Original subtitles

In this clip we are going to be taking a look at Keylight

keying fundamentals so let's get started.

Before we begin our keying let's take a look at the Keylight in detail.

Now we have several different inputs for our keylights.

We have BG, OutM, InM and the Source.

Now in this particular clip we will be focusing on the source input.

The other inputs are primarily used for more advanced keys so

that includes combining different alphas,

color correcting the edges and just refining them in detail and doing despill.

Let's take a look at how to setup this particular tool.

By default,

Keylight generally likes to have an alpha channel that

is either 100% black or 100% white.

If we have a 100% black alpha the Keylight will add a 100%

white alpha before we pull the matte.

Now what of we have a preexisting premultiplied image before pulling our key?

Well,

Keylight gets very confused by this area being 100% black and when we pull

a key it thinks that it should be part of the alpha.

Now there are two ways to resolve this.

We can either pull the existing key like we just did here and use a mask

to cut out that backing area that it was very confused by or we can use

the crops method inside of the Keylight tool.

So let's go back to the initial premultiplied image and see how to set that up.

So inside the Keylight, if you go inside of the properties bin here to the right,

scroll to the bottom.

You will find a toggle that we can open and close and it's called Crops.

Under Crops there are several different X and Y methods,

let's stick to the color to begin with.

Under edge color we are going to sample the greenscreen.

Ctrl+shift+left mouse button and drag and it samples the green.

To deselect,

Ctrl+shift+click and we will turn off that picker so it doesn't get

confused and we don't accidentally sample again.

Now that we have sampled this color we can fill in our black backing area.

So I'm just going to take the left hand side and pull this

in just a little bit and we're going to pull that back

because I think we went too far.

There we go.

And now we're going to take the other three sides and fill those as well,

which we have already done in this particular tool.

So now that our backing region, or our fake backing region,

I guess, is all green, we can pull a key.

Here we go and our alpha looks a lot better.

So those are the two different options that we have.

We can also go back to the color that we had here before.

Instead of color we have a couple of different options.

You can repeat the edges,

you can reflect the edges and you can also wrap the edges.

Now because our character here reaches the edges of frame that won't work

for this particular example but it may work for your individual shot so

those are the different options to play with.

Now that we've fixed this particular area let's go back to a full greenscreen.

So here's our full greenscreen and we are going to begin by pulling a key.

Again,

let's zoom in to this area particularly where the hair is because

that will be fine detail and we are going to select,

under the screen color, the greenscreen,

so Ctrl+shift+click and that draws a box and what this box

does is it will take the average of all the colors selected

and make that the sample color.

Now as previously noted,

wherever we sample and the pixel match it will turn the alpha

black and wherever they don't match at all,

it will turn the alpha white and where they somewhat match it

will be somewhere in between the two so,

a gray value.

This initial key is looking pretty good for the most part.

We have some information in the backing region.

Those values are below.

05 or 5% so it should be okay but let's see if we can't get a better key.

We can go back to the picker and we can continue to try to sample

different areas so we can sample down here at the bottom and we get a

better alpha here on the edge however it actually destroys this top

part up here so I think our first key was working a little bit better

so lets go back to this region and back to what we had previously which

looks a lot better.

So as always, we do want to take that LUT and look at our details,

refine it if need be because we know that these areas are already below.

05 we're going to leave them for now and really

continue to refine our alpha channel.

Next, let's take a look at how to do that.

We are going to look at the Screen Gain and we have a preexisting

alpha channel that I've pulled previously and we're going to look

at this value here so the Screen Gain,

what it does is it will increase or decrease the contrast of the alpha.

Now unfortunately,

this has some drawbacks so let's take a look at that default value

which is one and go in nice and tight here to our edge.

We can see here that dropping the value adds more information to our

backing region which we don't want and increasing the value will

resolve the information that we have in the backing region here that we

don't want however if we push too far, look what happens to our edges.

So there is better ways to resolve this so we're going to leave the Screen

Gain at one for now so that we can take a look at them.

