Aegisub/OverLua/docs/rgb2hsl.lua

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--- Convert RGB colour to HSL (hue/saturation/luminance)
-- The output image will have H instead of R,
-- S instead of G and L instead of B.
function render_frame(f, t)
local w, h = f.width, f.height
for y = 0, h-1 do
for x = 0, w-1 do
local r, g, b = f(x, y)
local h, s, l = RGB2HSL(r, g, b)
f[y*w+x] = {h, s, l}
end
end
end
function clip_colorval(v)
if v < 0 then
return 0
elseif v > 255 then
return 255
else
return math.floor(v)
end
end
function RGB2HSL(R, G, B)
local r, g, b = R/255, G/255, B/255
local h, s, l
local minrgb, maxrgb = math.min(r, math.min(g, b)), math.max(r, math.max(g, b))
l = (minrgb + maxrgb) / 2
if minrgb == maxrgb then
h, s = 0, 0
else
if l < 0.5 then
s = (maxrgb - minrgb) / (maxrgb + minrgb)
else
s = (maxrgb - minrgb) / (2 - maxrgb - minrgb)
end
if r == maxrgb then
h = (g - b) / (maxrgb - minrgb) + 0
elseif g == maxrgb then
h = (b - r) / (maxrgb - minrgb) + 2
else
h = (r - g) / (maxrgb - minrgb) + 4
end
end
if h < 0 then h = h + 6 end
if h >= 6 then h = h - 6 end
return clip_colorval(h*255/6), clip_colorval(s*255), clip_colorval(l*255)
end