Module Convert.Perceptual

Convert RGB color to ANSI-256 color code (0-255).

Uses perceptual color matching in LAB space to find the nearest xterm-256 palette color (codes 16-255, excluding basic 16 colors).

  (* Convert orange to nearest xterm-256 color *)
  let orange = Gg.Color.v_srgb 1.0 0.5 0.0 in
  let code = Perceptual.rgb_to_ansi256 orange in
  Printf.printf "\027[38;5;%dm■\027[0m Orange is code %d\n" code code

  (* Find nearest color for a purple shade *)
  let purple = Gg.Color.v_srgb 0.6 0.2 0.8 in
  let code = Perceptual.rgb_to_ansi256 purple in
  Printf.printf "Purple maps to xterm-256 code: %d\n" code

  (* Convert multiple colors *)
  let colors = [
    ("red", Gg.Color.v_srgb 0.9 0.1 0.1);
    ("green", Gg.Color.v_srgb 0.1 0.9 0.1);
    ("blue", Gg.Color.v_srgb 0.1 0.1 0.9);
  ] in
  List.iter (fun (name, color) ->
      let code = Perceptual.rgb_to_ansi256 color in
      Printf.printf "%s -> %d\n" name code
    ) colors

• parameter grey_threshold

  Optional threshold for grey detection (currently unused)

• parameter color

  RGB color to convert

• returns

  ANSI-256 color code (16-255)

Convert RGB color to ANSI-16 basic color code (30-37, 90-97).

Uses perceptual color matching in LAB space to find the nearest of the 16 basic ANSI colors.

  (* Convert red to nearest basic color *)
  let red = Gg.Color.v_srgb 0.9 0.1 0.1 in
  let code = Perceptual.rgb_to_ansi16 red in
  Printf.printf "\027[%dm■\027[0m Red is code %d\n" code code
  (* Likely maps to bright red: code 91 *)

  (* Test basic vs bright color mapping *)
  let dark_green = Gg.Color.v_srgb 0.0 0.5 0.0 in
  let bright_green = Gg.Color.v_srgb 0.0 1.0 0.0 in

  let dark_code = Perceptual.rgb_to_ansi16 dark_green in
  let bright_code = Perceptual.rgb_to_ansi16 bright_green in

  Printf.printf "Dark green: %d, Bright green: %d\n"
    dark_code bright_code
  (* Dark: 32, Bright: 92 *)

  (* Quantize a gradient to basic colors *)
  for i = 0 to 10 do
    let intensity = float_of_int i /. 10. in
    let color = Gg.Color.v_srgb intensity 0.0 0.0 in
    let code = Perceptual.rgb_to_ansi16 color in
    Printf.printf "\027[%dm■\027[0m " code
  done;
  print_newline ()

• parameter color

  RGB color to convert

• returns

  ANSI-16 color code (30-37, 90-97)