Material Modulation introduction.

APC from the movie Aliens, by Gabich.

Some material properties can be modulated by a texture, instead of using a global value. This technique is called texture mapping. The texture used can be a RGB image or a procedural texture. In general, there are seven types of modulable settings in YafaRay materials, which are:

• Diffuse color. ShinyDiffuse, Glossy and Coated Glossy.
• Specular color. ShinyDiffuse, Glossy and Coated Glossy.
• Specular intensity. ShinyDiffuse, Glossy and Coated Glossy.
• Alpha intensity. ShinyDiffuse.
• Bump intensity. All materials.
• Displacement mapping through a mesh modifier. All materials.
• Blend mapping. Blend material.

For instance, you can use a texture to have different values of glossy reflection on a surface. Some of these modulation modes are available for all material types, like bump intensity. Others are available only for some of them, depending on the material features.

Negative toggle mode is supported in intensity-mapping types, so texture values are inverted.

Diffuse color.

There are several options when using a texture to map diffuse color. These options are:

• To map the diffuse color with a RGB texture, use the COL slot [4] in the 'Map to' panel. Shinydiffuse, Glossy and Coated_glossy materials support diffuse color mapping. The applied RGB texture will hide the material's own diffuse color [1] defined in the material settings. However, you can control texture opacity so it blends with the material diffuse color, by using Col slider [5]. 
• Diffuse reflection value [2] is just a diffuse color multiplying factor, affects textures as well.
• If a texture with alpha data is used (RGBA) and you want to render alpha as transparent (white otherwise), enable UseAlpha button [7] in the Blender Texture buttons (F6). The alpha channel will be rendered transparent and the underlying diffuse color [1] will be seen.
• You can use a procedural texture to map the diffuse color. Colors in a procedural texture are defined by two controls: Color Swatch [6] in the Blender 'Map to' panel (F5) and material diffuse color [1] in the YafaRay settings interface. More info about procedurals here.
• When a diffuse color texture is used in a ShinyDiffuse material with Emit [3], the amount of light emission produced by that material will be defined by the texture brightness. At the moment, texture-based light emission only works with pathtracing.
• When a diffuse color texture is used in a ShinyDiffuse material with Transparency [8], the amount of transparency will be defined by the texture brightness. Enable Transparent Shadows in Settings section to get transparent shadows and color filtering from the texture.
• When a diffuse color texture is used in a ShinyDiffuse material with Translucency [8], the amount of translucency will be defined by the texture brightness. Enable Transparent Shadows in Settings section to get transparent shadows and color filtering from the texture. Translucent scattered light with transparent shadows & color fitering only works with Pathtracing, Bidirectional Pathtracing, and Photon mapping.

Below an example of diffuse color mapping in Shinydiffuse (left) and Glossy material (right). A bit of bump is applied in both cases.

Example of diffuse color mapping in Shinydiffuse material, with Transparency on the left and with Emit on the right.

Texture used:

Specular color.

There are two kinds of mappable specular in YafaRay, Mirror in Shinydiffuse, and Glossy in Glossy material. Both are specular components that can use the uniform color defined in the settings UI, or they can be also mapped with a RBG texture. The applied texture will hide the material specular color (mirror or glossy) defined in the settings UI. However, you can control opacity of the texture so it blends with the material specular color, by using Col slider [3] in the Blender 'Map to' panel. You can use a procedural texture as well.

Remember that coloured reflections are a particular feature of conductive materials, while non-conductive have neutral-colored reflections (white).

The images below are examples of specular color mapping. Both cases are using full specularity strength:

Mirror color mapping.	Glossy color mapping.

Texture used.

Specular Intensity.

You can use a texture to map the amount of specular reflection. There are two kinds of specular reflection in YafaRay: Mirror in Shinydiffuse and Glossy Reflection in Glossy material. Textures will be processed as a value scale. This means that if the RGB texture has got colors they will be transformed into tones of grey, so normally it is a wise idea to use desaturated textures to map intensity. This way users have more control over the final result. You can use a procedural texture as well.

The texture in fact will map in the range between the specular strength set in material setting [1] and Var [2]. For instance, if Mirror strength is 0.20, it means that black color in the texture will make the object to be at least 0.20 reflective. If Var=0.80, it means that white color in the texture will make the object to be as much as 0.80 reflective. The same happens with Glossy materials.

To map mirror strength in Shinydiffuse, use RayMir slot [3]. To map glossy reflection strength, use Spec slot [4]. Below are examples of specular mapping. Both cases are using strength=0 and Var=1:

Shinydiffuse mirror mapping.	Glossy reflection mapping.

Texture used.

Alpha Intensity.

