cmiVFX – Nuke Advanced Keying And Channel Operations with Expressions
| project files | .mov | 933Mb
In this in-depth training video you will learn, step-by-step, to create
perfect mattes from green/blue screen footage (process screens) in Nuke.
You will learn to use multiple keying approaches that will prepare you for
any shot, and the various challenges that inevitably arise. You will learn
proven ways to fix problems, such as preserving hair detail and removing
color spill from process screens. Color spill is almost always a problem
and dealing with it is one of the most important aspects of integrating
your process screen elements into a shot. After learning these techniques
Nuke will become an indispensible solution for even the most challenging
keying and channel operations.
Simple Color Difference KeySimple Color Difference Key
In a green screen shot, for example, simply subtracting the green from
the red channel can create a good starting point for a matte. All
commercial keyers will take you some of the way there but, more often than
not, your shot will require a multiple step solution. Having access to the
component parts of a multiple layer keyer can help you hone in on problem
areas and solve your keying issues in less time – freeing up time to
refine the composite layers and blending. (see also Modular Keying)
Combining Mattes: Inside, Outside & Edge Approach
Nuke & NukeX come with a range of excellent keyers. All of them are able
to produce (and output) an alpha channel and matte. These mattes can be
combined for a more refined approach when a single key does not achieve
the desired result. One method can create a solid, or hard, "inside matte"
that removes all the unwanted noise from the outside of the matte. Once
this hard matte is created, the artist can focus on refining the edges of
the subject to extract all the detail required. You will learn which shots
are the most appropriate for this more advanced approach to keying. There
are several training videos that focus on this approach to keying as well
as some free ones in our library.
Combining Mattes: Individual Areas of Interest
A general key might give a good matte, but there are usually areas that
need special treatment, i.e. hair, a dark shoulder etc. Utilizing what is
known as an "area of interest" we can focus on specific areas in the matte
and produce a key that addresses the specific problems for just this
selected area. When several mattes of this kind are combined into one
matte it is possible to solve an array of complex keying problems. This
method can also be used in conjunction with the "Inside, Outside & Edge
Approach". If you are familiar with "Maynard Keying" or "Blocking Out"
techniques (please refer to further cmiVFX keying videos on these
subjects) this section of the video will enable you to construct powerful
procedural keyers with the utmost control.
Despill
When working with green or blue screen material it is very common for the
color of the process screen to reflect onto the subject. This "spill" will
appear as a color cast on the subject when included in your composite. The
use of some simple expressions can remove this color cast and enable you
to achieve the best possible result. A substantial degree of control over
the "despill" area can be achieved in Nuke by the use of a despill node
network. Expressions are non-intuitive to many beginners but just a
limited knowledge of some simple expression code can save any artist a ton
of valuable time. This portion of the video is a staff favorite!
Changing the Color of the Despill
Simply suppressing the spill color does not always improve the
integration of the element into the shot. Usually this method simply
introduces a different cast to the subject's edges. When the "despilled"
color is not present in the background element it will be just as
out-of-place as the spill itself! In this chapter you will learn how to
change the spill color to integrate with the colors in the background
plate. There are several ways to do this using one of several
applications. However, one method is faster than the others in most
scenarios. We will share the proven method that our research shows is the
best and quickest process!
Retrieve Edge Detail
Even when a good, basic key is obtained it is still likely that some of
the edge detail will be lost along the way. This is almost always true
when one relies on the use of a single commercial keyer. You can make your
life so much easier by learning an alternative solution that enables you
to retrieve that missing detail. Using a clever method of applying the
original foreground element over the background plate (prior to adding our
keyed element on top) you can achieve an astounding result in no time – a
technique that you will use over and over again.
Evening / Leveling Green Screen
In order to use the above method to recover edge detail, you will need a
consistent, flat process screen with no irregularities. Such a flat
process screen would also be handy for other operations. By comparing a
clean plate, the actual shot, and a solid green constant we can produce a
matte that will enable us to level out any irregularities in the screen as
it was shot on set or location. It is true that even the best Visual
Effects Supervisor can be forced by time constraints or other
circumstances to present you with a less than optimal process screen! This
method of achieving a flat green screen is invaluable.
Mocking Up a Clean Plate
Quite often shortcuts in production, as illustrated above, can mean more
work for the artist. An adequate clean plate is not always supplied with a
set of shots. There are ways an artist can create such a clean plate from
the available elements and solve various problems in the shot. One method
is to remove the foreground that was shot in front of the process screen
and use neighboring colors to fill in the void. This is known as "color
remapping". Once a clean plate is produced it can be used to help produce
a flat process screen that can be used to retrieve the finest edge detail.
This technique can even be used to extract a key for an object on a
background that was never intended as a keying scenario – without process
screens.
Light Wrap
The effect of light coming from the background and engulfing the
foreground element can be essential to make a shot look convincingly real.
We will show you how to quickly build such a set up that will give you
full control of this effect. This will allow you to produce realistic
light wraps rather than just a bright fringe that other methods simply add
around the foreground object.
This is not your basic keying video. We bring you in-depth, "software
impartial" and intuitive techniques to add to your arsenal – techniques
that you will use in your own workflow every day. We are very excited to
bring you these tools because we know they will make your job easier and
much more fun!
Home page:
http://www.cmivfx.com/tutorials/view/271/Nuke+Advanced+Keying+and+Channel+OpsDownload Links:-
http://www.filesonic.com/folder/7357171——————–Or———————-
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