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Old 17th February 2008, 08:55 AM   #11
lisa
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Ambient Occlusion Map

Ambient occlusion is a measurement of how much ambient light reaches a point on a model based on how much the point is occluded--or blocked--by other parts of the model. Corners, creases and crevices tend to be very occluded, causing them to have dark shadows even when the rest of the model is well-lit.

An ambient occlusion map indicates how occluded each area of the model is.

Often for models with only diffuse maps, the effects of ambient occlusion are "burnt into" the diffuse map. Areas that would be made dark by ambient occlusion are simply painted a darker color.

Here is the ambient occlusion map:
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Old 17th February 2008, 08:55 AM   #12
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Here is the ambient occlusion map applied:
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Old 17th February 2008, 09:02 AM   #13
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Specular Lighting

To understand specular mapping, you first need to understand specular lighting.

Specular lighting is responsible for the appearance of "shiny highlights" on the surface of an object. The bright spot you see on the polished surface of a pool ball is a good example of specular lighting.

Unlike directional lighting, specular lighting is view-angle dependent. This means that the intensity of the bright spot changes depending not only on the position of the light, camera and object, but also on the position where the viewer is standing. Generally, specular highlights are most visible when viewed from straight-on.

You can change the specular color of a material the same way you change the diffuse color in the material settings. However, specular also has an additional setting called "specular power". Specular power is also sometimes called "brilliance" or "shininess". The specular power setting controls the size of the highlights. By making the highlights smaller, it makes the object appear as if it were made of a harder material such as glass or metal. By making the highlights larger, it makes the object appear as if it were made of a softer or duller material such as plastic or paper.

Here is the cube with and without specular lighting. The cube has been rotated to face the viewer so the highlights are more visible:
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Old 17th February 2008, 09:06 AM   #14
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Specular Map

A specular map indicates the color and intensity of specular lighting on a per-pixel basis. A specular map that measures intensity only, and not color, is also referred to as a gloss map. Gloss maps are more common than colored specular maps.

In a specular or gloss map, bright pixels indicate areas that have high specularity while dark pixels indicate areas that have low specularity. Areas of the map that are colored black will appear less shiny than areas of the map that are colored white.

It is also possible to create a two-channel specular map that measures both intensity (brightness of the highlights) and power (size of the highlights). That is what I have done here for illustrative purposes. However, this type of map is unusual in practice at least in games. Typically only intensity is mapped. Power is controlled solely by the material settings.

This is the specular intensity (gloss) map:
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Old 17th February 2008, 09:08 AM   #15
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This is the specular power map. Again, almost no one uses this variation, however, it is good for illustrating the concept of specular power. The brighter areas have smaller, sharper highlights:
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Old 17th February 2008, 09:09 AM   #16
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Here is what the cube looks like with specular mapping applied:
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Old 17th February 2008, 09:11 AM   #17
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Here is what the cube looks like with all of the map types we have discussed so far (ambient, diffuse, specular) combined. Note how the specular map makes the moss-covered areas appear matte:
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Old 17th February 2008, 09:13 AM   #18
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Emissive Map

An emissive map, or "glow map", controls which areas of the model are self-illuminating. Areas of the map with bright colored pixels appear to be lit by an internal light source.
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Old 17th February 2008, 09:14 AM   #19
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With the glow map applied:
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Old 17th February 2008, 09:25 AM   #20
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Environment Map

An environment map is a texture map that contains images of what is in the environment around the model, versus an image that is part of the model itself.
An environment map contains a 360 degree panorama of what the model can see.

Just like a specular map, the effects of an environment map are view-angle dependent. Where the viewer is in relation to the object and the camera will cause different parts of the environment map to be shown.

Many games and renderers will generate environment maps "on the fly" by rendering a panoramic image of the scene from the point of view of the model. This makes the reflections more realistic, because it then appears as if the model were actually reflecting the other objects in the scene.

However, "static" environment maps are common, too. Artists will use an image of the sky or other picture as an environment map when there are no other objects in the scene, to achieve special effects or when rendering environment maps on the fly is too slow.
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