Convert sRGB values to CIE 1976 Lab*

Source: R/color.R

Converts gamma-encoded sRGB (IEC 61966-2-1) values in [0, 1] to CIELAB under the D65 reference white (CIE 15:2004).

srgb_to_lab(rgb)

Arguments

rgb

Numeric matrix with three columns (R, G, B) in [0, 1], or a H x W x 3 array.

Value

Same shape as the input, with channels L, a, b.

Details

Steps: (1) inverse sRGB companding to linear light, (2) linear RGB -> CIE XYZ with the sRGB/D65 primaries matrix, (3) XYZ -> \(L^*a^*b^*\) with the CIE cube-root function and its linear segment below \((6/29)^3\).

\(L^*\) (0 = black, 100 = diffuse white) is the perceptual lightness used by MycoHalo as the primary melanization readout; \(a^*\) (green-red) and \(b^*\) (blue-yellow) carry the chromatic information that separates achromatic melanized hyphae from warm-coloured bacteria, pigments and halos.

Examples

srgb_to_lab(rbind(c(1, 1, 1), c(0.5, 0.5, 0.5), c(0, 0, 0)))
#>              L             a            b
#> [1,] 100.00000 -1.666667e-05 6.666666e-06
#> [2,]  53.38897 -9.969678e-06 3.987871e-06
#> [3,]   0.00000  0.000000e+00 0.000000e+00