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1 Tutorials LightWave 3D Lighting Techniques Part 1 em Qua Jan 26, 2011 3:14 am

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by Amaan Akram



PART 1 of 2
(Owing to excessive workload, I've had to split
this tutorial up in to two parts. The next part
will cover outdoor and indoor lighting and general
techniques for a 3D artist)

The goals of lighting in 3D
computer graphics are more or less the same as
those of real world lighting. Lighting serves
a basic function of bringing out, or pushing
back the shapes of objects visible from the camera's
view. It gives a two-dimensional image on the
monitor an illusion of the third dimension-depth.
But it does not just stop there. It gives an
image its personality, its character. A scene
lit in different ways can give a feeling of happiness,
of sorrow, of fear etc., and it can do so in
dramatic or subtle ways. Along with personality
and character, lighting fills a scene with emotion
that is directly transmitted to the viewer.

Trying to simulate a real environment
in an artificial one can be a daunting task.
But even if you make your 3D rendering look absolutely
photo-realistic, it doesn't guarantee that the
image carries enough emotion to elicit a "wow" from
the people viewing it. Making 3D renderings photo-realistic
can be hard. Putting deep emotions in them can
be even harder. However, if you plan out your
lighting strategy for the mood and emotion that
you want your rendering to express, you make
the process easier for yourself.

The overall thrust of this writing
is to produce photo-realistic images by applying
good lighting techniques. I will use Lightwave
3D to demonstrate the lighting techniques used,
but these techniques can be applied in any 3D
software.

COMPONENTS & PROPERTIES
OF LIGHT


Each light source can be broken
down in to 4 distinct components and analyzed
accordingly.


  • Intensity
  • Direction
  • Color
  • Size


I consider the abovementioned
terms to be self-explanatory, but I will give
some description of each in the following text.
Some people combine all these terms under another
term which they refer to as "Quality of Light".
This quality of light is determined by the contribution
of each of these 4 components towards the overall
lighting within a scene.

I would like to give a few examples
here from the world of photography. As I have
discovered, photographers are masters of lighting
and there is much to be learned from their work.

For example, the quality of
light varies from time to time in a natural environment,
and photographers choose their subjects according
to the quality of the available light at a given
time during the day. Some photographers shoot
only after dawn and just before sunset because
the light at these times of the day has stronger
colors, and casts long, dramatic shadows. You
can simulate this kind of environment inside
your 3D software and get some really dynamic
renderings. Low-angled incoming light is good
for sidelighting, which gives a good overall
three-dimensional quality to your subjects. Backlighting
them with similar lights can create outstanding
silhouettes.

I often light my characters
using low-angled lights that create long shadows
and highlight the form of the character. This
kind of lighting is also very good for landscapes,
so try such a lighting setup in your next landscape
rendering.

In overcast lighting conditions,
such as a cloudy day, photographers shoot close-ups
of flowers, for example. Overcast lighting translates
to a light source of considerable area (Area
light source in Lightwave). Other examples of
photography that can be shot in overcast conditions
(or with a big area light source) are portrait
photography and food photography. These don't
necessarily have to be done outdoors. The operative
phrase here is "Big Area Light Source."

I shall now individually describe
each of the 4 components of light.

LIGHT INTENSITY

Intensity of light can simply
be defined as the amount of light being emitted
from a source of light. As you increase a light's
intensity from zero (off)to very high values,
interesting things start to happen to the objects
being lit by such a light. Below is a series
of images that show some of these effects. I
wanted to highlight a sphere placed between some
objects, and I analyzed the effects of changing
the intensity of the light in the scene on the
overall composition.
<table align="center" border="0" cellpadding="2" cellspacing="2">
<tr align="center" valign="middle">
<td>
fig. 1.1
</td>
<td>
fig. 1.2
</td>
<td>
fig. 1.3
</td>
</tr>
<tr align="center" valign="middle">
<td>
fig. 1.4
</td>
<td>
fig. 1.5
</td>
<td>
fig. 1.6
</td>
</tr>
<tr align="center" valign="middle">
<td>
fig. 1.7
</td>
<td>
fig. 1.8
</td>
<td> </td>
</tr>
</table>

Fig. 1.1 is very under
lit and you can barely see the reflection of
the light source.

