In today's post, I am sharing an article I wrote for Enscape in 2018 that never made it to their new and updated blog. I collaborated with Enscape co-founder Thomas Willberger on this piece.
The post offers an introduction to material albedo and the impact it has on visualization in general, but Enscape specifically.
It is good to continue to develop your skills professionally. This is true in any profession, but even more so in the AEC space, given the complexity of the built environment; materials, costs, science, health, environment, art, efficiency, human comfort, and much more… When it comes to conveying one’s ideas through imagery and real-time experiences, we already know that Enscape makes this so much easier than in the past. However, there are small things that can be done to make the results even more appealing and realistic.
A rendering technique nearly perfected in the gaming world is the understanding and application of Albedo in materials. The result is a consistent, more realistic effect throughout all images and projects.
It’s important to know the meaning behind the colors if you want to create consistent renderings. For example, the brightness relation of concrete, paper, and snow can be easily mixed up and lead to implausible images. It becomes obvious for vegetation if you have unrealistic greens. Using albedo reference images or tables ensures that your materials are physically correct, and if you’re unhappy with the result, it might be a better idea to change the lighting conditions.
THE BIG PICTURE
Let’s start with a high-level overview of what this somewhat uncommon thing called Albedo is…
Albedo definition: “The fraction of incident light or radiation reflected by a surface or body, commonly expressed as a percentage.” From Wiktionary
- Albeo, where “ALB” is from the Latin “Albus” which means white.
- Albedo is distinguished from reflectivity, which refers to one specific wavelength (monochromatic radiation).
- The amount of light reflected back from a surface is defined by a value between 0.00 and 1.00.
Albedo is similar to, but not exactly the same, as Luminance which measures the brightness of light reflected off a surface. It is scaled by the material's albedo – a darker surface reflects less light, thus causing less luminance. We use the terms Luminance and Illuminance in lighting design, along with specific surface reflectance values.
For Albedo, the amount of light reflected depends on the surface. For example, fresh asphalt is very dark and reflects little light; 0.04 (RGB 59-59-59). At the other end of the spectrum, we have fresh snow, which is a light color and reflects a lot of light; 0.80 – 0.90 (RGB 243-243-243).
Back to the comparison with lighting design and surface reflectance briefly; some material manufacturers publish surface reflectance values for their products. For example, USG makes ceiling products in North America and has published this document – Light Reflectance - listing surface reflectance values for their products. Here, you will notice the ceiling components are mostly white and have a high light reflectance value between 0.81 – 0.89.
The fundamental principle is the same between Albedo and reflectance/luminance, in that darker colors result in lower numbers (less reflective) and higher numbers for lighter colors (more reflective).
THE ALBEDO CHALLENEGE
Why does the concept of Albedo matter in architectural visualization? Let’s look at a simple office rendering, comparing a bad and good image in terms of albedo.
Looking at the first image below, something just doesn’t look right. It is not believable or realistic. We know what the image represents – it’s an office space. Can you tell what’s wrong? The whites are too white, the grass is too dark, and the mousepad is solid black.
Now compare this with the albedo-corrected image below. The whites are softer, the grass is natural, and even the mouse pad looks better. When the proper albedo is applied, the combination of all elements will look more realistic from any view and lighting condition. We no longer need to compensate for a poor rendering engine by using full whites/blacks and other tricks. We can now focus on the physical environment and its measured attributes.
Unrealistic image due
to wrong albedo
More realistic image
due to correct albedo
REFERENCE CHARTS
Scientists have measured and documented the albedo of many materials. And, by the way, astronomers measure the albedo of planets and asteroids to help understand surface composition. Gaming developers have done a great job of applying those results in developing Physically Based Shader (PBS) materials to increase the level of realism and consistency in their game environments.
We can and should do the same in architecture!
Here is one simple list of albedo values for a few materials spread out across the full spectrum between 0.00 and 1.00. The links provided below offer more detailed charts.
Material Albedo RGB
- Charcoal 0.04 50-50-50
- Fresh asphalt 0.04 59-59-59
- Worn asphalt 0.12 91-91-91
- Bare soil 0.17 85-61-49
- Green grass 0.25 123-130-78
- Sand 0.40 177-168-132
- New concrete 0.55 192-191-187
- Ocean Ice 0.5–0.7 148-148-148
- Fresh snow 0.80–0.90 243-243-243
Enscape-rendered image
depicting the base range of the full albedo spectrum
I highly recommend you read what some of the gaming designers have written. Marcos Borregales published a nice reference on his blog Technical Art Adventures here: PBR - Albedo Cheat Sheet.
Unity offers this interesting document on representing dark materials, Materials authoring guidelines 1: dark dielectric materials (link to PDF).
This document starts with the following introduction:
“With the large adoption of Physically Based Shading, game materials parameters changed and replaced diffuse color with Albedo. This parameter represents the characteristic color of an object, and is independent from the lighting conditions. It can be measured and a lot of documents have appeared online, giving reference values for Albedo. Most of them recommend using a range of albedo comprised between 50 and 243 ( in 8 bit sRGB ).”
Finally, for reference material, if you really want to get into the “weeds” on this topic, you should also read these two posts by Sébastien Lagarde:
- DONTNOD Physically based rendering chart for Unreal Engine 4
- Feeding a physically based shading model
One last comment on these charts is that they are listed in various formats, such as 0-1, RGB, sRGB, and a three-digit number representing the RGB average. If they provide a color swatch, I sometimes use Photoshop’s color picker tool to sample the RGB value for entry into Revit or SketchUp.
ENSCAPE AND ALBEDO
Enscape encourages designers to consider the proper albedo to generate more consistent and realistic imagery. Thus, this blog post! You will even see the term used within Enscape’s Material Editor as shown in the image below (from within SketchUp in this example). In this context, albedo refers to the main texture or color from which the albedo value can be derived and compared (by you) to the “standards” charts previously mentioned.
GRASS EXAMPLE IN REVIT
A good example using a regular challenge introduced by a default Revit material (found in default Revit templates) used by many is grass. The image below contrasts the two default Revit-provided grass materials, left and right, with a custom material using a standard albedo in the center. The second image (to the right) is the raster image shipped with Revit for grass.
Here are two building renderings, one with the default grass (left) and the other with the preferred albedo (right).
For more on grass, check out my grass-specific post on the Enscape blog: Top Tips for Rendering Grass in Enscape.
CONCLUSION
We still cannot say that developing renderings of our proposed designs is a science… but we are getting closer thanks to Enscape and our consistent application of albedo described in this article. It can also be a challenge to find an albedo standard for all materials we use. But, with a solid understanding of the concept and application of the basics, we can make some assumptions that will result in beautiful images that will impress our clients and peers.
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