Next we're going to take a look at the Screen Balance.

So again,

a preexisting key that we had before and the Screen

Balance will balance between the red and the blue channels

and the red and blue colors here.

That is because we initially had a greenscreen so this can help

with the filling in the alpha channel over here,

so in our core, so let's take a look at an example.

Here we have partially our RGB image and partially our alpha so we're

going to zoom in to the skin tones and the core matte over here and

dial back and forth the Screen Balance.

If we drop the Screen Balance you're going to notice that it

starts to fill in my core matte so over here on the left hand

side it's filling in my core matte.

Now unfortunately, look what it's doing to my RGB image.

As I drop the Screen Balance it is starting to change my skin tones to red

so we've removed too much of that green reflection and while it's helping

the alpha channel it's actually destroying my image so bringing down the

Screen Balance a little bit is good,

it moves some of the extra reflection in our character but bringing

it down too far to really help our core is not the best method so we

can find other ways to resolve that.

I'm going to change the Screen Balance to three and move on to our next example.

So again, another preexisting alpha.

We'll go into our alpha channel and we're going to take

a look at the Clip Black and White.

So,

similar to what we had up here at the top with the Screen Gain where

it will make our alpha channel more contrasty,

anything under the Screen Matte will actually only affect the alpha so it

doesn't affect the RGB until the image has been premultiplied.

So the Clip Black will allow us to really dial back on the,

so Clip Black, let's go down here,

and it dials back again on all the artifacting from the background.

Don't push it too far because eat starts to eat away at

those edges so just a little bit.

I'm going to stick to around.

1, give or take.

That might be a bit too far but we can resolve that in a minute and the

Clip White allows us to really get those details in the core so dial

down the Clip White and fill in our core.

Now that has issues as well so if we bring down that Clip White

too far look what it's doing to those nice,

fine edges so we are filling in the core matte so that's the hard

matte inside of our key however we are losing that nice edge

detail so there is a way to resolve that.

Let's take a look again at a preexisting alpha that I have pulled.

We've already adjusted our Clip White and Black values.

Let's just dial down those Clip White just a little further to fix that alpha

and we're going to bring back some details in our edge work so with the Clip

Rollback we can reintroduce the eroding that we had in the Clip Black and the

hard matte that we started to add to our core.

So here we go with the Clip Rollback and the more that we push it we can see

that it's really starting to add back to our edge work.

So this was the default.

Here we start to have more soft edges which is really nice.

We're pulling back on that core, reintroducing some edges.

This is fine because again, it's low values so it's actually working very nicely.

So Clip Black to get rid of a lot of the artifact in the background.

Clip White to fill in our core and then Clip Rollback,

just to add back some of those details.

Now you will notice that we have some hard edges that have

been introduced by that Clip Rollback, we'll exaggerate that here,

and we can fix that by adjusting the Screen Softness.

So again,

here is a preexisting key that we have and lets dial in the Screen Softness.

The Screen Softness will allow us to blur that alpha ever so slightly.

We don't want to push it too far.

If we push it too far we start to lose those edges so just

enough to soften the edges of our matte and let's take a look

at what that looks like premultiplied.

So here is our nice edges, before and after.

The good news is that it's doing a little bit of a despill.

We're not losing that edge information.

We're retaining, for the most part, a lot of our edge work so overall,

for a very quick key, this is working very well.

Now there are extra elements that we can use to refine this key even

further but this is the basics of the Keylight.

A quick overview of what we learned in this particular clip.

We reviewed the different inputs of the Keylight and we

primarily just worked with the Source inputs.

We worked with how to pull a key and that of course is by

sampling this value up here in the picker.

We looked at refining that alpha.

So we stayed away from the Screen Gain and the Screen

Balance we only just changed a little bit.

For the most part we worked with the Clip Black and

White to add more contrast to our alpha,

refined that clipping with the Clip Rollback to make softer edges

and Screen Softness so that we can soften our edges of our matte

before premultiplying the image.