Reflection "sparks" issue

[salf]

Long time no post, I've been away from arch viz for like 5 years, just recently found more time to start practicing again.

 

Nowadays it looks like Vray is the favorite, there's more tutorials and info for vray than mental ray out there, and Vizdepot (my mental ray go to help forum) shut down.

 

Anyways, I'm having this problem with glossy reflections, I call them "sparks", doing a search for "artifacts" comes back with other types of issues.

 

I'm rendering a concrete wall, I want it to be a little aged, with rough parts, which is why I'm using a reflection map (specular in vray lingo) that way it will be reflective only on smooth areas and not in the rough parts.

 

The yellowish reflection is caused by a photometric light in the scene, a warm bright light. But it's causing those little sparks or artifacts, as you can see the reflections by the environment (mr sky + sun) are ok.

 

The first 3 images used 0.7 reflection, 0.7 glossiness and about 24 glossy samples, the location of the "specular map" is listed in the images.

 

For the remaining 3 I just upped the reflection to 1.0, and the last one I used Fall Off instead of the "specular map"

 

ANy ideas? Could it be the photometric light?, should I try other type? I'll keep on testing on my end, but maybe someone here could know how to fix it.

 

thanks!

 

EDIT: BTW, images 1 and 3 are more like it the reflections I want (based on the blueish environment reflections) the other seems like someone applied varnish on the concrete wall.

Edited March 28, 2012 by salf

[Justin Hunt]

Have you tried to turn specular off on the photometric light?

[salf]

Hey Justin, thanks for the tip!

 

Sadly it didn't work.

 

After a few more tries I gave up and just disabled the photometric light.

 

However I think I now know what was the problem, based on Ludvik Koutny's tutorial of the Esherick House, I think the issue was that I had the photometric light to be "visible" in the rendering, apparently MR's AA can't handle this very well.

 

I should rather use a glowing material instead.

 

I'll go back and try it out.

[Justin Hunt]

That was going to be my second suggestion, :-)

[salf]

Ok, I went back and gave it another try.

 

While it's better than before ( turning off the visibility of the photometric light) I'm still having some issues, not entirely happy with the image.

 

1- Reflections on the concrete (and even on the floor) looks too "shiny", almost as if the wall has been varnished. I'm setting the Reflection pretty low 0.2, glossiness around 0.4 and samples about 32, using a reflection map.

 

2- Still having some "sparks" on the floor. I clicked the NOT AFFECT THE DIFFUSE MAP option for the bump map just in case that's causing the issue, but not much change.

 

3- Some bad shadows/artifacts in the background room.

[Justin Hunt]

can you post the material settings for the concrete? and have you played with the BDRF curve? There is also an option to darken the reflection highlight intensity.

 

If its OK could you send me the file so I can have a look

 

jhv

[salf]

Concrete material screenshots.

 

Showing the DIffuse and Reflection textures used.

 

For BDRF I'm using an IOR of 2.0.

[Justin Hunt]

Try switching the BDRF to custom and play with the 0 degree values

[salf]

Ok, started tweaking the BRDF settings one thing led to another, tests, tests, more tests, after almost a whole day of different iterations, I "inverted" the reflection map (so it's more on the white side than dark) and that did it for the concrete.

 

The floor kept on having issues, it was either too shinny or with extremely "granular reflections" (if that makes sense)

 

I Think that the .jpg file I used for the floor (diffuse, bump and reflections) might be low quality, I gave it a try with regular A&D polished concrete and changing the default diffuse map for another and it look better.

 

At the end I just composed 3 different reflections passes in photoshop.