Achieving Realism: Scattering, Global Illumination And Cycles
What is Cycles Rendering
Cycles is Blender’s unbiased physically-based path tracing engine that simulates light transport for high levels of photorealism and quality. As a ray tracing renderer, Cycles traces virtual light rays from the camera through pixels in the rendered image plane until the rays encounter objects. The rendering equation then calculates lighting through multiple bounces to simulate real-world accuracy.
Cycles as a Physically-Based Path Tracing Engine
The Cycles path tracing engine utilizes ray tracing algorithms to simulate individual light rays traversing through scenes. Rays originate from the camera and bounce around objects, accurately calculating lighting interactions. By modeling real light transport, Cycles can render high levels of realism suited for product visualization, architecture, animation and visual effects.
Simulating Light Transport for Increased Realism
The path tracing approach in Cycles simulates light rays bouncing around a scene with realistic light interactions. Unlike rasterization rendering, path tracing calculates complex lighting like soft shadows, depth of field, motion blur, caustics and global illumination. Each rendered pixel contains lighting accumulated from multiple ray bounces, approximating solutions for the rendering equation in real-time as pixels converge.
Utilizing Multiple Bounce Lighting
Light rays in Cycles can bounce diffusely and glossily multiple times between surfaces and objects. This allows light to bleed and spread through a scene with realistic global illumination. However, more bounces also increases render times. An optimal balance is configuring enough indirect bounce lighting to achieve realism without excessively long rendering.
Enabling Diffuse and Glossy Bouncing
Cycles has settings for maximum diffuse and glossy ray bounces. Diffuse bouncing affects matte surfaces while glossy controls reflections. Enabling both bounce types allows realistic light interaction between objects. For example, a glossy floor can reflect light onto other objects. Controlling bounce counts reaches the best balance.
Setting Max Bounces for Balanced Quality and Render Times
Higher bounce values improve realism but lengthen render times. Settings between 3-8 offers a good compromise. Diffuse bounces can be set higher as they use fewer processing resources. Glossy bounces above 8 have diminishing improvements but consume more memory and rendering power due to the complex reflections calculated.
Working with Mesh Volumes
Cycles can simulate ray scattering through mesh volume objects. This allows effects like light passing through smoke, clouds and glass. Volumetrics provide realism but can also increase render times depending on their settings and complexity.
Principles of Volumetric Scattering
Volume scattering occurs when light rays encounter dense participating media like air, clouds, smoke, liquid or glass. The light interacts with tiny particles, adding an order of complexity for path tracing. Cycles offers different volume rendering methods to approximate these interactions.
Adding Homogeneous and Heterogeneous Volumes
Homogeneous volumes have evenly distributed particles while heterogeneous volumes vary in density and structure. Different distribution methods mimic real phenomena. For example, heterogeneous volumes work better for marble and wood while homogeneous fits smoke and fire.
Controlling Density, Anisotropy and Other Properties
Volume properties like density, anisotropy, homogeneous/heterogeneous and interpolation affect the realism and render cost. Lower density volumes render faster. Anisotropic scattering adds directionality with a bit more render time. Scaling these settings balances quality with speed.
Using Caustics and Global Illumination
Cycles simulates caustics from glass or water refraction and global illumination from indirect lighting. While more realistic, both effects increase render times depending on their settings and scene size.
Caustics from Refractive Materials like Glass
Caustics form from focused light refracting through materials like glass and water. In Cycles, enabling caustic photons calculates these light patterns for realism. However, caustics generate lengthy rendering, especially at higher sample counts, and typically only apply to certain materials.
Indirect Illumination for Realistic Lighting
Global illumination comes from diffuse inter-reflection between surfaces computed during light bounces. This captures actual scene lighting rather than manually boosting illumination. Cycles handles global illumination efficiently with path tracing for great realism.
Controlling Clamp Values
Indirect lighting clamping limits excessive noise at the cost of accuracy. Lower clamp values reduce noise but cut detail in diffuse or caustics illumination. Scene scale also impacts clamping. Raise clamps gradually until noise is managed for balanced quality without flat or dull rendering.
Optimizing Sampling and Noise Reduction
Samples control Cycles noise and quality while settings like branched path tracing and denoising reduce render times. Tuning these parameters optimizes scenes for fastest acceptable renders.
Managing Number of Samples
More render samples per pixel improves details and reduces noise but greatly increases render times. Start between 100-500 samples while checking noise levels. Then optimize for progressive refinement focusing most samples in brighter pixels to maintain efficiency.
Using Branched Path Tracing
Branched path tracing in Cycles splits ray paths to follow indirect diffusely reflected light and directly sampled glossy reflections faster. This accelerates noise reduction in diffuse and glossy areas better than path tracing alone.
Denoising for Faster Renders
Denoisers filter noise patterns to clean up images rendered at lower samples. This significantly reduces render times for comparable quality. Nvidia AI denoiser works well filtering noise while preserving detail. Intel Open Image Denoise also produces fast results but can lose fine image sharpness.
Example Scene Setup
Example Code for Basic Realistic Scene
Below shows a simple scene setup with key Cycles settings for realism:
Scene Properties - Color Management: Filmic - View Transform: Filmic - Engine: Cycles World Settings - Surface: Background - Color: rgb(0.05, 0.05, 0.05) Mesh Light - Power: 10 - Size: 0.1 Monkey Object - Base Color: rgb(0.85, 0.7, 0.5) Plane Object - Base Color: rgb(0.9, 0.9, 0.9) - Roughness: 0 Cycles Render Settings - Device: GPU Compute - Sampling > Render: 500 - Light Paths > Total: 8 - Filter Glossy: 2 - Volumes: Homogeneous Medium - Denoising: Optix
Key Cycles Settings Shown
This example enables several Cycles features for realism like indirect bounce lighting, mesh volumes and GPU acceleration along with the Filmic view transform and Denoising to optimize rendering. The light paths, filter glossy and sample values offer a balanced starting point for quality and speed.
