Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.

        /usr/bin/ruby1.9.1 extconf.rb
checking for Ruby version >= 1.8.5... yes
checking for gcc... yes
checking for Magick-config... yes

Warning: Found a partial ImageMagick installation. Your operating system likely has some built-in ImageMagick libraries but not all of ImageMagick. This will most likely cause problems at both compile and runtime.
Found partial installation at: /usr
checking for ImageMagick version >= 6.4.9... *** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

Provided configuration options:
	--with-opt-dir
	--without-opt-dir
	--with-opt-include
	--without-opt-include=${opt-dir}/include
	--with-opt-lib
	--without-opt-lib=${opt-dir}/lib
	--with-make-prog
	--without-make-prog
	--srcdir=.
	--curdir
	--ruby=/usr/bin/ruby1.9.1
extconf.rb:154:in ``': No such file or directory - convert -version (Errno::ENOENT)
	from extconf.rb:154:in `block in <main>'
	from /usr/lib/ruby/1.9.1/mkmf.rb:790:in `block in checking_for'
	from /usr/lib/ruby/1.9.1/mkmf.rb:284:in `block (2 levels) in postpone'
	from /usr/lib/ruby/1.9.1/mkmf.rb:254:in `open'
	from /usr/lib/ruby/1.9.1/mkmf.rb:284:in `block in postpone'
	from /usr/lib/ruby/1.9.1/mkmf.rb:254:in `open'
	from /usr/lib/ruby/1.9.1/mkmf.rb:280:in `postpone'
	from /usr/lib/ruby/1.9.1/mkmf.rb:789:in `checking_for'
	from extconf.rb:151:in `<main>'


Gem files will remain installed in /var/lib/gems/1.9.1/gems/rmagick-2.13.4 for inspection.
Results logged to /var/lib/gems/1.9.1/gems/rmagick-2.13.4/ext/RMagick/gem_make.out
An error occurred while installing rmagick (2.13.4), and Bundler cannot continue.
Make sure that `gem install rmagick -v '2.13.4'` succeeds before bundling.