Image Based Lighting is used to implement ambient lighting for dynamic objects coming from static objects in a game level. In most cases, it is used for specular lighting or reflections. In this process lighting information at the potential point of interests is stored in a special type of cube maps called Light probes. These Light probes are created using environment maps captured at same locations, which are then blurred in some special way depending on the BRDF  that will consume them at runtime. Each mipmap of a light probe contains a version of environment map blurred by a different amount depending roughness represented by that level. For example, if we are using 10 mip map levels to represent roughness from 0 to 1, then mip-0 will be blurred by a value representing roughness 0, mip-1 will represent 0.1 and so on. The last mip level mip-10 will be blurred by a value represent the roughness of 1.0. This process is also called Cubemap Convolution . All of this is done as a pre-process and resulting light probes are fetched at runtime to enable reflections or Image Based Lighting.
Gaussian Blur Filter is one of the most used effect in graphics programming. It helps to achieve many other effects like Bloom, DOF, etc.
I coded a version of it using pixel shaders in my naive pixel shader based HDR Renderer earlier. Even though it served the purpose it was very limited in terms of performance and hence quality since we can’t increase radius beyond some levels for real-time rendering.
Then I posted about first compute shader based implementation here which based on Frank Luna’s algorithm but even that was limiting in the fact that we can’t go beyond some blur radius (depends on GPU) for performance reasons.
Here’s a screenshot (800 x 600)-