ADVANCED THEORIES FOR CG LIGHTING
0.1 | INTRODUCTION
To become skilled at 3D lighting, one must have an understanding
of how light works. CG lighting has been established based on rules
from cinematography, painting, photography, stage design, and
architecture. Until a 3D scene has been lit and rendered, it merely
remains nothing more than a bunch of polysurfaces.
The qualities of real world lighting, CG lighting types, shadows,
lighting techniques, and some basic tips for rendering and layout
will be discussed. As a lighting artist, one should be concerned
with more than just the illumination of your scene. Scenes should
convey an appreciation of the composition and introduce drama.
1.1 | REAL WORLD LIGHTING
A. The Visible Spectrum of Light
The visilbe spectrum of light is represented
by wavelengths where the shorter waves
are near ultraviolet radiation and the
larger waves are near infrared radiation.
Moving from the shortest to the largest
wavelengths, the colors of violet, blue,
green, yellow, orange, and red can be seen.
All colors within the visible spectrum of
light can be created by the additive process
and combination of red, green, and blue;
also known as, the primary colors of light.
That is why all computer graphic programs
have RGB inputs to create color and allow
ranges between 0 and 255.
B. Monitor Calibration
One thing to note is that your CG lighting techniques are
affected by the calibration of your computer monitor. If
your screen is very bright, your scene will most likely be
under lit. If your screen is too dim, your scene will most
likely be over lit. It is recommended that you calibrate your
screen to maximize the full tonal ranges available.
In the publishing world, calibrating your screen means
to match the color and tones of your printer. In the
digital world, calibrating your screen means to adjust the
brightness and contrast of your monitor until you see the
full range of grays and read the word “Calibrate” in the
image above. Calibrating your screen ensures that you are
lighting a scene as effectively as possible.
C. Color Balance
Professional cinematographers use different films that have been color balanced at a
specific color temperature. This dictates which color of light will appear white when filmed
and how the other light sources will be tinted. The camera in a 3D software environment
does not use film and does not have the color balancing capability that real world film
provides.
To produce photorealistic renderings, you need to adjust the colors of your computer model
lighting to mimic the color balancing effects of film. Determine what type of light each light
actually represents and adjust the RGB values appropriately from shades of red, orange,
yellow, white, light blue, and dark blue (see the image above). It only takes a small amount
of color to begin to tint a surface; therefore, be careful not to make the tinted light too
bright. There is no set formula for tinting lights to produce a final look that mimics film. Use
your own eye and artistic judgment.
D. Behavior of Light
Light obeys many rules; however, in CG lighting, only a few
rules require understanding: the Inverse Square Law, Law of
Reflection, and the Index of Refraction.
The Inverse Square Law describes how light fades over a
distance. As light travels further from its source, it covers more
area; thus, the light loses its intensity. This law is important
to understand in 3D programs because this is how real lights
behave. In most programs, however, this option is not always
turned on by default. As you place lights in your scene, it is
recommended that you turn on the decay or attenuation
settings.
The Law of Reflection states that the angle of reflection equals
the angle of incidence, which is measured relative to the
surface normal at that point. This is simulated by rendering
engines that use raytracing. Raytracing simulates reflections
and refractions so that light and color bounces off of objects in
an accurate manner (see the reflectance values of real-world
materials on the next page).
The Index of Refraction (IOR) describes how light bends when
it passes through transparent and translucent objects. This
behavior determines the level of distortion that you can see
on and through that object. The index is never at a value less
than 1.0 and can be increased to a value of 2.0 or beyond. As
the value increases, the distortion increases (see the refraction
values of real-world materials on the next page).
Shadows: play a massive role in describing light adding realism,
consistency, relationships, and composition. Shadows are relative
areas within a scene where light is absent to a degree. When we
place lights, we also must think about the shadows that will be
cast. There will be more on this topic later.
associated positive and
negative effect to take
into consideration.
Blue light can paint an
unhappy or a calm and
serene scene; whereas,
Color: of light gives you a visual clue to what is happening within red is often used to set
a scene. Color of lighting can describe the type of light source,
a dangerous tone or a
time of day, season, type of weather, and the mood of your
passionate scene. Green
scene. Color is a sizable consideration in lighting a scene and
is associated with peace
should be carefully used.
and environmental
awareness, but can also
Yellow to orange light is typical of domestic lighting and blue light refer to greed, envy, or
is typical for light coming from the sky. Each color has an
nausea.
E. Qualities of Light
To ensure that your lighting efforts in CG appear convincing, there
are several characteristics that make a light source look real and
can be described by its intensity, shadow, color, softness, throw,
and motivation.
Intensity: describes how
strong or bright a light
source appears. The light
with strongest intesity in
a scene is known as the
dominant or key light
and will cast the most
noticeable shadows. A
light’s intensity (its color
and multiplier) needs to be
adjusted depending on the
context of the scene.
