what is missing in GPU renders?



  • EzDome related problem. No difference between CPU and GPU with background-emitter(cast light)-lighting, but no correct lighting with EzDome and GPU. And results will be probably different with SF-emitter/lightpath shader on EzDome with CPU too but this need experimentation.



  • @phdubrov Some HDR images are more contrasty than others. The image that I used has a really bright spot on the top. If I was to use another less contrasty image the problem would be less noticeable.



  • Not small difference - can post screens later, no difference at all no matter how you split renders.



  • Here. Think Factory Catwalk is contrast enough.
    0_1482967848616_env-light-test.png



  • @phdubrov where did you get that HDRI from? Is it free? I'd like to test it but need a link.



  • @phdubrov nevermind I found the file. Testing now.



  • @phdubrov here is my test using the catwalk HDRI. Looks like your results have Poser lights turned on spoiling your test.
    0_1482973861040_CPU GPU test 2.jpg



  • @phdubrov Just checked with a sphere as in your image. Looks like your result is IDL and OK. My reslult still different between the two.0_1482974414033_CPU GPU test 3.jpg



  • I can't find anything wrong with my settings so I might need newer drivers for my card. I just installed it the other day and used older drivers based on info from here about the newer drivers not working.



  • For what it's worth, I used exactly the same HDRI,on my Nvidia TitanX with the latest drivers, and I got the same results as you Ghost.



  • @matb let me try using a different sky dome and mat setting



  • @phdubrov The problem is with the shader setup in EZDome. If I take out all the extra nodes and just leave the Poser surface and the HDRI image plugged into ambient then everything is ok!



  • @ghostship Ahh interesting. I loaded the Poser hemisphere prop from the primitives folder, applied the catwalk hdri to the inside (had to use the HDR version because poser doesn't recognise sIBL natively). I plugged the image into the ambient node with a value of 1, colour white. This time the image rendered with no difference between CPU and GPU.

    I was beginning to suspect it could be the way the sIBL format interacts with skydome so I loaded the HDR version of the image into sky dome, and back to square 1. It's definitely starting to look as though skydome itself is the culprit - or rather, the way it's wired.

    <10 minutes later> Okay DEFINITELY a skydome problem. Went into skydome and wired HDRI version of text directly to inner and outer, bypassing all that weird maths stuff that Royston does. The two results are identical. Now the two questions are:

    1. Whyt does Royston do all of that math on the HDR
      23: Why does that interact differently with a CPU and a GPU?


  • @matb Looks like it has to do with the exposure tab in EZDome. In the past to make my dome brighter I would just crank up the amb or the value on the HSV node plugged into the image. How @Snarlygribbly has it set up is a little more interactive and probably easier for people to understand.



  • @ghostship Oh yes, you're probably right. Now that I look more closely, it's not that hard to understand what he's done. Still don't understand why this configuration suppresses the exposure but ONLY with the GPU. Surely that still suggests that the GPU processes something in there differently. It's also curious that phdubrov did not experience it. Perhaps he is not using nvidia?



  • @matb He's not using EZDome so never had the issue.



  • He did for his first test above. It says so in the top bar.



  • @matb I'm a knucklehead. He figured it out hours ago and I just did not read his post carefully enough.



  • The comment about the SF emitter lightpath? I didn't understand it. Was that the solution?



  • Not sure guys,but here are my results

    Here is rendered same ball with same HDR

    This one is rendered with CPU and BB EnvSphere

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    This one is rendered with CPU and BB EnvSphere

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    As you can see no difference,maybe in noise as with CPU I've rendered only at samples and with GPU I've rendered up to 30 samples

    In this one I've used CPU with EZDome

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    And this one is rendered with GPU and EZDome

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    As you can see difference between those two renders

    Hope this helps

    Thanks,Jura