diff --git a/lib/asciidoctor-diagram/blockdiag/extension.rb b/lib/asciidoctor-diagram/blockdiag/extension.rb
index 781e65f9..f826dc77 100644
--- a/lib/asciidoctor-diagram/blockdiag/extension.rb
+++ b/lib/asciidoctor-diagram/blockdiag/extension.rb
@@ -96,6 +96,7 @@ def self.define_processors(name)
         ::Asciidoctor::Diagram.const_set("#{name}BlockMacroProcessor", block_macro)
       end
 
+      include CliGenerator
       include Which
 
       def blockdiag(tool, parent, source, format)
@@ -105,7 +106,7 @@ def blockdiag(tool, parent, source, format)
         # a '3' suffix.
         alt_cmd_name = "#{tool.downcase}3"
 
-        CliGenerator.generate_stdin(which(parent, cmd_name, :alt_cmds => [alt_cmd_name]), format.to_s, source.to_s) do |tool_path, output_path|
+        generate_stdin(which(parent, cmd_name, :alt_cmds => [alt_cmd_name]), format.to_s, source.to_s) do |tool_path, output_path|
           [tool_path, '-a', '-o', Platform.native_path(output_path), "-T#{format.to_s}", '-']
         end
       end
diff --git a/lib/asciidoctor-diagram/erd/extension.rb b/lib/asciidoctor-diagram/erd/extension.rb
index b7809517..27136d4a 100644
--- a/lib/asciidoctor-diagram/erd/extension.rb
+++ b/lib/asciidoctor-diagram/erd/extension.rb
@@ -7,6 +7,7 @@ module Asciidoctor
   module Diagram
     # @private
     module Erd
+      include CliGenerator
       include Which
 
       def self.included(mod)
@@ -21,11 +22,11 @@ def erd(parent, source, format)
         erd_path = which(parent, 'erd')
         dot_path = which(parent, 'dot', :alt_attrs => ['graphvizdot'])
 
-        dot_code = CliGenerator.generate_stdin(erd_path, format.to_s, source.to_s) do |tool_path, output_path|
+        dot_code = generate_stdin(erd_path, format.to_s, source.to_s) do |tool_path, output_path|
           [tool_path, '-o', Platform.native_path(output_path), '-f', 'dot']
         end
 
-        CliGenerator.generate_stdin(dot_path, format.to_s, dot_code) do |tool_path, output_path|
+        generate_stdin(dot_path, format.to_s, dot_code) do |tool_path, output_path|
           [tool_path, "-o#{Platform.native_path(output_path)}", "-T#{format.to_s}"]
         end
       end
diff --git a/lib/asciidoctor-diagram/extensions.rb b/lib/asciidoctor-diagram/extensions.rb
index 93bf0c64..889aa145 100644
--- a/lib/asciidoctor-diagram/extensions.rb
+++ b/lib/asciidoctor-diagram/extensions.rb
@@ -115,7 +115,11 @@ def process(parent, reader_or_target, attributes)
                 raise e
               else
                 text = "Failed to generate image: #{e.message}"
-                warn %(asciidoctor-diagram: ERROR: #{text})
+                warn_msg = text.dup
+                if $VERBOSE
+                  warn_msg << "\n" << e.backtrace.join("\n")
+                end
+                warn %(asciidoctor-diagram: ERROR: #{warn_msg})
                 text << "\n"
                 text << source.code
                 Asciidoctor::Block.new parent, :listing, :source => text, :attributes => attributes
diff --git a/lib/asciidoctor-diagram/graphviz/extension.rb b/lib/asciidoctor-diagram/graphviz/extension.rb
index 0ae83886..36d589e7 100644
--- a/lib/asciidoctor-diagram/graphviz/extension.rb
+++ b/lib/asciidoctor-diagram/graphviz/extension.rb
@@ -7,6 +7,7 @@ module Asciidoctor
   module Diagram
     # @private
     module Graphviz
+      include CliGenerator
       include Which
 
