Contents

#!/usr/bin/env ruby -w
require 'rmagick'

# Demonstrate the Image#stegano method.

# Create a small watermark from the Snake image by
# shrinking it and converting it to B&W.
begin
  watermark = Magick::Image.read('images/Snake.wmf').first
  watermark.scale!(64.0 / watermark.rows)
  watermark = watermark.quantize(256, Magick::GRAYColorspace)
  wmrows = watermark.rows
  wmcols = watermark.columns

  # Read the image in which we'll hide the watermark.
  img = Magick::Image.read('images/Flower_Hat.jpg').first
  img.scale!(250.0 / img.rows)

  # Embed the watermark starting at offset 91.
  puts 'Embedding watermark...'
  stegano = img.stegano(watermark, 91)
  puts 'Watermark embedded'

  # Write the watermarked image in MIFF format. Note that
  # the format must be lossless - Image#stegano doesn't work
  # with lossy formats like JPEG.
  stegano.write('img.miff')

  # Read the image and retrieve the watermark. The size
  # attribute describes the size and offset of the watermark.

  # This can take some time. Keep track of how far along we are.

  monitor = proc do |_text, quantum, span|
    printf("Extracting watermark...%3.0f%% complete\n", ((1.0 - (quantum / span.to_f)) * 100.0))
    true
  end

  stegano = Magick::Image.read('stegano:img.miff') do
    self.size = Magick::Geometry.new(wmcols, wmrows, 91)
    self.monitor = monitor
  end

  stegano[0].monitor = nil

  # We don't need this any more.
  File.delete('img.miff')

  stegano[0].write('stegano.gif')
rescue Magick::ImageMagickError
  puts "#{$PROGRAM_NAME}: ImageMagickError - #{$ERROR_INFO}"
end

exit

Version data entries

2 entries across 2 versions & 1 rubygems

Version	Path
rmagick-3.1.0	doc/ex/stegano.rb
rmagick-3.0.0	doc/ex/stegano.rb