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General
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Lighting
Theory for CG
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This
Floor light actually simulates bounced
light from the floor (radiosity) to
some extent. Note that I have also turned
on ‘No Specular’ from the
Lights menu for the floor light. This
was done because if there were more
objects placed in the scene with specular
settings for their respective surfaces,
then you would see the specular spot
on the objects. The floor acts like
a huge area light source with low intensity
and would not cast specular hotspots
on objects. We are using a point light
here to simulate the floor’s reflected
light and that would lead to a specular
spot that is concentrated and not spread
out. Therefore, it is advisable to turn
on ‘No Specular’. (You could
replace the point light with an area
light for more realism, but then be
prepared to wait as the rendering times
will go up real high)
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Fig.7.3
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Also
note that I have turned on intensity
fall-off for the Floor light to produce
a more realistic lighting setting.
Before
moving onto the next section, I would
like to advise that if you use area
light sources in your scene, keep
their area small. A very large area
light may produce very ‘noisy’
shadows that you may not be able to
smooth out even with ‘Enhanced
High’ anti-aliasing settings.
If you have a use a huge area light
source and still want acceptable shadows,
break the one huge area light source
into smaller area light sources (the
trade off here is longer rendering
times)
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Some
tips on Lighting
While
I am no master of lighting as yet, I
would like to share a few things that
I have learnt about compositing a scene.
But before I do that, I would like to
point out that you should get yourself
a book on lighting if you are a beginner
(if you are not, then you should not
be reading this article J ). One book
that I have found very useful is Painting
With Light (University of California
Press). The book is written by the ace
cinematographer of the age of black-and-white
movies, John Alton. The book has no
colored illustration and concentrates
on some very effective techniques of
film lighting. I would recommend the
book to anyone who is planning to study
indoor/outdoor lighting.
I
have also found magazines of photography
as very helpful in studying lighting
techniques. One can learn so much by
studying the art of those who have mastered
the fine art of lighting.
Now
getting back to the subject at hand—lighting
tips. I would recommend that you start
out with simple black-and-white lighting
studies. While this will keep your mind
off the larger color spectrum, this
exercise will give you some knowledge
of how to play around with contrast
to bring your subject to the attention
of the viewer. John Alton once said,
“Black and white are colors.”
The
following renderings were done in Lightwave
after looking at some lighting concepts
in Alton’s book (In fact, they
are almost exact replicas). They illustrate
the concept of contrast and how it can
enhance the shape of your subjects.
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Fig.
8.1 (Average Approach)
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Fig.
8.3 (Better Approach)
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Fig.
8.3
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Fig
8.1 shows how lack of contrast leads
to a loss of shape definition for the
two cubes. In Fig 8.2, the places of
the cubes have been interchanged and
that has brought out their features
much more than in the previous case.
(You could also have solved the problem
by rotating the light by an angle of
about 90 degrees so that it would face
the wall behind the black cube in Fig.
8.1) Fig. 8.3 is just another very simple
example of the use of contrast and how
it has brought out the back of the cube.
However,
it is not necessary for your images
to have high contrast in them. It
depends on the scene and the mood
that you are trying to create. A comic
scene should be lit brightly, though
not necessarily. With a sad scene,
contrast can play a major role and
it should be thus emphasized more.
The mood of a scene that is tragic
can be enhanced by a strong contrast
of deep blacks and blazing whites.
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A
Practical Example
In
this section I shall take you through
the setup of a very simple scene in
which I shall apply the lighting concepts
discussed in the previous sections.
(Note that this scene does not require
any 3rd party plugins, but I will stress
the need to use one to enhance the image)
The
Scene: A roadside café. Time:
afternoon. We shall only concentrate
on a table, two chairs and other objects
to fill up the scene. (See Figure 9
below)
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Fig.
9
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Most
of the objects (the table, the chairs,
the stool, the ashtray, the plate, and
the potted plants) in this scene were
taken from Lightwave’s CD. The
cloth was modeled using Metanurbs, and
box and the cylinder are Lightwave’s
primitive objects. The road and the
sidewalk consist of planes and the curb
is just a plane extruded along a path.
In
Fig. 10 and Fig. 11 Below, I have
setup the scene in Lightwave. The
objects in the scene have default
surface settings for diffusion, specularity
etc. (Note that the objects taken
from the Lightwave CD come with preset
surface settings)
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Fig.
10
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Fig.11
(I
have temporarily removed the preset
surfaces
of
objects from Lightwave’s CD)
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Fig.
11 shows a rendered image of the textureless
scene. I applied some real world textures
of cement, concrete and wood to get
to Fig. 12 (below).
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Fig.
12
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