lib/prawn/images/png.rb in prawn-0.1.1 vs lib/prawn/images/png.rb in prawn-0.1.2

@@ -1,6 +1,6 @@
-# encoding: utf-8
+# encoding: ASCII-8BIT
 
 # png.rb : Extracts the data from a PNG that is needed for embedding
 #
 # Based on some similar code in PDF::Writer by Austin Ziegler
 #
@@ -82,15 +82,26 @@
 
           data.read(4)  # Skip the CRC
         end
 
         # if our img_data contains alpha channel data, split it out
-        unfilter_image_data if @color_type == 6
+        unfilter_image_data if alpha_channel?
       end
 
+      def pixel_bytes
+        case @color_type
+        when 0, 4    then 1
+        when 1, 2, 6 then 3
+        end
+      end
+
       private
 
+      def alpha_channel?
+        @color_type == 4 || @color_type == 6
+      end
+
       def paeth(a, b, c) # left, above, upper left
         p = a + b - c
         pa = (p - a).abs
         pb = (p - b).abs
         pc = (p - c).abs
@@ -102,50 +113,53 @@
 
       def unfilter_image_data
         data = Zlib::Inflate.inflate(@img_data).unpack 'C*'
         @img_data = ""
         @alpha_channel = ""
-        scanline_length = 4 * @width + 1 # for filter
+
+        # each pixel has the color bytes, plus a byte of alpha channel
+        pixel_length = pixel_bytes + 1
+        scanline_length = pixel_length * @width + 1 # for filter
         row = 0
         pixels = []
         until data.empty? do
           row_data = data.slice! 0, scanline_length
           filter = row_data.shift
           case filter
-          when 0 then # None
-          when 1 then # Sub
+          when 0 # None
+          when 1 # Sub
             row_data.each_with_index do |byte, index|
-              left = index < 4 ? 0 : row_data[index - 4]
+              left = index < pixel_length ? 0 : row_data[index - pixel_length]
               row_data[index] = (byte + left) % 256
               #p [byte, left, row_data[index]]
             end
-          when 2 then # Up
+          when 2 # Up
             row_data.each_with_index do |byte, index|
-              col = index / 4
-              upper = row == 0 ? 0 : pixels[row-1][col][index % 4]
+              col = index / pixel_length
+              upper = row == 0 ? 0 : pixels[row-1][col][index % pixel_length]
               row_data[index] = (upper + byte) % 256
             end
-          when 3 then # Average
+          when 3  # Average
             row_data.each_with_index do |byte, index|
-              col = index / 4
-              upper = row == 0 ? 0 : pixels[row-1][col][index % 4]
-              left = index < 4 ? 0 : row_data[index - 4]
+              col = index / pixel_length
+              upper = row == 0 ? 0 : pixels[row-1][col][index % pixel_length]
+              left = index < pixel_length ? 0 : row_data[index - pixel_length]
 
               row_data[index] = (byte + ((left + upper)/2).floor) % 256
             end
-          when 4 then # Paeth
+          when 4 # Paeth
             left = upper = upper_left = nil
             row_data.each_with_index do |byte, index|
-              col = index / 4
+              col = index / pixel_length
 
-              left = index < 4 ? 0 : row_data[index - 4]
+              left = index < pixel_length ? 0 : row_data[index - pixel_length]
               if row == 0 then
                 upper = upper_left = 0
               else
-                upper = pixels[row-1][col][index % 4]
+                upper = pixels[row-1][col][index % pixel_length]
                 upper_left = col == 0 ? 0 :
-                  pixels[row-1][col-1][index % 4]
+                  pixels[row-1][col-1][index % pixel_length]
               end
 
               paeth = paeth left, upper, upper_left
               row_data[index] = (byte + paeth) % 256
               #p [byte, paeth, row_data[index]]
@@ -153,20 +167,20 @@
           else
             raise ArgumentError, "Invalid filter algorithm #{filter}"
           end
 
           pixels << []
-          row_data.each_slice 4 do |slice|
+          row_data.each_slice pixel_length do |slice|
             pixels.last << slice
           end
           row += 1
         end
 
         # convert the pixel data to seperate strings for colours and alpha
         pixels.each do |row|
           row.each do |pixel|
-            @img_data << pixel[0,3].pack("C*")
-            @alpha_channel << pixel[3]
+            @img_data << pixel[0,pixel_bytes].pack("C*")
+            @alpha_channel << pixel.last
           end
         end
 
         # compress the data
         @img_data = Zlib::Deflate.deflate(@img_data)