DAZ Studio/Lighting

This is a learning project for exploring how to work with lighting in [http://www.daz3d.com/i.x/software/studio/-/? DAZ Studio], a type of 3D computer graphics software. If you are not familiar with the DAZ Studio software, start at Rendering models of living organisms or Bryce.

Reading
Read the chapter on lighting (Chapter 4) and read "About the Surfaces Tab" in Chapter 7 in the DAZ Studio manual.

Introduction
This tutorial covers both the use of light sources and examples of how to alter the surface properties of objects to change how they appear when exposed to light sources. Figure 1 shows an example of a scene that has a single light source, a glowing cube. There are two other types of objects in the scene, those with no "mirror-like" reflectivity and those with "mirror-like" reflectivity. The human figure and cat are from the [http://www.daz3d.com/i.x/software/studio/-/download? 3D Starter Pack].

The human figure and the cat have surfaces for which the reflection channel is set to 0%. For this example, the surfaces of the walls and floor were set to have the reflection channel set to 100%. The name "reflection channel" is somewhat misleading because the "diffuse", "specular" and "ambient" channels also allow objects in the scene to be rendered as they would appear because of reflecting light. In terms of physics, there is a distinction between Diffuse reflection and Specular reflection. The distinction is in the organization of the reflected light that leaves the surface. If there is a large amount of specular reflection then the organization and coherence of the original light falling on the object is retained in the reflected light. If there is mostly diffuse reflection then the directions of reflected photons are not consistent with the original directions of the photons that fell on the surface and it is not possible to obtain an image or coherent view (what we typically call a "reflection") of the original light source from the reflected photons. With diffuse reflection, the surface of the object scatters the reflected light in many different directions.

When we see objects that reflect light, the color of the reflected light depends both on the color of the light falling on the object and the material of the object. Materials can be selective in terms of which colors (wavelengths) of light they reflect. DAZ Studio allows you to control three channels ("diffuse", "specular" and "ambient") allow the rendering process to quickly simulate reflection of light from most surfaces. However, if you want to render a coherent reflection (such as a person's reflection in a mirror) you need to make use of the "reflection" controls in the "Advanced" settings for Surfaces.

Point sources of light
Figure 2 illustrates some results obtained by changing the settings for the "reflection", "diffuse" and "ambient" channels for the surfaces of the walls and floor in the scene. Panel A shows the appearance of a wall and floor made using default settings for panes made using the Create>Primitive command in DAZ Studio. All the light in this scene comes from a point light source positioned at the center of the sphere and set to intensity of 200%. The illumination provided by a point source drops off rapidly with distance from the source. For panels B-D a second point light source was added at the same position to increase the available light. For panels B-D the "reflection" channel of the floor and wall panes was set to 100%.

Activity
Create a simple scene in DAZ Studio and experiment with setting the "reflection" channel for some objects above 0%. Note that when you use "mirror-like" reflections, the rendering time increases significantly. Also note that "mirror-like" reflections can only be rendered using DAZ Studio's software rendering, not the hardware-based rendering options.

Changing the ratio of diffuse and "mirror-like" reflectivity
In Figure 2, panel C, the color for the "ambient" channel was changed from white to black. The ambient channel can often be used to help brighten parts of objects in scenes that do not have good illumination. In panel D the diffuse channel was set to 0%, leaving only the coherent "mirror-like" reflections.

Activity
Experiment with the "diffuse", "specular" and "ambient" channels for some surfaces of objects. Upload some of your results to Wikiversity.

Interesting light sources
Figure 1 shows a similar scene in which the point light source is inside a cube. Unlike the simple sphere in Figure 2, the "diffuse, "ambient", "opacity" and "refraction" settings were altered for the cube. Another view of the same "light cube" is shown in Figure 4. The goal was to make the cube look like a block of glass.
 * diffuse = 21%
 * ambient = 25%
 * opacity = 26%
 * refraction = 54%
 * index of refraction = 1.54

Activity
What is the refractive index for glass?

Changing the shape of light sources
Another spherical light source was used in the DAZ Studio D-Form tool tutorial. That tutorial shows how a light source such as "morphing laser ball" can have its shape changed using a DAZ Studio D-Former. For the sphere:
 * diffuse = 100%, pink
 * specular = 100%, white
 * opacity = 20%
 * reflection = 73%, light pink
 * refraction = 40%, dark pink
 * index of refraction = 2.4

Spot lights
Figure three shows the same scene elements from Figure 1 with some additions. A table was placed under the cube and the human figure is resting on another horizontal surface. The cat is on the table with the cube. In this preview of the scene, the location of the spotlight is indicated by the wire-frame outline above and behind the cat. The goal for the spotlight was to create the illusion of a blue "night light" running along the wall. A long thin cylinder was made using Create>Primitive and sunk into the wall. The spot light was aimed at the cylinder and its spread angle set to 33.

Figure 4 shows the rendered scene corresponding to the preview in Figure 3. You can see blue light from the spotlight illuminating part of the wall and the cylinder. This provides an example of using a spotlight to selectively illuminate a small part of a scene.

Distant lights
The third type of light source in DAZ Studio is the "distant light". Distant lights are used to provide relatively even illumination over large parts of a scene. Figures 3 and 4 made use of a distant light in order to make it easier to see where the objects were in the scene. For Figure 4A the distant light was set to 18%. For Figure 4B the distant light was set to 5%. In this case, the goal was to depict someone resting in a dark room, so very little illumination was used from the distant light source.

Animation
Figure 5 shows a short animation using all three types of light sources. The goal was to depict a resting person in a dark room who then gets up. Note that the cat is close enough to the "light cube" to cast interesting shadows and a fairly clear reflection on the wall. The human figure is not as close to the "light cube" and does not cast as clear of a reflection.

Activity
Create a short animation that shows some experiments with shadows, lighting and reflection. If you have not already done so. see Animation with DAZ Studio.

Where next
Note that in Figure 5 the camera is pulls back during the animation.
 * DAZ Studio camera control