I received a question about adding caustics to the matte/shadow/reflection material in mental ray. The setup I typically use for such a scenario might be useful for a broader audience so I turned my reply into a tutorial. Read on for the details.
Here lately I’ve been setting up my own scenes to allow more individual control over specific elements. In this particular scene I wanted to control the look of the caustics so I use a specific light source to generate the caustic photons and ONLY the photons. It doesn’t add light to the scene, etc., only caustics.
There are three lights in this scene. The first light is a skylight to provide general/low detailed illumination from the environment HDR. This isn’t really needed for this particular scene since the objects are chrome and glass. However since I’m providing the scene I figured I’d set it up for more typical usage where your objects would pickup some illumination from the HDR.
The second light is a mr area omni light. It’s sole purpose is to provide the hard shadows from the sun in the HDR. Typically the HDR + Skylight + FG combination doesn’t produce this type of shadows. For that you’d need to use something like the new IBL node or Importons/IP. The use of those options is outside of the scope of this tutorial so I went with the more standard route of using a light to generate the hard shadows.
The third light source is a direct light and it’s purpose is to generate the caustic photons. Here’s a screen capture of the light setup:
The skylight is configured to just use the scene environment, nothing special there. The other two lights however will need some adjustments. On the mr Area Omni light, named “Shadow Casting” in the scene, I disabled the Diffuse and Specular options. This prevents the light source from adding illumination or specular highlights to the scene. By default it will not generate caustic photons either. Therefore the only thing it will contribute to the scene is a shadow.
The target directional light source, named “Caustic Photon Generator” in the scene, also has the diffuse and specular options disabled. I did not want light or specular highlights from it either. Instead I wanted only caustic photons. Therefore it’s set to generate caustic photons (right click on the light, go to the mental ray tab and enable the caustic generating option).
I also decreased the multiplier of the “Caustic Photon Generator” light source. I did this because I found that the indirect illumination it was producing was washing out the shadows on the torus knot object where it’s focused. When the light multiplier is decreased, it also decreased the energy of the caustic photons. So to counter balance that I increased the Photon Energy multiplier of this light source to bring back the intensity of the caustic photons only. Below is a screen capture of the light properties for both the shadow generating light and caustic photon generating light.
Material wise there’s nothing unique here. The chrome is the A&D chrome preset, the Glass used on the torus knot is the A&D physical glass preset with the color red applied. The matte/shadow/reflection material has the typical setup for this type of scene. I did tint the shadows a bit to add some blue like the shadows in the back plate though.
With this type of setup I can easily manipulate the look of the caustics or even render them out separately for post adjustments by replacing the backplate with a black color, etc.. Lot’s of options there to make life easier.
You can download the file HERE. I think I saved it back to 3ds Max 2011 format.
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thanks Jeff again, I learn a lot from you. have a nice day!
its very very helpful 4 me jeff…..thnx for this tutorial…!!
Thanks again for your help with this Jeff!
Jeff I guess this file does not open in 3ds max 2012…can you please resave and upload the file again ?
Thanks for the info. Please try the download link again as I just updated the file to be compatible with 2010+.
thanks jeff for this tut
good luck
Thanks Jeff, I have learned so much from you.
If don´t you know somethink about max, tell me. hehehe Just Kidding…
Plenty of areas I need to learn more about. For example: I still struggle with detailed poly-modeling. For some reason that’s been a really tough topic for me to teach myself. I must have some kind of mental block when it comes to planning ahead for all the vertices to align properly or figuring out how to maintain quads across an entire model, etc..
Video & written tutorials have helped me to some degree. But I still haven’t reached my goal yet. Hopefully one day I’ll be able to work along side someone else and expand my knowledge of poly-modeling as well as other areas.
Thanks Jeff, tutorial helpful as always, I really enjoy your posts.
I am working on a scene where I have skyscrapers with mirror windows reflecting surrounding HDRI and some objects as well. It is an interior scene and the room is just floating in the air and buildings are in the windows. I don’t wont the room to be reflected in the buildings, and when in object properties I uncheck the reflection flag it is not reflected (when I have it close to the building I can’t see reflection at all which is good) BUT when the room is in it’s right location I still can see the reflection in the buildings (something white like over burned light or something like that). I have a daylight system FG+GI and 2 light portals).
Would you happen to have any ideas what could be a problem?
I found the problem, I had 2 portal lights in front of geometry and somehow they where reflected but not as rectangles but just as the shape of the object they were shining on, pretty weird, but disabling flag for rendering on them did the trick.
Sorry I didn’t reply in time, had a few busy days (and nights) here lately. Glad you got it sorted out and thanks for posting the findings as it will surely help someone else down the road.
No problem Jeff, I hope it will help someone.
Thanks a lot Jeff. Your articles helps a lot!!!
BTW, how can I get a avatar like others when I post on your website
Register yourself here http://en.gravatar.com/ then upload whatever picture you want to use for each email you registered there, then on all WordPress blogs on the net where you post it will be automatically used and changed if you changed it.
Thanks for answering Mike’s question. I wish some of the bigger sites like the AREA, etc. would use gravatar as well. Too many avatars to keep up with these days.
I really like gravatars idea, they should make something like facebook that you can log in with it so there would be no need for signing up on all the forums as it is really tedious process. (By the way I don’t use facebook or tweeter, I just don’t like them,over bloated spy sites).
hello sir
1) i have one problem
how can you set background backplate and hdri in iray
because when i use Environment/background Switcher it’s not properly work
so how can i setup with hdr & Backplate in iray ?
thanks a lot~ it is useful foe me
Hi Jeff,
Tanks for the tips. Why no exposure control?
Habit. I typically don’t use it in my daily workflow.
This is really great, thanks Jeff!