Empirical BRDF Model for Goniochromatic Materials and Soft Proofing With Reflective Inks

Area of Science:

• Computer Graphics
• Materials Science
• Optics

Background:

• Standard bidirectional reflectance distribution functions (BRDFs) fail to model goniochromatism, or angle-dependent material color.
• Existing extensions to model goniochromatism significantly increase model complexity.
• Material color is typically defined by diffuse reflectance and a spectral complex index of refraction.

Purpose of the Study:

• To develop a simplified BRDF model capable of accurately representing goniochromatism.
• To enable interactive preview of 3D objects with printed, angle-dependent color textures.

Main Methods:

• Measured the goniochromatism of structural color pigments used in additive color printing.
• Modified the standard microfacet BRDF model by incorporating an empirically based spectral parameter.
• Replaced the spectral complex index of refraction with a specular reflectance spectrum.

Main Results:

• The modified microfacet BRDF model successfully fits the measured spectral angular dependence of bidirectional reflectance.
• The model accurately represents the goniochromatism of red, green, and blue commercial structural color pigments.
• The proposed model offers a computationally efficient approach to simulating angle-dependent color.

Conclusions:

• A simplified BRDF model effectively captures goniochromatism in structural color pigments.
• The new model facilitates straightforward implementation in shaders for real-time 3D rendering.
• This research advances the accurate digital representation of materials with angle-dependent optical properties.