Modelling appearance printing: Acquisition and digital reproduction of translucent and goniochromatic materials

The key to successful 3D printing lies in the digital preview of objects before fabrication, enabling users to assess colour reproduction and quality. However, accurately representing colour in a digital environment is complex, as it depends on numerous factors, including illumination, object shape, surface properties, scene context, and observer characteristics. Traditional methods of previewing conventional 2D prints overlook this complexity.

This thesis addresses this challenge by focusing on two types of materials: semitransparent polymers commonly used in 3D printing, and goniochromatic colorants employed in printing to introduce unique effects unattainable with conventional inks for 2D printing. For semitransparent materials, we developed an empirical function to represent colour based on sample thickness, enabling efficient digital representation. Additionally, we adapted a colour measuring device to identify two key material parameters, absorption and scattering coefficients, essential for accurate colour reproduction.

Goniochromatic materials, such as thin film-coated mica particles, are slightly more complicated and less predictive in terms of their final colour appearance. Although not yet used in 3D printing, these particles used in conventional printing introduce colour variation while rotating the print. We found that goniochromatic properties can be expressed with an empirically found function after collecting angle-dependent light reflecting properties of the sample. We used this function and showed how prints with goniochromatic materials can be efficiently previewed on a computer monitor.