Houdini | Rendering with Mantra | 01
An introduction to rendering with Houdini with Mantra. We cover various aspects of rendering a scene, from lighting and camera to setting up multi-pass .exr rendering. The different kinds of light that we have in Houdini and how we can use the GI Light to create point clouds for both indirect illumination and caustics. We look at how Mantra handles sampling and how we can troubleshoot noisy renders. Introduction to Rendering with Houdini is as a follow up to a lecture for a class I teach in Houdini so the students can re-cap the in-class lecture. I apologize for any lack of polish. Hopefully there will be some good information in there.
You can download a free version of Houdini here.
Other Houdini Tutorials:
Houdini | Touchdesigner | Unity | Unreal
I love the visual aesthetic of point clouds and their ability to represent and recreate three dimensional space. I used to bake out final gather points out of Mental Ray and combine them to re-create a static visual cue of the entire animation sequence, or as combined elements for lighting calculations. With Houdini, working with point clouds is just so much fun. Now point clouds are everywhere, and we use them from everything from storing values, geometric reconstruction, volumetric video, and just pure visual beauty.
With the ability to now get depth maps from the Google Jump Assembler in resolutions up to 8k, we are now able to implement some more advanced film techniques into the world of virtual reality production. As well, we can begin to see how we will start to create production workflows that in near future will be tools for handling volumetric video for 3d reconstruction in order to create a more immersive experience. While not “lightfield” in that this won’t represent correct light changes that are view dependent, it will allow for greater depth and parallax. As well, it allows for better integration with CGI in the world of Stereo Virtual Reality, as this is very tricky and inherently has problems. In these examples I am using the Foundry’s NukeX, Cara VR, and Ocula on the front end, and Houdini from Side Effects on the back end.
This image shows the perspective of the viewing camera of the scene with both point clouds from Nuke and Houdini merged using deep and viewing through nukes viewer. The 3D tree is rendered through Mantra with a deep pass using the point cloud generated out of Nuke as reference geometry. This is important for correct spatial alignment of depth, as the depth, in this case, comes from the Google Jump Stitcher. This is not a spatially accurate representation of real world depth, rather a spherically projected approximation. At this time, the biggest caveat is the 8-bit banding. This can be solved with a special plug-in that would incorporate a bilateral filter that would process the points while preserving edge detail.
Reality Capture (www.capturingreality.com) is my current go-to program for photogrammetry. I am just getting the hang of how it functions but it is incredibly fast, especially if you compare it Agisoft. These photos were a test using my studio space. This is with only 377 photographs. I can see where I need more camera positions to capture the whole space and will shoot it again soon. The maximum amount of images that I can do with the version of Reality capture that I have is 2500, I am not sure that I need that much, but I would like to test with around 1500.
Since I have been using Redshift as my need speed, go to render engine when I just won’t have time for Mantra, I have been beefing up my Houdini to Maya Alembic pipeline. While straightforward, there are a few caveats. In this particular case, I was wanting to get my point/vertex colors from Houdini into Maya in order to render my geometry with the baked in colors from Houdini. A few notes, you will need to have a Cd attribute in Houdini of type vertex. In Houdini, Cd will usually be a point attribute, so a simple attribute promote will do the trick here. Just promote your Cd attribute from point to vertex and you should be good to go.
Unfortunately, the GUI Maya alembic importer does not do the trick, so we just need to import via the script editor with some very simple Mel. All you need to do is make sure you have the alembicImport plug-in on and type the following Mel command:
AbcImport -mode import -rcs “myPathToMyAlembic\myAlembicFile.abc”;
Obviously, you will substitute your own path and file name.
You should now see your alembic file in Maya with the vertex colors in the viewport.
Now that we have our geometry imported correctly and we can see the vertex colors, we need to set up our Redshift shader, though we are using Redshift in this example, this method works for Mental Ray and Vray.
In the modeling context, under Mesh Display you can see the Color Set Editor, which you can open to find the name of your color set. In our case, coming from Houdini, it’s just Cd.
Next, just create a redshiftVertexColor and under General, in the box labeled Vertex Set just add in the name of our color set, in this case, Cd. Now you just pipe out the outColor to whatever slot you want and hit the render button.
