$ ruby gradient.rb
/home/railsdev1/.rvm/gems/ruby-1.9.3-p385@default/gems/imageruby-0.2.3/lib/imageruby/pureruby.rb:156:in <': comparison of String with 255 failed (ArgumentError) from /home/railsdev1/.rvm/gems/ruby-1.9.3-p385@default/gems/imageruby-0.2.3/lib/imageruby/pureruby.rb:156:inblock (2 levels) in draw!'
from /home/railsdev1/.rvm/gems/ruby-1.9.3-p385@default/gems/imageruby-0.2.3/lib/imageruby/pureruby.rb:151:in each' from /home/railsdev1/.rvm/gems/ruby-1.9.3-p385@default/gems/imageruby-0.2.3/lib/imageruby/pureruby.rb:151:inblock in draw!'
from /home/railsdev1/.rvm/gems/ruby-1.9.3-p385@default/gems/imageruby-0.2.3/lib/imageruby/pureruby.rb:145:in each' from /home/railsdev1/.rvm/gems/ruby-1.9.3-p385@default/gems/imageruby-0.2.3/lib/imageruby/pureruby.rb:145:indraw!'
from gradient.rb:27:in block in <main>' from gradient.rb:26:ineach'
from gradient.rb:26:in `'
$ ruby gradient.rb /home/railsdev1/.rvm/gems/ruby-1.9.3-p385@default/gems/imageruby-0.2.3/lib/imageruby/pureruby.rb:156:in'
<': comparison of String with 255 failed (ArgumentError) from /home/railsdev1/.rvm/gems/ruby-1.9.3-p385@default/gems/imageruby-0.2.3/lib/imageruby/pureruby.rb:156:in
block (2 levels) in draw!' from /home/railsdev1/.rvm/gems/ruby-1.9.3-p385@default/gems/imageruby-0.2.3/lib/imageruby/pureruby.rb:151:ineach' from /home/railsdev1/.rvm/gems/ruby-1.9.3-p385@default/gems/imageruby-0.2.3/lib/imageruby/pureruby.rb:151:in
block in draw!' from /home/railsdev1/.rvm/gems/ruby-1.9.3-p385@default/gems/imageruby-0.2.3/lib/imageruby/pureruby.rb:145:ineach' from /home/railsdev1/.rvm/gems/ruby-1.9.3-p385@default/gems/imageruby-0.2.3/lib/imageruby/pureruby.rb:145:in
draw!' from gradient.rb:27:inblock in <main>' from gradient.rb:26:in
each' from gradient.rb:26:in `