trying to layer images on top of each other otherwise you might get something transparent like this and you might be wondering why isn't my um image layering on top of the other image and that's simply because you don't have a solid solid Alpha Channel and you do need one anytime you're trying to use the merge over operation to layer things up so that's why Alpha channels are important that's why we're always creating Alpha channels Alpha channels are also tools so if I wanted to grade something I could use the alpha Channel as my mask input I could use any mask I could use one that's already coming in with an image so let's just turn on this for a second so we can see now I'm grading this image and my grade note is calling for the alpha channel of this read note so we see now if I connect my grade note to this mask that I created we'll see that that turns red so the alpha channel is also can be used as a tool for your matte inputs I hope that explains a little bit more about the alpha channels and how the layering systems work leave it leave some comments in the comment section if you guys have any more questions about the alpha Channel I just want to do a brief overview so you guys can understand a little bit more about why the alpha channel is important and why it's necessary when you're compositing because usually when you're compositing the you're always layering things on top of each other so you're actually always needing an alpha channel to do those Integrations

Channel: Post Series: A Nuke course by Shonda Hunt

Views: 2,983

Keywords: #vfx, #nuke, #compositing, #learning

Id: GA2PTYfl5d4

Length: 9min 26sec (566 seconds)

Published: Mon Nov 21 2022