HDR Light Studio is a standalone lighting application providing a set of tools and content dedicated to lighting 3D scenes. Using HDR Light Studio connected to Houdini provides the ability to create custom HDRI maps to light your scenes, with lights chosen and positioned to provide the perfect effect on your model. As you work with HDR Light Studio, the lighting is updated in real-time in Houdini, where you can see the lighting interact with your 3D scene. You can also create and control Area Lights using HDR Light Studio.
This workflow tutorial will teach you how to use the connection between Houdini and HDR Light Studio.
It will not teach you how to use HDR Light Studio itself. Please see our 'Getting Started' content here to learn the HDR Light Studio interface and the basic features.
Requirements: Houdini with Mantra, Arnold, Redshift, V-Ray, Octane or RenderMan.
For compatibility with V-Ray, Octane or RenderMan ensure you are running 'at least' HDR Light Studio Tungsten Drop 3 and these renderer builds:
V-Ray Version: 220.127.116.11
Octane Version: 2021.1.0.4
RenderMan Version: 22
STEP 1: Start Houdini and load the Houdini project you want to light.
Ensure that the camera and the renderer is set-up. In this example, we are using Mantra and have set up the renderer in the Network View: Outputs by pressing the Tab key and selecting 'Mantra' (see Figure 1)
Figure 1: Mantra renderer setup
STEP 2: Create a HDR Light Studio Connection Controller in your Houdini scene
Press the Tab key in the Network View: Objects and select Digital Assets > HDRLSConnectionCtrl (see Figure 2). Not seeing HDR Light Studio Connection? See installation instructions
Figure 2: Creating a HDRLightStudioCtrl node
The HDR Light Studio Connection Controller has been created (see Figure 3).
Figure 3: Created HDR Light Studio Connection Controller
STEP 3: Use the 'Renderer' drop down in the HDRLSConnectionCtrl panel to select the Renderer being used for this project.
In this example we are using Mantra Renderer (see Figure 4).
Figure 4: Choosing renderer
STEP 4: Press 'Start' to start HDR Light Studio connected with Houdini (see Figure 5).
Figure 5: Starting HDR Light Studio connection
You will be asked to name your hook, in this case we will leave it at its default value; 'My_Mantra_Hook'. This will create a new lighting environment setup for your chosen renderer that's set up so that the HDR Light Studio connection will see and can control the environment image.
The HDR Light Studio application will open and is now connected to Houdini.
The HDR Light Studio interface should look like in Figure 6.
If not, in HDR Light Studio you can reset it by going to the menu: Window > Layout > Load > Default > Houdini
Figure 6: HDR Light Studio on startup with Houdini and Mantra
Using 2 displays provides the best work flow, with HDR Light Studio on one display, and Houdini on the other (see Figure 7).
Figure 7: Houdini (left) and HDR Light Studio (right) running on 2 displays
In Figure 8 we can see that 'envlight1' node has been created in Houdini that is associated with our hook 'My_Mantra_Hook'. This hook contains the environment setup for Mantra and is now listed as the selected Environment Hook by the HDR Light Studio Connection.
Figure 8: My_Mantra_Hook node
You can use the 'Select Light Object' feature (see Figure 9) to select the light node in Houdini that is associated with the hook selected from the IBL hook drop down (see Figure 10).
Figure 9: Select Light Object feature
Figure 10: 'envlight1' is selected as it is associated with the hook 'My_Mantra_Hook'
The HDR Light Studio connection has taken control of the image on the environment (see Figure 11).
Figure 11: File path points to a HDR Light Studio temp proxy image
The current HDRI map design in HDR Light Studio is shared with Houdini as a temp proxy (lo-res) image. A proxy is used because it's faster to calculate and faster for Houdini to load during the iterative lighting design process. When the lighting design changes in HDR Light Studio, this image is updated in Houdini to use a new temp with a new filename, to ensure the renderer uses the new image even when caching images.
STEP 5: In HDR Light Studio press the play button on Render View [HDR Light Studio] (see Figure 12).
Figure 12: Starting HDR Light Studio Render View
The Import Scene Geometry panel will pop up.
STEP 6: Press Import (see Figure 13).
Figure 13: Importing the scene from Houdini to HDR Light Studio render view
By default, the whole Houdini scene is exported as a temporary alembic file and loaded into the Render View [HDR Light Studio].
We will use this Render View in HDR Light Studio as the interface for positioning lights on the model, with real time feedback (see Figure 14).
Figure 14: HDR Light Studio render view with imported scene from Houdini
Let's make our first light in HDR Light Studio ...
By default, LightPaint is set to Reflection in this view. So lights are positioned to reflect in the chosen location on the 3D model when using LightPaint (see Figure 15).
Learn about LightPaint here.
Figure 15: LightPaint mode set to Reflection
STEP 7: Drag and drop a Preset Light onto the 3D model in the Render View (see Figure 16).
Figure 16: Placing a preset light onto the model
The Preset Light has been added to the lighting design in a location that is reflecting where the light was dropped on the 3D model.
You will see:
• A new light in the Light List in HDR Light Studio (see Figure 17).
• You can see the new light added on the Canvas (HDRI Map View) in HDR Light Studio (see Figure 17).
