Affordable Spectral Measurements of Translucent Materials

Abstract

We present a spectral measurement approach for the bulk optical properties of translucent materials using only low-cost components. We focus on the translucent inks used in full-color 3D printing, and develop a technique with a high spectral resolution, which is important for accurate color reproduction. We enable this by developing a new acquisition technique for the three unknown material parameters, namely, the absorption and scattering coefficients, and its phase function anisotropy factor, that only requires three point measurements with a spectrometer. In essence, our technique is based on us finding a three-dimensional appearance map, computed using Monte Carlo rendering, that allows the conversion between the three observables and the material parameters. Our measurement setup works without laboratory equipment or expensive optical components. We validate our results on a 3D printed color checker with various ink combinations. Our work paves a path for more accurate appearance modeling and fabrication even for low-budget environments or affordable embedding into other devices.

High-level overview

  1. Input: A thin material sample (solid, or liquid in a cuvette) is placed in a holder, and it is illuminated and measured with a spectrometer in three simple configurations:
    1) front diffuse illumination + black background,
    2) front diffuse illumination + white background,
    3) collimated beam from the back.
    All these steps only take a minute to measure, and are easy to setup and calibrate.
  2. Processing: We found and constructed a simple mapping between material appearance and its bulk optical properties. This mapping is generated in three dimensions, and is used to fit the material properties to the spectral intensities from the previous step.
  3. Output: The processing results in high-resolution spectrally resolved: single-scattering albedoextinction coefficient [mm-1], and phase function anisotropy. Or alternatively, absorption and scattering coefficients [mm-1]. These can be directly used as parameters in volumetric rendering and full-color 3D printing optimization pipelines.

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