pal.compress: Compress a colormap function to fewer colors

In pals: Color Palettes, Colormaps, and Tools to Evaluate Them

Compress a colormap function to fewer colors

Description

Compress a colormap function to fewer colors

Usage

pal.compress(pal, n = 5, thresh = 2.5)

Arguments

pal	A colormap function or a vector of colors.
n	Initial number of colors to use for the basis.
thresh	Maximum allowable Lab distance from original palette

Details

Colormap functions are often defined with many more colors than needed. This function compresses a colormap function down to a sample of colors that can be passed into 'colorRampPalette' and re-create the original palette with a just-noticeable-difference.

Colormaps that are defined as a smoothly varying ramp between a set of colors often compress quite well. Colormaps that are defined by functions may not compress well.

Value

A vector of equally-spaced colors that form the 'basis' of a colormap.

Author(s)

Kevin Wright

References

None.

Examples

# The 'cm.colors' palette in R compresses to only 3 colors
cm2 <- pal.compress(cm.colors, n=3)
pal.bands(cm.colors(255), colorRampPalette(cm2)(255), cm2,
labels=c('original','compressed','basis'), main="cm.colors")

# The 'heat.colors' palette needs 84 colors
heat2 <- pal.compress(heat.colors, n=3)
pal.bands(heat.colors(255), colorRampPalette(heat2)(255), heat2,
labels=c('original','compressed','basis'), main="heat.colors")

# The 'topo.colors' palette needs 249 colors because of the discontinuity
# topo2 <- pal.compress(topo.colors, n=3)
# pal.bands(topo.colors(255), colorRampPalette(topo2)(255), topo2,
# labels=c('original','compressed','basis'), main="topo.colors")

# smooth palettes usually easy to compress
p1 <- coolwarm(255)
cool2 <- pal.compress(coolwarm)
p2 <- colorRampPalette(cool2)(255)
pal.bands(p1, p2, cool2,
labels=c('original','compressed', 'basis'), main="coolwarm")
pal.maxdist(p1,p2) # 2.33
 

pals documentation built on Sept. 11, 2024, 5:28 p.m.