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PBR in apprentice

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Does it work?

Just trying to have a play with it and I can't get anything to look any different from standard rendering.

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Does it work?

Just trying to have a play with it and I can't get anything to look any different from standard rendering.

Oh yea, it certainly does. But if you're using regular lights and no diffuse bounces, it will look like regular raytracing. Remember to use Diffuse Limit in the PBR tab, and use HDR environments. If you're bold, create some caustic photons and play with that (which is really DEAD SIMPLE to use).

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Oh yea, it certainly does. But if you're using regular lights and no diffuse bounces, it will look like regular raytracing. Remember to use Diffuse Limit in the PBR tab, and use HDR environments. If you're bold, create some caustic photons and play with that (which is really DEAD SIMPLE to use).

I tried upping the Diffuse Limit but I was using an environment light with no HDR environment, from the help it seems to suggest it should work with regular lighting, of course as usual it would be really helpful if there was an example file (just one!!), so you're saying you have to use HDR environments?

http://www.sidefx.com/docs/houdini10.0/rendering/pbr

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I tried upping the Diffuse Limit but I was using an environment light with no HDR environment, from the help it seems to suggest it should work with regular lighting, of course as usual it would be really helpful if there was an example file (just one!!), so you're saying you have to use HDR environments?

http://www.sidefx.com/docs/houdini10.0/rendering/pbr

Sorry to mislead! It works with regular lights, oh yes - but HDRs just look so nice:)

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Then maybe its broken on the mac then cos I can't get it to do a thing.....

What shaders are you using? Your own? If so, do you have "F" connected/written to?

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I've found that using photon caching is the best way to avoid noise, that and reducing the Diffuse Limit to the minimum that will work, e.g 2, but with photon map caching I seem to lose the nice colour bleeding, is that correct behaviour?

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It seemed to me like using a photon cache just slows things down in H10 (since view-dependent photons were removed). Might have to play with it again... I don't think it should kill the color bleeding either way.

For regular PBR, Pixel Samples and Min Reflection Ratio are your quality dials, for MPPBR the important ones are Max Ray Samples, Shading Quality, and Min Reflection Ratio. Color Limit is also really handy if you get crazy noise from overly bright sources.

Edited by DaJuice

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Its not uncommon to have 30x30 pixel samples (or more!) for PBR:) -esp for highly diffuse surfaces like Clay. For metals and so on, you can get away with 15x15ish, I find.

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Hi Simon, I had a quick look at your scene and here are some thoughts about it:

The main one - check what version of mantra is set in your rop. If it's set to "Mantra Current" that's probably where the problem is. Recently I had similar issues with PBR. Whenever I set up a scene in the higher H10 build and continue to work in a lower one (a production 10.249.5), suddenly I was loosing ability to use Render View and PBR. That said if you set the renderer back to Mantra10 everything seems to work fine again, your scene too :)

I'm definitely not a rendering guru but here are some things to be aware of:

- PBR at least for exterior scenes should clear out with pixels samples 10-15. For interior scenes on the other hand (if you use env light only), this vales are FAR higher, 40+

- for MPBR which gives faster results with motion blur, pixels samples works as in micropolygon renderer, to remove noise you need to tweak Min/Max ray samples. <100 should be fine for start.

- you don't need that high settings for Diffuse bounces, 100 is far too much. I think if you stick with the default range you are good to go.

Lastly while testing your scene I've run across some mantra bugs as well. First of all there are huge differences in clearing out the noise between Mplay and render view. It only appears in PBR mode only. Surprisingly the noise was incredibly fastly removed in render view window whereas in mplay no matter how high I cranked up settings it was still there. It definitively didn't look right in this scene. Can anyone confirm this is a bug?

Also, reference to a cop image (op:/....) in a env light area map doesn't work anymore. I'm sure it worked in 9.5

Cheers,

kuba

pbr_test2.hipnc

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Lastly while testing your scene I've run across some mantra bugs as well. First of all there are huge differences in clearing out the noise between Mplay and render view. It only appears in PBR mode only. Surprisingly the noise was incredibly fastly removed in render view window whereas in mplay no matter how high I cranked up settings it was still there. It definitively didn't look right in this scene. Can anyone confirm this is a bug?

Both the PBR and MPPBR mantra nodes in the scene are set to Micropoly PBR. Could that be it?

I'm not seeing any weird discrepancy in speed/quality between mplay or ipr rendering of PBR.

