Quantitative Conversion of Soil Color from CIELAB to Munsell System
YUE Zhi-hui1, HUANG Qiang2, XIAO Li1, LI Jun1, HUANG Cheng-min1*
1. Department of Environmental Science and Engineering, Sichuan University, Chengdu 610065, China
2. State Key Laboratory of Networking and Switching Technology, Beijing University of Posts and Telecommunications, Beijing
Abstract：Color is one of the critical morphological features of soils, which can be used as a basic index or proxy to reveal numerous soil physical and chemical properties, processes and functions. Soil color is universally expressed by the Munsell color system, and detected by the visual sense through the match of soil samples with the soil standard charts. However, the errors and bias in soil color readily occur using the current method due to the constrain of the difference in individual vision and variation in optical environment. An objective, quantitative and rapid method to determine the soil Munsell color is urgent to be invented.Here, with the combination of color measurement using the colorimeter, automatic calculation and linear interpolation between the adjacent Value (V) isoplanes, a procedure for the conversion of CIE color to Munsell color was proposed to obtain the soil color conveniently, rapidly and precisely. This protocol includes: (1) CIELAB color values of the samples are measured by the colorimeter; and (2) the color coordinates and the Munsell V values are computed automatically with the program in Python language on a base of the knowledge of the conversion between CIE and Munsell color systems; and (3) the linear interpolation between the adjacent V isoplanes and color conversion chart are employed to assign the Munsell Hue (H) and Chroma (C). 419 color chips from Munsell Soil Color Chart of China and 22 soil and paleosol samples were used to validate the protocol. The Munsell H values of 12 chips using our procedure were different from those in Munsell Soil Color Chart of China, and the measured accuracy reached 97%. Meanwhile, the correlation coefficients in Munsell V and C between the measured values and standard values were 0.987 (p<0.001) and 0.976 (p<0.001), respectively, exhibiting a robust significance. For the soil and paleosol samples, the difference in Munsell H between the measured values using our protocol and judged by visual sense is least while a discrepancy in Munsell V and C occurs possibly because of the visual values affected by the visual sense and optical environment. Based on the previous literatures on transformation in soil color between CIE to Munsell color systems, we established a procedure, particularly in making a Python program in order to complete the automatic calculation from CIELAB to the color coordinates and the Munsell V values, and providing a new interpolation method to acquire the Munsell V and C values, to facilitate the rapid and applicable conversion of CIE color system to Munsell color system for soils.
[1] Fan Z S, Herrick J E, Saltzman R, et al. Soil Science Society of America Journal, 2017, 81: 1139.
[2] LIU Yan-de, WU Ming-ming, LI Yi-fan, et al(刘燕德, 吴明明, 李轶凡, 等). Spectroscopy and Spectral Analysis(光谱学与光谱分析), 2017, 37(8): 2424.
[3] HUANG Cheng-min, WANG Cheng-shan, HE Yu-rong, et al(黄成敏, 王成善, 何毓蓉, 等). Chinese Journal of Soil Science(土壤通报), 2004，(3): 251.
[4] Liedgren L, Hornberg G, Magnusson T, et al. Journal of Archaeological Science, 2017, 79: 62.
[5] Institute of Soil Science, Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences(中国科学院南京土壤研究所, 中国科学院西安光学精密机械研究所). New Standard Soil Color Chart of China(中国标准土壤色卡). Nanjing: Nanjing Press(南京：南京出版社), 1989.
[6] Munsell Color. Munsell Soil Color Chart—2009 revised ed. Michigan, USA: Munsell Color and X-Rite, 2013.
[7] JING Qi-cheng, JIAO Shu-lan, YU Bo-lin, et al(荆其诚, 焦书兰, 喻柏林, 等). Chromatics Theory(色度学). Beijing: Science Press(北京: 科学出版社), 1979.
[8] Kirillova N P, Vodyanitskii Y N, Sileva T M. Eurasian Soil Science, 2015, 48(5): 468.
[9] Mahyar F, Cheung V, Westland S. Coloration Technology, 2010, 126(1): 31.
[10] Rossel R A V, Minasny B, Roudier P, et al. Geoderma, 2006, 133(3): 320.
[11] YE Cheng, LIU Zhen, WU Guang-yuan(叶 程, 刘 真, 吴光远). Chinese Journal of Liquid Crystals and Displays(液晶与显示), 2016, 31(6): 626.
[12] Simon F T, Frost J A. Color Research & Application, 2010, 12(5): 256.
[13] XU Fu-shan, XU Hai-song, WANG Yong(徐芙姗, 徐海松, 王 勇). Acta Photonica Sinica(光子学报), 2007，(4): 650.
[14] Vodyanitskii Y N, Kirillova N P. Eurasian Soil Science, 2016, 49: 1259.
[15] CHEN Jian-ke, YUAN Da-gang, YAN Zhao-min, et al(陈剑科，袁大刚，晏昭敏，等). Acta Pedologica Sinica(土壤学报), 2019，56(1)：78.
[16] Stiglitz R, Mikhailova E, Post C, et al. Computers & Electronics in Agriculture, 2016, 121(C): 141.
[17] Rabenhorst M C, Schmehling A, Thompson J A, et al. Soil Science Society of America Journal, 2015, 79: 193.