Softness: of light is widespread in the real world and directly
correlates to the sharpness of shadows that are produced. In
CG environments and because of default settings, softness does
not appear as much as it should; therefore, we tend to see more
crisp-edge shadows than you would typically see in real life. Just
about every light produces soft-edged shadows.
Throw is the manner in which a light’s illumination is shaped
or patterned by the breaking up of the light through a physical
object or by texture map. An example of throw is the light shining
through a lampshade, foliage, or even venetian blinds.
Motivation: of light is a way to categorize light
sources by how they operate within in a scene
whether logically or emotionally. Logical lights, also
known as Practical Lights, are light sources that
represent an actual light source. If you can see a
light in the ceiling or see a lamp on an end table,
these should be actual logical light sources within
the scene. We expect that those components will
be a light source.
Placing only logical lights within a scene can have
uninspiring results; therefore, we need additional
lights placed that play an emotional role. These
lights are referred to as Pictorial Lights and are
placed simply because the effect that is produced
is aesthetically pleasing. These lights introduce the
drama and the emotional link for your image.
1.2 | Shadows
The Importance of Shadows
Shadows are the biggest
aesthetic consideration for
lighting a scene. Shadows
give the human eye a cue
to distinguish where a light
source is located, what an
object is made of, how far
away it is, and how it relates
spatially to its surroundings.
Shadows also add to the
3D nature of a scene. Since our rendering is a 2D image,
shadows can be used to show items within a scene that
may exist out of frame. Shadows also are a useful tool for
establishing the focal point within a scene and for hiding
imperfections. By obscuring the areas surrounding an object,
you are effectively framing that object as the focal point of the
image.
The Technical Side of Shadows
Shadows are the most computationally intensive part of lighting.
Knowing when to turn off shadows from a light source is an
important consideration while lighting a scene. Typically, only
your main lighting source should cast hard shadows and your
intermediate sources should cast softer shadows. Ambient and
area lights should have shadows turned off to save on render
times. If all light sources have shadow casting turned on, your
scene will be visually distracting because the light sources are
competing and will also add to your render times.
Shadow Saturation
If your shadows are too dark, you need to add ambient/fill lights
to the scene to lighten them up. Shadows in general are more
gray than black; therefore, adding fill lights will make almost
black shadows into grayer casts.
1.3 | Light Types
Omni/Point Lights are lights which emit an even
distribution of light around a single point. These
lights are best used to provide overall fill lighting.
Area Lights, such as Rectangular and
Linear Lights, provide a more realistic
light in that these lights provide
the ability to create a light source
that has an actual scalable size. The
larger the area light or the more area
lights that cover an overall area, the
softer the shadows will become. The
only down side to an area light is
that since it more closely represents
realistic lighting sources, it can be
computationally intensive.
Spot Lights cast a focused beam of light confined to a cone that is
aimed at a target. This light is the basic building block of lighting a
scene because it offers the most controllability. The cone is made up of
a hot spot and the falloff ring. The hot spot it the area in which 100%
of the light will shine; whereas, the falloff ring it the area in which the
light gradually falls off from 100% to 0%. The closer the hot spot to
the falloff ring, the sharper the boundary edge of the cone will appear.
Adding more distance between the hotspot and the falloff will create a
softer edge.
Experience Notes: Interior lighting, depending on the scene,
requires numerous types of lights set at low multiplier values
to simulate logical/actual lighting and additional pictorial lights
to add some drama and flare to the shot. If you add just one or
two lights to an interior shot, your rendering will appear flat.
Real lighting works by giving the scene an even distribution of
decaying light over a given area allowing the light to bounce off
of materials and surfaces to further light a space. Notice that
every interior space you walk into and occupy has a set of lights
spread out in a repetitive pattern. Paint colors and materials
selected add to the reflective value of space; thus, adding to
the amount of light bounced off of a surface. Interior lighting is
much about the indirect bounce of light, as well as, the direct
light source and target.
This image illustrates the final rendered shot of the UNCC
Student Union Rotunda. The next image shows the amount of
lighting required to create the scene. These images were created
within 3D Studio Max; however, the same concepts apply in
Rhinoceros using the VRay Plugin (the two images on the right
side of the previous slide are the lighting to rendered image
comparison within Rhinoceros using the VRay Plugin).
Directional/Sun Lights cast parallel light rays
in a single specified direction. Directional
lights often are used to simulate sunlight.
The position of a direction light does not
matter; only the rotation angle is crucial.
Directional lights are also used for fill lighting
also known as ambient light or the general
illumination of a scene.
