Convert a palette .png (num of colours x 1 pixel) to appropriate grayscaled palette (for colour swap shader)

convert-to-grayscale.lua

function love.load()
	for k, file in pairs(love.filesystem.getDirectoryItems("source")) do
		convert(file)
	end
end

function convert(file)
	local data = love.image.newImageData("source/" .. file)
	local width = data:getWidth()
	local div = 255/width

	for i = 0, width - 1 do
		local v = div * (i + 0.5)/255
		data:setPixel(i, 0, v, v, v, 1)
	end
	local file = data:encode("png", file)
end