- [Instructor] Nuke has a unique channel management system
where you can have up to 1,024 individual image channels.
These channels are grouped into layers
very much like Photoshop layers and channels.
The whole idea, is that any node can access these layers
and channels without running a separate data pipe to it.
Let's see how it all works.
Now I've just started Nuke, and there's no channels defined.
So the default list here, shows you rgb, rgba, and alpha.
These are the only channels or layers
that are defined when you first start Nuke.
Now this other layers pop up here, these are layers
that have been defined but not yet populated.
Once they've been populated with some data,
they'll pop over into this list, so, let's see that.
Here I have an EXR file that has
several layers and channels defined.
So if I enable that, Nuke reads the EXR file,
spots all those layers and channels,
and puts them up here in the layers list, there we go.
So for example, we can say, show me the reflection layer.
Or, we could say, show me the specular layer,
or show me the masks layer.
Okay, let's go back to rgba.
Now we can use the LayerContactSheet
to see all these layers at the same time.
So, come over here to the Merge tab
and go to LayerContactSheet, I'll hold down the Shift key,
so I get a branch connect, because I'm going to show you
something really interesting about this in a minute.
Okay, so let's hook up to the LayerContactSheet.
Now we can see all of the layers, now it's more helpful
if you'll come over here to the Property panel
and turn on Show layer names, okay, much better.
Let's hit the space bar and fill the frame with this.
So here was the rgba layer, now that's a four-channel image.
We can see that, by going to the Viewer and saying,
show me the alpha channel and sure enough,
there's something in the alpha channel,
none of the others have anything in the alpha channel,
so they're three-channel images.
Let's put the Viewer back to rgba.
Now here's the masks layer.
Let's push in a little bit on this guy,
maybe you can see the word masks down here, okay.
Now, this is not an rgb image, this is a layer of masks
and each channel is a separate mask.
So here's the rule of Nuke: the first channel,
whatever it's named, will be put into
the Viewer's red channel, there's my grunge mask,
the second channel will be put in the Viewer's green channel
and there's my occlusion pass, and the third channel,
will be put in the Viewer's blue channel,
and there's my shadow pass.
So there you go. That's the rule of Nuke.
Let's re-home the Viewer
and hit the space bar to restore normal display.
Now here's something interesting.
In the data stream coming out of the LayerContactSheet,
it has clipped out all those other layers and channels.
It's put them all into the rgba layer,
so if I come up here to my layers list, they're gone.
However, they still show up in the other layers,
there they are down here.
But they're not available in this data stream.
If however, I come back to my EXR file,
suddenly they're back.
I brought in a little illustration to help tell the story.
Switch over to that and let's hit
the space bar to fill the entire frame.
And let's push in a little bit here, okay.
So this sort of illustrates
all the channels and the layers idea.
This is the rgba layer that we've seen
and it has four channels, R, G, B, A.
Here's the specular layer,
but it only had three channels, R, G, B.
Same with the reflection.
Now here's the masks layer and it has three channels,
but, those channels are named grunge, shadow, and occlusion.
In other words you can name a channel anything you want.
It's just that Nuke is going to drop them
into the Viewer in one, two, three order, okay.
Okay, alright, let's go back to our story here.
Okay, so let's recap what we've seen.
This pop up is the layer that will be put into your Viewer,
into the rgba channels of the the Viewer.
So there's our reflection.
Now if this were a four-channel image, it would also throw
the fourth channel into the Viewer's alpha.
This pop up is what individual channel
will be seen in the Viewer's alpha.
So I could say, put the alpha there, check the Viewer,
or I could say, put the grunge pass in there.
And now if I look at the alpha channel in the Viewer,
there's my grunge pass, okay.
So reflection and rgb, grunge in the alpha.
We'll put the Viewer back to rgb.
So now the question is,
how are these layers and channels created?
Well we saw one method,
and that was by bringing in the EXR file.
As soon as we loaded it in, as soon as Nuke read it,
it spotted all those channels and layers
and thoughtfully added them to our list.
But there's another way, and that's to use the New command.
But that's another movie.
The channel system in Nuke, dramatically reduces
the number of data pipes running all over the screen,
making large Nuke scripts much cleaner
and easier to read than other compositing programs.