       def self.included(mod)
@@ -18,7 +19,7 @@ def self.included(mod)
       end
 
       def graphviz(parent, source, format)
-        CliGenerator.generate_stdin(which(parent, 'dot', :alt_attrs => ['graphvizdot']), format.to_s, source.to_s) do |tool_path, output_path|
+        generate_stdin(which(parent, 'dot', :alt_attrs => ['graphvizdot']), format.to_s, source.to_s) do |tool_path, output_path|
           args = [tool_path, "-o#{Platform.native_path(output_path)}", "-T#{format.to_s}"]
 
           layout = source.attr('layout')
diff --git a/lib/asciidoctor-diagram/meme/extension.rb b/lib/asciidoctor-diagram/meme/extension.rb
index 84096466..facf7245 100644
--- a/lib/asciidoctor-diagram/meme/extension.rb
+++ b/lib/asciidoctor-diagram/meme/extension.rb
@@ -36,7 +36,7 @@ def meme(p, c, format)
         options = c.attr('options', '').split(',')
         noupcase = options.include?('noupcase')
 
-        dimensions = CliGenerator.run_cli(identify, '-format', '%w %h', bg_img).match(/(?<w>\d+) (?<h>\d+)/)
+        dimensions = Cli.run(identify, '-format', '%w %h', bg_img).match(/(?<w>\d+) (?<h>\d+)/)
         bg_width = dimensions['w'].to_i
         bg_height = dimensions['h'].to_i
         label_width = bg_width
@@ -44,7 +44,7 @@ def meme(p, c, format)
 
         if top_label
           top_img = Tempfile.new(['meme', '.png'])
-          CliGenerator.run_cli(
+          Cli.run(
               convert,
               '-background', 'none',
               '-fill', fill_color,
@@ -62,7 +62,7 @@ def meme(p, c, format)
 
         if bottom_label
           bottom_img = Tempfile.new(['meme', '.png'])
-          CliGenerator.run_cli(
+          Cli.run(
               convert,
               '-background', 'none',
               '-fill', fill_color,
@@ -91,7 +91,7 @@ def meme(p, c, format)
 
         args << final_img.path
 
-        CliGenerator.run_cli(*args)
+        Cli.run(*args)
 
         File.binread(final_img)
       end
diff --git a/lib/asciidoctor-diagram/mermaid/extension.rb b/lib/asciidoctor-diagram/mermaid/extension.rb
index d870edb2..8c767793 100644
--- a/lib/asciidoctor-diagram/mermaid/extension.rb
+++ b/lib/asciidoctor-diagram/mermaid/extension.rb
@@ -1,4 +1,5 @@
 require_relative '../extensions'
+require_relative '../util/cli'
 require_relative '../util/cli_generator'
 require_relative '../util/platform'
 require_relative '../util/which'
@@ -7,6 +8,7 @@ module Asciidoctor
   module Diagram
     # @private
     module Mermaid
+      include CliGenerator
       include Which
 
       def self.included(mod)
@@ -19,7 +21,7 @@ def self.included(mod)
 
       def mermaid(parent, source, format)
         mermaid = which(parent, 'mermaid')
-        @is_mermaid_v6 ||= `#{mermaid} --version`.split('.')[0].to_i >= 6
+        @is_mermaid_v6 ||= ::Asciidoctor::Diagram::Cli.run(mermaid, '--version').split('.')[0].to_i >= 6
         # Mermaid >= 6.0.0 requires PhantomJS 2.1; older version required 1.9
         phantomjs = which(parent, 'phantomjs', :alt_attrs => [@is_mermaid_v6 ? 'phantomjs_2' : 'phantomjs_19'])
 
@@ -30,7 +32,7 @@ def mermaid(parent, source, format)
 
         width = source.attr('width')
 
-        CliGenerator.generate_file(mermaid, 'mmd', format.to_s, source.to_s) do |tool_path, input_path, output_path|
+        generate_file(mermaid, 'mmd', format.to_s, source.to_s) do |tool_path, input_path, output_path|
           output_dir = File.dirname(output_path)
           output_file = File.expand_path(File.basename(input_path) + ".#{format.to_s}", output_dir)
 
diff --git a/lib/asciidoctor-diagram/shaape/extension.rb b/lib/asciidoctor-diagram/shaape/extension.rb
index 200685e5..e4591af7 100644
--- a/lib/asciidoctor-diagram/shaape/extension.rb
+++ b/lib/asciidoctor-diagram/shaape/extension.rb
@@ -7,6 +7,7 @@ module Asciidoctor
   module Diagram
     # @private
     module Shaape
+      include CliGenerator
       include Which
 
