[Graham Harvey]

Hi

I have a very simple scene. A floor, a glass object and physical sky with sun. I cannot avoid white spots / noise in the glass which are visible when rendering high res. They start to appear at around SL10 and get progressively worse.

Glass has a gradient of colour - no colours are too bight.
The floors is simple grey diffuse not too bright.
Caustics are on.
Dispersion is on.

Low Res Render
https://www.dropbox.com/s/549x2xbnaut43 ... t.jpg?dl=0
Close up showing artefacts
https://www.dropbox.com/s/r2s94hl1wmrvc ... s.jpg?dl=0
Materials
https://www.dropbox.com/s/2xrlsre5j7lop ... s.jpg?dl=0

[Mihai]

This could be because of the difficult situation of caustics seen on or through specular surfaces. You could try adding just a bit of roughness (1-2) and see if that helps with the white dots, or try disabling indirect refracted caustics from the render options.

[Graham Harvey]

Yes - that solved the issue - Turned off Refr.Caustics - both direct and indirect. BUT the image looses a LOT.
I can't share the actual client scene but its the same set up and the caustics is the part that they like the best.

[Mihai]

There is not much else you can do in that case except use custom masks based on the material so you can make an easier selection of the trouble parts, and use the spot healing brush in PS which works pretty well on these isolated bright spots.

[Graham Harvey]

Spot healing is one solution though as you can imagine as the 3D form gets more complex, the retouching process becomes more involved. I hadn't thought that Maxwell would present problems with such a simple scene! I am actually going to render two scenes - one without refractive caustics, and compostit the two together. Thanks for your help Mihai.

[Mihai]

I think these spots are more common with the sun from the physical sky. Another alternative is to use multilight, and you get separate sliders for the sun and the overal sky lighting. I bet if you Solo the Sun slider you will see it holds all the white spots or most of them. So now you have a sort of separation between two layers, one which holds the entirety of the white spots. Open the MXI in PS and you already have two separate layers to work with, so there may be no need to render two versions.

[F. Tella]

This is a specially hard case for this kind of renderers.
Those dots, after a long (looong) time will compose the real caustics seen through the dielectric (around SL30).
To speed things up you can increase the size of the emitter (you can increase the radius of the sun too). The shadows will be more diffuse but the caustics will show sooner. I made a test with a pool some time ago: http://www.maxwellrender.com/forum/view ... sun+radius

Another option is to hide the geometry to GI. The internal look will be very similar, but it won't cast shadows or produce caustics on the floor. Additionally you can add a copy of the geometry with an AGS material hidden to camera, reflections and refractions so it generates a shadow and reflected caustics. (I would increase the opacity of the standard AGS)

You can then compose different parts of the renders depending of which one you prefer.