extractchannels.rb

require 'chunky_png'
require 'Base64'

image = ChunkyPNG::Image.from_file('source.png')

alph = image.to_alpha_channel_stream
red = image.to_rgb_stream.unpack('axx'*(image.to_rgb_stream.length/3)).join
green = image.to_rgb_stream.unpack('xax'*(image.to_rgb_stream.length/3)).join
blue = image.to_rgb_stream.unpack('xxa'*(image.to_rgb_stream.length/3)).join

IO.binwrite("Alpha.raw",alph)
IO.binwrite("Red.raw",red)
IO.binwrite("Green.raw",green)
IO.binwrite("Blue.raw",blue)