• The Render View has been updated to show the lighting effect on the loaded 3D model (see Figure 17).
Figure 17: HDR Light Studio interface after creating a light
You can see that the LightPaint tool is active in the toolbar within the Render View [HDR Light Studio] (see Figure 18).
STEP 8: Click, or drag, on the 3D model to reposition the selected light from the Light List.
This is a very interactive way to light your shot. Placing lights directly on the 3D model where you want them (see Figure 18).
Figure 18: Using LightPaint to paint light on the model
STEP 9: Let's start interactive rendering in Houdini to see what the lighting looks like (see Figure 19).
Figure 19: Starting Mantra interactive rendering in Houdini
Mantra starts interactive rendering using the lighting from HDR Light Studio (see Figure 20).
Figure 20: Mantra render view inside Houdini (left) running with HDR Light Studio (right)
We can leave Mantra rendering as we work in HDR Light Studio. When lighting changes in HDR Light Studio, it will update Houdini > Mantra to use the new lighting.
If the scene is large and rendering in Mantra is updating slowly, you can produce test renders from time to time instead of leaving Mantra interactive rendering running. It is up to the user to judge this performance and decide what to do.
So far the light we created is on the HDRI map. With a single setting, this light can be removed from the HDRI map, and created as an Area Light in 3D space in Houdini, mapped with the HDR content from HDR Light Studio.
STEP 10: In HDR Light Studio, enable the Area Light check box in the Light Properties panel for the selected light (see Figure 21).
Figure 21: Converting a light into an area light
As a result of enabling the Area Light setting, these things instantly happen:
• The Light in the Light List gets the suffix [AreaLight] and the text is now yellow - clearly showing which lights are Area Lights (see Figure 22).
• The light is removed from the HDRI map lighting the Render View (but is still represented and shown on the Canvas) (see Figure 22).
• A 3D Area Light mapped with the HDR light content (RGBA) is created in HDR Light Studio with a Smart Dolly distance of 1,000, this can be seen lighting the shot in Render View [HDR Light Studio] (see Figure 22).
• A 3D Area Light mapped with the HDR light content (RGBA) is created in Houdini, this can be see in the Houdini viewport and interactive rendering. (see Figure 22).
Figure 22: Light convered into an area light
STEP 11: Reduce the Smart Dolly slider value to move the light closer to the 3D model (see Figure 23).
Figure 23: Moving the area light closer to the model (LightPaint position)
HDR Light Studio has a scene scale setting that is useful when working with Area Lights in Houdini. If the area lights are too close or too far away by default. Adjust the Smart Dolly Scalar value in Preferences. This value scales all area lights in HDR Light Studio.
On the Houdini user interface, we can see:
• The Area Light in the viewport (see Figure 24) (If not, the area light is most likely too far away from your scene. To learn more about Smart Dolly - click here)
• Area lights made with HDR Light Studio shown in the 'HDRLS Area Lights' network box, mapped with HDR (RGBA) texture content (see Figure 24)
Figure 24: Houdini interface after creating an area light
STEP 12: In HDR Light Studio, use LightPaint in the Render View [HDR Light Studio] to move the Area Lights, just like moving a light on the HDRI map (see Figure 25).
In fact area lights are controlled just like any other light in HDR Light Studio, with the addition of distance settings.
Figure 25: Using LightPaint to position the area light
When using the HDR Light Studio area lights, please note:
Renaming/deleting/duplicating these area lights in Houdini (or any part of their associated shader network/file nodes) will cause problems!
STEP 13: Complete your lighting design (see Figure 26 for an example)
Figure 26: Completed lighting design
STEP 14: Render Production HDRI
Once you are happy with your lighting, press the Production Render button in HDR Light Studio (see Figure 27).
Figure 27: Production Render buttons
Set your Production Render settings and Press Render in this panel. Notice how the 'Orientation' is already set to 'Houdini/Mantra', this ensures that the rendered HDRI map is mapped correctly in the host, i.e. Houdini (see Figure 28). For more information see: Production Render Dialog
Figure 28: Production Render Panel
The production quality content will be calculated and saved. The connection will automatically update Houdini to use these final area lights and HDRI map images.
If any further changes are now made to the lighting in HDR Light Studio, all content will be updated to use the updated proxy versions again.
So please ensure you 'Stop' the HDR Light Studio connection after you have produced your production lighting, by Pressing the Stop button (see Figure 29).
Figure 29: Stopping the HDR Light Studio connection
STEP 15: Save Houdini scene
If you would like the HDR Light Studio project to be saved in your Houdini scene, you should save your Houdini scene now. This way the scene state matches the HDRI map and area lights that are currently in the HDR Light Studio project.
STEP 16: Saving and loading HDR Light Studio projects
HDR Light Studio projects can be saved from the HDR Light Studio interface at any time during the lighting process as a HDi file (native HDR Light Studio project file), even when using HDR Light Studio via a connection. If you were to open HDR Light Studio in a connection with Houdini, this project can be loaded into HDR Light Studio using Project > Open Project. The lighting design would load into HDR Light Studio replacing its current design, and would then be synced back into Houdini. This is how you can move lighting between Houdini projects or between other supported 3D software.