Path Tracing Vs. Rasterization: Understanding Cycles And Blender Internal Engines

What is Path Tracing and Why Use Cycles?

Path tracing is a ray tracing based rendering technique that simulates light transport in a scene. It works by tracing the path of light rays from the camera into the scene, bouncing around between objects and light sources. This allows for highly realistic rendering with effects like soft shadows, depth of field, motion blur, caustics and global illumination.

The Cycles rendering engine in Blender uses path tracing to produce noise-free and unbiased renders. Unbiased means that Cycles simulates light transport without shortcuts or approximations, leading to more accurate results. The tradeoff is increased render times compared to biased rendering.

There are several key advantages to using Cycles path tracing in Blender:

Table of Contents

Physically accurate materials and shaders like glass, water, metal and subsurface scattering.
Realistic lighting from indirect illumination, caustics and color bleeding effects.
Soft natural shadows from area lights and environment maps.
Depth of field, motion blur and other camera effects.
Procedural noise patterns and textures via nodes.
Easy integration with Blender materials, textures and workflow.

The downside to path tracing is that it requires more render time to clean up noisy images. Complex scenes with lots of light bounces can take hours to render. Luckily, Cycles has progressive rendering so you can periodically save out renders instead of waiting for full convergence.

Rasterization in the Blender Internal Engine

Rasterization is the legacy rendering approach in Blender’s original Internal engine. It works by projecting 3D geometry onto a 2D image plane before determining shading and colors. This rasterized output gets displayed pixel-by-pixel as the final render result.

Blender Internal uses a hybrid renderer combining rasterization with ray tracing features. Its strengths include fast render times for previews, customizable shaders and texture baking workflows. However, rasterization has some key limitations compared to path tracing:

Approximate lighting from missing global illumination.
Hard shadows instead of soft area shadows.
Limited shader capabilities for photorealistic materials.
No true depth of field, motion blur or caustics.
Pre-processing required for effects like ambient occlusion.
Artifacts from non-physically based tricks and hacks.

In summary, rasterization directly converts 3D geometry into pixels without simulating the full behavior of light. This can result in unnatural effects lacking realism. Cycles path tracing produces more accurate results but requires longer render times due to the complex light transport simulation.

Ray Tracing vs Rasterization

Ray tracing and rasterization take fundamentally different approaches to image synthesis. Ray tracing simulates rays of light in a 3D environment while rasterization projects geometry onto a 2D plane for efficiency.

Here is an overview of the differences between ray tracing and rasterization techniques:

Rendering Method – Ray tracing uses rays shot from camera into scene. Rasterization projects vertex data to image plane.
Lighting and Shading – Ray tracing calculates full light transport with global illumination. Rasterization uses local illumination only.
Shadows – Ray traced shadows have soft penumbras from area lights. Rasterized shadows are hard and aliased.
Materials – Ray tracing simulates microsurface behavior. Rasterization approximates surface shaders.
Effects – Depth of field, motion blur and caustics simulated with rays. Rasterization relies on post-process effects.
Render Speed – Rasterization is faster for simple scenes. Ray tracing scales with scene complexity.
Photorealism – Ray tracing is physically based and unbiased. Rasterization uses hacks that can cause artifacts.

Cycles leverages ray tracing techniques like path tracing, bidirectional path tracing and spectral rendering. This focus on accuracy over speed is what enables its realism, but also causes lengthy render times.

Blender Internal uses rasterization methods enhanced with some ray traced effects like reflections, refractions and shadows. It renders quickly but cannot match Cycles realism due to relying on shortcuts and approximations.

Setting Up Path Tracing in Cycles

It’s easy to set up path tracing renders in Blender Cycles. Here are the basic steps:

Switch to Cycles render engine in Properties > Render settings.
Add Materials, Lights and World settings for scene as needed.
Adjust Sampling settings to improve noise and rendering speed.
Enable GPU Compute if supported by graphics card for faster rendering.
Change device to GPU Compute to enable GPU acceleration.
Select output format as OpenEXR or MultiLayer for post-processing.
Setup layers or render passes for modifying render output.
Use Nodes editor to create complex shader nodes or compositing.
Click Render button to start path tracing the scene progressively.

That covers the basics – Cycles has tons of additional settings for optimizing renders. Things like clamping, caustics, subsurface scattering, motion blur and layered rendering. Dive into the docs to learn more about these powerful path tracing capabilities!

Optimizing Scene Performance

Path traced rendering in Cycles can easily become slow for complex scenes. Luckily there are many optimization tricks to improve speed and reduce noise.

Here are some top tips for optimizing scene performance in Cycles:

Use fewer light bounces for faster renders.
Lower sample counts in simple or foreground areas.
Enable Branched Path Tracing and Progressive Refinement.
Clamp fireflies using the Filter Glossy setting.
Set Texture Interpolation to Closest for sharp details.
Use Irradiance Volumes to cache indirect lighting.
Add Denoisers like Intel Open Image Denoise.
Generate UV Maps to reduce shader complexity.
Use simpler Principled, Glossy or Diffuse shaders.
Enable GPU rendering on NVIDIA or AMD graphics cards.
Render layers and passes for post-processing and compositing.
Reduce geometry complexity with modifiers before rendering.

Take advantage of Cycles advanced capabilities too. Things like baking for reusable textures, rendering to vertex colors or using Alembic caches to render particle simulations. Experiment with settings to find the right balance between quality and speed.

Examples of Path Traced and Rasterized Renders

Let’s compare some example renders created in Cycles and Blender Internal engines. This will demonstrate the differences between the path tracing and rasterization approaches.

Glass Material

Cycles path traced glass shows subtle reflections, distortions and caustics from the light. Internal uses environment maps and tricks that don’t match realistic light behavior.

Puddle with Ripples

The Cycles puddle has depth, scattering through water, reflection of the sky and accurately displaced ripples. Internal lacks these path traced interactions of light.

Soft Shadow from Area Light

Notice the soft shadow with smooth penumbra generated by the Cycles area light. Internal produces aliased hard shadows without support for large light sources.

Depth of Field Blur

Shallow depth of field blur naturally emerges from Cycles path tracing. Internal relies on inaccurate post-process depth of field effects.

Motion Blur

Realistic motion blur comes from Cycles tracing camera and object movement over time. Internal motion blur tends to show artifacts revealing limitations of rasterization approach.

Choosing the Right Render Engine

Should you use Cycles or Internal engine for rendering in Blender? It depends on your specific project needs and render system capabilities.

Cycles path tracing is best for:

Photorealistic results with accurate lighting.
Complex scenes requiring global illumination.
Water, glass, smoke, fire and advanced shaders.
Art scenes focused on quality over render time.
GPU or distributed network rendering.

Blender Internal rasterization works well for:

Fast draft renders to check modeling.
Simple scenes without global illumination complexity.
Projects using Blender-specific texture baking.
Cartoons, illustrations or non-photoreal styles.
Animations needing quick preview renders.

For maximum flexibility, set up materials to work in both Cycles and Internal. That way you can switch between engines and take advantage of hybrid workflows. Use Internal for speed, then hop into Cycles for final quality renders after everything looks good!