hcl {grDevices}

HCL Color Specification

Description

Create a vector of colors from vectors specifying hue, chroma and luminance.

Usage

hcl(h = 0, c = 35, l = 85, alpha, fixup = TRUE)

Arguments

h

The hue of the color specified as an angle in the range [0,360]. 0 yields red, 120 yields green 240 yields blue, etc.

c

The chroma of the color. The upper bound for chroma depends on hue and luminance.

l

A value in the range [0,100] giving the luminance of the colour. For a given combination of hue and chroma, only a subset of this range is possible.

alpha

numeric vector of values in the range [0,1] for alpha transparency channel (0 means transparent and 1 means opaque).

fixup

a logical value which indicates whether the resulting RGB values should be corrected to ensure that a real color results. if fixup is FALSE RGB components lying outside the range [0,1] will result in an NA value.

Details

This function corresponds to polar coordinates in the CIE-LUV color space. Steps of equal size in this space correspond to approximately equal perceptual changes in color. Thus, hcl can be thought of as a perceptually based version of hsv.

The function is primarily intended as a way of computing colors for filling areas in plots where area corresponds to a numerical value (pie charts, bar charts, mosaic plots, histograms, etc). Choosing colors which have equal chroma and luminance provides a way of minimising the irradiation illusion which would otherwise produce a misleading impression of how large the areas are.

The default values of chroma and luminance make it possible to generate a full range of hues and have a relatively pleasant pastel appearance.

The RGB values produced by this function correspond to the sRGB color space used on most PC computer displays. There are other packages which provide more general color space facilities.

Semi-transparent colors (0 < alpha < 1) are supported only on some devices: see rgb.

Value

A vector of character strings which can be used as color specifications by R graphics functions.

Missing or infinite values of any of h, c, l result in NA: such values of alpha are taken as 1 (opaque).

Note

At present there is no guarantee that the colours rendered by R graphics devices will correspond to their sRGB description. It is planned to adopt sRGB as the standard R color description in future.

Author(s)

Ross Ihaka

References

Ihaka, R. (2003). Colour for Presentation Graphics, Proceedings of the 3rd International Workshop on Distributed Statistical Computing (DSC 2003), March 20-22, 2003, Technische Universität Wien, Vienna, Austria. https://www.R-project.org/conferences/DSC-2003/.

See Also

hsv, rgb.

Examples

require(graphics)

# The Foley and Van Dam PhD Data.
csd <- matrix(c( 4,2,4,6, 4,3,1,4, 4,7,7,1,
                 0,7,3,2, 4,5,3,2, 5,4,2,2,
                 3,1,3,0, 4,4,6,7, 1,10,8,7,
                 1,5,3,2, 1,5,2,1, 4,1,4,3,
                 0,3,0,6, 2,1,5,5), nrow = 4)

csphd <- function(colors)
  barplot(csd, col = colors, ylim = c(0,30),
          names.arg = 72:85, xlab = "Year", ylab = "Students",
          legend.text = c("Winter", "Spring", "Summer", "Fall"),
          main = "Computer Science PhD Graduates", las = 1)

# The Original (Metaphorical) Colors (Ouch!)
csphd(c("blue", "green", "yellow", "orange"))

# A Color Tetrad (Maximal Color Differences)
csphd(hcl(h = c(30, 120, 210, 300)))

# Same, but lighter and less colorful
# Turn off automatic correction to make sure
# that we have defined real colors.
csphd(hcl(h = c(30, 120, 210, 300),
          c = 20, l = 90, fixup = FALSE))

# Analogous Colors
# Good for those with red/green color confusion
csphd(hcl(h = seq(60, 240, by = 60)))

# Metaphorical Colors
csphd(hcl(h = seq(210, 60, length.out = 4)))

# Cool Colors
csphd(hcl(h = seq(120, 0, length.out = 4) + 150))

# Warm Colors
csphd(hcl(h = seq(120, 0, length.out = 4) - 30))

# Single Color
hist(stats::rnorm(1000), col = hcl(240))

## Exploring the hcl() color space {in its mapping to R's sRGB colors}:
demo(hclColors)