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So this is the normal pbr render - 30 x 30 samples and 100 Max samples, Diffuse Limit 1, Reflect Limit 3, and the second image is the same but with photon maps, all the bleed vanishes....

post-509-1243722343_thumb.jpg

post-509-1243722394_thumb.jpg

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NEW IN H10! (ha! been waiting to say that one...): use min and max ray sample to fine tune raytraced PBR (even per-object), instead of driving up memory usage with pure pixel sample increase. also, photon maps yield the expected color bleeding result for me... be sure to use them as secondary GI cache. However, in some cases, rendering with photon maps will be slower with less accurate but also less grainy (more blurry) results.

post-1116-1243725174_thumb.jpg

cheers,

Abdelkareem

pbr_test2.hipnc

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NEW IN H10! (ha! been waiting to say that one...): use min and max ray sample to fine tune raytraced PBR (even per-object)

What the butt! Would be useful if this sort of stuff was mentioned in the docs. Thanks for pointing it out anamous.

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What the butt! Would be useful if this sort of stuff was mentioned in the docs. Thanks for pointing it out anamous.

This very seriously needs a proper tutorial from Sesi, and at the very least some example hip files setup and fine tuned "correctly". There seems to be a lot of guess work involved here on what works best.

Maybe as usual they simply don't want people to use it outside of the sidefx office. :angry:

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i tested pbr last week and was surprised that min ray samples are affecting the sampling. I was getting very good times with pixel samples set to 4*4 and min ray samples between 16-20. Only catch with this one that if You have DoF or MB, 4*4 is not good enough.

i agree that pbr needs a serious tutorial, i even don't know about hidden parameters that could speed things up like the min reflection ratio, which btw is not in the docs.

Guys, don't You think implementing irradiance cache with PBR would speed things up? At least in modo's render engine does (sharing samples etc), do they invented something special?

But overall if You have a bigger render farm, pbr is a very nice render engine in it's current state, just wish to know some more tricks to speed it up at least 2x, so a in-depth tutorial could be the answer.

ps. Anamous: the max ray samples have no effect, at least i tested it had none.

ps2: using an environment light is much more expensive than using a hdri image mapped on a sphere around the scene (tighter is better), i had much more less noise this way.

my biggest concern is that it would be better to use a blurry hdr for light and a sharp one for reflections, but could'nt figure out how to do that.

ps3: also if i color correct the hdr image so that the biggest values are at 2-3, also get less noise.

Edited by dbukovec

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Obviously PBR is a mostly uncharted wonderland right now, and some voodoo is needed. Part of SESI's problem is that Mantra generally and PBR in particular are high speed moving targets - a lot has been changed under the hood from 9.5 to 10.0, and some things are still in flux - a nightmare for any technical writer. The way I see it, Mantra is a very good rendering "engine", PBR or not. PBR is still experimental for lack of a better expression. Sometimes the results are dazzling for a comparatively easy setup, and sometimes you'll pull your hair over certain omissions and strange decisions (ten years later than everyone else, Mantra should finally get raytraced SSS for example).

That said, the perspective that PBR offers is unparalleled out there right now, so I believe that it's definitely worth hanging in there. On one hand, the most recent core changes will only slowly start to pay off since conceptually they differ a lot from what we're used to in rendering engines. PBR is now based on VEX, which basically means that we can take control of most of the rendering pipeline - this is a big one, and will make a whole lot of difference. There's simply nothing comparable in the market - a physically based engine with this level of control, and it's bound to increase once SESI introduces mechanisms that allow us to define our own BSDFs. On the other hand, usability and speed enhancements like irradiance caches, portal lights and so on are on the developers maps and I believe that they will be implemented sometime soon.

I realize that that's not helpful right now. For the time being, we have to live with a non-documented strange but also beautiful beast. Some of us are already using PBR heavily in production, and will try to help out as much as possible :) .

Tip of the day: predicing, yes that old micropolygon trick still has its uses. Specially when dealing with displacements, if you have some memory to spare (which you should, seeing that now you'll keep the pixel samples tight, almost never go over 12 opting for ray samples instead, so the engine's mem usage won't explode), use it on subd's, NURBs, and even polys. It will speed up things.

@dbukovec: you can see in the PBR VEX shader that it's taking max(minraysamples, maxraysamples) and using that as number of samples. Using a sphere instead of an env light will cost you one more diffuse bounce and the ability to create photon maps since they need light sources. As for treating the HDRI, try blurring it, and limit the amount of incoming light by using the "color limit" rendering parameter instead.

cheers,

Abdelkareem

Edited by anamous

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