Original subtitles

In this clip we're going to take a look at key mix and channel merge

nodes and that's for combining different alphas.

Now the following are some examples of workflows for combining multiple mattes.

So let's take a look at our script.

So if we take a look at our workflow down here,

we're going to notice that we have some red reference nodes and a green one.

Now those that are labeled in red are not recommended and

those that are labeled in green are.

Now the following matte combine methods are meant to

isolate and display only the most successful portions of

each input for the alpha matte.

We're going to take a look at some other examples

in the second part of this clip,

but let's take a look at how to isolate the best parts of our keyers first.

So in this example we have two different keylight

tools that are pulling fringe mattes.

Now they are made very different on purpose just so we

can see the differences between them.

Now by no means are they final mattes; this is for display purposes only.

So here's the first fringe matte 01,

here's fringe matte 02 and we're going to combine the best of both worlds.

So I want to isolate one of the fringe mattes over here

and the second fringe matte over here.

To do that I have taken a merge tool and through the

mask input attached a roto shape.

So what I think this is going to do is isolate my A input

over here inside the matte and then reveal the B input

over here so let's take a look.

So here's my merge tool and at first glance, it's doing what we want it to.

So here is my fringe matte 02,

isolating over here and fringe matte 01 on the left-hand side.

However, if we take a closer look, it's not quite doing what we want it to do.

So here is the matte 02.

Look at those edges very quickly, very carefully,

and it's growing them when we merge it together so instead of actually just

isolating A over here and B over here or rather fringe matte 01,

fringe matte 02,

it is actually combining the A and B inputs over here on the right-hand side.

So it's not isolating those mattes like we want them to.

So let's take a look at another example.

So here I have fringe matte 01, fringe matte 02,

and I'm taking a roto shape and I'm going to isolate it.

So here's the left-hand side, invert it.

Here is the right-hand side.

So that's what we want.

So we're going to combine the two of the perfect

sides together so there is left, there is the right,

and merge them.

Now at first glance, we finally got what we're looking for.

So let's take off that overlay and take a look at that fringe matte

02 and it's not changing the right-hand side,

which is great.

So this appears to be working,

but we have a very harsh line here in the middle where the two images meet.

So let's add a blur tool.

Now unfortunately,

with this method it is adding a seam in the middle and

the more that we increase that blur, the wider that seam gets.

So any sort of blur whatsoever starts to add that seam between the two of them,

which doesn't really help our cause because we need to blend

those two images or alphas together seamlessly.

So we're going to take a look at a third example and that is the keymix.

So the keymix works a little bit differently.

What the keymix does is it's going to take a fringe matte 01 and

then it's going to combine it with fringe matte 02.

So wherever A input is and the mask input is is going to reveal A.

So let's take a look at that alpha.

So here's my alpha.

It's going to reveal A over here.

Wherever this alpha matte is not present it will reveal B so let's take a look.

Here's our keymix.

There is the two of them combined together.

Again, very similar to our last example.

That harsh edge in the middle.

Have our list turn on our blur and it doesn't matter how

much we increase or decrease that blur,

we don't have that matte line that's appearing in the middle.

So this is a really great way to combine multiple different

mattes together and it allows us to take the best of both worlds

while seamlessly blending them together.

So now let's take a look at the channel merge and some different options for it.

So in this case I want to combine a core and fringe matte together.

We haven't necessarily modified them or we can modify them together.

So let's just say that the entire plate of the fringe is working so here is our

fringe and our entire core is working so there's our core.

Again similar to our last clip,

that core is dilating out further than our fringe so we are going

to erode and blur it slightly and merge the two of them together

and it's combined them together really, really well.

Now let's take a look at a different tool which is the channel merge

node and combine the same kind of workflow here,

so the same erode, the same blur.

Let's take a look at the alpha and it is identical.

So let's take a look at that difference operator.

Difference operator says that there are no difference between them so

the operations or at least the outcome is identical.

So why would we want to use one over the other?

Well, if we take a look at the merge tool,

it has multiple different options to it.

So it's going to combine rgba with rgba versus the channel merge,

which is a little bit more of a simplified tool.

So here by default we'll go to our rgb and well it says rgba,

but is it really combining rgb?

Let's take a look.

So here is rgb and here is 1, here is 2, and it is not.

It is actually only combining the alphas versus here rgb,

rgb, and it's combining the rgb and a together.

So what would be the benefit of this?

Well,

we don't really care about the rgb because we will despill

it separately and then pre-multiply it,

but rather is just the efficiency of that tool.

So the channel merge will only by default combine the two alphas versus the

merge operator or merge tool with the over operator rather,

is combining rgba.

So that makes the channel merge tool generally a faster tool for processing.

It's also really easy to recognize because it is a channel merge.

We recognize it for merging together specific channels and therefore we

won't get it confused with the regular merge over.

So as a brief summary of this particular clip,

we reveal that the keymix is the favorable tool for combining

portions of multiple mattes and the channel merge is the preferable

tool for combining two alphas together.

This is primarily because it is recognized easily as a tool for combining

channels and by default combines the alpha channels.