R help - Aug 2025 - grDevices- Feature proposal: color interpolation in color spaces of convertColor

Hi,

I needed to interpolate in the CIE XYZ color space, but the default 
colorRamp function does not exploit the color spaces available in 
colorConvert function. Please find below a few changes to colorRamp that 
permits to extend the choice of color spaces.

Best,
Samuel

colorRamp <- function(
 ??? colors, bias = 1,
 ??? space = c("rgb","Lab", "XYZ", "Apple
RGB", "CIE RGB", "Luv"),
 ??? interpolate = c("linear","spline"), alpha = FALSE)
{
 ? if (bias <= 0) stop("'bias' must be positive")
 ? if (!missing(space) && alpha)
 ??? stop("'alpha' must be false if 'space' is
specified")

 ? colors <- t(col2rgb(colors, alpha = alpha)/255)
 ? space <- match.arg(space)
 ? interpolate <- match.arg(interpolate)

 ? if (space != "rgb")
 ??? colors <- convertColor(colors, from = "sRGB", to = space)

 ? interpolate <- switch(interpolate,
 ??????????????????????? linear = stats::approxfun,
 ??????????????????????? spline = stats::splinefun)

 ? if((nc <- nrow(colors)) == 1L) {
 ??? colors <- colors[c(1L, 1L) ,]
 ??? nc <- 2L
 ? }
 ? x <- seq.int(0, 1, length.out = nc)^bias
 ? palette <- c(interpolate(x, colors[, 1L]),
 ?????????????? interpolate(x, colors[, 2L]),
 ?????????????? interpolate(x, colors[, 3L]),
 ?????????????? if(alpha) interpolate(x, colors[, 4L]))

 ? roundcolor <- function(rgb) ## careful to preserve matrix:
 ??? pmax(pmin(rgb, 1), 0)

 ? if (space != "rgb")
 ??? function(x)
 ????? roundcolor(convertColor(cbind(palette[[1L]](x),
 ??????????????????????????????????? palette[[2L]](x),
 ??????????????????????????????????? palette[[3L]](x),
 ??????????????????????????????????? if(alpha) palette[[4L]](x)),
 ????????????????????????????? from = space, to = "sRGB"))*255
 ? else
 ??? function(x)
 ????? roundcolor(cbind(palette[[1L]](x),
 ?????????????????????? palette[[2L]](x),
 ?????????????????????? palette[[3L]](x),
 ?????????????????????? if(alpha) palette[[4L]](x)))*255
}