       def self.included(mod)
@@ -18,7 +19,7 @@ def self.included(mod)
       end
 
       def shaape(parent, source, format)
-        CliGenerator.generate_stdin(which(parent, 'shaape'), format.to_s, source.to_s) do |tool_path, output_path|
+        generate_stdin(which(parent, 'shaape'), format.to_s, source.to_s) do |tool_path, output_path|
           [tool_path, '-o', Platform.native_path(output_path), '-t', format.to_s, '-']
         end
       end
diff --git a/lib/asciidoctor-diagram/util/cli.rb b/lib/asciidoctor-diagram/util/cli.rb
new file mode 100644
index 00000000..ad8a818a
--- /dev/null
+++ b/lib/asciidoctor-diagram/util/cli.rb
@@ -0,0 +1,19 @@
+require 'tempfile'
+require 'open3'
+
+module Asciidoctor
+  module Diagram
+    # @private
+    module Cli
+      def self.run(*args)
+        stdout, stderr, status = Open3.capture3(*args)
+
+        if status != 0
+          raise "#{File.basename(args[0])} failed: #{stdout.empty? ? stderr : stdout}"
+        end
+
+        stdout.empty? ? stderr : stdout
+      end
+    end
+  end
+end
diff --git a/lib/asciidoctor-diagram/util/cli_generator.rb b/lib/asciidoctor-diagram/util/cli_generator.rb
index a455be9c..12d6a753 100644
--- a/lib/asciidoctor-diagram/util/cli_generator.rb
+++ b/lib/asciidoctor-diagram/util/cli_generator.rb
@@ -1,11 +1,11 @@
 require 'tempfile'
-require 'open3'
+require_relative 'cli'
 
 module Asciidoctor
   module Diagram
     # @private
     module CliGenerator
-      def self.generate_stdin(tool, format, code)
+      def generate_stdin(tool, format, code)
         tool_name = File.basename(tool)
 
         target_file = Tempfile.new([tool_name, ".#{format}"])
@@ -20,7 +20,7 @@ def self.generate_stdin(tool, format, code)
         end
       end
 
-      def self.generate_file(tool, input_ext, output_ext, code)
+      def generate_file(tool, input_ext, output_ext, code)
         tool_name = File.basename(tool)
 
         source_file = Tempfile.new([tool_name, ".#{input_ext}"])
@@ -42,7 +42,7 @@ def self.generate_file(tool, input_ext, output_ext, code)
         end
       end
 
-      def self.generate(opts, target_file, open3_opts = {})
+      def generate(opts, target_file, open3_opts = {})
         case opts
           when Array
             args = opts
@@ -54,7 +54,7 @@ def self.generate(opts, target_file, open3_opts = {})
             raise "Block passed to generate_file should return an Array or a Hash"
         end
 
-        output = run_cli(*args, open3_opts)
+        output = ::Asciidoctor::Diagram::Cli.run(*args, open3_opts)
 
         raise "#{args[0]} failed: #{output}" unless File.exist?(out_file || target_file.path)
 
@@ -64,16 +64,6 @@ def self.generate(opts, target_file, open3_opts = {})
 
