Dennis Posted December 23, 2009 Share Posted December 23, 2009 Hi guys, I'm currently working on a project which highly depends on indirect diffuse illumination and therefore I thought PBR would be the perfect match for this project. Unfortunately I'm getting strange shading artifacts when using PBR. However, when I'm using raytracing with VEX GI set to Path Tracing i'm not getting any artifacts. Does anyone know how I might solve that problem? What exactly does the Sampling Quality on the VEX GI node do when set to Path Tracing? Is it essentially the same as upping the min ray samples when rendering with PBR but only for the indirect illumination? I've also noticed that the color limit parameter doesn't work in my current build of Houdini (10.0.465) on a Mac. Has anybody experienced the same issue? I've attached two images and the scene file. Thanks. Merry Christmas everyone, Dennis PBR_RT_Artifacts.hip.zip Quote Link to comment Share on other sites More sharing options...
Jason Posted December 23, 2009 Share Posted December 23, 2009 This is just a guess, but perhaps the PBR Ray Bias is different to the ray bias in RT mode? ie, perhaps the difference in look is really a ray self-intersection artifact? Perhaps increase the bias in PBR tab. Quote Link to comment Share on other sites More sharing options...
Dennis Posted December 23, 2009 Author Share Posted December 23, 2009 This is just a guess, but perhaps the PBR Ray Bias is different to the ray bias in RT mode? ie, perhaps the difference in look is really a ray self-intersection artifact? Perhaps increase the bias in PBR tab. Hi Jason, unfortunately that didn't help. Other ideas or suggestions are highly appreciated. Greetings, Dennis Quote Link to comment Share on other sites More sharing options...
anamous Posted December 23, 2009 Share Posted December 23, 2009 Is your geometry rendered as subd? cheers, Abdelkareem Quote Link to comment Share on other sites More sharing options...
Dennis Posted December 26, 2009 Author Share Posted December 26, 2009 Is your geometry rendered as subd? cheers, Abdelkareem Actually it wasn't rendered as subd. But unfortunately the subd version looks just the same. Cheers, Dennis Quote Link to comment Share on other sites More sharing options...
symek Posted December 27, 2009 Share Posted December 27, 2009 (edited) Actually it wasn't rendered as subd. But unfortunately the subd version looks just the same. Cheers, Dennis Call me... whatever, but for me it looks like specular/glossy reflections of PBR (obviously absent in GI/pathtrace mode). Are you sure, your shader in PBR performs equally diff/spec as in RT? ps Unfortunately I can't check your scene now to qualify my suspicions... Edited December 27, 2009 by SYmek Quote Link to comment Share on other sites More sharing options...
Dennis Posted December 27, 2009 Author Share Posted December 27, 2009 Call me... whatever, but for me it looks like specular/glossy reflections of PBR (obviously absent in GI/pathtrace mode). Are you sure, your shader in PBR performs equally diff/spec as in RT? ps Unfortunately I can't check your scene now to qualify my suspicions... That's actually what i thought too. But everything has just a basic clay shader applied at the moment so there shouldn't be any glossy reflections. For those who can't check the scene it might be interesting to know that the whole scene is just lit by luminous geometry. In another version I tried it with a big area light at the back and instanced spherical area lights for the floor and it resulted in the same issue. I noticed that i had flipped normals on my walls, but reversing them didn't help either. Quote Link to comment Share on other sites More sharing options...
sam.h Posted January 5, 2010 Share Posted January 5, 2010 I had some artifacts in PBR and SESI said that I should turn down ray samples and use pixel samples to up the quality ... ? I don't really understand it but it worked. Quote Link to comment Share on other sites More sharing options...
Dennis Posted January 7, 2010 Author Share Posted January 7, 2010 I had some artifacts in PBR and SESI said that I should turn down ray samples and use pixel samples to up the quality ... ? I don't really understand it but it worked. Thanks, I will try that. For now I went for a different approach using just raytracing. I will post here as soon as I can verify your suggestion. Hope this will work. Quote Link to comment Share on other sites More sharing options...
DaJuice Posted January 8, 2010 Share Posted January 8, 2010 I played with your scene the other day and I couldn't figure out what was causing the problem. When I changed the self-illuminated geo to an area light the problem went away though (and noise was cut too of course). Quote Link to comment Share on other sites More sharing options...
sam.h Posted January 8, 2010 Share Posted January 8, 2010 Just had a play, pixel samples of 12x12 and ray samples of 16 seems to have fixed it. I'm too impatient to render the whole thing .... laptop isn't very quick ... Quote Link to comment Share on other sites More sharing options...
Dennis Posted January 10, 2010 Author Share Posted January 10, 2010 (edited) I played with your scene the other day and I couldn't figure out what was causing the problem. When I changed the self-illuminated geo to an area light the problem went away though (and noise was cut too of course). Hmmm, thats strange. Did you just use a big rectangular area light at the same spot? I tried that in another scene and it seemed to not work for me. Maybe I was doing something wrong. Have to check it again. As I understood it PBR shoots one diffuse ray at a random light, another random diffuse ray and one specular ray whose propability is weighed by the specular function (hope this makes sense) into the scene. I had the impression, that the random light ray very rarely hit my area light as most of it is occluded by geometry. But maybe I have to check that again. Could you post the modified scene so I can have a look at the setup and verify your results? Just had a play, pixel samples of 12x12 and ray samples of 16 seems to have fixed it. I'm too impatient to render the whole thing .... laptop isn't very quick ... I just checked that and indeed it seems to have improved the artifacts. But if you increase the brightness they are still there. The strange thing is, that you used a total of 2304 samples. If I up the pixel samples to 45x45 and use a ray sampels value of 1 which gives me 2025 sampels I get no artifacts at all. I wonder if that is due to the unbiased way pathtracing works, because with more pixel samples I get more more randomness per pixel and thus a more correct result. Greetings, Dennis Edited January 10, 2010 by Dennis Quote Link to comment Share on other sites More sharing options...
Rvb Posted January 15, 2010 Share Posted January 15, 2010 Hmmm, thats strange. Did you just use a big rectangular area light at the same spot? I tried that in another scene and it seemed to not work for me. Maybe I was doing something wrong. Have to check it again. As I understood it PBR shoots one diffuse ray at a random light, another random diffuse ray and one specular ray whose propability is weighed by the specular function (hope this makes sense) into the scene. I had the impression, that the random light ray very rarely hit my area light as most of it is occluded by geometry. But maybe I have to check that again. Could you post the modified scene so I can have a look at the setup and verify your results? I just checked that and indeed it seems to have improved the artifacts. But if you increase the brightness they are still there. The strange thing is, that you used a total of 2304 samples. If I up the pixel samples to 45x45 and use a ray sampels value of 1 which gives me 2025 sampels I get no artifacts at all. I wonder if that is due to the unbiased way pathtracing works, because with more pixel samples I get more more randomness per pixel and thus a more correct result. Greetings, Dennis A quick question. How long did it take to render those frames? Rogier Quote Link to comment Share on other sites More sharing options...
Dennis Posted January 18, 2010 Author Share Posted January 18, 2010 A quick question. How long did it take to render those frames? Rogier The cleaner version with 45x45 pixel samples and min ray samples set to 1 took 23 minutes on my Mac Pro with 16 virtual cores @ 2.26 GHz. I should add, that the diffuse limit is set to 3 for these renders. Quote Link to comment Share on other sites More sharing options...
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