The energy conservation states that an object can not reflect more light than it receives.
For example material with sharper and bold highlights appears more reflective than the one with smooth and dull highlights, however it is the variance in microsurface (roughness map) that results in a sharper o smoother highlights while the specularity remains the same.
Albedo, commonly known as diffuse map. Contains the information about diffuse reflection of the specific material.
Common dielectrics albedo value ranges between 30-240 (12-94%) sRGB, 0.01 – 0.88 Linear
For transparent dielectrics and metals the albedo value is 0 (100% black)
Microsurface in PBR is being described by the microfacet theory which supposes that a surface is composed of small-scaled planar detail surface of varying orientation called microfacets. Each of these small planes reflects light in a single direction based on its normal.
The surface irregularities cause light diffusion which resuts in blurred reflections – scattered light rays are not reflected in parallel.
Rougher surfaces will have larger and dimmer looking highlights.
Smoother surfaces wil keep specular reflections focused and sharp which can appear to look brighter. However the amount of the reflection remains the same.
Fresnel is the percentage of light that a surface reflects at grazing angles.
All types of materials become 100% reflective at grazing angles so the fresnel should be set to 1 in the shader.
F0 is fresnel reflectance at 0 degree (when the light hits a surface straight on or perpendicularly) there is a percentage of that light that is reflected back as specular reflection.
It is the F0 reflectance value that we are concerned with in regards to authoring specular color texture.
Using the Index of Refraction (IOR) for a surface, you can derive the amount that is reflected back which is referred to as F0.
Trusted IOR values from internet:
To turn an index or refraction (IOR) to F0 use the following equation:
Disclaimer: all the numerical values are in Linear space.
For a practical sample, take the index of refraction of water (1.33) and put it inside the equation:
The result (0.02) is the specular color for water.
In specular color texture dielectrics will have a grayscale values and metals will have RGB values.
The F0 range for common Dielectrics and Metals:
Dielectrics: 0.02 – 0.05 Linear
Metals: 0.5 – 1.0 Linear