CIECAM02

The model can be used to predict these appearance attributes or, with forward and reverse implementations for distinct viewing conditions, to compute corresponding colors.

[2] The inner circle is the stimulus, from which the tristimulus values should be measured in CIE XYZ using the 2° standard observer.

The outer circle is the background, reaching out to 10°, from which the relative luminance (Yb) need be measured.

If unknown, the adapting field can be assumed to have average reflectance ("gray world" assumption): LA = LW / 5.

Intermediate values can be calculated by:[5] where surround F is as defined above and LA is the adapting field luminance in cd/m2.

[1] In CIECAM02, the reference illuminant has equal energy Lwr = Mwr = Swr = 100) and the reference white is the perfect reflecting diffuser (i.e., unity reflectance, and Ywr = 100) hence: Furthermore, if the reference white in both illuminants have the Y tristimulus value (Ywr = Yw) then: After adaptation, the cone responses are converted to the Hunt–Pointer–Estévez space by going to XYZ and back:[5] Note that the matrix above, which was inherited from CIECAM97s,[7] has the unfortunate property that since 0.38971 + 0.68898 – 0.07868 = 1.00001, 1⃗ ≠ MH1⃗ and that consequently gray has non-zero chroma,[8] an issue which CAM16 aims to address.

[9] Finally, the response is compressed based on the generalized Michaelis–Menten equation (as depicted aside):[5] FL is the luminance level adaptation factor.

[3] The 4.5 factor accounts for the fact that there are fewer cones at shorter wavelengths (the eye is less sensitive to blue).

A more commonly-used derivative is the CAM02 Uniform Color Space (CAM02-UCS), an extension with tweaks to better match experimental data.

Specifically, both its achromatic response A and red-green correlate a can be matched to EMEG activity (entrainment), each with their own characteristic delay.