Recolor images using any palette

photo-palette.R

library(ggplot2)
library(patchwork)

# get photo
img <- magick::image_read("https://www.yan-holtz.com/img/team/YH_pic_square.png")

# retrieve lightness
c <- magick::image_channel(img)
img_df <- tibble::as_tibble(as.data.frame.table(drop(as.integer(c[[1]]))))
img_df <- dplyr::mutate(img_df, across(c(Var1, Var2), as.numeric))

# base plot
r <- 
  ggplot(img_df) +
  geom_raster(aes(x = Var2, y = Var1, fill = Freq)) +
  scale_y_reverse() +
  coord_fixed(expand = FALSE) +
  guides(fill = guide_colorbar(reverse = TRUE)) +
  theme_void(base_size = 12) +
  theme(
    legend.position = "top",
    legend.key.height = unit(.5, "lines"),
    legend.key.width = unit(2.2, "lines"),
    legend.title = element_blank(),
    legend.text = element_blank(),
    legend.ticks = element_blank(),
    legend.justification = "left",
    legend.box.margin = margin(3, 0, 0, 0),
    plot.margin = margin(rep(7, 4))
  )
  
# define breaks for nice legend
s <- seq(0, 255, length.out = 100)


## ggplot blues ---------------------------------------------------------------
r + scale_fill_gradient(breaks = s)

## viridis --------------------------------------------------------------------
r + scale_fill_viridis_c(breaks = s)

## colorbrewer ----------------------------------------------------------------
r + scale_fill_distiller(palette = "YlOrBr", breaks = s)