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Use HSP for RGB-to-BW8 conversion

This commit is contained in:
Nils Dagsson Moskopp 2022-05-15 19:54:53 +02:00
parent 5b79bc6fb7
commit 2112637faf
Signed by untrusted user who does not match committer: erle
GPG Key ID: A3BC671C35191080
1 changed files with 8 additions and 4 deletions
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12
init.lua
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@ -107,11 +107,15 @@ function image:encode_data_r8g8b8_to_bw8_raw()
local raw_pixels = {} local raw_pixels = {}
for _, row in ipairs(self.pixels) do for _, row in ipairs(self.pixels) do
for _, pixel in ipairs(row) do for _, pixel in ipairs(row) do
-- see <https://alienryderflex.com/saturation.html> -- the HSP RGB to brightness formula is
-- sqrt( 0.299 r² + .587 g² + .114 b² )
-- see <https://alienryderflex.com/hsp.html>
local gray = math.floor( local gray = math.floor(
0.299 * pixel[1] + math.sqrt(
0.587 * pixel[2] + 0.299 * pixel[1]^2 +
0.114 * pixel[3] 0.587 * pixel[2]^2 +
0.114 * pixel[3]^2
) + 0.5
) )
local raw_pixel = string.char(gray) local raw_pixel = string.char(gray)
raw_pixels[#raw_pixels + 1] = raw_pixel raw_pixels[#raw_pixels + 1] = raw_pixel