Movie Making Manual/Visual Effects
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This Module is part of the Movie Making Manual
Note that this page covers Visual Effects and not Special
Effects. SFX are things like pyrotechnics, rain and snow. Visual
Effects (VFX) are the optical tricks that are used, including
projection, green-screen, miniatures, etc…
Visual Effects have always existed; they somewhat pre-existed
Cinema. Cinema itself, based on the illusion of movement, is an Effect.
Every second of projection is an illusion of movement, a lie told by
the director to the audience, a mandatory preface that brings us to the
practical aspects of visual effects. It is not possible to ignore the
revolution in the field brought by the employment of digital software.
The digital tools today replace a lot of arts in the past based just on
human skills.
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[edit] Visual Effects are at the core of the moviemaking process.
If you cannot get a special effect in the camera, then you must
create the visual effect in post production. With major motion
pictures, each shot can cost thousands of dollars. But for low budget
filmmakers, there are cheaper alternatives.
Do you want to start doing amazing special effects with your small
DV Camcorder? Then you have at least two options: Matte Paintings and
Budget Green Screen Shooting.
[edit] Budget Green Screen Shooting
Green screen is one way of adding beautiful backgrounds to live
action shots. Probably the most extreme example of this is Robert
Rodrigues’ Shark Boy and Lava Girl. But even if you are shooting with only a DV camcorder, you can do inexpensive green screen shots.
One can cut the cost of the shot substantially by doing your green
screen shooting outdoors using a themonuclear device (the sun) which is
free (on sunny days). This means that all you have to hire is the green
screen itself - none of the finely calibrated even lighting that’s
normally so essential for the computer to get a good key on the other
end.
As an alternative to purchase or rental, one can manufacture a green
screen. Commercial lighting supply houses sell paints specially
manufactured for the purpose, but it is probably possible to get by
with an ordinary house paint chosen carefully to be "green enough" for
the computer to pull a key.
The most common difficulties with green-screen are:
- getting even lighting on the screen.
- getting the lighting on the foreground to match the lighting of the (separately shot) background.
By shooting outside, with a diffusion frame hung over the shot you
will get naturally even sun-light all over the screen and actor. This
will also match the daylight conditions of the background that later
replaces the green. If your intended background is not going to be
normal daylight, or if you get a lot of cloud movement, this may not
work for you.
Make sure your foreground actor is a good distance from the screen,
so you don’t get even a hint of green light reflected back onto
him/her, as this will create problems later - but with your light
source being the sun (overhead), you’re less likely to get green spill
than if the lights were hitting the screen from the front, as they
probably would in a studio.
[edit] Front Projection
Front Projection (often abbreviated FP) is a technique which can
achieve the same result as green screen, but "in camera," that is to
say, the composition of subject and background is complete as the
combined image is acquired by the camera.
The technique uses a beamsplitter located in front of the camera in
such a way as to completely fill the camera’s field of view, and
oriented at a precise 45 degrees to the camera’s shooting axis. (This
rotation from the normal may be left-right or up-down.) The other
components to the system are a transparency projector (still or motion
picture), and a special retro-reflective lenticular screen positioned
behind the action.
A beamsplitter acts as both mirror and window, reflecting a portion
of the incident light, and reflecting another portion. Beamsplitters
are chosen for a specific application based on the ratio of reflectance
to transmission. Common types are 50R/50T (50% reflectance, 50%
transmission) and 70R/30T.
The beamsplitters used in Front Projection cinematography are of the
plate type, simply a piece of plate glass with a special coating on one
side designed to reduce the amount of light absorbed by the
beamsplitter, and consequently neither reflected nor transmitted. The
coated side faces the action, and is referred to as the "front"
surface. The purpose of this coating is to reduce the loss of light due
to absorption by the beamsplitter, which serves only to heat the glass.
