image_modify_rgb: Modify R, G, B Values of an Image
In plothelper: New Plots Based on 'ggplot2' and Functions to Create Regular Shapes

The function modifies the R, G, B values of an image and is used in the same way as image_modify_hsv in this package. The three channels can be modified separately. The ways to modify include: setting values to some specified values (set_*), adding (add_*), multiplying the original values (mult_*), rescaling the original values (rescale_*), using a function to recompute values (fun_*). The most useful way is to use some internal curves that mimic those PS-like apps.

image_modify_rgb(
  x,
  set_r = NULL,
  add_r = NULL,
  mult_r = NULL,
  rescale_r = NULL,
  fun_r = NULL,
  set_g = NULL,
  add_g = NULL,
  mult_g = NULL,
  rescale_g = NULL,
  fun_g = NULL,
  set_b = NULL,
  add_b = NULL,
  mult_b = NULL,
  rescale_b = NULL,
  fun_b = NULL,
  result = "magick",
  res = 144
)

`x`	an image created by `magick::image_read` or other functions in package magick.
`set_r`	set r values with specific values.
`add_r`	add specific values to current R values.
`mult_r`	multiply the current values with specific values.
`rescale_r`	a length 2 numeric vector specifying the desired range of R values, e. g., `rescale_r = c(180, 240)` which will make the smallest original value to be 180, and the largest, 240. Alternatively, it can be your own scaling function.
`fun_r`	your own modifying function (e. g., `fun_r = sqrt`). Alternatively, it can be a list that designates how to use internal curves. See `image_modify_hsv`.
`set_g, add_g, mult_g, rescale_g, fun_g`	parameters to change G values. Used in the same way as those for R. See above.
`set_b, add_b, mult_b, rescale_b, fun_b`	parameters to change B values. Used in the same way as those for R. See above.
`result`	the default is "magick", the output is a magick picture. When it is "raster", a matrix is created which can be use as a raster for `ggplot2::annotation_raster`.
`res`	when the result is a magick picture, the `res` parameter used by `magick::image_graph`. Default is 144.