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Flickering reflections in surfaces and how to get rid of them?
happens constantly in certain reflective surfaces.
 
I have rendered something and certain surfaces have massive flickering in the lighting for the reflections, and I don't know exactly what to do to fix it.
It seems to happen with sunlight object or even just an HDRi lighting the scene.

It doesn't look like anything major in these screenshots, but it happens constantly in just about every frame and it's very noticeable in the video. (you might have to download the photos and flip through to really see the difference)

I thought maybe the exterior flickering was just the clouds in the HDRi moving by the surface reflections, but what would explain the interior flickering on the car panels?
Edited: ssjenforcer - Mar 21, 2022 19:29
 
Administrator  Posts: 797
Mar 21, 2022 19:35
It's certainly hard to notice any flicker based on still images. I think the a noisy and lowres video can help.
Actually there should be no any flickering because CentiLeo is unbiased. The reflecion may produce bright effects from the sun.
Also the surface of the car needs some more subdivs to get smoother however this is probably not the source of flickers.
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Quote
Kirgman wrote:
It's certainly hard to notice any flicker based on still images. I think the a noisy and lowres video can help.
Actually there should be no any flickering because CentiLeo is unbiased. The reflecion may produce bright effects fr om the sun.
Also the surface of the car needs some more subdivs to get smoother however this is probably not the source of flickers.
It is some spots on the car that have bright spots turning dark and then bright again with each consecutive frame. These are all one frame to the next, and the changes occur like that for almost every frame. Look at the corners of the windshield. The changes to it just look jarring.

https://youtu.be/_SWDXoxoEVU

Here is a link to it. It is noticeable in the shots wh ere the car interior or exterior are visible, at the beginning and end.

EDIT:
I was just trying to remove light sources and identify any issues, but I noticed now that my car model (free from online) might actually be fairly low polygon. This could be causing the issue?
Edited: ssjenforcer - Mar 21, 2022 23:37
 
Administrator  Posts: 797
Mar 22, 2022 05:53
It's very lowpoly. Can you add a Subdivision Surface Object on top of lowpoly objects and apply 1-2 steps of subdivs?
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Are you sure, there is no other light objects? I have same issue in one scene where an area light created weird reflection.
The hdr may be creating the highlight around the glass.

Try to uncheck the noise remover and render the interior. May not be the right solution but it may help to identify the issue.

Remove the normal tag of the car and render. Sometime the normals may be random in those low poly models.
 
Administrator  Posts: 797
Mar 22, 2022 13:22
thrimanakatha, thanks for giving the list of extra potential reasons of that flickers. Indeed the noise removers / denoisers can produce the issues on low sample counts
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Quote
thrimanakatha wrote:
Are you sure, there is no other light objects? I have same issue in one scene where an area light created weird reflection.
The hdr may be creating the highlight around the glass.

Try to uncheck the noise remover and render the interior. May not be the right solution but it may help to identify the issue.

Remove the normal tag of the car and render. Sometime the normals may be random in those low poly models.
Where is the Noise Remover?
I don't have Denoise Images checked or Keep Raw and Denoised AOVs checked either.
The car didn't have a normal tag. I just applied my own materials for the surfaces and paint materials.
I did try to remove one light at a time and see if that helped, but I didn't notice any changes to flickering.

Also, unfortunately adding a Subdivision Surface to the car parts makes these gaps in the corners where some parts meet. I couldn't find a way to fill in the gap, either.
Edited: ssjenforcer - Mar 22, 2022 13:55
 
Administrator  Posts: 797
Mar 22, 2022 14:51
Send me a scene to info@centileo.com pls? I will check what's wrong there
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hello,

apply the following solutions, one at a time and render.

1. Change the hdr (download high resolution hdr from reputed source. Sometime hdr may not have the right light information.)

2. Turn off static noise in Centileo render (if it is already turned off, turn it on) and render. See if the interior flickering disappears or not.

3. Turn off denoiser and crank up the max ray bounce, clamp lights to the max. Also increase the max iteration. Render only the flickering frames and check.

4. Use two different sky objects, one for lighting and one for reflection.

5. Add bounce/fill/ambient light inside the car.

6. Check the poly normals (not the normal tag) of the glass object. If they have issues use align normals.

7. Check the car paint material. Try to use one reflection layer and render. Later add second layer.

Inorder to use subd, you need to convert your model to quad dominant. Add edge loops around those round corners.
 
Quote
thrimanakatha wrote:
hello,

apply the following solutions, one at a time and render.

1. Change the hdr (download high resolution hdr from reputed source. Sometime hdr may not have the right light information.)

2. Turn off static noise in Centileo render (if it is already turned off, turn it on) and render. See if the interior flickering disappears or not.

3. Turn off denoiser and crank up the max ray bounce, clamp lights to the max. Also increase the max iteration. Render only the flickering frames and check.

4. Use two different sky objects, one for lighting and one for reflection.

5. Add bounce/fill/ambient light inside the car.

6. Check the poly normals (not the normal tag) of the glass object. If they have issues use align normals.

7. Check the car paint material. Try to use one reflection layer and render. Later add second layer.

Inorder to use subd, you need to convert your model to quad dominant. Add edge loops around those round corners.
thanks I'll try.

