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Jason

Cool mantra GI renders?

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Hi all!

Looking about the place, I see no cool GI renders of Cornell boxes, glass spheres, brass rings on tabletops, characters on infinite white planes.

Any nice mantra GI renders out there besides changs?

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Hehe, a year ago I would have been all over this. I used to love getting my hands on different renderers (Brazil, mental ray, vray, BMRT, lightscape) and messing with GI. It was like getting a shiny new toy every other week and getting to play with it. :D

Not too productive though, so I've been holding off on really digging into mantra until I have something decent to put through it.

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I think Houdini users are coming from mainly the movie making industry, and as I know in movies Gi is rarely used, also simple raytrace renders are faked with enviroment maps if possible. The reason is the speed of renderings. I think out of my conversations with some insiders.

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This was a GI scene I set up a long time ago and I just whacked the render button today and ran it though Nuke to get a quick glow on top of it. Not very nice, but anyway:

post-15-1064453373.jpg

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Does anyone have any tips for using GI in Houdini? I've gotten nice results with Ambient Occlusion and IBI, but Full Irradiance and Photon Mapping are very difficult for me to get nice results with. I rendered this image using Full Irradiance. There's so many things I don't like about this picture, I don't know where to start.

post-15-1064516861.jpg

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Yeah, I'm a little weirded out by the irradiance cache thing. If you generate a cache with, say 256 samples and then later want to grow the cache by re-rendering (rw cache) at 2048 samples at a smaller error rate, the images always come out identical until you blow the cache away. This seems unintuitive for me.. surely you should be able to render and re-render with different "errors" and numbers of samples and improve the cache and your image? It seems like a waste of time to ever really use them except if you want exactly the same sampling every time.

Any ideas how to use the cache properly?

J

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Well, I always set the cache to write only, and send it to a subdirectory of my project. Once I get a *good* cache, I switch to read only, or maybe start a new cache. I never tried setting it to read/write... Maybe there's something wrong with that setting. If you set it to write only, it will overwrite the cache everytime.

I think I'm starting to figure this out... Now I just need a dual something or other computer with MMX technology and Blast Processing. My PC is pokey.

post-15-1064588382.jpg

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jeepers.. how did you find that? I searched for about an hour yesterday after talking to you about it :rolleyes:

eh well. I'm gonna give it a whirl. Why the hell not eh?

edit: ....er.... time permitting anyway :)

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Hey, that looks neat. Is the ground texture a texture map or a procedural? And what was the render time on that?

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Hi guys,

I used the VEX Gallery Brick shader, which is procedural, for the ground. I also used the VEX Krinkle shader for displacement.

The shadow was created with a Disk Arealight, size of 4 & 256 samples, which probably increased the render time by about 1.5 to 2 times. The image took about 27 mins to render on a 2.4Ghz Xeon.

Cheers!

steven

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Very nice pic, yep! Thanks Steven!

I've also been playing about with GI a bit; I'll post an image tomorrow based on the WinOSi comparison page. I'll log my experiences too, but some things are not that easy.

Cheers,

PS, The VEX Gallery Checkerboard seems to be broken. Please could SESI fix it? :)

PPS, Is the eta in the Glass shader inverted? It seems strange that the correct refraction values for traveling from a less dense medium to a more dense medium should be greater than 1, but I have to set my IOR to 1/1.33 to get the correct refraction. Is the fresnel function wrong? or is it the Glass shader inverting the eta at the wrong time?

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It was an experience rendering this image. Some things went very easily, others not so.

Here are the stats:

Raybounces are 3 all over. Only the floor and the chrome and glass balls and metal stand are reflective.

AreaLight: 64 samples

Full Irradiance: 64 samples

Photons: 10 million, taking about 4 minutes to cast.

CPU: 1.7Ghz

and the answers are::

...

Render Time: 764:55.76u 1:02.26s 766:16.82r Memory: 7.23 Mb of 8.91 Mb arena size

ouch!

Pretty sure that can be brought down, but at what cost? It's that arealight thats killing it, I'm sure. I'm going to play some more and see what happens. I tried not using a Light at all and just illuminating the scene with a bright plane, but things got very very noisy.

post-15-1070820286.jpg

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Here is Da Juices great little mascot immortalized in amber.

post-15-1070853335.jpg

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hi, some nice images in this thread.

i setup an ambient occlusion scene using an HDRI image, and the lighting is great. the problem is the environment from the HDRI is not reflected in the objects. i had to add the HDRI map as an environment map to get reflections.

im sure there is a better way to do it... the material was just standard shiny metal.. but it does raytrace because it reflects other objects in the scene, but not the HDRI.

if i can load this post with more than 1 question, how do you all do the SSS (sub surface scattering) style? forgive the buzzword.. i mean something that is translucent - lets some light through but not clear like glass. does houdini do this, or do you need to fake it? :)

thanks for reading, I feel like a kindergarten student on the university msg board here :D

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