Displacement Vs Bump Maps: Maximizing Realism In Cycles

Displacement and bump maps are procedural textures that allow 3D artists to increase the perceived detail and realism of models in Blender. Both work by manipulating the vertices of an object’s mesh, but use different techniques to achieve the illusion of depth and surface detail.

Displacement maps physically move the vertices along the object’s normal vector to create actual geometry changes. This allows deep cavities, ridges, grooves and other displacements to cast shadows and properly intercept light. However, rendering displacement maps is more resource intensive.

Bump maps use luminance values to algorithmically compute a perturbed normal vector per pixel without modifying the object’s geometry. This fakes lighting interactions to simulate depth and detail. Bump maps have almost no impact on render times, but cannot display subsurface scattering or displace surrounding objects.

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What are Displacement and Bump Maps?

Displacement maps are grayscale textures that are used to directly manipulate the vertex positions of an object’s mesh. Brighter values push vertices outward along the normal vector, while darker values pull vertices inward.

This allows deep cracks, indentations, bulges and other surface details to become actual 3D geometry alterations. Light can penetrate cavities and wrap around protrusions to create real displacements in the material.

Bump maps are textures containing luminance based normal vector perturbations. These are used to algorithmically compute slightly rotated normal vectors per pixel to fake surface details without modifying the underlying geometry.

By perturbing normals, bump maps can simulate how light would interact with a highly detailed surface by shading pixels differently. This provides the illusion of depth and texture at almost no render cost.

Key Differences Between Displacement and Bump Maps

While displacement and bump maps both add perceived detail, they work very differently under the hood. Here are some of the key differences between these procedural texturing techniques in Blender:

Geometry Changes: Displacement maps modify vertex positions to create actual 3D detail. Bump maps only change shading without altering geometry.
Light Interactions: Vertices displaced by maps can properly intercept and occlude light. Bump map perturbations are a lighting trick.
Surrounding Effects: Real geometric displacements in maps affect other objects and particles. Bump maps do not.
Subsurface Scattering: Light can penetrate and scatter properly beneath displaced geometry. Bump maps cannot displace light.
Render Overhead: High subdivision levels are required for quality displacements, increasing render times. Bump maps have very little overhead.

These differences inform when and how displacement vs bump maps should be used for optimal realism and render efficiency in Blender scenes.

When to Use Displacement vs Bump Maps

Should you use displacement maps or bump maps for a given material in your scene? Here are some guidelines for when to choose one over the other in Blender:

Use Displacement Maps When:

Accurate lighting interaction is needed for deep cracks and overhangs.
You need actual mesh deformations to displace other objects or particles.
Subsurface scattering is required for translucent materials.
You can afford the render time overhead of subdivisions.

Use Bump Maps When:

Only the illusion of depth and detail is required.
Fast rendering is critical.
Simulating details smaller than a pixel.
Faking details in the distance or background.

For environments like rocky terrains, brick walls and skin, combining both bump maps and some displacement mapping tends to deliver the best balance of quality and speed.

Creating Displacement Maps in Blender

Procedural textures are the most common and flexible type of displacement map used in Blender. Here is a quick workflow for generating procedural displacements:

Create a high-poly model with millions of polygons to capture fine details.
Retopologize and UV unwrap a low-poly version suitable for animation and rendering.
Project fine details from the high-poly model onto the low-poly in Texture Paint mode.
Use the resulting texture paint layer as a procedural displacement map.

This bakes microscopic details into a texture that can then displace macro geometry changes at render time. Adding noise, clouds and scratches enriches details.

Bitmap image textures painted in external programs can also be used. Grayscale values get translated directly into vertex displacements. Dark areas pull inward, light areas push outward.

Applying Displacement Modifiers and Textures

With your displacement map texture created, applying it in Blender involves just a few steps:

Add a Subdivision Surface modifier to increase mesh resolution.
Add a Displacement modifier and select your displacement texture.
Connect the texture to the material’s Displacement input.
Adjust texture parameters like Midlevel, Scale and Strength for the desired depth.

