Goal

I have a couple of icons (technically sRGB but mostly black-ish or white-ish with a transparent background). I want to change the color to darkblue (say).

My attempt

Input Pic

Code

library(magick)
pic <- image_read(file.path(system.file(package = "magick"), "images", "shape_rectangle.gif"))

## find dark spot and use `image_fill`

pixels <- pic |>
  image_data() |>
  as.integer()

(idx <- which(pixels[, , 3] == max(pixels[, , 3]), arr.ind = TRUE)[1, ])
# row col 
#  49  25 

image_fill(pic, "darkblue", "+49+25")

Result

Problem

While this approach works in this simple case, I am not happy with this “solution” for my real icons. The logos can consist of several “areas” and while I could fill all dark spots, this seems to be first of all a total overkill and I assume that there is a function more suitable for this task rather than flood filling the area.

In principle I want to do exactly the same in R as has been done on command line here: How to colorize a black-transparent PNG icon with ImageMagick

Example Logo