require 'chunky_png'

def go!
	Dir['*.png'].each do |img|
		write_alpha(img,img.sub('.png','-a.png'))
	end
end

def write_alpha(in_file,out_file)
	orig  = ChunkyPNG::Image.from_file(in_file)
	alpha = ChunkyPNG::Image.new(140,140, ChunkyPNG::Color::BLACK)
	orig.width.times do |x|
		orig.height.times do |y|
			a = ChunkyPNG::Color.a(orig[x,y])
			alpha[x,y] = ChunkyPNG::Color.rgba(a,a,a,255)
		end
	end
	alpha.save(out_file)
end

go!