I've been using Isotropix Clarisse in production for a little while now. Recently the VFX Facility where I work announced the usage of Clarisse as primary Look-Dev and Lighting tool, so I decided to start talking about this powerful raytracer on my blog.

Today I'm writing about how to set-up Image Based Lighting.

We can start by creating a new context called ibl. We will put all the elements needed for ibl inside this context.

Now we need to create a sphere to use as "world" for the scene.
This sphere will be the support for the equirectangular HDRI texture.
I just increased the radius a lot. Keep in mind that this sphere will be covering all your assets inside of it.

In the image view tab we can see the render in real time.
Right now the sphere is lit by the default directional light.
Delete that light.

Create a new matte material. This material won't be affected by lighting.
Assign it to the sphere.

Once assigned the sphere will look black.
Create an image to load the HDRI texture.

Connect the texture to the color input of the matte shader.

Select the desired HDRI map in the texture path.
Change the projection type to "parametric".

HDRI textures are usually 32bit linear images. So you need to indicate this in the texture properties.

I created two spheres to check the lighting. Just press "f" to fit them in the viewport.

I also created two standard materials, one for each sphere. I'm creating lighting checkers here.
And a plane, just to check the shadows.

If I go back to the image view, I can see that the HDRI is already affecting the spheres.
Right now, only the secondary rays are being affected, like the reflection.

In order to create proper lighting, we need to use a light called "gi_monte_carlo".

Right now the noise in the scene is insane. This is because all the crazy detail in the HDRI map.
First thing to reduce noise would be to change the interpolation of the texture to Mipmapping.

To have a noise free image we will have to increase the sampling quality of the "gi_monte_carlo" light.

Noise reduction can be also managed with the anti aliasing sampling of the raytracer.
The most common approach is to combine raytracer sampling, lighting sampling and shading sampling.
Around 8 raytracing samples and something around 12 lighting samples are common settings in production.