Nuke; Basic Workflows; Image Based Keyer (IBK) - Part 3 Video Lecture | Create Visual Effects with Nuke - Professional Skills

now we'll take a look at the IBK gizmo
color pic mode it's designed for
situation like this where you have a
green screen or a blue screen that has a
very uniform backing in this situation
you don't need to use the IBK color node
to create a clean plate we can plug this
plate directly into the IBK gizmo and
dial it in we'll put the gizmo up in the
property bin the first thing we'll do is
check the screen type and set it for pic
or color pic now the color here is going
to be the color of the backing screen
and we're gonna pick that by turning on
the eyedropper if I try to pick the
backing color off the output of the IBK
gizmo node you see nuke goes insane as
it toggles between the black and the
green black in the green this is another
situation where two viewers will help so
we'll come down here to the original
green screen add a viewer come up to our
pane and split it horizontally and I'm
gonna move the IBK gizmo to the right on
the left is the original green screen
now I can pick off the original green
screen like this and the IBK gizmo node
does not go insane checking the Alpha
Channel I can now cruise around sampling
different areas looking for the sweet
spot so let's say I'm happy with that
I'll go back to the RGB mode now I'll
set my viewer to look at the finished
composite you're now ready to go into
the IBK gizmo and dial it in for the
best look
here's a workflow tip on how to add more
control to the blended edges of your
composite when working with the IBK
keyer we're looking at the output of the
IBK gizmo here and I've added a grade
node between the background and the
input to the gizmo double-click on that
to use this you have to have either the
background luminance or the background
chrominance turned on otherwise the
background has no effect on your blended
edges so with those turned on if we go
to the grade node and for example
increase the gamma it lit up the edges
of the output of our gizmo we can take a
look at the color grade node and see why
the background plate is being seriously
changed and it's the input to the gizmo
so those pixels become blended with the
output looking at our composite we can
see it changes the edges of our
composite quite nicely so this is a
technique that you can use to add more
control to the blended edges of your IB
cakey or composites
in the normal flow of things you're
going to want to apply a color grade to
the output of your IBK gizmo to color
corrected over the background but this
introduces a problem but there's an easy
fix
here's the issue let's take a look at
the output of this grade node directly
and remember in our IBK gizmo
we've got background luminance and
background chrominance turned on so
we're getting edged blend pixels from
our background plate let's take a look
at what we got you can actually see the
background up here I've used this
checkerboard background to make it
easier to see what's going on now if I
adjust this grade node for example I'll
do a severe color correction here the
blended pixels with the background plate
have also been graded up and you don't
want this you want those to remain their
original color so the way we'll deal
with this is we'll apply a reverse color
grade to the incoming background plate
like this select the grade node copy
paste it put it in the property bin and
set it for it reverse then we'll hook it
in we've now applied a reverse grade to
the background plate before it came into
the IBK gizmo it's been darkened by
exactly the same amount that this grade
node is brightened it we've now restored
the background blended pixels to the
same color as the original background
now when we look at the composite our
edge blended pixels are more natural you
can see the difference as I toggle the
compensating grade node on and off
very often we want to apply a
transformation to the background prior
to the composite with the IBK keyer this
can introduce an issue let's take a
closer look at our composite here
again I'm using a checkerboard pattern
because it shows the problem better I'm
going to move the viewer over to the IBK
gizmo output and we can see the edge
blended pixels from the background this
comes from the fact that our background
is an input to the IBK gizmo returning
to the composite as I toggle the
background transform on and off you can
see that the edge blend pixels don't
move with it that's because they are
from the original input not the
transformed input so there's two easy
solutions for this problem one is you
can make a clone of the transform
operations and apply it to the
background input of the IBK gizmo or
connect the background input to the IBK
gizmo directly to the transforms
themselves now they'll all move together
and you will have a lovely composite the
IBK keyer is often used as one part of a
larger compositing workflow often called
the soft matte hard matte workflow the
IB cake here is extremely good at
pulling a soft edged mat and
compensating for the uneven green
screens or blue screen backings but
sometimes getting a good solid core mat
is a little difficult so here we're
going to take a look at a broader
workflow how the IB cake here is used as
part of a larger compositing setup
starting with our green screen here the
IBK color creates a clean plate the IBK
gizmo creates a soft edged mat very nice
soft edges but maybe it's got some
transparency in it so we'll back that up
with a hard mat and then we'll bring the
two together here so this represents the
final mat that combines the soft and the
hard mats together starting back at the
green-screen would do a separate spill
suppression then we want to bring
together the hard mat created here and
the spill suppress foreground there and
we do that right here and now we have
our finished mat with our spill
suppressed foreground first we have our
background here and we do a composite
here using an ad mix node or a merge
node the ad mix node is very cool
because you can blend your edges in it
very
so don't hesitate to use the IB cake
here as the component of a larger
compositing workflow