Ambient/GI Light is not a light source you place, but is the general/global illumination of a scene created
by light reflecting off of other objects. In real life, it is the ambient light that allows us to see into shadowy
corners, and in real life the ambient light actually varies based on the objects in which light is reflecting. In
computer graphic programs, ambient light cannot be calculated as it occurs in real life; therefore it is generally
applied evenly across a scene. The use of ambient light will generally make your scene appear flatter depriving
the scene of any depth or contrast. For realistic lighting results, the ambient light tool should be turned off or
set to black due to the unrealistic way it applies the illumination across a scene. Adding fill lighting such as low
valued point lights or directional lights is the best way to create ambient light.
2.1 | LIGHTING TECHNIQUES
A. Three-Point Lighting
The convention of three-point lighting is one that is firmly
established in cinematography and is the foundation
for CG lighting. Lighting with one source and behind the
camera view will always make your rendering look flat. In
this system, there are three light types involved and each
has a specific function. It should be noted that the threepoint lighting system is not meant to be taken literally.
You can have more than three lights in a scene. What is
important is that the way in which all the lights are used
should fit into the Three-Point Lighting categories: Key, Fill,
and Back Lighting.
The key/dominant light provides the main illumination in a
scene and casts the most obvious shadows. This might be
the sun in an exterior scene, the sunlight entering through
a window in a daylit indoor scene, or the logical lights in the
ceiling of indoor scenes.
The Key Light creates the subject’s main illumination, and
defines the most visible lighting and shadows. It is often set
at 15 to 45 degrees to the side (to the left or right and higher)
from the camera. Be sure to stop and do text-renders of your
key light, which should have a nice balance and contrast
between light and dark, and shading that uses all of the grays
in between. Your key light rendering should almost look like the
final rendering except there are probably pitch black areas or
very harsh contrasts visible, which are corrected with the next
lighting concepts.
The fill light is used to apply indirect lighting to the entire
scene and is usually placed on the opposite side of the subject
from the key light; thus, it opens up the lighting on the side of
the subject in shadow and reduces the shadow intensity. The
fill light softens and extends the illumination provided by the
key light, and makes more of the subject visible.
Typically fill lights consist of point and spot lights and a scene
can have several fill lights added to a scene. From the top view,
a fill light should come from a generally opposite angle than
the key light; however, in elevation, it should be lower than the
key light. At most, fill lights can be about half as bright and for
more shadowy environments, use only an eighth. Be careful
that multiple fills can overlap; therefore, the sum of their
values should still fit within the half to eighth range.
The backlight/rim light is used to separate the focal piece from
the background and to highlight the subject. Essentially, this
light creates a bright rim around the object in which you are
highlighting.
From the top view, add a spot light, and position it behind
your subject, opposite from the camera. From the right view,
position the Back Light above the subject. Adjust the rim light
until it gives you a clear, bright outline that highlights the
top or side edge of the subject. Rim lights can be as bright as
necessary to achieve the effect. A rim light also usually needs
to cast shadows.
B. Night Time
Moonlight is a neutral gray in color; however, it is best represented from an orangey-beige
color to a pale blue color as it approaches its highest point in the sky (Figure 9.09). The
best strategy in CG is to make the moonlight the overall color using the orangey-beige to
pale blue color and then adding in blue fill lights. Yellow-orange area lights can then be
placed to simulate artificial street lights or lighting from behind a window.
3.1 | TIPS & TRICKS
A. Rendering
It’s never too early to start rendering. As soon as you place your first light,
render a quick shot to test its effects on the scene. You lights should be
placed relative to the scene and camera view. Obviously, if you have more
than one view, you probably will have more than one three-point lighting
scheme. Set one light and get it right, then add the others. Start with
the key light, then the fill light, and then finally the backlight. With each
addition, you will most likely have to tweak the previously placed light to a
lower multiplier value. Sometimes it is also necessary to tweak the actual
construction of an object to make the lighting have more drama such as
chamfering or rounding the edges of an object to reflect/refract light in an
interesting way.
B. Common Shot Types
To ensure that your production sits comfortably within established
boundaries of recognizable cinematic conventions, it is useful to know the
different shot types. There are five commonly accepted shot types, all used
for specific purposes of conveying a scene’s intent and have been converted
from character shot types to architectural shot types:
Wide Shot
Often used to show the overall context and set the location, time of day,
and season that will run through the other images within the script.
Medium Shot
Generally is used to show the overall building with the context not so
apparent.
Medium Close-Up
Generally is used to show main features of the building.
Close-Up
Focuses on one particular area such as the main space of the building or a
particular detail.
Extreme Close-Up
Frames, highlights, and zooms-in on a specific detail from the close-up shot.
C. The Rule of Thirds
When putting together a shot, the rule of thirds can help ensure a higher
level of interest. By thinking of your image divided into three sections
vertically and horizontally, you can use these guides to help position
your main elements. Positioning objects in the dead center of a frame is
unexciting. By placing elements along the imaginary lines of any of the four
intersections, you’ll immediately have a far more appealing arrangement.