How to use interactive LightMix in Corona for C4D?

How to use interactive LightMix?

 

Interactive LightMix lets you adjust the 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 colors and intensities of the lights directly from the Corona VFB. It can be used after the rendering is finished and, also, like any other post-processing effect in Corona, during the rendering (be it production or interactive mode). Some of the improvements added over the years include:

• A possibility to bake LightMix parameters into the scene lights and light-emitting materials (the >Scene / Bake button)
• Better automatic creation dialog with different ways to group lights, information on RAM usage, and checkboxes for denoising and considering hidden lights
• A better, more user-friendly user interface

Starting from Corona 12, with the new VFB 2.0, it is possible to create and manage multiple LightMix setups within a single render by manually adding multiple LightMix passes.
See: Using multiple LightMix passes at the Chaos Documentation Portal

 

LightMix can be used on Corona EXR (.CXR) files outside of any 3D software using the Corona Image Editor.

 

 

How to set it up? 

LightMix can be set up either automatically or manually.

 

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:

 

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

 

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

C. Now you can proceed to:

1. Click on Multi-pass in the Active passes column
2. Click on Enable multipass
3. Click on  the Setup Interactive LightMix button
4. Choose how you want your lights to be added, then hit Generate.

 

Instanced lights – Separates LightMix layers by instances. All instances of a single light object end up on a single layer. Any unique light in the scene is stored in its own individual layer. 

Grouped lights – Separates LightMix layers by groups. Any group of lights ends up on a single layer. Any light that is not part of a group is stored in its own individual layer. 

Layers – Separates LightMix layers by layers. 

Individual lights – Every single light ends up on its own individual layer.

 

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

 

NOTE: 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 a loop with Cinema's Sun tag during interactive rendering, 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 pass (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 pass for every light or group of lights that you want to adjust in the LightMix:
   
   
   
5. Select a LightSelect pass. 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 How to use denoising?
   

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

 

 

LightMix and Denosing

You can decide whether denoising should be applied to each LightSelect render pass. To denoise the whole LightMix output, you must turn on the denoising option for all LightSelect passes:

Denoising can be enabled manually for each of the LightSelect passes.

 

Denoising can be also enabled automatically for all LightSelect passes using the "included in denoising" checkbox in the Corona Interactive LightMix Setup dialog:

Denoising can be enabled automatically for all of the LightSelect passes.

 

As of Corona Renderer 4, the "Rest (unassigned)" LightMix item can be denoised and saved just like any other render pass. 

This is achieved by allowing any LightSelect render pass to act as the "Rest (unassigned)" render pass by enabling the appropriate option ("Include lights not assigned to other LightSelect elements") for the LightSelect pass:

Turning on "Include lights not assigned to other LightSelect elements" allows saving and denoising

the LightMix pass with lights not included in other LightSelect passes.

 

This render pass will be denoised just like other LightSelect render passes as long as the "Apply denoising also to this render element" option is enabled.

 

Please note that if any lights are left unassigned to any LightSelect render passes and no LightSelect render pass has the "Include lights not assigned to other LightSelect elements" option enabled, these lights will still end up in the Rest (unassigned) section but you will not be able to denoise the render pass or save it.

 

To learn more about denoising, see: What is denoising?

How to use it?

After setting up LightMix, the color and intensity of each light can be changed in the VFB. Simply go to the LightMix tab in the 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 above the lights list:

Button	Description
	Bake currently set LightMix colors/intensities into the scene lights.
	Save settings of the current displayed light mix pass to a config file.
	Load LightMix settings from a config file to the currently displayed LightMix pass.
	Enables all entries if some are disabled or disables all if all are currently enabled.
	Set all intensities to 1.
	Set all colors to white.

 

Additional Tips:

• • LightMix colors can be copied by dragging and dropping a color swatch onto another swatch.
    
  • LightMix colors can be reset to pure white by right-clicking on a swatch.
    
  • You can also right-click on the light names on the LightMix list in the Corona VFB to select a specific light in the scene, add that light to the current selection, or remove that light from the current selection

Compositing LightMix layers in other applications

To compose different LightMix layers (LightSelect passes) so that the final image looks the same as in the Corona VFB open the layers in the application of your choice, and stack them on each other in any order using the "Add" blending operation. In Adobe Photoshop it is called "Linear Dodge (Add)". 

Using LightMix with multiple suns and environments

An example image with multiple suns and environments controlled by LightMix. 

You can add multiple suns and environment maps to your scene, and then control their appearance with LightMix. This means that you can render just once, and pick between completely different lighting conditions, adjust sun and environment intensity and color, and even have two or more suns illuminate your scene at a time. No re-rendering needed! 

See: How to set up multiple suns / environments

Using Multiple LightMix Passes

Starting from Corona 12, with the new VFB 2.0, it is possible to create and manage multiple LightMix setups within a single render by manually adding multiple LightMix render passes.
See: Using multiple LightMix passes at the Chaos Documentation Portal

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. 

Troubleshooting

I'm getting the message: "Interactive light mixing is currently not possible." under the LightMix tab of the VFB.
If you see this message, it means that LightMix has not been set up correctly. This could be due to some of the following reasons:

• LightMix is not being set up at all.
• The main Multi-pass checkbox is disabled on the Active passes section from the Corona Multi-pass window.
• There is no LightMix pass on the Active passes section from the Corona Multi-pass window, or its checkbox is disabled.
• There is no LightSelect pass on the Active passes section from the Corona Multi-pass window, or its checkbox is disabled.

The solution is to make sure that LightMix is properly set up and that the multi-passes are enabled. The easiest way to make sure LightMix is set up correctly is by following the above steps to automatically set up LightMix, or set it up manually as described above.