Original subtitles

In this clip, we are going to talk about operators.

Operators are used to determine how two images,

when merged together, will appear.

Each operator will then calculate the pixels

differently based on the matte used.

The most common operator is the over operator,

which is found within the Merge tool.

So let's have a look.

So if I double-click and I browse up to the top of the property bin,

we can see operation over.

Now I use the word operation and operator interchangeably,

just in case you're wondering.

So if I scroll down to over,

we can see all the different types of operators that are available to us.

Now for this particular clip, I am going to focus on just four operators,

and those are the most common ones used for green

screens and for changing alpha channels.

So back to my example here.

We have the green full screen constant and the full screen checkerboard.

Now because the checkerboard is the A input and it's full frame,

it will cover my green content.

So it's not available under here.

So it's totally hidden.

Let's go over to the Merge tool.

So we already know that the merge tool has multiple different operations.

So what about individual tools?

Now there are some individual operators that are available.

These are the three that we will work with today.

There's one more that is not available on its own.

So why would I work with an individual tool versus the Merge

tool that has everything inside of it, or so it seems?

If I double-click on the Merge tool and double-click on,

say, the matte mask tool,

we see that they're pretty much the same tool with the exception of

the operation which defaults to mask or over.

So the real benefit to this tool is that it's already pre-named

with the operation that we're going to do with it.

In most cases,

I like to use tools that are stripped-down or don't

have as many functions in them.

The reason for that is the more functions a tool has,

generally the more processor-intensive it is.

But in this case, they're somewhat interchangeable.

So let's go into our next example, which is the mask operator.

So here I have a circle and the alpha for the circle,

and that's going through the A input of the merged mask tool.

So here I have a full-screen green image,

and I'm going to mask it out by the alpha.

So the mask says wherever the alpha is 100 percent white,

make the B input visible; and where there is no alpha at all,

don't make it visible at all.

Next let's go on to the minus operator.

So the minus operator here, I have a blue square and another blue square,

but you'll notice that they are overlapping.

So what the minus does is it will actually take the A input

and it will subtract the B from the A.

So what should it do?

It should probably take a chunk out of my A square here.

So let's take a look.

And it did.

So not only did it take a chunk out of my A input square,

but it also took a chunk out of its alpha.

So it's subtracting from the A input.

Next let's take a look at the multiply operator.

So I have a blue square and a red square.

And keep in mind that it does math by multiplying.

So one times one means 100 percent visible.

One times zero means zero percent visible.

So the red box has absolutely no blue in it,

just as the blue box has absolutely no red.

So let's take a look at what it does to our RGB.

Nothing is visible,

and that's not surprising and that's because there's no

blue in the red or red in the blue.

Now let's take a look at our alpha instead.

So in our alpha here, we can see that where they are overlapping,

the alphas were both one.

Where they weren't overlapping, there was no matching alpha so to speak.

So it was by itself over here.

And when I multiplied it against this image that was slightly down lower,

it says there is no alpha there.

So this essentially was one times zero, which means zero percent opacity.

Moving on to an example.

So here I have a blue constant and I have a noise tool.

So let's just shuffle an alpha so now both images have an alpha.

Go back to full color.

And the multiply works really good for placing darker

images on top of lighter images.

So in this case it has dropped the 100 percent white.

And as we move away from white, it will make the darker colors more visible.

So it's great for stuff like AO and for shadows and so forth.

So anything that's darker that you want to make darker on a lighter background,

works very, very well.

On to the last one and that is the plus.

So again I have squares.

So here is one square,

here's two squares and they are going to add those values together.

So let's take a look.

So plus operator.

And if I take a sample, so Control + Shift + left mouse button drag,

you can see that it has added one in the green,

one in the blue, but double in my alpha.

So my alpha was already one, so it has now doubled my alpha.

So RGB, totally cool, it's totally cool to have values that are above one.

But alpha, not so much.

So alpha values fall between zero and one.

They can be zero or one, but definitely not above one.

Nothing is more visible than 100 percent visible.

So please try to remember to keep the plus operator

primarily for your RGB images.

So now that we know the basic operators for the green screen workflows,

let's review how to use them in more depth in our next clip.