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Lighting workflow |
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Author:
Martin
Level :
Intermediate
Environment :
Maya 7.0
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We have to experiment a lot to get a good result.
Most often, however, my best outputs are from a proper workflow.
This tutorial discusses the workflow, focusing on maintaining control
of your lighting.
Getting Started.
a. Monitor Calibration.
If your monitor is not adjusted properly, then your output
will vary from monitor to monitor. If you send your output image
to someone else, either it will be burnt or dark. No two monitors
show an image exactly the same way, you can at least see that
you meet a basic minimum requirement. The controls for adjusting
a computer display vary between brands of monitors, color-matching
software and video cards. To adjust the brightness and contrast,
you can use the Figure 1 below. We should be able to see the
first and last digits in the image.
Figure 1. Monitor Calibration.
b. Start in Darkness.
So you did your monitor calibration. Now
start a scene in total darkness. Put your key light first and then
all others. This will give you an overall control over the scene.
In live film this is not practical because of natural light.
Luckily
for us, we don't face that problem in the computer graphics
world.
c. Ambient Light.
In the real world, ambient light is widely
distributed, "indirect" light that has bounced off objects in the
environment. Dark or shadowed areas of a real room are sometimes
made visible only by the ambient light. In the real world ambient
light is tinted as it bounces around the environment and adds different
colors to different sides of objects, based on colors it has picked
up from the environment. This is a light source with no particular
source location or direction. Ambient light appears to come from
everywhere at the same time, like sunlight on a hazy day. Ambient
light is typically used to control the overall brightness and color
of a scene. An ambient light shines in two ways-some of the light
shines evenly in all directions from the location of the light (similar
to a point light), and some of the light shines evenly in all directions
from all directions (as if emitted from the inner surface of an
infinitely large sphere).
Figure 2. Ambient Light
d. Point Lights.
Point light emits light uniformly in all directions,
like a bare light bulb or glowing star in space. In the real world,
there is no light that is uniformly Omni directional. Most sources
emit light in some directions than others.
Figure 3. Point Lights.
e. Spot Lights.
Spotlight is a convenient light for many artists
because it can be controlled properly to aim light at a specific
target, as shown in Spotlight (1) below.
To create a spotlight
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Select Create > Lights > Spot Light.
The spotlight's icon will be at the center of the grid. This is a
cone shaped light with an arrow pointing out of it. It shows that
the light emits a beam of light that gradually widens with distance.
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Select Modify > Transformation Tools > Show Manipulator
Tool.
We will get two manipulators that we can move to position and aim
the light precisely. The look-at point specifies where the light
focuses. The eye point defines the position of the light source.
An alternative way to position a spotlight is
to select the light and then select Panels > Look Through Selected.
You can then dolly and pan the view to focus on the desired surface.
The area of focus is where the light strikes the surface. To return
to the perspective view select Panels > Perspective > persp.
Figure 4. Spotlight
Figure 4.1. Spotlight (1).
Figure 4.2. Spotlight (Penumbra)
Figure 4.3. Spotlight (Dropoff)
Spotlight limits the light within a specified
cone or beam.
f. Directional Lights.
A directional light sets a single vector
for all its illumination and it's every object from the same angle,
no matter where the object is located, behind or in front. All the
shadows cast by a directional light are cast in the same direction
and are orthogonal projections of each object's shape. The only
thing that matters in placing a directional light is which way it
is pointed.
A directional light is similar to sunlight. Its
parallel rays strike all objects in the scene from a single direction
as indicated by the arrow icon representing the light. The position
of the light is not so much important as the direction that the
arrow icon points to.
When you create a light, the scene view does not
display its effect, by default. The scene view instead uses default
lighting.
Select Lighting > Use All Lights (Hotkey: 7).
This lights up the scene view only with lights you've created and
not with default lighting. If you later want to see the scene view
with default lighting again, select Lighting > Use Default Lighting
(Hotkey: 6).
When you render the scene, by default, Maya uses all lights you've
created. If you don't create any lights, Maya creates a temporary
default directional light for you and then deletes it when the render
is complete.
Procedure to edit the Directional light.
With the directional light selected, rotate the light in various
directions. The shading of surfaces changes as you rotate the light.
