Global Illumination calculates the way photons reflect diffuse light from the surface when they hit an object and how these reflected rays go on to illuminate other surfaces. Global Illumination works well for scenes that are flooded with lights and have large features, but are not very detailed.
For more information, see Global Illumination and Caustics in [Indirect Illumination].
When you fine-tune a global illumination effect, start with a small number of photons and a high intensity value.
Values of around 1000 and 40 000 respectively should be good to begin with, but adjust the values until you are satisfied with the effect.
In general, use the following number of Global Illumination photons depending on the situation:
Keep in mind that Global Illumination is not designed to create the same effect as Final Gathering. Instead they are complementary and can often be used together to get a completely different result than you would get using either one individually.
Caustics are a subset of full global-illumination simulation where photons are only emitted toward any caustic-generating objects in the scene. Caustics work best when your object's material is mainly specular (little or no diffuse reflection).
For more information, see Global Illumination and Caustics [Indirect Illumination].
Final Gathering calculates both direct and indirect lighting, using rays cast from objects rather than from lights. Use Final Gathering in scenes that have smaller features and are highly detailed.
For more information, see Global Illumination and Caustics [Indirect Illumination].
Final Gathering can be used along with global illumination to increase photo realism in your scene. This will increase rendering time.
To tune the Final Gathering Accuracy value, start with a value of about 100-300, and then adjust it to get the look you want. Generally, you shouldn't need a value higher than 1000.
If you see high frequency noise (tiles, for example) in the rendered scene, increase the Final Gathering Accuracy value and lower the maximum radius value.
If you see low frequency noise (blotches) or flickering in animations, decrease the maximum radius value until the noise disappears. Keep in mind that lower values (below 1) give good results but do increase rendering time.
If you can't get rid of scene artifacts, increase the Final Gathering Accuracy values.
Keep in mind that Final Gathering is not designed to create the same effect as Global illumination. Instead they are complementary, and can often be used together to get a completely different result than you would get using either one individually.