         File.binread(target_file.path)
       end
-
-      def self.run_cli(*args)
-        stdout, stderr, status = Open3.capture3(*args)
-
-        if status != 0
-          raise "#{File.basename(args[0])} failed: #{stdout.empty? ? stderr : stdout}"
-        end
-
-        stdout.empty? ? stderr : stdout
-      end
     end
   end
 end
diff --git a/lib/asciidoctor-diagram/util/java.rb b/lib/asciidoctor-diagram/util/java.rb
index 1d13c851..7057144f 100644
--- a/lib/asciidoctor-diagram/util/java.rb
+++ b/lib/asciidoctor-diagram/util/java.rb
@@ -78,7 +78,7 @@ def self.create_error(prefix_msg, response)
         if content_type.start_with? 'application/json'
           json = JSON.parse(response[:body].force_encoding(Encoding::UTF_8))
           ruby_bt = Kernel.caller(2)
-          java_bt = json['stk'].map { |java_line| "#{java_line[0]}:#{java_line[3]}: in `#{java_line[2]}'" }
+          java_bt = json['stk'].map { |java_line| "#{java_line[0]}:#{java_line[3]}: in '#{java_line[2]}'" }
           error = RuntimeError.new("#{prefix_msg}: #{json['msg']}")
           error.set_backtrace java_bt + ruby_bt
           raise error
diff --git a/lib/asciidoctor-diagram/util/java_socket.rb b/lib/asciidoctor-diagram/util/java_socket.rb
index 76455980..c041cff6 100644
--- a/lib/asciidoctor-diagram/util/java_socket.rb
+++ b/lib/asciidoctor-diagram/util/java_socket.rb
@@ -1,6 +1,7 @@
 require 'socket'
-require 'rbconfig'
 
+require_relative 'cli'
+require_relative 'platform'
 require_relative 'which'
 
 module Asciidoctor
@@ -15,10 +16,10 @@ def initialize(java, classpath)
           args << '-Djava.awt.headless=true'
           args << '-cp'
           # special case for cygwin, it requires path translation for java to work
-          if RbConfig::CONFIG['host_os'] =~ /cygwin/i
+          if ::Asciidoctor::Diagram::Platform.os_variant == :cygwin
             cygpath = ::Asciidoctor::Diagram::Which.which('cygpath')
-            if(cygpath != nil) 
-              args << classpath.flatten.map { |jar| `cygpath -w "#{jar}"`.strip }.join(";")
+            if cygpath != nil
+              args << classpath.flatten.map { |jar| ::Asciidoctor::Diagram::Cli.run(cygpath, '-w', jar).strip }.join(";")
             else
               puts 'cygwin warning: cygpath not found'
               args << classpath.flatten.join(File::PATH_SEPARATOR)
@@ -77,15 +78,13 @@ def self.send_request(req)
 
       private
       def self.find_java
-        if /cygwin|mswin|mingw|bccwin|wince|emx/ =~ RUBY_PLATFORM
-          # Windows
-          path_to(ENV['JAVA_HOME'], 'bin/java.exe') || registry_lookup || ::Asciidoctor::Diagram::Which.which('java')
-        elsif /darwin/ =~ RUBY_PLATFORM
-          # Mac
-          path_to(ENV['JAVA_HOME'], 'bin/java') || path_to(`/usr/libexec/java_home`.strip, 'bin/java') || ::Asciidoctor::Diagram::Which.which('java')
-        else
-          # Other unix-like system
-          path_to(ENV['JAVA_HOME'], 'bin/java') || ::Asciidoctor::Diagram::Which.which('java')
+        case ::Asciidoctor::Diagram::Platform.os
+          when :windows
+            path_to(ENV['JAVA_HOME'], 'bin/java.exe') || registry_lookup || ::Asciidoctor::Diagram::Which.which('java')
+          when :macosx
+            path_to(ENV['JAVA_HOME'], 'bin/java') || path_to(::Asciidoctor::Diagram::Cli.run('/usr/libexec/java_home').strip, 'bin/java') || ::Asciidoctor::Diagram::Which.which('java')
+          else
+            path_to(ENV['JAVA_HOME'], 'bin/java') || ::Asciidoctor::Diagram::Which.which('java')
         end
       end
 
@@ -98,21 +97,90 @@ def self.path_to(java_home, java_binary)
         end
       end
 
