diff --git a/lib/rucaptcha/captcha.rb b/lib/rucaptcha/captcha.rb
index 1687f8b..51bf2da 100644
--- a/lib/rucaptcha/captcha.rb
+++ b/lib/rucaptcha/captcha.rb
@@ -3,6 +3,7 @@ require 'open3'
 module RuCaptcha
   class Captcha
     class << self
+      # Genrate ranom RGB color
       def random_color
         if RuCaptcha.config.style == :colorful
           color1 = rand(56) + 15
@@ -16,32 +17,84 @@ module RuCaptcha
         end
       end
 
+      # Genrate random Captcha code
       def random_chars
         chars = SecureRandom.hex(RuCaptcha.config.len / 2).downcase
         chars.gsub!(/[0ol1]/i, (rand(8) + 2).to_s)
         chars
       end
 
-      def rand_line_top(text_top, font_size)
-        text_top + rand(font_size * 0.7).to_i
-      end
-
       # Create Captcha image by code
       def create(code)
         chars        = code.split('')
-        all_left     = 20
-        font_size    = RuCaptcha.config.font_size
-        full_height  = font_size
-        full_width   = font_size * chars.size
+        full_width   = RuCaptcha.config.font_size * chars.size
+        full_height  = RuCaptcha.config.font_size
         size         = "#{full_width}x#{full_height}"
+
+        return convert_for_windows(size, code) if Gem.win_platform?
+
+        opts = command_line_opts(chars, full_width)
+        convert(size, opts)
+      end
+
+      private
+
+      def command_line_opts(chars, full_width)
+        font_size    = RuCaptcha.config.font_size
+        all_left     = 20
         half_width   = full_width / 2
         text_top     = 0
         text_left    = 0 - (font_size * 0.28).to_i
-        stroke_width = (font_size * 0.05).to_i + 1
         text_width   = font_size + text_left
-        text_opts    = []
-        line_opts    = []
 
+        opts = { text: [], line: [] }
+        rgbs = uniq_rgbs_for_each_chars(chars)
+
+        chars.each_with_index do |char, i|
+          rgb = RuCaptcha.config.style == :colorful ? rgbs[i] : rgbs[0]
+          text_color = "rgba(#{rgb.join(',')}, 1)"
+          line_color = "rgba(#{rgb.join(',')}, 0.6)"
+          opts[:text] << %(-fill '#{text_color}' -draw 'text #{(text_left + text_width) * i + all_left},#{text_top} "#{char}"')
+
+          left_y = rand_line_top(text_top, font_size)
+          right_x = half_width + (half_width * 0.3).to_i
+          right_y = rand_line_top(text_top, font_size)
+          opts[:line] << %(-draw 'stroke #{line_color} line #{rand(10)},#{left_y} #{right_x},#{right_y}')
+        end
+        opts
+      end
+
+      def convert(size, opts)
+        stroke_width = (RuCaptcha.config.font_size * 0.05).to_i + 1
+        command = <<-CODE
+          convert -size #{size} \
+          -strokewidth #{stroke_width} \
+          #{opts[:line].join(' ')} \
+          -pointsize #{RuCaptcha.config.font_size} -weight 500 \
+          #{opts[:text].join(' ')}  \
+          -wave #{rand(2) + 3}x#{rand(2) + 1} \
+          -rotate #{rand(10) - 5} \
+          -gravity NorthWest -sketch 1x10+#{rand(2)} \
+          -fill none \
+          -implode #{RuCaptcha.config.implode} -trim label:- png:-
+        CODE
+        command.strip!
+        out, err, _st = Open3.capture3(command)
+        warn "  RuCaptcha #{err.strip}" if err.present?
+        out
+      end
+
+      # Generate a simple captcha image for Windows Platform
+      def convert_for_windows(size, code)
+        png_file_path = Rails.root.join('tmp', 'cache', "#{code}.png")
+        command = "convert -size #{size} xc:White -gravity Center -weight 12 -pointsize 20 -annotate 0 \"#{code}\" -trim #{png_file_path}"
+        _out, err, _st = Open3.capture3(command)
+        warn "  RuCaptcha #{err.strip}" if err.present?
+        png_file_path
+      end
+
+      # Geneate a uniq rgba colors for each chars
+      def uniq_rgbs_for_each_chars(chars)
         rgbs = []
         chars.count.times do |i|
           color = random_color
@@ -56,43 +109,11 @@ module RuCaptcha
           end
           rgbs << color
         end
+        rgbs
+      end
 