The more directly the light points at a surface, the brighter the
shading. A directional light is affected by its rotation, not its
position. As you'll see later, the position of other lights affects
the lighting.
With the light still selected, open the Attribute Editor (under
the Window menu). Drag the Intensity slider to various values to
see the effects of intensity.
Higher values brighten the surfaces. For example, an Intensity of
1.6 brightens the lighting so much that the gray default shading
of some surfaces are bleached to white.
Figure 5. Directional light
g. Area Lights.
A type of light source that emits light
from a two-dimensional area. The bigger the light, the stronger the
intensity. Area lights are used for high reflective objects to simulate
the studio product photography look. The main purpose of area light
sources is to generate more realistic lighting, resulting in soft
shadows.
In Maya, area lights are two-dimensional rectangular light sources.
Use area lights to simulate the rectangular reflections of windows
on surfaces. An area light is initially two units long and one unit
wide. Use Maya's transformation tools to resize and place area lights
in the scene.
Compared to other light sources, area lights can take a longer time
to render, but they can produce higher quality light and shadows.
Area lights are particularly good for high-quality still images,
but less advantageous for longer animations where rendering speed
is crucial.
Area lights are physically based, so there
is no need for a decay option. The angles formed with the area light
and the point that is shaded determine the illumination. As the
point moves further away from the area light, the angle decreases
and so does the illumination, much like decay.
h. Volume Light.
A major advantage of using a volume light
is that you have a visual representation of the extent of the light
(the space within which it is bound).
You can use a volume light as a negative light (to remove or decrease
illumination) or to lighten up shadows.
The falloff of light in the volume can be represented by the color
ramp (gradient) attribute in Maya, which prevents the need for various
decay parameters, and also provides additional control. The color
gradient is also useful for volume fog.
You can achieve different effects with light
direction. Outward behaves like a point light and Downward acts
like a directional light. Inward reverses the light direction for
shading, giving the appearance of inward illumination. When using
shadows with the Inward light direction you may get unexpected results.
In all cases the light shape dictates the extent of the light.
Testing Your Lights.
Managing all your tests and revisions efficiently
is an important part of producing high quality renders. In a scene
with several lights, we need to know what each specific light is
doing for you, and which light to adjust if we don't like the shading
of a surface. There are several techniques to make tests that clearly
show the information you need to control our lighting.
a. Isolating a light.
By isolating a light we can easily find
where all lights are aimed. To set up this, deactivate all the other
lights in the scene. Be sure to turn off the default light. By doing
these we can give attention to our specific problems and by that
we can fix it. Rendering with single light is much faster than with
all lights. The process of "debugging" this kind of lighting problem
is made faster and more efficient by viewing lights in isolation.
b. False color lights.
We used to light our objects with several
lights. When two or more lights are hitting a subject, all their
illumination may overlap and blend together. To identify the illumination
of each light, we can use different colors. Generally this technique
is used in real lighting in film making.
Figure 6.1. False color lights. In the above background, I put two lights
from different directions.
Figure 6.2.
Background with only red light from one
direction
Figure 6.3. Background with green light from other
direction.
Figure 6.4. Overlapping of red and green lights.
Check the image above. There are two lights of
different colors which blends together. Its easy to differentiate
between two colors.
If we are looking at normally colored lighting in figure 6.1,
we might not able to tell where the light is spilling. With the
false colors, the light is given its color, we can easily locate
the light.
c. Comparison
This is a very simple technique, but it helps
us a lot while doing lighting. Very minute differences or adjustments,
which you might not be able to accurately perceive when viewing
two renders side by side, can be noticed as a movement or shift
in the image when you flip between them in the same window.
Look at the above image, in the red
circle the arrow pointing down is for keeping
the image in the window and the arrow pointing up is for
removing the image from the same window. By sliding the bar
(red arrow) we can see the previous render. So by sliding, we can
identify the minor changes in our render.
Shading.
The materials, shaders, and textures are
also factors that determine how a model responds to light. In production
a test without textures can help us better see what shading the
lighting is creating. Anyway, the final shading will make an enormous
difference to the output.
Conclusion
I hope you will try all these tips and tricks
in your production as well as in your personal work. I am expecting
your reviews about this tutorial. good luck.
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