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Transform colors to grayscale

Source: R/greyscale.R
clr_grayscale.Rd

clr_grayscale() has a selection of different methods to turn colors into grayscale.

Usage

clr_grayscale(
  col,
  method = c("luma", "averaging", "min_decomp", "max_decomp", "red_channel",
    "green_channel", "blue_channel")
)

clr_greyscale(
  col,
  method = c("luma", "averaging", "min_decomp", "max_decomp", "red_channel",
    "green_channel", "blue_channel")
)

Source

https://tannerhelland.com/3643/grayscale-image-algorithm-vb6/

https://en.wikipedia.org/wiki/Luma

Arguments

col

A colors object (see color()) or a vector of any of the three kinds of R color specifications, i.e., either a color name (as listed by grDevices::colors()), a hexadecimal string (see col2rgb()), or a positive integer i meaning grDevices::palette()[i].

method

A character string specifying the grayscaling method. Can be one of "luma", "averaging", "min_decomp", "max_decomp", "red_channel", "green_channel" and "blue_channel". Defaults to "luma".

Value

A colors object of the same length as col.

Details

If method = "averaging" then the red, green and blue will be averaged together to create the grey value. This method does a poor job of representing the way the human eye sees color. If method = "luma" (the default), a weighted average is used to calculate the grayscale values. The BT. 709 method from the ITU Radiocommunication Sector have determined the weights. If method is "min_decomp" or "max_decomp", then a decomposition method is used where the minimum or maximum color value have been selected for the color value. So the color rgb(60, 120, 40) would have the "min_decomp" value of 40 and "max_decomp" value of 120. If method is "red_channel", "green_channel" or "blue_channel", then the corresponding color channel will be selected for the values of grayscale.

Examples


plot(clr_grayscale(rainbow(10)))


plot(clr_grayscale(terrain.colors(10)))


viridis_colors <- c(
  "#4B0055FF", "#422C70FF", "#185086FF", "#007094FF",
  "#008E98FF", "#00A890FF", "#00BE7DFF", "#6CD05EFF",
  "#BBDD38FF", "#FDE333FF"
)

plot(clr_grayscale(viridis_colors, method = "luma"))

plot(clr_grayscale(viridis_colors, method = "averaging"))

plot(clr_grayscale(viridis_colors, method = "min_decomp"))

plot(clr_grayscale(viridis_colors, method = "max_decomp"))

plot(clr_grayscale(viridis_colors, method = "red_channel"))

plot(clr_grayscale(viridis_colors, method = "green_channel"))

plot(clr_grayscale(viridis_colors, method = "blue_channel"))