-        chars.each_with_index do |char, i|
-          rgb = RuCaptcha.config.style == :colorful ? rgbs[i] : rgbs[0]
-          text_color = "rgba(#{rgb.join(',')}, 1)"
-          line_color = "rgba(#{rgb.join(',')}, 0.6)"
-          text_opts << %(-fill '#{text_color}' -draw 'text #{(text_left + text_width) * i + all_left},#{text_top} "#{char}"')
-          left_y = rand_line_top(text_top, font_size)
-          right_x = half_width + (half_width * 0.3).to_i
-          right_y = rand_line_top(text_top, font_size)
-          line_opts << %(-draw 'stroke #{line_color} line #{rand(10)},#{left_y} #{right_x},#{right_y}')
-        end
-
-        command = <<-CODE
-          convert -size #{size} \
-          -strokewidth #{stroke_width} \
-          #{line_opts.join(' ')} \
-          -pointsize #{font_size} -weight 500 \
-          #{text_opts.join(' ')}  \
-          -wave #{rand(2) + 3}x#{rand(2) + 1} \
-          -rotate #{rand(10) - 5} \
-          -gravity NorthWest -sketch 1x10+#{rand(2)} \
-          -fill none \
-          -implode #{RuCaptcha.config.implode} -trim label:- png:-
-        CODE
-
-        if Gem.win_platform?
-          png_file_path = Rails.root.join('tmp', 'cache', "#{code}.png")
-          command = "convert -size #{size} xc:White -gravity Center -weight 12 -pointsize 20 -annotate 0 \"#{code}\" -trim #{png_file_path}"
-          out, err, _st = Open3.capture3(command)
-          warn "  RuCaptcha #{err.strip}" if err.present?
-          png_file_path
-        else
-          command.strip!
-          out, err, _st = Open3.capture3(command)
-          warn "  RuCaptcha #{err.strip}" if err.present?
-          out
-        end
+      def rand_line_top(text_top, font_size)
+        text_top + rand(font_size * 0.7).to_i
       end
 
       def warn(msg)
diff --git a/spec/captcha_spec.rb b/spec/captcha_spec.rb
index f2412a8..e594bec 100644
--- a/spec/captcha_spec.rb
+++ b/spec/captcha_spec.rb
@@ -34,4 +34,31 @@ describe RuCaptcha::Captcha do
       expect(colors).not_to eq colors1
     end
   end
+
+  describe '.rand_line_top' do
+    it 'should work' do
+      expect(RuCaptcha::Captcha.send(:rand_line_top, 1, 24)).to be_a(Integer)
+    end
+  end
+
+  describe '.uniq_rgbs_for_each_chars' do
+    let(:chars) { %w(a b c d e) }
+    let(:colors) { RuCaptcha::Captcha.send(:uniq_rgbs_for_each_chars, chars) }
+
+    it 'should work' do
+      expect(colors.length).to eq chars.length
+      expect(colors[0].length).to eq 3
+    end
+
+    it 'Be sure the color not same as preview color' do
+      pre_rgb = nil
+      colors.each do |rgb|
+        if pre_rgb
+          same = rgb.index(rgb.min) == pre_rgb.index(rgb.min) && rgb.index(rgb.max) == pre_rgb.index(pre_rgb.max)
+          expect(same).not_to eq true
+        end
+        pre_rgb = rgb
+      end
+    end
+  end
 end