make-averages.rb

#!/usr/bin/env ruby


# Assumes you have ImageMagick installed 

class MakeAverages

  def initialize base_name, ext, grouping, prefix = 'avg_'
    @base_name = base_name
    @ext = ext
    @grouping = grouping.to_i
    @prefix = prefix
  end

  def run
    images = Dir.glob("#{@base_name}*.#{@ext}").sort

    if images.size == 0
      raise "Faled to find any images matching '#{@base_name}*.#{@ext}'"
    end

    images.each_with_index do |img, idx|
      set = images[idx...(idx+@grouping)]

      if set.size < @grouping 
        warn 'Out of images!'
        return
      end

      new_file = "#{@prefix}#{@base_name}.#{idx.to_s.rjust 4, '0'}.#{@ext}"

      cmd = "convert #{set.join ' '} -evaluate-sequence mean  #{new_file}"
      puts cmd
      warn `#{cmd}`
    end
  end
end

if __FILE__ == $0
  if ARGV.size < 3
    puts "usage: #{__FILE__}  base_name, file_extension, grouping_number"
    exit
  end

  ai = MakeAverages.new  *ARGV
  ai.run
end