+      JDK_KEY = 'HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Development Kit'
+      JRE_KEY = 'HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment'
+
       def self.registry_lookup
-        key_re = /^HKEY_LOCAL_MACHINE\\SOFTWARE\\JavaSoft\\.*\\([0-9\.]+)/
-        value_re = /\s*JavaHome\s*REG_SZ\s*(.*)/
-        result = `reg query "HKEY_LOCAL_MACHINE\\SOFTWARE\\JavaSoft" /s /v JavaHome`.lines.map { |l| l.strip }
-        vms = result.each_slice(3).map do |_, key, value|
-          key_match = key_re.match(key)
-          value_match = value_re.match(value)
-          if key_match && value_match
-            [key_match[1].split('.').map { |v| v.to_i }, value_match[1]]
-          else
-            nil
+        registry_current(JRE_KEY) || registry_current(JDK_KEY) || registry_any()
+      end
+
+      def self.registry_current(key)
+        current_version = registry_query(key, 'CurrentVersion')
+        if current_version
+          java_home = registry_query("#{key}\\#{current_version}", 'JavaHome')
+          java_exe(java_home)
+        else
+          nil
+        end
+      end
+
+      def self.registry_any()
+        java_homes = registry_query('HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft', 'JavaHome', :recursive => true).values
+        java_homes.map { |path| java_exe(path) }.find { |exe| !exe.nil? }
+      end
+
+      def self.java_exe(java_home)
+        java = File.expand_path('bin/java.exe', java_home)
+
+        if File.executable?(java)
+          java
+        else
+          nil
+        end
+      end
+
+      def self.registry_query(key, value = nil, opts = {})
+        args = ['reg', 'query']
+        args << key
+        args << '/v' << value unless value.nil?
+        args << '/s' if opts[:recursive]
+
+        begin
+          lines = ::Asciidoctor::Diagram::Cli.run(*args).lines.reject { |l| l.strip.empty? }.each
+        rescue
+          lines = [].each
+        end
+
+        result = {}
+
+        while true
+          begin
+            begin
+              k = lines.next
+            rescue StopIteration
+              break
+            end
+
+            unless k.start_with? key
+              next
+            end
+
+            v = nil
+            begin
+              v = lines.next.strip if lines.peek.start_with?(' ')
+            rescue StopIteration
+              break
+            end
+
+            if !k.valid_encoding? || (v && !v.valid_encoding?)
+              next
+            end
+
+            if v && (md = /([^\s]+)\s+(REG_[^\s]+)\s+(.+)/.match(v))
+              v_name = md[1]
+              v_value = md[3]
+              result["#{k}\\#{v_name}"] = v_value
+            else
+              result[k] = v
+            end
           end
-        end.reject { |v| v.nil? }.sort_by { |v| v[0] }
-        java_exes = vms.map { |version, path| File.expand_path('bin/java.exe', path) }.select { |exe| File.executable?(exe) }
-        java_exes && java_exes[0]
+        end
+
+        if value && !opts[:recursive]
+          result.values[0]
+        else
+          result
+        end
       end
     end
   end
diff --git a/lib/asciidoctor-diagram/util/platform.rb b/lib/asciidoctor-diagram/util/platform.rb
index f1d436a1..d99e6b2b 100644
--- a/lib/asciidoctor-diagram/util/platform.rb
+++ b/lib/asciidoctor-diagram/util/platform.rb
@@ -7,6 +7,10 @@ def self.os
         os_info[:os]
       end
 
+      def self.os_variant
+        os_info[:os_variant]
+      end
+
       def self.path_separator
         os_info[:path_sep]
       end
@@ -14,20 +18,27 @@ def self.path_separator
       def self.os_info
         @os ||= (
         host_os = RbConfig::CONFIG['host_os']
+
+        path_sep = '/'
+        variant = nil
         case host_os
-          when /mswin|bccwin|wince|emc/
-            {:os => :windows, :path_sep => '\\'}
-          when /msys|mingw|cygwin/
-            {:os => :windows, :path_sep => '/'}
-          when /darwin|mac os/
-            {:os => :macosx, :path_sep => '/'}
-          when /linux/
-            {:os => :linux, :path_sep => '/'}
-          when /solaris|bsd/
-            {:os => :unix, :path_sep => '/'}
+          when /(mswin|bccwin|wince|emc)/i
+            os = :windows
+            variant = $1.downcase.to_sym
+            path_sep = '\\'
+          when /(msys|mingw|cygwin)/i
+            os = :windows
+            variant = $1.downcase.to_sym
+          when /darwin|mac os/i
+            os = :macosx
+          when /linux/i
+            os = :linux
           else
-            raise Error::WebDriverError, "unknown os: #{host_os.inspect}"
+            os = :unix
         end
+        {
+            :os => os, :os_variant => variant || os, :path_sep => path_sep
+        }
         )
       end
 
