aqp (version 1.4)

munsell2rgb: Convert Munsell Notation to RGB

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)

Arguments

the_hue

a vector of one or more more hues, upper-case

the_value

a vector of one or more values

the_chroma

a vector of one or more chromas

alpha

alpha channel value (for transparency effects)

maxColorValue

maximum RGB color value (see rgb)

return_triplets

should the function return raw RGB triplets instead of an R color

Value

• A vector of R colors is returned that is the same length as the input data. If return_triplets is TRUE, then a dataframe (of sample length as input) of r,g,b values is returned.

Warning

As of plyr 1.6 (CRAN), there are cases when this function will fail (https://github.com/hadley/plyr/issues/43). The next version of plyr should address this problem. Until then, be sure not to pass in Munsell (hue, value, chroma) as factors.

Details

This function generalizes to vectorized usage, as long as the length of each argument is the same.

References

http://casoilresource.lawr.ucdavis.edu/drupal/node/201 http://www.brucelindbloom.com/index.html?ColorCalcHelp.html http://www.cis.rit.edu/mcsl/online/munsell.php

Examples

# basic example: no factors!
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)

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


# 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])
}
)

# try again, this time annotate with LAB coordinates:
if(require(colorspace))
  {
  d.rgb <- with(d, munsell2rgb(hue, value, chroma, return_triplets=TRUE))
  d.lab <- as(with(d.rgb, RGB(r,g,b)), 'LAB')
  d <- data.frame(d, d.lab@coords)
  
  xyplot(value ~ factor(chroma) | factor(hue, levels=hues),
  main="Common Soil Colors - Annotated with LAB Coordinates", 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=7, col=d$color[subscripts])
    lab.text <- with(d[subscripts, ], paste(round(L), round(A), round(B), sep=''))
    panel.text(x, y, labels=lab.text, cex=0.75, col='white', font=2)
    }
  )
  
  # also demonstrate A ~ hue for each slice of chroma
  xyplot(A ~ factor(hue, levels=hues) | factor(value), groups=chroma, data=d,
  scales=list(alternating=1), strip=strip.custom(bg=grey(0.85)),
  main="A-coordinate vs. Munsell Hue", sub='panels are Munsell value, colors are Munsell chroma',
  xlab='Munsell Hue', ylab='A-coordinate', pch=16,
  type='b', as.table=TRUE, auto.key=list(lines=TRUE, points=FALSE, columns=4))
  
  }



# soils example
data(sp1)

# convert colors
sp1$soil_color <- with(sp1, munsell2rgb(hue, value, chroma))

# simple plot, may need to tweak gamma-correction...
image(matrix(1:nrow(sp1)), axes=FALSE, col=sp1$soil_color, main='Soil Colors')

# convert into a more useful color space
# you will need the colorspace package for this to work
if(require(colorspace))
{
# keep RGB triplets from conversion
sp1.rgb <- with(sp1, munsell2rgb(hue, value, chroma, return_triplets=TRUE))

# convert into LAB color space
sp1.lab <- as(with(sp1.rgb, RGB(r,g,b)), 'LAB')
plot(sp1.lab)
}