Table 2.

Relative frequencies and conditional relative frequencies of metameric pairs of surfaces in natural scenes, calculated with color-difference formula CIEDE2000,^{3, 27} adaptation model CMCCAT2000,²⁴ and nominal discrimination threshold ΔE^thr = 0.5^a

			Criterion degree of metamerism na
Illuminants	Scene	Estimate	0	1	2	3	4
25,000 K–4000 K	vegetated	unconditional	−3.58	−3.77	−4.16	−4.56	−4.95
			(0.42)	(0.34)	(0.36)	(0.43)	(0.50)
		conditional		−0.19	−0.59	−0.99	−1.37
				(0.14)	(0.28)	(0.45)	(0.60)
	nonvegetated	unconditional	−3.43	−3.71	−4.32	−4.80	−5.29
			(0.40)	(0.33)	(0.31)	(0.41)	(0.55)
		conditional		−0.28	−0.88	−1.37	−1.82
				(0.13)	(0.40)	(0.56)	(0.64)
4000 K–6500 K	vegetated	unconditional	−3.57	−3.91	−4.81	−5.78	−6.32
			(0.45)	(0.42)	(0.47)	(0.81)	(0.81)
		conditional		−0.34	−1.24	−2.11	−2.65
				(0.12)	(0.48)	(0.86)	(0.96)
	nonvegetated	unconditional	−3.39	−3.85	−5.02	−5.98	−6.63
			(0.41)	(0.37)	(0.52)	(0.74)	(0.60)
		conditional		−0.45	−1.63	−2.51	−3.13
				(0.16)	(0.66)	(0.83)	(0.69)
25,000 K–6500 K	vegetated	unconditional	−3.58	−3.91	−4.67	−5.36	−6.06
			(0.42)	(0.34)	(0.45)	(0.61)	(0.85)
		conditional		−0.34	−1.09	−1.80	−2.35
				(0.17)	(0.46)	(0.75)	(0.95)
	nonvegetated	unconditional	−3.43	−3.90	−5.01	−5.92	−6.48
			(0.40)	(0.32)	(0.55)	(0.74)	(0.62)
		conditional		−0.47	−1.55	−2.41	−2.97
				(0.16)	(0.59)	(0.85)	(0.77)

^aEntries show means (SDs) of log₁₀ relative frequency over 29 predominantly vegetated scenes and 21 predominantly nonvegetated scenes under successive daylight illuminants labeled by correlated color temperature. Number of pairs of surfaces sampled in each scene was 4,498,500. Entries for n = 0 are for pairs of surfaces with subthreshold color differences, i.e., ΔE < ΔE^thr, under the first illuminant and any color difference under the second illuminant; those for n = 1, …, 4 are for pairs of surfaces with ΔE < ΔE^thr under the first illuminant and suprathreshold color differences under the second illuminant, i.e., ΔE ≥ ΔE^thr, ΔE ≥ 2ΔE^thr, ΔE ≥ 3ΔE^thr, ΔE ≥ 4ΔE^thr, respectively. Conditional relative frequencies are not defined for n = 0. The observer was the CIE 1964 standard observer.3