diff --git a/lib/asciidoctor-diagram/wavedrom/extension.rb b/lib/asciidoctor-diagram/wavedrom/extension.rb
index 49718b01..ee060f5a 100644
--- a/lib/asciidoctor-diagram/wavedrom/extension.rb
+++ b/lib/asciidoctor-diagram/wavedrom/extension.rb
@@ -7,6 +7,7 @@ module Asciidoctor
   module Diagram
     # @private
     module Wavedrom
+      include CliGenerator
       include Which
 
       def self.included(mod)
@@ -22,7 +23,7 @@ def wavedrom(parent, source, format)
         phantomjs = which(parent, 'phantomjs', :alt_attrs => ['phantomjs_2'], :raise_on_error => false)
 
         if wavedrom_cli && !wavedrom_cli.include?('WaveDromEditor') && phantomjs
-          CliGenerator.generate_file(wavedrom_cli, 'wvd', format.to_s, source.to_s) do |tool_path, input_path, output_path|
+          generate_file(wavedrom_cli, 'wvd', format.to_s, source.to_s) do |tool_path, input_path, output_path|
             [phantomjs, Platform.native_path(tool_path), '-i', Platform.native_path(input_path), "-#{format.to_s[0]}", Platform.native_path(output_path)]
           end
         else
@@ -35,7 +36,7 @@ def wavedrom(parent, source, format)
             wavedrom = which(parent, 'WaveDromEditor', :alt_attrs => ['wavedrom'])
           end
 
-          CliGenerator.generate_file(wavedrom, 'wvd', format.to_s, source.to_s) do |tool_path, input_path, output_path|
+          generate_file(wavedrom, 'wvd', format.to_s, source.to_s) do |tool_path, input_path, output_path|
             [tool_path, 'source', Platform.native_path(input_path), format.to_s, Platform.native_path(output_path)]
           end
         end
diff --git a/spec/plantuml_spec.rb b/spec/plantuml_spec.rb
index aaf506bf..25af6a53 100644
--- a/spec/plantuml_spec.rb
+++ b/spec/plantuml_spec.rb
@@ -37,6 +37,42 @@
     expect(b.attributes['height']).to_not be_nil
   end
 
+  it "should generate PNG images when format is set to 'png'" do
+    code = <<-eos
+User -> (Start)
+User --> (Use the application) : Label
+
+:Main Admin: ---> (Use the application) : Another label
+    eos
+
+    File.write('plantuml.txt', code)
+
+    doc = <<-eos
+= Hello, PlantUML!
+Doc Writer <doc@example.com>
+
+== First Section
+
+plantuml::plantuml.txt[format="png"]
+    eos
+
+    d = load_asciidoc doc
+    expect(d).to_not be_nil
+
+    b = d.find { |bl| bl.context == :image }
+    expect(b).to_not be_nil
+
+    expect(b.content_model).to eq :empty
+
+    target = b.attributes['target']
+    expect(target).to_not be_nil
+    expect(target).to match(/\.png$/)
+    expect(File.exists?(target)).to be true
+
+    expect(b.attributes['width']).to_not be_nil
+    expect(b.attributes['height']).to_not be_nil
+  end
+
   it 'should support substitutions' do
     code = <<-eos
 class {parent-class}
diff --git a/spec/test_helper.rb b/spec/test_helper.rb
index 511aed87..e8f67a92 100644
--- a/spec/test_helper.rb
+++ b/spec/test_helper.rb
@@ -77,10 +77,10 @@ def load_asciidoc(source, options = {})
   c.around(:each) do |example|
     metadata = example.metadata
     group_dir = File.expand_path(metadata[:example_group][:full_description].gsub(/[^\w]+/, '_'), TEST_DIR)
-    Dir.mkdir(group_dir) unless Dir.exist?(group_dir)
+    FileUtils.mkdir_p(group_dir) unless Dir.exist?(group_dir)
 
     test_dir = File.expand_path(metadata[:description].gsub(/[^\w]+/, '_'), group_dir)
-    Dir.mkdir(test_dir)
+    FileUtils.mkdir_p(test_dir) unless Dir.exist?(test_dir)
 
     Dir.chdir(test_dir) do
       example.run