Note: the easiest way to get realistic materials is by using Chaos Cosmos. You can either apply the materials from Cosmos directly to your objects, or drag-and-drop them into the material editor to adjust them if needed. You can also load foliage models from Cosmos, which feature realistic ready-made materials out of the box.
Here are some guidelines for creating realistic materials for foliage such as leaves and grass:
- Always use the Corona Physical Material.
- Use curved geometry for leaves and grass blades instead of flat planes so that they can reflect light naturally.
- Use translucency, but don't make it too strong. Usually a translucency fraction value at about 0,1 - 0,3 works best. Too low values make foliage appear too solid and fake. Too high values can make them "glow" in bright light.
Note: to use translucency, you must first enable the "Thin shell (no inside)" option in a material!
- Use textures instead of flat colors for the diffuse color and translucency.
- Put the diffuse texture into the translucency slot and tweak its appearance using the Corona Color Correct map (for example make it slightly more yellowish). This defines the color of the light passing through the material.
- Tweak the roughness value until the material looks realistic and doesn't produce visual artifacts (See: I can see bright pixels in grass!)
- Interactive rendering is very helpful when tweaking material parameters (See: How to use interactive rendering?)
- Do not use subsurface scattering on objects with no thickness. For grass and leaves it is best to use translucency.
See: How to use subsurface scattering? - Do not use refraction for leaves/grass materials - use translucency.
Examples
Example grass material:
1 - "Thin shell (no inside)" option enabled. You can control translucency only when this option is enabled.
2 - Roughness set to a reasonable value. The reflections aren't very blurry, but also not mirror-sharp.
3 - Translucency Fraction set to 0.3. Too low values make the translucency effect too weak and too high values can make the material appear too bright.
The result of using the above material for the grass:
Thanks to translucency, the sunlight hitting grass blades from the back passes through them, just like in real life.
For comparison, here is the same scene rendered with translucency disabled in the grass material:
With translucency disabled, the sunlight is almost invisible making the image unrealistic.