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In this clip, we are going to talk about operators.
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Operators are used to determine how two images,
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when merged together, will appear.
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Each operator will then calculate the pixels
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differently based on the matte used.
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The most common operator is the over operator,
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which is found within the Merge tool.
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So let's have a look.
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So if I double-click and I browse up to the top of the property bin,
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we can see operation over.
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Now I use the word operation and operator interchangeably,
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just in case you're wondering.
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So if I scroll down to over,
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we can see all the different types of operators that are available to us.
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Now for this particular clip, I am going to focus on just four operators,
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and those are the most common ones used for green
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screens and for changing alpha channels.
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So back to my example here.
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We have the green full screen constant and the full screen checkerboard.
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Now because the checkerboard is the A input and it's full frame,
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it will cover my green content.
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So it's not available under here.
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So it's totally hidden.
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Let's go over to the Merge tool.
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So we already know that the merge tool has multiple different operations.
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So what about individual tools?
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Now there are some individual operators that are available.
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These are the three that we will work with today.
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There's one more that is not available on its own.
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So why would I work with an individual tool versus the Merge
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tool that has everything inside of it, or so it seems?
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If I double-click on the Merge tool and double-click on,
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say, the matte mask tool,
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we see that they're pretty much the same tool with the exception of
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the operation which defaults to mask or over.
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So the real benefit to this tool is that it's already pre-named
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with the operation that we're going to do with it.
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In most cases,
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I like to use tools that are stripped-down or don't
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have as many functions in them.
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The reason for that is the more functions a tool has,
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generally the more processor-intensive it is.
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But in this case, they're somewhat interchangeable.
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So let's go into our next example, which is the mask operator.
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So here I have a circle and the alpha for the circle,
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and that's going through the A input of the merged mask tool.
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So here I have a full-screen green image,
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and I'm going to mask it out by the alpha.
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So the mask says wherever the alpha is 100 percent white,
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make the B input visible; and where there is no alpha at all,
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don't make it visible at all.
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Next let's go on to the minus operator.
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So the minus operator here, I have a blue square and another blue square,
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but you'll notice that they are overlapping.
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So what the minus does is it will actually take the A input
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and it will subtract the B from the A.
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So what should it do?
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It should probably take a chunk out of my A square here.
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So let's take a look.
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And it did.
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So not only did it take a chunk out of my A input square,
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but it also took a chunk out of its alpha.
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So it's subtracting from the A input.
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Next let's take a look at the multiply operator.
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So I have a blue square and a red square.
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And keep in mind that it does math by multiplying.
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So one times one means 100 percent visible.
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One times zero means zero percent visible.
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So the red box has absolutely no blue in it,
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just as the blue box has absolutely no red.
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So let's take a look at what it does to our RGB.
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Nothing is visible,
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and that's not surprising and that's because there's no
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blue in the red or red in the blue.
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Now let's take a look at our alpha instead.
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So in our alpha here, we can see that where they are overlapping,
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the alphas were both one.
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Where they weren't overlapping, there was no matching alpha so to speak.
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So it was by itself over here.
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And when I multiplied it against this image that was slightly down lower,
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it says there is no alpha there.
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So this essentially was one times zero, which means zero percent opacity.
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Moving on to an example.
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So here I have a blue constant and I have a noise tool.
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So let's just shuffle an alpha so now both images have an alpha.
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Go back to full color.
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And the multiply works really good for placing darker
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images on top of lighter images.
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So in this case it has dropped the 100 percent white.
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And as we move away from white, it will make the darker colors more visible.
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So it's great for stuff like AO and for shadows and so forth.
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So anything that's darker that you want to make darker on a lighter background,
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works very, very well.
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On to the last one and that is the plus.
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So again I have squares.
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So here is one square,
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here's two squares and they are going to add those values together.
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So let's take a look.
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So plus operator.
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And if I take a sample, so Control + Shift + left mouse button drag,
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you can see that it has added one in the green,
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one in the blue, but double in my alpha.
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So my alpha was already one, so it has now doubled my alpha.
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So RGB, totally cool, it's totally cool to have values that are above one.
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But alpha, not so much.
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So alpha values fall between zero and one.
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They can be zero or one, but definitely not above one.
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Nothing is more visible than 100 percent visible.
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So please try to remember to keep the plus operator
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primarily for your RGB images.
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So now that we know the basic operators for the green screen workflows,
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let's review how to use them in more depth in our next clip.
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