Fig. 1.2 could still
benefit from a stronger lightsource. A sphere
reflecting the light source is now visible.

Fig. 1.3 shows most
of the objects in the scene, but doesn't make
a strong statement. Textures are beginning to
emerge.

Fig. 1.4 shows almost
all the objects in the scene. Note that you no
longer see the reflection of the light source,
and the texture on a third of the sphere has
been lost.

Fig. 1.5 brings out
all the objects in the scene in a clear manner.
The sphere's colors are now over-saturated because
of the stronger light (compared to Fig. 1.3)

Fig. 1.6 shows that
the objects surrounding the central sphere are
beginning to get over-exposed to light, and their
colors begin to saturate.

Fig. 1.7 simply intensifies
the effects mentioned in the description of Fig.
1.6.

Fig. 1.8 represents wildly
over-saturated colors and overly bright objects
with a considerable amount of texture and foreground
lost to over-exposure.

If we continue to analyze this
series of pictures, we'll notice that the contrast
between the sphere and its surrounding objects
is very much balanced in Fig. 1.5 as the surrounding
objects are nicely lit and the profile of the
sphere can be clearly recognized. In Fig. 1.8,
however, you'll notice that the sphere no longer
has a central role, leading to weaker composition.

That being said, there are occasions
where over-exposure may be very desirable. It
all depends on how you want to present an image,
and if over-exposure to light brings out some
of the subject's stronger features, then by all
means do as you want.

LIGHT DIRECTION

Imagine a scene where there's
light of equal intensity and color is incident
on a human face from all directions, and the
background is black. What would you see? You
would just see the 2-dimensional outline of the
face. Why? Because light rays of the same color
and same intensity will 'paint' all sides of
the face with the same color with the same intensity.
If a shadow were to be formed, it would be washed
out instantly by light rays incident upon the
shadowed region.

The point that I am making here
is that the reason we are able to recognize the
shape of an object is because light rays of different
intensities
hitting the object from different
directions
'paint' the object with highlights
and shadows.

The direction of incoming light
from a light source can enhance the shape of
the subject and the overall emotion in the scene.
It can also ruin what you are trying to capture
in the image. To give depth to the object being
lit, place the primary light source, or key light,
at a certain angle to the camera to bring out
highlights and shadows. Doing so will create
or enhance the illusion of depth in your object
by having a graduated fall off from bright to
dark over the surface of your object. What you
see on the monitor is actually a two dimensional
image, and the illusion of three dimensions is
created by highlights and shadows in your object.
To illustrate this point further, consider the
two rendered images below.
<table align="center" border="0" cellpadding="2" cellspacing="2">
<tr align="center" valign="middle">
<td>
fig. 2.1
</td>
<td>
fig. 2.2
</td>
</tr>
</table>

Fig 2.1 shows the object being
lit from a single light source placed at the
left of the camera. You can clearly see the folds,
the buldges and the depressions on the surface.
You can also clearly see the base of this object
touching the ground and casting a shadow.

Fig 2.2 represents the same
object, but the light source is directly behind
the camera. Frontal details are almost lost because
the cast shadows in 2.1 have been washed out
by the direct light. Some detail, however, on
the edges is still visible. It also looks...very
boring in my opinion.

