Generates a Gimp palette based on HSL color space with a fixed saturation level

generate_gimp_palette.lua

local floor = math.floor
function round(x) return math.floor(x+0.5) end

do
  local function hue2rgb(p, q, t)
    if t < 0 then t = t + 1 end
    if t > 1 then t = t - 1 end
    if t < 1/6 then return p + (q - p) * 6 * t end
    if t < 1/2 then return q end
    if t < 2/3 then return p + (q - p) * (2/3 - t) * 6 end
    return p
  end

  --- HSL COLOR SPACE
  -- @param h Range 0 to 360
  -- @param s Range 0 to 1
  -- @param l Range 0 to 1
  -- @returns r, g, b
  function hsl2rgb(h, s, l)
    h = (h % 360.0) / 360.0
    if s == 0 then
      return round(l*255)
    else
      local q
      if l < 0.5 then q = l * (1 + s) else q = l + s - l * s end
      local p = 2 * l - q
      local r = hue2rgb(p, q, h + 1/3)
      local g = hue2rgb(p, q, h)
      local b = hue2rgb(p, q, h - 1/3)
      return round(r * 255), round(g * 255), round(b * 255)
    end
  end
end

out = io.stdout

local hsltab = {}
do
  local hue_config = {
    { hue =   0, saturation = 2/3, levels = { 1/8, 1/4, 3/8, 1/2, 5/8 } },
    { hue =  30, saturation = 2/3, levels = { 1/8, 1/4, 3/8, 1/2, 5/8 } },
    { hue =  60, saturation = 2/3, levels = { 1/8, 1/4, 3/8, 1/2, 5/8 } },
    { hue =  90, saturation = 2/3, levels = { 1/8, 1/4, 3/8, 1/2, 5/8 } },
    { hue = 120, saturation = 2/3, levels = { 1/8, 1/4, 3/8, 1/2, 5/8 } },
    { hue = 150, saturation = 2/3, levels = { 1/8, 1/4, 3/8, 1/2, 5/8 } },
    { hue = 180, saturation = 2/3, levels = { 1/8, 1/4, 3/8, 1/2, 5/8 } },
    { hue = 210, saturation = 2/3, levels = { 1/8, 1/4, 3/8, 1/2, 5/8 } },
    { hue = 240, saturation = 3/4, levels = { 1/8, 1/4, 3/8, 1/2, 5/8 } },
    { hue = 270, saturation = 2/3, levels = { 1/8, 1/4, 3/8, 1/2, 5/8 } },
    { hue = 300, saturation = 2/3, levels = { 1/8, 1/4, 3/8, 1/2, 5/8 } },
    { hue = 330, saturation = 2/3, levels = { 1/8, 1/4, 3/8, 1/2, 5/8 } }
  }
  for _, conf in ipairs(hue_config) do
    for _, l in ipairs(conf.levels) do
      local r, g, b = hsl2rgb(conf.hue, conf.saturation, l)
      hsltab[#hsltab+1] = {h=conf.hue, s=conf.saturation, l=l, r=r, g=g, b=b}
    end
  end
end

do
  local i = 1
  local N = #hsltab
  while i < N do
    local r1, b1, g1 = hsltab[i].r, hsltab[i].g, hsltab[i].b
    local j = i + 1
    while j <= N do
      local r2, b2, g2 = hsltab[j].r, hsltab[j].g, hsltab[j].b
      if r1==r2 and b1==b2 and g1==g2 then
        table.remove(hsltab, j)
        N = N - 1
      end
      j = j + 1
    end
    i = i + 1
  end
end

out:write("GIMP Palette\nName: HuePalSorted\nColumns: 5\n#\n")

for i, v in ipairs(hsltab) do
  out:write(string.format("%3i%4i%4i\tH%i S%i L%i\n", v.r, v.g, v.b, v.h, v.s*100, v.l*100))
end

for i = 0, 9 do
  local v = (i / 9.0) * 255.0
  out:write(string.format("%3i%4i%4i\tGRAY %i\n", v, v, v, v))
end

HuePalSorted.gpl

GIMP Palette
Name: HuePalSorted
Columns: 5
#
 53  11  11	H0 S66 L12
106  21  21	H0 S66 L25
159  32  32	H0 S66 L37
212  43  43	H0 S66 L50
223  96  96	H0 S66 L62
 53  32  11	H30 S66 L12
106  64  21	H30 S66 L25
159  96  32	H30 S66 L37
212 128  43	H30 S66 L50
223 159  96	H30 S66 L62
 53  53  11	H60 S66 L12
106 106  21	H60 S66 L25
159 159  32	H60 S66 L37
212 212  43	H60 S66 L50
223 223  96	H60 S66 L62
 32  53  11	H90 S66 L12
 64 106  21	H90 S66 L25
 96 159  32	H90 S66 L37
128 212  43	H90 S66 L50
159 223  96	H90 S66 L62
 11  53  11	H120 S66 L12
 21 106  21	H120 S66 L25
 32 159  32	H120 S66 L37
 43 212  43	H120 S66 L50
 96 223  96	H120 S66 L62
 11  53  32	H150 S66 L12
 21 106  64	H150 S66 L25
 32 159  96	H150 S66 L37
 43 212 128	H150 S66 L50
 96 223 159	H150 S66 L62
 11  53  53	H180 S66 L12
 21 106 106	H180 S66 L25
 32 159 159	H180 S66 L37
 43 212 212	H180 S66 L50
 96 223 223	H180 S66 L62
 11  32  53	H210 S66 L12
 21  64 106	H210 S66 L25
 32  96 159	H210 S66 L37
 43 127 212	H210 S66 L50
 96 159 223	H210 S66 L62
  8   8  56	H240 S75 L12
 16  16 112	H240 S75 L25
 24  24 167	H240 S75 L37
 32  32 223	H240 S75 L50
 88  88 231	H240 S75 L62
 32  11  53	H270 S66 L12
 64  21 106	H270 S66 L25
 96  32 159	H270 S66 L37
127  43 212	H270 S66 L50
159  96 223	H270 S66 L62
 53  11  53	H300 S66 L12
106  21 106	H300 S66 L25
159  32 159	H300 S66 L37
212  43 212	H300 S66 L50
223  96 223	H300 S66 L62
 53  11  32	H330 S66 L12
106  21  64	H330 S66 L25
159  32  96	H330 S66 L37
212  43 128	H330 S66 L50
223  96 159	H330 S66 L62
  0   0   0	GRAY 0
 28  28  28	GRAY 28
 56  56  56	GRAY 56
 85  85  85	GRAY 85
113 113 113	GRAY 113
141 141 141	GRAY 141
170 170 170	GRAY 170
198 198 198	GRAY 198
226 226 226	GRAY 226
255 255 255	GRAY 255