6. Check the poly normals (not the normal tag) of the glass object. If they have issues use align normals.
I don't know what poly normals means, and I have never heard of quad dominant. I'll have to figure out how to add edge loops.
 
poly normals = polygon normals. You can turn it on by pressing alt+v then view> polygon normals = on Here is the help showing how to check and align the normals https://help.maxon.net/c4d/r25/en-us/Default.htm#html/5669.html?Highlight=normals

quad dominant object is usually used in animation. The object is made of 4 sided polygons only. No triangles, ngons are present. A 3d object with good mesh flow can easily be manipulated, animated, distorted and applied different modifiers.
Check the maxon help, showing the sumdivision modifier in action https://help.maxon.net/c4d/r25/en-us/Default.htm#html/OSDS.html?TocPath=Create%2520Menu%257CGenerato...

You can always use the help system by selecting anything within the c4d and pressing ctrl+f1.

Your car model has triangulated mesh. Using the command untriangulate may help to some extend.
Adding edgeloops, welding loose vertices will fix the round corner issue.
But I don't think the flickering is because of the low poly count.
 
I just remembered that for the windows I had to add a cloth surface to the original model polygons that make up the window surface, because it was just a flat plane. The IOR values wouldn't work without thickness, as I later learned.
So I wonder if being so low poly that is what is causing the flickering. It only occurs at the edges of the windows.
I'll try maybe adding some Subdivision to them or adjusting the thickness, or making sure it doesn't intersect with the car body.
Edited: ssjenforcer - Mar 26, 2022 19:08
 
Administrator  Posts: 797
Mar 27, 2022 14:37
Thanks for files and advices! I have detected the issue. It has 2 issues to consider:

1) The car windows are made of glass material and this glass geometry is too close to the surrounding non-glass parts. There is some small gap between rays launching from the windows objects and the gap is too small between objects. The geometry seems to be animated a little bit for a fraction of milimeter and it's also lowpoly. So we see the windows objects slight poping that affects the interior and creates the effect of flickering.
So the first solution would be to increase the distance between windows and other car parts.

2) The second solution would be for me to fine tune the computation of this small gap that's used for rays launching from the surface.
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I think it was a combination of intersecting polygons from the body and windows and the edges.
Looking more closely I found that the original windshield had a slight extrusion at the edges to fit the frame. And when I added the cloth surface it curved the edges and raised it off the car so it didn't touch properly.
I ended up lowering the Factor value on the cloth surface to 10% to reduce the curve created by the cloth surface.

When I added Sub.D surface to the car body only the Bilinear mode had it so the corners meet, but the surfaces were all warped and it didn't look correct. And none of the other modes had good corners (they all rounded and separated).
However, when I tried removing Sub.D surface and just subdividing the polygons of the car body it seemed much better and doesn't have gaps.
Edited: ssjenforcer - Mar 28, 2022 01:03
 
Nope, I am stuck again. I am having the same issue but with an astronaut character's helmet.
Different lights produce the same flickering of dark and bright spots around the edges.
I tried changing the HDRi, adjusting the sun light settings with that as the primary light source.

I tried changing the phong angle to 40 degrees--the default for the model was 180 degrees--but that didn't help.

None of the lights or the HDRi move. So I don't understand why this would happen. Even with the glass helmet section removed from render it still has this flickering effect.
Even with no glass or transparent objects it happens on regular material surfaces.

I changed the static noise pattern and increase max ray bounces and max iterations, but nothing helps. Not even raising the iterations from 4 to 64, it makes no difference.



https://sendvid.com/skdcmvbs

Here is the video link.

And I tried this exact scene with another renderer and it doesn't produce the same flickering lighting. So I am uploading my scene and maybe you could help me determine what is causing it? It has to be something with centileo.

*I didn't include the texture files in the rar, but not using them also produces the flickering.

If it is somehow caused by bad normals why would that produce different lighting around the object each frame?

I tried with other models and couldn't recreate the flickering.
Edited: ssjenforcer - Mar 29, 2022 11:38
 
Administrator  Posts: 797
Mar 29, 2022 11:58
Thanks for another case! Actually there can be z-fighting where two surfaces are aligned in the same positions and hence even without any glass they alternate and produce some flickershit. I will look at your files.
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Quote
Kirgman wrote:
Thanks for another case! Actually there can be z-fighting where two surfaces are aligned in the same positions and hence even without any glass they alternate and produce some flickershit. I will look at your files.
Thank you. Let me know if the texture files help and I can email them.
If the flickering happened in another renderer I wouldn't be so surprised but it's very strange it is happening with this model.
But luckily I couldn't find another model that does it, but I didn't try many.

It's strange because it behaves as if the lighting around the object is changing slightly with each new frame.
Edited: ssjenforcer - Mar 29, 2022 15:22
 
Hello ssjenforcer,
I downloaded your scene and checked. At first it rendered black, so I removed the bitmap nodes and increased the hdr value to 1. Rendered with high clamp values and ray bounces. The GI flickering is there but not intense as like yours. Something is wrong with GI bounce inside transparent objects with Centileo.
I will check this model into other renders.
 
1. I did a test with a sphere with a glass material applied to the front half and diffuse material to the back half. Placed a cube inside the sphere and rendered. The GI flickering is there, so the geometry is not causing the issue.

2. Added thickness by extruding the sphere, the issue is still there.
 
Administrator  Posts: 797
Mar 30, 2022 09:03
Quote
thrimanakatha wrote:
1. I did a test with a sphere with a glass material applied to the front half and diffuse material to the back half. Placed a cube inside the sphere and rendered. The GI flickering is there, so the geometry is not causing the issue.

2. Added thickness by extruding the sphere, the issue is still there.
Interesting finding! Can you please give me this scene for test? I am very curious. What was animated there? A camera?
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