Original subtitles

In this clip we will be reviewing pre-processing for green screens.

So before we begin, let's go through a few different things.

So this is the original image that we will be working with,

before it has been pre-processed.

The final image that we will be aiming towards is the following.

So here's our character on top of a new background.

His edges are looking pretty good.

We don't have any transparency in his alpha,

so it's integrated well into the plate.

We will also review our script.

So here's our script and you will notice that there is two main sections.

So on the left hand side is the workflow that I will be going through in this

particular clip and to the right is the completed template.

So this template is basically a step by step workflow.

It has the completed or optimized tools and step by step

instructions of what I did or what each tool is for.

Now each one of these tools will have slight variations in

comparison to the steps that we are about to take.

And that's just because these have been optimized for this particular shot.

I will also note that this is a fairly fast paced clip,

so if you need any of these workflows reviewed in

more detail or at a slower pace,

I do recommend going back to the previous clips and modules for that review.

So let's get started.

So back to our original image and we're going to take this image and

the first thing that we're going to do is denoise it.

So we're going to add a denoise tool.

So hit tab, N, denoise.

And I'm going to hook up the source to my image and

move the sample area to a solid area.

Next we're going to take a look a the blue channel,

just to modify it ever so slightly.

So there is the denoise image,

we notice that it does blur the image just a little bit more than we'd like,

so I'm going to turn down the Roll Off,

just to add a little bit more detail back.

Now refer to the template just to see more

revisions to optimize it even further,

but this should work for this particular example.

Next we're going to white balance,

so hit G for grade tool and inside the grade tool we're

going to select the whitepoint eyedropper.

Go back to full color, A,

A and I'm going to select a portion of the tablecloth that should be white.

So control, shift, drag, so there we go.

So there is the sample.

Let's take a look at it, there we go.

But the luminance has been changed.

So deselect the eyedropper, deselect the red little box,

so control, shift, click and I'm going to modify the luminance.

So hit y for luminance and hit one for denoise,

that's before the white balance and two for the after,

so you can see that one is lighter than the other.

At the top of the view port, we can compare the two images.

So select this dropdown menu to wipe and grab that,

so here we go, so we can see that the right hand side is our original,

the left is our modified version.

So we're going to take our grade tool into the gain and just pull it down

until we can't see the difference in the two colors,

so give or take a few pixels, that's gone too far,

so back up 2.

75 for where I sampled, yours might be a little bit different.

And that's working pretty well for us, so back to full color, A, A.

Now we can see that the luminance is looking a lot

better and we've rid of the color cast.

Onto the next step.

And that is the chrominance,

so we're going to blur the chrominance ever so slightly.

Hit tab and type in colorspace.

So our default colorspace is linear.

We're going to change it to the YCbCR, so the luminance and chrominance,

so we can separate them out and add a blur tool.

So B for blur, hook that up to the colorspace.

Make sure that we are only blurring the green and the blue,

so get rid of the red, get rid of the alpha.

This under channel's rgba.

And we're going to increase it to two.

Let's take a look at what that looks like.

Oh, it looks like we forgot to get rid of the wipe, so there we go.

Get rid of the wipe and into our, let's go with green channel.

So this is our blur, this is it before and after.

So it's pretty small but may make a huge difference with our keying.

So there's green.

And before, really, really improved that blue channel.

So back to full color again.

We're going to roundtrip back to linear space,

I'm going to copy, paste, control C, control V the colorspace tool.

Right now it's doing what I call a double LUT so we

don't want to do a double linear LUT, but rather go YCbCR out back to linear.

We've properly round tripped with a slight blur on the Chrominance.

So it's very small, but we are using a chroma keyer,

because we want to make sure that we get nice edges.

So now that we have optimized the clip so far,

we need to fix the uneven green screen, so Y,

check our luminance, down with the gamma.

See how uneven it is in the backing region.

So let's go in and correct that.

Back up to regular LUT.

Hit Y for full color again and we're going to be

using the IBK Keyer setup for this.

Now you can use other workflows to get the clean plate and

the final key or at least the key that we will use to fix

the green screen backing region, but I'm going to use the IBK Keyer setup.

So hit tab and hit IBKColour and IBKGizmo.

