addAlpha | R Documentation |
Takes a vector of colors and adds an alpha channel
at the given level of transparency. See also adjustcolor
.
addAlpha(COLORS, ALPHA)
COLORS |
Vector of any of the three kinds of R color specifications, i.e., either a color name (as listed by colors()), a hexadecimal string of the form "#rrggbb" or "#rrggbbaa" (see rgb), or a positive integer i meaning palette()[i]. |
ALPHA |
A value (between 0 and 1) indicating the alpha channel (opacity) value. |
# Make background image x <- seq(-180, 180, length.out=30) y <- seq(-90, 90, length.out=30) grd <- expand.grid(x=x,y=y) z <- sqrt(grd$x^2+grd$y^2) dim(z) <- c(length(x), length(y)) pal <- colorRampPalette(c(rgb(1,1,1), rgb(0,0,0))) COLORS <- pal(20) image(x,y,z, col=COLORS) # Add semi-transparent layer z2 <- grd$x^2+grd$y dim(z2) <- c(length(x), length(y)) pal <- colorRampPalette(c(rgb(0.5,1,0), rgb(0,1,1), rgb(1,1,1))) COLORS <- addAlpha(pal(20), 0.4) # alpha chanel equals 0.4 image(x,y,z2, col=COLORS, add=TRUE)
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