Further information relating to examination of SPD Curves

TM-30 - Calculation Summary

The TM-30-15 standard metric is a two-measure system describing colour fidelity (R_f) and colour gamut (R_g), which are calculated based the state-of-the-art uniform colour space CAM02-UCS (CIECAM02), using a set of 99 real, color evaluation samples (CES) with colour space uniformity and spectral uniformity.

• Starting with the test SPD curve, find the chromaticity xy co-ordinates of the test source from its calculated CIE 1931 color space XYZ values, using the 2^° colour matching functions.
• Determine the correlated color temperature (CCT) of the test source and select the appropriate black body reference source. This is done using a new linear combination of blackbody and daylight spectra for CCTs in the range 4500–5500 K.
• All subsequent calculations are carried out using the 1964 10° color-matching functions.
• For the colour fidelity (R_f) metric, the CAM02-UCS colour coordinates of the CES under the reference and test illuminants are calculated, along with the resulting colour error for each CES. The arithmetic mean of the errors is determined to obtain an average error ΔE for the SPD and an intermediate fidelity score using: R_f' = 100 − k * ΔE.
• This value is then scaled between 0 an 100 using: R_f = 10 * ln exp ( R_f'/10 ) + 1
• For the colour gamut (Rg) metric, the (J', a', b') color coordinates of the test samples under the reference illuminant and test source are computed, using the same test SPD curve and reference illuminant, and grouped into 16 hue bins of equal width.
• In each bin we compute the average values of a' and b', resulting in 16-point polygons in the (a', b') plane for the reference and test samples.
• The relative gamut is then: R_g = 100 * A_test/A_ref, where A_test and A_ref are the areas of the test and reference polygons.
• This very brief description was taken from: A. David, P. Fini, K. Houser, Y. Ohno, M. Royer, K. Smet, M. Wei, and L. Whitehead, "Development of the IES method for evaluating the color rendition of light sources," Opt. Express 23, 15888-15906 (2015).