Black spots on ceiling

[medzo]

Hi

I have encountered a little problem, little black spots on ceiling during the rendering and then in the final render. You can see it in attachement.

How can I get rid of those spots. The scene contains a few ies lights, lumi polygons in reflectors visible for camera but do not emit any light and under these polys larger 'standard' lumi polygons for illumination.

I did manage to reduce these spots by increasing FG rays - 600/1200 3passes, which i think is quite enough but spots are still visible. Any ideas?

[Janusz Biela]

They are not danger for final render. From size of this photon sampling (and info from Kray) I guess, You have too small GI resolution. For interiors enough is 200-300 mm. Try render in Photons Estimate - Precomputed render, this will show what is wrong there.
You do not need three passes - is enough two. You can increase parameter N, up to 3000 or more (this blur cells and can reduce color splotches). Also post Kray stetting cfg to see setup.

[medzo]

well in final render i admit that the effect is very subtle, but still it would be nice to know how to get rid of it.

I am posting photons estimate - precomputed render - which i still dont know how to use this function to help me with better renders

and my settings

PS: I just got an idea about K3.O menu. We could have an extra tab with all relevant settings (photons, fg, quality,...) and with a single click we could export this extra tab to jpg image and post it on forum. Much simpler than this print-screening and pasting in photoshop and.....so on...

[medzo]

Found out what was the problem. Lightwave's 'reflection shading' node was used on the suspended lamp and this node causes these black spots. I thought that this issue was already fixed...

[Janusz Biela]

Yes, be careful with Shader Nodes from LW.
I have some updates for Your menu:

[medzo]

Thanks Janusz, i will try your settings and compare. About the metal (conductor) materials - how do you make your shader? Aren't you using reflection shading?

[Janusz Biela]

Thanks Janusz, i will try your settings and compare. About the metal (conductor) materials - how do you make your shader? Aren't you using reflection shading?

Nodes which I use are done according to the realistic behavior of surfaces except consumption/scattering of photons (is not necessary to use that realistic surfacing as in Maxwell for architecture). They are completely free from shades which bring non stop problems (not always because of Kray - sometimes they are too slow or buggy).

[medzo]

WOW!!! Janusz you really know your ways around Kray!

This is render with my settings 2 and a half hours:

This is render with your settings - just half an hour:

I did mess up something with camera position...but that doesnt matter.

Basically I understand where the render speed comes - mostly from spatial tolerance and just 2 FG passes, some . There are very subtle differences between renders. With my settings the contact shadows are a bit stronger but very hardly noticable.

I still have some questions:

Photons map - 1milion global photons and N number 3000. Is this some sort of a general rule or it depends scene from scene. Is this also optimal for exteriors.

Final gather - 0,0 FG theshold - why is this better than 0,0001?
Final gather - I dont understand MIN and MAX DISTANCE settings - does this settings affect render times? Do these settings control contact shadows? What do these actually settings do?

And a simple question about metal materials. If you dont use reflection shading node - are you just using color highlights input?

Thanks again!

[Janusz Biela]

Basically I understand where the render speed comes - mostly from spatial tolerance and just 2 FG passes, some . There are very subtle differences between renders. With my settings the contact shadows are a bit stronger but very hardly noticable.

Do not pay attention for small problems - only we see it, client doesn`t.
Important is whole view and good balance.

Photons map - 1milion global photons and N number 3000. Is this some sort of a general rule or it depends scene from scene. Is this also optimal for exteriors.

1 million is minimum (You must fill each corner, place, etc by photons)
The N parameter can help when You have errors with photon map because of small windows, physical lights inside, small lumi lights, etc. This option just blur photons cells between each other. Of course it cost a bit contact shadow. I think value 2000-4000 is optimal when You have problems with color splotches. Normally try keep it under 1000.

Final gather - 0,0 FG theshold - why is this better than 0,0001?

I do not like any thresholds in renders (means: increasing speed of render by adding errors to GI) So, by value 0 I lost a bit time (sometimes is no difference) but I know Final Gathering works correctly in each part of render.

Final gather - I don`t understand MIN and MAX DISTANCE settings - does this settings affect render times? Do these settings control contact shadows? What do these actually settings do?

Yes this is major setup. MIN is minimum distance between samples. If two options min/max are too small (100/200 for example) then You get too many samples (which is not necessary) on the wall - which is "flat" with GI and color. You do not need thousand samples on the flat ceiling and MAX parameter should be high to increase speed render on that regions with less samples calculations.
I think 50/2000 is good. But this is also connected strongly with Spatial Tolerance and GI resolution.

And a simple question about metal materials. If you don`t use reflection shading node - are you just using color highlights input?

Thanks again!

Reflection surfaces are strongly dependent from environment! In completely dark room,the metals surfaces are dark dark because nothing is reflected from surface!
So metal surfaces are very dependent what is in environment.
I use high Fresnel value (15) for metal with diffuse subtraction. Nothing special. good metal effect coming later from good light, camera angle, tonemaping, post process.
Of course we need anisotropic reflection shader for Kray to increase realistic - this shader is very important. Is just UGLY effect, when reflection blur is scattering not parallely to camera (these from LW Nodes are useless - because speed which offer are unacceptable)