aqp (version 2.1.0)

spec2Munsell: Convert reflectance spectra to closest Munsell chip

Description

Convert reflectance spectra to closest Munsell chip

Usage

spec2Munsell(
  x,
  res = 10,
  convert = TRUE,
  SO = c("CIE1931", "CIE1964"),
  illuminant = c("D65", "F2"),
  ...
)

Value

output from col2Munsell()

Arguments

x

reflectance spectra, must range from 380nm to 730nm with resolution specified in res

res

spectra resolution in nm, typically 5nm or 10nm

convert

logical, convert sRGB coordinates to closest Munsell chip (see ?munsell)

SO

CIE standard observer: these are the color matching functions defined by CIE and used to represent "average" human color perception. CIE1931 is the 2 degree standard observer more useful for describing color perception over very small areas or at distance. CIE1964 is the 10 degree standard observer, used for most industrial color matching applications.

illuminant

CIE standard illuminants:

• D65 represents average daylight

• F2 represents typical fluorescent lighting

...

further arguments to col2Munsell()

Details

See the expanded tutorial for additional examples.

References

Marcus, R.T. (1998). The Measurement of Color. In K. Nassau (Ed.), Color for Science, Art, and Technology (pp. 32-96). North-Holland.

CIE Colorimetry – Part 1: CIE standard colorimetric observers. CIES014-1/E:2006 – ISO 11664-1:2007(E)

CIE. (n.d.). CIE 15:2004 Tables Data. Retrieved from https://law.resource.org/pub/us/cfr/ibr/003/cie.15.2004.tables.xls

Examples

# Munsell reference spectra
data("munsell.spectra.wide")

# convert to closest Munsell chip
# sRGB -> Munsell conversion via col2Munsell()
spec2Munsell(munsell.spectra.wide[, '10YR 3/3'])

# attempt several
cols <- c('10YR 6/2', '5YR 5/6', '10B 4/4', '5G 4/4', '2.5Y 8/2', '10YR 3/3', '7.5YR 2.5/2')

# most are exact or very close
z <- do.call(
  'rbind',
  lapply(cols, function(i) {
    spec2Munsell(munsell.spectra.wide[, i])  
  })
)

# format Munsell notation from pieces
z$m <- sprintf("%s %s/%s", z$hue, z$value, z$chroma)

# compare
colorContrastPlot(
  m1 = cols, 
  m2 = z$m, 
  labels = c('original', 'spectral\ninterpretation')
)

if (FALSE) {
if(requireNamespace("gower")) {
# mix colors, return spectra, convert to color
cols <- c('10YR 6/2', '5YR 5/6', '10B 4/4')
res <- mixMunsell(cols, keepMixedSpec = TRUE, mixingMethod = 'reference')

# note that they are slightly different
res$mixed
spec2Munsell(res$spec)

}
}