The direction of incoming light
also has an effect on the mood of the image.
Following is a typical example of a face being
lit from below, giving a very dramatic effect.
Consider the two images below. Each shows light
coming in from beneath the character's face,
but from different directions and each brings
out the personality of the character in different
way. Fig 3.1 directly brings out the menacing
personality of the character, whereas Fig 3.2
brings it out in a subtle way.
<table align="center" border="0" cellpadding="2" cellspacing="2">
<tr align="center" valign="middle">
<td>
fig. 3.1
</td>
<td>
fig. 3.2
</td>
</tr>
</table>
We are not very used to seeing such kind of
lighting. Outdoors, light comes primarily from
the sky above us and indoors we place lights
either on ceilings or on walls. Light coming
from almost directly below the face can 'hurt'
the eyes of the subject because usually in such
a situation, the light source is directly visible
to the human eye. In most cases, we try not to
look directly in to a light source. Seeing a
character who is comfortable with such direct
light--with facial features being brought out
in uncommon ways--does have a dramatic impact
upon our perception of the personality of the
character. If you think of light coming from
above as positive light, light coming from below
can be considered as the inverse of that positive
light, and it reduces the character's positive
traits.

However, not all situations
in which light is coming from under the face
are negative. I'll mention here a typical example
of a scene where light coming from below (like
a warm redish glow) gives a romantic look.

While lighting faces, or even
an entire character, keep in mind what features
of the character define his/her personality.
If we observe the character in figures 3.1 and
3.2, we will notice that the personality of the
character is defined by his long face, his heavy
brows and cheek bones, his somewhat small eyes
etc. All these features give his personality
a negative touch. But his nose, for example,
is very ordinary. Every character has certain
features that, when highlighted, have either
a negative or a positive influence on the character's
personality. These positive and negative features
can be highlighted with the appropriate kind
of lighting. If you look at the same character
in Fig. 2.1, and then compare the personality
which is being defined in Fig 3.1, you will notice
that there's a big difference in the readibility
of his emotions. Fig 2.1 makes him look like
a bit of a thinker (with a muscular bod). Almost
all the negative features of his face which I
just mentioned (the heavy brows and the cheek
bones etc.) are not very well picked up by the
lighting setup in Fig 2.2, and even in Fig 2.1.
In short, light your character to bring out or
enhance his/her personality.

There can be situations where
you may want to hide the negative features of
a character to make him or her look innocent.
In such a situation, directing your lights in
such a way that the negative shadows of prominent
features are washed out may help achieve the
desired purpose.

Light coming from directly above
a person's head was often used by Renaissance
painters to depict divinty and spirituality.
However, the effect of such light is greatly
dependant upon the subject. Check out figures
4.1 and 4.2. While the negative aspects of his
face have certainly been muted to a great extent,
they have not gone away completely.
<table align="center" border="0" cellpadding="2" cellspacing="2">
<tr align="center" valign="middle">
<td>
fig. 4.1
</td>
<td>
fig. 4.2
</td>
</tr>
</table>

Figures 4.3 and 4.4 again show
situations of light coming from top, but not
having any 'angelic' effect. The difference between
figures 4.1 and 4.2, and 4.3 and 4.4 is that
the latter have more localised concentrated and
harsh light spots. Such harsh and localised light
(along with harsh shadows) is adding to the negative
side of this character.
<table align="center" border="0" cellpadding="2" cellspacing="2">
<tr align="center" valign="middle">
<td>
fig. 4.3
</td>
<td>
fig. 4.4
</td>
</tr>
</table>
LIGHT COLOR

I stated earlier that the reason
we are able to recognize the shape of an object
is because light rays of different intesities hitting
the object from different directions 'paint'
the object with highlights and shadows. To make
this statement more complete, I'd have to add
here that our ability to recognize the shape
of an object depends upon the ability of light
rays of different intensities and different
colors
hitting the object from different
directions
to 'paint' the object with highlights
and shadows.

The color of incident light
depends upon its source. White light is composed
of all the possible colors that exist. A ray
of white light changes color if it encounters
an obstacle, which is not white and is not black.
If it hits a white object, the same ray is reflected.
If the object is black in color, the object absorbs
all the light, no matter what color it was originally,
and nothing is reflected. So basically when you
look at a totally black object, you see the color
black because no light enters your eye from that
direction. To prove this point, I ask you to
close your eyes for one second (and please try
not to doze off). Now...which color did we see?

In Fig. 4.5 below you can see
a white incident ray of light, which is reflected
off a blue floor. The floor absorbs all the colors
in the incident ray except blue, and reflects
it. Note that the light is reflected at the same
angle at which it was incident relative to the
floor.


