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Monitoring color alteration of ornamental flagstones using digital image analysis.

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  • Engineering
  • Computing & Technology :: Geological
  • Petroleum & Mining Engineering [C08]
  • Ingénierie
  • Informatique & Technologie :: Géologie
  • Ingénierie Du Pétrole & Des Mines [C08]
  • Chemistry
  • Design
  • Earth Science
  • Economics
  • Philosophy


1 INTRODUCTION The aim of this paper is to propose technical solu- tions and analytic methods for monitoring the color decay caused by weathering using digital image analysis. The mineralogy of three selected granites is first briefly described, followed by an overview of the complete testing protocol. The two main sections develop the calibration procedure for the imaging system and the image analysis methodology. Finally, the most significant results are presented and com- mented. A brief discussion about potential exten- sions of the proposed techniques and its limitations conclude the subject. The quantitative description of the behavior of ornamental stones submitted to natural or artificial weathering is a crucial challenge not only scientific but also economic. This is indeed one of the most important characteristics of these materials, deter- mining their field of use in the building market. Mineralogical or geochemical mechanisms of rock alteration have been widely studied (Delvigne 1998). Some works have been performed trying to quantify the degradation of mechanical and physical proper- ties (De Cleene 1995), but very little information is available about the aesthetic alteration of stones after weathering. However, from the consumer’s point of view, this aesthetic point of view is probably the most important one. For example, any deviation, even slight, in the predominant color of adjacent tiles in a paving badly affects the aesthetic of the work as a whole by emphasizing the color disconti- nuity induced by the cement joints. Of course, standard colorimeters or spectropho- tometers are available for quantitative measurements of color. But both devices integrate very limited fields of investigation (typically = 1cm²). They are thus largely irrelevant for monitoring color varia- tions in textured materials like granites. The idea of using digital image analysis to charac- terize or control the quality of ornamental stones (Muge et al. 1997) or ce

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