Add support for psd and psb files

lib/dimensions/reader.rb

@@ -5,6 +5,7 @@ class Reader
     GIF_HEADER    = [0x47, 0x49, 0x46, 0x38]
     PNG_HEADER    = [0x89, 0x50, 0x4E, 0x47]
     JPEG_HEADER   = [0xFF, 0xD8, 0xFF]
+    PSD_HEADER    = [0x38, 0x42, 0x50, 0x53]
     TIFF_HEADER_I = [0x49, 0x49, 0x2A, 0x00]
     TIFF_HEADER_M = [0x4D, 0x4D, 0x00, 0x2A]
 
@@ -45,6 +46,8 @@ def determine_type
           @type = :jpeg
         elsif match_header(TIFF_HEADER_I, bytes) || match_header(TIFF_HEADER_M, bytes)
           @type = :tiff
+        elsif match_header(PSD_HEADER, bytes)
+          @type = :psd
         end
 
         process @type ? :"extract_#{type}_dimensions" : nil
@@ -65,6 +68,13 @@ def extract_png_dimensions
       end
     end
 
+    def extract_psd_dimensions
+      if @size >= 22
+        @height, @width = @data.unpack("x14N2")
+        process nil
+      end
+    end
+
     def extract_jpeg_dimensions
       scanner = JpegScanner.new(@data)
       if scanner.scan

test/test_dimensions.rb

@@ -30,6 +30,10 @@ def test_tiff_dimensions
     assert_dimensions "short.tif", 50, 20
   end
 
+  def test_psd_dimensions
+    assert_dimensions "f-and-f.psd", 193, 147
+  end
+
   def assert_dimensions(filename, expected_width, expected_height)
     actual_width, actual_height = Dimensions.dimensions(fixture_path(filename))
     assert_equal "#{expected_width}x#{expected_height}", "#{actual_width}x#{actual_height}"