This feature is used to map mesh transparency with a texture. Information from the RGB texture is translated into amount of mesh transparency. To make it possible, textures need to be transformed into a value-scale. This means that if the texture has got colors they will be transformed into tones of grey. It is a wise idea to use desaturated textures to map intensity, so there is more control over the final result. You can use a procedural texture as well.

Don't confuse 'alpha intensity' with 'texture alpha'. The texture alpha channel (RGBA) is used in diffuse color mapping.

Alpha intensity mapping will just produce different values of transparency based on the texture values. Those different levels of transparency will produce colored transparent shadows, if transparency is applied onto a material with diffuse colors applied.

There are two kinds of transparency in YafaRay, specular Transparency [1] and diffuse transparency, also called Translucency [2]. To enable shadows calculation from alpha-intensity mapping, enable Transparent Shadows with enough Shadows depth, in the Settings section.

The texture will map in fact a range between the transparency value set in the material setting [1 or 2] and the Var value [5]. For instance, if Trasparency is 0.20, it means that black color in the texture will make the object to be at least 0.20 transparent. If Var=0.80, it means that white color in the texture will make the object to be as much as 0.80 transparent. The same happens with Translucency.

To map Transparency, use Alpha slot [3]. To map Translucency, use TransLu slot [4].

At the moment, Translucency scattered light with transparent shadows only works with Global Illumination methods, which are Pathtracing, Bidirectional Pathtracing, and Photon mapping.

Below are examples of transparency and translucency mapping. Both cases are using strength=0, Var=1:

Transparency mapping.	Translucency mapping.

Texture used.

Bump Intensity.

All four materials (ShinyDiffuse, Glossy, Coated_Glossy and Glass) support bump mapping.

Brian Lingard gives this definition of bump mapping: "Bump mapping simulates the bumps or wrinkles in a surface without the need for geometric modifications to the model. The surface normal of a given surface is perturbed according to a bump map. The perturbed normal is then used instead of the original normal when shading the surface using the Lambertian technique. This method gives the appearance of bumps and depressions in the surface."

Bump is an intensity-mapping type. Textures are transformed into a value-scale. It means that if the RGB texture has got colors, they will be transformed into tones of grey. It is a wise idea to use desaturated textures to map intensity, so there is more control over the final result. You can use a procedural texture as well. To map bump, the Nor slot [1] must be enabled for the texture channel. Nor slider [2] controls amount of bump. YafaRay uses comparatively lower values than Blender for bump mapping.

Displacement mapping.

	YafaRay supports displacement mapping applied not as a material modulator but as a Blender mesh modifier (F9, Modifiers panel). It can be applied to any mesh regardless of the material. Displacement is a modern version of bump mapping, in which the object geometry is actually modified by a texture. Displacement needs a great amount of mesh tessellation to work; the more tessellation the better result. The tessellation needed can be achieved by using a subdivision surfaces modifier (subsurf) on a mesh.
First, a texture must be created as usual, using Blender supported Texture buttons (F6). The texture will appear in the Texture channels stack (F5). Check your options to see whether this displacement texture is needed for a modulation mode as well or not. For instance, you might want to enable this texture for diffuse color mapping as well while is still being used for displacement, like the example above. This created texture is later used in the Displace mesh modifier (image below).
	Displacement is an intensity-mapping type. RGB Textures are transformed into a value-scale. It means that if the texture has got colors, they will be transformed into tones of grey. It is a wise idea to use desaturated textures to map intensity so there is more control over the final result. You can use a procedural texture as well. On the left there is an example of a Modifiers panel, using a subsurf modifier to add tessellation and a displacement modifier. The name of the texture used for displacement is input in the Texture field (green). This texture is previously defined in Blender texturing panels. More information about subsurf and displace modifiers here and here, respectively.

Blend mapping.

You can use a texture to control how two materials are blended. This texture is a mask in which values tell how big a percentage of each material is seen. If the RGB texture has got colors, they will be transformed into tones of grey. It is a wise idea to use desaturated textures to map blend, so there is more control over the final result. You can use a procedural texture as well. The texture should be mapped onto the object assigned with the blend material, using the Col slot.

If the texture is a black&white checker, it means black squares will show material 1 whereas white squares will show material 2 (example below). The texture can use tones of grey as well, which means that properties from both materials are blended in the same area.

Blend value works as a global opacity factor for the texture. If you want the texture to have a complete control of the blending, use a Blend value=0. If Blend value is 1, the texture will be completely transparent and only the material 2 can be seen.

Below an example of blend mapping, using a black&white checker. On the left a Blend value=0 is used whereas on the right Blend value is 0.50: