CPU/GPU render different outcomes

  • Probably it's down to one or more firefly nodes or PoS inputs broken in PT or BPT. So I try to figure which.
    Wall and floor mats are first to check.

  • I ran several tests comparing CPU and GPU renders with and without BPT, always using the same settings (Windows 7, nvidia GTX 1060). As far as I can see, there was no visible difference.

    I really do prefer the GPU render if I can leave my computer for a while because it is so much faster than CPU (approximately 10 times). The downside is that the UI is totally laggy while rendering, so I can hardly do anything else on the PC, not even watch a movie.
    I like rendering with BPT even better because it is so much faster, adds less noise and has better specularity on many materials (as already mentioned by @piersyf). So the fastest combination is definitely GPU & BPT. Unfortunately, transmapped hair reliably crashes the driver when using this dream team.

    Here is my solution until Poser and nvidia can get this to work properly:

    1. I make the hair figures/objects invisible and render the whole scene with GPU and BPT.
    2. Then, using the same settings, I switch to CPU, make the hair visible again and use the area render to render only these parts of the image that have hair in it. You have to think of hair shadows and reflections, but it is usually only a small fraction of the whole picture.
    3. Finally I combine both pictures in Gimp or something.

    Sounds like a lot of effort? But I can render a screen size image in 45 mins instead of 8 hours this way! And I get the specularity that I like, sampling the direct and indirect lights. No matter how many samples you throw at this in GPU rendering, you will never achieve a comparable gloss.

  • In my case, the floor is a physical surface (root node), so I CAN increase specularity by reducing roughness, but even at 0.01 it is still less shiny than using BPT. It still doesn't explain why it effects skin on characters as well, in this particular scene.

    I agree that GPU is generally faster, but I'm using a GTX970; to run GPU and BPT I need to reduce bucket size to 32 or it crashes (I haven't done the coding fix on timing).

  • Found it! Physical surface is broken. BPT on top, PT on bottom. Look for lights reflections on top of the ball.
    1_1487061519762_pys-bpt.png 0_1487061519761_pys-pt.png

    Pure Cycles surface is like BPT in both modes.

  • Nice... worth an experiment. I'll have a look at doing the material using a different node set up.
    Even if it pans out, it doesn't explain why figures (people) render 'flatter' than with BPT...
    As eager as I am for an answer to this, my study is being torn apart tomorrow and a new door fitted (to the outside; through a wall). I'll get back later...

  • @piersyf if you use EzSkin there are good chances that something in PoserSurface broken same way as PhysicalSurface.

  • @phdubrov There is a cycles root plug-in for EZSkin3 that should fix that problem if that is it.


    @bopperthijs is a regular here at the forum.

  • @ghostship this probably to @piersyf , I don't use EzSkin (now). Too complicated way to build my 50+ nodes shaders :), swap images in ready materials is far easier.