Development of reliably-distinguishable color legends for soil type maps based on calculation of the CIELAB color coordinates and differences

This MS Excel spreadsheet implements the procedure for calculating the CIELAB perceptually-uniform color attributes and color differences from the primary-defined RGB color coordinates. It may be used by map designers to obtain specific map legends comprising a large number of colors - all reliably-distinguishable from one another. The spreadsheet contains a starting list of 63 such colors – the Romanian color standard for soil type map legends (color-ordered, including lightness/chroma degrees, one color in a row). The CIELAB color attributes, color attribute differences and overall color difference are those defined by the CIELAB color model/space (CIE S 014-4:2007. Colorimetry - Part 4: CIE 1976 L*a*b* Colour space). This model/space represents a color by using three abstract coordinates (orthogonal axes): L* has values between 0 (black) and 100 (white), indicating the color lightness; a* has positive values indicating amounts of red, negative values indicating the amounts of green and the value zero indicating neutral grey; b* has positive values indicating amounts of yellow, negative values indicating the amounts of blue and the value zero indicating neutral grey. From these three coordinates, other important perceptually-uniform color attributes can be easily calculated: CIELAB chroma (C*ab), CIELAB hue angle (hab), CIELAB attribute differences (DL*, Da*, Db*, DC*ab, Dhab) and overall CIELAB color difference (DE*ab). The color differences calculated regarding a color are those between that color and the immediately-preceding color in the list. The list being color-ordered, the adjacent colors are normally the closest colors in the list, thus the color differences between them may be easily checked. Different other colors that appear as close in the list may be duplicated near others to see the color differences between them. The implemented calculation procedure consists of the following steps: (i) transformation of RGB coordinates to CIEXYZ coordinates, (ii) transformation of CIEXYZ coordinates to CIELAB coordinates (perceptually-uniform) and calculation of other CIELAB color attributes, and (iii) calculation of CIELAB color differences (perceptually-uniform). In order to obtain color lists (legends) appropriate for specific requirements, by using the "trial and error" method, the RGB coordinates (integer numbers between zero and 255) of the list colors can be easily modified/adjusted to define other colors that are reliably-distinguishable from one