imageScale: Make a color scale to accompany an image or other plot

In marchtaylor/sinkr: Collection of functions with emphasis on multivariate data analysis

Make a color scale to accompany an image or other plot

Description

The imageScale function is wrapper for image and accepts the same arguments. It converts a vector of values (z) to a vector of color levels. One must define the number of colors. The limits of the color scale ("zlim") or the break points for the color changes("breaks") can also be defined. When breaks and zlim are defined, breaks overrides zlim. All arguments are similar to those in the image function. Can be used together with layout or embedPlot to combine with other plots.

Usage

imageScale(
  z,
  zlim,
  col = hcl.colors(12, "YlOrRd", rev = TRUE),
  breaks,
  axis.pos = 1,
  add.axis = TRUE,
  xlim = NULL,
  ylim = NULL,
  ...
)

Arguments

z	A vector or matrix of values.
zlim	Limits of the color scale values.
col	Vector of color values (default is 12 colors from the heat.colors palette).
breaks	Break points for color changes. If breaks is specified then zlim is unused and the algorithm used follows cut, so intervals are closed on the right and open on the left except for the lowest interval which is closed at both ends.
axis.pos	Position of the axis (1=bottom, 2=left, 3=top, 4=right) (default = 1).
add.axis	Logical (TRUE/FALSE). Defines whether the axis is added (default: TRUE).
xlim	Limits for the x-axis.
ylim	Limits for the y-axis.
...	Additional graphical parameters to pass to the image function.

Examples

# Make color palettes
pal.1=colorRampPalette(c("green4", "orange", "red", "white"), space="rgb", bias=0.5)
pal.2=colorRampPalette(c("blue", "cyan", "yellow", "red", "pink"), space="rgb")

# Make images with corresponding scales
op <- par(no.readonly = TRUE)
layout(matrix(c(1,2,3,0,4,0), nrow=2, ncol=3), widths=c(4,4,1), heights=c(4,1))
#layout.show(4)
#1st image
breaks <- seq(min(volcano), max(volcano),length.out=100)
par(mar=c(1,1,1,1))
image(seq(dim(volcano)[1]), seq(dim(volcano)[2]), volcano, 
col=pal.1(length(breaks)-1), breaks=breaks-1e-8, xaxt="n", yaxt="n", ylab="", xlab="")
#Add additional graphics
levs <- pretty(range(volcano), 5)
contour(seq(dim(volcano)[1]), seq(dim(volcano)[2]), volcano, levels=levs, add=TRUE)
#Add scale
par(mar=c(3,1,0,1))
imageScale(volcano, col=pal.1(length(breaks)-1), breaks=breaks-1e-8,axis.pos=1)
abline(v=levs)
box()

#2nd image
breaks <- c(0,100, 150, 170, 190, 200)
par(mar=c(1,1,1,1))
image(seq(dim(volcano)[1]), seq(dim(volcano)[2]), volcano, 
  col=pal.2(length(breaks)-1), breaks=breaks-1e-8, xaxt="n", yaxt="n", ylab="", xlab="")
#Add additional graphics
levs=breaks
contour(seq(dim(volcano)[1]), seq(dim(volcano)[2]), volcano, levels=levs, add=TRUE)
#Add scale
par(mar=c(1,0,1,3))
imageScale(volcano, col=pal.2(length(breaks)-1), breaks=breaks-1e-8, 
  axis.pos=4, add.axis=FALSE)
axis(4,at=breaks, las=2)
box()
abline(h=levs)
par(op)

# examples of adding inside the plot region
op <- par(no.readonly = TRUE)
par(mar = c(1,1,1,1))
image(volcano, axes = FALSE, ylab="", xlab="")
box()
embedPlot(
  expr = expression({
    imageScale(volcano)
    mtext(text = "Elevation [m]", side = 1, line = 2)}), 
  at = c(0.5,0.98,0.15,0.2))
par(op)

op <- par(no.readonly = TRUE)
par(mar = c(1,1,1,1))
image(volcano, axes = FALSE, ylab="", xlab="")
box()
embedPlot(
  expr = expression({
    imageScale(volcano, axis.pos = 2)
    mtext(text = "Elevation [m]", side = 2, line = 2)}), 
  at = c(0.94,0.98,0.05,0.75))
par(op)

marchtaylor/sinkr documentation built on June 15, 2025, 1:17 a.m.