The Subdivision and Displacement modifiers work together – higher subdivision levels allow finer displacement detail. This increases render times, so balance quality vs speed.

Utilizing Noise Textures for Organic Displacement

Procedural noise textures are a fast way to generate organic displacement maps. Fractal, Voronoi, Musgrave and Wave textures simulate natural patterns:

Fractal Noise: Creates convincing ridges, pores and uneven surfaces like skin or stone.
Voronoi Texture: Forms interesting cell-like patterns for reptilian skin or cracked mud.
Musgrave Texture: Procedurally generates multi-fractal shapes for terrain, metals and weathered surfaces.
Wave Texture: Oscillating bands imitate flows for wood grain, wrinkles and water movement.

Layering multiple noise types at different scales and combining with painted image textures enables highly complex procedural displacements.

Optimizing Render Settings for Best Displacement Results

High subdivision levels are required for displacement mapping to resolve fine details – but also increase render times. Here are some tips for optimizing scenes:

Bake displacements to normal maps for distant objects to avoid heavy subdivisions.
Use adaptive subdivision to refine mesh only where needed instead of entire model.
Limit displacement to high-detail hero assets that appear close to camera.
Use lower strength displacements and complement with bump mapping which is faster.
Leverage GPU acceleration of subdivision and displacements for 10-100x speedups.

Test different quality vs speed tradeoffs to find the optimal balance for each project. CPUs vs GPUs have very different performance profiles for displacement mapping.

Creating Bump Maps in Blender

Bump maps can easily be created natively in Blender using the following nodes in the shader editor:

Generate a greyscale texture like clouds or noise.
Plug texture into a Bump Node’s Height input.
Connect the Normal output to the Material Output node.

This computes perturbed normals from the heightmap to fake self-shadowing and depth without geo changes. More advanced bump effects involve chaining multiple bump nodes together.

For even greater realism, baking high-resolution meshes to normal maps combined with hand painting height details in textures provides precision control over the illusion.

Applying Bump Maps to Materials and Textures

Bump maps are easily incorporated into most principled shader setups just by connecting the texture to the Normal input rather than the Base Color. This allows per-pixel normal manipulation independent of diffuse color.

For non-principled materials, add a Tangent node to split UV maps from actual geometric normals. Feed the texture into a Bump node, then combine the perturbed Tangent output back with the original normals.

This allows surface shading from multiple blended textures while preserving overall smoothing and contours definition from the mesh normals.

Maximizing Realism with Normal and Height Maps

In addition to college heightmaps, bump mapping can also leverage RGB normal maps containing detailed pre-computed normal perturbations packed into color channels:

R Channel: Stores X-axis tangent space normal direction.
G Channel: Stores Y-axis tangent space normal data.
B Channel: Encodes Z-axis tangent space normals.

Generating normal maps requires baking high-resolution models or paint tools. This extra detail realistically simulates everything from pore-level skin imperfections to micro-scratches on metals.

Chaining together bump nodes with both height and normal maps blended creates extremely convincing fake geometry at near-zero render cost in Eevee and Cycles.

Balancing Render Speed vs Quality with Displacements

Finding the optimal tradeoff between render speed and visual quality with displacement mapping involves a lot of experimentation. Here are some variables to tweak:

Subdivision Levels: Increasing mesh resolution improves displacement quality but slows renders.
Displacement Strength: How far verts move inward/outward – turn down for faster renders.
Scale: Detail size of the displacements. Raise for bigger details and less subdivisions.
Adaptive Subdivisions: Only subdivide in actual displaced regions by enabling this.

Test a range of settings across different scene objects to find the best balance. Using GPU acceleration and baking where possible helps maximize performance.

Complementing heavy displacements on key assets with bump mapping on background objects balances quality with fast rendering by concentrating detail where it matters most.