Strange speculars/fireflies on the floor! [SOLVED]

[Rimas]

Hello, good people of Coronia!

I need your help once more and hopefully someone can help me crack this...

I'm doing an interior render for a client and I ran into a problem with weird specular reflections coming out of seemingly nowhere.

The problem is as follows:

First, the reflections make no sense whatsoever - they appear in the shadow areas where the angle of view would probably reflect the dark wall anyway...



AND



Weirdly enough, it happens on the side closer to the camera. The floor looks fine further away:



Now onto the details:
I'm using my usual setup for parquet - a texture set bought from turbosquid (includes diffuse/ref/bump maps), somewhat reflective, half-way glossy...nothing special. I've double-checked that my texture maps are at blur value of 1 (default) and are not sharpened or overdone. Bump is at 0.3, the bump map itself is between values of 20% grey (tiles) to black (crevices), so nothing extreme either. Here's the shader itself (note that it renders fine in the preview):



I'm using Corona Sun&Sky to light the scene, default settings, nothing special once more:



This is the same scene that I was having trouble with black highlights on the sofas. The workaround was to render with no glass refractions for the skylight (roof) and render the frosted glass as a separate pass to comp in later. I can live with that. But the hite specs appear regardless of whether I use the frosted glass or nothing at all, prompting me to thing it has something to do with the engine itself or the way shader/light are set up?

Here's the overall view:



Dropping the obvious out of the way:
1) I've tried rendering with both frosted glass, no refraction and even no glass at all. Same results.
2) I am not willing to render without the bump map as it gives the flooring realistic look when looking at it against light.
3) The lighting has been approved by the client/director - I can't go to an HDRI easily now.

I hope someone can help with this issue as it's quite obviously destroying the picture. Please don't tell me this is an engine bug just like those black highlights (https://forum.corona-renderer.com/index.php/topic,6883.msg53754.html#msg53754) :/

Thanks!

[PROH]

Hi. Have you tried to turn down the Reflection value, or to force the Reflection Color map to load at gamma 1? What happens, if you removes/deactivates the Reflection Color map - does this make the floor look unnatural?

[maru]

Two things that come to my mind when I look at this:
-how is the parquet object made? Is it a flat plane that has no thickness?
-how is the bump made? Is it greyscale bump or normal map or...?

[romullus]

What Corona build you are using?

[Ludvik Koutny]

Corona has by default extremely strong bump mapping. So even default of 1.0 is too strong. You should usually keep in range of 0.05-0.3 for bump. The reason you see your problem only closer to camera is probably because your bitmap blur value in your map you use as bump is set too high, therefore more filtering occurs in distance which makes bump map more blurry and therefore weaker.

My suggestion is following:

Reduce bump mapping strength in CoronaMTL

Set blur value of the map you use as bump to something like 0.1.

[Rimas]

Hi!

Thanks for the replies!

PROH:
The reflection map is just a grayscale map with darker lines in the crevices, brighter values on the parguet tiles. I'll try to load it up at gamma 1 (if I haven't already), see if that changes anything.

MARU:
Flat plane, no thickness. Standard greyscale bump.

ROMULLUS:
Corona version: 1.00.02, Maxsdk version: 2015

RAWALANCHE:
I am aware of the bump strength, I did indicate in the original post that I am using a value of 0.3 in this material :)
I'll see if reducing blur does anything. I usually leave the bur at default because if bump is strong and sharp then terminator effects come into play (model becomes faceted, loses its unified smooth shading).

I'll try and play around with the suggestions, see what happens and report back!

Thanks! :)

[Rimas]

Hi, guys!

Thank you once more for the help!

Interesting case.

This is what happens after I use suggestion by PROH to load in the textures at gamma 1.0 and RAWALANCHE's suggestion to reduce the blur amount:



This exaggerates the problem!

But now we add some thickness to the flooring like MARU said and... [drumroll]



So it seems you were all pretty much right on the money :D
Gamma/reduced blur made the bump/reflection maps behave better and then the thickness sorted it out completely!

Thanks once again! :)

[maru]

Sweet, I'm glad it works.
Generally Corona does not like surfaces with no thickness. See: https://coronarenderer.freshdesk.com/support/solutions/articles/5000516209

[Rimas]

Sweet, I'm glad it works.
Generally Corona does not like surfaces with no thickness. See: https://coronarenderer.freshdesk.com/support/solutions/articles/5000516209

I'll keep that in mind! Dziękuję bardzo!

[maru]

Bug fixed in newest daily build, moving to resolved bugs.