Original subtitles

In this clip we're going to take a look at luma keying in depth.

Now in our previous clip we did take a look at the keyer and that included

luma keying and a couple of other different types of keys.

We looked at all the different parameters and how to

modify them to really get the best key.

Now in this clip we're going to look at practical examples.

So let's take a look at what we have.

So the first one is this image here which is a lighter image on

a darker background and the second one is going to be a darker

image on a lighter background.

Now the workflows for both of these are included in the script,

but we are going to be primarily focusing on our first image.

So let's take a look at it.

So here's our first image and we have denoised it just to get

better edges so that that noise isn't involved and I pulled a

really quick keyer so this is a keyer.

I have modified the A, B, C, and D sliders.

We can see that the backing region is uneven so

unfortunately we can't do a whole lot with this.

It's not going to allow us to push that key any further.

The backing region here is in around that magical 5% so we have

to modify our settings a little bit more.

So what do we need to do?

Well,

we need to look at possibly evening out that backing region and also

combining multiple different keys into a final matte.

So let's take a look at some of those workflows.

So back into our script and let's take a look at this section here.

So this section here that is in the teal color,

this is the part of the preprocessing that is slightly

different than what I have previously shown.

So if you are new to the preprocessing workflow,

I do highly suggest that you check out the NUKE Green Screen

Keying Fundamentals Course on Pluralsight and check out the module

and clips that go through this workflow.

So let's take a look at how I modified this for this particular example.

So the first thing that you will find that is different is that

this is a non-green screen or blue screen image.

So if I take a look at this we're going to have to find another

workflow to create a clean plate and a key.

So I have taken a luma keyer and I have used a gray tool

just to really optimize the alpha.

So I have changed the channel to alpha,

I have clamped the white value so that none of those alpha values

will go above 1 and I've aggressively increased the gain so that I

can really pump up that alpha channel.

Now from there I did a slight dilate out with the

filter erode and I inverted the matte.

I then took the regular RGB image and premultiplied it.

So again this is kind of an inverse premultiply

from what you're probably used to.

Now this is the little trick here.

So if you take the edge blur and you blur it ever so slightly so

maybe a little bit more than ever so slightly,

but you're looking to take that blur all the way into the center of your image.

When you un-premultiply that, what will happen is it will fill in the gaps,

which creates a clean plate.

So the idea being is that we don't change the

original image as much as possible, but that we just fill in those gaps.

So this is equivalent to the IBK color node that does a

better job for green screen and blue screens,

but this workflow serves as a really great alternative

for non-green screens or blue screens.

So the next one is pulling that difference keyer so that's

equivalent to the IBKGizmo and we hook up the difference tool up

to the clean plate and the denoise plate,

which gives us our difference.

So it pushes that into the alpha channel.

Again,

that alpha is not very clean here so let's take a look

at modifying that one more time.

So here is the gray tool.

Same thing, clamp the white alpha channel only, increase that gain.

I'm going to aggressively push this out,

blur it, and we're going to take a look at why.

So if you're familiar with the preprocessing workflow you are going

to shuffle the alpha into the rgba and invert it.

So before we move forward,

let's take a look at an alternative or an additional step that we

have to modify before we add this matte into place.

So with the denoise plate we have sampled an average of the

overall backing region with a constant.

We've taken a minus operator.

We've compared the original denoise plate to the constant,

which allows us to see where this backing region is uneven.

So we can see that it is very uneven here.

Wherever the image is too dark relative to this constant,

it will make it brighter and wherever it's too light

relative to the constant color,

it will make it darker and the result will be an even backing region.

So now we're going to take this image and we want to make

sure that nothing in here accidentally will change our image

that we're looking to really key.

So we have taken our matte and multiplied it against this image,

which basically prevents us from accidentally changing our image.

Now you're going to notice again that it's very soft

and we'll see why in just a moment.

You're going to take this result and plus it against the denoise plate,

which gives us the cleaner backing region.

So just to see again, here's the original plate and here's the evened out plate.

Now unfortunately, there are small changes we can see here.

Maybe it's actually very hard to see,

but believe me when I say that it's slightly off-color.

So let's check to see if it shows up in one of those channels, RGB.

It's a little bit in the blue channel, you can see those changes,

and the reason why I softened and dilated out was for this reason.

Let's take a look at that full color.

Let's take a look at those details.

So if I did not dilate out and I did not blur that initial alpha,

look at how much detail that we lose in our edges

before we even begin to pull a key.

So definitely something to take into consideration and that just helps us,

again even up the backing region and it allows us to pull that final matte.

So now what we're going to do is now that we have that clean backing region,

we're going to pull that luma key, so again,

add that keyer, attach it to our cleaned up image.

We are going to scroll down here so I'm going to

focus on the top screen left corner,

sample this corner over here so we're going to say 0.

92 and I'm going to look at some of the smaller pixels over here,

so I'm going to say 0.

21 and enter that.

Oh, we did that wrong.

Let's erase 11, not a huge deal.

Take a look at our alpha.

So at first glance it's much cleaner than what we had previously.

Let's just take a look at a finessed one, so here's one that I've modified.

I have changed that alpha.

So here's the one that we had and I've just brought this down so

that those values are give or take lower than 0.

05,

so here's an optimized version and let's take a look at what that

looks like in comparison to our original image.

So here is our evened out backing region and a single matte versus here's

our original one where the backing region was not cleaned.

So let's take a look at our RGB.

So here's our RGB and let's take a look at the top left-hand corner

because this is really what we are worried about.

So this is my refined backing region and this is my original one

with all the holes in it or the uneven lighting.

So already the evening out of the backing region is really doing a great job.

So I'm going to take a minute and skip forward.

We're going to pull a separate key for here,

a separate key over here,

and another one for the bottom down here and we're going to

combine them all together with a keymix tool.

So let's take a look at those over there.

So if I scroll to the far screen right of my image and we're

going to take a look at that finalized alpha.

So here we have, you can see it's a little bit brighter,

but again it's keeping to that rule of below 5% down here as well,

below, oh, that looks like it's pushed a little bit far.

Let's see what we can do to modify that.

So we'll go into our alpha and I'll pull this in just a tad.

There we go, and around there.

So it's looking a lot better already and let's just look at that again,

what that was looking like before.

So here is before we added that last piece and

after and look how that's growing.

It's adding lots of nice detail in the bottom of our image.

So now let's take a look at some refinements and our

original versus our final matte.

Now before we do that,

I do want to show that I garbage matted out all of the excess backing region.

Again, I used that handy gray tool so there is my final matte.

I took the gray tool and did the same thing.

No need to clamp the white because we're not affecting them,

in fact we are actually trying to up the contrast.

We are dilating out that matte,

blurring it ever so slightly and using it as a whole dot matte for our image.

Now if you want to soften that falloff, use the Gaussian.

Just make sure that we're not losing too much detail in

here so that's why I stuck to the box.

Now let's take a look at the original that we had so here is our

final image with our key and here is the original.

Now take a look at the difference down here.

Again, original, final matte.

So it really pays off to take that extra time out to combine

multiple mattes and even out the backing region.

So one last test that's going to be the RGB so RGB again of the original,

oh sorry, the final one versus the original so small details,

especially in those edge works or in that edge work rather.

And let's take a look at our final matte versus our image, our original image.

So some loss of detail.

Unfortunately that happens.

We did say that the luma key doesn't necessarily do

the best job with edge detail,

but it gives us a really great start and a great place to work with and again

combining those multiple mattes really makes a big difference.