A retroreflective screen is set behind the actors and other set
pieces. This screen is not just a typical diffusive projection screen,
which disperses light evenly so that a large audience composed of
people sitting at many different angles to the screen sees a uniformly
bright image. Instead, the retroreflective screen tends to send light
right back where it came from.
The classic material for retroreflective FP screens is a made by 3M,
and sold under the trademarked name of "Scotchlite". Scotchlite is used
in signmaking and conspicuity applications (nighttime motor vehicle
safety visibility). It is available from commercial signmaking supply
houses.
Retroreflection in Scotchlite is achieved using millions of
microscopic glass beads suspended in a transparent substrate bound to
opaque vinyl sheeting. It is available in rolls of up to four feet in
width.
While constructing the large (40 feet by 100 feet) screen of Scotchlite for the film 2001: A Space Odyssey,
director Stanley Kubrick and special effects supervisor Tom Howard
initially laid strips of Scotchlite side by side, but found that
variations in manufacturing made the seams between adjacent strips
glaringly obvious in the final product. Their solution involved tearing
the Scotchlite into irregular overlapping pieces, minimizing the
occurrence of variations of retroreflectivity large and regular enough
to be discernable to the audience. Still, as Martin Hart has observed,
careful examination of the FP scenes of 2001 reveal flaws introduced by variations in retroreflectivity between adjacent random patches.
A more sophisticated solution was presented in an SMTPE paper: a
review of this paper will be presented in a near future version of this
article.
Having discussed the nature of the physical components used in Front
Projection, we turn to the preparation and arrangement of these
components in a working FP system.
A still or motion picture transparency projector containing the
desired background image, or "matte," is placed so that the projection
axis is perpendicular to the camera’s shooting axis, meeting at the
place where the camera’s shooting axis touches the front surface of the
beamsplitter. (Thus the beamsplitter’s orientation is 45 degrees to
both camera and projector.)
When the projector is operating, the background matte is projected
onto the front surface of the beamsplitter. A portion of the image is
transmitted through the beamsplitter. In ordinary applications, the
transmitted part of the image is absorbed by a black surface on the
side of the beamsplitter opposite the projector, to avoid stray
reflections.
The portion of the image which is not transmitted or absorbed by the
beamsplitter is reflected through an angle of 90 degrees, and
consequently projected over the action along the camera’s shooting
axis, falling onto both foreground actors and objects as well as the
retroreflective screen behind them.
Retroreflective materials tend to reflect light back along the path
of incidence. In FP work, the background plate image is retroreflected,
back toward the beamsplitter. Part of the retroreflected background
image is again lost, as it is either absorbed by the beamsplitter or
reflected back into the projection lens. The remainder enters the
camera where it is photographed along with the action.
The only portion of the image not accounted for in the foregoing
discussion is that part of the projected background matte which falls
on the actors or other foreground subjects. Foreground lighting,
combined with the extreme deficit in retroreflectivity of the
foreground subjects in comparison to the special screen, mean that the
part of the projected image which falls on the actors is so dim as to
not be detectable in-camera.
Precise alignment of system components is required to make sure that
foreground objects perfectly cover their own shadows, cast by the
projector on the screen. This rules panning and tilting, except in the
special case where the camera is mounted so that either panning,
tilting, or both occurs around the rear nodal point of the camera lens:
so called "nodal pans" and "nodal tilts." In addition, the beamsplitter
must be large enough, and the camera close enough, so that the camera
does not take the edge of the beamsplitter into view.
Examples of nodal pan-and-tilt camera work in the context of FP can be seen in the "Dawn of Man" sequence in the film 2001: A Space Odyssey (1968), particularly the watering hole scenes. (The front projection effects on 2001 were executed by Stanley Kubrick with assistance from Tom Howard.)
A change of focal length (zoom) does not present the same difficulty
as do panning or tilting. The camera can zoom in or out as long as the
edges of the beamsplitter (or of the projected matte image) are not in
view at the widest point of the zoom. In 2001, Kubrick also
used large set pieces at either end of some FP shots in such a way as
to hide the edges of his already-gigantic retroreflective screen.
