IBL+PBR+Tone-Mapping+Gamma-Correction

IBL-Image based lighting

An HDR environment map to provide surround lighting.

PBR

A micro-facet BRDF to provide realistic surface lighting calculations

Tone Mapping + Gamma Correction

The mapping of a High-Dynamic-Range image onto a Low-Dynamic-Range device.

Tone mapping, exposure and Gamma Correction:
Sky box color and BRDF result used tone mapping to convert color into [0,1] and transfer into gamma space. I chose the exposure parameter as 2, and sRGB = pow(linear,1/2.2) as linear to gamma space conversion equation. Because color in HDR image is in linear space, I just do this calculation when output pixel color.

The first one is without gamma correction, but has tone mapping.
The second is without gamma correction and tone mapping.
The thired is using 2.0 as exposure parameter (with gamma correction and tone mapping).
The forth is using 5.0 as exposure parameter (with gamma correction and tone mapping).

Different Roughness.

origin image
irradiance map
Use irradiance map as irradians. diffuse color = Kd/PI * irradians. The irrandians map is generated by spherical harmonics algorithm.