How to use interactive LightMix in Corona for C4D?


Interactive LightMix is unique to Corona Renderer and lets you adjust intensity and color of your lights and light emitting materials during and after render – perfect for anything from subtle adjustments through to turning day into night.



What is interactive LightMix?


Interactive LightMix is a feature which allows for rendering an image just once, and then changing color and intensity of the lights directly from the Corona VFB. It can be used after the rendering is finished, and also, like any other post processing in Corona, during the rendering.



How to set it up? 


To set up LightMix automatically


Assuming you have your lights added to your scene, you can now take advantage of the Setup Interactive LightMix feature. This will automatically add your lights with corresponding names into the Interactive Lightmix.
    To do so:


  1. Under the Corona menu option in the main C4D toolbar, select the Multi-Pass... option:

  2. In the Corona Multi-Pass dialog, ensure that Muti-pass is enabled by checking the "Enbl" checkbox:
  3.  Click on Multi-pass in the Active passes column

  4.  Click on  the Setup Interactive LightMix button

  5. Choose how you want your lights to be added then hit Generate.



We can now see that our lights are correctly listed and ready for use in LightMix:




NOTE: The sky object will not be added using the Setup Interactive LightMix button and will need to be added manually. It's also worth mentioning that the automatic method will also work with Cinema's standard lights and luminescent material (if applied to a plane and added manually into LightMix) and the automatic method will support light instances. Lastly, if you are experiencing an IR loop with Cinema's Sun tag it's advised to remove it.



To set up LightMix manually:

  1. Under the Corona menu option in the main C4D toolbar, select the Multi-Pass... option:


  2. In the Corona Multi-Pass dialog, ensure that Muti-pass is enabled by checking the "Enbl" checkbox:

  3. Add at least one LightMix render element (double click on it under the LightMix category in the Pass Type list, or click to select it and use the > arrow to add it)

  4. Add one LightSelect render element for every light or group of lights that you want to adjust in the LightMix:



  5. Select a LightSelect render element. It is best to rename it to something descriptive. Click the arrow, and then click on as many lights (which can include objects with Light Emitting materials on them) in your scene as you wish to add to this LightSelect. Note that any light should only be in one LightSelect.



  6. If you want the LightMix to be denoised like the beauty pass, you will need to enable denoising for each LightSelect pass individually. To learn more about denoising, see What is denoising?



Now everything is set up to use the LightMix option in Corona VFB.




How to use it?


After setting up LightMix, the color and intensity of each light can be changed in the VFB. Simply go to LightMix tab in Corona VFB and change the desired parameters. Below you can see the image as it was rendered, followed by a "nighttime" version created by adjusting the LightMix values without re-rendering:






You can also use additional buttons below the list of lightselects to:

  • Save a LightMix preset and load it later
    This is useful, for example, when creating day and night versions of a scene. It is also possible to load a preset after a camera is changed and a different view is rendered!

  • Reset the colors of all lights
    Using "All white" reverts the colors of all lights to pure white in the LightMix UI, which results in having the initial colors of the lights in the scene. If a light color was altered in the scene, its color will not be affected.

  • Toggle all
    Turns all the LightSelect layers on or off. Useful if you have a lot of layers and want to only have a few active for example (simply use Toggle all to turn all the LightSelects off, then manually enable the few that you want active - easier than manually turning off many LightSelects!)

  • Set the intensities of all lights to 1
    This resets any adjustments made in the LightMix UI and restores the original intensity of all the lights in the scene.

  • Bake the LightMix values back into the scene
    This option takes the intensities and colors created in the LightMix UI and bakes those back into the scene itself. This lets you use LightMix to adjust your lighting, and then set the scene to use that lighting by default. The image below shows the result of baking the previous "nighttime" look into the scene and re-rendering - note how the LightMix intensities are all 1, and the LightMix colors are all white, as the nighttime colors and intensities are now baked into the scene:




What are the limitations?


There are some technical limitations when using LightMix:


  • Keep in mind that the LightMix color acts as a filter on the original light color
    The color in the LightSelect does not replace the original color of the light but instead filters it (for example, if a light has a strong red color in the scene itself and you add green in the LightSelect, the result will be an orange color in the LightMix render). This means that the more saturated the color of the light in the scene, the less control you will have over it in LightMix - this can be resolved for any lights that you plan to control extensively in the LightMix by leaving the light a white color in the scene.

  • Using extremely high or low intensities of lights
    Generally, LightMix is not intended for making drastic changes to light colors or intensities. In particular, raising the intensity of a light by an extreme amount may introduce noise in the image - if this happens, baking the new values into the scene and re-rendering can often give better results. Also, it can be best to ensure that lights are "too bright" in the Beauty pass and lower their intensity as needed in the LightMix, rather than having to take a low intensity light from the scene and raise its intensity in the LightMix.

  • Adding a lot of lights and rendering in very high resolution
    Each LightSelect pass needs its own memory allocated, so if you have a lot of LightSelect passes and / or are rendering to a large resolution, this can lead to excessive RAM usage.

  • Using the ShadowCatcher material
    LightMix does not interactively update shadow catcher material shading results - this is currently a limitation.
    See: Known bugs and limitations


Other than that, the results of using LightMix are only limited by your imagination. :)



A video tutorial will follow in the future showing how to use LightMix in Cinema 4D. In the meantime, the steps and principles are the same as shown in the 3ds Max tutorial video, shown below: