Controlling the Object's Reflectance

Basic Scene Setup
Add a simple plane and a sphere. Add a light and ensure that it casts shadows. Also, ray tracing must be enabled when the scenes are rendered. Finally, position the camera appropriately.

Setting Up Basic Surface
Select the Material Editor and add the "Wrapped Checks" color shader. Next, add a Reflectance, Shaderlab shader. Bring up its interface and pick fBm from the Enhance:TS - Noise section. Make Color1 Light Blue (0.0, 0.5, 1.0) with Color2 and Color3 Blue (0.0, 0.0, 1.0). As we want the color transition to be discrete but with a soft edge make Blend1=0.4, Blend2=0.5 and Blend3=1.0. Next, set up the alpha map to be Alpha1=1.0, Alpha2=0.0 and Alpha3=0.0. This means that the Alpha Map is basically 1.0 where the texture is Light Blue and 0.0 where the texture is Blue. Bear this in mind as we change the reflectance controls below. The basic scene should look like the one on the left.

Color Layer
The Layer parameter controls the opacity of the applied color when the shader is being used as a reflectance shader. When this parameter is negative the opacity affects all of the color irrespective of the Alpha Map. A value of -1.0 means the color is applied full on and totally opaque. A value of 0.0 means that the underlying color (either solid or from a color shader) shows through completely. Values in between will be a mix between these two extremes. Set the Layer to -0.5. The image on the left shows the result of this with a 50:50 mix of the under-lying color checks and the overlying fBm reflectance shader.
With the Layer parameter set to a positive value the Alpha Map is used to control the opacity of the reflectance shader's color. Set the Layer parameter to 1.0. Where the fBm was Light Blue the Alpha Map returns 1.0 meaning the color is totally transparent and the underlying checks show through. When the fBm is Blue the Alpha Map returns 0.0 so the color here is totally opaque. The image on the left shows this affect.

Ambient
The Ambient parameter controls the object's ambience (brightness or luminosity). When this parameter is negative the whole of the object's ambience is affected. The more negative the value the brighter the object appears. Reset the Layer value to -1.0 and set the Ambient parameter to -1.0. The image on the left shows that the whole object has now become much brighter as the ambience has increased.
With the Ambient parameter set to a positive value the Alpha Map is used to control the ambience of the object. The more positive the value the brighter the maximum possible ambience. The image on the left shows the fBm shader with an Ambient value of 1.0. Where the fBm is Light Blue the Alpha Map returns 1.0 and the object is made bright at these points. When the fBm is Blue the Alpha Map returns 0.0 and so that object's ambience will be 0.0 are these points. This is shown in the image on the left.

Diffuse
The diffuse parameter controls the object's diffusion. When this parameter is negative the whole of the object's diffusion is affected. The more negative the value the more the diffusion and the darker the object. Reset the Ambient value to 0.0 and set the Diffuse value to -0.5. The image on the left shows the results. The sphere has become darker or more diffused across the whole object.
With the Diffuse parameter set to a positive value the Alpha Map is used to control the object's diffusion. The more positive the value the higher the maximum possible diffusion. Make the Diffuse parameter 1.0. Where the fBm is Light Blue the Alpha Map returns 1.0 and the diffusion will be 1.0. Where the fBm is Blue the Alpha Map returns 0.0 and so that object's diffusion will be 0.0. This can be seen in the image to the left. The light blue areas have remained with a normal diffusion of 1.0 while the blue areas have become much darker or diffused with a value of 0.0.

Specularity
The Specularity parameter (Spec) controls the object's specular brightness. When this parameter is negative the whole of the object's specular brightness is affected. The more negative the value the more the brighter the specular highlight. Reset the Diffuse value to -1.0 and set the Specular value to -2.0. The image on the left shows the results, a bright specular highlight. Note: The size of the specular highlight depends on the Roughness parameter.
With the Specular parameter set to a positive value the Alpha Map is used to control the object's specular brightness. The more positive the value the brightness the maximum possible specular highlight. Make the Specular value 2.0. Where the fBm is Light Blue the Alpha Map returns 1.0 and the specular brightness will be 2.0. Where the fBm is Blue the Alpha Map returns 0.0 and the specular brightness will be 0.0 here. This can be seen in the image to the left. The light blue areas still have a bright specular highlight whereas there is no specular highlight in the Blue areas.

Roughness
The Roughness parameter controls the object's roughness and subsequently the size of the specular highlight. When this parameter is negative the whole of the object's roughness is affected. The more negative the value the more the larger the specular highlight. Reset the specular parameter to -2.0 and set the Roughness value to -0.2. The image on the left shows the results, a large specular highlight.
With the Roughness parameter set to a positive value the Alpha Map is used to control the object's roughness. The more positive the larger the maximum possible specular highlight. Make the Roughness value 0.2. Where the fBm is Light Blue the Alpha Map returns 1.0 and the specular brightness will be 0.2. Where the fBm is Blue the Alpha Map returns 0.0 and so that object's roughness will be 0.0 here. With the roughness being 0.0 the specular highlight will be very large giving a total white-out. By setting Alpha2 and Alpha3 to 0.5 a value of 0.1 will be returned for the Blue areas (0.2 x 0.5). This can be seen in the image to the left. The light blue areas still have a large specular highlight while the Blue areas have a smaller highlight.

Reflect
The Reflect parameter controls the object's reflectivity. When this parameter is negative the whole of the object's reflectivity is affected. The more negative the value the more reflective the object. Reset the roughness parameter to -0.2, the Specular parameter to 0.0, Alpha2 to 0.0 and Alpha3 to 0.0. Then set the Reflect parameter to -0.5. The image on the left shows the results, a totally reflective object.
With the Reflect parameter set to a positive value the Alpha Map is used to control the object's reflectivity. The more positive the value the higher the maximum possible reflectivity. Make the reflectivity value 0.5. Where the fBm is Light Blue the Alpha Map returns 1.0 and the reflectivity will be 0.5. Where the fBm is Blue the Alpha Map returns 0.0 and so that object's reflectivity will be 0.0 here. This can be seen in the image to the left. The light blue areas are reflective while the Blue areas are not.

Experimentation
First of all, try changing each of the reflectance controls (Layer, Ambient, Diffuse, Spec, Roughness and Reflect) to different values. For each one try -1.0, -0.5, 0, 0.5 and 1.0 in turn. Keep the Alpha Map as is. Next change the alpha parameters to value like 0, 0.25, 0.5, 0.75 and 1.0. See how the reflectance controls and their strength changes. All of the above examples use a fairly discrete Alpha Map. Try setting Blend1=0.0 and Blend2=1.0 and try all of the above again.


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