Figure 5
There are still a few more settings that must be adjusted to achieve
nice shadows. Blender uses something known as clipping to determine
which parts of the scene will be included in the shadow calculations
during rendering. All objects contained within the ClipSta
and ClipEnd values will cast and receive shadows. Fig. 6 is a
demonstration of a high ClipSta value. The value is so high
that the top part of the model cannot be seen in the spot lights view
when used as the camera.
Adjust the clipping values so that the model of the woman and the
ground plane fall inside of the visible boundaries of the spot
light (Fig. 7).
Before we test render, increase the values of the BufSi,
Samples, and Bias buttons (Fig. 8). These settings will
increase the quality of the shadows but will also increase render
time. BufSi sets the size of the shadow buffer in pixels and
Samples determines how many samples of the shadow buffer are
sampled to reduce aliasing. The best way to see the effect of these
values do is to make many test renders while adjusting the values and
comparing the renders to each other.
In order to do a test render we need to return the view from the spot
light back to the camera. Select the camera and press
ALT+ZERO
and then F12
to render. The result of all
this hard work so far can be seen in Fig. 9. Compare your settings with
those in the
"spot.blend"
file on the CD-ROM. Although we
have a nice shadow, our scene still needs a great deal of more work and
more lighting.
[subsection]Flood Fill and Back Lighting
The next light in a standard three-light setup is the Back
Lighting. The Back Light is not only used to illuminate the back
of the object but to also separate the foreground objects from the
background and add overall depth to the scene. The positioning is
usually above and behind the main subject and offset opposite
from the position of the Key (Fig. 10).
The default lamp settings will work well for back lighting. If only
one lamp is used then the energy value should be greater than or equal
to the key light. If needed increase the Dist setting as seen
in Fig. 11.
Test render the scene with just the back lighting in place. This can
be dome by moving the other lights in the scene to an inactive layer
or adjust their energy values to zero. Notice how a nice silhouette of
the model can be seen separated from the background.
The third and final style of light needed to complete our scene is the
Fill Light. The fill light is usually placed behind the camera
and is used to soften shadows from the Key and to add to the overall
ambience of a scene (Fig. 13). The intensity, or energy of the light is
usually slightly less than that of the key and back lights.
After test rendering the scene with just the fill light, we see
that parts of the model, not visible with the other two styles, can now
be seen. It is also noticeable that without a shadow there are no
visible clues available and the model seems to be floating off the
floor. This is one reason why shadows are so important in a lighting
solution.
Add all 3 lights to the scene and compare their settings to those in
the file
"three_lights.blend"
and render the scene. Not one of
the renders from the single lights was enough to properly render the
scene, but notice how rich the result is when all three lights are
used together, complimenting each other as a whole (Fig. 15).
[subsection]Shadow-Only Spots
Sometimes it is necessary to cast shadows without the need for the
bright, hard-edged light that a spot light casts, or you may just want
greater control over the intensity of the shadow itself. This is just
what the shadow-only spot light is for. Select the spot light in our
scene and duplicate it with SHIFT-D
. Turn one of the spot
lights into a standard lamp by clicking the Lamp button in
the Lamp Edit Buttons. Select the other spot light and click the
OnlyShadow button (Fig. 16).
Reduce the energy of the shadow-only spot light and render the scene.
Notice the softer mood that is achieved in Fig. 17 than that of
Fig. 15. Compare your settings with the settings in the file
"shadow_only.blend"
on the CD-ROM.
[subsection]Light Gels
A light gel in real life is when you place a colored piece of film
over a stage light or a slide with an image on it. The color or image
is then cast on the scene with the light. In Blender, this is as
simple as assigning a texture to a lamp. If you wanted to simulate the
shadow cast by a latticed windowpane, but without having to model the
architecture, you could use an image similar to Fig. 18. Add a new
image texture to your three light scene and use the window.jpg
image on the CD-ROM. If you are not familiar with adding an image
texture please review the chapters covering the use of materials and
textures in Blender.
With the spot light selected open the Lamp Edit Buttons and activate
the Add New menu to add the texture in the same way you would
add a texture to a material. Press the View button so that
the spot light will project the image properly (Fig. 19). Make sure you
return the spot light back to its default setting by removing the
OnlyShadow option.
The last step to take on the spot light is to change it to a square
spot light. Press the Square button next to the light preview
window. This is necessary so that the corners of the image don't get
cropped off.
The final result is quite convincing (Fig. 21). Color images can also be
used to simulate light from a stained glass window, and even animated
images and textures can be used for special effects.
[section]Volumetric Lighting
The term Volumetric Lighting refers to light with some type of volume
perceived. Usually this is in the form of light rays because of dust
in the air, fog, mist, or under water effects. This is best seen when
a volumetric light is obstructed by something and casting
shadows. Load the file
"volumetric1.blend"
from the CD-ROM.
Our scene consists of only a pre-calculated radiosity solution (Fig. 22).
A volumetric light (or halo spot) must start out as a spot light and
all the rules of a spot that cast shadows must also apply to a
volumetric light, including clipping. Use Fig. 23 as a reference when
placing your spot light. Adjust the clipping as needed.
There are three areas of interest when converting a spot light to a
volumetric light (Fig. 24). First, the Halo step value
must be changed from the default value of zero. The values range from
1 to 12, the lower the number the higher the quality and the longer
the render time. A setting of zero makes the halo rendering
inactive. Next press the Halo button to activate volumetric
lighting. This is where the name halo spot comes from. The intensity
of the light rays are adjusted with the HaloInt slider
button.
In the final render, the color of the halo spot was changed to a light
blue to help give the look of daylight (Fig. 25). This use of color is
used to suggest the time of day. It can easily be changed by rotating
the angle of the light rays and the color of the lamp. In Fig. 26 the
angle was lowered and the color of the lamp was changed to a
reddish-orange, to suggest a sunset mood (see
"volumetric2.blend"
).
-cw-
Last modified: Tue Nov 7 10:52:16 CET 2000