On location with Renderman
Behind the scenes on a new Renderman for Houdini Short
Eugene Riecansky takes his real-world knowledge of film sets and applies it to a scene in Renderman in this step-bystep guide
Having 20 years’ experience of directing music videos and films, I’ve spent many hours on a film set and I wanted to use this real-world experience and convey it across into my other passion… creating imagery in Pixar’s amazing Renderman.
I am currently creating a Renderman Houdini short for Pixar, so I thought it would be fun to create an image that played on the theme of being on set for that animation; giving a glimpse behind the scenes by using my real-world experience of film sets, lights, camera lenses and so on, I wanted to convey this knowledge into a 3D image.
01 TURBOSQUID KITBASH
Whilst creating each individual model from scratch would be ideal, time is not always on your side. Turbosquid has a great collection of quality models to use, most already UV’D and ready to texture. As this scene is based on a real-world film set, all the models were easily available, so taking the kitbashing approach to scene creation was ideal on this particular image and allowed for the majority of time to be spent on the creative process of texturing and lighting.
02 ASSET SCALE
By knowing that in Houdini a grid unit is 1 metre, and using a base model of a character where the height was 6ft as a guide, it helps as a scale and measuring guide for all assets. It is important to ensure that each asset is scaled to its real world size so that there are no problems further down the line. Working in a real scale helps with all aspects of the scene, from blocking out the studio dimensions through to how high the props should be (tables, lights, camera tripod and chairs).
03 ASSET MASTER FILE
Starting with a new Houdini file, each model from Turbosquid was imported and any model clean-up work was done. The pivots were fixed using a combination of Move Pivot to Centre and the Move Centroid to Origin feature in the Transform node. Each object was then centred in the 0x0 grid position. All scaled, cleaned up and pivots correct, it is now time to UV each one.
04 TEXTURING PREPARATION
Luckily, Houdini has a very good Auto UV node (which needs to be downloaded from the Sidefx Labs website). Plug the Auto UV node into each part of the assets and adjust the resulting UVS as needed. By plugging in a UV Visualize node, the UVS can be seen and checked for errors.
Add a Pxrsurface to each object that you want to be in the same texture set before you export the FBX, to ensure better texture organisation inside of Substance Painter. Make sure to name each
Pxrsurface appropriately. Each asset is then exported as FBX, ready to be textured.
05 TEXTURE IN SUBSTANCE PAINTER
Texturing Renderman assets in Substance Painter is a fast and intuitive experience, thanks to a great plugin developed by one of Pixar’s Renderman developers, Philippe Leprince. Available from his Github page (github.com/ pleprince/rfsp) is a plugin for Painter that allows the direct export of materials from Painter, converts them to TEX files, creates the Pxrsurface material and adds it into the Preset Browser, all connected and ready for use. Simply import your model into Substance Painter using a PBR Metal Roughness shader, paint your model and then a one-click export does the rest of the hard work.
06 HOUDINI ASSETS
A base lookdev scene is created so that each of the individual props can be worked on, with look development/shader tweaks applied in a consistent lighting environment across all the props. This ensures that all textures and shaders react consistently between each other and once imported into our master scene, will behave correctly.
Once each prop is ready, it then needs to be exported from the lookdev Houdini file as a Digital Asset. You can do this by selecting
which prop you want to use as the asset and then use the New Digital Asset from Selection option in the Asset menu.
07 SCENE LAYOUT
Once the assets have been created, it’s time to begin blocking out the scene. Start with the bigger objects that make up the main structure of the room. The bluescreen wall was the first object to be added to the scene, then the floor and then the main set table and onwards.
08 ADD CAMERA
Once the main structure of the shot has been assembled, it’s time to add in a camera. Knowing that we want to replicate real-world ‘behind the scenes’ photography, the camera is placed far back in the room to ensure we capture the full view. Lens choice is also hugely important for storytelling and exploring the various lenses before you get too far with scene setup is good practice.
Using a wider lens such as a 22mm or 28mm added too much distortion to the objects closer to the camera, whereas a lens of 50mm or 85mm becomes too narrow and doesn’t give us the whole view of the scene that we are trying to capture. In the end, a 35mm lens was chosen as it was able to deliver the right mix of perspective, depth and width.
09 BASIC LIGHTING
Now the camera is in a good place, lights can be added to the shot. As the scene is based on a real-world shoot, two softboxes are placed to act as Key and Fill lights on the main hero teapot. A Kino Flo style tube light is also placed above the stage (use a Pxrcylinder light to replicate this). These cylinder lights are often used on real-world sets for many creative lighting scenarios, so they have also been used in various other places around the shot.
Most real studio lights use a Kelvin temperature scale to control their colour. Renderman can replicate these colour settings accurately by simply activating the Enable Temperature feature in the light parameters.
Example of a 22mm lens
10 LIGHT MAPS
To add extra realism to the lighting, an HDR texture was applied to the Color Map attribute of the Pxrrect lights. This not only helps the realism of the emitted light but adds texture and details in the highlights and reflections.
11 DYNAMIC BOWLING PINS
To create a realistic set of falling bowling pins, a dynamic simulation was created in a separate scene using the RBD Bullet Solver SOP, available in Houdini 18. This simulation was then cached out to disk and imported into the master scene.
Use the Unpack and Edit node to adjust and move any objects from the imported sim that might require extra art direction.
12 DEPTH OF FIELD
Depth of field is an important visual element and Renderman has a very realistic bokeh/dof feature set. Use the camera’s focal point null to determine the focal point of the camera.
Add the Renderman controls to the camera node and set various bokeh effects. To render your scene with DOF, you finally have to enable DOF in the Renderman ROP node.
13 PXRVOLUME
To add some extra realism to the scene, a layer of atmosphere was added. To achieve this, a cube was created which is scaled to encompass the entire scene. A Pxrvolume material is then added and by adjusting the Density Float, this controls the thickness of the atmosphere. One visual benefit from adding the atmosphere is the beautiful lighting rays seen from the various lights in the shot.
14 INTERACTIVE DENOISING
Renderman has a feature-rich interactive rendering tool called “it”, which allows the artist to interactively render, light and art direct the scene. “it” also features denoising in these sessions, which helps clear up noise to deliver a cleaner image, faster.
Before this option can be accessed, the NVIDIA Optix Denoiser needs to be downloaded from the Render menu in Houdini.
Once installed, “it” will now interactively denoise the session.
15 AOVS
Before the final render settings are dialled in, it’s a good time to add in the AOVS that are useful in compositing to adjust the image. Renderman comes with a large number of AOVS out of the box and custom setups can also be created, along with per-light LPES to enable each light in the scene to be rendered in its own AOV for tweaking in post later.
16 RENDER SETTINGS AND DENOISING
The advantage of having a sophisticated denoiser built into Renderman means that the render settings can be set with lower samples, and we can let the denoiser do the work of cleaning the image as a post process. Simply connect a Renderman Denoise node to the RIS node, set the order to Node by Node and hit Render.
17 POST
Once the image is rendered, it’s time to add all that final visual creativity to the image. In this example, Nuke is used to import the denoised image and each AOV is colour corrected and combined back together. Final tweaks added to the image include lens flares, a LUT and a vignette added to draw the viewer’s eye further into the centre of the final image. •