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Description: Fast, Nimble PDF Writer for Ruby
Homepage: http://prawn.majesticseacreature.com
Clone URL: git://github.com/sandal/prawn.git 
Set an explicit Decode Array for CMYK jpg images
- see section 4.8.4 of the spec. We're swapping Dmin and Dmax to invert
  colours.
yob (author)
Fri Oct 31 08:32:37 -0700 2008
commit  827887ea2e1ca845a07af46241c83050440ae35e
tree    0a660c4ca4117d40dc34d905ef10a0fae73443dc
parent  0c97cc776ab65adc50e317768a6c3cc246cca9ed
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lib/prawn/images.rb 
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@@ -140,10 +140,12 @@ module Prawn
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       color_space = case jpg.channels
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       when 1
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         :DeviceGray
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+      when 3
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+        :DeviceRGB
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       when 4
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         :DeviceCMYK
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       else
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-        :DeviceRGB
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+        raise ArgumentError, 'JPG uses an unsupported number of channels'
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       end
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       obj = ref(:Type       => :XObject,
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           :Subtype          => :Image,
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@@ -153,6 +155,14 @@ module Prawn
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           :Width            => jpg.width,
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           :Height           => jpg.height,
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           :Length           => data.size ) 
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+
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+      # add extra decode params for CMYK images. By swapping the
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+      # min and max values from the default, we invert the colours. See
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+      # section 4.8.4 of the spec.
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+      if color_space == :DeviceCMYK
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+        obj.data[:Decode] = [ 1.0, 0.0, 1.0, 0.0, 1.0, 0.0, 1.0, 0.0 ]
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+      end
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+
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       obj << data
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       return obj
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     end

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