Nuke; Basic Workflows; Bounding Box - PartA Video Lecture | Create Visual Effects with Nuke - Professional Skills

a lot of times when artists experience
an unexpected slowdown with a nuke
scripts or excessive memory usage it's
due to the inefficient use of the
bounding box the bounding box is often
referred to in other applications as
data window domain of definition region
of interest crop box crop window these
are all different terms for the same
concept and in this tutorial we'll have
a look at this concept and at the nuke
specific workflow so looking at this car
render here you'll see that the area
we're actually interested in is pretty
small compared to the overall format
size so looking at the bounding box info
in the lower left corner here in the
status bar we'll see it starts at 0 0
which is lower left and ends at 1024 576
which is up here in other words the
bounding box in this example is as big
as the format and that means we're
wasting a lot of resources let's have a
look at what a heavy D focus node does
to this you'll see how the D focus node
wastes a whole lot of time and resources
to generate black pixels so this is not
really what we want
and also let's have a look at the memory
usage by selecting the node and going to
edit node info viewer and that tells us
that the refocus node at the moment uses
2.2 8 megabytes of memory to achieve the
effect now let's go back and make that
bounding box a bit more efficient using
a crop node if you don't check the
reformat knob in the crop node the crop
node essentially is a set bounding box
node if you will if you're a shake user
it's similar to the set dod node so
let's limit the bounding box a bit more
to the area we actually want to process
I usually look at the Alpha Channel and
crank up the viewer gamma to make sure
I'm not cutting off any transparent
edges HUP all right and let's go back to
just about the same zoom level and
reattach the refocus node and you'll see
that this process is a lot faster now
let me just step through time a little
bit to make sure we're not looking at
buffered images so that's a lot better
and also if we update the info you'll
see that we're now using about a third
of the memory that was required before
obviously when dealing with animated
footage setting a bounding box like this
is
really an option but there's tools and
nuke that will help you with this and
one of them is called curve tool and
lives in the image menu the curve tool
will generate various animation curves
for you based on certain image analysis
and in this case we can grab a curve
type that will do an auto crop for us so
I'll set this to auto crop and usually I
set the channels to be analyzed to only
the Alpha Channel and we'll just let it
process the whole thing let's just do
the first 50 frames and what this node
is doing is it will now analyze the
extents of the Alpha Channel and give us
a nice snug bounding box fitting right
around it which you can see if you go to
the auto crop data tab the node itself
doesn't do any cropping so we'll still
have to append the crop node and then
copy or link the resulting animation
into it I'm just going to hold shift and
drag the animation icon over into the
crop node to copy the animation curves
and now I can get rid of the curve tool
itself and the crop node will deliver
our efficient bounding box over the
course of the animation because this is
quite a helpful workflow there's
actually a Python script that ships with
nuke that does the same exact thing so
if you select your image and hit X
switch over to Python and just type in
nuke scripts which is the package dot
Auto crop followed by an empty set of
parentheses hit OK and this nuke script
now does exactly what we just did
manually it'll process the image
sequence through the curve tool and then
replace the curve tool with an actual
crop that holds the resulting animation
obviously this is something you might
want to tie into your interface or even
assign a hotkey to another way of
assigning a animated bounding box is
simply by rendering out EXR if you run
the exhaust you have the option to auto
crop images at render time now this adds
quite a bit of overhead to your render
and more memory consumption so I would
not recommend this for the interactive
workflow but rather for batch processing
such as using nuke as a post render job
to your CGI image renders
if your cg renderer can't produce a
bounding box so if you check auto crop
and run out anything out of uke let me
just run the first ten frames nuke will
automatically assign the most efficient
bounding box it can find at render time
so if we pull this back in Kirby logs
here you'll now find the car has a
bounding box these are some basics for
creating a bounding box now let's have a
look at managing and modifying an
existing bounding box the two nodes that
are usually used in the most wasteful
way and new are the Bezier node and the
merge node when it comes to bounding
boxes so let's have a look at those two
first I'm going to crop into this area
here because we have an oversized render
so I'll just attach a reformat real
quick and we don't want to resize you
want to crop into the center and we want
to crop to a size oops to a box of 1024
576 so that brings us back to a 1024
format but you can see that we're now
losing the data that was contained
within the bounding box before so make
sure to check the preserve bounding box
knob so if we now added a camera shake
for example we would pull in useful
pixels rather than black now let's
pretend I want to create a quick Bezier
node to color correct the back of the
car for example just going to check that
into some random layer let's just put
into depth and you can see that the more
I expand the Bezier node the more the
bounding box grows within the format
it'll clip to the format at the bottom
but within the format it will grow the
bounding box as big as it has to to
encompass the Bezier node in this case
because I only want to use it as a mask
for my render this is pretty wasteful
already the reason this happens is that
the default value for the clip to knob
is set to format which means the Bezier
node is allowed to grow the bounding box
as large as the format in this case it's
probably better to set it to incoming be
box which means the incoming bounding
box will dictate the maximum extents
that is allowed so you can see that now
we're keeping the incoming bounding box
and
we can move the Bezier around and it
won't affect the bounding box let's just
have a look at the other few modes for
example the noclip mode will not clip
the bounding box at all and depending on
how big the Bezier node is the bounding
box will always grow to make sure it's
within the data window or bounding box
or crop window or region of interest so
this probably only makes sense if you
are creating RGB content with your
Bezier that needs to be preserved at all
times other modes include the union of
the bounding box with a format and the
intersection so if we look at the Union
it will grow as large as the incoming
format and the incoming bounding box
together and so at the bottom we are now
allowed to go as far as the bounding box
and to the right we're allowed to go as
far as the format and the same is true
for the other directions because we see
here is the union of both format and
bounding box and the last one would be
the intersection obviously this will
crop the paths outside of the format
from the bounding box so we lose data
outside so in other words every time you
create a Bezier that draws straight into
some image stream always make sure that
the clip tool knob is set to the most
efficient setting in my case it will be
the B box setting