Transform back from colors to values

Transform back from colors to values

col2value(r, g, b, col_fun)

Arguments

r	red channel in sRGB color space, value should be between 0 and 1. The r, g and b argumentc can be wrapped into one variable which is either a three-column matrix or a vector of colors.
g	green channel in sRGB color space, value should be between 0 and 1.
b	blue channel in sRGB color space, value should be between 0 and 1.
col_fun	the color mapping function generated by colorRamp2.

Details

colorRamp2 transforms values to colors and this function does the reversed job. Note for some color spaces, it cannot transform back to the original value perfectly.

Value

A vector of original numeric values.

Examples

x = seq(0, 1, length = 11)
col_fun = colorRamp2(c(0, 0.5, 1), c("blue", "white", "red"))
col = col_fun(x)
col2value(col, col_fun = col_fun)
#>  [1] 0.0000000 0.1011984 0.2025821 0.3036648 0.4024652 0.5000000 0.5898071
#>  [8] 0.6857470 0.7876882 0.8938379 1.0000000
col2value("red", col_fun = col_fun)
#> [1] 1

col_fun = colorRamp2(c(0, 0.5, 1), c("blue", "white", "red"), space = "sRGB")
col = col_fun(x)
col2value(col, col_fun = col_fun)
#>  [1] 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0