Original subtitles

In this clip we will review the IBKColour and IBKGizmo.

Before we begin with that refinement let's go

through a couple of different terms.

You may have hear me talk about LUT.

So what exactly is LUT?

LUT stands for Lookup Table.

It means that we are applying a temporary curve or color correction to

our image and that can be our RGB image or our alpha.

Now that temporary color correction is not applied to our

final output so it isn't baked into our image and it's only

there for viewing purposes.

So why would we need it?

Well if we want to take a look at the details in our alpha,

for example,

if we want to see all the details in our white values we

can bring that LUT down and all the details in our

shadows we can bring that LUT up.

Now there's another term for that and the term is color slamming.

Color slamming really means pushing the extremes of our LUT.

So again, we color slam down,

see the details in our whites and color slam up to

see the details in our blacks.

Let's take a look at the IBKGizmo.

So by default we have it set to C-green and we can leave the color because

we don't have the pick selected so C-green overrides the color settings

here so don't worry about it being set to blue.

Next, we will take a look at the weights.

By default the weights are set to.

5.

The red weight really affects how the red channel is used to

calculate the opacity or hardness of our final alpha.

So let's take a look at what that looks like.

Here's our IBKGizmo and we are going to color slam down to see those

details and we are going to increase the red weight.

Increasing it will help our alpha and decreasing it will

almost erode away at it so let's increase it.

And it's helping, definitely helping.

Our values here are still quite low.

We do have an extreme LUT right now so that's partially why it looks

so extreme but its definitely made a difference in our alpha so

we're going to leave it up here at one.

Now let's take a look at our blue/green weight.

This can be somewhat confusing so when we have our C-green or

greenscreen we are adjusting our blue weight.

When we have a bluescreen we are adjusting the green weight.

So we can increase or decrease those values so we're going to increase

them because that really helped with our red weight.

It's helping a lot more, again, not 100% in our alpha and our core, it's around.

96 so a lot better than it was before so we're going to leave it.

Take a look at what's happening in our RGB.

And it looks like we've reintroduced that green spill or the

reflection from the greenscreen which isn't what we were looking

for so let's do the opposite extreme.

Let's go and change this value down and similar to what we've

mentioned in previous clips and that is blonde hair and light

colored items such as white hair,

white clothing or cloth tend to turn red when extremely

despilled so here we've pushed these values,

the weights too far and we have changed the white hair and the white

tablecloth to be too red so we're going to refine those further,

we've pushed them too far.

Let's modify them so that it's a happy medium of the both.

Here I've modified the red weight to approximately.

7 and this lighter here to approximately.

575 and is a lot better.

So we've rid of most of the green but we've retained the skin tone so

let's look at before with our original plate and after,

and our skin tones are staying the same,

maybe a sight one or 2% change but mostly we have rid of the

green so exactly what we're looking for.

However,

remember how we had to go to the extreme values of

the red weight and the blue weight?

Well,

it has changed our alpha back so we're a lot further

than we were when we first started.

Let's take a look at where we started.

This is where we started.

This is our modification.

It's a lot better but we still have holes in our alpha.

This is not uncommon.

If you are using the IBK setup to rid of the green spill and to also

create a matte you have to work with one or the other so we've rid

of the spill but we don't have the perfect alpha which means that we

have to introduce a core matte from another keyer or just a core

matte in general.

So we will have to combine multiple mattes to get the final alpha

plus premultiplied RGB image and that setup will be reviewed in

the more advanced clips and modules.

It's not unusual so don't worry about it if you don't get

that perfect alpha through the IBK setup.

It's totally fine.

Let's take a look at how to refine those details just a little bit further.

Our example here is a motion-blurred frame so let's go back to our

regular LUT and take a look at the newspaper over here.

We do have what's called the luminance match.

By default it is turned off so we're going to look at the alpha and

the luminance match will help add some information back to these

region so it's really good for a motion blur.

It's really good for hair detail and for things such as transparency in glass.

So if we increase this or turn it on it will add those

details back to the motion blur.

Let's sample those values.

Looks like it adds approximately six or 7% more to the alpha and

let's take a look at what that looks like in the RGB.

So back to the RGB and let's take a look.

So there's our RGB and turn on and off that luminance so, on?

Off?

It's very subtle.

We can barely see the difference but this is the type of modification

that we really want to do when we're finessing our keys.

So,

2% to 5% difference when we add a bunch of those up makes a big

difference so this is a great option to have.

So luminance match again, is for fine details,

particularly in transparent areas.

Back to our regular image and we are going to take a look at a couple

of last values and that is the screen subtraction,

background luminance and background chroma.

The screen subtraction, we do want to leave that on.

If we turn that off you're going to notice that it reintroduces the

green so leave that on by default but let's take a look at what the use

bkg luminance and the use bkg chroma does.

Here we have some nice edges.

We're trying to just massage them into the background here so we're using

a checkerboard for that and we are going to use the BG luminance so use

the BG luminance and you can see that it's actually making it worse rather

than better so it's not helping us.

Let's see if that helps if we attach it straight to the BG.

So on and off.

So it's still pruning those edges whether or not we hook it up to the BG or

not so I'm going to leave it as this as the default and so,

again, it's not really helping us.

The use background chroma is also not helping us

but what exactly are those doing?

So the use BG luminance and the use BG chroma or bkg as it's written is

affecting how the brightness of the edges is being affected.

So the use bkg luminance is affecting how the luminance of our

background image is affecting our edges and the use bkg chroma

is affecting how the color from our background is affecting the

brightness of those edges.