Dear Arion users,
Emitter materials and Light objects in the next builds of Arion will feature something called “Importance”. This value allows the user to alter the prevalence of a light source in the Importance Sampling table.
The IS table is a structure that determines how often each light source is sampled. This table is built during warm-up and it automatically assigns a value to each light based on its power output, and its size.
This a priori criterion makes sense, because power and size are the most evident factors that tell how much light a source will contribute to the scene. However, there are situations where a certain light source is really critical to your scene, yet it does not receive as much importance in the IS table as necessary. For example, imagine a very small and dim light that is illuminating the foreground of the scene. You may want it to be as noiseless as possible, while other larger, more powerful fill lights in the scene may not need as much sampling.
With this new feature one can give more importance to one light source, stealing sampling time from others.
Note that this feature does -not- alter the unbiasedness of the result. The render will be unaffected. Only the noise distribution will change.
This example below features a classic example where this IS drive may be very useful. The scene has two rooms. Both are equally important to the observer. However, the IS values assigned automatically give more prevalence to the larger emitter, making one room be over-sampled, and the other one under-sampled. Compensating for this with the IS drive, one can get both rooms clean in much less time:
Thank you for reading!