In fact, a special and inventive application of zooming was used by
Zoran Perisic, who worked as a rostrum or animation stand cameraman on 2001, to enhance the FP process for the film Superman: The Movie
(1978). Electronically controlled motorized zoom lenses are placed on
both camera and projector, and synchronized with one another so that
both lenses zoom together and at the same focal length at all times.
This means that the background image will not change its apparent size
when the camera zooms in, as the projector simultaneously projects a
reduced image. In Persic’s phrase, the projector zooms and the camera
zooms to "embrace" the smaller image. However, the zoom causes
foreground objects to appear to rush toward or away from the camera.
The combination of the "static" background and the "moving" foreground
enabled the visually effective flying scenes which helped to make the
film a success.
To enhance this effect still further, the use of FP in Superman
introduced two other innovations: use of travelling mattes (using a
motion picture projector instead of a still transparency projector, in
order to project a moving background); and the mounting of the entire
front projection rig (camera, projector, and beamsplitter) on a large
motion-controlled robotic-arm with six degrees of freedom, and using a
massive curved screen.
As in the use of travelling mattes in rear projection process
photography, the projector’s shutter must be synchronized with the
camera’s using mechanical or electronic means, in order to avoid
background flicker.
The motion-controlled front-projection mount was a masterpiece of
engineering for 1978, and used an early microprocessor for control.
Every aspect of the rig’s operation and motion could be recorded to
computer tape for later automatic playback, causing the rig to move and
operate exactly as trained.
[edit] Matte Paintings
The oldest and probably the most underrated visual effect is matte
paintings. We see these all the time but because they look so natural,
we don’t notice.
Originally, matte paintings was done on glass that stood directly in
front of the camera. To do matte painting, a partial set is created
which is only as big as the actors and only extends to where the actors
will perform. The rest of the movie set is empty space (or something
that you don’t want to be seen in the movie.) Except for a tiny spot of
the glass which is clear, the rest of the movie set is painting on the
glass. This allows you to add more scenery buildings as paintings. As
long as the actors can be seen through the clear space of the glass,
you cannot tell that the actors are not apart of the painted movie set.
Today, matte paintings are done with both paint and with CG
(computer generated visual effects). Rather than filmed through glass,
the actors are filmed normally and later composited into the matte
painting. Therefore, now the distiction between matte paintings and
computer generated visual effects is blurred. If the actors are filmed
on a partial movie set (without any green screen, etc.) then the effect
is a matte painting… even if you use computer generated effects to
get the effect.
[edit] 3D Animation for Visual Effects
When you start looking at the possibility of using 3D computer
generated effects, you need understand the different types of 3D
animation.
- 1. General Purpose Animation
- Programs such as Blender, LightWave, Maya, and 3D Studio Max are
general purpose animation programs. They are very powerful, expensive,
have steep learning curves and are used on most high end effects movies.
- 2. Special Purpose Animation Programs
- Program such as Vue, Bryce, Poser, and DAZ Studio are designed for
a specific purpose. Vue and Bryce are designed to create realistic
scenery from nature. Poser and DAZ Studio are designed to work with
special computer models called Poser figures or Digital Puppets. Some of these programs are even free such as DAZ Studio, Blender and Bryce.
- 3. Special software Plug-ins
- Software modules such as Character Studio work inside of a general
purpose animation program to create a special kind of animation similar
to a Special Purpose Animation Program. LightWave, Maya, and 3D Studio
Max can be greatly expanded through the use of plug-in modules.
- 4. Support Programs
- Programs that add in the animation but do not actually do any
rendering can be extremely useful when you have a general purpose
animation program which would be more awkward to use for a special
task. These expand the power of LightWave, Maya, and 3D Studio Max
without making these programs too cumbersome.
