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- Appendicies
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- Lighting Basics:
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- Lighting: ( diffuse, specular, and global )
- When A-Render calculates a scene, at least 1 light component must be
- present. As in the real world, if there is no light, nothing can be
- seen! There are several different lighting components that contribute
- to the total intensity calculation for an object in the scene.
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- These are:
- Global Lighting.
- Diffuse Lighting.
- Specular Lighting.
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- Global lighting :
- In the real world, a lot of light bounces around you and illuminates
- more than just what the light directly shines on. For example, look
- under a table. What do you see ? Well it doesn't really matter,
- the point is you can at least see under the table and see the floor,
- and maybe you leaned down far enough to see the bottom of the table.
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- Most probably, you don't have a light under the table, but you can
- still see things under it. How did the light get there for your eye
- to see ? The light started at the sun and came in a window, or it
- started at a lamp in your room. Then it bounced around your
- environment, off a few items, and scattered all around your room to
- create a general level of light. This light is called the 'global
- light' because it is applied globally (universally) to all the
- objects in a scene.
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- Now, really, the global intensity is not the same all over the room, but
- the lighting is most probably pretty even. We usually use a small
- amount of global lighting in an A-Render scene to be sure all surfaces
- will get some light and will be visible (remember, if there is NO
- light on a surface, that surface will not even be visible).
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- In A-Render, we assume the global lighting to be the same everywhere in
- the scene, not dependent on the 'light bouncing around a room' effect.
- When you specify global lighting, you specify the red, green, and blue
- intensities. All objects in the scene will be lit with this global
- lighting. Global lighting is usually a small to medium light
- contribution to a scene.
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- Besides global lighting, there are two other contributors to the
- lighting of a surface, diffuse, and specular lighting. Look at your
- computer for this example. Look at a large flat area, like the side
- of the monitor, or the top of your Amiga that is exposed around the
- monitor. Make sure the area you are observing is not in shadow, it
- must be directly illuminated by a light.
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- Diffuse :
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- Diffuse lighting is the major contributor to the light you see
- reflecting off of an object. Looking at your Amiga, the majority of
- the light you see is the diffuse lighting. It usually will illuminate
- the whole object, except what's in shadow. Diffuse light reflects in
- the color of the object. On your Amiga, the diffuse reflected light is
- beige, so you will see the object (the Amiga) as beige. Notice that as
- you move your eye around, the diffuse light does not appear to move,
- maintaining an unchanging illumination on the surface.
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- Specular :
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- The specular light reflection on your Amiga is the bright but usually
- small highlites you see on the edges of your Amiga. Specular lighting
- is usually closer to the color of the light source than to the color
- of the object. The highlights on your Amiga look white, assuming your
- light source is white.
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- Specular lighting is usually a small contributor to the amount of
- light you see reflected off an object, but it is very important to
- have it present to try and generate images with a high degree of
- realism. To make an object look shiny, make the specular contribution
- high, and the diffuse contribution low. Set the COEFFICIENTS for this.
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- Notice that as you move your eye around, specular light reflections
- appear to move along the edges. If your eyes are sharp, you will even
- see a white 'glare' off the surface off your Amiga. This specular
- light reflects in a large glare because the surface is rough and has a
- random texture. Remember, specular light always depends on the
- location of your eye, and will move when your eye does.
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