Simply put, albedo is the overall brightness of an object.
What is Albedo?
Albedo represents the total reflecting power of a material. In Corona, this value is calculated by adding together a material's diffuse, reflective, refractive, and translucent components. Please note that light emission is not factored into a material's albedo.
Why Avoid Pure White Albedo?
In the real world, almost no materials have a purely white albedo. Using a pure white setup in Corona - such as setting the Base Color to RGB 255 with a Level of 1.0 in the Corona Physical Material, or Diffuse Color to RGB 255 with a Level of 1.0 in the Corona Legacy Material - causes light to bounce almost endlessly. This results in an unrealistic image and significantly slower rendering times.
Recommended Settings
To maintain physical accuracy and optimal render speeds, follow these guidelines:
Keep the overall albedo of your materials below RGB 180.
Alternatively, if you prefer to use a base layer color of RGB 255, reduce the base layer level to 0.7 or lower.
Troubleshooting Dark Scenes
If keeping your albedo within these realistic limits makes your scene appear too dark, do not increase the material's whiteness. Instead, brighten the scene naturally by either increasing your camera exposure or raising the intensity of your light sources.
Each material component is calculated as LEVEL * COLOR (with 255 = albedo 1). So to decrease too high albedo of a white material, you can either:
- leave the color at RGB255 and lower the level to about 0,7 (Base color / Base color level in CoronaPhysicalMtl, or Diffuse color / Diffuse level in CoronaLegacyMtl) or
- leave the level at 1 and change the color to about RGB180
Corona's energy conservation model automatically reduces the diffuse/base color contribution of reflective materials.
How to Check Your Albedo Values
To easily verify if your materials have physically accurate albedo values, you can add the CShading_Albedo render element to your scene.
Interpreting the Albedo Pass
Once rendered, this pass provides a clear visual map of your scene's overall reflectivity:
Pink or Red Areas: These highlight materials where the albedo is too high. You should lower the brightness of these materials immediately. Leaving high albedo values on large, diffuse surfaces will result in an unrealistic look and significantly increase your render times.
Bright or White Areas: These indicate high albedo values. While not necessarily an error, they should be used carefully and sparingly.
Dark Gray Areas: These represent lower, safer albedo values.
Performance and Realism
Generally, a scene with an overall darker albedo pass will render faster and produce more realistic lighting contrast. Keep in mind that only the areas explicitly highlighted in pink or red require your immediate attention to prevent rendering issues.
Examples
Images below show the same scene rendered with exactly the same settings, except for the base color level (diffuse level in CoronaLegacyMtl) of the override material, with fixed number of passes (32):
Example 1a
Diffuse level: 0,2
32 passes
Rendering time: 03:47
Example 1b
Diffuse level: 0,4
32 passes
Rendering time: 05:19
Example 1c
Diffuse level: 0,8
32 passes
Rendering time: 09:12
Conclusion: brighter scenes take more time to render.
Images below show the same scene rendered with exactly the same settings, except for diffuse level of the override material, with fixed rendering time (3 minutes):
Example 2a
Diffuse level: 0,2
25 passes
Rendering time: 03:02*
Example 2b
Diffuse level: 0,4
18 passes
Rendering time: 03:06*
Example 2c
Diffuse level: 0,8
11 passes
Rendering time: 03:41*
Conclusion: you can render less passes in a given time as the scene gets brighter.
*time difference is the result of different UHD Cache calculation times
Images below show the same scene rendered with exactly the same settings, except for diffuse level of the override material and exposure settings, with fixed number of passes (32):
Example 3a
Diffuse level: 0,2
Default exposure
Example 3b
Diffuse level: 0,4
Exposure slightly decreased to compensate brightness
Example 3c
Diffuse level: 0,8
Exposure strongly decreased to compensate brightness
Conclusion: you can use exposure settings to control overall brightness of the scene but diffuse level always affects image's appearance (especially contrast, which is visible in shadows).
The Albedo render element
Example scene with too bright materials on some of the objects, and CShading_Albedo element of that rendering:
Note: the gray and dark-gray objects have correct albedo values. The objects which are marked red have too high albedo value.