Nuke – CG (Part 1)
AOV (Arbitrary Output Variable)
- Is a concept in 3D rendering that represents a custom data channel produced during the rendering process.
- These channels contain specific types of information about the rendered scene, such as lighting, shadows, color, reflections, and more.
- AOVs are significant for VFX because they provide more flexibility in controlling every pass and grade it according to background image
Key types of AOVs:
- Direct and Indirect AOVs: Capture light directly from the source and light that has bounced off surfaces.
- Standard Surface AOVs: Isolate material components such as diffuse, specular, and subsurface scattering for fine-tuning in compositing.
- Ultilities AOVs: Used in combination with tools to achieve various effects like defocus, motion blur, re-lighting, etc…
Passes
Passes, often part of the AOVs in a broader sense, are specifically categorized render outputs that represent different elements or effects within a rendered scene. While AOVs provide the technical variables, passes focus on the compositional elements that make up the beauty shot or contribute to visual effects, such as:
- Beauty Passes: The comprehensive render that includes all visual elements.
- Lighting Passes: Separate the lighting into its specific types (e.g., key light, fill light) for detailed lighting control.
- Reflection, Refraction Passes: Isolate reflective and refractive elements, allowing for adjustments to how surfaces interact with light.
- Beauty Passes: Used to recreate beauty renders
- Material AOVs: Used to adjust the Material Attributes (shader) of objects in the scene
- Data Passes / Helper passes
- Provide technical information used to adjust or apply effects in post-production
- Examples of data passes:
- Normals Pass
- Motion Vector Pass: Contains the direction and magnitude of motion for each pixel, enabling post-production motion blur.
- UV Pass: Stores the UV mapping information, allowing for post-production texturing or adjustments to textures.
- Position Pass: Gives the exact position of each pixel in 3D space, useful for integrating 3D elements or effects based on location.
- Material ID/ Object ID Pass: Assigns a unique color to each material or object, simplifying selection and isolation for adjustments.
- Z-Depth Pass: Offers depth information for each part of the image
Working with render passes:
- You can break down render passes by Using Shuffle nodes to separate out individual AOVs or passes from multi-layer EXR files
- When we build a cg beauty we simply combine information of highlights, midtones and shadows.
Rules for rebuilding CG assets:
Merge (Plus Lights): Diffuse / Indirect / Specular / Reflections
Merge (Multiply Shadows): AO / Shadows
- Each pass should be graded separately
- A final grade can be applied to the entire asset if needed
LayerContactSheet is used to view all the passes contained in the EXR
- Enable ‘Show layer names’ to display the name of each channel.
Tips: Ctrl+Shift Drag node onto another to swap/replace node
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