Camera Tracker for NUKE X - Part 2: Lens Distortion Video Lecture | Create Visual Effects with Nuke - Professional Skills

okay welcome everyone to the second in a
series of tutorials on the camera
tracker node for new cakes in this
second tutorial we'll look at using lens
distortion with the camera tracker so
let's just revisit the footage we solved
in the first tutorial so this is a nice
sequence we've got a camera tracker here
got lots of nice good tracks that we've
solved and we've got a camera so this
was the camera itself we had before but
we didn't use any lens distortion
information in this shot or any known
focal length but actually we shot a lens
grid so let's just read that and have a
look at that okay lens gives you lots
and lots of nice 2d points showing you
how the image is distorted so if I use
the lens distortion node in u'q I can
actually do a grid analysis here if we
analyze that grid we can calculate the
lens distortion parameters okay
so now we've got the distortion
parameters we can use this in two
different ways we can either under store
the plates create a camera tracker and
track and solve off the undistorted
footage cam tracker so I would retrack
from the undistorted plate the other way
is actually just to put the lens
distortion parameters into the camera
tracker so here we've got a camera
tracker that's tracked off the original
distorted plate what I'm going to do is
just set a known lens here copy the
parameters in
and now I can solve in the camera
tracker using the tracks for the
distorted plate but calculate a camera
for the undistorted footage so I can
understand the plate using the cam
tracker it solve
and the camera I get out to the end is
for the undistorted plate but actually
now that I'm using the undistorted
plates or the lens for the unsalted
plate I can go in and set unknown focal
length so this was with the prime lens
24 millimeters I can resolve with 24
millimeter focal length
okay so this is the ideal scenario I had
Allen's grid I can get the best possible
lens distortion estimation and I can
solve my camryn using the known exact
focal length for that plate so I'm
pretty confident in the 3d points I get
out of this and the camera path I get
out okay so the next shot I've got is
what you can do if you don't have lens
grids okay so here's a shot with nice
bit of distortion in it so you can see
the edge of the road here it's all
pretty distorted so already trap this
sequence let's have a look so you can
actually see the distortion coming out
and the tracks a little bit here so if I
go away and solve this with all those
distorted tracks you can see what it
does to the 3d world
yes let's switch to 3d and have a look
so what you can see here is they've got
a really curved point cloud coming out
for what should be a pretty straight
string if we create our scene let's look
at the camera path that we're getting
out of that so that's really curved and
that's essentially caused by the lens
distortion in the footage so there's
different ways you can handle lens
distortion if you haven't shot a lens
grid you can go into the lens tab when
you can ask the camera tracker to
estimate a lens for you so you can say
unknown lens so we can go away and solve
again so what this will do is it will
try and estimate the best possible lens
up front and use that into the solve so
it's initializing its best estimate of
those lens distortion parameters
so this is very similar to the image
analysis and you get in the lens
distortion node
okay so let's have a look at how that
solve works when I was trying to
calculate the lens distortion let's have
a look at 3d and the paths that looks
pretty bode lows look at those lens
parameters hasn't really done very much
there so we can understood the footage
have a look at the output - camera
tracker it's under estimated that lens
distortion it's too severe for it to
cope with in this shot so there's going
to show you a kind of a nice trick I
like to do we're going to use the
Gribben now the line analysis and the
lens distortion node to initialize our
distortion for the camera tracker so
let's pick a nice frame with lots of
distortion in it I'm going to go to the
line analysis I'm going to switch on
drawing mode and let's just put down
some rough points here so all I'm doing
is drawing the rough curves in for the
straight lines I'm not being too exact
here because I want it just to
initialize the camera tracker
let's add a few more in
I would ordinarily take a little bit
more care than this it's quite hard with
a trackpad okay let's just analyze from
the lines have a look at that Distortion
okay so what I'm going to do is until
the camera tracker to refine an own lens
and copy these parameters down they look
a little bit better
and let's go away and solve that camera
again using that line analysis to
initialize the lens distortion okay so
what the camera tracker has done is it's
picked up that initial lens model is
calculate 3d points and it's optimized
the parameters here for the lens to make
sure that a reprojection there is a rule
as small as possible so we've got a nice
solve error coming in here 1.1 so let's
now have a look in 3d and have a look at
that camera path so there we go nice and
straight okay so that's the end of the
second tutorial on the camera tracker
node how to use lens distortion ideally
you want to shoot a lens grid and he can
use that to set an own lens model for
the solve to get the camera model for
the undistorted plate what I've shown
you here is a little trick you can do if
you're going to shoot a lens grid you
can use the in line analysis in the lens
distortion node bring that in and use
refine known lens on the camera tracker