Small script to convert an image to printer commands, based on http://github.com/freerange/printer

convert_image_to_bytes.rb

#!/usr/bin/env ruby

# You should ensure that the `rmagick` and `a2_printer` gems are installed.

require "rubygems"
require "RMagick"
require "a2_printer"

if ARGV.length < 2
  puts "Usage: convert_image_to_bytes.rb <image_file> <output_file>"
  exit -1
end

image_file_name = ARGV[0]
output_file_name = ARGV[1]

# =========
#
# Firstly, get the pixels from an image.
# This code is roughly based on https://github.com/freerange/printer/blob/master/lib/jobs/image_to_bits.rb

# Use Ruby's wrapper around the ImageMagick library to get the image data
img = Magick::ImageList.new(image_file_name)[0]
width = img.columns
height = img.rows

# Read the pixels into an array, determining which should be black using the
# pixel 'intensity'.
pixels = []
white = (2**16)-1
limit = white / 2
img.each_pixel { |pixel, _, _| pixels << ((pixel.intensity < limit) ? 1 : 0) }

# ==========
#
# Next, convert that pixel array into the serial commands for a printer
# This code is roughly based on https://github.com/freerange/printer/blob/master/lib/print_processor/a2_raw.rb

printer_command_file = File.new(output_file_name, "w") # open the output file for writing
printer = A2Printer.new(printer_command_file)

# This roughly controls the darkness; for images with lots of black you will
# need to use less heat, otherwise I've found that the paper sticks. These little
# printers aren't great at printing lots and lots of black :-(
heat_time = 150
# printer.begin(heat_time)

# Convert the pixels into bytes (groups of 8 pixels)
bytes = []
pixels.each_slice(8) { |s| bytes << ("0" + s.join).to_i(2) }

# Use the A2Printer library to split the image data into chunks for us.
printer.print_bitmap(width, height, bytes)

# Feed enough paper to be able to nicely tear the paper
# printer.feed(3)

# Ensure that all the commands are written to the file, and close it.
printer_command_file.close