New perspectives to use Munsell color charts with electronic devices

Abstract

This article considers the evolution of the use of the Munsell system for assessing soil color. In the 1920s, Munsell color disks were recommended for soil color measurement. Munsell soil color charts (MSCs) were introduced in the 1940s. In 1942, the American Standards Association recommended that spectrophotometers be used for quantitative measurements and the Munsell system be used only for the psychological characterization of color. Despite this recommendation, soil scientists have continued using MSCs to measure soil color semi-quantitatively.The utility of MSCs for color determination depends on three qualities: ambiguity, adequacy and reliability. Quantitative color was measured with a spectrophotometer. Chip colors were compared using the CIELAB color difference (ΔEab∗). To examine ambiguity, we calculated the ΔEab∗ for every possible MSC color chip pair. Considerable ambiguity was found; 60% of the chips had duplicates. Chips were considered duplicates if the color difference was barely perceptible visually (ΔEab∗ < 3).To investigate adequacy, the color difference between 161 soil samples and their closest MSC chips was calculated. Only 52% of the samples had ΔEab∗ < 3. This indicated that the color range of the MSC does not adequately cover the range of natural soil colors.To study the reliability of MSCs, an old and a new MSC were compared. The identically designated chips in the old and new MSC generally had color differences of less than 3. Only 16% had ΔEab∗ > 3. In addition, chips within a chart or even within a sheet can fade over time in a non-uniform way. On the 2.5Y sheet, a stable group of color chips (∼63%) occurred. This stable group consisted of the chips that were the least prone to discoloration (ΔEab∗ < 3).This study determined that the inadequacy and ambiguity of MSCs can be overcome by using MSCs in combination with flatbed scanners. MSCs can be used to calibrate flatbed scanners for the purpose of soil color measurement. A procedure is proposed. The procedure calibrates the scanner using 7 chips from the stable group of the 2.5Y sheet. This procedure enables the measurement of soil color inexpensively and efficiently. The high efficiency of the method was confirmed by testing the accuracy of the soil color determinations for 20 soil samples, covering a wide color range. The calibration procedure quadruples the precision of color estimation compared to solely using MSCs and results in soil color measurements close to those achievable with spectrophotometers.