Add a tool to help split an image onto two pages

This is mostly for such things as world maps which span both the left and
right pages in an open book

2 files changed, 48 insertions, 0 deletions

diff --git a/Gemfile b/Gemfile
index f971301..ed581f0 100644
--- a/Gemfile
+++ b/Gemfile
@@ -6,4 +6,5 @@ gem "asciidoctor-epub3",
   git: "https://github.com/magentastripe/asciidoctor-epub3",
   branch: "magentastripe"
 gem "epubcheck-ruby"
+gem "mini_magick"
 gem "rghost"
diff --git a/script/image_splitter.rb b/script/image_splitter.rb
new file mode 100644
index 0000000..0add63c
--- /dev/null
+++ b/script/image_splitter.rb
@@ -0,0 +1,47 @@
+#!/usr/bin/env ruby
+
+require 'optparse'
+require 'mini_magick'
+
+image = nil
+left_out = nil
+right_out = nil
+
+# Parse and verify command-line arguments.
+parser = OptionParser.new do |opts|
+  opts.on("--input PATH") { |path| image = File.expand_path(path) }
+  opts.on("--left-out PATH") { |path| left_out = File.expand_path(path) }
+  opts.on("--right-out PATH") { |path| right_out = File.expand_path(path) }
+end
+parser.parse!(ARGV)
+
+if not image
+  $stderr.puts("FATAL: expected an image.")
+  exit 1
+end
+
+if not [left_out, right_out].all?
+  $stderr.puts("FATAL: expected L and R output images.")
+  exit 1
+end
+
+if not File.file?(image)
+  $stderr.puts("FATAL: no such file: #{image}")
+  exit 1
+end
+
+# Split the image into two halves.
+image_f = MiniMagick::Image.open(image)
+w, h = image_f.dimensions
+new_w = w/2
+$stderr.puts("Input image #{File.basename(image)} has dimensions #{w}x#{h}")
+$stderr.puts("Will create two images of size #{new_w}x#{h}")
+
+lefthand_crop = image_f.crop("#{new_w}x#{h}+0+0")
+lefthand_crop.write(left_out)
+
+# Need to open the original image twice in order to get back to the
+# "starting point."
+image_f = MiniMagick::Image.open(image)
+righthand_crop = image_f.crop("#{new_w}x#{h}+#{new_w}+0")
+righthand_crop.write(right_out)