PBR: A Guide to Moving From Specular to Metallic/Roughness

As of July 2019, the Blender Foundation Released version 2.8 with its new rendering engine, Cycles. (Blender Foundation, 2019)  Allowing for Global Illumination & RayTracing, Cycles is Physically-Based Rendering (PBR) Engine. 

This addition allows us to create truly photorealistic imagery within a free, open-source engine built from the ground up for customisation. But to fully take advantage of the power of photorealistic rendering, a re-think of how to apply texturing is required. 

In this blog post I will overview how to quickly suitably translate the old diffuse/specular workflow into the new diffuse, metallic & roughness environment, using the development of my 3D modelling project as a case study.

Fig.1. My Initial Render preview of the scene, in EEVEE

My model starts out with a homogenous material with specular set to match the shininess of the reference images provided. By starting out the texture process with material composition-first, rather than details we get a accurate representation of how the surface interacts with lighting.
Fig.2. Basic Model of the model with multiple materials

By comparing with the reflections on the real model we can limit ambiguity and back and forth tweaking. Shown in figure 2, I placed the camera at the identical angle, FOV (Field of View) and distance as the reference photo. Inspecting how sharp the intensity of the Key and Back Light (Detisch, 2025) bounces of the wooden glossy masks gives us a lot of information about the composition of the material.  

The next step is to add multiple materials. At this point I'd switched to PBR, using Principled BDSF which includes the following attributes:

Diffuse: The base colour attribute independent of lighting angle. Present in almost every 3D Graphics engine. For now we will be purely setting the colour attribute.

Fig. 3.  The final diffuse texture after adding detail and alterations in Photoshop.

Metallic: This is how metallic a material is, literally. It varies from a completely diffuse material to a stell/aluminium appearance. Materials tend to be either metallic or not, so this setting can be set for complete sections of the model as black and white, or close to that value(See figure.4). Because of that we can set its property in Blender face-by-face, we will only revisit this when applying dirt and grime details.




Fig.4 Example of a Metallic texture map. (Miki, 2017)

Roughness: This is another new texture map in Cycles, but in practice it is almost the exact as specular, but inverse. Other than the face that when roughness is closer to 0, the reflections will be reflection based instead of from the light source. When adding detail to the material this texture map is continually tweaked to add detail.


Fig.5. My final roughness map, sharing complex detail from diffuse.


Normal: This image is computed generated so not really part of the PBR workflow, but it helps to add this as a layer in photo editing software to identify where to paint extra detail and grime around baked details.
Fig.6. The Final normal map for the asset.

After setting the materials, convert the multiple materials using the Bake Options, making sure that you copy and paste the target image into the 

Fig.7. All the different materials in the objects before combining

After printing the textures into 3 individual textures we can use photo editing tools to add detail:

Brush Tool - Use Wet, Dry and standard brushes throughout the 3 textures to add dirt & grime, details, and fix inconsistencies.

Noise - Using a combination of perlin & general noise we can create a realistic surface texture for the diffuse & specular textures.

Filters: Adjust Lightness, contrast, saturation and blur layers to tint the textures to achieve the intended look.

Fig. 8.  The Metallic, Diffuse & specular texture output from baking multiple materials to texture

After utilising all the different texture methods through the workflow, I achieved a photorealistic looking model in a time effective manner.

Fig.9. Final Model




References:
Blender Foundation, 2019. 2.80 - Blender https://www.blender.org/download/releases/2-80/

Blender Foundation, 2019.  Principled BDSF Belnder 5.0 Manual https://docs.blender.org/manual/en/latest/render/shader_nodes/shader/principled.html

Detisch, Aj,2025.Film Lighting Techniques — How to Get a Cinematic Look https://www.studiobinder.com/blog/film-lighting-techniques/

Miki, 2017. PBR Shader Node for Blender. https://meshlogic.github.io/posts/blender/materials/nodes-pbr-basic-shader/


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