Original subtitles

In this clip we're going to look at combining channels with operators.

So in some cases keyers can't pull a 100% successful key so we have to look at

alternatives in order to really help enhance that final key.

So let's take a look.

So here we're going to be trying to extract the purple zigzags from

the gift bag and the way that we're going to do that is by examining

the different channels in the image.

So here we're looking at the red, the green, and the blue channel individually.

Now we have taken a shuffle node and shuffled the red into all the channels,

all of the green channels, and now the blue.

Now it appeared to be that the green channel had the highest contrast,

except for the purple portion of the bag appears to be black

in our alpha so we have to invert that.

So here is the green shuffle to all the channels and I'm going

to invert the alpha so there's the alpha,

so that the purple portion of the bag is now white in our alpha.

Now unfortunately the alternating portion is not 100%

black so we have to modify that.

So add a gray tool and I have modified the white point and the black

point so let's just take a look at where it was.

So here is in around the default value and I'm going to crunch

those colors until the what was white portion,

which is now black, is black.

So let's just sample down here.

So Ctrl + Shift + click,

and I'm going to push that black point until these

values down here turn to be 0.

So let's just keep pushing them and see where they're at.

We're getting close.

So that's pretty close down there.

It's not going to be perfect.

Again,

this type of modifications to our channels often yield poor results in

our edge work so use them with caution and only use the portions of

them that work well for your final matte.

So from there I'm going to garbage matte out my box

or my gift bag with a roto shape.

I'm going to premultiply it, blur those edges ever so slightly,

only a pixel or two so there's off and that's it on and that's

just to get rid of the artifacting on that edge.

So we can probably increase it to 2.

There you go.

Now you can see it little bit better.

And we're going to copy that final matte over to our

original image and premultiply it.

So if I turn off that blur, you can see that those edges get a little better,

hence why we had a tiny little blur before and it's pulling a

little bit of the white from the carpet in and a little bit of

the shadows in here on the screen right,

but overall this is doing a really great job considering that

we're not working with the typical chroma keyer.

So now let's look at some other methods of isolating those

channels to try to get a refined alpha.

So here I have taken the blue channel instead.

It's not quite as contrasty as the green, but let's see what we can do with it.

So I've taken two instances of the same channel and

I've plus-ed it over top of itself.

So you can try different types of operators to try to get the

most refined results over here on your image and different

operators will give you different results.

In this case a plus gave us the best results.

So keep in mind that a plus will push your values

above 1 so we have to modify that.

So again,

the purple portion of the bag here is not white in our alpha so

invert and we're going to work in that alpha channel so add that

gray tool and push the values again.

Now unfortunately, as we noticed to start with,

the blue channel is not as successful as the green channel to start with,

but we'll see what we can do with it.

So again we've really pushed those values until this hits around 1 and

we're trying to push these here again until they hit black,

but if you push them too far,

you're going to get artifacting on your edges and we're going to start to

lose this and so then we're going to have to push it back and you can see

here it starts to invert if we push too far.

So not as successful as our first example, but still not bad.

So again let's garbage matte it out with that roto shape,

blur the edge ever so slightly, and premultiply.

So our original test was like this and our second test was like this,

so not quite as successful,

but again I just want to go over the different methods that you

can try to get a really successful alpha.

So our third example over here is isolating each channel on

its own so I've shuffled out the red, green,

and the blue again; however, I've modified each one individually.

So here I've modified the red separately and the green a little

different and the blue a little bit different.

Again,

always make sure to clamp those whites if we're working with

the alpha and I've plus-ed them over to try to increase this

contrast and plus-ed one more time.

Inverted that alpha so let's take a look at that alpha

and try to color correct it further.

So again it's having problems with the shadow portion screen right here.

Garbage matte it out, blur that edge, and premultiply.

So it's similar to our second example.

It really depends on the image, ever so different,

so it's probably the least successful of the three; however,

again something to consider when you're trying to isolate

the channels for pulling a matte or a key.

So our last one is more of a real world example so here is

a green screen and typically you would use a chroma keyer

to pull this type of key,

but we're going to show how you can use individual

channels to do something similar.

So we've once again shuffled out these three channels

and instead of modifying all three,

we're going to only modify the green channel since it is a green screen.

So we've inverted this image and we've taken a gray tool and

really pushed those values one more time.

So here's a gray tool and I've just increased that black point

until the backing region is in around 5%.

So if we push it, push it, push it too far, in around there is really good.

Our core is going to need a little bit of work so we can fix that in a

moment so let's take a look at the plus and the plus.

So it's looking pretty good.

We're going to have to fix that backing region portion over here again.

So we've plus-ed them together,

added another gray tool just to modify that alpha a little bit further.

Again keep those values so they're no more than 5% in the backing region.

So somewhere around there is pretty good.

We've modified the white point just to fix her core.

So this was it by default and we can wish it down in

around there and it fills in her core.

Now keep in mind,

it is going to degrade her edges potentially so here

let's take a look at this at the default.

So there's the default and watch how it will push

out on her edges ever so slightly.

So it's growing those edges; however, it's given us an overall pretty good matte.

We're keeping those values below 5%.

Garbage matte out your image and premultiply.

So I have added a very simple temporary despill on the image just

so we're not thrown off by that green spill,

but overall concerning that we did not use a chroma keyer,

this is pulling a not bad alpha and again,

is a great solution perhaps if you're trying to get

detail in her hair for matte purposes.

So overall in this clip we took a look at modifying individual

channels and using operators to basically combine them together as an

alternative method for pulling keys and alphas.