PyCoupole

GPU-accelerated Monte Carlo uncertainty quantification for SVBRDF measurements on the La Coupole setup. Companion code to the associated Optics Express paper and measured dataset.

Installation

Simply install it from PyPI:

pip install pycoupole

Interpreting the output

computeBRDFDistribution returns a probability density, not a histogram of counts. The density carries the inverse unit of the BRDF (sr), and integrates to 1 over its support — so its values are not bounded by 1 and will be large for a sharply peaked distribution. Recover the per-bin probability mass, then the moments and credible intervals, as:

binWidth = brdfValues[1] - brdfValues[0]
mass     = pdf * binWidth                    # sums to 1

mean   = float(np.sum(mass * brdfValues))
std    = float(np.sqrt(np.sum(mass * (brdfValues - mean) ** 2)))

cdf      = np.cumsum(mass)
median   = float(np.interp(0.50,  cdf, brdfValues))
ci95_low = float(np.interp(0.025, cdf, brdfValues))
ci95_up  = float(np.interp(0.975, cdf, brdfValues))

For a well-conditioned acquisition the deterministic value sits near the centre of the distribution and the out-of-range fraction (1 - nbAccepted / nbTotal) is negligible.

Citation

If you use this software, please cite the associated paper as below (see also CITATION.cff).

La Coupole: an SVBRDF measurement device for large and non-planar objects. Antoine Lucat, Pierre Mézières, François Margall, Louis De Oliveira, Marjorie Paillet, Arnaud Tizon, Pierre Bénard, Romain Pacanowski. Optics Express, Vol. 34, Issue 7, pp. 11695-11709 (March 2026). DOI: 10.1364/OE.587877.

@article{Lucat:26,
  author    = {Antoine Lucat and Pierre M\'{e}zi\`{e}res and Fran\c{c}ois Margall and Louis De Oliveira and Marjorie Paillet and Arnaud Tizon and Pierre B\'{e}nard and Romain Pacanowski},
  journal   = {Optics Express},
  keywords  = {Camera calibration; Imaging systems; Light sources; Physiology; Printed circuit boards; Spatial resolution},
  number    = {7},
  pages     = {11695--11709},
  publisher = {Optica Publishing Group},
  title     = {La Coupole: an SVBRDF measurement device for large and non-planar objects},
  volume    = {34},
  month     = {Apr},
  year      = {2026},
  url       = {https://opg.optica.org/oe/abstract.cfm?URI=oe-34-7-11695},
  doi       = {10.1364/OE.587877},
}

License

PyCoupole is distributed under the MIT License. See LICENSE.txt for more information.