Hi gvzmedia,
I assume that you refer to this text:
Ray Threshold [0..100%]
This value helps to optimize render time. With complex scenes, particularly those containing many reflective and transparent surfaces, 90% of the processed rays contribute less than 10% to the general picture brightness and color. With a threshold value of, for instance, 15%, the rays stop their movement from the camera into the scene as soon as their brightness falls below this value.
For reflections/transparencies, this generally means that the higher the value, the greater the degree to which very small reflections/transparencies will be taken into consideration - with correspondingly longer render times.
Very simplified said, it is the information produced from a given surface for example, based on its transparency or reflection. Think of many mirrors set up so the one that is “calculated’ can see another mirror, of course this mirror reflects something, and so on. This “chain” of visibility based on mirrors is explored by that mirror. Since nothing really reflects 100%, after a while the mirror on the chain’s end will be not given a huge change anymore. This change is then measured by the threshold. The ray stops here. Two mirrors set up parallel could reflect for ever and crash the system perhaps, but since each reflection will naturally have a little loss, if not set to an un-natural value of 100% or even more (yes it’s possible), this threshold will stop it.
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Yes it is confusing to use the “value” here without specifying if the value means the threshold or the value of the brightness. Small reflections in the image can have a high value, and even very small, based on its high value, it is included, even if the object has only the size of a pixel. Typically the term parameter is used for entries and value is used for a given appearance in the scene, based on a parameter, perhaps that old rule is not really applied clearly. All the three “depth” parameter work in the same way, but with with a fixed number of “iterations” instead of “signal power”.
I hope the function of this parameter is clear now as I think you understood it correctly from the start.
All the best