Back to Beauty - Rendering for Compositing

Introduction

If you render straight out of LightWave - you hit F9 or F10 and take whatever you get - but for compositing work or more control over your renders and to speed them up (rendering depth of field adds time to a render, but rendering out a depth pass and using a compositing package to create a depth of field effect takes no additional time) using LightWave's buffers is the only way to go. The question always remains, "which buffers do I need" and the answer depends on your scene's content but for general use the following equation should see you right:

(Diffuse_(Direct and Indirect) + Specular_(Direct and Indirect) + Clearcoat(Direct and Indirect) + etc. +  Refraction + Transparency + Luminosity + Fog) * Volumetric Transmittance + Volumetric_((Direct and Indirect))

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Remember, you only need the buffers you use, so if your scene has no Clearcoat, Fog or Volumetrics you do not need to include those buffers in your render

All the following buffers should just be added together, and because adding is commutative the layer order does not matter. In Photoshop, the Blend Mode is called "Linear Dodge (Add)".

The Buffers

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• Images are PNGs here for demonstration purposes but should be EXRs or similar for full flexibility

• If you are going to use PNG, you need to set your Depth Map distances correctly so that the range of steps is small enough to be contained by the 255 levels an 8-bit per channel image provides

• You decide what buffers you need to use by the details you use in surfaces - if there's no SSS, you don't need that buffer and so on. Normally, the bare minimum is Diffuse (Direct and Indirect); Specular (Direct and Indirect); plus Refraction for transparent materials

• Buffers can add a little extra time to a render because there will be more files to write out than a single image >

Volumetrics

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Note that a Multiply blend mode must be used for Volumetric Transmittance

When we say volumetrics in this sense we are referring to the new volumetrics that LightWave can now create, not volumetric lights or the HyperVoxels that came with LightWave 2015 and before. If you have Volumetric primitives or VDB files in your scene, you need to make sure that the Volumetric Transmittance buffer uses a Blend Mode of Multiply to combine it with the others for a render and that any other Volumetric buffers are added.

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Contributed by Richard Feeney