Original subtitles

In this clip we're going to look at despill with expressions.

So expressions can be used for despill by forcing 100% of the color

to be shifted or removed entirely from the image.

Other, more complex variations of these expressions can be used,

and that is so that you don't necessarily remove 100%

of that particular color or channel.

But we're going to be just focusing on the basics of

expressions for this particular clip.

So let's take a look at our script.

Here is our image sequence, and I'm going to add an expressions node,

and the expressions node is basically a lot of math,

and we can apply it to one or more of the channels.

Now because this is a green screen, we want to to focus on the green channel,

so let's take a look at a couple of different

expressions and what exactly they do.

So here's the first expression.

And you might want to keep these handy 'cause honestly,

sometimes they can be a little bit hard to remember.

So the first one says that if the green color,

or green channel, is greater than the red channel,

set the green value to the same as red.

So let's take a look at what that does for our despill.

It's doing pretty good, there is a little bit of green in here,

still, in the backing region, but it's not bad,

it's fairly close to our character's hair color.

But we're going to see if we can get it a little bit closer.

Now let's just double-check that her skin tone and her

hair overall is staying the same.

So that was it before, that's it after,

and it's not majorly changing anything that we don't want it to,

so that's really great.

The next expression that we're going to look at is the following.

So if green is greater than blue, set the green value to the same as blue.

So let's take a look.

So here is what we talked about with being very aggressive with our despill.

So it has changed her color overall, especially her skin tone,

so let's take a look.

So this is it before, this is it after, so she's very,

very red in her skin tones, even her highlights have turned quite red.

So this is a very aggressive despill and it's definitely

not usable for this particular image.

It may be useful for other images, but this is a no-go for this example.

So now let's take a look at our last example,

and that is comparing the green value to the

average of the red and blue channel.

So this one's probably the most complex of them all, again, keep them handy.

Let's take a look at that output.

So this one's looking the best of all three.

Again, we can see that the hair color is very close to what it is over here.

So let's just sample that.

So.

675 and three, so it looks actually further off than what I expected,

so this is a little bit different, but again,

fairly close considering and a lot closer than our first example,

which, in comparison, looks quite green.

So we can see that variation.

That's where the despill is really changing and there it's more even.

And again, it's not changing our character,

the core of our image,

so this is probably the best example to go with for

the despill of the backing region.

So now let's take a look at what this does with a blue screen and how we

can apply the same principles to our blue screen image.

Now, the same expressions can be used for the blue screen despill.

And that is basically by swapping the expression

placement of the green and the blue channels.

So in this example,

the same expressions unfortunately are a little less

successful for the blue screen image.

So let's just take a look.

So if I took a look here, here is the expression,

we've moved it down to the blue.

So it's pretty much identical.

Here and here we've just swapped out blue for green.

Let's take a look at the results.

So if blue is greater than red, set the blue to the same as the red channels.

So there we go.

So the despill's acting not bad back here,

however, look at all the blue that we still have in her hair.

So this expression is not catching all the blue in her hair.

However, we are for the most part keeping the core of the image,

so that's good, however, this despill is not usable as is.

So let's take a look at the second one.

So if the blue is greater than green, set the blue to the same as the green,

so they'll level.

Here, it's doing even less of a despill,

again, we're still fighting with the colors up in here,

so unfortunately, when it's pre-multiplied,

she's still going to have a gray slash, I guess blue halo in here.

So that's also not going to work.

And the last one, again, same as the green screen, so here's our expression.

And again, similar to that first one, here's the first one,

almost a little bit closer than this one,

it's quite teal in the background, but again,

this blue in here is not working.

So even though we've used the same expressions,

but just swapped it out for blue instead of green,

they're not very successful for this particular blue screen,

especially in the fine wispies around the edge of her head where the fringe is.

So these techniques might require the addition of the huecorrect and despill

matte workflows in order to really take the despill to final.

So these workflows will be reviewed in the next few clips in this module,

and we're going to really be able to fine-tune these edges so that we can

integrate them properly into our final background image.