Painting Onto Geometry with RotoPaint Video Lecture | Create Visual Effects with Nuke - Professional Skills

in this tutorial we will look at
painting through geometry which was the
technique used in creating the blood in
this shot the footage from Gallup Walker
with confirmation from Jack Bauer and
black Jew 7:30 limited so here we have a
camera track with the geometry model
which only approximates the actors face
as there was no scan available the point
being here is that it is not accurate so
I have a script set up with the geometry
and I have a camera re projecting the
UVs onto this via a UV project node and
then through an apply material node will
UV wrap our paint strokes onto the
geometry so naively I might try and
paint while viewing the result however
because the image our need for the
geometry are supplied by 3d is not the
same size as the final plate or find I
have painted outside of the image area
so if I view the paint node and pained I
will see I'm painting across the face
but it's difficult to locate the area I
want to paint in
although it is possible to get uv-map of
the face through the matched geometry in
this case I am simply going to use a
colored grid which I'll add via the UB
projection seen earlier and this grid
will give a much better idea where to
paint as we animate through you can see
it's locked to the face and if we zoom
in on this section here you can see we
need to paint within an area h1 to j1 in
the cyan
so if we go back to our paint node and
just half mix the grid and paint in that
section we should now see our blood
appearing in approximately the right
place so we're going to paint between h1
to j1 in the cyan
and if we switch to the face we can see
that it's approximately correct however
this setup is still not ideal so I'll
switch to a to view setup and now I can
see more interactively what I'm doing so
now I have my first paint strokes in
place I can now remove the grid and go
back to the roto paint and work on this
area
now as we move through the shot because
we have painted onto the geometry and
through the camera we have the blood
moving with the head however there is
slippage occurring due to the inaccuracy
of the model so to fix this we want to
animate the position for all these paint
strokes so to do this we'll create a
layer select the paint strokes and move
them into this layer
now in the transform tab we can animate
their position in one go so I'll set a
keyframe move further down and adjust
the position
so with a small amount of Correction we
are able to get the blood to lock to the
eye as we go through and keep checking
where it goes off and readjusting it
will end up with a more accurate result
and here you can see how the paint
strokes are actually moving in the 2d
plate
now to make the blood disappear into the
eye we are going to create a second rate
of paint which will merge with an inside
on the first and basically do a scratch
back so as a painter stroke I'm
revealing the blood I'll set the
lifetime to all and then we'll view it
and we see it's just a white brushstroke
to animate this I can adjust the right
on end or right on start parameters like
this and in this case I want to animate
the right on end so I set a key here and
go down a few frames and you can see the
blood strokes are being wiped off
with everything else you've done you can
now see it shrinking into the eye this
has been Howard Jones for the foundry
goodbye