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The Hunt For The Black Dots (simple test renders) (updated)

Posted: Tue Jun 21, 2005 6:46 pm
by Aldaryn
Hi!

Had some freetime, and built a simple cornell like testing environment. I wanted to localize, and understand how black dots populate the scene.

No tweaking through the UI (shutter, ISO) or PS was done.

Image

Posted: Tue Jun 21, 2005 6:56 pm
by n1tram
Great test Aldaryn! I tried something like this and found a strong correlationship with black dots and UV roughness + sunlight.

I then tried a interior scene with emitters behind dielectrics (all caustic layers on) and my whole render was a big white dot :cry:

Every object was outlined by white dots, and mos of my textures where not even visible.

Any thoughts?

Posted: Tue Jun 21, 2005 7:06 pm
by Thomas An.
Very nice test !
Thank you :D

Posted: Tue Jun 21, 2005 7:15 pm
by aitraaz
Good god. Magenta dots. Anarchy :shock:

Posted: Tue Jun 21, 2005 8:24 pm
by Aldaryn
I've attached a new image. I think all the dot related problems are mainly from multiple transmitted light. The more complex a transmitted light situation is, the more dots you get.

There is no problem with direct, and mainly diffuse indirect light. But even a dielectric seen through another generates white (or with higher abbe, colored) dots.

Posted: Tue Jun 21, 2005 8:45 pm
by Aldaryn
I've uploaded the image to imageshack, the previous one was a hungarian image hosting service, maybe a bit slow from abroad.

Posted: Tue Jun 21, 2005 8:58 pm
by Aldaryn
Btw, has anyone notieced how sss brightens up the whole image? This needs further testing... 8)

Posted: Tue Jun 21, 2005 9:28 pm
by Hervé
thanks.... well it kinda gives more bightness to the sss surfaced objects, that is why I think we see it brighter...

Posted: Tue Jun 21, 2005 9:28 pm
by Becco_UK
Aldaryn: That is an impressive amount of testing you have done. At the very least it informs users what combinations to avoid until the problem is fixed.

Have you noticed the 'pink' dots are virtually the same colour as the garish pinkish purple in the Maxwell Render spectrum gradient. Might there be a connection?

Posted: Tue Jun 21, 2005 9:34 pm
by Hervé
the now famous garish pinkish.... hehe

Posted: Tue Jun 21, 2005 9:40 pm
by tom
thank you for your valuable time aldaryn! nice test!

Posted: Wed Jun 22, 2005 12:00 am
by aitraaz
Ah Ah..."While this solution worked, it was fundamentally flawed, creating the otherwise contradictory systemic anomaly, that, if left unchecked, might threaten the system itself."...

Another test.

Posted: Wed Jun 22, 2005 11:52 am
by Aldaryn
Becco_UK: I dont think there is a straight connection between the pink in the spectrum and the doths here, however, there might be some.
In this case, it might just be a result of the color from scattering objects.

Another indirect situation:
Image

Mutiple specular reflected light hitting a scattering plane, and not a single black dot. :) Seem so, dots mostly appear in multiple transmitted light situations.

The black dots on the white plane are just noise. The preview showed no dots at level 14.