And set those two up, so IBKColour will go to the Color Space,

that is the last corrected image that we have there.

So hit that,

I'm going to hit control so I get this nice little elbow in here

and hook up the foreground to there as well,

control click for another elbow.

And see, from the color to the IBKGizmo.

Change that to green.

And green again and let's get started.

So into the IBKGizmo,

view that alpha and I Want to make sure that I get

this as clean as I can for now.

Bring down the gamma and the LUT and let's modify the IBKColour.

So I'm going to go -0.

01, fills in that little hole there, so that's good,

let's see if we can increase it to fill in anything else.

No, let's not do it a whole lot.

If I go.

5, probably pushing it too far.

Yeah, way too far, so let's keep it at.

1.

Then go back to full color.

Back to my regular LUT and go back into the IBKColour

tool itself to fix the Clean Plate.

Down with the LUT one more time, see if there's any variation.

There really isn't, pretty small.

To be safe, I'm going to bring it down to 0.

9.

Again, to be safe, again, just erode ever so slightly,

but most importantly, fill in my black.

So full frame, F for full frame.

Doesn't look like we went far enough, so we're going to increase it to seven.

Not quite far enough, so let's say 7.

5 and that should do the trick.

So now we have our Clean Plate.

Back to our regular LUT and our final key.

So let's make sure nothing changed in that alpha.

So back to alpha, A for alpha.

I can see already something isn't quite right there.

Let's bring down my LUT and it looks like we need to fix it.

So in the IBKGizmo, increase the red weight.

It gets rid of most of it but this little section over here.

And increase the blue weight, because, of course,

we have a green screen so we modify the blue weight.

Increase that until it's almost gone, little bit more.

And that should do the trick, we are down pretty far in our LUT,

so we will go full color and that should do the

trick for what we're looking for.

So now we have a completed alpha and a completed Clean Plate.

Moving on, so we're going to invert my alpha, so hit tab, invert.

Hook that up there,

invert all and add a shuffle to shuffle my alpha to all of

those channels so put the alpha in the red,

the green, the blue and it's already there in the alpha.

So this is going to help us to isolate our Clean Plate patch so that it

doesn't modify my character and his foreground elements.

Next we're going to create a constant.

So tab and constant.

And we're going to sample the overall green screen.

So back up to my Color Space because that's where my last optimization was.

And I'm going to take my constant and sample with the eyedropper,

control, shift, drag.

I have a nice overall green color.

Deselect, control, shift,

click to get rid of that red box and now we can start to create the patch.

So first I'm going to do the minus operator so M for merge,

hook up the A input to the constant, the B to my shuffle,

no, it looks like we did the wrong one.

Should be actually up to the clean plate, not the shuffle quite yet.

Control, click to get that nice and clean.

It's going to tell us where the difference is between

the clean plate and my constant color.

So change those to minus and here it is showing us where

there is differences between the two images.

So the difference between my clean plate and my constant is this.

Now I don't want it to color correct or change/modify where my character is,

so I want to multiply.

Multiply remember, it will multiply the alpha against the rgb.

So M for merge.

You can use a multiply tool, which will do the same thing.

And I'm going to control click, keep this nice and clean,

and change my merge to multiply.

And now it's going to cut out my clean plate patch so

that my character is not being changed.

Now I have to apply this patch to my original green screen.

So add another merge,

hook it up to your clean plate patch and up to my original image up here.

So I've hit the period key,

it will give me another one of these nice little elbows.

Bring this way down to the bottom here so we can

hook it up to my clean plate patch.

Let's change your patch merge tool to plus.

There we go,

shift X and I have my clean plate so this is my before and that is my after.

And if I take a look at my character's edges,

it's looking pretty good, so before and after,

it hasn't changed but look how clean my green screen is now.

So I have optimized it so that the color casting is

removed so any artifacting is removed, noise is removed and I have a nice,

even green screen.

Now the last thing I would suggest to do is to

pre-comp this particular image sequence.

So have a write node,

it just means to write this out as a new image sequence so that it

doesn't bog down or really slow down our next script.

So now that we have optimized our workflow,

or at least our green screen footage.

We're going to move onto keying it in our next clip.