Fig. 4.5

Other things being equal, any
object that is in the path of this reflected
blue ray will be lit by blue light only. Furthermore,
the ability for a color to reflect light depends
on its brightness and richness. Bright red, for
example, will bounce off more light than dark
blue.

Different colors also convey
spatial and temporal relationships. OK. Lemme
explain what those fancy words are. A spatial
relationship is based on the distance (or space)
between two or more objects. A temporal relationship
is based on time. (Ever heard the phrase "temporal
displacement" in Star Trek?)

The color Blue is often used
to represent depth. Just take a look at any TV/film
and all night time filming will have a slight
blue tint. An object lit with the darker (less
saturated) shades of blue generally has a tendency
to stay in the background.

Generally speaking, saturated
colors represent close proximity, whereas unsaturated
represent distance. A good example to quote here
is foggy/misty mornings. As objects recede in
to the distance, they tend to lose their color
saturation. To sum it up, brightly saturated
colors tend to stay in the foreground, and less
saturated colors find their place in the background.

Take a peek at the following
three figures (5.1-5.3) of Gramps (modeled and
textured by David
Maas). All these images were tinted with
different colors in Photoshop, and each represents
a different time of the day. Even though the
shadows don't change position through each of
these three images, a different point in time
during the day is depicted by each.
<table align="center" border="0" cellpadding="2" cellspacing="2">
<tr align="center" valign="middle">
<td>

fig. 5.1
(Early Morning)
</td>
<td>
fig. 5.2
(Mid-day-winter)
</td>
<td>
fig. 5.3
(evening-summer)
</td>
</tr>
</table>

Mornings usually have a blue
tint. Around mid-day, you get more or less even
colored light. There is some blue light present
(reflected from the sky), but its effect is not
as much pronounced. Evening light is typically
characterized by warm, orange hues.

Gaze upon the next set of three
images. The shadows change positions in the first
two. Fig. 5.4 represents summer mid-day again,
and 5.5 represents evening time. Fig 5.6 depicts
a scene lit by a moon high in the sky. The blue
tint is there to give the illusion of night time.
<table align="center" border="0" cellpadding="2" cellspacing="2">
<tr align="center" valign="middle">
<td>

fig. 5.4
</td>
<td>
fig. 5.5
</td>
</tr>
<tr align="center" valign="middle">
<td colspan="2">
fig. 5.6
</td>
</tr>
</table>
LIGHT SOURCE SIZE

The size of the light source
has a major effect on the overall feeling of
the scene. A small sized light source casts very
sharp and distinct shadows, bringing out the
element of tension in the image. An example of
a light source small in size would be a flashlight's
bulb and it does indeed cast very sharp shadows.

A light source occupying a bigger
area casts a much softer (less distinct) shadow,
and brings a relaxed feeling to a scene.

Fix your eyes on our familiar
Mr. Gramps in figure 6.1 below for a moment.
You will realize that his face is lit from a
very small, concentrated source of light that
casts very distinct shadows, most noticeable
under the nose and the brows. The light source
brings out the sadness, hopelessness in the scene
in a much stronger way than in figure 6.2. Both
figures are lit from light sources placed above
Gramps, but the light source in 6.2 is much bigger
(evident from the soft shadows) than the one
in 6.1.
<table align="center" border="0" cellpadding="2" cellspacing="2">
<tr align="center" valign="middle">
<td>
fig. 6.1
</td>
<td>
fig. 6.2
</td>
</tr>
</table>
The softer/bigger light source in 6.2 almost
gives Gramps an element of hope that is missing
in 6.1. He looks sad, but hopeful (note that
both 6.1 and 6.2 use the same Gramps, with the
same facial expression).

END OF PART I

Part II coming soon Smile

Amaan
Akram
- [Você precisa estar registrado e conectado para ver este link.] - [Você precisa estar registrado e conectado para ver este link.]

Special thanks to David Mass
of the order of STICKMAN,
for his support and feedback, and of course,
for Gramps.
]

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