V-Ray Light Bake or just V-Ray Bake is the process of creating lightmaps with complex light interactions and diffuse interreflection using the V-Ray render engine and it's GI and Lighting calculations.
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The light bake quality depends on the following:
the lightmap resolution of the meshes;
the lightmap UVs quality, better unwrapped UVs better bake quality;
the V-Ray settings in the settings tab.
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Note that actors with vrmeshes assigned will not have their lightmaps baked but will still contribute to the scene for shadows and GI
However, it is possible to import a proxy and bake it with a light map, provided the mesh has correct UV mapping.
Select the proxy and go to Static Mesh > Import Settings rollout. Press the Reset to Default button, which converts the proxy to a static mesh. The static mesh can now be baked.
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Below are mentioned all the settings and parameters that modify the quality of the V-Ray Bake.
Camera Settings
Auto Correction Mode – Specifies which camera to use the automatic exposure and white balance setting.
All cameras Cameras without exposure only
Auto Exposure – Automatically determines an appropriate exposure value for the render. It requires Light Cache to be set as a GI engine and Interactive turned off.
Auto White Balance – Automatically determines a suitable white balance value for the image. It requires Light Cache to be set as a GI engine and Interactive turned off.
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Auto Exposure and Auto White Balance work only when using Light Cache as GI solution.
Render Settings
Time Limit (Minutes) – Specifies the maximum time (in minutes) for refining the image.
Noise Limit – A threshold that determines when to stop refining a pixel. Higher values allow more noise in the image, but the render is faster. Lower values help reduce the noise, but take more time to render. A value of 0.0 traces the entire image unconditionally.
Sample Limit – Specifies the maximum number of samples per pixel for refining the image. V-Ray performs adaptive sampling on the image, trying to put more samples into areas with more noise.
Global Illumination
GI Engine – Specifies the type of secondary engine. Note that Brute force is always used as a primary engine.
Brute Force
GI Depth – The number of bounces for indirect illumination.
Light Cache
Subdivs – Determines how many paths are traced from the camera. The actual number of paths is the square of the subdivs (the default 500 subdivs mean that 250,000 paths will be traced from the camera).
Sample Size – Controls the size of the individual light cache samples.
Retrace – Enables retracing of GI near corners. This helps prevent light leaks and flickering. The value specifies the extent to which GI near corners is retraced instead of being read from the light cache. A value of 0.0 disables retracing. A value of 2.0 is good for still images. Higher values will result in more rays traces at render time.
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For better parity between Render and viewport we recommend to use Brute Force as a GI solution
Environment – Specifies which VRaySettingsEnvironment blueprint will be used at render time for environment overrides. Blueprint must be picked from the level and assigned using either the drop-down list or the picker.
Lights
Shadow Bias – A global parameter for lights. This value moves the shadow toward or away from the shadow-casting object (or objects). Higher values move the shadow toward the object(s) while lower values move it away. If this value is too extreme, shadows can "leak" through places they shouldn't or "detach" from an object.
Materials
Fallback Material – Specifies what material to be used at render time for unsupported materials. If the slot is empty actors that have unsupported materials assigned will be rendered transparent.
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Fallback Material only works with V-Ray Material Instances
VRay CUDA Device Select
You may not want to use all available GPU devices for rendering, especially if you have multiple GPUs and you want to leave one of them free for working on the user interface or you may want to combine your CPU and GPU together. Enable the desired render device by ticking the checkbox.
Textures
Max Size – When the Mode parameter is set to Resize, this value specifies the resolution to which textures will be resized.
Distributed Rendering
On – Enables or disables distributed rendering for V-Ray for Unreal. Use the Render Servers list to specify the machines that will be used for distributed rendering.
Render Servers – Specifies the render servers. Click the + button to manually add a server by entering its IP address or network name followed by its port number (default is 20207) (e.g. 127.0.0.1:20207)
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In this short example, a .vrscene file is loaded. Before we bake the lighting we first make sure that all lights in the scene are set to Static. Next we click on the Bake button in the V-Ray drop-down. The VFB pop up and the the lightmaps begin to render. When it is done they are encoded ad and imported into Unreal. Finally, we start the IPR rendering and start walking around to see the parity between the lightbake and the actual render.
