alpha default now omits the -alpha option

Author: rubikan

lib/grim.rb

@@ -18,7 +18,7 @@ module Grim
   COLORSPACE = "RGB"
 
   #Default Alpha
-  ALPHA = "Set"
+  ALPHA = ""
 
   # Default exception class for Grim.
   class Exception < ::StandardError

lib/grim/image_magick_processor.rb

@@ -26,7 +26,8 @@ def save(pdf, index, path, options)
       quality = options.fetch(:quality, Grim::QUALITY)
       colorspace = options.fetch(:colorspace, Grim::COLORSPACE)
       alpha   = options.fetch(:alpha, Grim::ALPHA)
-      command = [@imagemagick_path, "-resize", width.to_s, "-alpha", alpha, "-antialias", "-render",
+      alpha   = alpha == '' ? alpha : "-alpha #{alpha}"
+      command = [@imagemagick_path, "-resize", width.to_s, alpha, "-antialias", "-render",
         "-quality", quality.to_s, "-colorspace", colorspace,
         "-interlace", "none", "-density", density.to_s,
         "#{Shellwords.shellescape(pdf.path)}[#{index}]", path]

spec/lib/grim_spec.rb

@@ -27,7 +27,7 @@
   end
 
   it "should have ALPHA constant set to 'Set'" do
-    expect(Grim::ALPHA).to eq('Set')
+    expect(Grim::ALPHA).to eq('')
   end
 
   describe "#reap" do