Towards Colour-Accurate Documentation of Anonymous Expressions

  • Adolfo Molada-Teba Department of Cartographic and Land Engineering, Higher Polytechnic School of Avila, University of Salamanca, Hornos Caleros 50, 05003, Ávila
  • Geert J. Verhoeven Ludwig Boltzmann Gesellschaft - LBI ArchPro, 1190 Vienna, Austria
Keywords: camera characterisation, CIE colour spaces, colorimetry, colour transformation, COOLPI, graffiti, image processing, Python, RAW photo


Colour is a powerful communication element in most forms of cultural heritage. This importance of colour notwithstanding, the documentation of cultural heritage typically captures the geometrical aspects and seldom the spectral dimensions of an artefact. This is partly because the science of colour (called colorimetry) is non-trivial. In addition, capturing accurate colour data with digital cameras remains challenging due to the operating principle of standard imaging sensors and the need for a stable and well-characterised illumination source. Despite these limitations, the heritage science project INDIGO made it one of its central aims to generate colour-accurate photos from graffiti captured with standard digital cameras in varying outdoor illumination conditions. This paper first discusses the importance of colour accuracy in graffiti documentation. Afterwards, the text details (in a non-mathematical manner) essential colorimetric and camera principles that underlie the generation of colour images from raw image sensor data. This in-depth coverage supports clarifying the main hurdles to accurate photo colours. Finally, the paper introduces the open-source COOLPI software resulting from this research. We are confident that COOLPI will benefit any other heritage documentation project, or any application where digital cameras play a fundamental role in acquiring correct colour values.

Author Biographies

Adolfo Molada-Teba, Department of Cartographic and Land Engineering, Higher Polytechnic School of Avila, University of Salamanca, Hornos Caleros 50, 05003, Ávila

Adolfo Molada-Tebar (°1975) is a researcher at the TIDOP group at Universidad de Salamanca (Spain). He studied Technical Surveying Engineer (1999), Engineer in Geodesy and Cartography (2013) and has a Master’s Degree in Geomatics Engineering and Geoinformation (2016) plus a PhD in Geomatics Engineering (2020), all from the Polytechnic University of Valencia (Spain). He has extensive surveying experience in civil engineering and the building sector. His professional achievements include teaching as a professor at the University Cardenal Herrera CEU of Valencia (2004-2013). His doctoral thesis focused on developing software for proper colour registration for documenting cultural heritage. In 2021-2022, Adolfo was part of project INDIGO and developed the COOLPI package for colour image processing. His research profile can be found at

Geert J. Verhoeven, Ludwig Boltzmann Gesellschaft - LBI ArchPro, 1190 Vienna, Austria

Geert J. Verhoeven (°1978) is a senior researcher in archaeology at the LBI AchPro and is currently leading the academic graffiti project INDIGO. He received his Master’s and PhD degrees from Ghent University (Belgium) in 2002 and 2009, respectively. Since 2010, Geert has been working on many 3D modelling, remote sensing and data visualisation topics at the LBI AchPro, a research institute of which he is currently the vice director. In September 2021, Geert took a deep dive into the colourful graffiti world through project INDIGO. His research output can be found at Verhoeven-2.

How to Cite
Molada-Teba, A., & Verhoeven, G. (2023). Towards Colour-Accurate Documentation of Anonymous Expressions. Document | Archive | Disseminate Graffiti-Scapes, 86 - 130.