Firefly filter intensity adjustment

freee

I have several renders that I need to apply firefly filter on. I have no idea what are the constraints so I'm just bumbling about like an idiot and I need some assistance.

My issue is that setting the firefly filter to 100 dulls all the fireflies easily, however it also changes the scene lighting. Upping the filter to 1000 had no effects on the image, so I'm guessing there's a max value for it? If so what is it?

My main question is: is there a way to both use the firefly effect and not lose the light value of the scene, and if not, how do you deal with the changed color of your renders when using firefly filter? I've tried changing the values of the scene lighting and various render settings but it was with mixed results. Any advice?

Sevrin

I've always had the Iray firefly filter on, but I've never found it necessary to change the default (Nominal Luminance = 0) filter settings, or come across discussions here about doing that.  With the filter on, your images will get a little brighter with more iterations.  With higher nominal luminance, you are telling Iray that there is more light in your image.  If there isn't really more light, your renders will be darker the higher your nominal luminance setting.

crosswind

"The firefly filter works best in combination with the built-in tonemappers. If the tonemapper is not enabled, the filter estimates can be too pessimistic for some scenes, resulting in some fireflies to still appear... So it is required to either disable the firefly filter completely or to set a correct Nominal Luminance value whenever there is no internal tonemapper enabled, to avoid incorrect simulation results...."

"The nominal luminance is a hint to Iray Photoreal on what is considered a “reasonable” luminance level when viewing the scene. This luminance level is used internally to tune the firefly filter and error estimate. When the nominal luminance value is set to 0, Iray Photoreal will estimate the nominal luminance value from the tonemapper settings. If a user application applies its own tonemapping without using the built-in tonemappers, it is strongly advised to provide a nominal luminance."

-- above quoted from NVIDIA Iray – Programmer's Manual ( out-of-date to some extent but still a general principle )

Since as default,  Tone Mapping is Enabled in Render Settings, setting a Nominal Luminance value is not necessary let alone a must... that's why it is 0 as default. At least from various testing, even if you give it some value, it won't noticeably contribute more to 'eliminating fireflies' but only influencing with 'brightness'. So as what @Sevrin  mentioned, we usually keep its value as default...

If one has interest, he/she may test a scene yielding significant fireflies, count the number of fireflies in the render with default Firefly filter settings, then increase Nominal L. value and render, and count again...