Original subtitles

In this clip we're going to review how to analyze a piece of

greenscreen footage before we begin to pull keys.

Now,

it's really important for us to analyze this footage in

order to strategize our workflow in advance.

In this way we can figure out what the most appropriate tools are going to be

and how to use those tools for the most successful outcome.

So a couple things that we want to take a look at,

of course, is the quality of the footage.

So, was it shot cleanly?

Is it crisp?

Was something out of focus that we did not want it to be?

How about the evenness of the greenscreen?

So let's take a look at that.

We can look at it in a couple of different channels and we can already

see that the greenscreen is a little bit uneven.

And this is pretty natural.

This was shot in a green screen room and it's just the difference

between the back wall and the ground plane here.

So it is possible that we may need multiple keys in order to

complete a final alpha channel for the shot.

Now let's take a look at a couple of other issues that we might have.

So,

when we pull this key because of all of that uneven light

in here we might have some artifacting.

The definition of an artifact in visual effects is an undesired or

unintended alteration in the data and is usually introduced by a digital

process and in this case it was through keying.

So we do want to be mindful of that.

Artifacting can also be any detail in the edge work

that we may have issues with.

Now,

this piece of footage was denoised and if you're not familiar with

that process we will be going through it in a few more modules but

for now we're just going to work with this denoised piece of footage

and analyze the rest of the shot.

Now the second thing that we want to take a look at is the reflection.

So we take a look at the original piece of footage again and we see that

there's a strong reflection in the glass over here and over here in the

watch face and we take a look at that alpha we can see that we have almost a

hole in our alpha and another hole over here and the reflection that has

reflected on the table cloth so,

definitely something to be mindful of when you're shooting.

We will have to do some extra work to refine those areas and we can see that,

over here, we've just analyzed it.

So we can see, again, in the glass and in the watch face.

Now the second thing that we want to do is we want to

take a look at the color values.

I've already preselected these colors and if we wanted to analyze these colors,

I'm just going to show you over here,

it is a jpeg versus the original was an exr but if you hold down

Ctrl+Shift+drag you're going to get the numbers down here and that is

the read out for the values on the greenscreen.

If you just want to sample a single pixel hold down

Ctrl+click and it will select a single pixel.

Hold down Ctrl+Shift+click again to get rid of that box.

So in evaluating this we can see that the red values are somewhat similar,

the blue values are somewhat similar but the green are definitely different,

in fact,

in some cases it's 10% different so that shows us again not only visually that

these greens are slightly different but with the numbers and numbers never lie

so it's always great to check in with those numbers.

Let's take a look at a couple of other last things and that is,

of course, where we're going to sample the greenscreen.

Some areas to keep in mind are fine hair detail.

So this will create wispies and or transparencies are in a matte.

These areas down here where maybe there isn't a lot of

greenscreen that's showing and because of that,

some of the edge work will spill over into the greenscreen and

it will be definitely hard to key this area.

We may get some transparency but not 100% transparency like we'd like.

The other area of course is motion blur.

So again,

we want to keep this to be nice and transparent and keying it on a

motion-blurred frame such as this it'll get a sample close to the

element but not actually sampling it,

otherwise we won't get the correct key and so we want to sample on a

motion blur frame versus a non-motion-blurred frame.

So again, in looking at this,

we do have some details that we should pay extra attention to

and we may need multiple keys in order to complete this

particular shot and take it to final.

Now that we've evaluated the greenscreen image or the image sequence,

we can start to begin to determine the most appropriate workflow.