Learning Mantra

[David Cordeiro]

Well, here we go then... I've just started to really invest my time in houdini , as a starter I want to grasp the workflow with mantra, so to keep my footing on something familiar, I grabed this free scene from http://www.evermotion.org/download/show/196/room , converted-it to FBX, imported-it, cleaned-it to the best of my knowlege, saw two mantra masterclasses, all Petter Quint vimeo videos on rendering, and ... Dam... I'm confused

There are so many ways you can approach a scene in houdini that it get really daunting, so I would appreciate your help to understand the different techniques we can use to deal with a typical scene like this, a room illuminated from two windows (one off camera on the right ). I know it's pretty lame archviz stuff i could do in Vray in a snap, but i want to do this to learn, not to compare.

Here's what i've got-to so far:

-All tests I've made were using PBR, could I approach this with micropoly / raytrace ? And I mean using indirect ilumination, not manually lighting the scene.

-materials seem to have a huge contribution in render time, a 50 % grey clay renders much faster than a 50 % gray mantra surface even if I turn off true displacements. Plus when I imported the fbx it had all these different materials from the convertion and it took a really huge toll on the render time, got twice as fast after a cleansing.

-i've tried Photon maps but i could not figure out how to shoot them from the distant light and trough a portal into the room. Can i do that ?

-If I wanted to animate the camera ? can I cache In PBR ?

Anyway, I'm in the process of shading and texturing so I can try different solutions.

This image took about 50 minutes in a quadcore I5 Imac at 1280X720, Im working in gamma 2.2, converting the textures to 0.454 (except for the background that's why it's bright),

I have a distant light as the sun and a Portal Light with 0,5 sampling qual in Direct Lighting mode, using the window's glasses as portal geo.

In the ROP I have the standard PBR with Pixel Samples at 5 x5 Min/Max ray 12/300 noise level 0,02 and reflect refract and difuse limits at 4.

how would you do this scene ? I'm I far of track ? Would you deal with it differently for animation ?

Edited March 6, 2011 by David Cordeiro

[David Cordeiro]

Ok, i've checked Petter Quint videos again and he does talk about photons emission filters by lights, so I added a Gi light emitting photons. Ialso added some materials and textures, and found out that I really need to learn more about Uv's and surfacing in Houdini. So i'm learning about that now to fix some obvious errors.

This frame took over an hour and a half with the same sampling as before and a gi light emitting 200000 photons with 6 photon map filter samples.

[Erik_JE]

Try 9x9 pixel samples and Min/Max set to default. Also try reducing the Color Limit to 5.

Also try with Diffuse Limit a little lower. Dont think you need 4.

[David Cordeiro]

Thank's I tried that and it saved half an hour with very similar results.

[David Cordeiro]

Ok, for a test scene I think I'm where I want, still need to fix some Uvs, the problem with the carpet and really optimize the shaders, all standard mantra surface for now.

I like the look you can get with Pbr, the realistic glows and such, it looks quite rich even before post. I really need to optimize though as I would like to try and render a test animation. Maybe I should try to reproduce the render in Micropoligon rendering ?

Any tips are welcome .

This is the render straight from Mantra, no post

[altbighead]

Since your room is a enclosed room , have you tried the portal light setup?

I have never tried it yet ,it's worth experimenting if you haven't already.

For the doc

Adds an environment light that only shines through geometry you select. This is much more efficient for enclosed environments where the environment light can only enter through a few portals (windows, doors).

http://www.sidefx.com/docs/houdini11.0/shelf/portallight

Also check the recent Mantra video posted by one of the developer Andrew.He walked through the setup in the video.

Edited March 10, 2011 by altbighead

[David Cordeiro]

Yes i'm usin a portal light with the window's glass as geometry, I'll make sure to check if I missed something, thanks for the tip. Right now I'm looking for solutions for gi caching with Mantra Pbr and looking at what factors can slow donw a render.

[neonbulbs80]

Hi David,

Great work so far. It's an interesting project you have there. May I know how long did you take to render the scene? I been willing to try PBR on interior scenes and I noticed from your last render the lighting is coming along nicely but there are a number of over exposed lights in the room which brings me to a question on how to clamp exposure like in mental ray we use mia_exposure_photographic to do tone mapping.

Cheers..

[David Cordeiro]

Hi neonbulbs80 , I'm still researching on this, the render time must have been about 3 hours for the last image, utterly unacceptable I know but i'm certainly doing all kinds of mistakes . I'm using a low detailed and highly filtered Photon map this is probably where the over exposition comes from. I found that photon maps + pbr give noise free results except in reflective surfaces. I'm afraid I can't help you out as I'm struggling myself but I'll point you to some discussions I'm reading attentively.

http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=20382&start=0&postdays=0&postorder=asc&highlight=

http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=21548&start=0&postdays=0&postorder=asc&highlight=

[morean]

great work you have done hats off bro