Two methods to transform primary chromaticities and white point into primary tristimulus values are examined and compared. One method appears in numerous places in the literature; we refer to this as the "familiar'' method, and provide a novel interpretation of it. The second is much less well-known and is referred to as the "unfamiliar'' method. Necessary and sufficient conditions for computing primary tristimulus values from their chromaticities are identified; in brief, the triangle in the (x,y) chromaticity diagram must have non-zero area. The computational burdens for the methods were compared; the familiar method required slightly more arithmetical operations. Two problems with the familiar method were identified: high potential for rounding error and the inability to contend with a non-luminous primary. The unfamiliar method is less prone to rounding error, and is able to contend with primaries on the alychne. It is recommended that the unfamiliar method be preferred.
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School of Photographic Arts and Sciences (CAD)
Viggiano, J A Stephen; Salvaggio, Nanette; and Sampat, Nitin, "Chromaticity Matrix to Tristimulus Matrix Conversion for RGB Color Spaces – Even In the Dark" (2018). Accessed from
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