Colour description and quantification in mosaic images of soil thin sections

Abstract

Quantitative micromorphological approaches have been developed for a variety of purposes in recent years. This paper describes a methodology developed for contexts where the spatial distribution of a large number of small objects is of interpretative value, and where colour is a determining criteria of the object description. Such contexts include anthropic soils, particularly plaggen soils, and geoarchaeological settings where objects may be variable in size, in relative distribution, and in colour, but where advances in interpretation are made through the quantification of these factors. Two novel methodological steps developed for such contexts are described in this paper. First, an approach using Munsell colour terms within micromorphological description is detailed. For both transmitted and reflected illuminations, the conversion of machine analytical colours captured by a camera to Munsell values is demonstrated. Second, the production of mosaic images is considered. These images are contiguous and cover a large area of the microscope slide at high resolution. This paper describes the successful use of these methods in an anthropic soil context and in doing so, variation in section thickness, regardless of the illumination method adopted, emerges as critical, highlighting that quantitative image analysis of preexisting sets of thin-section slides should be restricted to intra-slide comparison.