Material inputs : relation between "Specular" and "Metallic" ?

Development Rendering
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The documentation page about the Human Skin shows that the shader provided for the “SkinMaster” material uses the material input “Specular” with a fixed value of 0.35.
I can also see it in the “ContentExamples” project, level “SkinRendering”.

In the same level, the material “M_DemoWall” is also used. For that material however, “Specular” is not used, however “Metallic” is used.
It is probably because both materials use different shading models, one that uses the “Specular” input parameter, the other the “Material” input parameter. Does it sound right?

In that case, if I want to convert a material that uses the “Specular” parameter, to a material that uses the “Metallic” parameter, which value should I use?

Alternately, maybe I could find the relation between both parameters if I knew which function of BRDF.usf are used by those materials. Is there any information about that?

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Hi Wil_ -

Specular has no relationship with Metallic. It is only a 0 to 1 value which effect non-metallics by scaling their specular. Assuming the specular workflow you are referring to is a specular map, then you can try two things one is if it is normalized between 0 and 1 and completely greyscaled you can pass it into the Specular input directly, but it will not have the effect you are used to seeing in a non-PBR workflow. Alternatively you can make sure the representative brightness of your Specular is baked into your Base Color which the engine will then use the Base Color, Metallic and Roughness Settings to drive the Specular output of your material.

Thank You

Eric Ketchum