Weird smudge on render

[Pero Blatina]

Hello guys,

I created a simple scene to test few things out in 3ds Max + V-Ray. An issue that's appearing in the render is a weird smudge caused by some kind of interference between an imported model of a sofa, and floor material on the area where the sofa casts shadows. I attached the image of the render below. Do you guys maybe know what's going on. I suspect it could be the imported model causing this.

Edit: Just wanted to add that it seems like the shadow cast by sofa is completely washing out the diffuse map of the floor. You can tell that the the reflection of the back leg of the sofa is very visible in that area.

Edited May 28, 2020 by Pero Blatina

[Francisco Penaloza]

First check that there is not overlapping geometry on the floor.

Also what type of material is the bottom of that couch? if it is the same fabric, check the polygons under the couch and see if the normal are not inverted, or make the fabric double sided.

Also it could be a glossy reflection from the window or something outside that is reflecting on the floor.

Try overwriting the floor material with a flat color, not reflection, if the bright area still there then it may be a light or something.

Otherwise you'll have to share that model to debug, it is always hard to guess what's the problem without looking at the actual file.

Cheers.

 

 

[Pero Blatina]

14 hours ago, Francisco Penaloza said:

First check that there is not overlapping geometry on the floor.

Also what type of material is the bottom of that couch? if it is the same fabric, check the polygons under the couch and see if the normal are not inverted, or make the fabric double sided.

Also it could be a glossy reflection from the window or something outside that is reflecting on the floor.

Try overwriting the floor material with a flat color, not reflection, if the bright area still there then it may be a light or something.

Otherwise you'll have to share that model to debug, it is always hard to guess what's the problem without looking at the actual file.

Cheers.

 

 

Hey man, thanks for replying. I played around with material parameters of the floor, and it seems to be an issue connected to fresnel. When it's turned off, the spot dissapears, and it reappears if I turn fresnel on. So what it appears to me is that in these situations shadow is basically bleaching out the diffuse map of the material, which makes V-Ray calculate that the area in the shadow should be reflective. Not sure whether it's a bug in V-Ray, or if I messed something up.

I checked the sofa model, underside is also fabric, normals are fine. I don't have the scene file anymore, but I can recreate it if you guys are interested in checking it out.

[Francisco Penaloza]

How was your lighting setup??

Did you use a dome light with an HDRI and a portal sky light in the window??

if you that glossy area could be the glossy reflection of the HDRI or the portalSky.

Fresnel is a natural phenomenal so it should be always on in every material. now maybe your floor is too glossy or your lighting is bouncing indifferent directions, or there is something very bright some were that is creating that bright spot. Not sure if it is a bug, Sometimes real work effect react in ways we do not expect, believe me

 

[Thomas Edward Allen]

Make sure bottom of couch is black. If it really bugs you, and still there just render a few passes. A reflect pass as exr on difference and paint it out in photoshop.

[Tommy L]

reflection bounce limit? Havent used VRay in a while, but it may be you're clipping the number of bounces to 1 and its returning your override color. Thats possible in your rneder settings or your material settings. 

[Pero Blatina]

Thank you all for replying, I wasn't able to check in with you sooner.

On 6/2/2020 at 5:35 PM, Francisco Penaloza said:

How was your lighting setup??

Did you use a dome light with an HDRI and a portal sky light in the window??

if you that glossy area could be the glossy reflection of the HDRI or the portalSky.

Fresnel is a natural phenomenal so it should be always on in every material. now maybe your floor is too glossy or your lighting is bouncing indifferent directions, or there is something very bright some were that is creating that bright spot. Not sure if it is a bug, Sometimes real work effect react in ways we do not expect, believe me

 

The only lighting used in the scene was the HDRI, and a rectangle light placed just in front of the window with affect specular turned off.

I agree the fresnel should always be on, I was just playing around with parameters to see what might be causing the smudge, and it seems that fresnel affects it the most. I double checked the entire scene and there's no weird lights or anything that should make a reflection like that appear. Yeah, sometimes there are real world effects can be strange, but I suspect it was either me messing something up which I still can't figure out, or it might be the way V-Ray handles the calculations or their order.

 

On 6/4/2020 at 4:28 AM, Thomas Edward Allen said:

Make sure bottom of couch is black. If it really bugs you, and still there just render a few passes. A reflect pass as exr on difference and paint it out in photoshop.

I actually did try to play around with materials of the couch, but the spot still shows, so I don't think that's what causes it. Photoshopping it out seems like the only solution so far, indeed.

 

On 6/4/2020 at 5:15 AM, Tommy L said:

reflection bounce limit? Havent used VRay in a while, but it may be you're clipping the number of bounces to 1 and its returning your override color. Thats possible in your rneder settings or your material settings. 

I think that parameter is called max depth in V-Ray, which determines the number of times a ray can be reflected. I tried both increasing and decreasing it but the smudge still remains.

 

I will recreate the scene sometime today and I'll get back to you guys. Cheers!

Edited June 7, 2020 by Pero Blatina

[Pero Blatina]

So, I recreated the scene, using a different floor material, and slightly different camera angle. The result is a little bit better, however, you can still see the reflections, especially in the area where the shadow is lighter. It's present regardless of the lighting source used (comination of dome light and rectangle light placed at the window, or each used separately). I'm not sure anymore whether it's something that actually should be present in the real world when it comes to semi glossy surfaces.

I'll play around with it a little bit more, feel free to add any further suggestions!

[Pero Blatina]

Sorry for triple posting. I think I found the reason why these reflections happen. I isolated individual render elements of shadows and lighting, and it seems that V-Ray doesn't calculate the shadowed area below the sofa as a shadow, but rather uses lighting to make it appear as such, which in return causes these pronounced reflections in the end result. So far it seems that the only solution to this is to play around with lighting setups, or to edit the image in photoshop. Or maybe there's some other, simpler solution that I'm not seeing right now?

Edit: Just to make it clear, the first image I attached is the shadows render element, the second one is lighting

Edited June 8, 2020 by Pero Blatina

[Francisco Penaloza]

I think what you see is the reflection/glossiness of the white wall behind the couch.  The light is bouncing from that wall to the floor also showing the reflection of it.

maybe is one of those cases where CG accentuate the effect, but I found some photos online that have similar effect.