Nuke; Basic Workflows; Colour Correction - PartB Video Lecture | Create Visual Effects with Nuke - Professional Skills

so now let's have a look at the grade
node and the histogram node the grade
node is probably one of the most
underestimated nodes in Nuuk so let's
hope we can demystify it a little bit
here it's best understood reading the
interface top-down so starting with a
black point we are basically remapping
the incoming pixels of this value to be
zero and with a white point we are
remapping the white point the pixels of
this value to be one if you're a shake
user black and white point are the same
as shakes expand node if you now look at
lift and gain those are pretty much
similar to shakes compress node these
now take the new zero point and white
point respectively and map them to this
new value here so if I adjust the gain
down our incoming pixel that used to be
one point four four was mapped to zero
by the white point and then remap to
0.76 by the gain and the same applies to
black point and lift so this is great
for matching colors between two elements
and after you do the color match you can
then apply multiply plus or offset as
it's called here and gamma to do an
arbitrary color correction on top of
your color matched element so let's have
a look at this in action let's say we
want to match these guys skin tones
together because one will shot inside
the other one outside and with no much
heat paid to the white balance so we've
got to fix it in post and the grade node
can get us most of the way there if not
all the way so how you want to start is
you want to assemble your black point as
in the darkest skin tone we can find so
I'm going to grab this and I'll hold
ctrl or command on a Mac to sample and
I'm going to hold shift to sample an
area and I'm also going to hold old
while I'm added to make sure I'm
sampling the input image and not what I
see in the viewer because that is going
to be changed by the grade node and I'm
going to sample this area here so this
turns black and now we do the same thing
with a white point and I'm just going to
grab let's say a highlight on his nose
here holding all three modifiers again
so that will give me a nice normalized
range between those two chosen color
values and now we want to move ahead and
match the darks and the brights to what
we see in our reference image over here
so I go on to pick the lift and now I'm
only holding command or control + shift
because now I want to sample this viewer
and not the grade nodes input and
starting with the darkest areas I'm
going to grab some over here and you can
already see the docks over here are
starting to lighten up and getting a bit
warmer and we'll do the same with again
and brighter skin tones let's grab the
stuff on this eyelid here and sample
that and that kind of brings us into the
ballpark of what we need to be already
so just by sampling colors we went from
here to there and now we can go ahead
and fine-tune those match values using
the color wheel for example like so that
looks a bit better and then we can use
the additional multiply offset and gamma
to apply whatever color correction want
to put on top of that
and I'm just going to swap this out for
the grade here and looking at the
histogram we pretty much have similar
control we have black point which is
this slider here and we've got white
point controls which is this slider here
note that the curve is doing the same
thing except you will note that we're
always clamping values here and in fact
even worse we're clamping the brights as
well this is actually a reason why I
never use the histogram but instead the
grade tool in addition you can use the
slider in the middle which will apply a
gamma correction between your new black
and white points and if you will this is
the equivalent to your lift and you gain
but once again be aware of the toll and
shoulder being clamped by this tool
speaking of let's move on to the clamp
tool which is pretty straight forward
and that it cuts off everything in the
toe at the minimum value and everything
in the shoulder at the maximum value but
it also lets you remove those clamped
areas to a custom color which is kind of
cool for graphic effects and also for
debugging and quality control to
visualize a certain range like this for
example so you can create your own clip
tool with this okay onto the saturation
node and for this we actually want to
slice through a color part of the image
so I'm moving this up here and a
saturation basically is the difference
between red green and blue in a given
pixel so if I increase saturation those
color values are being pushed apart and
you've got to be careful that you don't
clamp one of your channels or push them
into negative space because that might
give you some funny color artifacts down
the line and if you decrease the whole
thing all the color values are drifting
towards each other until they end up the
same value and you end up with a
monochrome image the luminance math is
simply different algorithms that do that
calculation for you and I guess from an
artist point of view just use whatever
looks best finally let's have a look at
the colour correct node which combines
all those basic color elements we talked
about earlier
find your saturation you find your
contrast which is a little bit more like
a white point adjustment followed by a
gamma you have your basic gamma here you
have a gain or multiply and you have an
offset or plus or add whatever you want
to call it you find the same set of
controls in the shadows drop down in the
mid-tones and the highlights section so
you can actually use those sort of
controls in isolated areas of your image
and if you want to isolate a certain
range you can use the second tab and
adjust your curves so let's have a look
at how that works let's say I want to
work on only the highlights but I
actually want to bleed my color
correction more into this area here
which is currently being controlled by
the mid-tones set of controls so if I
adjust my highlight curve over here I
can bleed that more into the mid-tones
and if I adjust it over here I can
actually make the transition between
mid-tones and highlights of it harsher
and let's say this is exactly the area I
want to work on everything white will be
controlled by my highlights everything
black by my shadows and everything gray
will be controlled by the mid-tone set
of controls magenta and green are the
transition areas so let's say the white
area is exactly what I want to work on I
can now uncheck test go back to my color
correct tab into the highlights node and
bring down the gain for example to see a
bit more detail in the hair like so
without affecting the face however be
careful with those adjustments as they
are prone to introduce color
discontinuity and ugly artifacts if you
overdo those selective color Corrections