06 June 2009, 09:54 AM
Ok so a run down of the portal light. I'm pretty sure this is accurate, but if anyone has more knowledge please correct whatever needs to be corrected.
The portal light more-or-less helps with lighting your scene and getting a better quality of a render. To create it you first create an area light, point it into the room from where you are having your main light coming through. Scale it to fit. Go to the MR tab of the Shape node of the light and tell it to use the light shape and turn on visible. You will have to up the samples-sometimes substantially-to get a smooth render.
Then scroll down to the bottom to the custom shader part and in the light shader slot pipe in the portal light, pipe that same portal light also into the photon emitter slot. If you have an environment such as Physical sun and sky, pipe that through the environment slot of the portal. Since you are using GI, turn the emit photons and set your photons to the appropriate value.
What the portal light does:
The portal light blocks the final gather rays from leaving your room. It takes everything that lives outside the room, samples it and turns it into a direct illumination model and it automatically sets the corect color of the light and the intensity of photons properly. However, you can change this by adding something like an mib_blackbody to the color multiplier slot of the portal light and choosing the temerature that you want.
The portal light helps ground objects and helps the final gather so you can lower your fg settings once this is in place. It essentially gives your fg an extra bounce, brightning up the scene because it turns what is outside into the direct illumination model.
Do you need this for a realistic scene? No. Sometimes it's more of a bother and can up render times if you are not careful, but it can offer some nice results. It definately takes some tinkering to get the desired result. If you are still unsure about this, you can ask more detailed questions or in this case google is your friend. If you query "how to use portal light in mental ray" you should get some good results.
On a side note about your renders they are definately coming along, it looks like you are using the physical sun and sky so make sure that is piped through the envirnoment shader of the light.
The lighting is getting there, but I think what would really bring this piece together are more fine tuned shaders. Shaders go a long way and do a lot of the selling. The floor and a lot of the objects in the scene are waay to reflective . Things seem a little washed out in a couple renders so maybe tweaking the lens shader a smidge.
Also, if you are using any textures with the lens shader/physically correct light you will want to adjust the diffuse texture's gamma to .455 i believe. You can do this by just connecting a gamma correct node to the texture and changing the values. Also toss in an AO pass to help ground things such as objects to the floors and where there are corners.
06 June 2009, 09:57 AM
I came across the blog a while ago and just managed to find it again (http://2cos3d.net/blog1/). It gives a good detailed explanation of the portal light
06 June 2009, 09:57 AM
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