[edit] 3D Modeling
All elements in 3D animation must be modeled. Programs such as
LightWave, Maya, and 3D Studio Max come with a modeler module built in.
Programs such as Vue, Bryce, Poser, and DAZ Studio do not but in the
case of Poser and DAZ Studio, you can buy hundreds of figures designed
for these programs.
[edit] 3D Animation
Animation is done in three parts, the modeling, the actual animation and the rendering. The actual animation can be:
- 1. Keyframe animation
- Each movement is entered into the computer system by noteing the
position of objects at specific frames or points in time. The movement
between these key points is then calculated by the animation program
based on rules set up by the animator (straight line, curved, etc.)
- 2. Programmed animation
- For a flock of birds, rather than record the position and movement
of each bird, a computer program calculates where all the birds go and
how they move.
[edit] Compositing
Compositing is the process of combining various elements, such as 3D
imagery, live action film footage and still imagery, to create a
finished shot. All visual effects that include live actors will require
compositing. As mentioned above, matte paintings are no longer painted
onto glass. Rather the live action is composited with matte paintings
using a compositing program such as Adobe After Effects or Apple’s
Shake.
Software Compositing Applications
- Apple Shake
- Adobe After Effects
- Autodesk Combustion
- D2 Software Nuke
- Eyeon Digital Fusion
- Jahshaka
Software & Hardware Compositing Systems
- Autodesk Inferno
- Autodesk Flame
- Autodesk Flint
All compositing applications provide the same basic tools and there
is no hard and fast rule regarding which applications are for film and
which applications are for commercials. For example, while After
Effects has been used on such films as "The Aviator" it is also very
widely used for broadcast and title design. Some applications do,
however, come with specific tools which may prove advantageous
depending on the task at hand.
The primary difference between software based compositing
applications and the combined software and hardware solutions is that
the large Autodesk systems are significantly more expensive but provide
near real-time performance at film or HD resolutions.
Compositing applications typically follow two different working paradigms.
Layer based compositing applications may seem more easily
approachable to the novice or beginner compositor especially those who
have worked with still footage in Photoshop or The Gimp. While layer
based applications can provide the same results as node based
applications, node based applications are far easier to composite with
when dealing with numerous elements and multiple 3D render passes.
While daunting at first, node based systems may provide the compositor
with greater control over the shot and easier problem solving. Even a
beginning artist may benefit from learning a node based package in that
she will gain a deep understanding of the exact operations which are
taking place in order to create the effect.
[edit] 8-Bit Graphics
Every pixel of an image used in a composite is composed of four
color channels: Red, Green, Blue and Alpha. Each channel has an 8-Bit
color depth resulting in a 32-Bit image. Higher color depths include
16-Bit per channel and 32-Bit per channel (float). These higher color
depths allow for smoother display of color variation, for example, in
gradients.
[edit] Rotoscoping
Rotoscoping, or masking, is the basis of compositing. It is the
process of drawing a mask around an element in a frame or sequence of
frames. The resulting image is a combination of the Red, Green and Blue
color channels in addition to an Alpha channel which defines
transparency.
[edit] Tracking
Tracking is the process of matching a foreground-element’s motion to
that of the background. Basically you pick a decent (i.e. defined,
unique, contrasty) point on your background and tell the computer to
follow that point. What you get is the motion-path of your point, which
you can then apply to your foreground.
Tracking is divided into two categories:
2D Tracking:
Described above… (most times referred to only as "tracking", almost all compositing applications support it)
3D Tracking:
3D Tracking attempts to "solve" or derive spatial relationships between
points you tracked in 2D space and approximate the distance and
parallax between these points in 3D space through the use of complex
photogrammetry algorithms. The end result is an approximation of the
motion of the camera used to film the scene that can be exported to a
3D application or 2D application to aid in the process of matchmoving.
Shots which track most effectively tend to be those with a constant
camera path and a significant amount of parallax.
Many compositing applications can handle 3D tracking data with varying degrees of proficiency.
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