Colour calibration and analysis of digital rock photographs

Matic Potočnik (2014) Colour calibration and analysis of digital rock photographs. EngD thesis.

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Abstract

In this diploma thesis, we have described the development of an application for colour correction and analysis of field and laboratory photographs in geology. The current methods used by geologists to determine the colour and colour coverage are expensive, time-consuming, and/or subjective. In this work, we present a method which will make such tasks simpler and more objective. First, we briefly overview the field of colour theory, focusing on the Munsell colour system, which has been used by geologists for decades as the standard for determining colour, and on colour spaces which we have used for colour correction and analysis, particularly CIE Lab, CIE XYZ, and sRGB. We present the colour calibration target Macbeth ColorChecker, and its newer model, the X-Rite ColorChecker Passport, which is more appropriate for terrain work. We describe an approach to detecting the ColorChecker colour target, using the ASIFT algorithm, and then we describe four algorithms for automatic colour correction of photographs using the ColorChecker colour target. Lastly, we present test results for the colour correction algorithms, and results of an experiment in which we have compared colour analysis performed using our application, with colour analysis performed by students of geology, who have used a comparative colour chart, the Munsell Rock-color Chart. In conclusion we have listed a few ideas and guidelines on how the application could be developed further in the future, and in which fields, besides geology, it might find its usefulness.

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