aqp (version 0.99-8.1)

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.

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

Examples

library(aqp)

# basic example:
d <- expand.grid(hue='10YR', value=2:8, chroma=1:8)
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:
d <- expand.grid(hue=c('5YR','7.5YR','10YR'), value=2:8, chroma=1:8)
d$hue <- factor(d$hue, levels=c('5YR','7.5YR','10YR'))
d$color <- with(d, munsell2rgb(hue, value, chroma))

xyplot(value ~ chroma | hue,
main="Common Soil Colors", layout=c(3,1), 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])
}
)

# 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)
}