aqp (version 2.1.0)

munsell2rgb: Convert Munsell Color Notation to other Color Space Coordinates (sRGB and CIELAB)

Description

Color conversion based on a look-up table of common soil colors.

Usage

munsell2rgb(
  the_hue,
  the_value,
  the_chroma,
  alpha = 1,
  maxColorValue = 1,
  return_triplets = FALSE,
  returnLAB = FALSE
)

Value

A vector of R colors is returned that is the same length as the input data. When return_triplets = TRUE and/or returnLAB = TRUE, then a data.frame (of sample length as input) is returned.

Arguments

the_hue

a vector of one or more more hues, upper-case (e.g. '10YR')

the_value

a vector of one or more values (e.g. '4')

the_chroma

a vector of one or more chromas (e.g. '6'), may be NA for neutral hues

alpha

numeric, transparency setting used when return_triplets = FALSE and returnLAB = FALSE

maxColorValue

maximum sRGB color value, typically 1 (see rgb)

return_triplets

logical, return sRGB coordinates (range 0-1) instead of standard hex notation of sRGB (e.g. '#8080B')

returnLAB

logical, return CIELAB coordinates (D65 illuminant)

Author

D.E. Beaudette

Details

This function is vectorized without recycling: i.e. the length of each argument must be the same. Both functions will pad output with NA if there are any NA present in the inputs.

Neutral hues are approximated by greyscale shades ranging from 20\

Gley soil colors that are missing a chroma will not be correctly interpreted. Consider using a chroma of 1. Non-standard Munsell notation (e.g. '7.9YR 2.7/2.0') can be matched (nearest-neighbor, no interpolation) to the closest color within the munsell sRGB/CIELAB look-up table via getClosestMunsellChip(). A more accurate estimate of sRGB values from non-standard notation can be achieved with the munsellinterpol package.

See examples below.

References

• http://www.brucelindbloom.com/index.html?ColorCalcHelp.html

• https://www.munsellcolourscienceforpainters.com/MunsellAndKubelkaMunkToolbox/MunsellAndKubelkaMunkToolbox.html

• https://www.rit.edu/science/munsell-color-lab

Examples

# neutral hues (N) can be defined with chroma of 0 or NA 
g <- expand.grid(hue='N', value = 2:8, chroma = 0, stringsAsFactors = FALSE)
(m <- munsell2rgb(g$hue, g$value, g$chroma))
soilPalette(m)

# back-transform to Munsell notation
col2Munsell(t(col2rgb(m)) / 255)


# basic example
d <- expand.grid(hue = '10YR', value = 2:8, chroma = 1:8, stringsAsFactors = FALSE)
d$color <- with(d, munsell2rgb(hue, value, chroma))

# similar to the 10YR color book page
plot(value ~ chroma, data = d, col = d$color, pch = 15, cex = 3, las = 1)

# multiple pages of hue:
hues <- c('2.5YR', '5YR', '7.5YR', '10YR')
d <- expand.grid(
  hue = hues, 
  value = c(2, 2.5, 3:8), 
  chroma = seq(2, 8, by = 2), 
  stringsAsFactors = FALSE
)
# convert Munsell -> sRGB
d$color <- with(d, munsell2rgb(hue, value, chroma))

# extract CIELAB coordinates
with(d, munsell2rgb(hue, value, chroma, returnLAB = TRUE))

# plot: note that we are setting panel order from red --> yellow
library(lattice)
xyplot(
  value ~ factor(chroma) | factor(hue, levels = hues),
  main = "Common Soil Colors", layout = c(4, 1), scales = list(alternating = 1),
  strip = strip.custom(bg = grey(0.85)),
  data = d, as.table = TRUE, subscripts = TRUE, 
  xlab = 'Chroma', ylab = 'Value',
  panel = function(x, y, subscripts, ...) {
    panel.xyplot(x, y, pch = 15, cex = 4, col = d$color[subscripts])
  }
)



# convert a non-standard color to closest "chip" in `munsell` look-up table
getClosestMunsellChip('7.9YR 2.7/2.0', convertColors = FALSE)

# convert directly to hex notation of sRGB
getClosestMunsellChip('7.9YR 2.7/2.0')