Author Topic: White dots  (Read 6568 times)

2016-01-30, 20:37:39

ska

  • Active Users
  • **
  • Posts: 76
    • View Profile
Hello,
I have some issues with those white dots. I saw them in previews and wonder whats happening there?
Its simple scene with studio hdri and sun for shadows.

2016-01-30, 22:13:08
Reply #1

SairesArt

  • Active Users
  • **
  • Posts: 686
  • Pizza | The Cheesen One
    • View Profile
    • SairesArt Portfolio

Nah, joke.
Welcome to rendering issues 101.
These are reflective fireflies. This is a common phenomenon and is not a bug. The Corona Freshdesk should be your first stop to check for documentation on all sorts of stuff (link below)
The reflective Metall is apparently bumpy and some spots reflect sun light direclty into the camera, like some drops of water blinding you in the eye.
One of many solutions: lower MSI or make sun in reflections invisible or make hdri LDR to reflections (if firefly from hdri) or remove metal bump (if any) or sample more. (If reflection alteration from bump = more samples less rays, if firefly from gloss, more rays, less samples)

Check: https://coronarenderer.freshdesk.com/support/solutions/articles/5000529356
For reflective fireflies.
And https://coronarenderer.freshdesk.com/support/solutions/articles/5000501983-how-to-get-rid-of-excessive-noise-
For noise in general.


2016-02-01, 00:59:15
Reply #2

ska

  • Active Users
  • **
  • Posts: 76
    • View Profile
Ohh tank you so much for this explanation, those links are great :)

btw i'm fresh :)

2018-09-27, 12:20:41
Reply #3

Taiwolf

  • Active Users
  • **
  • Posts: 13
    • View Profile
Hello guys!
From some time I get this problem really frequently! I am using Corona on Cinema 4d and most of the times when I use corona lights, I get this white spots problem. I have about MSI, Light sample multiplier, GI/AA, I had played with these settings but nothing. It is something that I don't know to control it. I can't get sharp and clean renders at all.
I have this problem with white spots on some materials. In some situations, when I get more exposure the spots are more and more visible. There, in the picture I am using a frosted glass wich I've downloaded from www.corona-materials.de and had worked fine in other scenes. So, In the scene is no window, so no natural light. I have 6 spots(corona light object), and I get this kind of lines on that glass. I don't understand perfectly how corona works. Could someone help me please to understand what I have to do?
Thanks a lot.

2018-09-27, 12:38:37
Reply #4

pokoy

  • Active Users
  • **
  • Posts: 1562
    • View Profile
This looks like it could be caused by anisotropy which you can set smaller values. Or very strong bump, in that case decrease its strength and see if that helps.

2018-09-27, 12:43:30
Reply #5

Taiwolf

  • Active Users
  • **
  • Posts: 13
    • View Profile
Thank you, but I dont have so much bump. I have overrided the scene except that glass panel with a simple white material and I get similar results.Indeed, smaller but the same..The glass doesn’t have any bump.I have bump only on concrete, but is small. The anysotropy is the MSI?or we talk about different things? I am usong cinema 4d.:)

2018-09-27, 13:10:34
Reply #6

subpixelsk

  • Active Users
  • **
  • Posts: 460
    • View Profile
    • johny.mrazko.visualization
maybe something wrong about mesh itself? can you try and replace this wall by a simple box and render again?

2018-09-27, 13:11:28
Reply #7

pokoy

  • Active Users
  • **
  • Posts: 1562
    • View Profile
Anisotropy would still be my first guess then. It's a parameter somewhere in the material's reflectivity section (using Max so not sure where to look). If it's at 0, reflection is isotropic (uniform in all directions), any higher values will introduce anisotropy, which at too high values will produce something like you're seeing there. It can then introduce reflections form strong light sources even in unexpected places, similar to brushed aluminum where reflections from a light source above are visible on the entire surface.

2018-09-27, 13:15:19
Reply #8

balatschaka

  • Active Users
  • **
  • Posts: 19
    • View Profile
Those are nasty.. happen to appear when you use the bg overrides in corona setup. ArionFx can fix those, if quick and dirty is acceptable.

2018-09-27, 13:17:51
Reply #9

Taiwolf

  • Active Users
  • **
  • Posts: 13
    • View Profile
Anisotropy level is 0 on reflection.I have changed the object. Still the same result.Oh my gosh..and it should be a simple scene..:(

2018-09-27, 13:30:14
Reply #10

Taiwolf

  • Active Users
  • **
  • Posts: 13
    • View Profile
I have played with lightmix and have observed that those spots are caused by the corona light from above. But in reality is not normal to have this kind of reflections...

2018-09-27, 14:07:12
Reply #11

pokoy

  • Active Users
  • **
  • Posts: 1562
    • View Profile
Anisotropy level is 0 on reflection.I have changed the object. Still the same result.Oh my gosh..and it should be a simple scene..:(
Is the material using a map for anisotropy? This would still override the general value I think.

Other than that... what happens if you disable any phong shading? Or make it a pure reflective mirror without any refraction, still there?

2018-09-27, 14:08:28
Reply #12

sprayer

  • Active Users
  • **
  • Posts: 786
    • View Profile
you should't 'play' if you don't know how to  play, too high value in lightmix  gives you noise,the same for all parameters, bump, light. etc. Do not  change corona  preference if you don't know what you need. Would  be faster to solve your  problem if  you look video at youtube corona channel about common mistakes and lightmix or share the scene. Cheers

2018-09-28, 11:53:22
Reply #13

maru

  • Corona Team
  • Active Users
  • ****
  • Posts: 10498
  • Marcin
    • View Profile
It's hard to debug scenes like that without actual access to them in 3ds Max.
My first guess would be messed up geometry. Was it by any chance imported from some other 3d soft like Revit or Autocad?

2018-09-28, 12:06:51
Reply #14

Taiwolf

  • Active Users
  • **
  • Posts: 13
    • View Profile
The scene is imported from Archicad and optimized individual objects in Cinema 4d. The frosted glass panel I have made it separately in Cinema4d, from object. So, no errors here. I have tried to cancel reflections and refractions on light objects. I will try to put some light material on spot lights from the ceilling and use Corona light objects only for lighting the scene. Reflections and refractions I will try to achieve from light material. I will poste the results, too!
Thank you very much for your interest!